Research On The Length Optimization Of Traffic Bottleneck Zone For Freeway Maintenance Work

Freeway maintenance work requires closed lanes,resulting in a decline in the traffic capacity of the maintenance work zone,which easily forms a traffic bottleneck.Traffic safety and traffic congestion in the bottleneck zone are the main problems facing the maintenance work zone.How to effectively improve the traffic congestion and safety in the bottleneck zone is great significant for improving the service level of maintenance work zone.This paper studies the traffic congestion and safety in the Freeway maintenance work bottleneck zone,and proposes a method to optimize the length of the traffic bottleneck zone.The specific research contents are as follows:Firstly,based on the traffic datas,the traffic flow characteristics of the maintenance work zone are analyzed.Through the analysis of the formation mechanism and types of traffic conflicts in the traffic bottleneck zone,the Time to Collision(TTC)model is improved based on traffic collision index,the traffic conflict discrimination threshold is determined,and the severity of traffic conflict is divided:for rear-end conflicts,TTC ? 2.0s is serious conflict;2.0s< TTC ? 3.9s is general conflict;for lane-change conflicts,TTC ? 2.5s is serious conflict;2.5s< TTC ? 4.4s is general conflict.Secondly,the simulation model of the traffic bottleneck zone is constructed based on VISSIM,and the simulation model of the traffic bottleneck zone is calibrated by comparing the simulated traffic flow generated and the observed traffic flow.Meanwhile,the basic principle of the SSAM model is analyzed,and the traffic conflict threshold of SSAM model is calibrated.Based on the Mean Absolute Error Percentage(MAPE),the validity of the traffic bottleneck zone simulation model and threshold are verified,and a linear regression model is established to analyze the relationship between simulated traffic conflicts and observed traffic conflicts.Finally,based on the VISSIM simulation model of traffic bottleneck zone,the simulation section of warning zones and upstream transition zones of different lengths are constructed.The SSAM model is used to analyze the vehicle trajectory output by VISSIM and obtain the number of traffic conflicts,analyze the relationship betweentravel time,delay and traffic conflict with the length of traffic bottleneck zone.Based on the number of traffic conflicts and safety evaluation index,the optimal length of the freeway maintenance work traffic bottleneck zone is determined.Meanwhile,the relationship between traffic bottleneck zone length and safety evaluation index is analyzed.The results show that when the warning zone length is 2.2-2.6km and the upstream transition zone length is 160-180 m,the safety of freeway maintenance work traffic bottleneck zone is better.Moreover,when the warning zone length is 2.2km and the upstream transition zone length is 160 m,the traffic conflict number,delay and safety evaluation index are the smallest and the safety is the best.