United States Department of Transportation
i
Indoor Simulator and Field Study Evaluation of Sequential Flashing Chevron Signs on Two-lane Rural Highways
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2017-11-30
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[PDF-22.80 MB]
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Abstract:Past research has found that the average crash rate along horizontal curves of two-lane rural highways is three times higher than on tangent road segments. Single-vehicle run-off-road crashes are four times more likely on horizontal curves relative to tangent roadway sections. One sign application that offers potential safety improvements along horizontal curves on two-lane rural highways is the Sequential Dynamic Curve Warning System (SDCWS), which uses solar powered flashing lights embedded in the sign to delineate the curve. The flashing lights can be simultaneous (i.e., each sign is flashing at the same time as the other signs) or a sequence of lights moving toward or away from the driver. The purpose of this study was to identify the optimal flash rate, speed-activation threshold, and flashing sequence when deploying the SDCWS along horizontal curves on two-lane rural highways. This was accomplished using two independent evaluations. A driver simulator study was undertaken to identify several SDCWS settings that produced the lowest operating speeds along a horizontal curve on two-lane rural highways. The results of this effort found that a low flash rate and a flashing pattern moving away from the driver, as well as a high flash rate with a simultaneous flashing pattern, produced the desirable speed reduction effects on study participants. A field study was then undertaken to further assess the flash rate and flashing patterns identified in the simulator study. Four different conditions were studied in the field, including a speed-activation threshold that was either 5 or 10 mph above the curve advisory speed, two different flash rates, and two different flashing patterns. These conditions were compared to a baseline condition (static chevron signs) and to the settings used in a previous study. The findings, based on comparisons to a previous study at the same sites, indicate that a flashing pattern away from the driver, at a 1 Hz flashing rate, with a speed-activation threshold equal to the curve advisory speed, was the optimal setting for the SDCWS, based on several speed-based performance metrics.
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