Effect of Head Turning on Driver Perception-Reaction Time at Passive Railroad Crossings

Passive railroad crossings provide significant challenges to motorists. These crossings continue to claim too many lives and result in too many injuries. Without flashing lights or gates to alert motorists of an approaching train, drivers are left to their own perceptual resources for detecting trains. The AASHTO Green Book is widely accepted as the standard in the U.S. for most design criteria for roadways. It adopts a minimum perception-reaction time of 2.5 seconds at all locations, including railroad crossings. However, several authors have investigated perception-reaction times and have recommended that railroad crossings be considered a special circumstance and a longer perception-reaction time be adopted as the minimum. AASHTO has not accepted these recommendations, and without being adopted by AASHTO, the usual allowance at most crossings is no more than 2.5 seconds. The studies referenced by AASHTO as underlying its policy are based on driver responses after hearing a horn or seeing the onset of a red light. Railroad crossings are different and more complex because motorists must turn their heads and search the tracks for oncoming trains in two opposing directions, which consumes additional perception-reaction time. To assess this extra time, the head-turning behavior of unalerted motorists in traffic streams was videotaped and analyzed. To accommodate 95% of motorists it was found that 0.74 sec was needed for head-turning from center to side to search one approach, and another 1.08 sec was needed for head-turning from side to side to search for trains approaching from the other direction.