Modelling perimeter controls: Detailed simulation

In our previous project (Improved network performance prediction through data-driven analytics and simulation), we numerically simulated perimeter control (gating) based on macroscopic fundamental diagrams (MFDs). The results demonstrated the benefit of gating and how the Perth road network could be optimally divided into multiple zones for this purpose.

As the next step towards operationalising it in Perth, this project aims to extend the work by more detailed simulation of traffic behaviour and gating strategies.

It will produce better estimates of the potential benefits and effectiveness of the MFD-based controllers and enable Main Roads to make informed decisions. It will pave the way for an actual trial if the estimated benefits are significant.

The main project scope includes:

• Repurposing the existing CBD model and the new Aimsun Live model (offline) for testing perimeter control, including dividing MFD zones, developing scripts for generating MFD diagrams for each zone, programming in controllers and gating strategies
• Sensitivity testing of key assumptions such as driver response
• Evaluation of potential benefits and effectiveness

Participants

• • Main Roads Western Australia
  • University of Western Australia

Project background

Perimeter control (also known as gating) works by dividing the network into multiple zones and regulating their flow exchange at the boundaries. It aims at load-balancing between zones across the network to achieve a stable and optimum operation at the global level.

Controllers prevent overflow of traffic into busy zones by leveraging spare capacities in less busy zones as temporary storage space. This contrasts with local congestion relief strategies that focus on individual pinch points, which can result in pushing too much traffic downstream and creating another bottleneck. The basic idea is similar to ramp-metering, but expands it to the whole network.

By keeping the whole network at a steady state, gating has the potential benefit of maximising the total productivity and reducing the need for local capacity expansions. However, its effective implementation requires a good understanding of the behaviour of each zone. Macroscopic Fundamental Diagrams (MFDs) are commonly used for such purposes. They describe underlying relationships between a zone’s speed, flow and density at the aggregate level.

The accurate measurement of MFDs has become possible in recent years with the advent of ‘big data’. As Main Roads’ Network Operations Directorate is making rapid progress in this space, the feasibility of implementing perimeter control becomes increasing likely.

MFD-based perimeter control is a potential paradigm shift for network operations, and it can maximise the productivity and reliability of the whole network by utilising spare capacity in zones with low demand-to-capacity ratio to alleviate stress for those under high demand. The productivity gain and avoidable cost of unnecessary road expansions could generate significant social, economic, and environmental benefits.

In our previous report Implementing Multi-Zone Perimeter Controls on Perth’s Road Network we have theoretically shown the benefit of applying perimeter controls based on MFDS, and how the Perth road network could be optimally divided into multiple zones for this purpose.

Project objectives

This project aims to extend the work with more detailed modelling of traffic behaviour and gating strategies. It will produce better estimates of the potential benefits and effectiveness of MFD-based controllers and enable Main Roads to make informed decisions on whether an actual trial should be conducted.

Its main objectives are:

• Further development and confirmation of the theoretical proof-of-concept of application of perimeter control based on MFDs at the zonal level, through better and more detailed modelling
• Better understanding of potential benefits and wider implications including possible challenges
• Comparison of different controller logics and their pros and cons
• Formulation of feasible gating strategies, such as changing phasing plans

Final report

This project has been completed, and a wrap-up of the project can be found at Implementing perimeter controls for the Perth CBD. Included is an overview of the earlier work conducted in this area, objectives, the model, conclusions, directions for future research, and expected project impacts. Also is available is a downloadable copy of the final report.