The M4 is a motorway that runs from London, all the way to south Wales, stretching across the west of the UK. It opened in 1961, and was completed in 1996. The M4 carries over 130,000 vehicles every day, according to data from Highways England.
The starting point for it is Chiswick, and it ends at Pont Abraham in Carmarthenshire. The full length of the M4 motorway is 189 miles, and M4 traffic passes several major cities and towns along the route, including Reading, Bristol, Cardiff and Swansea. It also runs past Heathrow Airport, providing access to all five terminals via Junction 3 and Junction 4B. The area of the UK that runs alongside the M4 is often referred to as the M4 corridor.
There are several notable sections on the M4. It has two four-level stack interchanges - at Junction 20 and Junction 4B - which is a key feature considering there are only three in the UK. The M4 is also one of only three motorways in Wales. There’s a toll bridge on the M4 that crosses the River Severn; drivers pay the toll to enter Wales but not to enter England. And, the section between Junction 29 and Junction 32 was widened to six lanes in 2010.
Worst Junctions on the M4
As you’d expect from one of the UK’s busiest motorways, there are junctions on the M4 that may cause problems - do check M4 travel news and M4 traffic updates before starting your journey to avoid delays. These junctions can be congested:
Known as the Almondsbury Interchange, this junction near Bristol is one of the four-level stack interchanges noted above. When traffic is heavy, it gets extremely busy as this also connects to the M5. There are only two lanes to handle M5 traffic - it’s best to avoid this at peak times.
Junction 40 and 41
These junctions, in Port Talbot, have been problematic for years with tailbacks and speed cameras blighting motorists. It’s a major traffic congestion blackspot and there is an average speed camera system in place; with a 50mph limit in place it catches out plenty of drivers.
This is Chiswick roundabout, one of the oldest motorway junctions in the UK. It’s a meeting point for the north and south circular roads coming in and out of London so traffic can be very slow at times.
Junctions 25A and 26
There is frequently heavy congestion in this area around Newport, with a two lane section at Brynglas Tunnels. The tunnels are scheduled for overnight closure until 2018 for safety refurbishment works.
Accident Hotspots on the M4
Before driving on the M4, always look up M4 traffic updates to be aware of any road traffic accidents that may have occurred, and take steps to avoid the aftermath of incidents. Although motorways generally have a good safety record, accidents can happen at any junction.
In recent times, the area of motorway between Junction 18 and Junction 20 has been the scene for a large number of accidents. The area around Junction 16 of the M4, near Swindon, is also considered an accident blackspot. The Pont Abraham Interchange, at Junction 49, is where the M4, A48 and A483 intersect, has also seen a number of accidents.
Upcoming M4 Major Roadworks
There are some major roadworks and road improvement projects scheduled for the M4 in future years. Be aware of the impact these could have on M4 traffic, and consult M4 travel news before and during any journey to try to minimise disruption.
Upcoming M4 major roadworks include:
M4 Junctions 3-12 - this a major scheme scheduled to finish in March 2022, possibly with a total cost of around £860 million. The development will make the M4 motorway a ‘smart motorway’ between junctions 3 and 12, the stretch between Hounslow and Reading.
M4 Junctions 10-11 - a maintenance scheme on the River Loddon Bridge started in late 2017 and will continue into 2018. Speed restrictions and overnight closures are expected to be in place during this work.
M4 Junctions 12 to 13 - refurbishment work on the Hermitage Bridge, including replacing the beams, is scheduled for completion in the spring of 2018. Overnight closures and speed restrictions of 50mph will be in place during this time.