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  • Writer's pictureSafer Highways

Major M4 upgrade now fully open

A 32-mile motorway upgrade stretching from Greater London across Berkshire which will cut congestion and further improve journeys is now fully open, National Highways has announced today (Monday 5 December).

As part of a phased opening, the eastern section of the M4 between junctions 3 (Hayes) and 8/9 (Maidenhead) has now moved to 70mph. This means that the whole scheme – from junction 3 to junction 12, a full 32 miles – is now fully open.

The western section of the scheme (from junction 8/9 to junction 12) was fully opened to traffic at national speed limit in December 2021.

Cones and temporary signs on the eastern section of the motorway had previously been removed although it was running at 60mph while systems were tested and commissioned. This busy section of motorway now has the technology to set variable speed limits to smooth out traffic and tackle frustrating stop-start congestion.

A section between junctions 3 and 4 in West London will remain at 60mph to help manage air quality in the area. This is in line with a previously announced commitment to operate a small number of 60mph zones across England to reduce emissions levels.

If drivers get into difficulty, there are 34 new emergency areas between junctions 3 and 12, providing a place to stop in an emergency every 1.3 miles on average, with 16 of these on the newly opened section.

All motorways, with or without a hard shoulder, are designed and operated with drivers centrally in mind, to be easy and straightforward to drive on. On motorways where the hard shoulder has been converted to a traffic lane, there is a whole system of inter-related features, working together to help keep traffic moving safely. They include:

  • Variable speed limits to help keep traffic moving, reducing frustrating stop-start traffic and making journeys quicker

  • Clearly signed and orange-coloured emergency areas set back from the road and with telephones linking directly to our control rooms

  • Detection systems to monitor traffic for changes in flows

  • Stopped Vehicle Detection (SVD) technology that can identify a stationary vehicle and get help on the way quicker

  • CCTV cameras that operators are able to move and zoom to monitor and manage congestion and incidents, where notified. The system has the ability to see 100% of the carriageway

  • Signs and signals to provide information to drivers which can alert them to hazards ahead

  • Red X signs to close lanes to other traffic when a stopped vehicle is identified

  • Enforcement cameras to deter the minority who break speed limits and ignore Red X signs.

The graphic below illustrates the features of the new upgraded motorway between junctions 3 and 12, which has been under construction since 2018.

The Department for Transport announced in January that the roll out of new all lane running smart motorway schemes, yet to start construction, would be paused until five years’ worth of safety and economic data is available for schemes introduced before 2020. Schemes already in construction – including the M4 – would continue as leaving cones and barriers in place during the pause would be disruptive.

Mike Grant, National Highways Delivery Director, said:

“Hundreds of thousands of people across the South East are already benefiting from the significant investment on the M4 which has taken place over the last few years and since we opened the upgraded western section between Junctions 8/9 and 12 last year.

“It means motorists along this 32-mile stretch of the M4 will benefit from improved journey times, and we would like to thank drivers for their patience during construction.

“All construction work is now complete on the eastern section between Junctions 3 and 8/9 and with the successful calibration of the technology, including stopped vehicle detection, we are now able to restore the national speed limit. A maximum 60mph limit remains in place between junctions 3 and 4 to help improve air quality in Hounslow and to smooth traffic flows into London.”

More information about safe driving on motorways is available here:

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