A PRELIMINARY CALIBRATION EXERCISE OF HDM-4'S ROAD USER EFFECT RELATIONSHIPS FOR JAPANESE CONDITIONS

The Highway Development and Management Tool (HDM-4) is a state-of-the-art tool for road investment decision analysis based on the comparative evaluation of costs and benefits of alternative investment strategies. The costs and benefits of the alternative investment strategies are estimated using relationships classified under two broad categories: Road User Effects (RUE) and Road Deterioration and Works Effects (RDWE). Relationships under the RUE include models to estimate vehicle operating costs (VOC), travel time and exhaust emissions, whereas relationships under the RDWE include models to predict the deterioration of pavement and the impacts of maintenance activities on the pavement condition. The RUE components are estimated as a function of factors such as vehicle characteristics, pavement condition, etc., whereas the RDWE are predicted as a function of factors such as environmental conditions, traffic characteristics, etc. As these factors vary from country to country, local calibration of both the RUE and RDWE relationships is a prerequisite for a sound road investment decision-making. The transferability of the HDM-4 tool across countries to suit local conditions is ensured through a set of calibration factors that are adjusted in such a manner that the differences between the estimated RUE and RDWE components and the observed ones are minimized. This paper presents the results of a preliminary calibration exercise, one of the first in Japan, of the RUE relationships of five typical vehicles i.e., small passenger cars, medium passenger cars, medium trucks, heavy trucks and heavy buses. The basic input data required for the calibration were obtained from reports published by the Japanese trucks and buses operating companies, car dealers, etc., and earlier studies on VOC and exhaust emissions undertaken by different Japanese government agencies. Calibration factors were estimated for the parts consumption and labor hours for the VOC relationships and for the nitrous oxide, carbon monoxide, hydrocarbon, particulates, carbon dioxide and sulfur dioxide exhaust for emissions relationships. It was found that the use of HDM-4 default parameters overestimates both the parts consumption and labor hours in comparison to the actual consumption in Japan for all the five vehicle types considered. However, the estimates of the exhaust emissions were found to be less for some vehicles and high for others.