What's this then?
Down in the south of England...
I'm looking for it on the map here - give me a clue!
OK, stop looking. You won't find it.
Because although a small part of it has been built, it's never been allocated the number for the full route.
OK, tell me all about this one then!
First off, the M31 is a strange beast.
It's the opposite of most motorways, where the number is allocated near to the end of the process, when it appears in what was called the "Preparation Pool" - in other words, confirmed future builds.
Oddly, the M31 never appears in that list.
So, where did you get it from?
The number appears to have been allocated quite early in the process, and so the consultants' report into the M3 - M4 Link Motorway proudly shows the M31 number.
Where would it have gone?
The preferred route started north of the M4 near Reading, crossed the motorway at junction 10, and headed south towards the M3.
Hang on a minute! A motorway from Reading, crossing the M4 at J10, and then heading south... That's the A329(M)!
Yes, it certainly is.
Now you can see why the junction between the M4 and A329(M) is so huge - it's to take account of the M31, not just the relatively minor A329(M).
So, where did it go from there?
Surprisingly enough, southwards.
It would have passed to the east of Wokingham, and west of Bracknell (just avoiding the Met Office!) before hitting the M3 near to junction 3 at a trumpet interchange.
However, that's not the end of the journey...
Because the consultants recommended an extension of the planned route. As mentioned, the original idea of the M31 was the M3 - M4 Link Motorway.
However, the consultants noticed that a 9 mile (14km) extension to the south would make a massive difference to the traffic situation. They recommended that the motorway be extended to Ringway 4, the South Orbital Road (today's M25), where it would have met just north of junction 10, the A3 junction.
This meant that all traffic between Reading, Bristol and South Wales to the south of London and Kent would have been able to avoid the section of the M25 that today is one of the busiest stretches, and would have been able to save 10 miles on their journey. In addition, much of the pollution caused by traffic queues on that stretch of M25 would be eradicated.
So why wasn't it built?
The decision was taken to widen the M4 Maidenhead Bypass instead.
A slightly odd decision when you bear in mind that it costs as much to widen a motorway by a lane as it does to build a whole new three-lane motorway...
So, can you show me in more detail the route it would have taken?
Can I comment on this motorway?
Of course! Contact me and I'll put them here!
Have any other visitors commented?
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