This report describes a two-year study of some of the basic problems involved in improving the design of active warning devices intended to make motorists more aware of grade crossing hazards. Emphasis was placed upon improvement of the attention-getting aspect (conspicuity) of active crossing warning devices which was presumed to positively correlate with improvements in grade crossing safety. An indoor laboratory test was conducted in the FAA Low Visibility Research Facility located at the University of California. In excess of 150 subjects gave over 20,000 responses to flashing light displays. Results were analyzed to determine effects of color, flash rate, brightness, size and placement under daylight, darkness and daytime fog conditions. The laboratory tests resulted in development of two improved devices which were field tested on actual grade crossings. The first device consisted of an array of three eight-inch white (clear) strobe lights added to a standard flashing warning system at a high accident rate urban crossing in Richmond, CA. The second was a gate arm add-on device consisting of three small strobes, red, white (clear) and blue in color installed at a rural highway grade crossing with high speed truck and automobile traffic. Due to project constraints, no long term safety improvement analysis could be conducted. Because there was no evidence of driver confusion during the conduct of these field tests, it was concluded that colored lights other than red can be used in moderation as add-on to existing active crossing warning devices to increase the attention getting property of the warning system. The high composite (not from a single source) flash rate devices that were installed did not result in any erratic driving behavior on the part of approaching motorists. /FHWA/