A21 - M25 - M26

Chevening Interchange

Where is it?

Chevening Interchange, junction 5 of the M25. The point where London's orbital meets the A21, a major route to the south coast, and the M26, a shortcut between the M25 in the south and the M20 towards the Channel Ports.

What's wrong with it?

It appears to have been designed blindfolded. The priority route is M25 to M26 — while a fair amount of traffic does go that way, surely the M25 should have priority over all else, what with it being a ring road to 6 milion people and the busiest road in the country.

Traffic from Sevenoaks is also badly served: to head east from there and join the M26/M20 route, traffic must use the narrow and winding single-carriageway A25 parallel to the M26 since there's no access to the motorway network eastbound from the A21 here. Kent County Council continue to lobby for a change to this situation, all to no avail.

Why is it wrong?

The M25 wasn't meant to be the through route here. The interchange is built around a section of the once-upon-a-time A21 Sevenoaks bypass, which used to be the north-south route here, explaining why that is a mainline carriageway. When the M25 was built, it stopped here, the A21 continuing north and the M26 continuing east. When finally the ends of the M25 were joined up, it was too late, and the junction had to be adapted. The M25 is now carried on little two-lane sliproads.

What would be better?

First of all, let's have access between the A21 and M26 — a left turn M26-A21 is easy enough to add; then A21 to M26 could be achieved by either shifting the north-western sliproad out a bit to make way for a loop, or tunnelling a new sliproad underneath the whole thing (this has been done elsewhere before). As for the M25, how about giving it more lanes and more priority at merges and diverges?


Right to reply

Well, I think we need a map drawing to decide that one. And a very large amount of money.
You say the slip for westbound M25 appeared unexpectedly, but there is a sign warning of the split at least two miles back. How much warning would you like?

I am not quite sure it ought to have caused a panic. There is a junction plan 2 miles out, repeated at 1 ½ miles, 1 mile and ½ mile. The road markings go to hazard lines for the left hand carriage way a mile out with carriage way markings. There are two overhead gantries at around 600 and 300 indicated yards out but the slip road is extended way beyond that.

Its no good complaining, as NOTHING has been or is being done, the only time anything will happen is if somebody high up in Government or Highways England have to use it on a regular basis then they will realise what a mess it is...

Floyd 28 June 2021

Well, one thing is for certain; it would be a pretty easy and not to costly job to widen the two lane M25 E to N slip You could even use the hard shoulder to make it three lanes or, hard shoulder AND add another lane to make it four without encroaching on any houses. The problem of M26 W to A21 South is more tricky. A slip could be squeezed in going over Chevening road, but it would probably be only two lanes looking at the available space. Still far better than using the A25 though, certainly for all the people who live near it. I wonder if the disused railway line could be used to any benefit?

Kevin Higginson 14 July 2021

All of this because it was decided that linking ringway 3 from the M20 and Ringway 4 at Sevenoaks was the best plan. This meant a bodged junction from the beginning.
Building Ringway 3 where it should gave been would have meant the M25 would gave carried on to the M20 rwnaming the M26.

Ahh this could be fixed by renaming the M26 as the M25 and the M25 from here to the A282 as the M21........

So then coming south on the M25, once you got to Dartford it would change to the M21? How would that help matters? And how on earth would it remove the need to use the congested A25 and provide access from the M26 to A21 (both ways) and more lanes for the M25 E to N left turn- which is what this article is all about?

Of course it wouldn't fix it. But it would keep some planners employed for years, some politicians can claim something has been done and we would not have to 'turn off to stay on'. Sounds like a perfect UK fix to me!

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Published21 February 2017

Last updated5 March 2017