Motorway Central Reservation Crash barriers

BrianD

I notice that work is underway to retro-fit central reservation barriers on the M7, M9 and M1.

One thing that is liitle odd. At regular intervals there are cross over points on the m-way. This I assume is to allow a contra-flow system to be implemented or allow emergency vehicles to cross from one carraigeway to the other. The new barriers are going to block off all of these cross over points. To me this seems to be a short sighted. Any idea why they are doing this?

Tommy Vercetti

I *think* some of them were originally planned as toll booths, I am probably wrong though

BrianD

In the wrong place for toll booths. These are the gaps in the median that you see on all dual carraigeways at home and abroad.

Victor

It is possible that they are designed to be easily demounted, while retaining their safety role.

But this is Ireland.

BrianD

I doubt it! They new central barriers are not armco barriers but the steel rope type that is tensioned. Unless they wamt to remove a large section of it, these cross-over points are as good as closed.

You're right, this is Ireland!

laoisfan

would the tensioned steel ropes not pose a risk? i mean if a motorist crashed into them or even if the steel rope snapped?

--laoisfan

drane2

Correct me if I'm wrong here but as far as I recall all motorways in France have a strong crash barrier in the middle. The reason for this (or so I'm led to believe) is that it prevents people who go out of control on one side of the motorway from crossing over to the other side and into the path of oncoming traffic.

Genghis

Perhaps the tensioned rope provides a safer barrier - cars may 'bounce' better off this, helping them get back on their side of the road in the right direction, and the barrier may not be damaged afterwards (hence posing a risk of a second collision not being properly dealt wit and / or the cost or replacement / repair)?

Victor

I don't know the different performance criteria, but some barrier is better than none and apparently the cable barrier is much cheaper, so more of it can be installed for the same cost.

BrianD

Cable barrier is cheaper than continuous armco barrier. The barrier is about the same height as normal m-way barriers. To be quite honest, given the wide central medians on Irish m-ways it is less than necessary. The number of accdents involving cars going through the central median is very low.

mike65

Originally posted by BrianD
Cable barrier is cheaper than continuous armco barrier.

This is Ireland

The barrier is about the same height as normal m-way barriers. To be quite honest, given the wide central medians on Irish m-ways it is less than necessary. The number of accdents involving cars going through the central median is very low.

Dead ppl are dead ppl and you should'nt penny pinch if willing to spend billions on the primary nation routes.

Mike.

Victor

Originally posted by mike65
Dead ppl are dead ppl and you should'nt penny pinch if willing to spend billions on the primary nation routes.

Fair point, but there is a limit that you should spend on road or any other safety. That point is where that money would be better spent on other measures to improve overall life and society.

For example, putting a double barrier along the median won't save twice as many lives.

BrianD

My view is that on Irish m-ways and dual carraigeways where there is a wide median (much wider than those in the UK) crash barriers are surplus to requirement. If you want them on dual carraigeways why not require them on standard national roadways?

You could kit out a hospital for the cost of retrofitting these barriers!

mike65

Have you ever tried braking hard on wet grass....?

Mike.

BrianD3

There is a cable barrier on the Mullingar bypass (dual carriageway) It's only been there a few months and already has been hit twice. One accident was a fatal one involving a tractor and articulated lorry.

The cable barriers work on the same principle as the armco style barriers. When a vehicle hits, the barrier deforms and with the vertical supports giving way. The idea is to "guide" the vehicle along the barrier at a shallow angle. If the barrier is too rigid the vehicle could bounce back into traffic. If it's too weak the vehicle could break through into traffic on the opposite side of the carriageway.

BrianD3

BrianD

BrianD3 nice to meet you!

BrianD3

BrianD, cool nick

BrianD3

Kaner

I've seen these tensioned rope barriers in the US - they look really ugly after a few years when they get rusty - but I suppose they do the job.

Borzoi

Originally posted by BrianD

This I assume is to allow a contra-flow system to be implemented or allow emergency vehicles to cross from one carraigeway to the other. The new barriers are going to block off all of these cross over points. To me this seems to be a short sighted. Any idea why they are doing this?

Following reading this, I paid a little more attention to the median strip on my way up and down to Belfast today on the M1.

Yes, the new barriers do partly protrude to the cross-over points - I would guess that as the steel wire system relies on tension in the cables - they need to make use of the foundations here to properly anchor the system.

More bizarrely the existing Armco barrier is being dismantled where it did exist - around bridge supports on the median, to be replace with the cable system.

BTW the A1 north of the border has a narrower median and no barrier of any type.


On the way home the tiopic was being discussed on The Last Word, the NRA spokesman had three points:
1) They prefer a very wide median to a barrier system ie 25mtr, but land costs make this too expensive
2) Any median less than 15mtr wide will be fitted with a crash barrier, eventually. Some new roads will be built and then have the barrier added to avoid delays in renegotiating the entire road contract.
3) With regards to motorcyclists, the wire barrier system compared to Armco, the barrier is injury nuetral based on US research. His main point being that cyclists tend to skitter along at ground level in case of an accident and the most dangerous (ie potentially fatal) thing would be hidding the barrier supports - not the barrier per se.

Not necessarily agreeing with him here, but he did seem to be basing his and the NRA's opinions on research

BrianD

There is no doubt that the medians on the majority of Irish dual carraigeways are wider than their counterparts in the UK where often the central barrier is the median. I would surmise that many drivers who go through the central reservation either fall asleep at the wheel or have a lapse of concentration. The wide grass area will often allow them to recover control of their vehicle. With respect to the very small number of people who have been killed as a result of vehicles going from one caraigeway to another, many of them have travelling at excess speeds. Should we put armco barriers on our standard roads to protect these people from themselves?

Crossley

This NRA myth about 15m being enough to 'recover' is patent nonsense. At 70mph it takes 24 metres before a driver even reacts. After 24m you are well into lane 2 of the opposite carriageway ! On top of that the braking distance from 70mph is 73 metres and that's 73m on a dry surfaced road not grass ! When a car gets on to grass at that sort of speed all steering control is lost. You may as well be on ice. Ever seen what happens during a BTCC race say when a car goes off the circuit on to the grass ?

Also the argument that they're rarely needed is flawed. Next time you're on the road have a look at one of the few locations where armco barriers are installed. I'll challenge you to find a continuous length that's straight and unbuckled from numerous impacts. This leads to another topic of course, the fact that barriers when installed are never maintained and repaired. Bottom line is barriers cost money and so they're not a priority for the NRA.

Andrew Duffy

So multilane roads with grade seperated junctions and wide alignments are free, and it's just the barriers that cost money?

Have a quick think here, guys - which do you think is more expensive - buying a 15 metre wide strip of land or installing a steel barrier?

Victor

Originally posted by Crossley
This NRA myth about 15m being enough to 'recover' is patent nonsense. At 70mph it takes 24 metres before a driver even reacts. After 24m you are well into lane 2 of the opposite carriageway !

Most crossings would be at a fairly shallow angle, meaning that after 100m+ they would still be in the median.

Kaner

Seems to me that this is a political decision resulting from some flak Brennan got after an accident on the M1 last year.

There was a self-contradictory explanation of the NRA policy on barriers on their website, talking about lack of international standards, etc.

I think that wide medians are a great idea, especially when the time comes to add extra lanes. Maybe in rural areas they can use narrower medians to cut down costs. I would hope they use aramco or concrete rather than cable barriers on narrow medians. I can't see the cable barriers working with heavy trucks on a narrow median.

Crossley

So if wide non-barrier medians are such a good idea how come the only other country to use them is the U.S. which has a pitiful road safety record. And there from what I've seen they are seriously wide. I can't think of one European country that doesn't use barriers.

Kaner

I think the use of cable barriers in Ireland is a good thing. They don't cost that much and they will save lives.

The 2002 per capita road deaths for the US are the same as Spain, France and Belgium.

BrianD3

Also the argument that they're rarely needed is flawed. Next time you're on the road have a look at one of the few locations where armco barriers are installed. I'll challenge you to find a continuous length that's straight and unbuckled from numerous impacts. This leads to another topic of course, the fact that barriers when installed are never maintained and repaired. Bottom line is barriers cost money and so they're not a priority for the NRA.

The mullingar bypass is a prime example. A dual carriageway with a mixture of armco and cable barriers. The armco has been badly damaged in at least two places (and not repaired even though the impacts happened some time ago) The cable barrier is only there a couple of months and has already been hit 2 or 3 times. Before the cable barrier there was "chicken wire" and a hedge and there are a few lumps gone out of the hedge where vehicles have crossed over before the installation of the barriers.

Most crossings would be at a fairly shallow angle, meaning that after 100 they would still be in the median

Even 100m+ is not enough room to regain control of a car travelling at 70 mph or even worse an articulated lorry travelling at 50 mph. It is virtually impossible to steer or brake on wet grass at these speeds. As was already said, it's like driving on ice.

Should we put armco barriers on our standard roads

It would be impractical/impossible to put median barriers on single carriageway roads. With motorways and dual carriageways, installation of barriers is entirely practical and possible.

The type of barrier I would like to see would be a thick concrete wall with some sort of energy absorbing material in front of it. The idea of this material is to dissipate some energy so that there is reduced chance of a vehicle bouncing off the concrete and back into the traffic. Concrete is the only type of barrier that will stop truck crossovers. Cable/armco barriers can stop a truck crossover but only if the truck hits at a very shallow angle. Also a concrete barrier would be more motorcyclist friendly as there would be no barrier supports for the motorcyclist to become impaled on. The third advantage is that concrete would not need repairing after an accident. The impact absorbing material in front of it could be replaced easily enough. From what I've seen, armco and cable barriers require a lot of repair after an accident because the barrier supports are designed to be ripped up when hit (this is what allows the barrier to dissipate energy I believe) A lot of the time, the barriers are just not repaired after accidents - see above example of mullingar bypass.

Just my 2 cents

BrianD3