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Traffic coordinator for arterial traffic system |
| RE31044 |
Traffic coordinator for arterial traffic system
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| Patent Drawings: | |
| Inventor: |
McReynolds, et al. |
| Date Issued: |
September 28, 1982 |
| Application: |
06/185,437 |
| Filed: |
September 9, 1980 |
| Inventors: |
McReynolds; Marshall B. (Arlington, VA)
Oscar; Irving S. (Washington, DC)
Van Tilbury; Jack (Arlington, VA)
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| Assignee: |
TRAC, Inc. (Alexandria, VA) |
| Primary Examiner: |
Gruber; Felix D. |
| Assistant Examiner: |
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| Attorney Or Agent: |
Schwartz, Jeffery, Schwaab, Mack, Blumenthal & Koch |
| U.S. Class: |
340/913; 340/914; 340/915; 700/3; 700/83; 701/118 |
| Field Of Search: |
364/436; 364/437; 364/132; 364/188; 340/35; 340/36; 340/37; 340/40; 340/41 |
| International Class: |
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| U.S Patent Documents: |
3241107; 3278896; 3302170; 3305828; 3358126; 3374340; 3482208; 3506808; 3737847; 3774147; 3818429; 3920967; 4061902 |
| Foreign Patent Documents: |
450602; 1187504; 1230249; 1375813 |
| Other References: |
Crouse-Hinds: Technical Data Bulletin-Two Phase DM-200 Series Digital Controller Units, Nov. 1976..
Range: The Flo-Master Fixed Time Traffic Signal System, ATE Journal, vol. 19, No. 3/4, pp. 94-104..
"DARTS" two-page brochure together with Texas State Department of Highways and Public Transportation Special Specification for Dynamic Artery-Responsive Traffic Signal Coordination System.. |
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| Abstract: |
A traffic coordinator is disclosed which utilizes a master unit and a plurality of secondary units wherein the secondary units are positioned at artery cross streets for controlling the main artery traffic in a coordinated fashion. Both the master unit and secondary units contain microprocessors for calculating parameters utilized in the coordination system. The coordination system may be installed in already existing timer-controlled intersections and serves to provide a highly efficient real time control of artery green bands, offsets and splits to achieve optimum traffic flow. |
| Claim: |
What is claimed is:
1. A coordinator for use with a plurality of controllers for coordinating traffic at least along an artery, each controller associated with a side street intersection forcontrolling traffic signals at said intersection, said coordinator comprising:
(a) means for storing a plurality of values corresponding to cycle lengths, said cycle length values associated with platoons of traffic moving along said artery, and
(b) means connected to said storing means for retrieving said cycle length values and for sequentially controlling each of said plurality of controllers in an individual manner to effect said retrieved cycle length values at each associatedintersection as said platoons of vehicles move along associated intersections of said artery to thereby coordinate said controllers and traffic along said artery.
2. A coordinator as recited in claim 1 further comprising:
means for receiving input signals, and
means cooperating with said storing means for calculating said plurality of cycle length values in response to said input signals, whereby said stored cycle length values correspond to said calculated cycle length values.
3. A coordinator as recited in claim 2 wherein said calculating means and said means for receiving
input signals form a master unit which further comprises means for transmitting said calculated cycle length values, and said means for storing and retrieving said plurality of cycle length values form a plurality of secondary units, eachsecondary unit associated with one of said plurality of controllers and each secondary unit further comprises means for receiving said transmitted calculated cycle length values from said master unit.
4. A coordinator as recited in claim 3 wherein said input signals are generated in response to vehicles.
5. A coordinator as recited in claim 4 wherein said input signals are generated in real time, and said calculating means of said master unit comprises means for calculating said cycle length values in real time for each of said platoons ofvehicles.
6. A coordinator as recited in claim 5 wherein said calculating means of said master unit is programmable.
7. A coordinator as recited in claim 6 wherein each of said secondary units comprise programmable calculating means.
8. A coordinator as recited in claim 7 wherein said input signals comprise volume signals generated from volume detectors positioned to sense vehicle volume entering said artery, said calculating means of said master unit calculating said cyclelength values in response to said vehicle volume signals.
9. A coordinator as recited in claim 8 wherein said cycle length value consists of a red band time and a green band time and said programmable calculating means of said master unit calculates said cycle length value during a green band time andoperates:
(a) to monitor a gap time between successive volume signals,
(b) to compare the gap time to a reference time to determine when the gap time exceeds the reference time to establish a gapout condition,
(c) to count the number of volume signals corresponding to traffic actuations, A.sub.R, by vehicles during at least the artery red band time immediately preceding the artery green band time,
(d) to multiply the number A.sub.R by a red headway time E.sub.R to form a product T.sub.R,
(e) to determine if a gapout condition occurs prior to a maximum green band time, and,
(i) to determine the quantity T.sub.G =(A.sub.G)(E.sub.G) where,
A.sub.G is the number of actuations during the green band time prior to the occurrence of the gapout condition, and
E.sub.G is a green headway time, and
(ii) to compare the quantity S.sub.G =T.sub.R +T.sub.G to the time at which the gapout condition occurs from the start of the green band time, and
(iii) to select the larger of the two compared times as the calculated green band time to establish said cycle length for transmission to said secondary units, and
(f) to restrict the cycle length value transmitted to said secondary units to correspond to a green band time less than or equal to said maximum green band time.
10. A coordinator as recited in claim 9 wherein said reference time is a linear decreasing function time.
11. A coordinator as recited in claim 10 wherein said master unit comprises manually operable switches for selecting the slope of said linear decreasing function of time.
12. A coordinator as recited in claim 9 wherein said master unit further comprises manually operable switches for selecting said maximum green band time.
13. A coordinator as recited in claim 9 wherein said programmable calculating means of said master unit further operates to restrict the cycle length value transmitted to said secondary units to correspond to a green band time greater than orequal to a minimum green band time.
14. A coordinator as recited in claim 13 wherein said master unit further comprises manually operable switches for selecting said minimum green band time.
15. A coordinator as recited in claim 9 wherein said master unit further comprises manually operable switches for selecting said red headway time A.sub.R.
16. A coordinator as recited in claim 9 wherein said master unit further comprises manually operable switches for selecting said green headway time A.sub.G.
17. A coordinator as recited in claim 9 wherein said input signals further comprise occupancy signals, said occupancy signals generated from occupancy vehicle detectors positioned to sense vehicle occupancy within said artery.
18. A coordinator as recited in claim 17 wherein said occupancy signals have a variable pulse width corresponding to vehicle occupancy and said master unit further comprises means for converting said variable pulse width signals into acorresponding cycle length value.
19. A coordinator as recited in claim 18 wherein said converting means comprises means for selecting a linear function of cycle length values to pulse width signals.
20. A coordinator as recited in claim 19 wherein said selecting means comprises manually operable switches on said master unit.
21. A coordinator as recited in claim 20 wherein said manually operable switches select end points of said linear function to correspond to green band time values having said minimum green band time and said maximum green band time.
22. A coordinator as recited in claim 18 wherein said calculating means of said master unit further operates to select the larger of the cycle length values as calculated in response to said volume and occupancy input signals for transmission tosaid secondary units.
23. A coordinator as recited in claim 8 wherein said input signals further comprise occupancy signals, said occupancy signals generated from occupancy vehicle detectors positioned to sense vehicle occupancy within said artery.
24. A coordinator as recited in claim 23 wherein said occupancy signals have a variable pulse width corresponding to vehicle occupancy and said calculating means of said master unit further comprises means for converting said variable pulsewidth signals into a corresponding cycle length value.
25. A coordinator as recited in claim 24 wherein said converting means comprises means for selecting a linear function of cycle length values to pulse width signals.
26. A coordinator as recited in claim 24 wherein said calculating means of said master unit further comprises means for selecting the larger of the cycle length values as calculated in response to said volume and occupancy input signals fortransmission to said secondary units .
27. A coordinator as recited in claim 25 wherein said selecting means comprises manually operable switches on said master unit.
28. A coordinator as recited in claim 27 wherein said calculated cycle length consists of a red band time and a green band time and said manually operable switches select end points of said linear function to correspond to green band valueshaving a minimum green band time and a maximum green band time, said master unit further comprising means for setting said minimum and maximum green band times.
29. A coordinator as recited in claim 28 wherein said master unit further comprises manually operable switches for selecting said red band time.
30. A coordinator as recited in claim 28 wherein said master unit further comprises manually operable switches for selecting a plurality of red band times, said master unit comprising means for selecting said red band times in response to thevalue of said calculated green band time.
31. A coordinator as recited in claim 9 wherein each of said plurality of secondary units comprises means for selecting an offset value in time units, said offset value selectable independently of said calculated cycle length values.
32. A coordinator as recited in claim 31 wherein each of said plurality of secondary units comprises means for manually selecting said offset value, and wherein said secondary units are positioned adjacent said associated controllers.
33. A coordinator as recited in claim 9 wherein said coordinator is operable in an inbound and outbound mode, said inbound mode operative for coordinating said plurality of controllers to produce a favored inbound direction of traffic and flowand said outbound mode operative for coordinating said plurality of controllers to produce a favored outbound direction of traffic flow.
34. A coordinator as recited in claim 33 wherein said master unit further comprises means for selecting separate values for E.sub.R and E.sub.G corresponding to each of said inbound and outbound modes and said calculating means of said masterunit operates to utilize same in calculating the quantity S.sub.G for the corresponding modes.
35. A coordinator as recited in claim 34 wherein said means for selecting said separate values for E.sub.R and E.sub.G of said master unit comprises manually operable switches.
36. A coordinator as recited in claim 8 wherein each of said plurality of secondary units comprises means for selecting an offset value in time units, said offset value selectable independently of said calculated cycle length values.
37. A coordinator as recited in claim 36 wherein said time units is seconds of vehicle travel time.
38. A coordinator as recited in claim 37 wherein each of said plurality of secondary units comprises means for manually setting said offset value.
39. A coordinator as recited in claim 38 wherein said secondary units are positioned adjacent said associated controllers.
40. A coordinator as recited in claim 36 wherein said input signals further comprise occupancy signals generated from occupancy vehicle detectors positioned to sense vehicle occupancy within said artery.
41. A coordinator as recited in claim 40 wherein said master unit further comprises means for changing the offset value of said secondary units in response to said occupancy signals.
42. A coordinator as recited in claim 41 wherein said master unit comprises manually operable switches for enabling selection of the change in offset value.
43. A coordinator as recited in claim 42 wherein said master unit further comprises manually operable switches associated with said switches for enabling selection of the change in offset value, said associated switches corresponding to setpointoccupancy values, whereby different changes in offset values are selected in response to different values of occupancy.
44. A coordinator as recited in claim 3 wherein each of said plurality of secondary units comprises means for selecting an offset value in time units, said offset value selectable independently of said calculated cycle length values.
45. A coordinator as recited in claim 44 wherein said time units is seconds of vehicle travel time.
46. A coordinator as recited in claim 45 wherein each of said plurality of secondary units comprises means for manually selecting said offset value.
47. A coordinator as recited in claim 46 wherein said secondary units are positioned adjacent said associated controllers.
48. A coordinator as recited in claim 9 wherein said calculating means of said master unit additionally operates to count the number of actuations during a last car passage time (LCP) immediately preceding said red band time, and said quantityT.sub.R is formed by:
49. A coordinator as recited in claim 48 wherein said coordinator is operable in an inbound and outbound mode, said inbound mode operative for coordinating said plurality of controllers to produce a favored inbound direction of traffic flow andsaid outbound mode operative for coordinating said plurality of controllers to produce a favored outbound direction of traffic flow.
50. A coordinator as recited in claim 49 wherein said master unit further comprises means for selecting separate values for LCP corresponding to each of said inbound and outbound modes.
51. A coordinator as recited in claim 3 wherein said coordinator is operable in an inbound and outbound mode, said inbound mode operative for coordinating said plurality of controllers to produce a favored inbound direction of traffic flow andsaid outbound mode operative for coordinating said plurality of controllers to produce a favored outbound direction of traffic flow.
52. A coordinator as recited n claim 51 wherein said input signals comprise volume and occupancy signals and said calculating means of said master unit calculates a cycle length value in response to said volume and occupancy signals and furthercomprises means for selecting the larger of said calculated cycle length values for transmission of same to said secondary units.
53. A coordinator as recited in claim 52 wherein said coordinator is operative in an average mode and said master unit further comprises means for generating average cycle length values.
54. A coordinator as recited in claim 53 wherein said master unit comprises a plurality of manually operable switches for setting a plurality of average cycle length values and means for selecting one of said values for transmission to saidsecondary units in said average mode.
55. A coordinator as recited in claim 54 wherein said selecting means comprises means for averaging said larger value of cycle length in said inbound mode with said larger value of cycle length in said outbound mode and means for comparing saidaverage value with said set plurality of cycle length values.
56. A coordinator as recited in claim 3 wherein said secondary units comprise means for retrieving said last received cycle length value for controlling said controllers in the event of communication breakdown between said master and secondaryunits.
57. A coordinator as recited in claim 3 wherein said secondary units comprise means for sending force-off commands to said associated controllers for controlling same.
58. A coordinator as recited in claim 57 wherein said secondary units comprise manually operable switches for selecting times for issuing said force-off commands for different phases of traffic flow.
59. A coordinator as recited in claim 58 wherein said selected times are in seconds.
60. A coordinator as recited in claim 59 wherein said force-off commands are selectable independently of cycle length values.
61. A coordinator as recited in claim 2 further comprising means for sending force-off commands to said associated controllers for controlling same.
62. A coordinator as recited in claim 61 further comprising manually operable switches for selecting times for issuing said force-off commands for different phases of traffic flow.
63. A coordinator as recited in claim 62 wherein said force-off commands are selectable independently of cycle length values.
64. A coordinator as recited in claim 2 wherein said coordinator is operable in an inbound and outbound mode, said inbound mode operative for coordinating said plurality of controllers to produce a favored inbound direction of traffic flow andsaid outbound mode operative for coordinating said plurality of controllers to produce a favored outbound direction of traffic flow.
65. A coordinator as recited in claim 64 wherein said input signals comprise volume and occupancy signals and said calculating means calculates a cycle length value in response to said volume and occupancy signals and further comprises means forselecting the larger of said calculated cycle length values for controlling said plurality of controllers.
66. A coordinator as recited in claim 65 wherein said coordinator is operative in an average mode and comprises means for generating average cycle length values.
67. A coordinator as recited in claim 66 further comprising a plurality of manually operable switches for setting a plurality of average cycle length values and means for selecting one of said average cycle length values for controlling saidplurality of controllers in said average mode.
68. A coordinator as recited in claim 67 wherein said means for selecting one of said average cycle length values comprises means for averaging said larger value of calculated cycle length from an inbound mode with said larger value ofcalculated cycle length from an outbound mode.
69. A coordinator as recited in claim 1 wherein said coordinator is operable in an inbound and outbound mode, said inbound mode operative for coordinating said plurality of controllers to produce a favored inbound direction of traffic flow andsaid outbound mode operative for coordinating said plurality of controllers to produce a favored outbound direction of traffic flow.
70. A coordinator as recited in claim 69 wherein said coordinator is operative in an average mode and comprises means for generating average cycle length values, said coordinator further comprising:
means for sensing vehicles entering said artery in both inbound and outbound directions to provide inbound and outbound direction signals, and
means for selecting an inbound, outbound or average mode in response to said inbound and outbound direction signals.
71. A coordinator as recited in claim 1 further comprising means for selecting offset values for said controllers in time units, said offset values selectable independently of said cycle length values.
72. A coordinator as recited in claim 71 wherein said time units are in seconds of vehicle travel time.
73. A traffic coordination system controlling vehicle traffic flow along a main traffic artery and a plurality of side street intersections comprising:
(a) a master unit having programmable computing means,
(b) at least one inbound and one outbound volume vehicle detector each measuring vehicles entering said artery and for providing inbound and outbound vehicle volume signals to said master unit in response to inbound and outbound vehicle volumerespectively, said inbound and outbound vehicle detectors positioned proximate opposite extremities of the artery under control by said coordination system,
(c) at least one inbound and one outbound occupancy vehicle detector for providing inbound and outbound occupancy signals to said master unit in response to inbound and outbound vehicle occupancy respectively, said inbound and outbound occupancydetectors positioned within said artery and removed from said corresponding inbound and outbound volume detectors,
(d) a plurality of secondary units each unit interconnected to said master unit and having means for receiving and storing data therefrom,
(e) said master unit computing means comprising means for calculating a cycle length value for artery traffic in response to received vehicle volume and occupancy signals,
(f) a plurality of controllers, one controller connected for operating traffic signals at each side street intersection of said artery, and
(g) a secondary unit connected to each controller for providing traffic signal control commands thereto in response, at least in part, to data received and stored from said master unit,
whereby traffic is coordinated along said artery in response to sensed vehicle flow.
74. A traffic coordination system as recited in claim 73 wherein each secondary unit issues force-off commands to associated controllers for terminating a green time interval in response to data from said master unit.
75. A traffic coordination system as recited in claim 73 wherein said system is operable in inbound, outbound and average modes of operation as determined by said master unit in response to said vehicle volume signals, said inbound modeeffective to favor inbound traffic flow, said outbound mode effective to favor outbound traffic flow and said average mode effective to favor average traffic flow.
76. A traffic coordination system as recited in claim 75 wherein said computing means of said master unit calculates a cycle length value appropriate for a platoon of vehicles sensed in real-time and transmits data corresponding to saidcalculated cycle length value to each of said secondary units.
77. A traffic coordination system as recited in claim 76 wherein said means for storing data of each secondary unit comprises memory storage means for storing cycle length values received from said master unit and each secondary unit furthercomprises means for retrieving said cycle length values for providing said traffic signal control commands to said connected controller after a period of time determined by an offset value, whereby each platoon of vehicles may be optimally passed througheach intersection by application of the associated stored cycle length value upon arrival of said platoon at each intersection.
78. A traffic coordination system as recited in claim 76 wherein said means for receiving and storing said cycle length values comprises programmable computing means.
79. A traffic coordination system as recited in claim 78 wherein each secondary unit comprises means for selecting said offset value in time units, said offset value selectable independently of said cycle length values.
80. A traffic coordination system as recited in claim 79 wherein said offset value is selectable in seconds.
81. A traffic coordination system as recited in claim 78 wherein said secondary unit comprises means for presetting said offset value in percent of cycle length value.
82. A traffic coordination system as recited in claim 78 wherein each secondary unit is positioned adjacent said connected controller at the corresponding side street intersection.
83. A traffic coordination system as recited in claim 73 wherein each secondary unit is positioned adjacent said connected controller.
84. A traffic coordination system as recited in claim 83 wherein each secondary unit comprises means for selecting the offset value independently of said cycle length values.
85. A method of coordinating a plurality of traffic signal lights associated with side street intersections for controlling traffic at said intersections and along a common roadway comprising steps of:
(a) storing a plurality of cycle length values, said cycle length values associated with groups of vehicles moving along said roadway,
(b) automatically retrieving said stored cycle length values, and
(c) automatically, sequentially and individually controlling said traffic signal lights in response to said retrieved cycle length values at offset times corresponding to the position along said roadway of the side street intersections, therebyproducing cycle lengths at said intersections corresponding to said retrieved cycle length values.
86. A method as recited in claim 85 further comprising the steps of:
(a) receiving input signals, and
(b) automatically calculating from said received input signals said cycle lengths values.
87. A method as recited in claim 86 further comprising the steps of sensing vehicles entering said roadway and generating said input signals in response to said sensed vehicles to provide a directional coordination of said traffic signal lightsfor said groups of vehicles entering said coordinated roadway.
88. A method as recited in claim 87 wherein said sensing step comprises sensing vehicles entering said roadway in both an inbound and outbound direction and generating input signals in response thereto to provide a directional coordination ofsaid traffic light signals in response to sensed inbound vehicles and sensed outbound vehicles.
89. A method as recited in claim 88 further comprising the steps of:
(a) sensing vehicles within said coordinated roadway,
(b) generating additional input signals in response to said vehicles sensed within said coordinated roadway, and
(c) calculating said cycle length values from said input signals and said additional input signals.
90. A method as recited in claim 89 further comprising the steps of:
(a) calculating a modification of said offset times in response to said additional input signals, and
(b) controlling said traffic light signals at said modified offset times.
91. A method as recited in claim 88 further comprising the steps of:
(a) sensing vehicles within said coordinated roadway,
(b) generating additional input signals in response to said vehicles sensed within said coordinated roadway,
(c) calculating a modification of said offset times in response to said additional input signals, and
(d) controlling said traffic light signals in response at said modified offset times.
92. A method as recited in claim 89 wherein said calculating step comprises:
calculating one cycle length value in response to said input signals,
calculating another cycle length value in response to said additional input signals, and
said method further comprising the steps of selecting the larger cycle length value from said one and another cycle length values and storing said selected larger value for coordinating said traffic signal lights.
93. A method as recited in claim 92 wherein the step of sensing the vehicles entering said roadway comprises sensing vehicle volume and the step of sensing vehicles within said roadway comprises sensing vehicle occupancy.
94. A method as recited in claim 93 wherein the step of sensing the vehicles entering said roadway comprises sensing vehicle volume and the step of sensing vehicles within said roadway comprises sensing vehicle occupancy.
95. A method as recited in claim 85 further comprising the step of sensing vehicles on said roadway to provide inbound, outbound and average modes of coordinating said traffic signal lights.
96. A method as recited in claim 85 wherein the step of controlling said traffic signal lights comprises the step of generating force-off command signals to controllers associated with said traffic signal lights.
97. A method as recited in claim 85 further comprising the steps of:
(a) sensing vehicle volume entering said coordinated roadway for providing input vehicle volume signals, and
(b) calculating the cycle length value in real time from said input vehicle volume signals for the group of vehicles being sensed,
whereby said stored cycle length values correspond to groups of sensed vehicles entering said coordinated roadway.
98. A method as recited in claim 97 wherein said cycle length values comprise red band times and green band times and said calculating step comprises calculating a gap time between successive sensed vehicles and terminating said green band timein response, at least in part, to said gap time.
99. A method as recited in claim 98 wherein the step of controlling said traffic signal lights comprises the step of generating force-off command signals to controllers associated with said traffic signal lights.
100. A method as recited in claim 99 wherein said step of terminating said green band time further comprises calculating the number of input vehicle volume signals and delaying the termination of said green band time for numbers exceeding areference value.
101. A method of coordinating a plurality of traffic signal lights positioned along a common roadway for controlling said roadway and a plurality of side street intersections comprising the steps of:
(a) sensing vehicles along said roadway to provide input signals to a master unit,
(b) calculating in said master unit cycle length values in real time corresponding to said sensed vehicles,
(c) transmitting said cycle length values to a plurality of secondary units, each secondary unit associated with a side street intersection,
(d) storing said cycle length values in said secondary units,
(e) individually retrieving said cycle length values in said secondary units for sequential application as force-off commands to associated controllers controlling said traffic signal lights at said side street intersections, and
(f) generating said force-off commands at said secondary units at offset times corresponding to the position of the secondary units along said roadway.
102. A method as recited in claim 101 wherein said sensing step comprises sensing vehicle volume entering said roadway for providing said input signals.
103. A method as recited in claim 102 wherein said sensing step further comprises sensing vehicle occupancy within said roadway for providing additional input signals, and said calculating step comprises calculating said cycle length values inresponse to said input signals and said additional input signals.
104. A method as recited in claim 101 wherein said sensing step comprises sensing vehicles entering said coordinated roadway in both inbound and outbound directions and said method further comprises the step of coordinating said traffic signallights for favoring traffic flow in one of said inbound and outbound directions in response to the number of sensed inbound and outbound vehicles.
105. Apparatus for coordinating a plurality of traffic signal lights along an artery having a plurality of side street intersections comprising:
(a) means for storing in sequence a plurality of cycle length values, said cycle length values associated with platoons of traffic moving along said artery, and
(b) means connected to said storing means for retrieving said cycle length values in sequence and for individually and sequentially controlling said plurality of traffic signal lights to effect said retrieved cycle length values at eachassociated intersection as said platoons of vehicles move along associated intersections of said artery to thereby coordinate said traffic along said artery.
106. Apparatus as recited in claim 105 further comprising:
means for receiving input signals, and
means cooperating with said storing means for calculating said plurality of cycle length values in response to said input signals, whereby said stored cycle length values correspond to said calculated cycle length values.
107. Apparatus as recited in claim 106 wherein:
said calculating means and said means for receiving input signals form a master unit which further comprises means for transmitting said calculated cycle length values, and
said means for storing and retrieving said plurality of cycle length values form a plurality of secondary units, each secondary unit associated with one of said plurality of side street intersections and further comprises means for receiving saidtransmitted calculated cycle length values from said master unit.
108. A coordinator as recited in claim 107 wherein said input signals are generated in response to vehicles.
109. A coordinator as recited in claim 108 wherein said input signals are generated in real time, and said calculating means of said master unit comprises means for calculating said cycle length values in real time for each of said platoons ofvehicles.
110. Apparatus as recited in claim 109 wherein said input signals comprise volume signals generated from volume detectors positioned to sense vehicle volume entering said artery, said calculating means of said master unit calculating said cyclelength values in response to said vehicle volume signals.
111. Apparatus as recited in claim 110 wherein said cycle length value consists of a green band time and a red band time and said transmitting means of said master unit comprises means for transmitting a sync signal during said green band timeat a time related to the calculated cycle length value, and each of said plurality of secondary units comprises means for determining from said sync signal the calculated cycle length value.
112. Apparatus as recited in claim 111 wherein said sync signal corresponds to a change in state of a binary signal.
113. Apparatus as recited in claim 112 wherein said sync signal precedes the end of said green band time by a fixed time interval.
114. Apparatus as recited in claim 113 wherein said transmitting means of said master unit further comprises means for transmitting a coded message corresponding to said cycle length value, and each of said secondary units comprises means fordecoding said coded message, whereby said coded message serves as a redundancy check of said received calculated cycle length values as determined from said received sync signal.
115. Apparatus as recited in claim 114 wherein said coded message is transmitted after said sync signal and during the red band time of the next cycle.
116. Apparatus as recited in claim 109 wherein each of said secondary units comprises first counter means for providing a unique running time count of each platoon within said coordinated artery, said running time count stored in said storingmeans with corresponding cycle length values of said platoons and means for retrieving said running time count and said corresponding cycle length values, whereby said running time count provides an offset value check for platoons passing through saidintersections.
117. Apparatus as recited in claim 116 wherein each of said plurality of secondary units comprises a second counter means resettable at the end of each cycle length value for clocking operations within said secondary unit, said second countermeans in synchronization with said platoons of vehicles passing through said corresponding intersections.
118. Apparatus as recited in claim 117 wherein each of said plurality of secondary units comprises a third counter means in synchronization with platoons of vehicles associated with said master unit and resettable at the end of cycle lengthvalues at said master unit, said first, second and third counter means operable to ensure coordinated vehicle flow through said artery.
119. A traffic coordinator for use on a roadway having a plurality of intersections and traffic lights and means for sensing vehicle traffic along said roadway, said sensing means including means for generating signals indicative of said sensedtraffic, said coordinator comprising:
(a) a master unit comprising:
(i) input interface means for receiving said signals,
(ii) data processing means connected to said input interface means, said data processing means including a microprocessor, data memory storage means and program memory storage means for programming said microprocessor, said data processing meansoperable for calculating a cycle length value in response to said received signals and for generating cycle length signals corresponding thereto,
(iii) output interface means connected to said data processing means for transmitting said cycle length signals,
(b) a plurality of secondary units, one secondary unit associated with each of said intersections along said roadway and associated with an offset time from a preselected reference, each secondary unit comprising:
(i) input interface means operable for receiving said transmitted cycle length signals from said master unit,
(ii) data processing means connected to said input interface means of said secondary unit and including a microprocessor, data memory storage means and program memory storage means for programming said microprocessor, said data processing meansof said secondary unit operable for storing representations of said cycle length signals and for retrieving same in the order of storage for generating force-off command signals corresponding to said cycle length signals at time determined by saidassociated offset times, and
(iii) output interface means connected to said data processing means of said secondary unit for receiving said force-off command signals and for applying same to actuate traffic lights at said associated intersections. .Iadd.
120. A coordinator for coordinating traffic at least along an artery having traffic lights at a plurality of intersections along said artery, said coordinator comprising:
(a) a digital computer means for calculating values corresponding to cycle length green times, said green time values calculated in real-time in response at least to traffic flowing along one intersection of said plurality of intersections ofsaid artery,
(b) means connected to said calculating means for controlling traffic signals at said one intersection for implementing a green time value equal to at least said calculated green time value at said one intersection to thereby define a platoon ofvehicles at said one intersection,
(c) means for setting a plurality of offset times, each offset time corresponding to the distance of each of the remainder of said plurality of intersections from said one intersection, each offset time being a predetermined constant value inunits of time, and
(d) means for controlling each of said plurality of traffic signals at the remainder of said plurality of intersections of said artery in a sequential and individual manner to implement an artery green time value equal to at least said calculatedgreen time value, said green time value implemented at said fixed offset times at each of said remainder of intersections as platoons of vehicles approach said intersections to thereby coordinate traffic along said artery. .Iaddend. .Iadd.121. Acoordinator as recited in claim 120 wherein said coordinator is operable in an inbound, outbound and average mode of operation in response at least to vehicles flowing along said artery, said inbound mode effective to favor inbound traffic flow, saidoutbound mode effective to favor outbound traffic flow and said average mode effective to substantially equally
favor inbound and outbound traffic flow. .Iaddend. .Iadd.122. A coordinator as recited in claim 121 wherein said calculating means are operable in said average mode to automatically calculate optimum offset values corresponding to optimumgreen time values to substantially equally favor traffic flow in both said inbound and outbound directions. .Iaddend. .Iadd.123. A method of coordinating a plurality of traffic signal lights associated with a plurality of side street intersections forcontrolling traffic at said intersections and along a common roadway comprising the steps of:
(a) automatically calculating a green time value in a digital computing means, said green time value calculated in real-time in response at least to input signals indicative of sensed traffic flowing along said common roadway at one of saidplurality of intersections,
(b) implementing a green time value equal to at least said calculated green time value along said common roadway at said one intersection substantially simultaneously with said calculating step by controlling traffic signal lights at said oneintersection to thereby define a platoon of vehicles moving along said common roadway at said one intersection,
(c) setting a plurality of offset times for each of the remainder of said plurality of intersections, said offset times being predetermined constant values in absolute units of time and being constant from one cycle to another and independent ofsaid calculated green time values,
(d) automatically implementing a green time value equal to at least said calculated green time value at the remainder of said plurality of intersections by sequentially controlling traffic signal lights at the remainder of said intersections toeffect at least said calculated green time value along said common roadway at said predetermined offset times, and
(e) while maintaining said offset times at said predetermined value, repeating steps (a), (b) and (d) above to define another platoon of vehicles for coordinating flow of sequential platoons of vehicles along
said common roadway. .Iaddend. .Iadd.124. A method as recited in claim 123 wherein said input signals represent sensed vehicles entering said roadway in both an inbound and outbound direction and wherein said calculating step is done inresponse to said input signals to provide a directional coordination of said traffic signal lights in response to sensed inbound vehicles and sensed outbound vehicles. .Iaddend. .Iadd.125. A method as recited in claim 124 further comprising the stepof automatically calculating an average offset value for each of said plurality of intersections, said average offset value calculated to provide optimum green band times to substantially equally favor traffic in said inbound and outbound directions. .Iaddend. .Iadd.126. A method as recited in claim 123 further comprising the steps of:
(a) sensing vehicles within said coordinated roadway,
(b) sensing additional input signals in response to said vehicles sensed within said coordinated roadway,
(c) calculating a modification of said predetermined offset times in response to said additional input signals, and
(d) controlling said traffic signal lights in response to said modified
offset times. .Iaddend. .Iadd.127. Apparatus for coordinating a plurality of traffic signal lights along an artery having a plurality of side street intersections comprising:
(a) programmable digital computer means for sequentially determining green time values, each green time value being part of a cycle length value, and
(b) additional programmable digital computer means connected to receive signals corresponding to said determined green time values for individually and sequentially controlling said plurality of traffic signal lights to effect cycle length valueshaving green time values at least equal to said determined green time values at said intersections as said platoons of vehicles move across said intersections to thereby coordinate said traffic along said artery. .Iaddend. .Iadd.128. An adaptivetraffic coordination system for use on a roadway having a plurality of intersections and traffic lights and means for sensing vehicle traffic along said roadway, said sensing means including means for generating signals indicative of said sensed traffic,said coordinator system comprising:
(a) a programmable digital computing means for receiving said signals and for calculating in real-time green time values in response to said received signals, said green time values tailored to individual groups of vehicles entering said roadwayas determined by said received signals, and
(b) additional programmable digital computing means positioned at and associated with said intersections for controlling traffic lights at said intersections by sequentially effecting cycle lengths having green time values at least equal to saidcalculated green time values at said traffic lights thereby maintaining flow of said groups of vehicles along said
roadway. .Iaddend. .Iadd.129. An adaptive coordination system as recited in claim 128, wherein said additional programmable digital computing means are operable for controlling said traffic lights to effect cycle phases tailored to eachindividual intersection. .Iaddend. .Iadd.130. An adaptive traffic coordination system comprising:
(a) a first computing means for receiving signals indicative of vehicles traveling along a traffic artery and for calculating green time values in response thereto,
(b) said first computing means having:
(i) a central data processing unit,
(ii) data memory storage means for storing data utilized by said central data processing unit, and
(iii) program memory storage means for storing programs controlling operation of said central data processing unit,
(c) a plurality of second computing means positioned along at least some intersections of said artery for controlling traffic lights at said at least some intersections in response to said calculated green time values, each of said secondcomputing means having:
(i) a central data processing unit,
(ii) data memory storage means for storing data utilized by said central data processing unit, and
(iii) program memory storage means for storing programs controlling operation of said central data processing unit;
whereby said green time values are tailored to individual groups of vehicles moving along said artery and said traffic lights are coordinated to maintain traffic flow of said individual groups. .Iaddend. |
| Description: |
INDEX
BACKGROUND OF THE INVENTION
Field of the Invention
Description of the Prior Art
SUMMARY OF THE INVENTION
BRIEF DESCRIPTION OF THE DRAWINGS
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
SYSTEM OVERVIEW
MODULE DESCRIPTION AND DEFINITIONS
Master Unit 50
Directional Module
System Module
Inbound and Outbound Modules
Volume Module
Occupancy and Speed Modules
Average Module
Display Module
Secondary Unit 40
Split 1 and Split 2 Modules
Offset Module
Display Module
Selector Position
Interface Module-Master and Secondary
SYSTEM HARDWARE DESCRIPTION
FUNCTIONAL DESCRIPTION OF THE MASTER UNIT
Overall Description
Real Time Traffic Sampling
Master Cycle Length Computation
Volume Computations
Occupancy Computation
Average Cycle Length Selection
Directional Commands
Commands Based Upon Occupancy
Output Decisions Update Intervals
Manual Override
System Percent Average
Display
FUNCTIONAL DESCRIPTION OF THE SECONDARY UNITS
Average Offsets
Transition Response
Force Off Operation
Free Operation
Flash/Pre-Emption Operation
Timer Monitoring
Standby Operation
Automatic Input Test
SOFTWARE DESCRIPTION
MASTER UNIT
Update
PREXMIT
COMPOSE
GAPOUT
GAPEND
SYNCEND
GRNUPDIR
REDTIME
GRNIN
DIRSEL
CONVRT (Calls OCCSEC)
GRNUPAVG
MANUAL CYCLE
CTRMNTR (Counter Monitor)
CYCTWS
RANAVG
QUEUE ROUTINES
SECONDARY UNIT
Overview of Secondary Operation
Cycle Execution
Transitions
Queue Recovery
Timing
Dual Counter Concept
Direction Change Processing
Overall Block Diagram of Secondary Unit
LATCHES
LAMPFORM
FORMATCP (Format, Complement, Pack)
LDECLP (Load ECLP)
DECISION
TRANSMOD
LIMITCKK
NUMPHASE (Phase Number)
SECONDARY UNIT (Continued)
SPLITIME
PHDR (Phase Decrement)
PHTMSET, TWS, SPLITSUM, PERSEC
TRANSITION
LENGTHEN
MODO
SECSYNC
CKRANG
QRECOV (Queue Recovery)
STORE
AV/DIR (Average to Directional)
QUEUE
SHORTEN
OFFSEC, OFFMAS
CTRMAS
CTRSEC
FREEOP
MONITOR
SCREEN
STREETPH
GETPHASE
APPENDIX
Master Unit
Secondary Unit
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention is in the field of traffic coordinators, particularly those coordinators utilized for controlling arterial systems.
2. Description of the Prior Art
Many different types of traffic control systems have been devised in the prior art to meet particular traffic needs. Typically, traffic controllers are located at an intersection and may be either pretimed or traffic actuated devices. Manyattempts have been made to coordinate the operation of the various controllers. Simple systems utilize time clocks or simple program units to coordinate a plurality of timers to thereby permit progressive traffic flow patterns. More sophisticatedsystems utilize a separate master coordinator (traffic computer) unit which may be programmed to control arterial systems or a complete grid network. Examples of such prior art systems are shown, for example, in U.S. Pat. Nos. 3,818,429, 3,660,812,3,506,808, 3,258,745, 3,307,146 and 3,252,133. Typically, traffic control systems provide means for determining cycle lengths, offset and split information by utilizing either traffic actuated vehicle detectors to monitor traffic flow or storedparameter programs set to correspond to historical data for the intersection or artery under consideration. U.S. Pat. No. 3,258,745, for example, illustrates a traffic control system for an artery utilizing traffic actuating controllers and permittingadaptive control of split data in response to vehicle presence. U.S. Pat. No. 3,506,808, for example, discloses the utilization of both volume and occupancy detectors to determine appropriate cycle length in an analog computing and control system. Digital processing techniques for a traffic control system are shown, for example, in U.S. Pat. No. 3,818,429. Most of these prior art systems, however, lack the flexibility necessary to control a large number of traffic conditions, are complicated toinstall and control no provisions for coordinated operation during communication breakdown. Additionally, prior art coordinated traffic systems do not permit a means for achieving different cycle lengths simultaneously throughout the coordinated systemto follow a platoon of vehicles through the system. As a consequence, cycle length is typically changed throughout the entire system at one time so that the coordinated system cannot truly operate to optimize the traffic flow pattern for the differentplatoons travelling therein.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a traffic coordination system which overcomes the disadvantages of the prior art and provides an economical and easily installed system for controlling arterial traffic.
Another object of the invention is to provide a traffic coordinator which operates in a real time to vary cycle length in a rippled fashion such that new cycle length information is sequentially applied at the controlled intersections to insureefficient movement of each of a plurality of platoons of cars through the system.
Another object of the invention is to provide a distributed processor coordination system such that system commands and calculations applicable to the entire artery are done in a single master unit whereas the interpretations of these commandsparticularized to the condition at the individual controlled intersections are carried out in secondary units by separate microprocessor means.
Yet another object of the invention is to provide a data communication system for use in a distributed processor traffic coordinator.
Yet another object of the invention is to provide a means for enabling coordinated traffic control during a breakdown in communication between a master unit and a plurality of secondary units in a coordinated system.
Another object of the invention is to provide a traffic coordinator sensitive to both volume and occupancy values within a controlled artery to achieve a real time calculation and selection of cycle lengths for each platoon of vehicles enteringthe artery.
In accordance with the invention, an arterial traffic coordinator is provided for use with a plurality of controllers and traffic detectors. Each controller is associated with a side street intersection for controlling traffic signals at theintersection. The detectors sense vehicle volume into the artery and vehicle occupancy within the artery for providing corresponding volume and occupancy signals. The coordinator comprises a means for receiving the volume and occupancy signals, a meansfor calculating an optimum cycle length in response to the received volume and occupancy signals and a means for storing the calculated cycle lengths corresponding to each platoon of vehicles. The coordinator further comprises means, connected to thestoring means for retrieving the calculated cycle lengths, and for sequentially controlling the plurality of coordinators to effect the calculated cycle length at each associated intersection so that each platoon of vehicles moving through theintersection is controlled by its own optimum cycle length thereby achieving a coordinated traffic control.
The invention further provides for a means of changing the cycle length without the necessity of changing offset. To accomplish this end offset times are settable in seconds of travel time as opposed to percentages of cycle lengths. In thismanner a constant speed through the system may be obtained while permitting variable cycle lengths.
The invention is further characterized as a distributed processing coordination system comprising a programmable master unit and a plurality of programmable secondary units. The master unit calculates system parameters such as cycle length anddirectional information in response to sensed volume and occupancy values. The secondary units response to the received master information, but act in accordance with separate program instructions and in accordance with individual input parameterscorresponding to the associated intersection. The independent processing capability of the secondary units prevents undesirable rapid and/or blind response to information from the master unit.
Further subject matter disclosed herein is the subject of a copending application of Marshall B. McReynolds and Jack D. VanTilbury, Ser. No. 843,730, filed Oct. 19, 1977 and assigned to the same assignee as herein and entitled "Average/ModeTraffic Control System". For directional inbound and outbound modes, the coordinator operates to calculate a specific cycle length to each platoon entering the artery and the calculated cycle length is rippled through the artery as the platoon ofvehicles moves through the intersections. In the average mode of operation an optimum cycle length is calculated to effect substantially equally by favored traffic flow in each of two directions. More generally, an average mode apparatus is providedwhich comprises means for establishing a directional offset time for each of the intersections which is proportional to the distance of the intersection from a reference intersection, as for example the first or last intersection in the artery. Theapparatus further comprises means for dividing a reference cycle length time into each of the directional offset times for determining a remainder fraction, means for selecting an average-mode offset time for each intersection from one of the group ofapproximately zero percent and approximately fifty percent of the reference cycle length time in accordance with the value of the remainder fraction, and means for controlling traffic signal lights at the intersections by utilizing the selectedaverage-mode offset times as offset values with respect to the reference intersection.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other objects of the invention will become clear in relation to the foregoing specification taken in conjunction with the drawings wherein:
FIG. 1 is a diagrammatic illustration of a typical artery having side streets and showing the interconnection of the master and secondary units forming the coordination apparatus;
FIG. 2 illustrates the orientation of FIGS. 2A and 2B in a master unit;
FIGS. 2A and 2B are front plan views of the modules employed in accordance with the invention;
FIG. 3 is a front plan view of a secondary unit illustrating the various front panel controls of the modules utilized in accordance with the invention;
FIG. 4 is a block schematic diagram of the different types of modules utilized in the master and secondary units;
FIG. 5 is a schematic diagram of the central processor utilized in the master and secondary units in accordance with the invention.
FIG. 6A is a schematic diagram of a random memory storage means utilized in the master and secondary units;
FIG. 6B is a schematic diagram of a programmable read only memory utilized in the master and secondary units;
FIG. 7 is a schematic diagram of a switch module in accordance with the invention;
FIG. 8 is a schematic diagram of the LED display circuitry;
FIGS. 9A-9D are schematic drawings for the circuitry in the display module of the master and secondary units;
FIG. 10 is a schematic drawing of the master calling circuitry within the interface module of the master unit;
FIG. 11 is a schematic drawing of the circuitry within the interface module of a secondary unit;
FIG. 12 shows a timing diagram depicting cycle length computation utilized by the master unit;
FIG. 13 is an overall flow diagram of the operation of the master unit in accordance with the invention; and
FIG. 14 is a flow chart of the main driver routine for the operation of the secondary unit in accordance with the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
SYSTEM OVERVIEW
As illustrated in FIG. 1, the traffic control system of the instant invention may most advantageously be utilized to control artery traffic as shown in FIG. 1. A main artery 10 which may comprise a four lane highway, two inbound lanes and twooutbound lanes, for example, is shown intersected by a plurality of side streets 12a-12e. Although only five side streets are shown it is readily understood that the number may be greater or less than five to control various lengths of artery traffic. Artery 10 comprises an inbound roadway 14 and an outbound roadway 16. At the beginning of inbound roadway 14 are positioned two inbound volume detectors 18a and 18b which may be conventional vehicle traffic detectors actuated by the vehicle. Naturally,if the inbound roadway consists of only one lane, then only a single detector 18a is employed. Similarly, at the beginning of the outbound road 16 two outbound volume detectors 20a and 20b are positioned to detect vehicle passage. Additional vehicledetectors are positioned between the inbound volume detectors and outbound volume detectors as for example the inbound occupancy detectors 22a and 22b and the outbound occupancy detectors 24a and 24b.
At the intersection of each sideway street 12 with the main artery 10 there is shown a traffic signal 30a-30e respectively. It is understood that the traffic signal at each intersection may comprise a plurality of lights, one governing eachlane, and additional lights directing right and left turns, pedestrain crossing, leading greens and so forth as may be desired. The various traffic flow patterns governed by the signals are referred to as phases. Each traffic signal is controlled bymeans of associated controllers 32a-32e which may, for example, be of conventional type such as the Crouse-Hinds model DM-200. Controllers 32a-32e are effectively timers which serve to energize the various traffic signals 30a-30e and are capable ofbeing forced off (force to red) after selectable time periods. The issuance of force-off commands to the controllers is, in fact, the mechanism by which coordination is obtained. For a detailed explanation of the operation of an exemplary controller,reference is made to the Crouse-Hinds Technical Data Bulletin, TDB-106T, November 1976, incorporated herein by reference. The coordination system described herein may coordinate any of a large number of types of controllers, and is designed inaccordance with specifications of the National Electrical Manufacturers Association (NEMA) as set forth in the Standards Publication, NO. TSI-1976. Secondary units 40a-40e connected respectively to controllers 30a-30e serve to override the normalcontroller function by issuing force-offs as dictated by coordinated master/secondary system considerations. Each secondary 40a-40e is connected by a plurality of conductors 42a-42e to each associated controller 32a-32e, respectively. Each secondaryunit 40a-40e is connected to a master unit 50 by means of a communication path 52. The communication path 52 may comprise either multi-conductor cables or conventional telephone interconnections so as to permit relatively easy installation into existingtraffic control equipment.
The controllers 32a-32e may be of actuated type having associated traffic detectors for the side streets. The traffic control system in accordance with the invention effectively coordinates the operation of all of the conventional controllers 32since the force-off information is now provided by the controllers associated secondary unit 40 as directed by the master unit 50. Additionally, each controller 32 is fed a large maximum artery green time (MAX II), and a continuous recall is made in thecontroller 32 to green artery phase. As a result the controllers 32 will always permit artery green unless forced-off by a secondary unit command.
The master/secondary communication scheme is a simplex-type communication. The master unit 50 operates in a broadcast mode to transmit data to all secondaries, each of which responds to the incoming data.
Lines L18a-L18b are associated with detectors 18a and 18b respectively and provide vehicle sense data to the master unit 50. Similarly, lines L20a-L20b, L22a-L22b, and L24a-L24b are connected to master unit 50 to provide corresponding vehicledetection information thereto. Although these input lines to the master unit 50 are shown connected to vehicle sensing detectors, it is clear that input signals to the master unit may originate from other sources such as weekly programmers or the liketo set up desired platoons on the artery. The coordinator, in accordance with one aspect of the invention, may thus store externally generated cycle length values (whether or not generated from vehicle sensing means) and apply them in sequence tocontrol the traffic light signals at each intersection.
The front panel controls and interconnections of the master and secondary units are shown in FIGS. 2 and 3 respectively. The master unit 50 is seen to comprise a plurality of separate modules labeled inbound, volume, outbound, system, direction,interface, display, average, occupancy and speed. Secondary unit 40 comprises a plurality of modules labeled interface, display, offset, split 1 and split 2. Both the secondary unit 40 and the master unit 50 contain as interface module and a displaymodule. The remaining modules in both the secondary and maaster units may be characterized as switch modules in that they primarily comprise a plurality of thumbwheel switches (TWS) which may be set by the operator. Additionally, these switch modulescomprise individual indicators to provide various output data.
The various thumbwheel switch settings which provide input data and the various indicators which provide output data are explained more fully below wherein the various terms adjacent to the switches and indicators are described.
MODULE DESCRIPTION AND DEFINITIONS
Master Unit 50
Direction Module
Thumbwheel switches are provided on the direction module for setting the set points utilized in determining whether the coordinated system should operate in the INBOUND, OUTBOUND or AVERAGE mode. Actuations on the inbound (IN) and outbound (OUT)volume detectors are utilized in the formula IN/(IN+OUT).times.100, and compared to the percentage values selected on the IN and OUT thumbwheel switches to select among the three possible modes.
The minimum green time is also settable on the direction module of the master unit. The minimum green is settable in seconds and is an overriding criteria for insuring that the arterial green period always exists for the settable minimum time.
The average sample time in minutes is settable on the direction module for two conditions. If a decision has been made to change from directional to average during a given cycle time the "INTO" thumbwheel switch selects a time period over whichthe decision must persist as dictated by persistent traffic conditions. The master unit will thus not enter into an average mode of operation from a directional mode unless the conditions dictating the change persists for the time period set on the"INTO" thumbwheel switch. Similarly, the master unit remains in the present average cycle length for a time period settable by the thumbwheel switch labeled "IN".
SYSTEM MODULE
The maximum side street green time is settable on two sets of thumbwheel switches, each set comprising three thumbwheel switches defining time periods set in seconds. The first set of switches is for the Split 1 condition (S-1) whereas thesecond set of switches corresponding to a larger side street time is for the Split 2 condition (S-2). An indicator is energized corresponding to the selected split. The master unit will automatically select the Split 2 condition if a predeterminedgreen band is exceeded. The settable maximum side street time is essentially the Red phase (artery) time.
The system module also contains a set of thumbwheel switches utilized to set the maximum green period for the artery green as given in seconds. This maximum green period is an overriding criteria similar to the minimum green period.
The system module also contains three thumbwheel switches labeled Y.sub.in, Y.sub.out and X. These thumbwheel switches are utilized to convert occupancy levels as measured by the occupancy detectors into cycle length in seconds. The Y valuescorrespond to a percentage value having a cycle length equal to the maximum green time setting, and the X switch corresponds to a percentage of cycle length corresponding in time to the minimum green time in seconds.
INBOUND AND OUTBOUND MODULES
The inbound and outbound modules are essentially identical and apply to the inbound and outbound directions respectively. The upper pair of thumbwheel switches is utilized to set a time value in which an initial gap time between cars is linearlyreduced to a minimum gap time between cars. Thumbwheel switches are separately provided to set both the initial gap in seconds and the minimum gap in seconds as well as the time to reduce in a linear fashion from the initial gap to the minimum gap. Ifthe gap between any two cars exceeds the time allowed for the gap then a "gap out condition" occurs which, under certain circumstances, terminates the green artery phase.
Separate thumbwheel switches are also provided to allow a time period settable in seconds for the last car passage. This time interval effectively enables a car just crossing a volume detector to pass through the intersection prior to itsturning red. The last car passage time is thus added to a green band calculated on volume figures and/or occupancy figures. After a gap out condition is recognized, a time which is equal to the front panel setting of the last car passage is typicallyadded to the green band after which the green period terminates. A last car passage time of at least two seconds is provided even if the front panel thumbwheel switches are set to less than two seconds.
VOLUME MODULE
The volume module is divided into an inbound portion and an outbound portion wherein each portion contains pairs of thumbwheel switches labeled red and green. These thumbwheel switches correspond to headway settings in seconds for the red arterytime and the green artery time in both inbound and outbound directions. The red headway time essentially corresponds to the amount of time alloted a car which passes a volume detector during an artery red. The headway time given for a vehicle actuatinga volume detector during the green period (green headway) is typically less than the red headway time inasumch as the vehicle is already moving and less time would be required for it to enter and pass through the intersection.
OCCUPANCY AND SPEED MODULES
The occupancy and speed modules contain corresponding sets of thumbwheel switches to permit the master unit to direct speed changes to the secondary units. In principal one wishes to increase the traffic flow speed to compensate for increasedoccupancy values. A change in the speed of the system will effectively increase or decrease the offset of the secondary units from the offset figure initially put in on the secondary unit thumbwheel switches. Each occupancy value, expressed in percentof occupancy, on the master Occupancy module corresponds to an adjacent percent speed change on the Speed module of the master unit. Four separate speed modifier settings are possible. 100% indicates no modification; 101% to 199% indicates an increasewhile 000 to 099% indicates a decrease in system speed. The effective speed modification percentage is indicated by an energized indicator (LED) adjacent to the selected thumbwheel switches.
AVERAGE MODULE
The average module is utilized to set four different average cycle lengths in seconds, one of which is selected by the master unit during the AVERAGE mode of operation. A maximum cycle length of 299 seconds may be selected. One of the fourpresettable cycle lengths is selected depending upon which one is closest to the calculated value of (IN+OUT)/2 where the IN and OUT values are the larger of either the volume cycle length value or occupancy cycle length value. The presettable values onthe average module may be optimally determined using a nomograph supplied by TESCO of Alexandria, Virginia and described in U.S. Pat. No. 4,122,994 incorporated herein by reference.
DISPLAY MODULE
The numeric display located on the face of the display module indicates the following parameters as enabled by the adjacent select switch. For cycle lengths in excess of 199 seconds a +(plus) is activated indicating numbers of 200 to 299. Forparameters expressed in percentage a - (minus) is activated. A flashing display denotes manual override operation.
Ten selectable parameters from throughout the unit are available and appear on the 21/2 digit display of this unit.
The ten position selector shall be assigned as follows:
______________________________________ 3 An alternate display of Vol./Ocp. in seconds 2 An alternate display of Occupancy ex- pressed in Sec./% INBOUND 1 Green band in seconds derived from volume 0 Present effective green band in seconds 9Green band in seconds derived from volume 8 An alternate display of Occupancy ex- pressed in Sec./% OUTBOUND 7 An alternate display of Vol./Ocp. in seconds 6 Gap value in seconds and tenths of seconds 5 Present effective cycle length in seconds 4 An alternate display of T.sub.r in Sec./ ##STR1## ______________________________________
This computation is based on IN and OUT vehicle counts per each cycle.
SECONDARY UNIT
Split 1 and Split 2 Modules
The Split 1 module is utilized to allow setting of various force-off times in seconds for associated phases of the intersection. The top thumbwheel switch is reserved for the artery phase whereas the bottom three sets of thumbwheel switches arereserved for side street phases. The Split 2 modules is essentially identical to the Split 1 module although different force-off times may be utilized. Typically, the Split 2 module has a longer side street service time for the arterial traffic flowwhich may correspond also to a larger green time dictated by the master unit.
The phase thumbwheel switches permit association of the artery phase (as well as the side street phases) from the secondary unit 40 to the controller without the need for special logic circuits or wiring changes. Identical secondary units 40 maythus be employed for use at intersections wherein controllers have any assignment of artery and side street phases.
OFFSET MODULE
The offset module of the secondary unit has a plurality of thumbwheel switches for setting the offset time for inbound and outbound traffic with respect to a reference point. The reference point may, for example, by any point in the system notnecessarily physically associated with the master unit location and is typically selected to be at the first intersection for inbound traffic flow or at the first intersection for outbound traffic flow. The offset is set in seconds by simply dividingthe distance from the reference point by the velocity of traffic flow. Percent offset may also be selected during the average mode of operation utilizing the two thumbwheel switches provided in the offset module. Indicators are energized adjacent theinbound and outbound offset directions depending upon which is in effect at the time. Additionally, a percent and automatic indicator are provided to correspond to the percent offset and for the automatic computation of average offset when in theAverage mode.
DISPLAY MODULE
A two and one-half (21/2) digit numeric display is provided on the display module to indicate the following information when selected by an adjacent selector: A plus indication displayed along with the 1 in the most significant digit positionimplies the value 2=200.
SELECTOR POSITION
0--Effective speed wrap in % to 199%.
1--Incrementing secondary cycle in either seconds or %.
2--Effective cycle length in seconds.
3--Offset in seconds (Difference between Master and Secondary units in seconds.)
4--Offset transition, i.e., necessary correction expressed in seconds and updated each cycle. Will normally be 0 when no transition is underway.
Selector Position 5 thru 9:
Incrementing arterial phase followed by decrementing side street phase intervals in seconds or %.
Positions 5 thru 9 enable settable standby cycle lengths of 50 thru 90 seconds respectively. Positions 0 thru 4 enable a standby cycle length of 40 seconds.
The standby cycle length is in effect upon initial turn on of the unit and upon a communications failure that has exceeded time out. Operation in standby is indicated by the appearance of the "minus" sign preceding the numeric display.
INTERFACE MODULE-MASTER AND SECONDARY
The interface and display modules of the secondary unit 40 comprises two I/O pin connectors 70 and 72 respectively. Similarly, the interface and display modules of master unit 50 have I/O pin connectors 80 and 82 respectively. I/O pin connector70 of each secondary unit is interconnected to the I/O pin connector 80 of the master unit via the communication path 52 (FIG. 1), and the I/O pin connector 72 of each secondary unit is interconnected to its associated controller 32 via conductors 42. I/O pin connector 82 of the master unit is interconnected to the various vehicle detector lines L18a-b, L20a-b, L22a-b and L.gtoreq.a-b. Each display module is seen to further comprise a display and a thumbwheel selector switch. The interface module ofboth the secondary and master units are seen to comprise, in addition to the I/O pin connectors, a plurality of manual buttons. For the master interface module manual override buttons are provided in the form of slide switches, and in the secondaryinterface module spring loaded pushbutton switches are provided for automatic test purposes.
SYSTEM HARDWARE DESCRIPTION
FIG. 4 shows a block schematic diagram of the various modules which are represented in both the master and secondary units. Both the master 50 and secondary 40 each have an interface and display module, the front panel of which is shown in FIGS.2 and 3 respectively. The remaining modules shown in FIGS. 2 and 3 are switch modules and are of the same general type described in detail hereinbelow. The master unit 50 and secondary unit 40 also comprise modules which are internal to the units andhave no front panel access. These internal units (which may have rear panel access, for example) include a CPU module, RAM module, PROM module and power supply modules. Consequently, FIG. 4 is representative of a block diagram for both the secondaryunit 40 and the master unit 50. In this connection it is emphasized that the secondary unit and the master unit each contain computing means and memory storage means. Each secondary unit is, of course, programmed identically with the necessary inputparameters for each secondary unit fed into its CPU via the front panel thumbwheel switches as available on the switch modules and via connections to the master unit from the interface module. The master unit 50 is programmed to control the secondaryunits 40 in such a fashion as to provide a system control consistent with the design objectives as explained more fully below.
FIG. 5 illustrates the CPU module which is utilized in both the master and secondary units. The CPU module may comprise for example, an Intel Model 8080A microprocessor together with its associated clock generator Model 8224. For a completeexplanation of the operation and use of the microprocessor, reference is made to the Intel 8080 Systems User Manual published by Intel Corp., Santa Clara, California and incorporated herein by reference. The WAIT output of the microprocessor is fed totwo "D" flip-flops Model 4013 which are clocked utilizing the TTL phase 2 output of the clock generator. The Q output of the second series flip-flops is utilized to provide the "ready" signal to the microprocessor. The effect of the two flip-flops isto extend the allowable response time for CPU associated RAM, PROM and I/O, in order to provide reliability of operation for the overall system and to permit the use of slower, commercially available components.
Address lines A0-A15 are utilized to address various other modules and memory locations in the master and secondary units. Communications between master and secondary units utilize data lines D0-D3 which are also used for all I/O. Data linesD0-D7 are used for data communication to PROM and RAM. Address lines A10-A14 are fed to comparator, Model 14585, and are utilized to provide an I/O command signal along line 90. The I/O command signal must be present during all I/O operations. Readand write strobes are also provided from the CPU along the RD and WR lines respectively.
FIG. 6A is representative of a RAM memory module utilizing for example a plurality of 256.times.4 static MOS RAMs, Intel Model 2112. The chip enable and read/write inputs are provided via decoders, Model No. 14556, conditioned by address linesA8, A10-A14, the read strobe RD and write strobe WR. Data and address lines are interconnected to the memory chips in a conventional manner as shown.
An exemplary PROM module is illustrated in FIG. 6B. The module is seen to comprise a plurality of 1024.times.8 MOS erasable PROMs such as Model No. 2708 (Intel), and decode logic circuitry consisting of Model No. 14556 decoders and NAND gates asshown. A 12 volt regulator Model 7812 is also provided. Typically, three or four PROM circuit boards may be provided each as shown in FIG. 6B. A switch means 94 is provided to enable addressing of a desired circuit board.
A detailed schematic diagram of a switch module (inbound, outbound, etc.) is illustrated in FIG. 7. The circuit shown in FIG. 7 is positioned on a single printed circuit board and is capable of reading eight different thumbwheel switches. Within certain modules, two printed circuit boards of the type shown in FIG. 7 are required wherein any excess switch reading capabilities are ignored. For example, the outbound module of master unit 50 (FIG. 2) contains a single printed circuit boardas shown in FIG. 7. The system module of the master unit, however, requires two boards with the resulting capability of reading sixteen thumbwheel switches. In practice, only twelve switches need be read so that the circuitry for the remaining fourswitches is not utilized.
FIG. 7A shows the position of the switches which are labeled S1-S8 and are addressed respectively by the binary number 0-7. Each switch module contains a four bit comparator 91, Model No. 14585, for example, which compares the address code alongthe address lines A3-A6 with a hard wired address code unique to each particular switch module location. Consequently, the address bits A3-A6 are compared with the four bit hard wired code, and, if equal, an output strobe is provided along line 92. TheI/O command along line 90 is also fed as a conditioning input to the comparator 91. The output of the comparator 91 goes high whenever the address matches the hard wired address code, so that a logical 1 is placed along a line 92 and fed to NAND gate96. A second input to NAND gate 96 comes from the read strobe RD so that its output goes low whenever the particular switch module is addressed for reading. The low signal from the NAND gate 96 is fed to an analog mux/demux Model No. MC14051 used as athree-to-eight data selector. Depending on the particular code appearing on the address lines A0-A2, one of the switches S1-S8 is selected which subsequently provides an output along the data lines D0-D3. These data lines, of course, are part of thebidirectional data bus and are fed to the CPU shown in FIG. 5.
The output of the comparator 91, along line 92 is also shown connected to another NAND gate 98. The second input to this NAND gate is the write strobe WR. The output of NAND gate 98, the output enable signal, is fed to a quad display circuitduring an output or write command. In reference, for example, to master unit 50 it is seen that the outbound module contains eight thumbwheel switches and three display indicators. The eight thumbwheel switches are simply the switches S1-S8, whereasthe display indicators are shown in FIG. 8 and form part of the quad display circuitry. Thus, each switch module in both the master and secondary units contains at least one quad display and a maximum of four indicators may occur on any given module. The output enable signal is fed to a quad latch 99, for example, Model No. 14042 to latch the write data appearing on the data lines D0-D3. The latched data is fed to power inverter 100, for example Model No. ULN2003A (Sprague) which subsequently feedsindicating diodes D1-D4. In this manner, the hard wired address code provided as an input to the comparator 91 of FIG. 7 serves to direct the address decoder for both the switches S1-S8 and the indicators D1-D4.
The display module is shown in detail in FIGS. 9A-9D. FIG. 9A illustrates the address decode for the display module which is implemented by logic circuit 102 utilizing address lines A3-A6. Additionally, the command I/O is provided as an inputto the logic circuit 102. The output of the logic circuit 102 is fed along line 104 to NAND gates 106 and 108. NAND gate 106 is provided with an input from the write strobe WR and NAND gate 108 is provided with an input from the read strobe RD. Theoutput of NAND gate 106 goes low whenever the display module is being addressed and a write command is to be implemented. The low or logically zero output is fed along line 110 to the inhibit input of an analog mux/demux 112 (Model 14051 for exampleused as a three-to-eight decoder). Decoder 112 provides a plurality of write strobes WS to be utilized with additional circuitry of the display module. These write strobes are identified by their binary decode so that decode 2 corresponds to writestrobe WS-2 etc.
In a similar fashion the output of NAND gate 108 provides a logically zero output along line 114 to the inhibit input of decoder 116. Decoder 116 provides a plurality of read strobes RS, for use with additional circuitry in the display module. The particular line selected from the decoders 112 and 116 is dependent upon the address appearing on address lines A0-A12. The read strobe lines are also identified by their address decode. The circuitry shown in FIG. 9A is common to both the masterand secondary display modules.
As may also be seen in FIG. 9A, two thumbwheel switches S1 and S2 are provided and are shown connected to the decoder 116. If a read command is given to the display module, these switches S1 and S2 may be addressed from address lines A0-A2 asaddress # zero and one respectively. Upon selection of either switch S1 or S2 the input lines to the decoder 116 are fed to the common pin 3 terminal of 116 so that the data bus D0-D3 may carry the BCD signal generated by each thumbwheel switch. It isnoted that switch S1 is optional and is not utilized in the display modules for the secondary or master units as shown in FIGS. 2 and 3 respectively. Upon issuance of a write command the decoder 112 may be activated by address lines A0-A2. A decode ofa binary zero or one is used to display one of two digits of the three digit seven-segment display shown for both the master and secondary display modules. The circuitry of FIG. 9A may be utilized to select either the intermediate significant digit(ISD) or the least significant digit (LSD) of the seven-segment display. The display circuitry for the ISD and LSD may comprise Model No. 14511 BCD to seven-segment decoder/driver, a resistor dropping network, and seven-segment LED display, Model No.MAN 3640A (Monsanto).
FIG. 9B illustrates additional circuitry for the display module which is common to both the master and secondary units. The circuitry of FIG. 9B controls the most significant digit in the seven-segment display as well as the "+" sign. The writestrobe WS2 is utilized to activate a quad latch 120 (Model 14042) to drive LED display 122 (Model MAN3630A). Additional latches 124 and 126 are strobed by write strobes 3 and 4 to provide 24 volt level output of connectors labeled - . For the masterunit 50, these 24 volt level output lines are fed to the I/O pin connectors 82 whereas for the secondary unit 40 these 24 volt output level lines are fed to the I/O pin connectors 72. The current sinks operating from a 24 volt level are provided onthese output pin connectors from the 5 volt logic signals provided from the latches 124 and 126 via power inverters 128 (Model ULN2003A) and resistor network 130. Thus, these strobes are utilized to provide output data either to the display 122 or the24 volt output level lines. The data originates from the data bus D0-D3. Various additional write strobes are fed to other circuitry within the display module as to be described hereinbelow.
FIG. 9B illustrates some of the read strobes which are utilized to latch input data into the data bus D0-D3. The input data is provided to the master or secondary via I/O pins 82 or 72 respectively which pins are connected to lines - as shown. The 24 volt level signal is passed through conditioning circuit 132 to translate the voltage level to 5 volts as utilized for inputs to the strobed inverter buffers 134 and 136. Input data from these buffers is fed to the CPU along the data lines D0-D3.
Additional read/write strobes are passed to still other circuitry of the display module to be described hereinbelow.
FIG. 9C illustrates additional circuitry for the display module which is applicable to the secondary units. Write strobes WS5 and WS6 are utilized to feed data from the data line D0-D3 to the interface module and I/O pins 72 respectively. TheI/O pin outputs are spares and may be available for additional expansion of the system. The 24 volt level outputs to the interface module are provided by power inverters and resistor networks as in FIG. 9B. The four outputs conditioned by WS5 comprisethe test level call signals which test operation of the secondary interface modules at 100%, 84%, 67% and 50% voltage levels. Write strobe WS6 is utilized to strobe a data code for activating a flash call generated by the secondary software. The flashcall would be generated, for example, under system software control if the controller associated with the particular secondary did not respond to force-off commands and additionally failed to respond to the interval advance procedure. The D0 bit in thedata bus line together with the write strobe WS6 would provide a signal along line 140 through power driver circuit 142 and solid state relay circuit 144. The output of solid state relay circuit 144 along pin 22 provides a 115 V 60 Hz source to thecontroller 32 for calling the flash condition.
Read strobes are also shown in FIG. 9C for strobing in the test call information and coded message data from the secondary interface module. The coded message data originates from the master data bus and is transmitted to the interface module ofthe secondary units via communication path 52. Read strobe RS4 is utilized to strobe in the test call information whereas read RS6 is used to strobe in the coded message information. Read strobe RS5 strobes 60 Hz sync data to enhance synchronization ofoperation of the master and secondary units. Read strobe RS7 is utilized to gate in additional input data from the I/O pin connector 72. Spare pins are also provided.
FIG. 9D illustrates additional display module circuitry which is applicable to the master unit only. Write strobe WS5 latches output data from the data bus D0-D3 to provide 24 volt level data which is the coded message transmitted to thesecondary (via the master interface module and I/O pin connector 80). Write strobe WS6 is utilized to gate failure detection data to the master I/O pin connector 82 output via latch 150 and a power inverter and resistor network as shown. Additionaloutput data may be provided by the write strobe WS6 and latch 150 to energize the indicators D17 and D18 which appear on the face of the master display module. Latch 150 also controls the selection of groups of behind front panel switches 152 to providedata to the master unit CPU permitting external programming for system data which typically will not change once the system is installed. For example, these switches may be used to store a BCD code for instructing a change from Split 1 to Split 2operation. The data is selected utilizing a quad select gate, for example, Model No. CD4019.
Also illustrated in FIG. 9D are the read strobes which provide additional information to the master from the I/O pin connectors 82. Four lines of input data are provided via RS4. RS5 enables sensing of the 60 Hz sync information as was done inthe display module of the secondary units. Read strobe RS6 is utilized to strobe data from input pin 15 to the data bus, and input pins 13 and 14 are connected to a data selector 154 (Model No. 14053) which is also connected to receive manual IN andmanual OUT information from the interface module.
FIG. 10 is a schematic diagram of the interface module appropriate for the master unit 50 of FIG. 2. Information is transmitted between the master unit and secondary units via communication path 52 (see FIG. 1). A 24 V DC level communicationline may be provided or, optionally, a 115 V AC level line and appropriate circuitry (not shown) may be used. The circuitry illustrated below provides a 24 volts DC level. The coded message signal is represented as a single line, but it is understoodthat in practice four lines are provided with four separate transistor circuits to provide the coded message to the secondary units along the pins 5 - 8 of I/O pin connectors 80 of the interface module for the master unit 50. The transistors shown areutilized to convert the 24 volt sink lines to 24 volt source lines for driving the data over the communication path 52 to the interface modules of the secondary units. All output data on the right hand side of FIG. 10 is fed along the communication path52 to all secondary units simultaneously. Flash calls, pre-empt calls and free op calls shown on the left hand side of FIG. 10 may be provided as optional input calls along I/O pin connectors 80.
The manual switches located on the face of the interface module of the master unit 50 are represented by switches S1-S4 in FIG. 10. The manual enable switch S4 may be closed together with switch S1 to provide IN and OUT directional signals tothe master CPU. The manual enable switch S4 activated in conjunction with switch S2 selects the Split 2 condition whereas activation of manual enable switch S4 in conjunction with switch S3 selects "free-op" operation via a line fed directly to outputpin 4 , on the I/O pin connector 80. For transient isolation optical isolators are provided between the flash, pre-empt and free-op interconnections from pins 11 , 12 and 14 and their associated output conductors.
FIG. 11 illustrates the 24 volt DC interface circuitry for the interface module of the secondary unit 40 shown in FIG. 3. The coded message and free op information are provided along pins 4 - 8 illustrated in the drawing as a single line foreach of representation. Filter circuitry and optical isolators are utilized to convert the 24 volt signals from the master unit to logic level signals for feeding further circuitry in the secondary display module. Test level command information isgenerated in the secondary units for testing operation of the secondary interface module which may be subject to damage from transients and the like. The system's software steps the test level commands from the 100% to 84%, 64% and 50% levelssequentially to provide tests for the flash call, pre-empt call, free op call and coded message call.
Tables I and II show the pin assignments for the 24 pin I/O connectors 72 and 82 and 1 pin I/O connectors 70 and 80 respectively. The tables list the pin assignments for both the master and secondary units. The "phase green in" data listed inTable I for the secondary unit allows the master unit to monitor the green phase of the corresponding timer for two different timing rings each having as many as four green phases. Force-off outputs are provided for each ring on pins 9 and 13 , and theMAX III, Call and call to artery green is provided on pins 10 and 12 respectively. The master pins 12 - 15 permit percent average calls to be made as selected by the operator by external means (not shown). Table II lists the pin assignments for the I/Opin connectors 70 and 80. Clock, data and sync information appear on pins 5 - 8 . The data communication telemetry format is discussed in detail below.
TABLE I ______________________________________ MASTER SECONDARY Function Pin Function ______________________________________ Inbound Vol. Det. 1 1 Inbound Vol. Det. 2 2 Outbound Vol. Det. 3 3 Outbound Vol. Det. 4 Phase 4 Inbound Ocp.Det. 5 Green 5 Inbound Ocp. Det. 6 6 Outbound Ocp. Det. 7 7 Outbound Ocp. Det. 8 8 Indicator Inhibit Call 9 F.O. Ring 1 Spare Call 10 Max II Split 2 Call 11 Int. Adv. % Avg. Call,CL-1, No SC 12 Call Artery .phi. % Avg. Call,CL-2, SC-2 13F.O. Ring 2 % Avg. Call,CL 3, SC-3 14 .phi. , Omit % Avg. Call,CL-4, SC-4 15 Indicator Inhibit Unit Fail 16 Call Non. Art. .phi.s. Det. Fail 17 Sum. Checks 24V 18 24V Inbound 19 P.E. Out(115 V) Logic. Gnd. 20 Logic Gnd. Chassis Gnd. 21 ChassisGnd. Occupancy 22 Flash Out(115V) 115V Neut. 23 115V Neut. 115V AC 24 115V AC ______________________________________
TABLE II ______________________________________ MASTER PIN SECONDARY ______________________________________ Flash 1 Flash Call P.E. 2 P.E. Call Spare 2 Spare Call Free Op. 4 Free Op. Call CMA CLOCK 5 CMA Call CMB (D.sub.0,D.sub.2) 6 CMBCall CMC (D.sub.1,D.sub.3) 7 CMC Call CMS (SYNC) 8 CMS Call Spare 9 Spare 115V AC Input 10 Spare (AC only) Flash Call 11 Spare P.E. Call 12 Spare Spare Key 13 Spare Free Op. Call 14 Spare 24V Input for Call 15 Spare Ground 16 Ground ______________________________________
FUNCTIONAL DESCRIPTION OF MASTER UNIT
Overall Description
The master unit 50 is designed to provide all of the system control functions for the coordinator system in accordance with the invention. The master unit basically samples traffic conditions, performs various traffic control decisions andcommunicates the results of these decisions to the plurality of secondary units 40. The prime function of the master unit is to calculate the most effective cycle length for the present sensed traffic pattern considering both the traffic detected by thevolume detectors as well as by the occupancy detectors. The master unit may also be utilized to control the effective offset for each of the secondary units as well as to provide special "system" commands such as flash, free-op, pre-empt (P.E.),alternate split and percent average commands. The master unit also contains manual override switching means to effect manual operation of the system commands.
REAL TIME TRAFFIC SAMPLING
The master unit is responsive for sampling traffic conditions from both the volume and occupancy detectors. Volume detectors 18 and 20 provide a pulse signal upon actuation by a vehicle whereas the occupancy detectors, which serve to provide aninternal traffic sampling, are of the pulse-duration type and thus stay in one state when a vehicle is present and in another state when a vehicle is not present. Indicators associated with the volume and occupancy detectors are energized to indicatevehicle activity. The master unit provides a failure indication by means of these indicators. These indicators are energized in a flashing mode whenever a fault condition is detected. The indicators for the volume detectors 18a, 18b and 20a, 20b areshown on the volume module of FIG. 2, and the indicators for occupancy detectors 22a, 22b and 24a, 24b are shown on the occupany module. The indicators associated with the detector flashes upon a failure condition as determined by the program in themaster unit. The criteria established for indicating a failure condition for the volume detectors are a lack of any activity for sixteen minutes or a continuous actuation which exceeds two minutes. The criteria for a failure condition for the occupancyinputs are a lack of activity for sixteen minutes and a continuous activation which exceeds five minutes. Input signals which exceed the above criteria are ignored in the master unit.
MASTER CYCLE LENGTH COMPUTATION
The prime purpose of the master unit is to calculate the effective cycle length which is derived utilizing input information from both the volume and occupancy detectors. The coordinator system may operate in the INBOUND mode, OUTBOUND mode orAVERAGE mode. For each of these three conditions the master unit determines the most effective cycle length which is communicated to each of the secondary units. For example, if the system is operating in an INBOUND directional mode the larger of thetwo inbound volume detector signals is utilized in the volume computation, and the larger of the two inbound occupancy values are utilized in the occupancy computation. The specific manner in which the volume and occupancy values are utilized is setforth in detail below. The resultant cycle length is communicated to the secondary units. Two constraints are placed on the overall calculation. The first constraint is that the calculated cycle length cannot be less than the sum of the minimumarterial green time plus the maximum side street time. The second constraint is that the calculated cycle length cannot be more than the sum of the maximum arterial green time plus the maximum side street time. The minimum and maximum green times arepresettable on thumbwheel switches in the directional and system module of the master unit 50 respectively. The maximum side street time is also settable for two separate values corresponding to the Split 1 and Split 2 system configurations. Thesethumbwheel switches for the Split 1 and Split 2 configurations appear on the system module of the master unit 50. An associated indicator is energized to indicate which value is in effect.
VOLUME COMPUTATIONS
The volume computations are utilized in determining cycle length for both directional mode and average mode of operation. Basically, the volume computation depends upon the extent of sensor activity and the periods within the cycle that thesensor activity occurs. The system cycle may thus be defined as comprising two time periods or bands:
The red period, S.sub.R is equal to the effective side street time which is the Split 1 or Split 2 side street times presettable on the system module of the master unit. This maximum side street time is equivalent to the red time for the artery. The green period, S.sub.G, is calculated each cycle from activity detected during the red period, S.sub.R, and the preceding last car passage (LCP) time, and continuing through the green period S.sub.G itself.
S.sub.G may be defined as comprising two time intervals, namely, S.sub.G =T.sub.R +T.sub.G. T.sub.R is the time interval determined by activity occurring during the red period, S.sub.R, and the preceding last car passage time. T.sub.G is thetime interval determined by activity occurring during the green period before gapout is recognized. S.sub.G is, however, at all times constrained such that it may not exceed the front panel setting of the maximum green time as settable on the systemmodule of the master unit 50.
The time intervals T.sub.R and T.sub.G are calculated as follows:
OR the minimum artery green whichever is greater, where:
E.sub.R =the extension time per actuation time (front panel setting of the red headway on the volume module), which actuations occur during the period S.sub.R and the preceding last car passage time; and
A.sub.R =the number of actuations detected while E.sub.R is in effect.
The calculation for the quantity T.sub.G is similarly given as:
where:
E.sub.G =the extension time per actuation (front panel setting for green headway on volume module of the master unit), which actuations occur during the S.sub.G period less the last car passage time; and
A.sub.G =the number of actuations detected during time E.sub.G is in effect.
The green period, S.sub.G, is normally terminated by gapout, plus the time allowed for the last car passage, unless the quantity T.sub.R +T.sub.G, plus the last car passage time represents a longer green time than would be allowed by gapouttermination. In this case, the longer period is used. In either case, S.sub.G is not allowed to exceed beyond the maximum green time.
Gapout termination is determined as follows: At the start of S.sub.G, gap time equals the initial gap time (thumbwheel switch setting on inbound and outbound modules of the master unit 50) and retains the initial value until the gapout inhibitperiod is ended. At the end of the gapout inhibit period, the time to reduce period (thumbwheel switch settings on inbound and outbound modules) begins, and the gap time is reduced linearly over this period until the gap time equals the minimum gapsetting (thumbwheel switches). If the minimum gap value is reached, it is retained for the remainder of the cycle.
Gapout recognition is inhibited and thus the appearance of a gap is ignored for an interval called the gapout inhibit period. This time period is simply the time T.sub.R minus the last car passage time (thumbwheel switches on inbound andoutbound modules). When the gapout inhibit period is terminated, gapout timing begins. At the beginning of such gapout timing, the gapout time is equal to the initial gap setting, and the gap size is then linearly reduced. The gapout count continuesunless a car is sensed by either of the volume detectors in which case the count is set to zero and beings again. When the gapout count equals the gap time, gapout occurs. When gapout occurs, the system operates to terminate S.sub.G after assuringsufficient time for the last detected car to clear, i.e. LCP time. An overall constraint, however, is that the total green time may not exceed the maximum green as set on the system module. Additionally, the gapout may not necessarily terminate S.sub.Gif the accumulated volume or occupancy totals demand further extensions of the green time within the overall maximum green constraint. The basic reason for inhibiting the gapout count for a time period related to the value T.sub.R is to allow time forcars which have been backed up beyond the volume sensor during the red arterial phase, and therefore cannot immediately move as the light turns green, to pass across the volume sensor. If time were not provided an anomalous gap reading would appearshortly after the light turned green and the cycle could terminate too soon.
FIG. 12 illustrates a cycle length computation based on volume sensing utilizing the algorithm set forth above.
OCCUPANCY COMPUTATION
The occupancy values are based upon a running average obtained from thirty second increments averaged over a two minute period. The two minute averaging period may be varied over one minute increments to a maximum period of eight minutes viaprogram memory modifications. Typically, a two minute window is set and the average is recomputed every thirty seconds for the most recent two minute window (most recent four readings). The occupancy values are derived from occupancy sensors whichprovide an input for the complete duration in which the vehicle is over the sensor position. Consequently, if during the thirty second sensing time a vehicle is stationary over the senor a 100% occupancy will be registered for this particular thirtysecond time period. The 100% occupancy value will be averaged into the preceding three 30 second occupancy values to give a total two minute window which is updated every thirty seconds in a sliding fashion. The occupancy values are thus expressed inpercentage of time in which the occupancy signal is present indicating the presence of a vehicle. It is necessary, however, to convert these percentage occupancy values into a cycle length counterpart value so that a comparison may be made with thecycle length as computed from the volume detectors described above. For the purpose of converting the occupancy percentage figure into a cycle length, thumbwheel switches labeled "Y.sub.in ", "X" and "Y.sub.out " are provided on the system module of themaster unit 50. The conversion is derived from a straight line conversion of a portion of the occupancy values whose endpoints are defined by these preset values and whose endpoints match the two limits of the possible cycle length, namely, the minimumcycle defined by the minimum artery green time (direction module) and the maximum cycle defined by the maximum artery green time (system module). The minimum cycle match point is preset on the thumbwheel switch labeled "X" and is settable throughout arange of 0-9 corresponding to a 0-90% of occupancy. This set point is effective for both directions and is termed the "X" set point. The maximum cycle match point is determined by the setting of the thumbwheel switch labeled either Y.sub.in orY.sub.out depending upon the directional mode in effect. The thumbwheel switch positions range from 1 to 9 corresponding to a 10 to 90% occupancy and the zero value of the thumbwheel switch corresponds to the 100% occupancy value. Consequently, anyoccupancy value may be converted utilizing the linear conversion defined by the two endpoints into a cycle length value.
The actual directional cycle length selected for transmission to the various secondary units is simply the larger of the cycle lengths as calculated from volume considerations and from occupancy considerations separately.
AVERAGE CYCLE LENGTH SELECTION
The master unit also provides a means for selecting the average cycle length which is communicated when a non-directional (average) traffic mode is in effect. Four values of the average cycle length are presettable on the average module of themaster unit 50 (FIG. 2). A maximum of 299 seconds may be selected for a cycle length. When the average mode of traffic flow is in effect, the larger of the inbound and outbound cycle lengths, whether derived from either a volume input or an occupancyinput, is applied to the formula (IN+OUT)/2, and the result of this computation is compared to the four preset values available for the average system configuration. The preset value which most closely approximates the absolute value of the computationis the effective cycle length communicated to the secondary units when the average mode or system configuration is being utilized. The system cycle for the above is taken to be the outbound system cycle. An adjacent indicator indicates which cyclelength is presently being communicated to the secondaries.
DIRECTIONAL COMMANDS
An additional function of the master unit is to determine when a directional command need be given so as to change the mode of operation of the coordinator system between the three modes, INBOUND, OUTBOUND and AVERAGE.
In order to accomplish the directional commands the master unit totals the number of volume vehicle actuations which are achieved within the present effective length. The larger number of actuations selected from the two volume detectors at eachend of the system (inbound detectors and outbound detectors) are applied to the following formula: ##EQU1## The derived value expressed in percent is compared to the two preset values (thumbwheel switches) which are expressed in percentages on thedirection module of the master unit. Values derived exceeding the higher preset value cause an inbound directional command. Directional values lower than the lower preset value cause an outbound directional command. Derived values falling between orequal to the two preset values cause an average directional command. The program of the master unit is also provided with error detection subroutines such that if the inbound preset limit is lower than the outbound preset limit the associated IN/OUTindicators flash alternately and an average directional command is issued by the master unit until the fault condition is corrected. Proper operation is achieved for directional offset commands when the inbound percentage value is set higher than theoutbound percentage value.
COMMANDS BASED UPON OCCUPANCY
The master unit issues "speed change" commands which act to change the effective offset at the secondary units depending upon the level of occupancy detected within the system. The offset changes are effectively speed modification commands whichare based upon the occupancy level within the system as selected from the inbound and outbound modes of operation. The occupancy level expressed in percentage is determined using the running average obtained from thirty second increments averaged over atwo minute window as explained above. These occupancy levels, expressed in percentage, are compared to four preset levels which correspond to the thumbwheel switch settings on the occupancy module of the master unit 50. Occupancy values exceeding thehigher preset value (upper set of thumbwheel switches) cause a speed change #4 command to be issued. The speed change #4 command is a percent change in the offset and is settable using the upper set of thumbwheel switches of the Speed module of themaster unit 50. Three additional speed change commands (labeled #3-#1 from top to bottom) are settable with thumbwheel switches on the Speed module. Occupancy values lower than the lowest preset value results in no speed change being issued. Occupancyvalues falling between these preset values cause preset speed change numbers #1-3 to be issued whenever the occupancy level exceeds the associated preset set point value. In the event that the preset value has been incorrectly set, i.e., not inincreasing values, the four associated indicators flash and no speed change command is issued. A unit fault command is issued under these circumstances.
OUTPUT DECISION UPDATE INTERVALS
The master unit continuously provides updated information to the secondary units. The update intervals are controlled by the effective cycle lengths as derived from the system cycle. The transition from green to red (S.sub.G to S.sub.R) is thesynchronization point for update information. No output of the master unit changes more frequently than or out of synchronization with the green to red synchronization point. There are, however, two exceptions as to the interval of update. These twoexceptions are, however, still synchronous with the system cycle.
The first exception is the offset decision which effects a directional to average change. The directional to average update change is governed by a preset update interval of 0-9 minutes as determined by the "INTO" thumbwheel switch on theDirection module of the master unit 50. The value of zero on this thumbwheel switch implies the effective cycle length.
The second exception to the update interval is that pertaining to cycle length selection decisions in the average configuration. These are governed by a preset update interval of 0-9 minutes. The update interval is selected by a thumbwheelswitch labeled "IN" in the directional module of the master unit 50. The value of zero implies the effective cycle length.
MANUAL OVERRIDE
The master unit contains a plurality of slide switches utilized for manual control. When the manual override is enabled, the thumbwheel selector switch on the face of the display module of the master unit is utilized as a cycle length selectorallowing individual call to any of four average cycle lengths as follows:
______________________________________ Select Position Effective Cycle Length ______________________________________ 1 Average No. 1 2 Average No. 2 3 Average No. 3 4 Average No. 4 5-9-0 Average No. 1 ______________________________________
The associated indicator is energized and the numeric display flashes to indicate manual override operations. The numeric display indicates the cycle length selected in seconds.
SYSTEM PERCENT AVERAGE
When called, by external control, the system percent average operation is effective at the next system cycle S.sub.G to S.sub.R transition. Lacking any other input call the accompanying cycle length is taken to be the #1 TWS average setting onthe average module with no speed change. When the above call is enabled along with another call (see Table I) the accompanying effective cycle length is:
Average No. 2 with Speed change No. 2
Average No. 3 with Speed change No. 3
Average No. 4 with Speed change No. 4
DISPLAY
The display module of the master unit 50 utilizes two seven-segment displays for the least significant digit (LSI) and the intermediate significant digit (ISD). The most significant digit (MSD) is a combination of the plus or minus sign and a"1". For cycle lengths in excess of 199 seconds the "+" sign is activated indicating numbers of 200 to 299. For parameters expressed in percentage, the "-" sign is activated. A flashing display is utilized to denote manual override operation.
Ten selectable parameters from throughout the unit are available and appear on the display unit as governed by the selector switch on the display module as described here | | | |
