Variable Speed Limit Method And Sign Setting Of Expressway Maintenance Area Based On Traffic Conflict Index

With the rapid development of transportion industry and increasing number of vehicles in China,expressway pavement suffers different degree injury,so expressway mainteance projects increase gradually.Expressway work zones for maintenance often need to close lanes,which will lead to capacity reduction.Additionally drivers slow down and change lanes frequently,so traffic environment is very complex.Excessive speed difference in warning zone is one of the main reasons why work zones encounter frequent traffic accidents.Therefore,it is significant for improving traffic efficiency and assuing driving safety to implement speed limit control on the warning section of work zone.Traditional speed control which can not adapt the traffic real—time change in work zone has low accuracy and unsatosfactory effect.So the purpose of the study is how to set reasonable variable speed-limit control considering traffic real-time fluction,drivers compliance,road alignment and other factors.The paper studyed variable speed limit control on the warning area of maintenance work zones under the operation mode of closing external lane on a two-way and six-lane expressway.The contents of this paper can be divided into five parts:traffic characteristics during expressway maintenance、modeling of variable speed limit control benchmark model on expressway maintenance work zones、evaluation of the variable speed limit control benchmark model effect using vissim simulation、modification of variable speed limit control benchmark model on expressway maintenance work zones、the setting of variable speed-limit signs on expressway maintenance work zones.The definition,type and organization of freeway maintenance work zones were introduced.Traffic characteristic of freeway maintenance work zones was studyed from driver-traffic flow-traffic environment.the traffic risk of freeway maintenance work zones was analyzed based on traffic conflicts and traffic conflict was given which provided theoretical underpinning for setting speed limit control benchmark model.The action principle of variable speed limit control was explained firstly.Based on the METANET macro traffic flow model,variable speed limit rate _ib(k)was introduced into the model.The multi-objective optimization variable speed limit benchmark model under conditions of at-grade straight lines section,high driver compliance,good wather was constructed in which the objective function is Hourly Composite Conflict Risk Index(HCRI)and Total Travel Time(TTT),setting variable speed limit rate _ib(k)as control variable.VISSIM simulation software was used as the platform to use the VB language to develop the platform twice,and the simulation section of the section of the maintenance section of the US101-S freeway in Ventura Country was builded where the variable speed limit control benchmark model was implemented.The results show that comparing with static speed limit,variable speed limit control on the warning section of work zone can imrove the operation efficiency and reduce the possibility of accidents.This paper analyzed influence factors of variable speed limit control from man-road-environment and quantified some factors.The definition about the correction factor of variable speed limit control was given by which variable speed limit control model was modified.Finally,correction coefficient forms were given accroding different design speed.Variable speed limit control signs setting model was designed considering drivers can read the most information about speed limit control.in this model,variable speed limit control area located in the warning section of work zone was divided into several parts as optional areas for Variable speed limit control signs firstly.Then particle swarm optimization was used to choose some of optional areas setting speed limit control signs in order that drivers can make full use of information on the variable speed limit signs.