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Route of the A308(M)

The A308(M) is a short spur from the M4 near Maidenhead, and is the second spur to begin at the confusingly-numbered junction 8/9.

Initially the M4 had a junction, number 8, with the A308 south of Maidenhead. When it was extended west towards Reading, a new interchange was required to connect to the original line of the motorway, what is now the A404(M). That new junction was too close to junction 8 so junction 8 was closed, being replaced by a short spur road from the new junction back to the A308. That short spur is the A308(M), and it is the reason the new junction is number 8 as well as number 9.

This little spur might be the UK's shortest motorway. It's about half a mile long, and it has one straight section and one curve, which means that the eastbound carriageway, running around the outside of the corner, is marginally longer than the westbound. But the argument over the UK's shortest motorway rests on a knife edge and it depends very much on how you decide to measure it. The other candidate for that title is the A64(M), an urban motorway in Leeds whose exact start point is uncertain and has one carriageway significantly longer than the other.

The whole situation is fraught with uncertainty and the only thing you can be sure of is that you won't have time to figure it out on your short trip along the A308(M).


Start Stud Green (M4, A404(M))
Finish Maidenhead (A308)
Passes None
Length 0 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
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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
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