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Route of the A308(M)

This one is 'the other' motorway spur from the confusing junction 8/9 of the M4. Chris Bertram points out that since its sibling the A404(M) has junctions numbered 9A and 9B to fit in better, this should end at 8A.

The reason this exists is that the A404(M) was originally the western end of the M4. When the westward extension came, it left the A404(M) as a spur, and a new junction here. This was too close to the original junction 8, which had served the A308, and so a connection was built to link the new junction with the A308. The new road was called A308(M).

This might be the UK's shortest motorway — but it depends which way you interpret "shortest". Take a look at the page of this road's rival in shortness, the A64(M), for the full story.


Start Stud Green (M4, A404(M))
Finish Maidenhead (A308)
Passes None
Length 0.5 miles
Connects to M4, A404(M)


Views of the A308(M) from on and off the road. If you have a photo to contribute, contact me.


Looking west from the A308 end, and you can see pretty much the entire motorway. The A308(M) is fully featured in terms of alignment: as you can see here, it has a straight bit and a bend.
Photo by Dave Ryan


Approaching the A308 from the M4, the direction sign looks poor for a motorway terminus - not even a primary route to continue along! The surface here isn't looking too healthy either.
Photo by Dave Ryan


Getting nearer the end - where do we go?! The carriageway seems to come to an abrupt halt in front of a large bush ahead, but in reality it's a roundabout. Thank heavens for that.
Photo by Dave Ryan

Construction Timeline

When the various parts of the A308(M) were built, listed in chronological order.

Open Jct Section
1971 Entire motorway

Exit List

All the junctions and destinations along the route.

Junction   Westbound               Eastbound
(M4 J8/9)
45.2 km
Heathrow Airport
M4 Link (M25 Link)
M4 Link
High Wycombe
A404(M) Link

(Roundabout Interchange)


N/A More information about this junction
LanesLanesLanesLanes LanesLanesLanesLanes
0.6 miles, 2 lanes Up   Down 0.6 miles, 2 lanes

46.2 km
N/A A330



Maidenhead A308
Windsor A308
Bracknell A330
More information about this junction
LanesLanesLanesLanesSigns LanesLanesLanesLanesSigns