CENTRAL TRAFFIC SIGNAL CONTROL

• US 3,764,972 A
• Filed: 03/02/1971
• Issued: 10/09/1973
• Est. Priority Date: 11/21/1969
• Status: Expired due to Term

• Current Assignee: Gregory Siklos, James B. Rudden
• Original Assignee: Gregory Siklos, James B. Rudden
• Inventors: Siklos, Gregory, Rudden, James B.
• Primary Examiner(s): Cooper, William C.
• Application Number:
  US05/120,254
• Time in Patent Office: 952 Days
• Field of Search: 340/35,40
• US Class Current: 340/915
• CPC Class Codes: G08G 1/081 Plural intersections under common control

Abstract

There is disclosed a central control station and a plurality of local stations each including a signal controller responsive to commands from the central control station for controlling the signal lights at each local station. A computer at a central control station monitors changes in traffic trends and can send a signal to a local station to control the signal controller sequence at any intersection with an appropriate offset between intersections. The system smoothly changes from local (isolated) operation to remote (computer control) operation without adversely effecting traffic flow. The central control station includes a slave driver associated with each local station. Each slave driver is connected over a two-wire telephone type line to a corresponding slave unit which in turn is coupled to the signal controller associated with that local station. In a non-actuated system with the signal controller of the local station at its rest or dwell position, the computer can issue a hold command that is transmitted by the slave driver over the two-wire line to the slave unit. This command changes control from local to remote. Thereafter, the computer may issue an advance command that moves the signal controller to its next position. The advancement of the controller is sensed by the slave unit which in turn transmits a status command to the slave driver and thence to the computer indicating that the controller did, in fact, advance. If no status command is received the intersection is dropped by the computer and returns to local operation. In a semi-actuated or fully actuated system one or more detectors are provided at the intersection. For example, one or more detectors could be used for phase A (main street), and one or more detectors for phase B (cross street). With an actuated system one or more detection responsive means may couple to one or more detectors and the signal controller for controlling the stepping of the signal controller. Local signal controller sequencing may thus be responsive to computer commands and local vehicle detections.

Claims

1. A traffic control system comprising:

a central control station;

at least one local station including a traffic signal controller for controlling the traffic intersection;

a two wire communication line intercoupling the central control station and the local station;

said central control station including circuit means for selectively impressing a first signal level on the communication line when the central station is conditioned to control the local station and a second signal level on the communication line for a predetermined duration when the central station is conditioned to advance the signal controller at the local station;

said local station including circuit means responsive to said first signal level for selectively rendering said local station responsive to said second signal level and means thereafter responsive to said second signal level for advancing said signal controller;

said local station also including means responsive to the advance of said signal controller for generating a status signal during said predetermined duration of the second signal indicative of advancement of the controller;

said central control station including means for receiving said status signal over said two-wire communication line during said predetermined interval, wherein said local signal controller is adapted to control traffic flow on at least two streets associated with the intersection at least one vehicle detector being associated with at least one of the streets, said local station comprising detection responsive means intercoupled with said vehicle detector, the circuit means of the local station, and the local signal controller, and including a vehicle memory for storing a vehicle presence indication from said vehicle detector.

2. A traffic control system as set forth in claim 1 wherein said central control station includes a computer programmed to transmit control commands to said circuit means of said central control station.

3. A traffic control system as set forth in claim 1 wherein said detection responsive means comprises controller advance control means coupled to the means for advancing the signal controller and the vehicle memory for selectively inhibiting said means for advancing during at least a first interval of said signal controller when no vehicles have been detected by said vehicle detector thereby preventing controller advance out of the first interval.

4. A traffic control system as set forth in claim 3 wherein said detection response means also comprises timing circuit means coupled to said controller advance control means and adapted to receive said advance signal having a predetermined duration;

said timing circuit means responsive to said advance signal and the presence of a vehicle presence indication for passing said advance signal to said means for advancing during the first interval.

5. A traffic control system as set forth in claim 4 wherein said timing circuit means is also responsive to said advance signal which occurs during the absence of a vehicle detection for blocking said advance signal and preventing the signal controller from advancing out of the first interval.

6. A traffic control system as set forth in claim 4 wherein said timing circuit means is also responsive to an extended advance signal generated at said central control station and which occurs during the absence of a vehicle detection for passing at least part of said extended advance signal to said means for advancing.

7. A traffic control system as set forth in claim 4 wherein said timing circuit means is also responsive during a vehicle extension interval associated with one phase of said signal controller to said advance signal and the continued indication of detected vehicles associated with another phase for blocking said advance signal and preventing the signal controller from advancing out of the extension interval.

8. A traffic control system as set forth in claim 7 wherein said timing circuit means is also responsive to said advance signal which occurs during the absence of detected vehicles over a predetermined time period for passing said advance signal to said means for advancing during the extension interval.

9. A traffic control system as set forth in claim 7 wherein said timing circuit means is responsive to an extended advance signal generated at said central control station during said extension interval associated with one phase and the continued indication of vehicle detections associated with another phase for passing at least part of said extended advance signal to said means for advancing.

10. A traffic control system comprising:

a central control station;

at least one local station including a traffic signal controller for controlling the traffic intersection;

a two-wire communication line intercoupling the central control station and the local station;

said central control station including circuit means for selectively impressing a first signal level on the communication line when the central station is conditioned to control the local station and a second signal level on the communication line for a predetermined duration when the central station is conditioned to advance the signal controller at the local station;

said local station including circuit means responsive to said first signal level for selectively rendering said local station responsive to said second signal level and means thereafter responsive to said second signal level for advancing said signal controller;

said local station also including means responsive to the advance of said signal controller for generating a status signal during said predetermined duration of the second signal indicative of advancement of the controller;

said central control station including means for receiving said status signal over said two-wire communication line during said predetermined interval, wherein said local signal controller is adapted to control traffic flow on a main street and a cross street, at least one vehicle detector being associated with the main and cross streets respectively;

said local station comprising at least two detection responsive means, one coupled to the main street vehicle detector and the other coupled to the cross street detector, each said detection responsive means also coupled to the circuit means of the local station and the local signal controller and including a vehicle memory coupled to the vehicle detector for storing a vehicle demand indication.

11. A traffic control system as set forth in claim 10 wherein each said detection responsive means comprises controller advance control means coupled to the means for advancing and its vehicle memory, for selectively inhibiting said means for advancing during both a main street dwell interval of said signal controller when no vehicles have been detected by the cross street vehicle detector, and a cross street dwell interval of said signal control when no vehicles have been detected by the main street vehicle detectors, respectively.

12. A traffic control system as set forth in claim 11 wherein each of said controller advance control means selectively inhibits said means for advancing during both a main street extension interval when vehicles continue to be detected by the main street detector, and a cross street extension interval when vehicles continue to be detected by the cross street detector, respectively.

13. A traffic control system as set forth in claim 10 wHerein at least two vehicle detectors are associated with the main street and the cross street respectively, and the local station comprises one detection responsive means coupled to each vehicle detector;

said local station including AND circuit means intercoupling the detection responsive means associated with one of the streets for permitting advancement out of the extension interval associated with that street only when vehicle indications associated with both vehicle detectors associated with that street terminate.

14. A traffic control system comprising:

a central control station;

at least one local station including a traffic signal controller for controlling the traffic intersection;

a two-wire communication line intercoupling the central control station and the local station;

said central control station including circuit means for selectively impressing a first signal level on the communication line when the central station is conditioned to control the local station and a second signal level on the communication line for a predetermined duration when the central station is conditioned to advance the signal controller at the local station;

said local station including circuit means responsive to said first signal level for selectively rendering said local station responsive to said second signal level and means thereafter responsive to said second signal level for advancing said signal controller;

said local station also including means responsive to the advance of said signal controller for generating a status signal during said predetermined duration of the second signal indicative of advancement of the controller;

said central control station including means for receiving said status signal over said two-wire communication line during said predetermined interval, wherein said local station includes an enabling circuit coupled to said means for advancing the signal controller and operative during at least a second interval of operation of said signal controller during local control of said signal controller to permit the first signal level transmitted from said central control station over said communication line to control the local station thereby reverting the system from local to remote central control.

15. A traffic control system as set forth in claim 14 wherein said enabling circuit inhibits said first signal level during other intervals than said at least a second interval during local control of said signal controller thereby preventing the central station from controlling local operation.

16. A traffic control system comprising:

a central control station;

at least one local station including a traffic signal controller for controlling the traffic intersection;

a two-wire communication line intercoupling the central control station and the local station;

said central control station including circuit means for selectively impressing a first signal level on the communication line when the central station is conditioned to control the local station and a second signal level on the communication line for a predetermined duration when the central station is conditioned to advance the signal controller at the local station;

said local station including circuit means responsive to said first signal level for selectively rendering said local station responsive to said second signal level and means thereafter responsive to said second signal level for advancing said signal controller;

said local station also including means responsive to the advance of said signal controller for generating a status signal during said predetermined duration of the second signal indicative of advancement of the controller;

said central control station including means for receiving said status signal over said two-wire communication line during said predetermined interval, said means for generating a status signal including means for generating a status signal of a first polarity during a firsT predetermined period and a status signal of a second polarity during a second successive predetermined period.

17. A traffic control system comprising:

a central control station;

at least one local station including a traffic signal controller for controlling the traffic intersection;

a two-wire communication line intercoupling the central control station and the local station;

said central control station including circuit means for selectively impressing a first signal level on the communication line when the central station is conditioned to control the local station and a second signal level on the communication line for a predetermined duration when the central station is conditioned to advance the signal controller at the local station;

said local station including circuit means responsive to said first signal level for selectively rendering said local station responsive to said second signal level and means thereafter responsive to said second signal level for advancing said signal controller;

said local station also including means responsive to the advance of said signal controller for generating a status signal during said predetermined duration of the second signal indicative of advancement of the controller;

said central control station including means for receiving said status signal over said two-wire communication line during said predetermined interval, wherein the circuit means at said central control station is adapted to selectively impress a third signal level on the communication line when the central control station is conditioned to re-synchronize the timing at the local station.

18. A traffic control system as set forth in claim 1 wherein said local station includes means for preventing local signal controller advancement during the pendency of the third signal level thereby maintaining the signal controller under remote control during re-synchronization.