The author analyzed the relationships of operating speed (V85), speed limit and crash rate for Sanfu expressway of Fujian province. Statistics of speed data from twenty-nine cross-sections surveyed by research team showed that drivers compliance to speed limit was disappointed and speeding rate remained high despite rigorous enforcement for excessive speed. There were only seventeen cross-sections of which truck V85 speeds were less than 80 km/h when vehicle type considered, and three cross-sections with V85 below 90 km/h if not differentiating the vehicle type. This result may implied that speed limit determined based on design speed could not reflect practical traffic conditions and reasonableness of speed limit deserved doubt. Speed survey also indicated significant disparity of V85 between passenger cars and trucks. Speed difference exceeded 20 km/h for majority of surveyed cross-sections, and even more than 40 km/h for some cross-sections. In addition, large amounts of traffic detector data were extracted from three traffic monitoring sub-centers. Relationships of between crash rate (per million vehicle-km) and V85, speed dispersion (DEVI-average speed of one segment minus average speed of whole route) were explored based on forty-two sample records generated by integration of speed (most from traffic detectors and some from field speed survey), crashes and traffic volume data of eighteen moths. Two regression models were established by SPSS software suits. The models told us that under current traffic circumstances for Sanfu expressway: (1) crash rate was the lowest when V85 was approximately equal to 104 km/h; and (2)the lowest crash rate occurred if DEVI was near to -4. These conclusions provide some suggestions and reference when to make speed limit more appropriate. (A) For the covering abstract ofthe conference see E216632.
Samenvatting