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 Travel Demand Forecasting: Theory and Concepts

 
The Logit Model

The logit model, which will be discussed again later in the Mode Choice module, has been used by the Portland, Oregon metropolitan area. The probability of selecting a particular destination zone is based on the number of trip attractions estimated for that destination zone, relative to the total attractions in all possible destination zones. The probability is applied to trip productions estimated for the origin zone, making it conceptually similar to the gravity model.

Pij = e^Vij/(Summation of e^Vij)

where

Pij= probability of trips from zone i choosing destination j
Vij= Aj-a tij+b t2ij where a and b are parameters to be estimated
Aj=trip attractions estimated for zone j
tij= highway travel time to zone j from zone i
Z= total number of zones

Multiplying the probability of traveling from zone i to zone j by the number of trips produced by zone i will yield the number of trips produced by zone i that will travel to zone j.