Sensory Cause of Railroad Grade-Crossing Collisions: Test of the Leibowitz Hypothesis

Abstract

Railroad crossing collisions are costly in both lives and property damage and are a principal limitation preventing meaningful increases in train speed. At a recent TRB workshop on means of minimizing the frequency of these events, it was agreed that a major hypothesis aimed at explaining the collisions had never been tested. That hypothesis, attributed to Leibowitz, is that the speed of larger objects, like trains, is underestimated by observers owing to a normal deficiency of visual processing. The elements of this hypothesis have begun to be tested in a laboratory setting. While there are numerous aspects to the judgment of speed of approach, studied has been one narrow aspect of the problem that relates to the rapidity with which a gradual increase in the size (starting size 3.7°, 5.3°, and 7.6° side) of a square is perceived by normal human observers. The object is a light gray rectangle set either in a dark gray surround or with no surround. The time required to react to the gradual change averages around 280 milliseconds (ms) after onset. In a significant number of tests on six individuals across conditions ranging from day to night light intensities, expansions in either width or height, and proportional increases in size or fixed increases, the time required to render the judgment increased with the starting size. The rate of increase was approximately 3 ms divided by the degrees of angle subtense (360° = full circle). Apparently, the initial approach of larger objects is seen more slowly or later than that of smaller ones. If so, this can be shown to translate to a more slowly perceived object speed. Leibowitz may have been correct.