Sign target value and angular position, the two major factors in compelling driver attention, are studied. Target is the ability of sign to be visible against its background and provide early recognition and discrimination of the sign type which prepares the driver for the potential message moments before actual reading of the legend. Major factors affecting the target value of a sign are its colour and brightness, producing whatever measure of contrast the natural environmental background permits. Although target value is greatly influenced by background, it is somewhat dependent on the position of the sign with respect to the drivers central point of fixation. The field study consisted of recording a sample of sign backgrounds on interstate highways and simultaneous recording of the angular position relative to the drivers visual axis, including a comparison of these findings with Matsons criteria. Information obtained was categorized by types of terrain. It was determined that the ability of a sign to compel a motorists attention in the daytime is related to the background with which it must compete. Backgrounds most frequent are dark trees, sky and bridge. Limits are suggested for maximum angular displacement of signs relative to the drivers visual axis. The information presented establishes the need for improved sign positioning if angular position relative to the drivers visual axis is to be obtained. The basic information on the nature and frequency of traffic sign backgrounds should be of interest in the design and placement of traffic signs for maximum effectiveness and attention value.
Abstract