Most states require that motorists yield the right-of-way to locomotives and their consists at highway–railroad grade crossings. One method of alerting motorists to the proximity of a train is to sound an audible warning using an air horn. In litigation, the effectiveness of a locomotive’s air horn to alert the driver of a vehicle can be a crucial element that allows a jury to determine liability and award financial penalties. Locomotive air horn signal strength, acoustic propagation over distance, excess attenuation, sound isolation of vehicle shells, ambient sound level masking, signal detection ratios, and driver distraction must be considered, measured, and evaluated before the audibility of the air horn can be surmised from the driver’s perspective. The final evaluation must then be presented to a jury through the process of direct and cross examination. Several case examples are discussed relating to this process.