Non-Vital Advance Rail Preemption of Signalized Intersections Near Highway-Rail Grade Crossings

Project Description

Simultaneous preemption of traffic signals near highway-rail grade crossings shortens standard signal intervals to clear queued vehicles prior to a train's arrival. While useful in clearing vehicles from the crossing, shortening or omitting the standard 20-second signal interval can lead to trapped pedestrians in the crosswalk who have no protection to finish crossing the intersection.

Researchers at the Texas Transportation Institute developed and tested two alternative strategies to resolve the simultaneous preemption dilemma. Both strategies, called Non-Vital Advance Preemption (NVAP), are designed to ensure safe pedestrian clearance at highway-rail grade crossings. The first strategy used a different preemption sequence than was originally in place. The second strategy prevented the signal controller from activating pedestrian permission if there was not enough time to complete a crossing.

The researchers found that both NVAP strategies reduced the number of times the pedestrian clearance interval needed to be shortened compared to interval lengths with simultaneous preemption strategies. Neither of the NVAP strategies caused a significant change in the average vehicle queue lengths on the intersection approaches. This research showed that using NVAP strategies could potentially enhance safety by enabling vehicles to clear the track without shortening pedestrian walk times enough to trap individuals in the crosswalk.

During the project, the researchers found that it is extremely difficult to predict arrival times of trains at a grade crossing using solely the preemptions from upstream intersections. To achieve the necessary accuracy in timing, researchers recommended that the Texas Department of Transportation (TxDOT) deploy active devices to measure train speeds and movements directly in a rail corridor. Using these devices, TxDOT can minimize the arrival time estimation problems observed in this project.

Project Publications

Non-Vital Advance Rail Preemption of Signalized Intersections near Highway-Rail Grade Crossings: Technical Report 0-4746-3

Non-Vital Advance Rail Preemption of Signalized Intersections Near Highway-Rail Grade Crossings 0-4746-S

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