A48(M)

The A48(M) is a little spur from junction 29 of the M4 to let traffic flow more smoothly between Cardiff and the Severn Bridges. Once upon a time, for about three years, the M4 ended here, but this little bit of road was only ever going to be a spur and its life as part of a major motorway was always meant to be short-lived. The road was laid out from the outset to allow construction of the M4 Cardiff Bypass - it was built complete with the overbridge for junction 29 in place.

One of the mysteries of this road, much discussed at Pathetic Motorways, is the A48(M)'s ghost carriageway. About half this motorway's brief mileage is spent with the two carriageways separated as it approaches the merge with the M4. But alongside the westbound carriageway, there appears to be another roadway running parallel - exactly 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. But that's not 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, isn't very clear.

The A48(M) now has an uncertain future, with plans for the new M4 alignment at Newport threatening to relegate this to a non-motorway route as part of the widespread changes the new motorway will bring.

Start

Castleton

End

St Mellons

Passes

None

Connects to

M4

Length

2 miles

Click a section name to see its full details, or click a map symbol on the right to see all motorways opened in that year.

Completed Name Start End
Tredegar Park - St Mellons J29 Castleton J29A St Mellons Chronology map for 1977

Exit list

Symbols and conventions are explained in the key to exit lists. You can click any junction to see its full details.

Junction   Eastbound               Westbound  
M4 J29 Casnewydd
Newport
M4 Link

M4
EAST


M4
N/A
LanesLanesLanesLanes LanesLanesLanesLanes
2 miles, 2 lanes 2 miles, 2 lanes
Llaneirwg
St Mellons
A48

A48
WEST
A48



Caerdydd
Cardiff
A48
LanesLanesLanesLanes Signs LanesLanesLanesLanes Signs
Routes

Picture credits

With thanks to Maurice Frank for information in this section.

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