The M4 was only made a continuous motorway a few years ago. Prior to that, travellers between Swansea and Cardiff suffered the indiginity of the motorway giving way to A-roads, roundabouts and traffic lights on two stretches near Baglan and Port Talbot. A new bypass and cutting has produced a raised section of motorway which avoids these delays. The smells of the industrial plants and rural emissions in this area are no better but at least travellers can now pass more quickly.
Travellers from London find that the M4 begins on raised sections in London's west red-route area, and after negotiating the Heathrow and M25 intersections settles down for the long stretch to Bristol, mostly in 3-lane glory. Oxford is loosely served by the M4, with 3 intersections to choose from, dependent on whether you are travelling from the west, the east or in a heavy lorry which had better take the central junction and head north without diagonal advantage.
Quickly passing Reading and Swindon, the unwary traveller enters Wiltshire and the West Country in good time. Several motorway spurs are offered in the Bristol section, the M32 lancing into the heart of the city, the M5 taking you down towards Clifton and the M49 offering travellers over the new Severn Crossing a short cut to the South West to link up with the M5 avoiding the M5/M4 intersection. The M48 provides passage over the original Severn Bridge to Chepstow. Please note that Wales charges admission, whereas the Welsh are allowed free passage over the bridges into England. The tollbooths on the old crossing are on the English side, while the new crossing has Welsh booths - and the possibility of a queue on the bridge!
Newport, Cardiff and Swansea are all well endowed with junctions, there being several options to enter each city. Indeed, the first turning to Swansea on a long spur is posted before the Neath exit and the main Swansea turnings. Two distinctive junctions feature at the far end of the motorway, one Swansea turning has a slip road that comes off the inside lane of a roundabout, and your author's home lies off the penultimate junction, J48, where a simple crossroads with no roundabout meets the slip roads under the motorway carriageway. The motorway tangles with the A48 at many junctions in South Wales and finally gives way to west Wales A roads at the J49 services.