Current procedures for calculating road-user-benefits by the Ontario Ministry of Transportation and Communications required examination in view of concerns raised about the likelihood for overestimation of benefits in certain applications. A review of the theoretical framework, behind the user-benefit methodology, identified the need for a revised travel-time volume curve for estimating future travel speeds on urban freeway and arterial roads. The need for a new viewpoint in placing a value on travel time savings became apparent during the review. This paper describes the typical application of travel time volume (or speed flow) curves as used in most transportation planning offices. The use of the curves for trip assignment purposes and for the evaluation of road networks is illustrated. The reasons for questionable estimates of user time benefits are identified. The problem is basically due to the use of partial-equilibrium estimates of future systems demands in concert with travel-time volume curves which assume a full equilibrium analysis. A new travel time curve is recommended for use in the partial equilibrium analysis which is typical of the usual approach to systems planning. This relationship is a modified version of Davidson's formula. Sensitivity tests are used to evaluate the degree of benefit overestimation that could result from application of previous procedures. This work was carried out in the Summer of 1979 for the Priority Planning Section of the Ontario Ministry of Transportation and Communications. The new procedures are presently being incorporated into the Ministry's Road User Benefit computer package. (A)
Abstract