Modelling a complex give-way situation - AIMSUN vs LINSIG

摘要

This paper reports on an extensive traffic modelling of the most complex roundabout in Adelaide which formed the key part of a safety and efficiency improvement concept. Both AIMSUN and LINSIG models were constructed to help concept development and to provide reliable inputs to benefit-cost analysis. The most difficult task of the modelling was to have valid base case models that represent existing peak hour traffic operation of the roundabout. The initial modelling results identified the key issues concerning the existing roundabout operation. However, both the AIMSUN and LINSIG models failed to replicate traffic performance in terms of delay and queuing. The non-standard nature of the five-arm roundabout and the resultant unusual give-way behaviour challenged the ability of both modelling tools. The key challenge to the LINSIG model was how to capture the entry-circulating flow relationship of an unconventional give-way arrangement of the roundabout. In contrast, how to reproduce the very aggressive vehicle behaviour that breaks the normal give-way rule was the focus of the AIMSUN model calibration. In addition, to perform a fair comparison of the existing conditions and proposed future scenarios (i.e. improved geometry design with simplified give-way arrangement), the calibrated parameters of the valid base models had to be changed in the scenario models, which contradicted the normal practice of model development and calibration. Lessons learned from this modelling process would be beneficial to both the modellers, who are responsible for the validity of traffic models, and the decision makers, who use modelling results to inform major decisions.