Evaluation of Diagrammatic Signing at Capital Beltway Exit No. 1

About the report:

Much research to eliminate driver confusion at high-speed interchanges is being directed toward the application of diagrammatic signing. In this study, one conventional sign on the westbound approach to Exit No. 1 of the Capital Beltway was replaced by a diagrammatic sign to determine the effect of the new sign on driver behavior. Before and after phases of the study evaluated the effects of the sign in terms of erratic maneuvers, which were classified into the following types: weaving (across solid line and gore area), hesitating, stopping/backing and partial weaving. The analysis of each maneuver within designated zones throughout the interchange revealed the numbers of maneuvers at critical points. The significant findings are as follows: 1. A significant decrease in weaving maneuvers took place over the gore area after Installation of the diagrammatic sign, which indicates a safer condition than existed before the sign was installed. 2. A tradeoff is seen in the increased partial weaves and vehicle hesitations accompanied by fewer vehicles stopping or backing after the installation of the sign. Much of the increased maneuvering could be attributed to tourist traffic, yet the total effect of the tradeoff is probably a safer condition. 3. Statistical tests showed more consistent patterns of driver behavior following the sign installation. 4. During the four months the diagrammatic sign has been utilized, no accidents have been reported on the approach, which denotes a considerable reduction in the accident rate. General conclusions are that diagrammatic signs can be initially confusing to motorists because their use on major routes is still practically nonexistent. However, driver interviews indicated a favorable reaction to this type of signing and future research was encouraged. This research served as a pilot study for planned statewide tests of diagrammatic signs by the Virginia Highway Research Council. In the future study, an attempt will be made to correlate laboratory findings to the results of field studies.

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