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AN ADVISORY SPEED PLATE often supplements warning signs when comfortable speed is less than the speed limit. The advisory speed does not imply the maximum operating speed at which skid and rollover occurs. The advisory speed is intended to inform unfamiliar drivers of a possible hazardous situation and recommend them a comfortable and safe speed to drive around the curve. Several studies and surveys suggest that advisory speeds on curves are generally set too low and are not set consistently from state to state or even within a given state. 1, 2 Studies on rural highways have shown that the lack of uniformity in US practice reduces the credibility and effectiveness of advisory speed signing at horizontal curves. 3 Drivers using the highway repeatedly become accustomed to the speed that road condition and curvature will allow; consequently, the presence of advisory speed signs does not have much affect on their driving behavior. However, an unfamiliar motorist who finds it comfortable and safe to usually drive 10 miles per hour (mph) over the advisory speed will be placed in a potentially hazardous situation when encountering the occasional curve posted with a realistic and meaningful advisory speed.

Despite dramatic improvements in tires and vehicle handling characteristics, the current criteria for setting advisory speeds on curves have remained essentially unchanged for over 50 years. The question is, are these criteria relevant today? The purpose of the study presented in this paper was to evaluate the validity of current criteria for determining advisory speeds on horizontal curves. The study also explores whether the actual …