TDM strategies that impact travel costs and travel times are estimated using pivot point logit model approach. This consists of a simplified version of the traditional four-step travel demand forecasting procedure to estimate changes in vehicle miles traveled (VMT) and the related number of trips spanning from generalized cost and travel time changes. At the core of the model is the following basic pivot point logit equation:
eU1 + eU
e + eU Um
P(m)= share of mode m; e = exponential function; Um = utility equation for mode m; and,
U1...i = utility of other alternative modes
It is then sufficient to use the above equation to enter the initial or base mode share, mode use ad-hoc or default parameters entering each mode’s utility function to obtain the projected change in modal share due, for example, to a change in generalized cost. The modal share is produced by TDM programs or projects that change the cost or time costs across modes.
The model estimates and reports the following:
Baseline and final mode share by mode, including percent of trips eliminated;
Percent of trips shifted by peak period;
Change in VMT (based on trips removed multiplied by percentage of workforce
affected and average trip length); and, as a result of the change in VMT,
Total daily emission reduction for each pollutant.