SW M25 Relief

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John McAdam
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Re: SW M25 Relief

Post by John McAdam »

Heading between Kent and the south west, I often leave the M25 for the A3 then A31 (Hogs Back / Alton) to Winchester then onto the southern end of M3. This cuts out some 7 miles of the busy SW quadrant of the M25 between J10 and J12. Whether it's worth it for that alone is hard to say. But west of Farnham, the A31 never seems that busy, so it can be a more relaxing route to drive than the M25 and M3 when they are bustling with traffic. Several roundabouts on the A31 of course! A little less distance that way too.
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Vierwielen
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Re: SW M25 Relief

Post by Vierwielen »

When I travel from Fleet to Gatwick, I also usually use the A3 rather than the M3.
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Re: SW M25 Relief

Post by booshank »

WHBM wrote: Sat Aug 21, 2021 14:22 It's Daily Mail stuff that the M25 is a permanent car park. Not only is it not, but it's a magnet for all sorts of somewhat indirect journeys. For example, can you believe that the shortest journey time between Dover and Selsey, both on the south coast, is by the M25 ? Someone who regularly did Cambridge to Bristol told me the same.

Following satnav lines is a fine story for those who don't know the situation, but the majority of traffic on any route is pretty regular and well aware of the various options. Just like your own regular routes.
I often use a satnav for journeys where I'm familiar with the route(s) because those with real time traffic will respond to unexpected congestion, accidents, closures etc. Also many regulars will start off checking such services to find the best route before they become familiar with it.
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Vierwielen
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Re: SW M25 Relief

Post by Vierwielen »

jackal wrote: Sat Aug 21, 2021 15:02 Personally I am very sceptical of how much difference these corner cuts could ever really make to M25. Suppose there was a full motorway corner cut from M3 J3 to M4 J10. The problem is that a very small proportion of clockwise traffic approaching M25 J12 is actually heading to M4 J10 or west of there. The vast majority is heading into London, going to Heathrow, accessing other local junctions along the M25, or making for strategic routes like the M40 or M1, none of which the corner cut is any use for. I'd be shocked if you even took 10% of traffic off the M25.

If you want to help out the M25 you'd get vastly more value from improvements to the M25 itself, whether widening, C/D lanes, or a parallel bypass with minimal junctions. And frankly it would be no more controversial than a motorway or HQDC bypass of Bracknell.
Or alternatively continue the cut to give good access to Woking and to either link up with the A3 or to join the M25 close to the A3 junction.
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Re: SW M25 Relief

Post by Micro The Maniac »

jackal wrote: Sat Aug 21, 2021 15:02 Personally I am very sceptical of how much difference these corner cuts could ever really make to M25. Suppose there was a full motorway corner cut from M3 J3 to M4 J10. The problem is that a very small proportion of clockwise traffic approaching M25 J12 is actually heading to M4 J10 or west of there. The vast majority is heading into London, going to Heathrow, accessing other local junctions along the M25, or making for strategic routes like the M40 or M1, none of which the corner cut is any use for. I'd be shocked if you even took 10% of traffic off the M25.
While AADTs show part of the story, they dont tell the full story... we know how much joins or leaves at each junction, but not where through traffic goes.

I'd be interested to know the distribution of traffic approaching J10 clockwise... how much actually passes J16 - or how much turns off (each way) at J10-J16. And where does the joining traffic go.

If you want to help out the M25 you'd get vastly more value from improvements to the M25 itself, whether widening, C/D lanes, or a parallel bypass with minimal junctions. And frankly it would be no more controversial than a motorway or HQDC bypass of Bracknell.
I've long held the view that the clockwise M25 should split before J11 into a three (??) lane C/D with the three (??) lane mainline having no access to J11-J15 - the two combining at the J15 (M4) merge. Yes, this makes probably J15 quite complicated... Likewise, anticlockwise should split before J15 and recombine at the J12 merge. This is arguably the most congested 10 miles on the motorway network - and having five junctions (including M3, M4 and LHR) really doesn't help.
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Re: SW M25 Relief

Post by Bryn666 »

The most recent M25 widening was deliberately done to minimise land take - this might have made getting shovels in the ground easier but it now means there's no way to fix this bit without an astronomical land purchase in some of the most expensive commuter belt areas we have.

Short termism coming back to bite once more. Contrast with how the Dutch have resolved to have one final push to fix all the motorway gaps and problems.
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Gav
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Re: SW M25 Relief

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Bryn666 wrote: Sun Aug 29, 2021 09:57 The most recent M25 widening was deliberately done to minimise land take - this might have made getting shovels in the ground easier but it now means there's no way to fix this bit without an astronomical land purchase in some of the most expensive commuter belt areas we have.

Short termism coming back to bite once more. Contrast with how the Dutch have resolved to have one final push to fix all the motorway gaps and problems.
this ios probably why I feel that the recent ieas of expanding a motorway in the foot print has always been a bad idea - going from D3M with HS to D4M and no hard shoulder is false economies as it decreases the safety of the road and increases capacity.

Like a cable - Its rated to 100A... I can get 150A through it but it gets Hot... So i take off the plastic insulation so it doesnt burn...
it takes the extra amps but the cable is sitting live... its okay just dont touch it... Increased risks but the cable is taking more amps.

That motorway without the hardshoulder there is less room for any out of the ordinary issues - okay cars are better these days less breakdowns but when you do that shoulder was a haven out of the traffic flow. now your going to be sitting still in a potentially dangerous environment. Yup I totally get a hardshoulder isnt a playground but it is a relative place of refuge.
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jackal
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Re: SW M25 Relief

Post by jackal »

Micro The Maniac wrote: Sun Aug 29, 2021 06:54
jackal wrote: Sat Aug 21, 2021 15:02 Personally I am very sceptical of how much difference these corner cuts could ever really make to M25. Suppose there was a full motorway corner cut from M3 J3 to M4 J10. The problem is that a very small proportion of clockwise traffic approaching M25 J12 is actually heading to M4 J10 or west of there. The vast majority is heading into London, going to Heathrow, accessing other local junctions along the M25, or making for strategic routes like the M40 or M1, none of which the corner cut is any use for. I'd be shocked if you even took 10% of traffic off the M25.
While AADTs show part of the story, they dont tell the full story... we know how much joins or leaves at each junction, but not where through traffic goes.

I'd be interested to know the distribution of traffic approaching J10 clockwise... how much actually passes J16 - or how much turns off (each way) at J10-J16. And where does the joining traffic go.
Those would be useful numbers! But even without them it can be shown that, under any reasonable assumptions, very little traffic goes from M25 J10 to M4 J10.

One way of thinking about it is as a decision tree. I happen to have numbers for M25 J10 (I will use 7-8am peak hour as it seems to be the busiest):

**************************A3 North 1311=0.18
************************/
Clockwise M25 J10 - M25 Clockwise 4406=0.61*
************************\
*************************A3 South 1553=0.21

I won't draw out the whole tree of course! But basically M25 J10 to M4 J10 traffic is that which has made an incredibly specific combination of decisions - it has made the 'right' (asterisked) decision at 11 consecutive junctions along the M25 and M4. A very small proportion of traffic does that.

We can see that at M25 J10 61% of traffic has made the 'right' decision. For illustrative purposes, suppose that 61% of traffic also carries straight on at J12, that 30% turns left onto the M4 at J15, and that at all other junctions 85% of traffic carries 'straight on'. Under those assumptions we can calculate the percentage of clockwise traffic approaching M25 J10 that goes all the way to M4 J10 as follows:

0.61*0.85*0.61*0.85*0.85*0.85*0.3*0.85*0.85*0.85*0.85=0.03=3%

Or if we assume 90% 'straight on' rather than 85% at the secondary junctions:

0.61*0.9*0.61*0.9*0.9*0.9*0.3*0.9*0.9*0.9*0.9=0.05=5%

Anyway, the point should be rather clear - that a corner cut only relieves an orbital route of traffic that makes one ultra specific set of decisions, and as such will have minimal impact compared to direct improvements to orbital journeys.
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Re: SW M25 Relief

Post by Peter Freeman »

^ The calculations could be made without the first two terms, in order to represent the OP's first suggested diversion: exiting at J12, not J10, to reach the M4. The diverted proportions then work out at 6% or 10%. Not quite as shabby, but nevertheless your point is made.

For this reason I realised that the gain would be real but minor, and so could not justify lots of $$$ on a Bracknell bypass, only an el-cheapo improvement. Not to mention the NIMBY reason!

The trade-off calculation is the same, though on a different scale, as that for adding a dedicated left turn slip at a roundabout.

I agree that improvements to M25 itself would be more cost-effective than this corner cut, but they need to be good capacity improvements, not half-hearted short-term ones.

BTW, there is a much older thread already discussing "M25 and over-capacity junctions":
viewtopic.php?f=1&t=1687&p=22747&hilit= ... ons#p22747
And others of course - hardly a new subject hey?
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Re: SW M25 Relief

Post by MotorwayPanda »

Having been on a journey on this route recently, I can say that M4/A329(M)/A322/M3 is already a sensible, fast and high quality route avoiding this section of M25. The main issue in my opinion is that the road is taking on a much larger role than ever expected.

Back when the M25 was first conceived, it was part of the London Ringways Plan, which would have seen 4 motorway orbitals around London - Ringway 1 around the City Of London, Ringway 2 around an upgraded North Circular and new-built South Circular, Ringway 3 around Greater London, and Ringway 4 further out avoiding London completely. The modern M25 was created from already built sections of 3 and 4 when the project was cancelled.

Therefore, it is currently one motorway taking on the traffic volumes originally intended for four. This is the underlying issue here. London has never had a well thought-out road system, therefore the most sensible way to get from say, Croydon to Heathrow, is the M25, which also happens to be the quickest way to get from towns like Reading, Oxford, Swindon etc. to Kent and the Channel Tunnel.

In my opinion, the best way to solve the issue of the M25 SW corner is to get London's local traffic off the road. The north already has the HQDC A406 and an excellent railway system, however the south has never seen such treatment. This is partly why this particular section of road has suffered so much compared to the north.
Therefore, I propose that the best solution would be to create a new HQDC South Circular and build a new Underground line serving the south.

Obviously, there is no sensible way to achieve a better road network in south London without mass demolition of properties and destruction of communities. Even just minor improvements to existing roads are not possible due to the vast amount of development along the "major" routes such as the A205. Therefore, this new road ever being built is extremely unlikely.

However, I do not see any reason why a new deep-level bored Tube line cannot be built (other than the cost), and to my understanding a north-south Crossrail has already been proposed. This would be much more beneficial, in my opinion, than a new SW bypass as it would mean the vast majority of local traffic would be taken off the road as public transport would be generally much quicker, and the section would only have to cope with the originally intended traffic volumes. It would also mean that local residents in both south London and Bracknell would be unaffected, as all the construction work and noise would be buried far underneath the streets of London.

Overall, I see no need for a SW relief road when it would only marginally affect the M25 traffic volumes and there are better alternatives already being considered. The current route does its job fairly well, and a new road would be quite unnecessary.
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Re: SW M25 Relief

Post by chaseracer »

La solution Française: https://en.wikipedia.org/wiki/Grand_con ... t_de_Paris

Admittedly, they have more room and a greater acceptance of tolls on strategic routes...
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Re: SW M25 Relief

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chaseracer wrote: Mon Aug 30, 2021 21:15 La solution Française: https://en.wikipedia.org/wiki/Grand_con ... t_de_Paris

Admittedly, they have more room and a greater acceptance of tolls on strategic routes...
There is work towards something of a British equivalent, with the A428 and A27 improvements and even Lower Thames Crossing.

Of course the Oxford to MK section is the one that got away. Perhaps it would have fared better if marketed as a central part of a national transport strategy rather than a glorified development corridor.
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Re: SW M25 Relief

Post by Micro The Maniac »

Gav wrote: Sun Aug 29, 2021 11:11 That motorway without the hardshoulder there is less room for any out of the ordinary issues
You mean like:
  • Stopping for a wee
  • Changing a baby's nappy
  • Swapping drivers
All three of these were observed yesterday on the two-lane bit of the M3... all within a few hundred yards of Winchester Services (admittedly not the best on the network, but...)
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Re: SW M25 Relief

Post by Micro The Maniac »

jackal wrote: Sun Aug 29, 2021 11:26 Those would be useful numbers! But even without them it can be shown that, under any reasonable assumptions, very little traffic goes from M25 J10 to M4 J10.
I think two subthreads are getting mixed here...

I was suggesting C/D from M25/J11(A319/A320) to M25/J15(M4) and the question was how much traffic goes from before J11 to after J15 (and vice versa)

But since you've raised the M4/J10 question, this doesn't take into account the M40/J4 traffic that *could* be diverted away from the M25 if the mythical M31 and the A404 were a better option...
One way of thinking about it is as a decision tree. I happen to have numbers for M25 J10 (I will use 7-8am peak hour as it seems to be the busiest):

Code: Select all

                    A3 North 1311=0.18
                  /
Clockwise M25 J10 - M25 Clockwise 4406=0.61*
                  \
                    A3 South 1553=0.21
Those numbers, in themselves, justify a free-flow left at J10 clockwise! And I suspect the matching anti-clockwise figures would show a similar justification... so adding four free-flows would make ahuge difference at the roundabout (as many of us have long suspected)

MotorwayPanda wrote: Mon Aug 30, 2021 10:31 Having been on a journey on this route recently, I can say that M4/A329(M)/A322/M3 is already a sensible, fast and high quality route avoiding this section of M25. The main issue in my opinion is that the road is taking on a much larger role than ever expected.
Agreed... and for many of us (locals?) the A329(M)/A3095*/A331 to M3/J4 offers an alternative for further south - throw in M40/A404 and the corner is well and truly cut. It is a pity, though, that the A3095 is not a DC

* = plus the obligatory cut-through of the Southern Industrial Estate... the steady flow of traffic through here must be a cause for concern, and I can imaging restrictions being put in place to reduce through traffic!
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jackal
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Re: SW M25 Relief

Post by jackal »

Micro The Maniac wrote: Tue Aug 31, 2021 08:43
jackal wrote: Sun Aug 29, 2021 11:26 Those would be useful numbers! But even without them it can be shown that, under any reasonable assumptions, very little traffic goes from M25 J10 to M4 J10.
I think two subthreads are getting mixed here...

I was suggesting C/D from M25/J11(A319/A320) to M25/J15(M4) and the question was how much traffic goes from before J11 to after J15 (and vice versa)
Fair enough, consider that a response to the other subthread!
But since you've raised the M4/J10 question, this doesn't take into account the M40/J4 traffic that *could* be diverted away from the M25 if the mythical M31 and the A404 were a better option...
M40 J4 to M25 J12 is:

34 miles via A404 and A329(M)/A322
27 miles via A404 and M4
23 miles via M25 J16

So I don't see how the M31 could really offer a viable option for such a journey. If anything bypassing Bracknell is likely to lengthen the route.

As those distances suggest, the A404 does have more potential in combination with the M4, though that's really another subthread...

This does highlight one big reason the M25 is such a draw - it's designed as a single long distance route and therefore tends to be more direct than the hodgepodge of alternative routes.
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Re: SW M25 Relief

Post by thatapanydude »

I'll chime in with some thoughts.

1) Close M25 J11. Replace access with a junction on the M3 at Longcross on the B386, at Staines Road A320 (London bound entry and exit) and at Shepperton B376. I get that its pushing traffic (local rather than strategic) a bit more into residential area's but at least traffic is off the M25 and utilising the London end of the M3 which has capacity.

2) Dual the A243 to Chessington then link up to the A3. I would then D4 the A3 and give free-flow westbound access to the A309. This can take journeys from e.g. Leatherhead to Sunbury off the M25 and M3. Link below with a map.
Attachments
A243 dualling.gif
A1/A1(M) >>> M1
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Re: SW M25 Relief

Post by Peter Freeman »

jackal wrote: Tue Aug 31, 2021 13:07
Micro The Maniac wrote: Tue Aug 31, 2021 08:43 But since you've raised the M4/J10 question, this doesn't take into account the M40/J4 traffic that *could* be diverted away from the M25 if the mythical M31 and the A404 were a better option...
M40 J4 to M25 J12 is:

34 miles via A404 and A329(M)/A322
27 miles via A404 and M4
23 miles via M25 J16

So I don't see how the M31 could really offer a viable option for such a journey.
...
As those distances suggest, the A404 does have more potential in combination with the M4, though that's really another subthread.
Just for the record, my OP was promoting two separate corner cuts : A329(M) and A404(M). They relieve different parts of M25. Each one is marginally worthwhile now in terms of travel time, though only one in terms of distance. Each one is capable of being improved at low cost to make them more attractive, and thereby to benefit the M25.

I didn't suggest that they could ever be worthwhile to use in series.
jackal wrote: Tue Aug 31, 2021 13:07 If anything bypassing Bracknell is likely to lengthen the route.
My suggested el-cheapo Bracknell bypass would be at most 1 mile longer than the current through-route, but would undoubtedly save time. Even though not HQDC, and even though not necessarily completely dualled. It would also de-congest Bracknell.
Last edited by Peter Freeman on Thu Sep 02, 2021 12:12, edited 1 time in total.
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Re: SW M25 Relief

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MotorwayPanda wrote: Mon Aug 30, 2021 10:31 However, I do not see any reason why a new deep-level bored Tube line cannot be built (other than the cost), and to my understanding a north-south Crossrail has already been proposed. This would be much more beneficial, in my opinion, than a new SW bypass as it would mean the vast majority of local traffic would be taken off the road as public transport would be generally much quicker, and the section would only have to cope with the originally intended traffic volumes. It would also mean that local residents in both south London and Bracknell would be unaffected, as all the construction work and noise would be buried far underneath the streets of London.
Hello, welcome to SABRE!

I'm not sure that Crossrail 2 will make much difference to traffic on the M25. It will link local train services on the South West Main Line around Wimbledon with local services on the East Coast Main Line around Finsbury Park, and as such it's designed to serve commuters travelling in and out of Central London - in part by reducing the need for some of them to change onto the Underground to reach destinations in the West End. It will also free up train paths and terminating space at Waterloo and King's Cross/St Pancras which might enable more long distance services to be run.

The flows of traffic on the M25 are made up of people doing very different journeys, and in particular, it's hard to see that many people using the south west quadrant of the M25 - making journeys that are predominantly northwest/southeast in direction - would transfer to a through-London commuter railway running northeast/southwest in alignment.

I'm not sure what public transport intervention you could make in Central London that would materially affect traffic levels on the M25; the two are generally serving very different needs. But you could definitely make a case for better public transport in outer London and the home counties that might have an impact. Better orbital rail links between places like Guildford, Woking and Heathrow Airport would potentially attract journeys that are currently mostly made on the M25, for example.
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Re: SW M25 Relief

Post by Herned »

Chris5156 wrote: Wed Sep 01, 2021 12:51 I'm not sure what public transport intervention you could make in Central London that would materially affect traffic levels on the M25; the two are generally serving very different needs. But you could definitely make a case for better public transport in outer London and the home counties that might have an impact. Better orbital rail links between places like Guildford, Woking and Heathrow Airport would potentially attract journeys that are currently mostly made on the M25, for example.
The problem is that outer suburban journeys tend to be from many destinations to many locations, rather than radial journeys which are in and out of a central district. That makes it far harder to provide a decent public transport solution for many of those journeys. Of course there is a lot of room for improvement, as you suggest links to Heathrow could be much better and any pretty much any orbital links would be better than what exists now
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Re: SW M25 Relief

Post by Gareth Thomas »

Perhaps the amount of traffic using this stretch of M25 might decrease a bit when the Lower Thames Crossing opens?

This section is opposite that of the Dartford Crossing. The Dartford Crossing is forever causing problems and costs money to use. So, if for example you are coming up the M23 and heading somewhere north of London, which way do you go? Anti-clockwise where you pay to go through a tunnel, or clockwise where the road is free?

If traffic eased at Dartford (and the tolls were taken away) then there might be a reduction of traffic using the Heathrow stretch. Of course, that would mean more traffic crossing from Kent to Essex, so it would be swings and roundabouts.....
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