The railroad signal community and the grade crossing equipment suppliers have reported an increase in the occurrence of loss of shunt on railroad grade crossing island circuits, as confirmed through an October 1990 Association of American Railroads’ (AAR) survey of railroad signal officers. Loss of shunt is described as a brief deactivation of flashers or gate arms while passing trains are still occupying highway grade crossings. Grade crossing island circuits are short (110’-120’) track circuits that span the highway crossing. They keep the flashers on and/or hold the gates down at grade crossings, while any railroad car in a train is in the island circuit. Once the last car of a train leaves the circuit, the island relay becomes activated allowing the flashers to go off and the gates to return to their upright position thereby permitting highway traffic to cross. A temporary loss of shunt (which may cause a deactivation) in grade cross warning devices, while the train spans the crossing, may create a question of reliability in the minds of individuals dependent on them. For this reason, the railroad signal community has asked the AAR Research and Test Department, in cooperation with the Federal Railroad Administration (FRA), to study the loss of shunt problem. This report describes work results and recommends future direction for FRA funded efforts. It also describes AAR/Committee funded efforts.