One of the suitable techniques used to improve safety on freeways is to establish the speed limits .At present, the main problem of speed limits on freeways is how to set the standards. However, the methodsand the research on this field has not been adequately done. In China, the posting of speed limits has been simply based on the design speed for a long time, but the design speed has a minimal impact on operating speeds. In general, drivers operate at speeds in excess of the design speed in many sites on freeways. Considering the problems in the existing speed limits which are based on design speed, this research establishesa highway speed limits theoretical system. The system is considering the relations between the operating speed (the 85th percentile speed) and the roadway characteristics. The speed limits system has been takeninto practice for more than one year and achieved positive effect in Hunan province.
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