Abstract
Activity-Based (AB) models represent a new modelling paradigm that might look totally incompatible with the 4-step structure. However, there can bea realistic plan of gradual transition that was adopted by several local authorities in the US. This was based on principles which are described indetail in this paper. Also described are the individual stages of the gradual transition strategy, along with a description of the related benefits, and estimates of time and cost for each one.