I-285 Matrix Variegator

Abstract

When trip tables from travel demand models are applied to simulation modeling, the demands are often unrealistically high. Unreasonable demands produce extreme congestion in simulation models, resulting in unusable results. This problem is often resolved by using travel demand model trip tables as seed matrices for matrix estimation procedures. Matrix estimation procedures leave simulation model developers with difficult decisions of how to factor estimated existing trip tables to produce future trip tables, which may also produce unreasonably high demands. Matrix capping reduces trip tables to ensure select links are not over capacity. And although matrix capping has been justified by assuming peak spreading occurs, historical efforts have not applied a systematic process for estimating peak spreading for all trip interchanges. A method is described to refine travel demand model trip tables for use in simulation modeling. Trip table refinement procedures are validated against observed traffic counts by using base year travel demand model trip tables as input. The validated procedures can then be applied to future year travel demand model trip tables to produce reasonable trip tables for simulation purposes. The selected method applies a unique temporal distribution to each origin–destination pair, when appropriate temporal distributions are based on the amount of congestion that is present between each pair. The experience of applying the procedures in the development of a large simulation model of Interstate 285, a major circumferential freeway around the city of Atlanta, Georgia, is summarized.