Evaluating Approach of Travel Time Reliability for Highway Network under Rain Environment

Rainfall always has a direct impact on the travel time reliability of the highway network. Taking into account the adverse driving conditions under rain environment, such as poor visibility and low friction coefficient, the improved model of free flow speed, capacity and demand is established based on the analysis of spatial distribution pattern of rainfall. Thus, the generalized road travel time function is proposed to elaborate these factors. With user optimal equilibrium assignment formula and the series-parallel theory, the model to evaluate the travel time reliability of the road unit, path, OD pairs and network system is proposed by analyzing the network supply and demand levels. Then, the distribution of the rainfall on the highway network is simulated by the Matlab toolbox, and the model is solved with the Monte Carlo methods. Finally, a simple example illustrates the methods in the application to evaluate the travel time reliability of highway network under rain environment. The results indicate that the methods enable effectively identify the critical road sections with high sensitivity about travel time in the network.