Under sponsorship from the U.S. Department of Transportation Federal Railroad Administration, Office of Research and Development, the John A. Volpe National Transportation Systems Center performed an evaluation of the four-quadrant gate/obstruction detection system at the School Street crossing in Groton, CT. The primary objectives of this evaluation were to assess the safety benefits and to document the operational performance provided by this non-standard technology. Highway-railroad grade crossing risk mitigation research in the United States has historically focused on the safety benefits of active warning devices, such as flashing lights, bells, and dual crossing gates. In addition, clear agreement has predominated within the research community that grade separation or closure provides the highest level of risk treatment. As the economic and societal costs of these treatments have increased, however, research has been increasingly concentrated on technologies that provide many of the same benefits without the obtrusiveness of grade separation or closure.