The Effect of Posted Speed Limit on the Dispersion of Traffic Flow Speed

• Main Authors: Chao Gao, Jinliang Xu, Qunshan Li, Jie Yang
• Format: Article
• Language: English
• Published: MDPI AG 2019-06-01
• Series: Sustainability
• Subjects: speed dispersion; posted speed limit; traffic flow; expressway
• Online Access: https://www.mdpi.com/2071-1050/11/13/3594

Speed dispersion is an important indicator to portray the quality of traffic flow and is closely related to the road safety operation level. In order to clarify the influence of posted speed limits on the dispersion of traffic flow speed, three sections with speed limits of 80 km/h, 100 km/h and 120 km/h on the same expressway were selected for observation, and traffic volume, speed and other parameters were collected. The characteristic speeds, such as average speed, V₁₅ and V₈₅, were evaluation indicators, where V₁₅ and V₈₅ are the speeds of the 15th and 85th percentiles measured at the feature points of the road when the traffic is in a free-flow state and the weather is good. The relationship between different posted speed limit values and the above indicators was analyzed using the statistical analysis software, SPSS. The results show that the speed limit has a high correlation with the average speed of traffic flow, V₁₅ and V₈₅ in free-flow state, with the coefficient of determination being as high as 0.84, 0.85 and 0.92, respectively. In the restricted flow state, the factors affecting the driver’s driving speed are mainly the decrease in driving freedom caused by the increase of traffic volume rather than the speed limit value. In a free-flow state, when the posted speed limit is increased and the average speed and the V₈₅ also increased by approximately the same magnitude. The posted speed limit values of 80 km/h, 100 km/h and 120 km/h correspond to the 90, 88 and 97 percentile speeds of the traffic flow, respectively. The higher the speed limit is, the larger the speed difference between V₁₅ and V₈₅ becomes. The results of the study are very useful for rationally determining the speed limit scheme under different traffic flows.