An overview of the Transims micro-simulation model: application possiblities for South Africa

Abstract

Paper presented at the 20th Annual South African Transport Conference 16 - 20 July 2001 "Meeting the transport challenges in Southern Africa", CSIR International Convention Centre, Pretoria, South Africa. ABSTRACT:The Transportation Analysis and Simulation System (TRANSIMS) model was developed as a replacement of the traditional four-step travel demand model. The goal was to provide a simulation model that could analyze many of the issues facing transportation planners such as sustainable development, environmental impacts of proposed projects, and Intelligent Transportation Systems (ITS) deployment. While a simulation approach is powerful and potentially useful, a challenge for transportation modelers is that they will need to fully understand the new modeling paradigm so that the new model is not simply treated as a “black box”. The focus of this paper is on providing on overview of TRANSIMS based on lessons learned from research on real, calibrated transportation networks in Texas. An overview of the TRANSIMS model in terms of its main components along with a brief comparison to the four-step model will be provided. This is followed by an analysis of the highway link supply relationship in the TRANSIMS micro-simulation model with an emphasis on the implications for transportation planning practice. One of the benefits of a micro-simulation model is that the fundamental traffic flow properties are emergent from the model. This appears to eliminate the need for the modeler to assume a prior link flow-density-speed relationship. However, it is shown that the results from the model can be very sensitive to the calibration parameters chosen. Lastly, the paper examines implementation implications from a South African perspective and what transportation planners should be doing in order to prepare for the transition to micro-simulation planning models.