I agree that a second freeflow right turn will eventually be needed, though probably the cheapest way to do this will be with a loop, given the base price is £64m for a loop compared to £125m for the whirlpool-type turn (option 2) and £150m for the semi-direct connector (option 6). In fact one of the leaked designs seems to combine a loop with a windmill/octopus-type turn.Philip_Baum wrote:Your right; they are quite similar to the two options I proposed although Highways England only propose free flow from M25 northbound to A12 eastbound. I think there should really be free flow to/from the A12 to/from East Anglia to/from the M25 north and southbound given it is better for A12 westbound traffic heading into London to use the M25 northbound to leap over to follow the M11 or use the M25 southbound to follow the A13. Then I would expect my first option (similar to option 2) to be cheaper than my second option (similar to option 6) given only 4 over bridges are required as oppose to 6 in my second option (6 not 7 given the two carriageways over Brook Street could run over the same bridge). That option basically forms an incomplete whirlpool (incomplete given it does not need to provide free flow to/from the A12 to/from Romford to/from the M25).
M25 junction 28 improvements
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Re: M25 junction 28 improvements
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Re: M25 junction 28 improvements
Whirlpool style grade separated freeflow junction from A12 westbound to M25 southbound and M25 northbound; from M25 northbound to A12 eastbound; and from M25 southbound to A12 eastbound. Only 4 over bridges are required.
Last edited by Philip_Baum on Thu Dec 22, 2016 01:07, edited 1 time in total.
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Re: M25 junction 28 improvements
Just put a speed limit on it then. The M11/M25 whirlpool jct has a speed limit of 30mph on some of its slip roads! You don't want grade separated junctions taking up loads of land just so cars can drive at 70mph on its slip roads. My proposed grade separated junction is compact and gives all strategic movements free flow i.e. A12 west to M25 clockwise and M25 anticlockwise + M25 clockwise and M25 anticlockwise to A12 east) without needing to use the Brook Street roundabout. The roundabout would then be intended for local traffic to/from Romford via A12 or to/from Brentwood via A1023 and traffic requiring the service area. Also traffic on the A12 west should then be directed into London via M25 anticlockwise and M11 south or M25 clockwise and A13 west as these are grade separated routes whereas the A12 into London is at grade with a lot of traffic jams due to the numerous traffic light controlled junctions.Glom wrote:Still very tight.
Last edited by Philip_Baum on Thu Dec 22, 2016 00:51, edited 6 times in total.
Re: M25 junction 28 improvements
No worse than the M1/M50 junction in Dublin.Glom wrote:Still very tight.
Bryn
Terminally cynical, unimpressed, and nearly Middle Age already.
She said life was like a motorway; dull, grey, and long.
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Terminally cynical, unimpressed, and nearly Middle Age already.
She said life was like a motorway; dull, grey, and long.
Blog - https://showmeasign.online/
X - https://twitter.com/ShowMeASignBryn
YouTube - https://www.youtube.com/@BrynBuck
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Re: M25 junction 28 improvements
Exactly. I can't understand the UK obsession that a free-flow link must have a design speed equal (or nearly equal) to its parent roads. This, and a couple of other UK obsessions such as M-status and LARs, has always been an obstruction to pragmatic value-for-money improvements.Philip_Baum wrote: Just put a speed limit on it then.
Re: M25 junction 28 improvements
As posted in another thread, these are the minimum advisory speeds at some UK full access freeflow interchanges:Peter Freeman wrote:Exactly. I can't understand the UK obsession that a free-flow link must have a design speed equal (or nearly equal) to its parent roads. This, and a couple of other UK obsessions such as M-status and LARs, has always been an obstruction to pragmatic value-for-money improvements.Philip_Baum wrote: Just put a speed limit on it then.
M25/M23 50mph
M25/M3 50mph
M25/M40 50mph
M25/M4 40mph
M60/M62/M602 40mph
M6/M62 40mph
M4/A329(M) 30mph
M25/M11 30mph
A19/A66 30mph
The only remaining full access freeflow interchanges are the two cloverleafs, the Motherwell octopus and Almondsbury stack, all of which are rather tighter than the likes of M25/M23 or M23/M3.
In short, most, if not all, complex freeflow interchanges in the UK are considered safe for ramp speeds of 30-50mph, which doesn't strike me as unreasonably high.
Re: M25 junction 28 improvements
Yes, but that was then and this is now. Those junctions were all built long before the current view that free-flow slip roads should have a high design speed came in. Interestingly, the A1(M)/M62 junction has mandatory 50 limits on the slip roads, even though many of them can be taken quite comfortably at NSL. I can't see why that junction would be different from others so that does suggest that there is a move away from advisory limits in that kind of situation.jackal wrote:As posted in another thread, these are the minimum advisory speeds at some UK full access freeflow interchanges:
M25/M23 50mph
M25/M3 50mph
M25/M40 50mph
M25/M4 40mph
M60/M62/M602 40mph
M6/M62 40mph
M4/A329(M) 30mph
M25/M11 30mph
A19/A66 30mph
The only remaining full access freeflow interchanges are the two cloverleafs, the Motherwell octopus and Almondsbury stack, all of which are rather tighter than the likes of M25/M23 or M23/M3.
In short, most, if not all, complex freeflow interchanges in the UK are considered safe for ramp speeds of 30-50mph, which doesn't strike me as unreasonably high.
Re: M25 junction 28 improvements
There is no fixed policy of high design speed - it's just a question of what gives best value for money, which will sometimes mean a high speed, sometimes a low speed. This is nicely illustrated by the M25 J28 scheme itself, which examined both 85kph semi-direct/cyclic options and 75kph loop options, and found the best value came from 75kph, so that's what will get built.Stevie D wrote:Yes, but that was then and this is now. Those junctions were all built long before the current view that free-flow slip roads should have a high design speed came in. Interestingly, the A1(M)/M62 junction has mandatory 50 limits on the slip roads, even though many of them can be taken quite comfortably at NSL. I can't see why that junction would be different from others so that does suggest that there is a move away from advisory limits in that kind of situation.jackal wrote:As posted in another thread, these are the minimum advisory speeds at some UK full access freeflow interchanges:
M25/M23 50mph
M25/M3 50mph
M25/M40 50mph
M25/M4 40mph
M60/M62/M602 40mph
M6/M62 40mph
M4/A329(M) 30mph
M25/M11 30mph
A19/A66 30mph
The only remaining full access freeflow interchanges are the two cloverleafs, the Motherwell octopus and Almondsbury stack, all of which are rather tighter than the likes of M25/M23 or M23/M3.
In short, most, if not all, complex freeflow interchanges in the UK are considered safe for ramp speeds of 30-50mph, which doesn't strike me as unreasonably high.
Re: M25 junction 28 improvements
*Minimum* advisory speeds?jackal wrote: As posted in another thread, these are the minimum advisory speeds at some UK full access freeflow interchanges:
M25/M23 50mph
M25/M3 50mph
M25/M40 50mph
M25/M4 40mph
M60/M62/M602 40mph
M6/M62 40mph
M4/A329(M) 30mph
M25/M11 30mph
A19/A66 30mph
Derek
Free the A11
Re: M25 junction 28 improvements
Yes. For instance, if some slips have 50mph advisories, some 40mph, only 40mph gets listed.Derek wrote:*Minimum* advisory speeds?jackal wrote: As posted in another thread, these are the minimum advisory speeds at some UK full access freeflow interchanges:
M25/M23 50mph
M25/M3 50mph
M25/M40 50mph
M25/M4 40mph
M60/M62/M602 40mph
M6/M62 40mph
M4/A329(M) 30mph
M25/M11 30mph
A19/A66 30mph
Derek
Re: M25 junction 28 improvements
You mean lowest advisory speed limit. Calling it a minimum implies traffic needs to be going at least that fast.
Re: M25 junction 28 improvements
No, I mean precisely what I said.Glom wrote:You mean lowest advisory speed limit.
No it doesn't.Calling it a minimum implies traffic needs to be going at least that fast.
Last edited by jackal on Tue Aug 22, 2017 10:46, edited 2 times in total.
Re: M25 junction 28 improvements
Option 5F has been selected. While it's the only option with two lanes on the new loop, the start of the loop looks too tight to me, though apparently it's the same design speed. It will be a good improvement anyway.
http://roads.highways.gov.uk/projects/m ... rovements/
http://roads.highways.gov.uk/projects/m ... rovements/
Re: M25 junction 28 improvements
Curves are supposed to have easements so they start and finish with larger radii and tighten up in the middle. This one has a really sharp bend soon after leaving the M25.
How would you like your grade separations, Sir?
Big and complex.
Big and complex.
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Re: M25 junction 28 improvements
Good to see this getting nearer to at least some kind of resolution.
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Re: M25 junction 28 improvements
Unless there is some obstruction that cannot be worked around, I can see that being tweaked a bit during design.
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Re: M25 junction 28 improvements
They went with the fancier design. Let's appreciate this while it lasts.
Re: M25 junction 28 improvements
That's a horrible horizontal alignment and I fully expect it to be savaged at a safety audit - as said unless there is something subtle we can't see that loop could be much smoother.
Bryn
Terminally cynical, unimpressed, and nearly Middle Age already.
She said life was like a motorway; dull, grey, and long.
Blog - https://showmeasign.online/
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Terminally cynical, unimpressed, and nearly Middle Age already.
She said life was like a motorway; dull, grey, and long.
Blog - https://showmeasign.online/
X - https://twitter.com/ShowMeASignBryn
YouTube - https://www.youtube.com/@BrynBuck
Re: M25 junction 28 improvements
It seems a little bit of a long detour free-flow link but much appreciated either way. However, I feel a free-flow link from the A12(S) ---> M25 Clockwise is also needed as I feel a lot of traffic is moving back and forth in this direction as the A12 is essentially the gateway to East Anglia from the Dartford Crossing and the near continent. However, HE have made there decision and it is expensive at some £80m but much needed to some degree.