Freeway capacity, saturation flow and the car following behavioural algorithm of VISSIM microsimulation software

This paper has set out to identify the changing values of capacities over time as applied to freeway traffic conditions. The paper examines capacity in the context of observed volumes to date from both an Australian and international experience. This paper then examines the car following algorithm in the VISSIM microsimulation software to benchmark the similarity of the maximum freeway capacity against these observed volumes. This review of existing literature was initially undertaken when developing a VISSIM microsimulation model to examine the application of forecast future year traffic volumes on a motorway network. Initial discussion queried the method that microsimulation software packages such as VISSIM use to determine capacity. Microsimulation packages are capacity oriented rather than demand focused. For this reason, microsimulation models are regularly applied to capacity constrained transport situations such as town centre and urban design studies. Existing publications exploring the research behind VISSIM examined the appropriateness of components in the algorithm to recreate traffic operations. However, there was little documentation to identify the midblock capacities represented with the car driver following model to simulate freeway conditions. This paper sets out to explore the maximum capacities that can be achieved when simulating freeway operations for both current and future year conditions. (a) For the covering entry of this conference, please see ITRD abstract no. E216058.