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Factfile - Images - Timeline - Exit List
A little spur from J29 of the M4 to let traffic flow more smoothly between Cardiff and the Severn Bridges. Once upon a time the M4 ended here, but even back then the road was laid out to allow construction of the Cardiff bypass - it was built complete with the overbridge in place.
A source of much controversy over at Pathetic Motorways was the A48(M)'s ghost carriageway. About half this motorway's brief mileage is spent with the two carraigeways separate as it approaches the merge with the M4. But alongside the westbound carriageway there appears to be another parallel one - where the eastbound side would be if it wasn't busy flying over the M4. This appeared to be evidence that the A48(M) had been originally built without provision for this junction, as it looked like an old abandoned version of the eastbound side. This turned out not to be the case - the official, somewhat incredible story is that this was a temporary carriageway built while the westbound side was being reconstructed. Quite why the highway authorities went to such lengths to rebuild one half of a short spur motorway, or why they would need to when the road must have been less than 20 years old at the time, remains unresolved.
Factfile
| Start | Castleton (M4) |
| Finish | Cardiff (A48) |
| Passes | None |
| Length | 2 miles |
| Terminates | None |
| Spurs | None |
| Meets | None |
Images
Views of the A48(M) from on and off the road. If you have a photo to contribute, contact me.
The A48(M) is... a very boring two lane motorway. Sorry.
Photo by Steven Jukes
Flying over the M4, the bridge is very wide. Just like the mystery of the parallel carriageway, nobody's fully sure why. M4Man Simon suggests that the most likely reason is to provide adequate forward visibility, not for any additional lanes.
Photo by Steven Jukes
Construction Timeline
When the various parts of the A48(M) were built, listed in chronological order.
| Open | Section |
|---|---|
| 1977 | Entire motorway |
Exit List
All the junctions and destinations along the route.
| Junction | Northbound | Southbound | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| (M4 J29) | Newport Bristol London M4       |
M4 | NORTH |
M4 | N/A |
|||||
2 miles, 2 lanes  |
 2 miles, 2 lanes |
|||||||||
| 29A | N/A  |
 A48 SOUTH |
A48 |
Cardiff A48  |
With thanks to Maurice Frank for information in this section.
