Evaluation of High Intensity Sheeting for Overhead Highway Signs

About the report:

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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