A Technique for Evaluation of the Visual Effect of LED-Based Railroad Crossing Signals

This paper describes psychophysical methodology, more precise than conventional photometry, to evaluate the visual effect of LED railroad grade crossing signals. LED devices are attractive replacements for incandescent railroad crossing signals. Up to 700% longer life, 75% lower energy consumption, 300% longer battery operation, and communication capabilities as yet unutilized, have prompted replacement tests. A parallel with highway traffic signals suggests that widespread incorporation is imminent. As for traffic signals, a key question to answer, prior to acceptance, is whether these devices will have the same effect on the eye as the devices that they replace. We previously developed a method to answer this question for traffic signals, for which we described a quality index termed the “usability factor”. Here we extend this technique to red LED railroad crossing signals and report sample measurements which suggest, for a small sample of normal observers, that these LED signals have at least the same, if not better visibility at a given intensity level than the devices that they replace. We describe how the usability factor can be used in combination with conventional photometric intensity measurements to evaluate overall visual effectiveness. We also present the results of visibility field tests. There is a viewing distance dependence of relative intensity between any individual LED signal and the standard incandescent signal. This must be taken into account when considering the LED device as a replacement. TRB 2003 Annual Meeting CD-ROM Paper revised from original submittal. Cohn and Greenhouse 3