Effect Of Differentiated Per-lane Speed Limits On Driving Behavior And Traffic Flow On Freeways

As a new speed limt measure,differentiated per-lane speed limits(DPLSL)have been widely applied in China’s freeway systems.Nonetheless,because of the error in understanding the policy,the compliance of drivers with DPLSL is poor and the performance of DPLSL has been affected.Therefore,a clear understanding of the influence of DPLSL on driving behavior and traffic flow is of great significance for guiding the traffic management agencies to improve the management effect of DPLSL.Based on the driving simulator experiments,questionnaire data,mathematical statistics method and traffic flow simulation,this study investigates the effect of DPLSL on driving behavior and traffic flow.Firstly,the difference of drivers’ driving behavior and workload are analyzed based on the results of driving simulator experiments and questionnaire data.Lane changes are found to be less frequent with lower speed and have shorter durations as well as increasing lateral acceleration under DPLSL,especially under complex DPLSL.An apparent rise in driving workload under DPLSL scenarios have been observed,especially under complex DPLSL.Secondly,a back-propagate(BP)neural network based microscopic lane changing decision model(LCDM)is established.By considering the effect of different speed limits in corresponding lanes with other corresponding effecting factors,the proposed LCDM has good accuracy in prediction of driver’s lane changing decision.Then,by adopting the determined BP neural network as the LCDM,a CA traffic model of two lane freeway is established,of which the validation is verified by field traffic flow data.By using the proposed CA model,the effect of DPLSL on traffic efficiency and traffic safety is analyzed and quantified.According to the results of traffic flow simulation,the DPLSL is able to effectively improve the traffic capacity when high propotion of slow vehicles exist.In the meantime,the DPLSL,especially the complex configuration is able to effectively raise the safety levels of freeways.Under the DPLSL scenarios,the lane changing frequency and the variation of speed are smaller than the ones of the regular scenario,and also the DPLSL setting could reduce the occurrence of dangerous situations “improper lane changing” and “overtaking from right” significantly.Besides,the effect of the compliance rate of the lane of slow-vehicles has been studied by traffic simulation.The results show that the safety level of freeway decreases with the compliance rate decreasing.At last,in view of the actual traffic conditions of the freeway in China,the complex DPLSL should be adopted at present.In the meantime,it is suggested that the policy-makers should clarify the standard of law enforcement on the violation of DPLSL,and improve the compliance to DPLSL through propaganda and education for freeway traffic practitioners.