Assessing Benefits of Chevrons with Full Retroreflective Signposts on Rural Horizontal Curves

Driving a horizontal 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 advance warning and positive guidance through the curve. Some agencies place supplemental retroreflective material on chevron signposts 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 signposts. This study evaluated three scenarios in a before-and-after experimental design. The before evaluation presented no vertical delineation (baseline). The two after evaluations consisted of a series of standard chevrons (chevrons) and chevrons with fully retroreflective posts (full-post chevrons). Traffic counters measured vehicle speed and lateral lane position at the point of curvature and midpoint of the curve at two separate study sites. Findings showed that chevrons and full-post chevrons moved vehicles away from oncoming traffic by about 15 in. 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 full-post chevrons obtained a 2.20-mph reduction. The findings determined that the benefits of full-post chevrons were not substantial. Researchers recommend that the Manual on Uniform Traffic Control Devices (MUTCD) should continue to present full-post chevrons as an optional delineation tool. On the basis of this research, the researchers do not recommend any changes to the MUTCD.