Motorway Layouts.
While driving through the road works on the western section of the M25 at various times of the day (including rush hours) I was struck by the following observation.
Northbound, two lanes are moved into the opposing carriageway with no access off for three junctions. Two lanes remain for access on and off the motorway.
Even during high demand, during rush hour, the two ?no access lanes? (assuming no accidents or breakdowns) flow smoothly at the posted 40mph limit. The two ?access? lanes are backed up constantly.
This leads me to assume that it?s the act of leaving and joining motorways that cause the most agro.
So my idea, on urban motorways in the UK that suffer jams, is to provide two lanes for local, joining and leaving, and two physically separated lanes for through traffic, perhaps with leaving and joining intersections every three or four junctions or so..
The two outer lanes would obviously be the ?through lanes? and the joining intersections in the outside lane of the ?local lanes?
In effect a Motorway within a Motorway.
I have seen similar ideas in use in the UK and abroad, but these seem to be by accident rather than design usually after extra lanes or junctions have been added.
If the M25 was built with 2 outer lanes ?through traffic? and two inner lanes ?local and access? with crossovers every 4 junctions I bet it would be transformed.
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I've seen that in the US & Brazil. And it works in both. And quite frankly, anything which can persuade the Brasilians to drive properly would be a dead cert. to work here.
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Would it be cynical or realistic to suggest that our anti-car government would never implement a scheme like this for risk of making the motorist's life easier?
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If you really want to go the whole hog, "reverse" the carriageways ("northbound" lanes to the right of "southbound" lanes but "slow" lane still on the left" - and all junctions go down the central reservation. This way the two slow lanes are closest together so the speed at any cross-over accident should be greatly reduced. One of the motoring mags did an article on this many years ago but it has never caught on. Shame.
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These schemes sound very workable, if drivers understood them -- though I do rather doubt whether those who can't understand the existing lane system would grasp something even more sophisticated.
However, it couldn't be retrofitted to existing motorways -- it's something which would have to be designed in from the outset. Even if new mways were being built (which sees unlikely), we'd still end up with only a few rare stretchs of road with this new layout, which would further reduce the chances of it being understood.
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The problem with UK motorways is simply that in most cases there are too many junctions too close together.
Thus there is a mix of local and long distance traffic.
Thus there is a lot of joining and leaving.
The M25 is a prime examble.
IMHO the function of a motorway should be to carry long distance traffic at high speed, so access/exits should be no closer than 20 miles apart.
A class roads should then be the distributors.
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>>The M25 is a prime example.>>
That has always, as you rightly point out, been the main cause of the immense jams on the M25.
It's not a local road to nip on at one junction and then off at the next as so many local drivers do but, supposedly, a motorway.
As you say, junctions should be spaced well apart and ensure that the route is used as originally intended for these type of roads.
I live in the north and there are very few motorways with junctions situated so closely as the M25.
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But virtually each M25 junction joins on to a very major road/motorway, and all the rest onto major roads. VERY few don't adjoin dual carriageway.
30:A13
29:A127
28:A12
27:M11
26:errr
25:A10
24:errr
23:A1
22:A414(?)
21:M1
20:A41
19:A41
18:err
17:A412 (?)
16:M40
15:M4
14:A3044 (?)
13:A30
12:M3
et cetera
Take away most of these junctions & you put a huge hole into the motorway network.
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When the M25 was completed, some prof predicted the havoc that would ensue. His solution was to allow access only from the motorways, but to keep all the exits. Local traffic would have kept on local roads, long distance through traffic would have run fine (which was the purpose of the M25, after all)
At the time I though it made sense, as all the people who subsequently flocked onto the M25 for short trips hadn't yet done it.
V
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>>His solution was to allow access only from the motorways, but to keep all the exits.>>
I can't quite understand this, although I think I know what you mean.
>>But virtually each M25 junction joins on...>
Then it's surely not a motorway but a link road?
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>>>But virtually each M25 junction joins on...>
>Then it's surely not a motorway but a link road?
Are the two mutually exclusive?
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In this particular instance that's the way I would view it.
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I've been in big tailbacks on the M25, I've been round it when it's free flowing, I've been carved up by all sorts and I've heard those 'world's biggest car park' jibes.
But I never lose sight of the fact that going round the good ol' M25 is a whole lot better than driving through London, which is what everyone had to do before it was built. 2-3 hours from Brentwood to Heathrow via the A12/North Circular/M4? No thanks!
Cheers, SS
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And my solution to the M25 congestion problem: - Upgrade the A34/A43 route up the centre of southerh England from Winchester via Oxford to Northampton and as far as the A1 into a proper motorway, the M34. That would be environmentally friendly (relatively) as it would not be taking virgin countryside, just a widening the existing route.
Cheers, SS
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And my solution to the M25 congestion problem: - Upgrade the A34/A43 route up the centre of southerh England from Winchester via Oxford to Northampton and as far as the A1 into a proper motorway, the M34. That would be environmentally friendly (relatively) as it would not be taking virgin countryside, just a widening the existing route. Cheers, SS
No, this is not the cause of congestion on the M25. The problems are caused in large part by some rather odd road layouts. Like, the arrangement at the A10 clockwise, one lane becomes the slip road for the A10, thus squeezing any traffic not turning off, into two lanes. This doesn't work, and the traffic often backs up all the way to South Mimms because of this. Or, the lane layouts coming clockwise from the M40 towards Watford. Several times, traffic in the inside lane has to filter across, while a new outer lane opens up a few hundred yards further on. So no overall increase in the number of lanes, but everyone is lane-changing, and going uphill to boot, so you constantly have slow traffic merging from the left - result, very very slow progress most of the time!
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The point is not the type of road that the junctions lead to/from, but the fact that what should be local traffic using local A roads is overloading the motorway.
I am guilty of this myself, as I use the M11 between Loughton and the North Circular each day.
In general, if you restricted the junctions to other motorways and A roads with numbers below (say) 20 it would halve the number of junctions (I did work out the exact configuration a few months ago but don't have the map in front of me at the moment) and displace half the local traffic.
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but the fact that what should be local traffic using local A roads is overloading the motorway.>>
That was precisely the point I made earlier in the thread.
Multiply this by virtually every junction (and if I remember rightly the M25 is about 117 miles long if you complete the full circle) and you get the picture.
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The problem with UK motorways is simply that in most cases there are too many junctions too close together. Thus there is a mix of local and long distance traffic. Thus there is a lot of joining and leaving. The M25 is a prime examble.
Yes. I've followed people all the way from Rickmansworth, out on the A404, onto the M25 anti-clockwise at junction 18, only to watch them leave again at junction 17 for Maple Cross. Local roads would have been simpler and quicker!
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