USE OF INCREMENTAL FORM OF LOGIT MODELS IN DEMAND ANALYSIS

Many transportation systems management policies are geared toward making minor changes in the level of service (LOS) provided by transportation networks in an urban area. Estimation of changes in travel demand is usually prerequisite to assessing the costs and benefits associated with such policies. The pivot-point technique, which uses the incremental logit model, is especially suited for this type of analysis. This procedure predicts revised travel behavior based on existing travel behavior and changes in LOS experienced by a trip maker. The major advantage of this procedure is that no knowledge of detailed existing LOS data on all relevant alternatives available to a trip maker is required. Only estimates of existing market shares and proposed changes in modal disutilities are necessary. Based on the values of the coefficients of travel time and travel cost reported in transportation literature, default values of the coefficients of in-vehicle travel time, out-of-vehicle travel time, and out-of-pocket travel cost have been suggested. These coefficients can then be used to calculate the changes in modal disutilities due to changes in travel time, travel cost, or both. The use of this technique is discussed by using a case study.