Different Travel Patterns: Interzonal, Intrazonal, and External Trips

Abstract

Intrazonal and external trips are usually excluded from the modeling process because they are difficult to measure. The exclusion of such types of trips generally affects the accuracy of a calibrated distribution model. The present research aims at overcoming the limitation of estimating the travel cost of intrazonal and external trips. The increase or decrease in accuracy resulting from the exclusion of different trip types is also estimated. Moreover, the effects of different shares of intrazonal trips pertaining to different zoning systems on the accuracy of other trip types is investigated. These objectives were achieved by analyzing a database pertaining to Texas-commodity flows. A set of doubly constrained gravity models was calibrated for two zoning systems, 254-county and 24-district. The analysis reveals that the accuracy of estimates of different trip types would increase if the intrazonal trips were excluded. A two-step method to estimate complete, interzonal, intrazonal, and external trip matrices is suggested as follows: (1) calibrate the complete matrix to estimate the intrazonal and external trips while ignoring the estimates of interzonal trips; and (2) delete intrazonal and external trips and calibrate the remaining origin-destination matrix to estimate the interzonal trips, resulting in a new distribution model or a new cost parameter.