Computerized traffic control apparatus

• US 3,920,967 A
• Filed: 02/22/1974
• Issued: 11/18/1975
• Est. Priority Date: 02/22/1974
• Status: Expired due to Term

• Current Assignee: Curtis L. Barnfield, Daniel T. Martin, Donald L. Cooper, Herbert C. Coleman, Morton A. Serrell, Robert J. Walinchus, Robert M. Knox
• Original Assignee: Curtis L. Barnfield, Daniel T. Martin, Donald L. Cooper, Herbert C. Coleman, Morton A. Serrell, Robert J. Walinchus, Robert M. Knox
• Inventors: Martin, Daniel T., Serrell, Morton A., Coleman, Herbert C., Cooper, Donald L., Knox, Robert M., Barnfield, Curtis L., Walinchus, Robert J.
• Primary Examiner(s): Dildine, Jr., R. Stephen
• Application Number:
  US05/444,933
• Time in Patent Office: 634 Days
• Field of Search: 235/150.24 340/35,40,36-38 444/1 445/1
• US Class Current: 701/118
• CPC Class Codes: G08G 1/08 according to detected number or speed of vehicles

Abstract

Disclosed is a computerized apparatus for controlling the flow of vehicular traffic through a network of intersections. Detectors in proximity to selected intersections generate electrical signals representative of the commencement and termination of vehicle presence. One or more field preprocessors receive these signals and responsively generate secondary signals representative of vehicle count and speed. These secondary signals are transmitted to a computer which analyzes them and responsively generates control signals which are transmitted to and govern the sequential operation of traffic signal heads at the controlled intersections.

Claims

1. An on-line, real-time traffic control apparatus for optimizing the flow of traffic between a plurality of intersections in a controlled network, said apparatus comprising:

at least one automated detector means in proximity to each of selected ones of the intersections, each of said detector means adapted to generate, in response to the proximate presence of a vehicle, an electrical signal pulse, the commencement of which indicates the commencement of the vehicle presence and the termination Of which indicates the termination of the vehicle presence;

at least one signal head in proximity to each of the intersections, said signal head adapted to successively display traffic flow directing lights;

controller means adapted to control the operation of said signal heads;

electronic computer means;

means for electrical communication between said detector means and said computer means and between said computer means and said controller means, said communication means including signal processor means adapted to receive the signal pulses from a plurality of said detector means and to generate, in response to said signal pulses, an encoded binary electrical signal representing both the total number of signal pulses received by said processor means during a specified time span, and the duration of each, said total number indicative of vehicle count and each of said durations indicative of the speed of a vehicle in proximity to one of said detectors;

said computer means being adapted to receive said encoded binary electrical signals from said processor means and, based thereupon, to generate necessary command electrical signals for said controller means, said command signals transmitted to said controller means through said communication means.

2. The apparatus as recited in claim 1 wherein said signal processor means is adapted to respond to signal pulse discontinuities.

3. The apparatus as recited in claim 2 wherein said discontinuities comprise signal pulse leading edges.

4. The apparatus as recited in claim 2 wherein said discontinuities comprise signal pulse trailing edges.

5. The apparatus as recited in claim 1, wherein said electronic computer means comprises:

a. foreground computation means adapted to receive said encoded binary electrical signals from said processor means and, based thereupon, to generate necessary command electrical signals for said controllers, said command signals transmitted to said controllers through said communication means, b. background computation means in mutual electrical data signal communication with said foreground means, said background means adapted, in response to data from said foreground means, to generate a plurality of electrical data signals together representing an optimized pattern of commands for those of said controllers which control the operation of those said signal heads in proximity with said selected ones of the intersections, and c. executive operational means adapted to schedule the operation and the mutual interaction of said foreground means and background means.

6. The apparatus as recited in claim 5, wherein said executive operational means comprises:

electronic computer means for clocking an interval of time known as an execution cycle, which is defined as the sum of time allotted for completion of all foreground programs;

electronic computer means for generating a program interrupt at the completion of an execution cycle;

electronic computer means in response to said program interrupt for;

stopping execution of a background program so as to perserve the background program environment, and executing the next and succeeding foreground programs in queue;

electronic computer means for reactivating the interrupted background program and executing the next background program in queue at the completion of execution of all foreground programs; and

electronic computer means for cyclically repeating above.

7. The apparatus as recited in claim 5, wherein said foreground computation means includes apparatus for converting, in real time, speed and count data into relevant traffic parameters comprising:

electronic computer means for constructing and updating a vehicle position/speed/direction matrix;

electronic computer means for propagating vehicle counts at the measured speeds through a representation of a system of streets comprising the traffic control network; and

electronic computer means for calculAting link input and output volume, number of stops, stop delay time, queue length, and travel time.

8. The apparatus as recited in claim 7, wherein said means for constructing and updating said vehicle position/speed/direction matrix comprises:

electronic computer means for constructing each column of said matrix to correspond to one-directional links within said network;

electronic computer means for constructing the row elements of a specific column to correspond to fixed travel time units along said link; and

electronic computer means for defining surveillance pointers corresponding to specific ingress or egress points along the link with respect to matrix elements where count data is to be entered, summed, modified or deleted.

9. The apparatus as recited in claim 8, wherein said means for propagating vehicle counts at the measured speeds through a representation of a system of streets comprising the traffic control network comprises:

electronic computer means for adjusting the relative positions of said surveillance pointers with respect to said matrix elements in unit travel time increments to account for variation in speed between surveillance points; and

electronic computer means for decrementing the starting row number in a circular fashion for a preselected group of rows and columns within said matrix as each unit travel time elapses to advance unimpeded traffic forward in time and distance.

10. The apparatus as recited in claim 9, wherein said means for calculating link input and output volume, number of stops, stop delay time, queue length and travel time comprises:

electronic computer means for defining a set of surveillance pointers for each link;

electronic computer means for summing and differencing input and output counts in each propagation time interval;

electronic computer means for computing stops and delays from propagated vehicle counts and current signal light status;

electronic computer means for computing queue length from said input and output count difference; and

electronic computer means for summing said queue length each propagation time interval to determine travel time.

11. The apparatus as recited in claim 7, further including:

electronic computer means for computing signal phase termination times for minor intersections, said minor intersections located between major intersections and having minimal instrumentation using a pressure function.

12. The apparatus as recited in claim 7, further including:

electronic computer means for computing additional required measures of effectiveness from a basic set of surveillance parameters;

electronic computer means for arranging said set of surveillance parameters in summary tables; and

electronic computer means for normalizing surveillance count data by differencing and zeroing to prevent storage cell overflow.

13. The apparatus as recited in claim 5, wherein said foreground computation means includes apparatus for optimally calculating and implementing splits at each intersection on a cycle-by-cycle basis within the constraint of maintaining the network progression comprising:

electronic computer means for calculating the required effective green time for each signalized approach;

electronic computer means for computing a first difference between the network cycle length and the maximum sum of green time required for each street at an intersection;

electronic computer means for apportioning said first difference between each street based on the ratio of effective green times between any adjacent streets in said intersection;

electronic computer means for calculating a new split based on said apportionment of total green time per street; and

electronic computer means for optimally implementing the difference between the new split and the old split for each signalized approach.

14. The apparatus as recited in claim 13, wherein the means for calculating the required effective green timE for each signalized approach comprises:

electronic computer means for averaging the traffic volume over n cycles through each signalized approach to an intersection, whether left turn or straight through;

electronic computer means for calculating the effective green time required to service the average volume in accordance with the following formula;

tG V . HD/n where tG is the effective green time V is the average volume HD is the discharge headway per lane and n is the number of lanes per signalized approach; and

electronic computer means for performing the first two steps for each signalized approach at said intersection.

15. The apparatus as recited in claim 13, wherein the means for computing a first difference between the network cycle length and the maximum sum of green time required for each street and intersection comprises:

electronic computer means for summing the green times per conflicting signal movements on each street;

electronic computer means for summing the maximum green time for each street based on said sums of the green times per conflicting signal movements; and

electronic computer means for computing said first difference between the network cycle length and said sum of maximum green times for each street.

16. The apparatus as recited in claim 15, wherein the means for apportioning said first difference between each street based on the ratio of effective green times between any adjacent streets in said intersection comprises:

electronic computer means for calculating the ratio of effective green time per street by dividing said sum of green times per conflicting signal movements by said sum of the maximum green times for each street;

electronic computer means for calculating the split per street as follows;

multiplying said ratio of effective green times per street by said first difference;

adding said sum of the green time per conflicting signal movement; and

electronic computer means for repeating the above two steps for each street in said intersection.

17. The apparatus as recited in claim 16, further including:

electronic computer means for comparing said new split with a preselected minimum value; and

electronic computer means for adjusting said new split to be equal to said minimum value if said new split is less than said minimum value.

18. The apparatus as recited in claim 5, wherein said background computation means includes apparatus for calculating optimum traffic signal settings for a traffic control network, in real time, including breaking down said network into subnetworks, optimizing each subnetwork, and interfacing each subnetwork wherein the means for optimizing each subnetwork comprises:

electronic computer means for selecting a signal cycle range;

electronic computer means for determining whether or not to reoptimize;

electronic computer means for playing a series of Monte Carlo games for each signal cycle and using a gradient search technique to determine the optimum signal offsets for minimum delay and stops; and

electronic computer means for determining the optimum signal cycle and corresponding offsets.

19. The apparatus as recited in claim 18, wherein said background computation means further includes:

electronic computer means for constructing a link weighting matrix, and electronic computer means for triangularizing and inverting said weighting matrix.

20. The apparatus as recited in claim 18, wherein said apparatus is adapted to minimize the following function with respect to intersection offsets:

21. The apparatus as recited in claim 18, wherein said apparatus is adapted to employ the following