THE 1985 HIGHWAY CAPACITY MANUAL AND ROAD USER COSTS FOR 2-LANE ROADS

This article investigates the effect of speed-volume curves and the PTD (percent time delay) parameter on road user costs computed for two-lane roads. The article also attempts to provide a brief description of a proposed model for cost of comfort and convenience that may be helpful to traffic when they use the 1985 Highway Capacity Manual's speed-volume curves for estimating user costs for 2-lane roads. Details of the study data and method of analysis are summarized. The cost-volume curves of the 1965 and 1985 HCMs are compared, and the cost of comfort and convenience are discussed. The changes in the information and analysis procedures suggested in the 1985 HCM are expected to have significant impact on the user cost in highway economic anslysis for 2-lane rural roads. The new speed-volume curves, when employed with the traditional values of cost factors and parameter values, may result in much lower cost as compared with 1965 HCM. The analysis of unit cost versus V/C ratio curve indicates that a significant underestimation of the cost of user congestion could result if the old cost factors and statistics are used with the 1985 HCM information and procedures. To reflect the cost of deterioration in service with increasing traffic volume on 2-lane roads, it is suggested that a cost of comfort and convenience be computed and added to the other components of the user cost.