Smart motorway plan for M4 Junctions 3 - 12

Highways England is proposing to improve the M4 motorway between Junction 3 and Junction 12 by introducing a Smart motorway scheme, which will:

  • relieve congestion and smooth the flow of traffic
  • improve journey times and journey reliability
  • maintain safety levels for all road users
  • support economic development.

The council has held meetings with the Highways England regarding the impact on Slough residents and businesses during the project and on completion. These discussions will be continuing over the coming months.

We have obtained from Highways England a plan indicating the structures that are affected. This plan is to assist residents and businesses in understanding the implications of the works.

Some affected residents have received letters from Highways England indicating there may be some land required to facilitate the project. The council recognises this an area of concern for many residents and so will continue to work with Highways England to limit the impact on our communities.

There is a longer report (700+ pages) detailing various environmental considerations. If you want to view this, you can make an appointment to visit our offices at St Martins Place. Call Savio DeCruz on 01753 875640 to arrange.


Air quality 

The M4 Junctions 3 to 12 Smart Motorway Scheme air quality assessment has modelled 303 individual properties within the Slough AQMA. Of these, 11 are predicted to be above the air quality objective for annual mean NO2 with the scheme in place, and are predicted to experience a small (0.4-2 µg/m3) increase in annual mean NO2 concentrations.

Junction 6 / Chalvey

The row of eight properties closest to the northeast side of the junction are predicted to experience a small increase in annual mean NO2 concentrations above the objective value with the scheme in place.

The locations around junction 6 anticipated to be above air quality objectives with the scheme are located within 50m of the junction. The maximum concentration predicted here (at approximately 42µg/m3) is to the north east of the junction.

One property, closest to the northwest side of the junction is also predicted to experience a small increase in annual mean NO2 concentrations above the objective value with the scheme in place, bringing the annual mean concentration at this receptor to 40.0µg/m3.

The Myrke

There is potential for the construction compound proposed near The Myrke (compound eight) to have adverse impacts on nearby sensitive receptors through dust generation and plant emissions. However, proposals to control these potential impacts are set out in the Outline Construction Environmental Management Plan, which will be included with the proposed Development Consent Order (DCO) application.

The 13 properties on The Myrke closest to the M4 have been explicitly modelled in this assessment, as these receptors will experience the highest pollutant concentrations and the biggest change in concentrations. The receptor closest to the M4 is predicted to be just below the annual mean NO2 objective, with all other properties below or well below. All receptors are predicted to be well below the objective for annual mean PM10. The largest change in annual mean NO2 concentrations is small (1.9 µg/m3) with imperceptible changes predicted for PM10.

Noise effects of the scheme

The estimated noise changes resulting from the operation of the scheme are most effectively presented in the drawings below, which are extracted from the environmental statement to be submitted as part of the DCO application.

The drawings cover the scheme corridor in the Slough area from Dorney Reach in the west to Datchet in the east. Drawing 12.2 keyplan, sheet 10, sheet 11 and sheet 12 show:

  • the noise barriers in place in 2022 if the scheme did not go ahead
  • the stretches of low noise surfacing in place in 2022 if the scheme did not go ahead
  • the additional noise barriers to be installed as part of the scheme.


A formal consultation process has started where the HA want to engage with residents, community groups and other major stakeholders. 

There were a series of consultation events in late 2014.

More information on SMART motorways can be found on the Highways England website where there is also more detail on the proposed M4 project.

Development Consent Order (DCO)

Hard copies of the DCO will be available to view in the Library at The Curve, Cippenham Library and Chalvey Community Centre from 21 May.

You can also view the project planning page.