Conspicuity of mirror-mounted turn signals

Abstract

One of the potential benefits of mirror-mounted turn signals is that, in certain important traffic situations, they are viewed at a smaller peripheral angle than are conventional turn signals. This smaller eccentricity in the visual field is likely to lead to better signal conspicuity. The present study examined this potential benefit of mirror-mounted turn signals. Specifically, this field study evaluated the effect of the eccentricity of a signal on its detectability under bright sunshine, while subjects performed a concurrent central visual task. Two levels of eccentricity were tested: 45° (representing a conventional turn signal when the observer is in the adjacent lane and just behind the signaling vehicle), and 30° (representing a mirror-mounted turn signal). Four levels of luminous intensity were used (1, 3, 9, and 30 cd) with older and younger subjects. There are two main results of this study. First, luminous intensity of a signal had a strong effect on its detectability. The older subjects had difficulties with all levels of intensity tested, and only the two highest levels led to reasonably good performance by the younger subjects. Second, for the conditions in which the overall performance was reasonably good, the effect of eccentricity was statistically significant and moderately large in favor of the smaller eccentricity. There are two implications of these results. First, under the demanding conditions represented by bright sunshine and a concurrent central visual task, low but legal levels of intensity led to poor detection performance, especially for older drivers. Second, under these conditions, the smaller eccentricity of mirror-mounted turn signals is likely to result in them being better detected than conventional turn signals.