This report uses signal detection theory (SDT) to model motorists' decisionmaking strategies at grade crossings in order to understand the factors that influence such decisions and to establish a framework for evaluating the impact of proposed countermeasures. This report is intended to update and expand the original analysis conducted by Raslear (1996), which examined the effectiveness of grade crossing warning devices and determined whether their effectiveness was due to variations in the signalto- noise ratio (sensitivity), bias to stop, or a combination of these two components of signal detection theory.