Assessing Benefits in Vehicle Speed and Lateral Position when Chevrons with Full Retroreflective Sign Posts are Implemented on Rural Horizontal Curves



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Driving a horizontal roadway curve requires a change in vehicle alignment and a potential reduction in speed. Curves may present a challenging situation during adverse conditions or to inattentive drivers. Chevron signs provide advanced warning and positive guidance throughout the curve. Some agencies place supplemental retroreflective material on sign posts to enhance the signs? conspicuity and visibility. The objective of this study was to determine any incremental benefits in vehicle speed and lateral lane position when retroreflective material was applied to Chevron sign posts (ChevFull). This study analyzed three separate evaluation scenarios in a before, after, and after-after experimental design. There was an existing Baseline evaluation with no vertical delineation, a standard Chevron evaluation, and an experimental ChevFull treatment evaluation. Data collection measured vehicle speed and lateral position data at the point of curvature and mid-point on two separate curves. Findings showed that both Chevrons and the ChevFull treatment moved vehicles away from oncoming traffic by about 15 inches. Overall, there was little difference between the lateral position findings of the two Chevron treatment scenarios. Chevrons achieved a 1.28 MPH reduction in mean vehicle speed from the Baseline evaluation and the ChevFull treatment obtained a 2.20 MPH reduction. The findings determined that the benefits of the ChevFull treatment were not substantial. The author recommends that the MUTCD should continue to present the ChevFull treatment as an optional delineation tool. Based on this research, the author does not recommend any changes to the MUTCD.