Crash Barriers
Discussion
Assembled bods - in the office we've been commenting on how wonderful the new Heads Of The Valleys road will be when it's finish. But... we've also been speaking about crash barriers. Can anyoone answer the following for us?
What are the three usual types of barrier seen on dual carriageways ('box' type, usually on the shoulder by signs or walls; 'wave' type, looks like a B in profile and the most often seen on the central reservation; and thick cable type, increasing in popularity)?
Following on the the thread about Gary Hart, can anyone tell me how effective the cable-type barriers are in doing what they're meant to do? Does seem to my colleagues that, particularly locally, when these are newly installed they look like they couldn't stop a Smart going at 15mph from crossing to the other carriageway.
What are the three usual types of barrier seen on dual carriageways ('box' type, usually on the shoulder by signs or walls; 'wave' type, looks like a B in profile and the most often seen on the central reservation; and thick cable type, increasing in popularity)?
Following on the the thread about Gary Hart, can anyone tell me how effective the cable-type barriers are in doing what they're meant to do? Does seem to my colleagues that, particularly locally, when these are newly installed they look like they couldn't stop a Smart going at 15mph from crossing to the other carriageway.
wanty1974 said:
Assembled bods - in the office we've been commenting on how wonderful the new Heads Of The Valleys road will be when it's finish. But... we've also been speaking about crash barriers. Can anyoone answer the following for us?
What are the three usual types of barrier seen on dual carriageways ('box' type, usually on the shoulder by signs or walls; 'wave' type, looks like a B in profile and the most often seen on the central reservation; and thick cable type, increasing in popularity)?
Following on the the thread about Gary Hart, can anyone tell me how effective the cable-type barriers are in doing what they're meant to do? Does seem to my colleagues that, particularly locally, when these are newly installed they look like they couldn't stop a Smart going at 15mph from crossing to the other carriageway.
Wanty, these cables are extremely effective in absorbing the initial impact of the vehicle and absorbing it progressively, rather like progressive crumple zones on a vehicle; softest parts to the outside becoming more resiliant as you near the passenger cell.
When a vehicle hits the cables it "traps" it like a net and as the vehicle stretches the cable it becomes progressively tighter until it stops it.
With a fixed barrier, if a vehicle penetrates it and it breaks the game is over; the vehicle is through and from that point onwards, the crash barrier is useless.
What concerns me is that these barriers are still too low, allowing larger, higher vehicles to capsize over them, that is my only concern.
But the main problem with the cable type is that they tend to cut through motorbike leathers and human flesh like a hot knife through butter.
I read that the box type ones you see on bridges can stop an 18 wheeler hitting them at an angle of something like 30 degrees at 60mph. Surely that's enough? The problem with the Gary Hart accident was that his car left the road before the bridge barriers started, didn't it?
I read that the box type ones you see on bridges can stop an 18 wheeler hitting them at an angle of something like 30 degrees at 60mph. Surely that's enough? The problem with the Gary Hart accident was that his car left the road before the bridge barriers started, didn't it?
IOLAIRE said:
What concerns me is that these barriers are still too low, allowing larger, higher vehicles to capsize over them, that is my only concern.
Well, that was our concern too. They only appear to be 18 inches from the ground and the support posts seem to be glued in place with filling foam!
Bonce said:
I read that the box type ones you see on bridges can stop an 18 wheeler hitting them at an angle of something like 30 degrees at 60mph. Surely that's enough?
Unfortunately lighter vehicles tend to ricochet off them and back into the traffic
I guess there's no "one size fits all" solution to crash barriers.
pdV6 said:
I read that the box type ones you see on bridges can stop an 18 wheeler hitting them at an angle of something like 30 degrees at 60mph. Surely that's enough?
Unfortunately lighter vehicles tend to ricochet off them and back into the traffic
I guess there's no "one size fits all" solution to crash barriers.
Sorry I couldn't come back earlier lads, had to go out.
This is a good point about bike riders being cut by the cables; the problem is that you are so vulnerable at all times on a bike compared to a motor vehicle.
I stopped riding a bike years ago simply because of the horrendous things I saw while working at accident scenes.
Streetcop also did a piece a few weeks ago about whether or not he should stop riding, and it's simply because you can be the greatest rider on earth but there are so many motorist who have no idea about the concepts of riding a motorcycle and make no allowances for it.
These cable barriers really are effective though; the reason foam is used is the same as that for the cables, it will take progressive stress much better than concrete. If a steel post cracks the concrete at it's root then it just pulls straight out, whereas the foam will grip all the way round the post because of it's adhesive properties and hold on a lot longer.
In Scotland quite a few of the motorways in rural areas have very wide divides between the carriageways and I think that is the answer; like a racetrack with soft surface run off areas, these will stop even an artic in no time and with virtually no damage.
Can't remember what the program was but I did see a film on TV recently of a Artic crashing into one of these barriers at I guess around 40 degrees, (certainly greater than 30 deg) and I must say it did control it. Any BiB's seen the results of accidents with HGV's and this type of barrier?
Crash barriers are primarily aimed at deflecting angled impacts to prevent vehicles spilling off the road or into oncoming lanes.
They aren't intended to contain vehicles that impact directly or do not deflect off, but do have a capacity to do so.
The upstands tend to be embedded in concrete at quite a depth.
Barriers are designed to withstand an HGV 60-something mph impact at, i think, a 70 degree angle to the line of the barrier.
They aren't intended to contain vehicles that impact directly or do not deflect off, but do have a capacity to do so.
The upstands tend to be embedded in concrete at quite a depth.
Barriers are designed to withstand an HGV 60-something mph impact at, i think, a 70 degree angle to the line of the barrier.
Bonce said:A large proportion of the TRL's Research looks in to crash barrier design. There was a programme last year showing what happens when different types of vehicles meet different types of barriers at different speeds and different angles of approach. One problem with cables is that the older type especially can sling shot a vehicle back in to traffic if it glances in to the wires. The wavy barrier performed best overall but with a compromised performance.
But the main problem with the cable type is that they tend to cut through motorbike leathers and human flesh like a hot knife through butter.
Another research group has been looking in to crash barriers and their effects on motorcylists.
The box type barriers depend to be used where an impact with a structure (bridge, railway cutting etc) would cause potentially more damage/injury than to the occupants of a vehicle.
Ultimately, there is no one single, absolute, best solution at least not one that is sensible or affordable. Must be a nightmare for planners and designers.
MC
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