M4 J3-12 Managed Motorway

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Scheme Outline

Scheme details

Under construction
Upgrade to existing road under motorway restrictions
£ 586.4m
Highways England
Region: South East
Central Government
31 km
19 miles

Upgrade of the existing M4 between junctions 3 (Hayes) and 12 (Theale) to Smart Motorway, with the hard shoulder converted to an extra traffic lane for most of that length.

Unusually for a Smart Motorway scheme, bridge widening and replacement works will be carried out to provide extra space on parts of the motorway that presently carry three lanes with no hard shoulder. The M4 Slough and Maidenhead Bypass sections were subject to "rapid widening" in the 1970s which left the motorway with a discontinuous hard shoulder through bridges.

All Lane Running will be continuous through junctions, with the exception of 3 and 12 at the ends of the scheme, and 4B (M25) and 10 (A329(M)), where the volume of turning traffic will require the fourth lane to be dropped through the junction.

The stated aims of the scheme are to relieve congestion and improve journey times and reliability.

The start of development work was announced on 8 May 2012.

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3 June 2015 The application for the Development Consent Order was approved on 27 April 2015.
5 September 2016 The scheme has been approved by the Planning Inspectorate despite a number of high-profile objections.
21 March 2017 Enabling works for the scheme have started, with average speed cameras being installed along the affected stretch.

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More information

Official website
Highways England: M4 Junctions 3-12 Smart Motorway
News story
BBC News: Hayes to Theale M4 hard shoulder will be widened to become fourth lane

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Other schemes on the M4

CBRD also has details on the following road schemes happening on the M4.

With thanks to Barry Salter, TheBowlOfPetunias and Michael Pritchard for information on this page.

This scheme was last updated on 22 March 2017.