Evaluation of Raised Pavement Markers for Roadway Delineation

About the report:

Reduced visibility on the highway due to adverse weather conditions results in an inability of motorists to readily observe pavement markings, signs, and vehicles. The condition that presents the most serious restriction is fog, although rainfall during the night frequently creates serious visibility problems. Because of the ability of reflex reflective devices and materials to provide pavement and roadway delineation at relatively low costs, the feasibility of using them for roadway delineation and vehicle guidance during fog was investigated, with emphasis on the nighttime visibility characteristics. Also, consideration was given to various experimental methods of marker placement for roadway delineation and to protecting the markers from snowplow damage. Two types of corner-cube raised markers were placed along the highway edge line on 20-ft. (6.1 m) centers. In one placement concept, snowplowable and non-snowplowable markers were placed on the pavement surface; in a second, concept, the markers were recessed below the pavement surface in grooves. The marking systems were subjectively evaluated by observing the legibility properties during fog and noting the number of markers visible. Based on the observations, the raised pavement markers were thought to provide sufficient nighttime roadway delineation for vehicle guidance during light to medium density fogs. Although data were not available for dense fog, it is felt that adequate delineation would be provided for such fog conditions. The method of grooving the pavement in the vicinity of the edge line for the purpose of recessing the markers to provide snowplowability was found to be feasible, providing adequate drainage is provided and a groove is placed in front of the marker. The length of the groove depends upon the reflectivity-distance requirements.

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