Sharp horizontal curves can pose dangers to the driver when dealing with speed adjustment, vehicle placement, and judgment of the appropriate operating speed. Roadway designers use various warning methods to aid drivers in such situations, primarily with warning signs and pavement markings. There is a suspicion, however, that these devices are often misinterpreted or disregarded by drivers, thus reducing their effectiveness and not achieving intended reduction in operating speeds. The objective of this study was to evaluate the use of several warning signs and pavement markings at problematic rural horizontal curves, and to evaluate their effectiveness in relation to speed reduction. A series of treatments, including one-direction large arrow signs, chevron alignment signs, the new sign that combines horizontal alignment and advisory speed, addition of flags to the existing sign, addition of flashing lights to the existing sign, post delineators, and transverse lines, was applied to three curves and speed data were collected over a two-day period at three locations approaching the curve over a distance of approximately 350 m. The results indicated that the most promising treatments in reducing operating speeds are flashing lights and transverse lines. An analysis of the over the 85th percentile speeds showed also significant reductions indicating that there was a greater impact for the higher operating speeds: a fact which could be considered more important than the smaller overall reductions noted. Another treatment that also showed some potential for reducing speeds is the new combination sign.
Abstract