Differential speed limit analysis and regulations on rural expressways

摘要

Speed on rural expressways is of paramount importance to drivers. The main objective for constructing rural expressways is to significantly improve travel time, safety and comfort. The speed limit is usually a trade-off between travel time and safety. General speed limits or the 'same' speed limit for all conditions and types of traffic, with the provision that drivers reduce speed at adverse conditions, are subjective and difficult to enforce. In practice, such speed limits include all traffic, daytime and nighttime, and speed limits during dry and rainy weather conditions. Thus, they are usually too conservative for some of the most commonly occurring conditions and least conservative for other commonly occurring conditions. This paper analyses common practice for differential speed limits and examines their theoretical justification, particularly for heavy vehicles vs general traffic, day vs night, and dry vs wet or rain conditions. It concludes that safety consideration necessitate differential speed limits for various commonly occurring conditions. However, innovated regulation, management, and enforcement are needed to implement multi-differential speed limits in the same jurisdiction.