Just came off south bound M25 onto the M4 and the slip road has a sign "Adverse camber".
Daughter didn't fully understand what it mean so I was trying to explain, then wife pipes up saying "it's a bit of a bog admission to have to put a sign up admitting that they built it wrong". I said I thought they probably deliberately designed with with no or adverse camber to slow traffic, as I cannot believe that it was a mistake, what with the millions it takes to design and build a new road.
So for the next few minutes we discussed it, and, not reaching any conclusion, I thought I'd ask the collective brains here. Why are roads built with an adverse camber?
|
Adverse Camber sign in the roadworks on the A1(M) northbound in North Yorkshire.
The camber is quite severely adverse.
Presumably in this case the camber will be corrected when the works are finished.
I always understood camber to be mostly about drainage, although why it should be purposefully built as adverse, I don't know.
|
|
Imagine that I wrote something witty here.
|
The design of adverse camber is permitted but only if the radius of the carriageway is sufficiently large for it not to be significant. In this case signs would not be needed.
On early motorways it was permitted to design hard shoulders with adverse camber. It is a long while since I drove through the M25/M4 junction but is it possible that the old hard shoulder has been turned into a running lane to increase the traffic capacity?
|
I'd always assumed it meant the road was not dipping toward the outer side, or it was, but there was a RH bend so it's not 'banked'.
Does that make sense?
|
|
The ground around the m25/M4 junction has been on the move for a while. There is a fair chance the camber was ok at one point but moved later.
|
Were you heading east or west on the M4, smokie? I've looked at Google Streetview and can't see the sign.
Each of the sliproads at that junction has a diverge followed by a merge before rejoining the main carriageway. At the diverges and merges each of the routes has a different radius and therefore a different requirement for optimum camber. With such a compact junction as this there is often not enough room to change from one camber to another without introducing an unacceptable bump in the profile along the road.
It would be nice if all the movements on the junction could be undertaken at 70mph but that would require a massively increased landtake. So we are left with advisory speed limits on the bends.
Without knowing exactly where it was I wonder if the camber was not truly adverse (i.e. in the wrong direction ) but merely insufficient for the speed drivers were attempting to take the bend.
|
All three slips at the A5103/M60 interchange have adverse camber These are all very tight bends and are some of the busiest ( and fastest )in the area.
Many people have come to grief and some years ago an East European trucker was killed when his Artic overturned on the southbound. I pulled a BMW out of the Armco on the other side some years ago.
I can't recall any warning signs.
I think they're far too tight bends and should have proper camber. But what do I know ?
Ted
|
>>But what do I know ?
You know not to take them too fast or you too will come to grief.
There are bend signs with "Reduce Speed Now" warnings on both the M60 offslips (on Streetview) but too many people ignore these type of signs. Also the bends appear (on the map) to tighten up which is always a bad thing since by the time you realise you are going too fast for the radius you are on you are onto an even tighter bend.
I'm sure the landtake issue was also a very restricting factor for the designers here. The M25/M4 junction is four levels and still is far from perfect.
|
They've boogled up a roundabout on the A50 in this way. There are always lorries tipping over inspite of the warning signs of a lorry tipping over in a red triangle! Why they don't fix it is beyond me as the road gets closed for hours every time it happens. The roundabout is also a bit too tight for a lot of lorries.
Adverse camber just means the roads banks the wrong way so any lean in the vehicle is increased rather than countered.
|
Yes Crocks, I think you hit the nail "if the camber was not truly adverse (i.e. in the wrong direction ) but merely insufficient for the speed drivers were attempting to take the bend".
I was coming from the north and heading out West. And of course the slip road merges with that coming from the South, who would want the camber at a different angle. So I guess it's just flat.
I can't see the signs on streetview either btw, but I'm sure there was one!
The one which I remember as being particularly adverse was joining the eastbound M2 from Detling Hill. I did that bit daily for a while and regularly saw all sorts who had managed to drop off the edge!
|
I've only been there a few times, but there are problems with any sliproad which turns 270° left at a constant radius. Drivers have plenty of time to accelarate to the limit of adhesion (and often beyond)!
There is a similar layout at the sliproad onto the A3 at Ladymead, Guildford. I swear it tightens up just as you think you've got the hang of it. There is an unofficial sign warning motorbikes who think it might be a good place to get try and get the pegs down.
|
Designers never seem to learn. They should have taken a lesson from the railways.
The Victorian engineers knew all about 'adverse camber '....Superelevation.
That's why even non-tilting trains can get round bends fairly rapidly.
Ted
|
Its really easy to build camber on 4' 8.5" of railway road.
Its harder on 40 yards of multilane motorway.,
|
>> The Victorian engineers knew all about 'adverse camber '....Superelevation.
Indeed the theory of superelevation on roads is based on the original ideas of the railway engineers. Superelevation is now a term used only for highway design. On railways it's called 'cant'.
The rules for the application of superelevation on bends are quite strict but can be difficult to apply in tight situations where there are 'S' bends, especially if there is no appreciable longitudinal gradient to take the surface water away.
|
On railways the radii are usually larger and the speeds are known and tightly controlled so cant design is not usually too difficult.
Where it gets really tricky is on tram systems where the requirements of the railway engineers and the highway engineers interact and often conflict.
|
>> Where it gets really tricky is on tram systems where the requirements of the railway
>> engineers and the highway engineers interact and often conflict.
Don't I know! Been there, done that. :-)
|
>>Don't I know! Been there, done that. :-)
Whereabouts? Not in Rattle and Ted's back garden I hope.
|
So what's superelevation?
|
Superelevation is the technical term for the tilting of the carriageway to assist vehicles to make the turn and counteract centrifugal force (or centripetal acceleration if you prefer).
Last edited by: Arctophile on Sun 4 Apr 10 at 19:19
|
So I might call it banking?
In the case of a railway, one rail a bit higher than t'other.
|
|
Yes, you could call it banking. As mentioned above, on railways it's called 'cant'.
|
'Cant', 'camber', and 'banking' were all in my vocabulary with the meanings we are talking about here.
Superelevation is a word of which I'd not previously heard.
I recall being on a slow train running on a fast line.
If it went very slowly around a bend, you could feel the carriages tilt inwards.
|
>>If it went very slowly around a bend, you could feel the carriages tilt inwards.
.....and your coffee spills!
The theoretical perfect superelevation on roads, and cant on railways, can be calculated for any given speed but in the real world the designers need to consider the lorries/trains coming to a stop.
You wouldn't want to stop your car or your fully loaded lorry at the top of the Brooklands banking!!!
|
|
In cars with non-assisted steering, especially RWD ones you could feel changes in camber. Even in power assisted FWD ones it was still transmitted a bit through the wheel. One of the characteristics of cars which have "electric" power steering is an alarming feeling of detachment from the conditions of the tarmac. I don't like it, but I'm probably old fashioned. The PlayStation generation don't seem to care about such things.
Last edited by: Humph D'bout on Sun 4 Apr 10 at 20:01
|
...and your coffee spills!...
Strewth, didn't realise the implications were that serious.
|
I travelled on trains more when was I younger - a trip to the buffet car was an essential part of the experience.
Always surprised me there weren't more mishaps with clumsy oafs like me making their way through moving carriages carrying hot drinks.
|
>>You wouldn't want to stop your car or your fully loaded lorry at the top of the Brooklands banking!!!
If you did, it wouldn't, if you see what I mean.
|
Of course, the classic example of Cant, Superelevation or whatever is a track like Brooklands or the Manchester Velodrome.
I think you'd have trouble stationary on a bike at the top !....it's about 45 degrees.
Our progressing tramway has nice gentle curves, it was the main line to London.
Well before Rattolingus' time !
Ted
|
|
The altea was up there. And I didnt.
|
As I understand it camber on a road is mainlyabout drainige. As teabelly pointed out there are examples on roundabouts on the A50. Same issue on the A43 round Brackley; lorries fall over with monotonous regularity.
On the UK mixed traffic railway track cant is a bit of a compromise. Cant to "bank" a highspeed train so that the centriptetal force appears directly downward will result in discomfort on slower trains (offee spills to insode of curve) and/or those stopping at stations on the curve. Wolverton on the west coast line is an example. More seriously, heavy freights will wear the inner rail so the max permissible cant is prescribed at a level where such damage is minimised. This however results in a cant deficiency for fast passenger trains (coffee spills to ouside of curce). The answer here is tilt.
|
Surely the requirements of cant and camber are slightly different?
If there are two lanes, the outer, faster lane would in theory need to tilt more than the inner?
But on a single carriageway road that is the opposite of the requirements of camber, which is to have a rounded flattened crown, for drainage and also to cover the possibility of overtaking from the opposite direction.
|
Bromptonaut:
“As I understand it camber on a road is mainly about drainage.”
It's about both drainage and reducing sideways force. On a new straight road the crossfall (yet another word with the same meaning) would be 2.5% (1:40), this is purely for drainage purposes. On a bend the crossfall would be increased up to a normal maximum of 7% (1:14) depending on the radius of the bend and the design speed of the road. In urban areas the normal maximum is 5% (1:20).
If lorries are falling over regularly on roundabouts then someone has plainly got it wrong. The design standards include specific requirements and warnings intended to avoid this happening.
Cliff:
On a dual carriageway with 2 or more lanes in each direction the normal practice is to adopt the same design speed and crossfall for all of the lanes travelling in the same direction. It is assumed that vehicles may operate up to the design speed in all lanes.
On a straight single carriageway road the crown is 'rolled' to smooth out the change in crossfall at the centre. On bends the whole carriageway would have a constant fall right across it for the benefit of both the overtaker and the overtakee (good word that, I just invented it).
It's where the straights join the bends that life gets difficult, but I won't go into clothoid spirals here. :-)
|
Arctophile,
Interesting post. The camber for drainage would, presumably, generally fall evenly either side of the crown to the respective gutter. Or in other words the camber would always fall to the nearside. So is there in fact an adverse camber on most right hand bends, or does adverse relate to one which is counter to accepted sense and works with the centirpetal force on the vehicle (hence the rollovers)?
In both my examples on the A43 and Teabelly's on the A50 there is ample signage - it just seems some drivers miss it or know better.
|
"Or in other words the camber would always fall to the nearside."
No, on bends the fall should always be towards the inside of the curve. So on an 'S' bend the fall will be first towards one edge then towards the other edge. Between the bends there will be a point where it is flat across the carriageway; this is where the drainage problems arise.
If vehicles are regularly having accidents at a given location, say a roundabout, then there is a problem with the road design that is misleading drivers. The trouble is finding the money to fix it.
|
Adverse camber... - Iffy
