M4 corridor M4 corridor The M4 corridor is an area in the United Kingdom adjacent to the M4 motorway, which runs from London to South Wales. It is a major high-technology hub. Important cities and towns linked by the M4 include (from east to west) London, Slough, Bracknell, Maidenhead, Reading, Newbury, Swindon, Bath, Bristol, Newport, Cardiff, and Swansea. The area is also served by the Great Western Main Line, including the South Wales Main Line, and London Heathrow Airport. Technology companies with major operations located in the area include Amazon, Citrix Systems, Dell, Alcatel-Lucent, Huawei, Lexmark, LG, Microsoft, Novell, Nvidia, O2, Panasonic,
M4 relief road and narrows to a restricted two-lane section through the Brynglas Tunnels, where heavy congestion occurs at peak hours. A variable speed limit is in place between junctions 24 and 28. M4 sliproads at Junction 25 (Caerleon Road) are diverted to reduce traffic through the tunnels. M4 Westbound traffic joining at Junction 25 is diverted via Junction 25A/A4042 (Heidenheim Drive)/A4051 (Malpas Road) to Junction 26. Similarly eastbound traffic wishing to exit at Junction 25 is diverted from Junction 26 via the A4051/A4042/Junction 25A. This adds to congestion on Malpas Road and other local roads near Newport city centre at peak times.