移動時間信頼性を考慮した道路の除排雪レベルの評価に関する研究

抄録

In cold regions, winter road maintenance is very important for securing both social and economical activities. Therefore, road management authorities spend large amounts of money on winter road maintenance. Winter road maintenance reduces mean travel time and strengthens travel time reliability, but an evaluation of the efficiency of winter road maintenance has not been carried out. Possible effects of winter road maintenance include improvement in travel time, travel cost, carbon dioxide (CO2) emissions and travel time reliability. The purpose of this study was to evaluate the level of winter road maintenance by applying a stochastic user equilibrium assignment model, which we developed, with traffic capacity of a road expressed as a random variable, i.e. normal distribution. The resultant travel time of a route in a road network is expressed as a random variable. Mean travel time, travel cost, CO2 emissions, and travel time reliability were then chosen as the evaluation indexes for winter road maintenance. Using the variance of random route travel time, evaluation of travel time reliability can be determined. In cold regions, the effect of ‘travel time reliability' is thought to be an indispensable index. Previous studies have not attempted to quantify the effect of travel time reliability due to both the lack of winter traffic data and the absence of adequate network models that can address the uncertainty of travel time under winter traffic conditions. In this study, mean traffic capacity, the variance of traffic capacity and free flow velocity were assumed to change depending on the level of winter road maintenance. This study evaluates three road conditions, conditions in summer, conditions in winter i.e. present road conditions in winter, and conditions where the level of winter road maintenance for the national roads is decreased to the level for other types of roads. The road network used in this study was the whole road network in Hokkaido, Japan, the numbers of links and nodes in the network are 7,167 and 4,619, respectively. A slight increase in the CO2 emission costs compared with the present winter conditions was estimated when the level of winter road maintenance was decreased. As for the travel time reliability, there was a large difference when compared with the total travel costs. If the level of winter road maintenance decreases, an estimated total loss of 102.05 billion yen per year will occur.

JEL Classification: R42, R48