Verhead Guide Signs can be illuminated to sufficient target value and uniformity with certain 100 watt mercury vapor lighting units. Coating materials based on thermal setting polyester, and thermal setting polyvinylidene fluoride have been found to be satisfactory coating materials for Overhead Guide Signs. Preliminary field evaluations and legibility studies indicate that approximately 40% of the Overhead Guide Signs in the State would not require illumination if the legend is reflective.

This synthesis will be of interest to traffic engineers, planners, and others interested in making sure that motorists' needs for directional information on freeways are being met. Information is provided on policies and procedures used by states in evaluating freeway guide signs and replacing those that are outdated or deteriorated. Many signs on freeways and other controlled-access highways have exceeded their service life and are no longer serving motorists' needs. This report of the Transportation Research Board describes the policies, proceduress, and criteria used by states for freeway sign evaluation and replacement programs.

The current practice in Virginia is to reflectorize and illuminate all overhead highway signs because of their important role in the safe and orderly flow of traffic. Reflectorization is obtained by using reflective sheeting as background and legend materials, and diffuse illumination is provided on the sign surface by lighting fixtures. The performance of the high intensity sheeting has shown significant promise and the purpose of this research was to determine the feasibility of using the material on overhead highway signs without external illumination. Since sign brightness standards have not been established, a comparative technique was employed whereby the brightness of six high intensity overhead signs without illumination was compared to that of six conventional illuminated signs. All experimentation was conducted in the field under the physical and environmental conditions experienced by the highway user. Luminance measurements were made with a telephotometer at the driver's eye position of eleven conventional automobiles. A total of 5,446 luminance measurements were recorded from the travel lanes of illuminated and non-illuminated roadways. The study concluded that the unlighted high intensity signs were brighter than the lighted conventional signs for the motorist traveling on straight sections of roadways using high beam headlights. For the same motorist using low beams the luminances of the high intensity signs were not as bright as those of adjacent conventional signs. Under stream traffic conditions, the average luminances of the conventional signs were slightly higher than those of the unlighted high intensity signs, however, in many cases there were no statistical differences and the people who viewed the signs stated they preferred the high intensity sign because its uniform brightness provided better legibility. On a curved approach, where only a limited amount of light from the vehicles was projected upon the overhead signs, the brightness of the unlighted high intensity signs was not sufficient to provide the motorists with sign visibility and legibility equivalent to those obtained from the lighted conventional signs.

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