Aarhus' path to climate neutrality requires offsetting its current annual carbon footprint of 1.3M CO2e. Around half of these emissions come from transportation. Changes in traffic and the wider transport system will be needed if the city's net zero plans are to be achieved.
The complexity of urban transportation requires detailed models with which to analyse and optimise traffic flows both at macro and micro levels. BIPED is helping Aarhus to manage energy transition in its transport network by providing digital tools for multiscale traffic analysis (Road Twin) and traffic-related energy and pollution assessment (Traffic-Enviro Analyst).
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Macroscopic traffic model
The model captures relationships between traffic flow characteristics such as density, mean speed, and interactions between vehicles and infrastructure. The calibrated traffic network, origin-destination (OD) matrix, and demographic data are some of the inputs used by the macroscopic model to enable 'what-if' scenarios that show how changes like road closures or traffic reductions affect city-wide traffic.
In BIPED, the street-network of the macroscopic model for Aarhus is based on the OpenStreetMap, which was manually enhanced by adding streets or specific traffic features like one-way routes and on-ramps. For its part, the OD matrix - obtained from TomTom - uses data from embedded SIM cards and transportation records.
Users can interact with the macroscopic model and conduct 'what-if' analysis using Road Twin's front-end or VC Map. As well as creating traffic scenarios and visualising results on a map, users can compare two scenarios, aggregate data comparisons, and compare real-world measurements with the traffic model.
Traffic related energy consumption
Outputs of the macroscopic model, such as aggregated traffic flows and average volumes, provide foundational inputs to the Traffic-Enviro Analyst. This is a new tool created to enhance our understanding of traffic-related energy consumption and air pollution by focusing on the specific impacts of different vehicle types, route characteristics, and overall traffic density. Specifically, the Traffic-Enviro Analyst evaluates traffic flows across multiple road segments and incorporates propulsion type distributions (electric, hybrid, conventional vehicles) to provide detailed energy assessments for urban mobility systems. The results can support urban planners in assessing energy impacts of proposed traffic scenarios at the level of cities and districts, including PEDs.
Microscopic traffic model
While macroscopic models are useful for large-scale analysis, they often aggregate data to the extent where localised effects become less noticeable. This is where microscopic models come in. By using flow information and average traffic volumes from aggregated outputs, the microscopic traffic model simulates lower-level properties like the position and velocity of single vehicles.
In BIPED, the microscopic model is designed to simulate individual vehicle movements within the Brabrand district where PED is being developed. The objective is to provide detailed representations of traffic dynamics and the associated environmental impacts within the district with the potential for integration into digital twin platforms for real-time monitoring and control.
BIPED's microscopic model incorporates:
Road Network Geometry: Detailed representation of intersections, road segments, traffic signals
Driver Behavior: Variability in acceleration, deceleration, route choices
Traffic Dynamics: Simulation of congestion, queuing, spillback effects
The model will be designed using the SUMO framework, while leveraging the output of the macroscopic model to ensure consistency between scales.
Next steps
With regards to the microscopic model, we are going to assess the potential for direct integration within the digital twin platform based on the model's performance and resource requirements. With regards to the macroscopic model, planned upgrades include increased network density, particularly in the Brabrand district, and calibration to deliver more accurate and actionable results. In addition, air quality data will be added to support pollution assessment from traffic, so as to further enhance its role in strategic urban planning.
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