The FRA has identified several types of auxiliary external alerting light arrangements as acceptable locomotive conspicuity measures and issued two Interim Rules in 1993 and 1994. This study investigated the performance of currently available external visual alerting devices for installation on locomotives. A variety of passive (paint schemes and reflective materials) and active (lights) systems were reviewed. These devices were evaluated in terms of their ability to assist the motorist to: (1) detect the approaching train, (2) recognize the potential of the hazard, and (3) estimate its approach, and thus avoid a collision with a train at a grade crossing. Controlled field testing was conducted to measure the effect of selected locomotive alerting light systems on observers. In-service railroad test operational experience for locomotives equipped with crossing lights, used in combination with the standard headlight, was also evaluated in terms of capital costs, maintenance, operational concerns, and accident data. The results of the controlled field tests indicate that the use of selected alerting light systems, rather than use of the standard headlight alone, is an effective means of enhancing locomotive visibility. The preliminary in-service accident data provided by participating railroads indicates a potential for significant accident rate reduction with the use of the crossing light system.