Project Managers: Arup for Sheffield City Council Brief: Build a large model incorporating route choice to model the effects of public transport priority proposals and help develop new transport models.
The Sheffield City Centre Aimsun Model has been developed by Arup for Sheffield City Council over a number of years. It was originally intended to test the impact of a major development proposal and has subsequently been expanded and developed to cover the inner ring road and many of the surrounding streets.
The latest version of Arup’s model uses the integrated mesoscopic and microscopic models within the Aimsun software to tackle the route choice problem within the complex city centre environment.
Arup used the mesoscopic model to determine a dynamic user equilibrium (representing habitual route choice), which was then used within the microsimulation model together with dynamically chosen paths (representing drivers reacting to congestion), to realistically represent route choice on the network.
The Sheffield model includes buses, the Sheffield Supertram infrastructure, bus rapid transit (BRT) vehicles, including both segregated running and sections where the vehicles run on-street in general traffic, which have a considerable impact on the operation of the network. These larger models incorporating route choice allow the effects of public transport priority proposals to be modelled over a much wider area, allowing, for example, the assessment of the impact of the redistribution of traffic due to reduced capacity.
Due to the way in which microsimulation models treat traffic signals, they are able to model bus priority at bus pre-signals and also pre-emption at traffic signal controlled junctions.
In summary, microsimulation provides an effective way to inform the design and model the effects of public transport priority measures. Over time these large models gradually gain in legacy value and can be re-used for many different purposes.
For example, the model that Arup produced to model bus priority measures as part of Sheffield City Council’s Penistone Road Smart Route proposal has subsequently been used to test the impact of a development proposal and a number of other interventions along the corridor.
The model will eventually incorporate Aimsun Next hybrid simulation, which will allow bus priority measures, such as bus lanes, pre-signals and pre-emption at traffic signals to accurately feed into wider strategic modelling, further enhancing the scale over which the impact of these measures can be assessed.