A practical comparison of VISSIM and SIDRA for the assessment of development impacts

Abstract

This research project was devised to provide a comparison of the engineering uses of VISSIM and SIDRA (two traffic modelling programs) in the assessment of traffic-based development impacts. SIDRA is a micro-analytical traffic evaluation tool, whereas VISSIM is a multi-modal microsimulation traffic modelling software. The key objectives of the study were to compare the output results of SIDRA and VISSIM, particularly the key performance measures of delay and queue length, and to also investigate the potential advantages and disadvantages of using VISSIM to perform development impact assessments. The key outcome of the model comparison was that SIDRA tended to calculate higher average delay statistics than VISSIM for intersections with low traffic demand and where some geometric negotiation is required. Further investigation identified that SIDRA automatically includes a geometric delay component within its calculation of average vehicle delay. By contrast, the equivalent statistic calculated by VISSIM ignores geometric delay (when coded using reduced speed areas) and incorporates only genuine control delay. This identifies a key difference between the methods used by each package to report a performance measure that is commonly assessed in TIAs. No consistent trend was apparent in the comparison of queue length data generated by each package, although there was some evidence that VISSIM reported larger queues than SIDRA at over-saturated intersections. In summary, SIDRA is likely to be more appropriate for projects with tight timeframes and smaller budgets. Assessments that require analysis of intersections with irregular geometry, or where multiple intersections are in close proximity to one another, are better conducted with a microsimulation model. The study concluded that the general modelling context needs to be identified before a choice of model is made. Consideration should be given to the network extents, intersection types, project budget and project timeframe.