I realised today that everytime I travel over a large road bridge, the usual suspects being the Thelwall Viaduct, and the Barton Bridge, I find myself wondering whether the 2 1/2 foot (guestimate) barriers would actually prevent a vehicle from going over and into the drink should one actually hit it at speed.
Scares the life out of me when I have to cross such bridges (the Forth road bridge really scares me) and I always find myself moving into either lane 2 or 3, to keep away from the edge.
Surely the barriers should be much higher? Anyone know whether anyone has ever been unfortunate enough to go over the edge on road bridges.
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I have similar thoughts when going over Barton Bridge and Scamonden Reservoir on the M62 - especially when in the smart on a windy day! Didn't a wagon go over a parapet on the M60 a few months ago?
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I suspect that building a safety barrier capable of preventing a 40 tonne artic from going over is possible but to support that structure the bridge would need re-inforcing.
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On a related subject, in France I regularly drive at about 50mph across a bridge approx 30m long and not much more than 3m wide with only flimsy protection rails before the 15m drop into a river valley. I have often commented that if the rails were not present, you would probably stop and refuse to drive on!
It appears that you get a visually perceived sense of security from the presence of the rails, even tho you know they do nothing in the event of a blow out, sneeze or suspension failure!
Has anybody experienced this?
pmh (was peter)
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When I recently went over the forth road bridge, and looked down to my right, i realised that I could see the estury below through the the metal grille kerbside, just a foot from my wheel. The fear I felt was immeasurable.
It's daft, but the thought of crossing water really does put the willies up me.
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>>Has anybody experienced this?
I used a bridge regularily in the Andes - two tracks of wooden planks on a wooden frame, each about 2ft wide and about the right separation for placing one set of wheels on each, about 100ft about a rather nasty set of rapids and something like around 50ft long.
I used to go over it at about 300 cigarettes per minute.
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Wow,
Just like the one in the film "The Wages of Fear"?
Regards,
John R @ Work :¬)
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Yes, they are designed to prevent vehicles going through them, they should spring you like a catapult back into the carriageway, don't forget that you may be going 40mph, but maybe only 7mph in relation to the barrier if you sideswipe it.
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I'd never thought about the danger in that way before when going over Thelwall Viaduct until this thread I guess it could cause concern for people especially in fast moving traffic and bad side winds but on Thelwall i doubt any traffic could move fast enough to break through the barrier!
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I'd never thought about the danger in that way before when going over Thelwall Viaduct until this thread I guess it could cause concern for people especially in fast moving traffic and bad side winds but on Thelwall i doubt any traffic could move fast enough to break through the barrier!
"Fast moving traffic" and "Thelwall Viaduct" are very much mutually exclusive!
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Recall a tale of somebody in Barton Bridge's early days, stopped lost and feeling vulnerable on the lack of(?) hard shoulder decided they'd be safer if they jumped over the wall.
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There was always talk of someone who hopped over the viaduct on the M1 at Sheffield for a 'call of nature'. Nevr found out if it was true or myth.
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I remember witnessing a lorry going through a bridge in Glasgow, for those of you who know the area its the offramp just after the Kingston Bridge Eastbound.
As previously mentioned, these barriers are supposed to stay intact and the theory is they become "elastic" but never break and push you back onto the road.
However, if you hit the barrier at close on 90 degrees in a juggernaut, nothing will stop it!
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Was thinking this just the other day as we took a real buffeting from high winds on the QEII Bridge on the M25 at Dartford. There doesn't seem much in the way of a barrier but then I guess that's why they have a 50mph limit on what is a 4 lane section of motorway. Given the height of the bridge I wouldn't give much for the survival chances of anyone in a vehicle which smashed through it.
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It's all in the mind. On an ordinary single-carriageway road people cheerfully pass cars going in the opposite direction at a combined speed of 120mph plus, separated by a few feet and no barrier.
You have to trust all the oncoming drivers not to sneeze or use mobile phones - in the bridge scenario it's all down to you, so you ought to feel much safer.
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>combined speed
more like 160mph plus! Good point, Cliff.
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It's all in the mind.
Try telling that to those of us with vertigo!
I'd try and detour but they always build these high bridges in places where there isn't an alternative route....
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It's all in the mind. Try telling that to those of us with vertigo! I'd try and detour but they always build these high bridges in places where there isn't an alternative route....
I would have thought that's why they built the bridge in the first place
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As previously mentioned, these barriers are supposed to stay intact and the theory is they become "elastic" but never break and push you back onto the road.
This is exactly right.
I remember watching a programme several years ago about this, which showed slow-motion footage of a HGV hitting one, several of the supports break away from their moorings, but the barrier as a whole acts like a rubber band, it bends out, but guides the vehicle back towards the carraigeway.
In fact, it went into details of the different gauge barriers they use. The standard barriers are designed to do that witha normal sized car, but in places where the danger involved in leaving the carriageway is particularly high - such as a viaduct - they use barriers which will basically withstand anything that hits them.
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There was a very sad incident a couple of years ago on a raised section of the M56 near junction 12, a petrol tanker HGV (the tanker was fully laden having left Stanlow refinery minutes earlier) clipped a car which was stationary on the hard shoulder and then went out of control veering left and straight through the safety railings landing cab first 30 or so foot below.
The driver was tragically killed instantly.
My point is that these barriers cannot always stop a laden HGV.
PP
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I was working a contract for ICI at The Heath that day, next to J12. Saw the aftermath.
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Parapets were up until recently designed to withstand a range of vehicles at a range of speeds, it also depends on what the bridge is crossing. For example it was a requirement that parapets for bridges over railways at high risk locations are designed to resist a 30t vehicle at 64 km/h. This is the highest level of containment parapets are usually designed to. 'Normal containment' for all purpose roads (excluding railways & high risk locations) are designed to resist an impact from a 1.5t vehicle travelling at 113 kmh. The examples above have now been superceeded by a new design code, but it gives you an idea of the figures involved.
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I can't wait to drive over the new bridge over the Tarn gorge in France when it opens soon.
Designed by Norman Foster, the Viaduc de Millau is over 2km long, with the roadbed 270 metres (900ft!) above the river.
My wife says she will wait for me on the other side.
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Why do the Froggies build their bridges so high? I can understand it for crossing a gorge but river bridges I would have thought, would be designed to allow ships underneath and no more. However, the Pont de Normandie over the Seine, bridges at Caen, Nantes, Rochefort, Bordeaux etc seem to be hundreds of feet high - spectacular yes, but why?
Incidentally, how come there seem to be loads of these in France, just part of the network yet we see them as a fantastic engineering achievement worth building only every 20 years or so? We could do with a couple more over the Thames estuary for a start. And most of the French one are free (Pont de Normandie excepted
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Beats the Millau traffic jam or the trip through the cherry orchards to avoid them.
www.viaducdemillaueiffage.com/
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Roll on December, the bridge is opening ahead of original plan date! It just means that you get to the Lodeve traffic jam more quickly.
I am really waiting to see what happens next July/August when the traffic jam will move on to Pezenas, where the dual carriageway will finish (for about the next 5 years). All our peaceful small villages in the Herault valley are bound to suffer.
pmh (was peter)
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I am really waiting to see what happens next July/August when the traffic jam will move on to Pezenas, where the dual carriageway will finish (for about the next 5 years). pmh (was peter)
Surely the next traffic jam will be where the motorway follows that little chicane around the restaurant atl\'Hospitalet owned by (erm... allegedly) a \"friend\" of the local mayor, or prefect, or something.
Could you imagine a motorway in the U.K. being diverted around a small business?
Perhaps pmh, with his local knowledge, has some news on this.
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>>at l'Hospitalet owned by (erm... allegedly) a "friend" of the local mayor,
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interesting comment, I had often wondered! I had always assumed that the major reason for the bridge was not the 14 hr traffic jams in summer, but to divert the traffic from passing McDonalds and give Jose an opportunity to sell his fields ;).
pmh (was peter)
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Reminds me of Blott on the Landscape....
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"Could you imagine a motorway in the U.K. being diverted around a small business?"
You mean like that farmhouse that lies between the two carriageways of the M62? No can't imagine it!!
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quelle horreur!
what an ugly blight on the countryside.
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Mr (or Mrs) VR6 is clearly a Civil Engineer and is spot on.
It is my understanding that parapet design is a balance between containment and the serverity of impact experienced by the errant vehicle. You wouldn't want the things killing people because they are like hitting a solid immovable block of concrete.
I guess that current standards are based upon experience & statistics that indicate the preferred balance for the various situations.
I think most parpaets are quite capable of restaining a car impacting at an angle.
Its when a heavy vehicle impacts square to the parapet that the vehicle is likely to penetrate the barrier.
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Psychologically, we tend to worry about dropping off the edge of bridges or down steep drops. Yet this is no more likely (and the consequences would be no worse) than colliding with an oncoming artic, should it or we veer off course for any reason. Yet we pass oncoming large vehicles with hardly a thought, counless times on most trips.
Makes ya think, dunnit!
Cheers, Sofa spud
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I can't wait to drive over the new bridge over the Tarn gorge in France when it opens soon. Designed by Norman Foster, the Viaduc de Millau is over 2km long, with the roadbed 270 metres (900ft!) above the river. My wife says she will wait for me on the other side.
lets hope he gets the damping right. Millenium bridge mkII anyone?
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