M3 Junctions 2-4a: Smart Motorway

Project status:   Planned

Start date:   Between January and March 2014
End date:  Spring 2015

Type:   Major Scheme
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Major Scheme

Part of our programme of improvements (value >10m)

Cost:  £134 million to £183 million


Environmental assessments carried out on the proposed M3 smart motorway scheme between junction 2 and junction 4a on the M3 show that there is likely to be an adverse impact on local air quality if the motorway continues to operate at the national speed limit (70mph).

We want to deliver the much needed extra capacity and increased traffic flow that this scheme will provide without creating a significant adverse impact on local air quality. As such we are proposing to put in place a maximum speed limit of 60mph between junctions 3 and 4. This speed limit would be in place between 7am and 7pm for seven days a week and would help manage traffic and reduce congestion and air pollutants locally.

The consultation ran from 13 February 2014 to 11 April 2014 and we would like to thank everyone who responded.

All comments are being reviewed and a summary will be included in the report on the consultation which will be published in due course.

What is happening?

We propose to improve the M3 by making it a "smart motorway" between junctions 2 and 4a (13.4 miles / 21.6km). Smart motorways help relieve congestion by using technology to control traffic flows and assist in the management of incidents and providing information to road users. They deliver these benefits at a significantly lower cost than conventional motorway widening and with less impact on the environment during construction. This will be achieved by converting the existing hard shoulder to a permanent running lane.

The project is in the development stage and a number of assessments are being undertaken to fully understand the impacts of the scheme on residents along the route. The full environmental assessment is due to be completed in the new year. The works currently ongoing are ground investigations to inform the detailed design of the proposed smart motorway scheme between junctions 2 and 4a on the M3.

The project team are planning to hold public information exhibitions next year at which time further information on the design will be made available. Further details of these public information exhibitions will be made available on this website nearer the time.

We are aware of concerns being raised by residents living close to the project route regarding possible noise and visual intrusion issues. These concerns have been noted and are being considered as part of the projects ongoing development and design.

Find out more about Smart Motorways.

When and where is this happening?

In the November 2011 autumn statement, the Chancellor announced that the M3 junction’s 2-4a smart motorway (formerly known as managed motorway) scheme would be prepared for construction before 2015. Following this, the 2012 Budget confirmed the start of work for this scheme to be in financial year 2013/14, subject to the outcome of statutory processes. Since then, the Prime Minister announced that this scheme would be one of four schemes to be included in a pilot to significantly reduce the delivery time of road schemes; we have been challenged to complete this scheme by Spring 2015. We expect this scheme to commence construction between February and June 2014. Find out more about our Current Delivery Programme.

The project team are planning to hold public information exhibitions next year at which time further information on the design will be made available. Further details of these public information exhibitions will be made available on this website nearer the time.

Why is this happening and what will it cost?

The strategic case for providing additional capacity on the M3 within ThamesValley was examined in the Thames Valley Multi-Modal Study which recommended against widening the motorway prior to 2016 in favour of demand management measures. The Secretary of State endorsed these recommendations in 2003. However the March 2008 ' Advanced motorway signalling and traffic management feasibility study' identified this motorway link as a priority for the provision of additional capacity and Ministers agreed that smart motorways, as an alternative to widening, should be investigated.

The M3 between J2 and J4a experiences high traffic flows during both peak periods (am and pm) and has a higher than average accident rate.

The estimated cost of this scheme is in the range of £134 million to £183 million.

How will the scheme be carried out?

Smart motorway schemes have been in operation for a few years on the strategic network e.g.M42 and the concept together with their benefits is better understood. Further improvements have been made to the original concept and these developments include permanently converting the hard should to a running lane and developing the design so that schemes will have:

  • Fewer overhead gantries which span the whole motorway
  • Fewer signals over each lane and more verge mounting signing
  • Comprehensive CCTV camera coverage – although there will no longer be the need for dedicated cameras to open and close the hard shoulder.

A number of cameras, information signs and signals on gantries will be installed as part of the improvement scheme. As the scheme design progresses we will provide more information on the location of these features.

The feasibility study for the M3 identified a single option which will allow vehicles run on the Hard Shoulder on the M3 J2-J4a without Through Junction Running (TJR). This option is being further developed to ensure best Value for Money and minimal environmental impact can be achieved. The design is being further developed to ensure best Value for Money with minimal environmental impact.

The scheme will comprise the following elements:

  • MIDAS Queue protection technology
  • CCTV coverage
  • MS4 information signs
  • Lane specific speed signals at certain locations
  • Variable speed limits
  • Speed enforcement
  • Permanent hard shoulder usage as a running lane
  • Emergency refuge areas with emergency telephones
  • Low noise road surfacing (at locations where resurfacing is likely to be required as part of the project)

What are the benefits?

This project will:

  • relieve congestion
  • smooth the flow of the traffic
  • improving safety and reduce serious accidents
  • improve journey times
  • provide better information to road users

These benefits will also support economic development in the region.

We already have evidence of the benefits that a smart motorway scheme can bring. The first smart motorway scheme opened to traffic on the M42 motorway in 2006. Recent analysis of the data gathered since opening has found that journey time reliability improved by 22 per cent and reduced emissions by up to 10 per cent due to traffic flowing more smoothly. In addition, personal injury accidents have reduced by more than half (55.7%) since hard shoulder running was introduced. There was also an overall reduction in the severity of accidents with zero fatalities and fewer seriously injured.

How do I find out more information ?

More information will be posted on this project page as it becomes available. You can subscribe to be alerted when updates are made.

If you have any queries about this project you should contact the Highways Agency Information Line by emailing ha_​info@​highways.​gsi.​gov.​uk or calling 0300 123 5000.

Business Case

M3 Junctions 2-4a Managed Motorway Business Case
Business Case - Information correct as at December 2010


M3 Junctions 2-4a Smart Motorway Environmental Assessment Report
The purpose of the Environmental Assessment Report (EAR) is to assess whether or not significant environmental effects would be likely to occur as a result of construction and/or operation of the Scheme.



M3 Junctions 2-4a Managed Motorway Statutory Instrument Consultation Report
M3 Junctions 2-4a Managed Motorway - Response to the Consultation Report - September 2013