This study investigated the effects of adverse weather conditions on vehicle operating speeds and evaluated the consistency of horizontal alignment of two-way, two-lane rural highways. Twenty-two horizontal curve sections were selected, within easy reach of Irbid, Jordan. Roadway geometric design variables were obtained through field measurements, as were data on pavement condition, skid resistance, and posted speed limits. The speeds of passenger cars, light trucks, and trucks were measured on each curve and its approaching tangent, under various weather conditions, dry and rainy, during the day and night, in winter. Additional speed data were also collected in summer. The results of the analysis indicate that speed limit and rainfall intensity have significant impacts on operating speeds on the tangent. For each type of vehicle, the operating speed on curves and the 'inconsistency indicator', which by definition is a measure of the speed reduction between the tangent and the following curve, were found to be significantly affected by the degree of curve, rainfall intensity, and night-time conditions. Speed reduction models for each vehicle category were developed; these can help traffic engineers in the design and redesign of curves so that they have at least 'good' or 'fair' levels of consistent horizontal alignment. (a).
Abstract