• PTV Vissim increasesroad capacity in Birmingham

    PTV Vissim increases
    road capacity in Birmingham

Mott MacDonald: Birmingham Box Smart Motorways


Project title:
Birmingham Box Smart Motorways Rollout, UK

Contracting authority:
Highways Agency

Governmental Institution
: Mott MacDonald
Project duration:

Project description:
One of the key problems on British roads is the high level of traffic demand, which will continue to increase in the future. A cost effective, intelligent and efficient way to ease the problems caused by this development is to implement Smart Motorways on the strategic highway network. Smart Motorways are a new, technology driven approach to the use of our
motorways, reacting to traffic conditions on the highway and changing driver behavior according to these conditions. This in turn increases road capacity during peak periods by managing demand, using variable speed limits and hard-shoulder running.

The Birmingham Box is in the center of the UK and consists of the M5, M6 and M42 motorways. The rollout of Smart Motorways began with a pilot on the M42 and subsequent construction of three schemes on the M6, traversing Junctions 4 to 10A.

Smart Motorways in Operation on the M42

Mott MacDonald was commissioned to undertake modelling work to forecast the impact of Smart Motorways both strategically and operationally. The software chosen for the operational analysis was PTV Vissim, a microsimulation software which is typically used for detailed operational analysis of junctions and vehicle interactions, but importantly in this case, a software capable of applying innovative and custom-built control methods through its COM interface.

The aim of the Smart Motorways modelling was to assess the benefits of Birmingham Box Phases 1 and 2, and to test junction layouts as part of  Phase 3. These were all on the M6, as shown in the diagram below.

Birmingham Box and the location of Smart Motorways Phases 1 and 2

The key challenge for this study was to create a tool which could interact with the Vissim models to simulate Smart Motorways effectively. The Smart Motorways algorithm is complex and requires data to be both extracted and entered in the model during a simulation run. A tool was developed in Microsoft Excel which allowed the user to configure the infrastructure required for Smart Motorways (loops and sign gantries). This tool ran and interacted with the Vissim models to apply the Smart Motorways algorithm. Every sixty seconds the algorithm extracted speed and flow information from the model and fed this back into the active simulation run to set variable speed limits and to open and close the hard shoulder. This meant that the model could reflect the changing speed limits of the M6 in the same way that speed limit gantries would change under Smart Motorways control.

One of the Modelled Variable Speed Limit Gantries

More information about the techniques used in building this tool can be found in the paper “Evaluation of the Benefits of Active Traffic Management Schemes Using Microsimulation Programming”, presented at European Transport Conference 2009, Millard, M / Unwin, P (2009).

More information on modelling Smart Motorways can be found in the paper “Managed Motorways: modelling and monitoring their effectiveness”, presented at 91st Annual TRB Meeting, Washington DC, January 2012 and published in Transportation Research Record, Vol 2278, pp 85-94, Van Vuren, T, Baker, J, Ogawa, J, Cooke, D and Unwin, P (2012).

Project Results

For Phase 1 and 2, the models allowed the benefits of the Smart Motorways scheme to be forecast and reported to the Highways Agency.

Phase 3 had a different aim, and the scope of one of the Phase 3 studies was to test different junction layouts for the M6 Junction 6 (known as “Spaghetti Junction”) under Smart Motorways control.

The Vissim network included the M6 Junction 6, the adjacent section of the M6, and the A38(M) from M6 Junction 6 into Birmingham City Centre, inclusive of five major junctions on this section of the A38(M). The modelled Spaghetti Junction can be seen below.

VISSIM model of M6 Junction 6 – Spaghetti Junction

Base models were built for 2008 and validated according to UK DMRB guidelines with the focus on the complex Junction 6. The base model included coding three signalized junctions and a tidal flow system active on the A38(M) in peak hours. Programming through the COM interface was used to control the tidal flow operation. Traffic demand was forecast using the PRISM model, a strategic PTV Visum model of the West Midlands built and maintained by Mott MacDonald and RAND Europe.

Option modelling involved the coding of Smart Motorways on the network and modelling different junction designs for 2013 and 2028 using the aforementioned Excel Tool. Through-junction running, ghost island and two-plus-two junction layouts were tested. In addition, closing lane one to HGVs and testing the impact of an incident were modelled on the network under Smart Motorways control. These were compared with “Do Nothing” models which did not contain Smart Motorways, and the relative strengths and weaknesses of each option were reported to the client, along with screenshots and video outputs.

A recommendation of the best option was made, with suggestions for why other options were not as successful. This was fed into the decision making process for the design of the Phase 3 scheme.

Software & modules used: PTV Visum, PTV Vissim, COM-interface

Mott MacDonald

Highways Agency