Study On The Safe Exit Distance Of Eight-lane Expressway Based On Drivers' Behavioral Characteristics

With the rapid development of China's economy,urbanization,and motorization,leads the traffic flow of more and more expressways to reach its maximum.Therefore,the current expressways cannot meet the need of increasing traffic flow,at present,some bidirectional expressways with four lanes have been extended to eight lanes and some are planned to be extended.However,some relevant new traffic safety issues have appeared along with the implement of the eight lanes project.The most serious one is the problem of entrance and exit ramps as accident blackspots.Most of the accidents happen because of the special speed limits of the eight lanes expressways,as well as the quite wide cross sections of the lanes,which increase the potential risk of lane changing,and the emergent lane changing triggers more traffic conflicts that lead to a series of safety issues,such as rear-end collision,illegal parking and reversing,especially when a car in inner lane expecting to pull out at the exit without changing lanes correctly.Thus,it is very urgent to have researches on the reasonable setting of safety facilities at the exits of eight-lane expressways.This dissertation,based on the behavioral traits of drivers,puts forward a model of safe distance setting for the exit warning signs at the exits of eight-lane expressways.This paper is significant for the improvement of relevant road supporting facilities,traffic safety and even the manless driving both in theory and application.The study aims at solving the problem of setting a generalized safe distance of the exit warning signs for eight-lane expressways.It intends to fully combine the traffic traits of current expressways with the behavioral traits of drivers,and collect as well as analyze the basic data of eight lanes expressways through traffic acquisition equipments.In addition,the paper designs a few real vehicle tests to acquire the data of the drivers' behavioral traits for research,sets up a model of safe distance setting,and demonstrates its feasibility by instance analysis.Details about the dissertation are as follows:Firstly,according to the practice,the paper analyzes the accidents on the eight-lane expressways based on the time,type,and cause.With the method of accident cumulative frequency curve and accident identification which is based on an equitable subsection,the paper finds out that the accident blackspots mainly lie in the entrances and exits of ramps,and then the paper analyzes the causes of the accidents;at the same time,the dissertation studies the influence factors of traffic flow traits by studying the traffic flow traits,speed traits and time headway traits.On account of the small probability density of time headway in each lane whose distribution cannot be precisely fitted,the dissertation poses the fitting of front-end index,figures out the fitting function and the relevant parameter value as well as goodness-of-fit value of each lane.Secondly,the experiments in this dissertation are conducted based on driver's psychological,physiological,and behavioral characteristics,finding that drivers' estimation on the speed is higher than the real speed,and the estimation becomes larger as the distance become longer.What's more,drivers' subjective estimation about the distance between cars can be different from the real distance,and the estimation becomes larger as the the distance become longer.Based on the eye tracking technique Dikablis,experiments were conducted on different lanes on the eight-lane expressway to get some pattern on drivers' different cognitive perspectives,visual cognitions,and the time being taken to make decisions when driving on different lanes.By doing this,researchers tend to establish a visible drivers' model of exit warning signs for the eight-lane expressway to get visual distance,perceived distance,reading distance and decision-making distance aiming at different side road signs and door frame signs.By using speed meter VBOX on different lanes of the eight-lane expressway,it can be seen that drivers tend to first change lanes and then slow down when the exit is far away.However,when the exit is near,they prefer to slow down first,then continue slowing down and change lanes at the same time.The latter is much faster with a shorter distance.According to the free changing lanes situations in this experiment,the safe distance between cars for changing lanes can be analyzed,and time interval model can be structured based on probability distribution of SGompertz's.Thirdly,this study proposes that in order to minimize the delay of traffic flow,a blue zone for cars that doesn't slow down when changing lanes,and a red zone for cars that to slow down because they seek for more opportunities to change lanes should be considered.Thus a complex distance model for drivers to change lanes in the eight-lane expressway should be constructed,resulted in setting up different changing spots under corresponding traffic flows.What' more,the best solution relate to this model is offered,which relies on computer assistant.Lastly,on the one hand,combined with traffic flow traits of the eight-lane expressway and drivers' traits,based on traffic flow parameters,visible distance model for drivers,decisionmaking distance model as well as delay complex model,this paper is trying to construct a safe exit distance model for the eight-lane expressway.On the other hand,this paper will also try to verify the feasibility of this model on actual expressways.From all the researches above,this paper aims to provide a more humanized,more reasonable,and more universal exit warning sign setting plan as well as to enrich the traffic flow theory and improve China's existing traffic signs setting standards.