Sydney: CBD Commuter-Aimsun Next Model

Sydney: CBD Aimsun Next Model


Transport for New South Wales (TfNSW) in conjunction with GTA Consultants and Azalient.


To develop an innovative, multi-layered traffic model of Sydney’s central business district (CBD) to test the impacts of a wide range of projects particularly the introduction of light rail through the city centre.


The Sydney CBD model enables a multi-layered assessment of the transport operation of the Sydney CBD including in its scope overall regional impacts for both general traffic and public transport.

The mesoscopic model is one of the first of its size to provide operational modeling in such detail. It is even able to accurately mimic a SCATS traffic control system and offer close detail at intersections, which was previously only possible in small-area microscopic level models.

It is the attainment of such breadth of scope combined with such depth of detail that makes the Sydney CBD model so innovative.


While the model will allow for testing transport policy decisions and infrastructure proposals of any size, the main project currently under consideration is the Sydney CBD Light Rail, which is part of Sydney’s Light Rail Future project.

Sydney already has 7km of light rail in place but the new CBD and South East line is being built to reduce bus congestion in the CBD and provide higher capacity public transport to the Sydney Football Stadium, Sydney Cricket Ground, Randwick Racecourse and the University of New South Wales, which are currently served only by buses. In contrast to the Inner West line, which is the light rail network’s original line, the route is mostly on-street and follows a similar path to routes used by the former tramway network.

The light rail expansion is set to run alongside a redesigned bus network that will see a reduction per hour of more than 220 buses entering the CBD in the morning peak, benefiting customers travelling from all over Sydney.

Work on the $1.6-billion project is already underway and will take five or six years to complete.


TfNSW took a multi-level approach to account for regional traffic diversions resulting from changes in the capacity of the Sydney CBD road network and hence plan for a realistic demand.

Iterations with the strategic model were time consuming and of limited accuracy; in contrast, covering a wider area mesoscopically helps to provide updated and time-dependent demand at boundaries providing a higher order of accuracy, and it can take into account rerouting inside and outside the microscopic/nanoscopic area and also any changes in the nanoscopic area that may affect the demand at its boundaries.

The modelling process included the development of an area wide mesoscopic Aimsun Next model with a large part modelled using a hybrid model concept. The hybrid simulator concept allowed for dynamic simulation of an area large enough to account for regional route diversion, as well as microsimulation modelling of smaller pockets that require representation of dynamics individual vehicles in the detailed road network.

Because of the evolving forecast of traffic congestion over time, the need to establish the most efficient approach for optimising signal timings at intersections was considered desirable for the detailed analysis. First of its kind SCATSIM operation of signal controls in the Aimsun meso model with the aim to provide a more precise estimation of the magnitude of traffic issues so that tailored congestion management plans can be developed.

The model offered an efficient method for data exchange or model transformation from the macroscopic level (Sydney Traffic Forecasting Model (STFM) and the Public Transport Project Model (PTPM)) to the mesoscopic level (Aimsun Next). The model was enhanced by coding detectors and signal groups at all signalised intersections to match SCATS real world detector and signal groups.

Plans for light rail in the Sydney CBD - Modelling with Aimsun Plans for light rail in the Sydney CBD

Sydney CBD - Multi-level modelling with Aimsun Click to enlarge – Sydney CBD – Multi-level modeling with Aimsun Next

Sydney CBD - The Aimsun mesoscopic model study area in relation to the STFM strategic road network Click to enlarge – The mesoscopic model study area in relation to the STFM strategic road network

Sydney CBD Traffic heading into the CBD