The Highway Safety Acts of 1973 and 1976, and the Surface Transportation Assistance Act of 1978, provide funds to individual states to improve safety at public rail-highway crossings. This report was undertaken in support of a U.S. DOT effort to develop a resource allocation model designed to select and rank crossings, and recommend warning device improvements in a cost-effective manner. Input to the model included the effectiveness of active warning devices, flashing lights and flashing lights with gates, in reducing accident potential. The effectiveness is defined as the percentage of accident reduction at crossings which result from the installation of warning devices. Previous effectiveness values were available from a 1974 California Public Utilities Commission study. This report is based on inventory and accident data available from computerized FRA data bases, and computes new effectiveness values in three categories: (1) flashing lights at formerly passive crossings, (2) flashing lights with gates at formerly passive crossings, and (3) flashing lights with gates at crossings formerly equipped with flashing lights only.