One lane from M25 anticlockwise to M40 northbound??

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BF2142
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One lane from M25 anticlockwise to M40 northbound??

Post by BF2142 »

There's one lane from M25 anticlockwise to M40 northbound. Whoever designed this stuff? You think the UK's roads can't get anymore underwhelming and then you encounter this. :shock:
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Bryn666
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Re: One lane from M25 anticlockwise to M40 northbound??

Post by Bryn666 »

BF2142 wrote: Thu Jun 16, 2022 14:13 There's one lane from M25 anticlockwise to M40 northbound. Whoever designed this stuff? You think the UK's roads can't get anymore underwhelming and then you encounter this. :shock:
Google shows there to be two lanes around the loop. Has this changed since August 2021?
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Chris5156
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Re: One lane from M25 anticlockwise to M40 northbound??

Post by Chris5156 »

Bryn666 wrote: Thu Jun 16, 2022 14:24
BF2142 wrote: Thu Jun 16, 2022 14:13 There's one lane from M25 anticlockwise to M40 northbound. Whoever designed this stuff? You think the UK's roads can't get anymore underwhelming and then you encounter this. :shock:
Google shows there to be two lanes around the loop. Has this changed since August 2021?
There’s one lane in the opposite direction, M40 eastbound to M25 clockwise. But that seems reasonable enough: it’s not the dominant turning flow at this junction, and all traffic for M25 clockwise from both directions on the M40 has to combine into two lanes before merging. If it was a two lane sliproad it would have to narrow down somehow.

Single lane sliproads aren’t unusual. I’m not seeing the issue but would be glad of an explanation.
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Re: One lane from M25 anticlockwise to M40 northbound??

Post by c2R »

Far worse is the situation of the M25 anti-clockwise to M11 northbound..... no thought has been given to the dominant turning movements at the junction, while the M25 has been widened but the M11 merges have remained unchanged since their original design.

The situation could probably be improved with simply some while lining and signage changes....
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Re: One lane from M25 anticlockwise to M40 northbound??

Post by trickstat »

While I don't think I've ever been on it on a weekday but I've never encountered a problem with it myself. It is quite a tight radius so I think that's another reason to discourage overtaking. I wouldn't think it's a movement used that much for commuting relative to some others.
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Re: One lane from M25 anticlockwise to M40 northbound??

Post by Truvelo »

The loop from the M42 to M6 south was reduced to a single lane around 20 years ago and drivers losing control was the reason given. This loop is much longer than the M25 example and being stuck behind slower traffic can be annoying. Fortunately I have no reason to use it where I live now.
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Re: One lane from M25 anticlockwise to M40 northbound??

Post by Bryn666 »

Truvelo wrote: Fri Jun 17, 2022 12:45 The loop from the M42 to M6 south was reduced to a single lane around 20 years ago and drivers losing control was the reason given. This loop is much longer than the M25 example and being stuck behind slower traffic can be annoying. Fortunately I have no reason to use it where I live now.
I have doubts about that supposed safety argument of single lane loops - a lot of it seems to be overcautious 'engineering' looking for a problem to solve.

The M50 loops in Dublin have two lanes despite having a radius equivalent to that of a 5p coin.
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Re: One lane from M25 anticlockwise to M40 northbound??

Post by M4 Cardiff »

I used this today. The layout has not changed recently. it is 2 lanes all around the loop, but turns into one wide lane at the merge with the M40, so 2 vehicles can run parallel so no need to get held behind a slow vehicle, but it is not tiger-tailed as a proper 2 lane merge.
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Re: One lane from M25 anticlockwise to M40 northbound??

Post by Keiji »

trickstat wrote: Fri Jun 17, 2022 08:18 While I don't think I've ever been on it on a weekday but I've never encountered a problem with it myself. It is quite a tight radius so I think that's another reason to discourage overtaking. I wouldn't think it's a movement used that much for commuting relative to some others.
The simple solution to discourage overtaking if two lanes' capacity is required would be to put double whites down the middle (and perhaps a "Stay in Lane" sign as well) like is done at some tunnels and certain junction complexes (somewhere on the M8 Glasgow does this for a bit, IIRC).
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Re: One lane from M25 anticlockwise to M40 northbound??

Post by swissferry »

Keiji wrote: Tue Jun 21, 2022 14:10 The simple solution to discourage overtaking if two lanes' capacity is required would be to put double whites down the middle (and perhaps a "Stay in Lane" sign as well) like is done at some tunnels and certain junction complexes (somewhere on the M8 Glasgow does this for a bit, IIRC).
M8 and Clyde Tunnel. Both effective at keeping people in lane but neither are correct use of double white lines.
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Re: One lane from M25 anticlockwise to M40 northbound??

Post by Chris Bertram »

swissferry wrote: Tue Jun 21, 2022 20:45
Keiji wrote: Tue Jun 21, 2022 14:10 The simple solution to discourage overtaking if two lanes' capacity is required would be to put double whites down the middle (and perhaps a "Stay in Lane" sign as well) like is done at some tunnels and certain junction complexes (somewhere on the M8 Glasgow does this for a bit, IIRC).
M8 and Clyde Tunnel. Both effective at keeping people in lane but neither are correct use of double white lines.
It is supposed to be a single unbroken white line, isn't it?
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Re: One lane from M25 anticlockwise to M40 northbound??

Post by WHBM »

BF2142 wrote:There's one lane from M25 anticlockwise to M40 northbound. Whoever designed this stuff? You think the UK's roads can't get anymore underwhelming and then you encounter this.
Although as covered above this is actually two lanes throughout the 270-degree loop, I recall it well from when I had my Ford XR3i (showing my age here), and was a regular going round it, for it would take it nicely at 60 mph - except that the fuel gauge seemed to have no capacitor, so as you went round it would lose nearly 1/2 tank of its starting indication, slowly recovering over the next mile as you straightened out on the M40 !

The reciprocal direction does have a short single lane section, only between other (2-lane) loops diverging/merging, which would otherwise require four instead of three lanes on approach etc, not only over capacity but hazardous. Note that the single lane section is a full 36' carriageway, hatched down, so it is done for traffic management reasons rather than cheapness of civil engineering design.

Regarding "whoever designed this stuff", I did, at a more junior stage, work on the design team for some other motorway construction projects, sometimes covered here, where we modelled the traffic flows and put in a number of single lane interconnectors, which have worked fine for (many now) years. There are a few others here who have done the same. Any questions ... ?
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Re: One lane from M25 anticlockwise to M40 northbound??

Post by Chris5156 »

WHBM wrote: Wed Jun 22, 2022 07:13Although as covered above this is actually two lanes throughout the 270-degree loop, I recall it well from when I had my Ford XR3i (showing my age here), and was a regular going round it, for it would take it nicely at 60 mph - except that the fuel gauge seemed to have no capacitor, so as you went round it would lose nearly 1/2 tank of its starting indication, slowly recovering over the next mile as you straightened out on the M40 !
I can confirm with pleasure that the opposite loop, M25 clockwise to M40 eastbound, which I think is the same size, can be taken at 55 in a Skoda Fabia, to the great surprise of people in sportier vehicles taking a more cautious approach :)
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Re: One lane from M25 anticlockwise to M40 northbound??

Post by Herned »

Isn't this complaint a little overdue? The road has been open for ~40 years
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Re: One lane from M25 anticlockwise to M40 northbound??

Post by WHBM »

Chris5156 wrote: Wed Jun 22, 2022 08:00 I can confirm with pleasure that the opposite loop, M25 clockwise to M40 eastbound, which I think is the same size, can be taken at 55 in a Skoda Fabia
Does indeed look the same. Presumably the draughtsman used the same radius pieces from their box of Railway Curves (this being designed well before CAD stations). A designer really keen on symmetry might have done one, then turned the tracing paper over and placed it underneath the other to get the exact same angles (used to know someone who did this).

It may be that those "people in sportier vehicles" are in fact being a bit cautious and leaving a bit of leeway for someone coming up from behind at speed through the curve. I do, not here but notably at the M25/M11 Turbine, when turning from the clockwise M25 carriageway onto the M11 southbound towards London, a double reverse curve which progressively tightens with poor forward visibility where I have seen several in lane 2 not manage the curvature and slalom across my path, despite considerable superelevation (gosh, completely forgotten the old manual calcs for superel on a tightening transition curve, something about Newton's 4th law in there somewhere :) ).
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Re: One lane from M25 anticlockwise to M40 northbound??

Post by ChrisH »

Chris5156 wrote: Wed Jun 22, 2022 08:00
WHBM wrote: Wed Jun 22, 2022 07:13Although as covered above this is actually two lanes throughout the 270-degree loop, I recall it well from when I had my Ford XR3i (showing my age here), and was a regular going round it, for it would take it nicely at 60 mph - except that the fuel gauge seemed to have no capacitor, so as you went round it would lose nearly 1/2 tank of its starting indication, slowly recovering over the next mile as you straightened out on the M40 !
I can confirm with pleasure that the opposite loop, M25 clockwise to M40 eastbound, which I think is the same size, can be taken at 55 in a Skoda Fabia, to the great surprise of people in sportier vehicles taking a more cautious approach :)
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Our loops at M4 J10 are noticeably tighter than on the M25/M40, and you'd struggle to do more than 35mph, Fabia or no Fabia.
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