A3/M25 Wisley Upgrade

[lefthandedspanner]

I can't believe option 20 (the cloverleaf) even made it off the drawing board, and I'm not surprised it was dropped from the running early on.

The lane-swapping is not too bad when the roads involved don't have much traffic, but when one of those roads is the M25!...

[jackal]

I can't believe option 20 (the cloverleaf) even made it off the drawing board, and I'm not surprised it was dropped from the running early on.

It probably didn't even make it onto the drawing board. But if it did, I'd like to see the drawings!

I'm happy to see less standard (in UK terms) designs like this considered. Because there are few four-way freeflow interchanges in the country, and none built for several decades, there is not much experience with them here. Hence the temptation to just trot out the four designs in TD 22/06 (stack, cloverstack, cyclic, partially-unrolled cloverleaf), which are not suited to all sites.

[Bryn666]

It really shows a lack of problem solving skill and a mere focus on the bottom line of the works estimate that the default in TD 22/06 is a stacked roundabout.

Low speed free-flow would be far superior at many junctions than a high speed stacked roundabout which is just inviting entry path conflicts and delays.

It isn't beyond the wit of designers either, after all the A1(M)/M62 junction is magnificent. Presumably that only got approval because there was a failure of a stacked roundabout on the old road already.

[jackal]

I honestly think it would help if a drawing of an octopus/windmill-type design was in DMRB, as well as a 'clovermill', which is a standard solution in Germany and the US.

The long list for Wisley doesn't contain any weaving-free low speed freeflow options like these. Five out of six are taken from TD 22/06 (the exception is the cloverleaf). Four out of six would presumably have all four right turns at 50mph. This raises costs significantly, for little benefit considering one of the turns only has 300vph.

[jackal]

Get Surrey have excelled themselves by getting their hands on technical drawings for the rejected options. Some of the more interesting ones:

[jackal]

http://www.getsurrey.co.uk/news/surrey- ... t-12767957

[Johnathan404]

Well done indeed. It's sad that they will never be built but still nice to know that there are still people paid to create fantasy GSJs.

The drawings make it clear how much more space a full GSJ would require, and how impossible all of them (with the possible exception of the whirlpool and skewed diamond) would be to build while maintaining traffic flow.

[Bryn666]

Whirlpool daganabbit!

Who seriously thought a cloverleaf was worth bothering with?

[Truvelo]

Any of the full freeflow options is vastly superior regardless of the landtake.

[SouthWest Philip]

The whirlpool in option 19 is interesting in that it would've been a double exit and single entry in all directions whereas normally they are arranged as a single exit with double entry.

[jackal]

Or just single entries and exits in all directions like Thorpe.

It's sad that they will never be built

Probably not, though if 9 is built it should be possible to upgrade it later.

[jackal]

Who seriously thought a cloverleaf was worth bothering with?

If you zoom in on the cloverleaf, they seem to have C/D lanes on the A3, but none for the M25, meaning weaving would be on the mainline. That would have been... interesting.

[Peter Freeman]

1. Extremely interesting finds. And it is somewhat reassuring that more free-flowing options actually WERE considered.

2. It's curious that option 17 is described as a 'skewed diamond'. Topologically it's a stack, but it has maximum-3-level structures (not rare in USA and other places).

[Glom]

The whirlpool is my favorite.

[Johnathan404]

If you zoom in on the cloverleaf, they seem to have C/D lanes on the A3, but none for the M25, meaning weaving would be on the mainline. That would have been... interesting.

It looks like they would have maintained the A3 overbridge, restricting the width of the M25, but built the A3 C/D lanes on new bridges. If the new bridges mimic the old one they would have been impressive structures, and those loops would have been pretty steep too.

Come to think of it, the cloverloop has the loops merging in the middle of the existing bridge. That would have been interesting. I suppose you could close the flyover and build a new one but it wouldn't be easy.

[jackal]

It's curious that option 17 is described as a 'skewed diamond'. Topologically it's a stack, but it has maximum-3-level structures (not rare in USA and other places).

I agree, it is essentially a stack, but you could argue that one of the slips is actually a cyclic ramp (like you have in a whirlpool) rather than semi-direct (like you classically have in a stack).

[lefthandedspanner]

Who seriously thought a cloverleaf was worth bothering with?

If you zoom in on the cloverleaf, they seem to have C/D lanes on the A3, but none for the M25, meaning weaving would be on the mainline. That would have been... interesting.

That alone would have made it possibly the most terrifying junction in the country.

[jackal]

It looks like the semi-direct connectors for the stack would all have been above the interchange, meaning it would actually be on five levels!

[jackal]

Alan Titchmarsh has been sticking his oar in. Hard to assess the merits of the case as the consultation wasn't about alternative widening schemes, from what I remember.

Also the preferred route announcement is apparently due in a month.

http://www.telegraph.co.uk/news/2017/08 ... s-england/

[Richardf]

I am afraid I am with the RHS and Mr Titchmarsh on this one. Other ways should be found to improve the junction without blighting the Gardens or destroying woodland. The HE are being very heavy handed on this one.

I should point out that Wisley Gardens were there before even the A3 in its current form, let alone the M25.