Calibrating a trip distribution gravity model stratified by the trip purposes for the city of Alexandria

The trip distribution is the most important yet the most misunderstood model in the Urban Transportation Planning Process (UTPP). One overlooked aspect is the different sensitivities in choosing the destinations based on the trip purposes. This paper proposes a framework to calibrate a doubly-constrained gravity model for the trip distribution of the city of Alexandria based on a Household Travel Survey carried out in 2002. The trip ends are estimated from the available census data. Important parameters for the trip attraction models were estimated and validated in the course of this research. Since a small sample is used, a simple, effective weighing technique is applied to mitigate the sample bias. The purpose-based dispersion parameters are estimated based on the weighted sample. The model validation is also introduced in terms of trip length distribution, intrazonal trips and the distribution of the trip interchanges between city parts. The proposed model demonstrates the different patterns of trip distribution per purpose. It also shows a considerable shift toward non-compulsory trip purposes in the city of Alexandria.