Motorway Barriers?

MrPudding

bk wrote:

I disagree with this, I don't have actual figures, but if you watch the news, you'll see that the most serious accidents where multiple people are killed are almost always head on collisions.

TBH you can disagree all you like but the fact remains that of all the people that died on Irish roads over the years only a very small proportion were the result of a vehicle crossing the median. I agree that when they do happen they tend to be big, kill loads of people, are very very sad and create huge headlines. In the mean time deaths due to poor "country" roads, poor driver training and various other things just plod along, not making the big headline but killing more people.

bk wrote:

The reason is very simple, the velocity of the impact is the sum of the speed of the two vehicles. So if the two vehciles are travelling at 60km, then the impact is equivalent to a 120km crash.

I do understand how the impact velocity is worked out. No one is debating the physics of it. We are simply saying that pound for pound we might have been able to save more lives by putting the money elsewhere.

BrianD3, it was alos BrianD's posts on this subject that changed my mind.

MrP

spacetweek

Hoof Hearted wrote:

For the sake of completeness if a car travelling at 120kph hits the barrier at a 5° to the motorway (a reasonable assumption), its 90° speed will be 10.5kph (This is the effective sideways speed against the barrier which is really what counts) An analogy is an aircraft landing at 220kph its decent speed is about 6kph on touchdown.

Another bit of maths (I love maths): someone said if a median was barrierless and you enter it you have less than a second to regain control. Assuming it was 15m wide, entering it at 5° angle and 120 km/h means the distance you travel is 15/cos (90-5) = 172m. At 33.3 m/s this gives you 5.16 sec to regain control. OTOH, barrierless medians have been debunked, as also pointed out.

I saw some pics on Wiki of Chinese motorways and on one the author showed a section that had a barrierless median. He commented on how odd this was and then said they had retrofitted a barrier since. They must have made the same mistake as us and come to the same conclusion.

Aidan1

Forward speed only causes injury to you if limbs get caught in the barrier - which is what happens with wire rope ... The component of velocity at right angles to what you hit is irrelevant to the force of the collision provided you are hitting a smooth surface. A wire rope barrier is an aggressive surface.

Oh, ok, so forward speed is not an indicator of damage when hitting a fixed object? Really? I'll ask you again, same angle of approach, 30kph crash vs 120kph crash, take yer pick. 8.3ms vs 33.33ms at 5 degrees angle of incidence (say). Is the force of impact the same, to both bike and rider, in both cases? Impact having a role in causing injury, after all.

At 33.3 m/s this gives you 5.16 sec to regain control

And given that you're speed will probably drop off, and you may well have two wheels still on the road surface, you may have slightly longer. However most people still wouldn't have a hope of catching a slide like that, the odds of them locking up and going straight across into the other carraigeway (worst case), or veering back into their own (not so bad in that impact speeds, if any, will be much, much lower). The best hope you have is that cars come to a stop in the median. Still comes down to a CBA though, if you can save more lives on B roads, thats where the money should go

Hotblack Desiato

Aidan1 wrote:

Oh, ok, so forward speed is not an indicator of damage when hitting a fixed object? Really?

Yes. Really. I'm not going to explain the physics again. Suffice to say if you're moving towards the barrier at, say, 2 metres per second, your impact force against the barrier will be the same NO MATTER WHAT your speed along the barrier is.

I'll ask you again, same angle of approach, 30kph crash vs 120kph crash, take yer pick. 8.3ms vs 33.33ms at 5 degrees angle of incidence (say).

How on earth would the angle of impact be the same at high speed? As I said in my first post, the angle of impact at high speed will be far shallower. I'm starting to wonder if you're actually reading what I'm posting, or just picking out sentences at random and trying to contradict them.
In practice, at low speed, you could find yourself going off the road at an angle not too far off 90 degrees, and will likely experience a MORE severe impact than at high speed where the angle of impact is shallower, therefore speed TOWARDS the barrier, not ALONG the road, TOWARDS the barrier, is small, and there's a lot more time for friction between you and the road to slow that small impact speed down even more.

And given that you're speed will probably drop off, and you may well have two wheels still on the road surface

As I already said, the scenario is where the rider has parted company with the bike. If the rider is still aboard when they hit the wire their body shouldn't touch the wire (though they may well get flung over the top and into the opposing carriageway...)

Aidan1

Suffice to say if you're moving towards the barrier at, say, 2 metres per second, your impact force against the barrier will be the same NO MATTER WHAT your speed along the barrier is.

Thats my point. Your movement towards, and impact against the barrier, at any given angle of incidence is a function of your forward speed. The faster you are going, the harder you hit.

Your '2 metres per sec' is a straw donkey, as is insisting, all of a sudden, you were talking about different angles of incidence all along.

In other words, you still haven't answered my question. 30kmh at 5 degrees, or 120kmh at 5 degrees. Still saying theres no difference?

popebenny16

Just to reply to Mr P above:

In the mean time deaths due to poor "country" roads, poor driver training and various other things just plod along, not making the big headline but killing more people.

I drive on average 45,000 km per year on Irish Roads. The number one reason, by far, for road deaths is driver error, and that error includes drink driving, dangerous driving, unsafe overtaking, speeding. I read a lot about poor country roads. If they were that poor then road deaths would be the number one killer in the country. The roads themselves arent dangerous, it is the idiots doing 80kph on them just because the limit is 80 kph.

The actual cost of putting crash barriers on motorways is a small part of the cost. We have not had many motorway deaths simply because we have not had that many motorways. 5 years ago there was the Naas by-pass, Portlaosie by-pass Celbridge to kilcock and the small bit of M1 and M11 as well as M50. Now there is continious motorway from Dundalk to Portlaoise, as well as many other extensions (eg the M4 is now twice the distance it was). This will logicly increrase as motorway milages increase. Motorways are ther safest roads because you cannot cross over them, and dangerous overtaking is the main cause of road accidents in Ireland.

There is no point in waiting for a big crash and someone else getting killed, or as you have so crassly suggested wait untill more people get killed on motorways by cross over deaths than on other roads before something is done about it, there is plenty of money for it to be done now.

Hotblack Desiato

Aidan1 wrote:

Thats my point. Your movement towards, and impact against the barrier, at any given angle of incidence

That's where you're going wrong. The angle of incidence is a function of the forward speed (strictly, forward component of velocity) pre-accident.

The faster you are going, the harder you hit.

Wrong. You're confusing speed (scalar) with velocity (vector). You don't go TRON-like from 120km/h forwards to 120km/h sideways.

Your '2 metres per sec' is a straw donkey, as is insisting, all of a sudden, you were talking about different angles of incidence all along.

Of course I was talking about different angles all along, because that is what happens in reality, and I've explained this to you several times now.
2 metres/sec is an example, but it's a realistic enough one, giving a rider in the centre of the outside lane 0.5 - 1 sec before hitting the barrier. It could well be slower than that, it could well be faster, but not by all that much.

MrPudding

popebenny16 wrote:

Just to reply to Mr P above:



I drive on average 45,000 km per year on Irish Roads. The number one reason, by far, for road deaths is driver error, and that error includes drink driving, dangerous driving, unsafe overtaking, speeding. I read a lot about poor country roads. If they were that poor then road deaths would be the number one killer in the country. The roads themselves arent dangerous, it is the idiots doing 80kph on them just because the limit is 80 kph.

Funny, I don't see carriageway crossovers on your list.

popebenny16 wrote:

The actual cost of putting crash barriers on motorways is a small part of the cost. We have not had many motorway deaths simply because we have not had that many motorways.

The death stats for different road type are worked out on miles traveled. Kind of like saying people in Ireland buy more Mercs per capita than people in germany. Yes there are less miles of actual motorways but the death are worked out on a ratio not something so simple as how many have died on one type compared to how many have died on another.

popebenny16 wrote:

Motorways are ther safest roads because you cannot cross over them, and dangerous overtaking is the main cause of road accidents in Ireland.

It is only recently you have not been able to cross over them. Even before the barriers were installed they were still the safeest type of road.

popebenny16 wrote:

There is no point in waiting for a big crash and someone else getting killed, or as you have so crassly suggested wait untill more people get killed on motorways by cross over deaths than on other roads before something is done about it, there is plenty of money for it to be done now.

You seem to be missing my point. The last thing I am trying to be is crass, just because you don't seem to understand an opposing point of view is no reason to call someone crass. I was simply pointing out that motorways and dual carriageways are a lot safer than other types of road. Every weekend people are dieing on our roads. We are so used to it now it is effectivly being ignored.

When there is a crossover accident it tend to be a very spectacular affair (probably because they did not / do not happen often.) As a result there is a media frenzy and our knee jerk government reacts by deciding to install barriers everywhere simply to be seen to be doing something. It is an easy win for them.

They know hardly anyone dies but it is easy to get good publicity from doing something after major media hype.

I will say again, it is sad for anyone to lose their life but in a situation where there is a finite budget the money should go where it would be most effective. I mean most effective at saving lives not most effective at answering a histerical media.

MrP

Hoof Hearted

Aidan1 wrote:

Thats my point. Your movement towards, and impact against the barrier, at any given angle of incidence is a function of your forward speed. The faster you are going, the harder you hit.

Your '2 metres per sec' is a straw donkey, as is insisting, all of a sudden, you were talking about different angles of incidence all along.

In other words, you still haven't answered my question. 30kmh at 5 degrees, or 120kmh at 5 degrees. Still saying theres no difference?

There is a difference, but still sideways speed is small.

5 degrees at 120kmh: Sideways speed will be 10.4kmh.
5 degrees at 30kmh: Sideways speed will be 2.6kmh

If you take into account the protruding supports of the cheese graters barrier, these will strike the vehicle at the full 120kmh. If the vehicle is a motorcycle, may the motorcyclist jump at the right moment to avoid being turned into shredded......

Eye

As a motorcyclist myself and it being my only form of transport i have to say i am utterly appalled at the decision to use these wire barriers on roads, as i speak the N24 from carrick-on-suir (where i live) to mooncoin is being fitted with these and all i can say is god help bikers.

The poles are spaced approx 10-15ft apart and then the cable running along them under what i believe will be approx 100lbs of tension. if a biker comes of his/her bike for whatever reason then I'm sorry to say but they stand little or no chance with these barriers.

If your going to use a barrier use a proper concrete barrier, if the same biker is to hit that, fair enough they may still be killed, but they will most likely be in 1 piece then the family wont have to pick up body parts from the road as would be the case with these death traps they are busy installing.

Between getting sliced by the wires or impalled on the poles, i think i'll be sticking to secondary roads in future, and doing what i can to protest against these ridiculous barriers