Research On Urban Road Traffic Evacuation Models In Emergency

In recent years,with the development of urbanization,increasing number of people choose to live in the cities,which have increased the urban traffic pressure.Once an emergency were broke out,it is ease to cause urban traffic paralysis and further severe economic losses and casualties.To avoid or at least decrease the loss,all relevant governments and research institutions are actively studying emergency measures.Making an emergency transportation evacuation plan is considered to be one of most effective ways to avoid or reduce the harm caused by emergency disasters.Studying on how to accurately predict evacuation demand curve and assign evacuation traffic,as two core contents of emergency evacuation,is greatly meaningful for evacuation plan making and protecting the safety and the property of the affected area.This paper focuses on modeling evacuation demand curve and evacuation traffic assignment.First of all,factors influencing people' evacuation decision are analyzed.In the view of social contagion of decision making,a method based on Susceptible-Infective(SI)model is proposed to formulize the evacuation demand curve.We also proposed a solution algorithm and relevant sensitivity analysis method.Features in this model are talked in detail by an example.Then,in the traffic assignments about evacuation vehicles composed of private cars,the efficiency and social fairness should both be considered.Based on CTM(Cell Transmission Model),a linear programming model is developed to dynamically assign the evacuation traffic compromising the efficiency and fairness.Features in this model are also talked in detail by an example.At last,a disaster event of the "Tianjin Explosion" is used as a case for the empirical research.In the analysis of characteristics about the two models,many important conclusions are found.For the evacuation demand predicting model,the model results have same characteristic like S-curves and,in other word,the cumulative percentage of evacuation in this model presents same rule of growth like the shape of S-curves.Moreover,the model result is significantly related with all influencing factors.For an example,in the analysis of the effect of the social factor on the model,we find that,due to low social influence,the cumulative evacuation demands in isolated communities will be less than the communities with many adjacent communities.For the evacuation dynamic traffic assignment model,we get a crucial conclusion that is "compromising objective is optimal".This conclusion means that when the model objective changes from almost efficient optimization to compromising evacuation efficiency and social fairness(k=1)the evacuation efficiency of the whole region decreased slightly while the efficiency of the high-risk communities increased sharply and,when the objective changes to social efficiency optimization,the evacuation efficiency of the whole region will also decreased sharply.In addition,when factors(such as the decrease in the number of shelters open)are changed,the conclusion still holds.In the empirical analysis of the "Tianjin Explosion",we find phenomena in the model results are conformed to the conclusions in the analysis of the model characteristics,such as the evacuation of isolated community demand lags.In addition,in the model objective of compromising evacuation efficiency and fairness,the traffic evacuation path distribution for each community is very simple and there are totally three kinds of traffic assignment condition in the whole process of evacuation.In practice,this evacuation traffic scheme is easier to be performed.