The M4 starts in west London, Chiswick and heads west. Main routes crossing it are the M25, A34, A419, M32, M5, M48, A449. It serves Reading, Newbury, Swindon, Bristol, Newport, Cardiff, Bridgend, Port Talbot, Neath, Swansea and Carmarthen. It ends at jcn 49 A48 a few miles east of Carmarthen.
An extremely important road, which connects London to all points west and south Wales. Connects to some of the most important freight routes in the country, and carries an extremely high volume of traffic. The M4 suffers greatly from being both a local route and a cross country route, as points around Bristol, Newport and Cardiff fill up with local traffic very quickly. In summer, the M4 is a major holiday route for people heading west.
The M4 is a motorway with so much and so varied scenery. From London (where for the first few miles it sits on top of the A4, known as the Chiswick Flyover, or the Elevated Section) you progress through the suburbs and commuter land. Then past Reading, things get more rural, with rolling hills and farmland everywhere. Builds up again around Bristol, then splits up, the M48 taking traffic across the old Severn Bridge and the M4 taking the new or Second Severn Crossing. (I haven't driven over the new one yet - but all things are possible). From here, we skirt Newport (or as all signs are by now bi-lingual Cas Newydd) and it gets tremendously busy here at times. After Cardiff, you begin to get occasional glimpses of the sea and then you get stuck in horrendous traffic around Neath. When this was the A48(M), you could sit for days without moving. Maybe I exaggerate. Past Neath, gets quieter again then comes Swansea and ends at the Little Chef a few miles from Camarthen.
Anybody remember the 70s when the Severn Bridge only ever had one lane each way open? Always the inside lane coned off. I hope the Second Severn has cured all that. I still believe the Elevated Section and the original Severn Bridge are the most interesting, but the Port Talbot-Neath stretch is pretty good, what with all the industry on the skyline. What do you prefer?
Lots of the South Wales M4 started life as the A48(M). A bit of that remains around Cardiff, with that fabbo little bit that heads into the city. The most important change is the renumbering of the Severn Bridge section, which is now the M48. The M4 cuts across the Second Severn crossing, with a little link to the M5 southbound called the M49. If they are able to use two such important numbers in cheesy little bits of mway link, this should tell us a lot about the future of mway building in the UK. I don't really think it has one.
You can get anywhere from London to South Wales to the south west to the Midlands from the M4. Check your atlas.
Another holiday route from when I was a kid. When we turned off at the "Gateway roundabout" (or to most of us jcn 24 - the A449 northbound, and the A48 into Newport and that little road that goes to the Industrial Area and Goldcliffe). I used to look up at the M4 on the hill above us and think "Burry Port is that way" and wish I could go there. Our relatives live in Ringland, which is east Newport. We would sometimes go to Goldcliffe, which is a big seawall on the Severn, where me dad used to cycle to when he wuz a nipper. I loved (and still love) Newport. Great place.