The traditional rail warning system and interconnected traffic signal controllers typically operate semi-independently in both Simultaneous Preemption and Advance Preemption. The only communication that the railroad equipment provides is a preemption call (the presence of trains) to the highway signal controller. In the Advance Preemption operation, the preemption occurs before the warning lights are activated, typically to provide for pedestrian clearance. However, because the right-of-way transfer time (RWTT) could be very short or even zero, it is possible for the track green to time out before the railroad warning system activates, potentially creating a Preempt Trap. The paper demonstrates that intersection operation and safety are greatly enhanced through the use of an improved communications between the rail subsystem and the highway subsystem. An LADOT implementation using IEEE 1570 and improved controller software clearly demonstrations the benefits of this improved communication in eliminating the preempt trap and accommodating pedestrians even with variable RWTT.
Abstract