System Dynamics-Based Quantitative Study Of Traffic Risk Of PPP Highway Projects

With the rapid development of the social economy,we need more and more highways.Owing to the limited financial resources,government can not build these highways alone.In addition,private capital is plenty and seeking the right channel to invest.As a result,the PPP(Public-Private-Partenership)model was introduced into the highway projects.Compared with traditional toll road projects,PPP is a new model for private public partnership to provide public goods.It can ease pressure on the finance,improve service quality and supply efficiency and share the risk reasonably.However,there are still many problems in the PPP highway projects at present.There is a high degree of uncertainty as to the highway traffic and revenue.The traffic risk has been the difficult point of the theory research internationally.Compared with ordinary highway projects,PPP highway traffic risk involves tripartite subjects.Therefore we must consider the various factors while conducting simulations to predict the highway traffic.In addition,the PPP highway is essentially a toll road.It has a certain commercial nature.But as public infrastructure projects,it should reflect a certain public welfare to protect the public interest.This is a big difference from the non-PPP highway projects.So the feelings of the public must be considered in the process of pricing and use.Only in this way can we control the traffic risk of the PPP highway projects better.As the traffic volume depends on the allocation rate and the allocation rate depends on the road impedance,the road impedance is key to the path selection and traffic distribution.In order to better control the highway traffic risk and guarantee the interests of the investors and public,this paper deeply analyzed recent cases of PPP highway projects that had issues,identified the main risk factors of the road impedance and led into the risk coefficients such as time cost coefficient,charging impedance coefficient and comfort coefficient to quantify relevant risks based on the users' subjective feelings.Thus the PPP highway comprehensive road impedance function was constructed.The regression equations of the main risk coefficients were established based on the questionnaire survey after multiple linear regression analysis with SPSS.The traffic time was replaced with comprehensive road impedance to improve the traditional multipath distribution model.Then the paper used the system dynamics to establish the traffic volume model of PPP highway projects in order to quantitatively study the effect of risk factors on the traffic volume.At last,this paper selected a highway case to simulate it and compared the simulation results with the historical operational data.Error rate is very low.The result shows that the traffic forecasting model of PPP highway and the actual situation reach a high fit so as to verify the reliability of traffic forecasting model based on System Dynamics.It could be used to forecast PPP highway traffic trends in the future.