The Impacts of Differential Speed Limits on Speed

Design speed is generally used as a basis for determining the post speed limits in China. Therefore the fixed value becomes the post speed for the whole road. Because of the big difference in operational characteristics between cars and trucks, this method is clearly inappropriate, considering the effects of Differential Speed Limits (DSL) are controversial. This paper expatiates the advantages and disadvantages of DSL, using hypothesis testing and analysis of variance methods (ANOVA) to analyze the difference of 15^th percentile speed, 85^th percentile speed, mean speed, speed variance, speed limit compliance between DSL and USL (uniform speed limit). Finally, consider truck mixed rate and traffic volume as variables to establish a linear regression model between speed limit differences and speed statistical indicators.