Traffic signals that are located near railroad-highway grade crossings are designed to permit vehicles that may be stopped on the tracks to move to safety when a train approaches the crossing. In some cases, the warning time provided to the traffic signal system is as little as 20 seconds before the train arrives at the crossing. Often, the short duration of this warning time can cause crossings to operate in a potentially unsafe and inefficient manner. Further, existing standards, primarily the Manual on Uniform Traffic Control Devices (MUTCD), allow traffic signal controllers to cut short the pedestrian phases and vehicle phases that conflict with the track clearance phase. Such heavy-handed preemption treatment, while effective at arriving at the track clearance phase, may leave pedestrians with curtailed WALK and/or flashing DON’T WALK indications while they are crossing the street, and it may lead to short and confusing signal indications for motorists. This project developed a new method for controller treatment of railroad preemption calls that is based on advanced train detection and controller notification. Detection and preemption systems that are in use today would remain as a fail-safe default preemption where the new strategy, known as the transitional preemption strategy (TPS), is implemented.
The objective of the TPS logic developed and refined during this research was a reliable method for providing improved intersection controller response to the preemption of adjacent highway-rail grade crossings. TPS will ensure that phases that conflict with the trackclearance phase receive the minimum time required for vehicles and pedestrians to clear the intersection; if such time is not available, the phases will never be initiated. The smooth transition into intersection phases that clear vehicles from the highway-rail grade crossing is made possible by advanced detection and warning of the arrival of approaching trains. Placement of advanced train detection devices (Doppler radar) was intended to provide the necessary minimum times for both pedestrians and vehicles on phases that conflict with the track-clearance phase before it is initiated. The fact that TPS avoids the display of short green indications for motorists at the intersection can also lead to operational improvements in terms of the intersection’s ability to smoothly and safely process vehicles.
