The M48 crosses the River Severn alongside the M4. It's an oxbow lake of motorway, being the old route of the M4 across the original Severn Bridge. When the Second Severn Crossing was built, the M4 moved across there, and the M48 took its place.

Despite being effectively bypassed, this little motorway does have a life of its own. It has two of its own junctions, one in England for the A403, making it an easy way into Wales from the industrial areas of Avonmouth, and one in Wales serving Chepstow and the A466. As well as carrying local and commuter traffic, it's also an important diversion route in the event that the Second Severn Crossing is closed.

The Severn Bridge itself makes a journey on the M48 more than worthwhile. The bridge is spectacular. It's not as big as the Second Severn Crossing, whose epic scale makes it a wonder in its own right, but it is particularly handsome and was always far more famous than its newer cousin. The M48 also crosses the Wye Bridge immediately to the west of the Severn, which would - anywhere else - be a famous landmark in its own right. It's a fine cable-stayed bridge that crosses the River Wye and, with it, the border between England and Wales.

Nonetheless, now that it's not the main road any more, it's not a priority for funding. When the motorway's number changed, money was saved on new road signs by just blanking out the first digit of the junction number - the former junction 21 becoming 1 and 22 becoming 2.

The M48 may not be correctly numbered. Despite connecting to the M4 at each end, it lies north of the M4 and west of the M5, so according to the rules established for motorway numbers in the late 1950s, it should really have a number beginning with a 5. It may be that the number M48 was chosen because it connects to the M4 at each end and runs parallel to part of the A48, so while its number may be technically in error, it looks perfectly at home. This numbering oddity is explored in considerable depth in our pages on Road Numbers.







Connects to



12 miles

Open Junctions Section
Sep 1966 Severn and Wye Bridges Opened as M4; became M48 in 1996

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 J21
189.5 km
M4 Link

M4 N/A
LanesLanesLanesLanesLanesLanes LanesLanesLanesLanes
2 miles, 2 lanes 2 miles, 2 lanes
194 km
Severn Beach
Services Severn View

A403 Severn Beach
Services Severn View
LanesLanesLanesLanes LanesLanesLanesLanes
3 miles, 2 lanes  
River or canal River Severn River or canal River Severn
River or canal River Wye
Welcome to England
River or canal River Wye
Croeso i Gymru
Welcome to Wales
  3 miles, 2 lanes
2 Chepstow
A466 (A48)
A466 (A48)
LanesLanesLanesLanes LanesLanesLanesLanes
7 miles, 2 lanes 7 miles, 2 lanes
M4 J23 N/A M4


M4 Link
LanesLanesLanesLanes LanesLanesLanesLanesLanesLanesLanes

Picture credits

With thanks to Meic Young for information on this page.

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About this page

Published22 April 2017

Last updated13 August 2018