The conspicuity of a traffic control device (TCD) is defined as the probability that the device will be noticed. However, there is no agreed-upon measure of what constitutes being noticed. Various measures have been suggested, including eye fixations, recall, and verbal reports. Four conspicuity studies are discussed in this report. It has been observed that conspicuity is not solely a property of a TCD but must include consideration of the surrounding environment. The first of the studies described in this report used multidimensional scaling (MDS) to identify factors that characterize drivers’ perceptions of TCD environments. The MDS study revealed that two dimensions, clutter and predictability, characterized the roadway environments included in the study. In the second study, drivers’ eye glances to TCDs were recorded on a 34-mi (55-km) drive. After passing selected TCDs, drivers’ recall of the TCD was assessed by asking them to identify it. That study showed that warning signs are seldom glanced at and only about half of them are recalled just 2 s after they are passed. About 20 percent of speed limit signs received glances, but drivers were aware of the posted speed limit about 80 percent of the time. The third study examined drivers’ ability to detect speed limit and warning signs. The ability to detect speed limit signs, as measured by conspicuity angle, was degraded by cluttered backgrounds. However, the detectability of fluorescent yellow-green warning signs was not affected by background clutter. The fourth study examined the effect of background environment on drivers’ ability to read TCDs. Background had no effect on speed limit sign readability and had a small effect on warning sign readability. Recommendations for enhancing the conspicuity of regulatory signs are proposed. (Author/publisher)
Abstract