Timing submission of transit signal priority requests to reduce transit vehicle stop times

1. A method of submitting transit signal priority (TSP) requests, comprising:

receiving TSP information of a vehicle by a phase selector at a current time;

determining from the TSP information, an estimated time of arrival (ETA) of the vehicle at an intersection having a traffic signal controlled by an intersection controller;

determining a phase of the traffic signal at the ETA, wherein the phase at the ETA is an arrival phase;

determining a phase-relative arrival time of the ETA in the arrival phase;

determining a time to issue the TSP request based on the phase-relative arrival time and one of a non-green truncation threshold and a green extension threshold relative to the arrival phase; and

issuing the TSP request by the phase selector to the intersection controller at the determined time.

2. The method of claim 1 , wherein:

the determining the phase at the ETA includes determining whether the arrival phase is a green phase or a non-green phase; and

the determining the time to issue the TSP request includes determining to truncate a non-green phase that precedes the arrival phase in response to the arrival phase being a green phase and the phase-relative arrival time preceding the non-green truncation threshold.

3. The method of claim 1 , wherein:

the determining the phase at the ETA includes determining whether the arrival phase is a green phase or a non-green phase; and

the determining the time to issue the TSP request includes determining to extend a green phase that is the arrival phase in response to the arrival phase being a green phase and the phase-relative arrival time succeeding the non-green truncation threshold.

4. The method of claim 1 , wherein:

the determining the phase at the ETA includes determining whether the arrival phase is a green phase or a non-green phase; and

the determining the time to issue the TSP request includes determining to extend a green phase that precedes the arrival phase in response to the arrival phase being a non-green phase and the phase-relative arrival time preceding the green extension threshold.

5. The method of claim 1 , wherein:

the determining the phase at the ETA includes determining whether the arrival phase is a green phase or a non-green phase; and

the determining the time to issue the TSP request includes determining to truncate a non-green phase that is the arrival phase in response to the arrival phase being a non-green phase and the phase-relative arrival time succeeding the green extension threshold.

6. The method of claim 1 , further comprising:

wherein the determining the phase at the ETA includes determining whether the arrival phase is a green phase or a non-green phase;

wherein the determining the time to issue the TSP request includes determining whether to truncate a non-green phase or extend a green phase based on the phase-relative arrival time relative to the non-green truncation threshold and the green extension threshold in the arrival phase; and

determining the non-green truncation threshold and the green extension threshold based on an average of deviations of ETAs of a plurality of vehicles from associated actual times of arrival (ATAs) of the vehicles.

7. The method of claim 1 , wherein the determining the ETA includes:

determining an initial ETA based on the TSP information; and

adding an ETA offset to the initial ETA, resulting in the ETA, wherein the ETA offset indicates an average of differences between actual times of arrival and initial ETAs of a plurality of vehicles.

8. The method of claim 1 , wherein the determining the arrival phase includes:

determining an amount of time remaining in a current phase at a time of the receiving the TSP information; and

totaling an amount of time including the time remaining in the current phase and a respective time of each phase between the current phase and a first phase change after the ETA using an average length of green phases and an average length of non-green phases.

9. The method of claim 8 , wherein the determining the amount of time remaining in a current phase includes performing, in response to a transition from a non-green phase to a green phase, operations including:

setting a time-to-non-green timer to the average length of green phases plus an average length of green extensions in response to an expected green extension;

setting a time-to-green timer to the average length of green phases plus the average length of non-green phases in response to the expected green extension;

setting the time-to-non-green timer to the average length of green phases in response to an expected non-green truncation;

setting the time-to-green timer to the average length of green phases plus the average length of non-green phases minus an average length of non-green truncations in response to the expected non-green truncation;

setting the time-to-non-green timer to the average length of green phases plus the average length of non-green phases in response to no expected green extension and no expected non-green truncation;

setting the time-to-green timer to the average length of green phases in response to no expected green extension and no expected non-green truncation; and

starting the time-to-non-green timer and the time-to-green timer.

10. The method of claim 1 , wherein the determining the time to issue the TSP request includes:

determining a target TSP time indicative of a time in a phase at which a non-green truncation extension is targeted; and

computing the time to issue the TSP request as a difference between the target TSP time and a non-green truncation offset value.

11. The method of claim 10 , further comprising:

determining whether or not the time to issue the TSP request is within a period in which the intersection controller will grant a non-green truncation, based on the non-green truncation threshold; and

bypassing issuing TSP request to the intersection controller in response to determining that the time to issue the TSP request is within a period in which the intersection controller will not grant a non-green truncation, based on the non-green truncation threshold.

12. The method of claim 10 , further comprising:

starting a time-to-TPS-grant timer in response to the issuing of the TSP request;

stopping the time-to-TPS-grant timer in response to a transition from a non-green phase to a green phase;

determining after stopping the time-to-TPS-grant timer, whether or not the non-green phase was truncated;

storing a value indicated by the time-to-TPS-grant timer in a data set, in response to determining that the non-green phase was truncated; and

determining the non-green truncation offset from the data set.

13. The method of claim 1 , wherein the determining the time to issue the TSP request includes:

determining a target TSP time indicative of a time in a phase at which a green extension is targeted; and

computing the time to issue the TSP request as a difference between the target TSP time and a green extension offset value.

14. The method of claim 13 , further comprising:

determining whether or not the time to issue the TSP request is within a period in which the intersection controller will grant a green extension, based on the careen extension threshold; and

bypassing issuing TSP request to the intersection controller in response to determining that the time to issue the TSP request is within a period in which the intersection controller will not grant a green extension.

15. The method of claim 13 , further comprising:

starting a time-to-TPS-grant timer in response to the issuing of the TSP request;

stopping the time-to-TPS-grant timer in response to a transition from a green phase to a non-green phase;

determining after stopping the time-to-TPS-grant timer, whether or not the green phase was extended;

storing a value indicated by the time-to-TPS-grant timer in a data set, in response to determining that the green phase was extended; and

determining the green extension offset from the data set.

16. A traffic signal control system, comprising:

a phase selector configured and arranged to:

receive TSP information of a vehicle at a current time;

determine from the TSP information, an estimated time of arrival (ETA) of the vehicle at an intersection having the traffic signal;

determine a phase of the traffic signal at the ETA, wherein the phase at the ETA is an arrival phase;

determine a phase-relative arrival time of the ETA in the arrival phase;

determine a time to issue a TSP request based on the phase-relative arrival time and one of a non-green truncation threshold and a green extension threshold relative to the arrival phase; and

output the TSP request at the determined time; and

an intersection controller coupled to the phase selector and to the traffic signal, the intersection controller configured and arranged to adjust a phase of the traffic signal in response to the TSP request.

17. The system of claim 16 , wherein:

the phase selector is configured to determine the phase at the ETA by determining whether the arrival phase is a green phase or a non-green phase; and

the phase selector is configured to determine the time to issue the TSP request by determining to truncate a non-green phase that precedes the arrival phase in response to the arrival phase being a green phase and the phase-relative arrival time preceding the non-green truncation threshold.

18. The system of claim 16 , wherein:

the phase selector is configured to determine the phase at the ETA by determining whether the arrival phase is a green phase or a non-green phase; and

the phase selector is configured to determine the time to issue the TSP request by determining to extend a green phase that is the arrival phase in response to the arrival phase being a green phase and the phase-relative arrival time succeeding the non-green truncation threshold.

19. The system of claim 16 , wherein:

the phase selector is configured to determine the phase at the ETA by determining whether the arrival phase is a green phase or a non-green phase; and

the phase selector is configured to determine the time to issue the TSP request by determining to extend a green phase that precedes the arrival phase in response to the arrival phase being a non-green phase and the phase-relative arrival time preceding the green extension threshold.

20. The system of claim 16 , wherein:

the phase selector is configured to determine the phase at the ETA by determining whether the arrival phase is a green phase or a non-green phase; and

the phase selector is configured to determine the time to issue the TSP request by determining to truncate a non-green phase that is the arrival phase in response to the arrival phase being a non-green phase and the phase-relative arrival time succeeding the green extension threshold.

21. The system of claim 16 , wherein:

the phase selector is configured to determine the phase at the ETA by determining whether the arrival phase is a green phase or a non-green phase;

the phase selector is configured to determine the time to issue the TSP request by determining whether to truncate a non-green phase or extend a green phase based on the phase-relative arrival time relative to the non-green truncation threshold and the green extension threshold in the arrival phase; and

the phase selector is further configured to determine the non-green truncation threshold and the green extension threshold based on an average of deviations of ETAs of a plurality of vehicles and associated actual times of arrival (ATAs) of the vehicles.

22. The system of claim 16 , wherein the phase selector is configured to determining the ETA by:

determining an initial ETA based on the TSP information; and

adding an ETA offset to the initial ETA, resulting in the ETA, wherein the ETA offset indicates an average of differences between actual times of arrival and initial ETAs of a plurality of vehicles.

23. The system of claim 16 , wherein the phase selector is configured to determine the arrival phase by:

determining an amount of time remaining in a current phase at a time of receipt of the TSP information; and

totaling an amount of time including the time remaining in the current phase and a respective time of each phase between the current phase and a first phase change after the ETA using an average length of green phases and an average length of non-green phases.

24. The system of claim 23 , wherein the phase selector is configured to determine the amount of time remaining in a current phase, in response to a transition from a non-green phase to a green phase, by:

setting a time-to-non-green timer to the average length of green phases plus an average length of green extensions in response to an expected green extension;

setting a time-to-green timer to the average length of green phases plus the average length of non-green phases in response to the expected green extension;

setting the time-to-non-green timer to the average length of green phases in response to an expected non-green truncation;

setting the time-to-green timer to the average length of green phases plus the average length of non-green phases minus an average length of non-green truncations in response to the expected non-green truncation;

setting the time-to-non-green timer to the average length of green phases plus the average length of non-green phases in response to no expected green extension and no expected non-green truncation;

setting the time-to-green timer to the average length of green phases in response to no expected green extension and no expected non-green truncation; and

starting the time-to-non-green timer and the time-to-green timer.

25. The system of claim 16 , wherein the phase selector is configured to determine the time to issue the TSP request by:

determining a target TSP time indicative of a time in a phase at which a non-green truncation extension is targeted; and

computing the time to issue the TSP request as a difference between the target TSP time and a non-green truncation offset value.

26. The system of claim 25 , wherein the phase selector is further configured to:

determine whether or not the time to issue the TSP request is within a period in which the intersection controller will grant a non-green truncation, based on the non-green truncation threshold; and

bypass issuing TSP request to the intersection controller in response to determining that the time to issue the TSP request is within a period in which the intersection controller will not grant a non-green truncation, based on the non-green truncation threshold.

27. The system of claim 25 , wherein the phase selector is further configured to:

start a time-to-TPS-grant timer in response to the output of the TSP request;

stop the time-to-TPS-grant timer in response to a transition from a non-green phase to a green phase;

determine after stopping the time-to-TPS-grant timer, whether or not the non-green phase was truncated;

store a value indicated by the time-to-TPS-grant timer in a data set, in response to determining that the non-green phase was truncated; and

determine the non-green truncation offset from the data set.

28. The system of claim 16 , wherein the phase selector is configured to determine the time to issue the TSP request by:

determining a target TSP time indicative of a time in a phase at which a green extension is targeted; and

computing the time to issue the TSP request as a difference between the target TSP time and a green extension offset value.

29. The system of claim 28 , wherein the phase selector is further configured to:

determine whether or not the time to issue the TSP request is within a period in which the intersection controller will grant a green extension, based on the green extension threshold; and

bypass issuing TSP request to the intersection controller in response to determining that the time to issue the TSP request is within a period in which the intersection controller will not grant a green extension, based on the green extension threshold.

30. The system of claim 28 , wherein the phase selector is further configured to:

start a time-to-TPS-grant timer in response to the output of the TSP request;

stop the time-to-TPS-grant timer in response to a transition from a green phase to a non-green phase;

determine after stopping the time-to-TPS-grant timer, whether or not the green phase was extended;

store a value indicated by the time-to-TPS-grant timer in a data set, in response to determining that the green phase was extended; and

determine the green extension offset from the data set.