THE INSTALLATION OF PRE-SIGNALS AT RAILROAD GRADE CROSSINGS

Each signalized intersection adjacent to a highway-rail grade crossing presents the danger of extending queues onto the tracks. Railroad preemption, which connects the traffic signals to the railroad active warning devices, can often be designed to clear the tracks of queued vehicles. There are some instances, however, where railroad preemption alone cannot clear the tracks, and other measures must be implemented. This paper documents one design alternative, the installation of advance presignals, to aid railroad preemption in the clearance of the grade crossings. This design was considered at two locations as part of the Old Colony Railroad Rehabilitation Project in Massachusetts. The 1988 Manual of Uniform Traffic Control Devices sets 200 ft (61 m) between the railroad crossing and the adjacent intersection as the upper limit at which preemption should be considered. This paper illustrates that suggestion of any threshold is misleading. Calculations to set railroad preemption timing and the use of presignals to control queues and provide additional protection at grade crossings are also presented.