Primary Author : John Bennett
Co-authors : Brian Betts
Organisation : AECOM
Mesoscopic level modelling for the purposes of project assessment has increased in prevalence across Australia and is considered to provide a bridge between macroscopic modelling and microsimulation modelling.
Aimsun provides a software tool to bridge this gap by facilitating integration between macro, meso and micro levels of detail. The mesoscopic assignment is based upon a simplified application of the car following model, which is more commonly used for microsimulation.
Despite the rise in use of Aimsun as a tool for project assessment, very little research exists to guide practitioners on best practice for calibration at the mesoscopic level. This paper investigates the key parameters that influence the calibration of Aimsun mesoscopic models and recommends a process that achieves comparable traffic operations between the mesoscopic and microsimulation level models.
The simplified car following model used in Aimsun mesoscopic assignment does not account for key factors in traffic operation, including vehicle acceleration/ deceleration and detailed lane changing/ merging/ weaving behaviour. This lack of detail often leads to difficulties in achieving representative levels of congestion on approach to intersections – a common finding is that the mesoscopic assignment underestimates congestion in comparison to a microsimulation assignment within the same network.
The analysis presented in this paper utilises an existing Aimsun model to identify a best practice process to calibration of traffic conditions at the mesoscopic level. The process focuses on how vehicle reaction times and section (link) speeds can be used to sufficiently calibrate operation within a mesoscopic assignment and to provide comparable operation with a microsimulation assignment within the same network. Recommendations on a range of values to adopt for vehicle reaction times and vehicle speeds are provided for a range of situations, to be used as guidance for industry practice.