Research On Passing Sight Distance Model On Two-lane Highways

Two-lane highways consist of a substantial proportion of the road network in our country.Overtaking is one of the most common traffic phenomena on it.Whether overtaking is safely completed is largely determined by passing sight distance,so it is necessary to conduct special research about it.In this thesis,a general model is established based on the kinematical theory as well as overtaking reality.If vehicles' state is given,overtaking condition and passing sight distance can be determined.Firstly,the function expression between overtaking duration and vehicle state is established based on the kinematical theory.Secondly,safe following distance is defined and its mathematical model is also built up which has explicit physical meaning.Thirdly,the overtaking duration is divided into the time for passing vehicle to catch passed vehicle and the time from catching to passing vehicle back to original lane,both of them can be ascertained based on the mathematic relation with safe following distance.Finally,the concept of safe react time is proposed to calculate the safe distance between passing vehicle and opposite vehicle at end moment.A detailed numerical analysis is performed based on proposed model.The results show that:(1)there is a close connection between the safe following distance and the velocities of passing vehicle and passed vehicle at initial moment.If passing vehicle speed given,there is a quadric relationship between following distance and passed vehicle speed.When passing vehicle speed fixed,safe following distance decreases with the increasing of passed vehicle speed,however,when passed vehicle speed fixed,it increases with the increasing of passing vehicle speed.(2)If the two vehicles' speeds keep constant during overtaking with fixed passing vehicle speed,both the time needed to overtake and passing sight distance decrease with the increasing of passing vehicle speed.(3)If passing vehicle and passed vehicle accelerate during overtaking,the time needed to overtake and passing sight distance are not only influenced by the two vehicles' speeds but also by the highway speed limit.Both the time needed to overtake and passing sight distance decrease with the increasing of passing vehicle speed when overtaking duration is less than the time needed for passing vehicle accelerating from initial speed to highway speed limit.Otherwise,they could increase with the increasing of passing vehicle speed.Whether overtaking is possible and how long the safe following distance is at initialmoment can be determined by using proposed model,provided vehicles' running state and other essential parameters are given.If passing possible,we can calculate the safe following distance,the safe distance between passing vehicle and opposite vehicle,the time needed to overtake and passing sight distance at end moment,one of which has an unique value corresponding specific state.The research results have significant positive effect on the line design of two lane highway,driver behavior decision and traffic accident analysis and prevention.