Crash barrier design

strassenwolf

I was thinking about putting this post in the recent thread on "NRA muppetry", but I'm not sure that what I'm about to describe definitely is muppetry. It does look a bit like it though.

I was driving along the M1 today between Dublin and Drogheda. (I don't drive much). They're installing/have installed crash barriers in the central reservation. The crash barriers are of the type often referred to as the "cheesecutter" - a long series of posts along the reservation with three pretty thick wires running from post to post. I know there are different types of barriers, each with their own claims.

The puzzling thing is not the type of barrier being installed, but the way it is being done.

Every so often along the motorway, there is a gap in the reservation. The gap is closed with a series of about 20 red and white poles. It could be opened (by lifting out the poles) to allow traffic use the opposite carriageway if necessary, e.g., in the event of resurfacing or to allow emergency vehicles to travel "the wrong way" down the motorway to get to a pile-up.

The wires and posts used as the barrier have, in at least three places south of Drogheda, been installed parallel to the red and white poles - ie there is a continuous stretch of barrier for several miles. I would have thought it would be more sensible to stop the barrier either side of these gaps. That way, if there was an emergency, all that would be needed would be removal of the poles, rather than also having to do a lot of wire cutting and removal of the metal poles which hold the wire.

I'm probably not explaining this very well. It just struck me that building the barrier in this way seems rather odd and could be a hindrance in the future. I don't know if this is the case along the other motorways, but I'm sure other people on the board do.

Muppetry?

Andrew Duffy

Perhaps the wire barriers are easy for emergency services and motorway maintenance to detension, allowing continuity of the barrier across the emergency crossover points?

DubTony

I've noticed this on other roads. (Can't remember where exactly) It's madness. The lst thing an ambulance driver wants to do is get out of his vehicle and start taking barriers apart. After all, the reason the poles are there is to allow emergency and work vehicles access to the other side of the carraigeway. And with our roads clogged up more than ever, they're even more important.

I wonder how long it will be before someone sues the state because a relative died after an accident because the amergency services couldn't get there quickly. While I'd imagine that a fire engine / rescue vehicle might have the necessary cutting equipment, and people with the ability to use it, it still adds valuable seconds, or even minutes, to their journey.

Another point is how close these barriers are to one side of the motorways. Instead of lifting the chickenwire and replacing it, on some sections it has been installed just a couple of feet from the road. A car coming through the median would go through the hedge and travel almost to the carraigeway before hitting the barrier. This would still cause panic on the other side as a natural reaction to seeing a car travelling toward you is to swerve. It would take a very calm and collected person to figure out that the barrier wil stop it so there's no need to take evasive action.

strassenwolf

strassenwolf wrote:

Muppetry?

Apparently not.

Andrew Duffy wrote:

Perhaps the wire barriers are easy for emergency services and motorway maintenance to detension, allowing continuity of the barrier across the emergency crossover points?

I've been in touch with the NRA road safety division. They say that it is possible to remove the wires from the posts which hold them. The emergency services have been/are being trained to remove them so that a vehicle could cross over into the other lane. It only takes, I was told "a couple of minutes" to do this. (Could still be a crucial couple of minutes, as DubTony points out,but I suppose one fireman could remove the red/white poles, while another lowers the wires). They didn't tell me how this whole procedure works, i.e. how to remove the wires from the holding posts. (see below for one reason they might not wish to tell me!)

The reasons why they have to have the continuous wire barrier are twofold. Firstly, if someone crashed into the red/white poles, they would not be strong enough to stop the vehicle going into the opposing lane. Fair enough. But wait for the second reason. Apparently, there is a problem with people sometimes removing the poles to (as I was told) "take a short cut". I suppose this might be where someone has missed their junction and won't wait until the next junction to turn back! i.e. they will park their car beside the fast lane of the motorway while they remove these poles. (Whatever you say about the NRA, they are up against it with some people).

DubTony wrote:

Another point is how close these barriers are to one side of the motorways. Instead of lifting the chickenwire and replacing it, on some sections it has been installed just a couple of feet from the road. A car coming through the median would go through the hedge and travel almost to the carraigeway before hitting the barrier. This would still cause panic on the other side as a natural reaction to seeing a car travelling toward you is to swerve. It would take a very calm and collected person to figure out that the barrier wil stop it so there's no need to take evasive action.

Absolutely agree. I noticed this yesterday. They haven't completed putting in the barrier on the Dublin-Drogheda section yet. It is in place from, I suppose, one of the Balbriggan exits to the Drogheda exit alongside the South to North carriageway. I though perhaps they were working in one direction (North to South) and then going to go back (South-North) putting in the wire alongside the other carriageway.

Victor

DubTony wrote:

Another point is how close these barriers are to one side of the motorways.

Barriers are usually placed on the concave side of a curve.

http://273k.net/cyclegallery/images/2005-06-30/2005-06-30_161044_1185.small.jpg

In this pic, in the event of loss of control, the default direction the red car would take would be towards the first bridge column*. For the high truck in the distance, it would be towards the hard shoulder.

* Bridge columns, etc., will tend to have barriers on both sides anyway.

Instead of lifting the chickenwire and replacing it, on some sections it has been installed just a couple of feet from the road.

Why remove the chickenwire? (a) it provides support to the hedge which prevents glare from oncoming headlights (b) it provides that much little more protection (c) to date 100% effective at preventing chickens from crossing motorways.

BrianD

Something tells me the NRA forgot about these cross over areas that they designed into the road and have some story concocted to cover it up.

The story about the people removing poles is hillarious. I don't doubt it happens (actually I have seen someone do a u-turn at one of these) but it is very Irish that something of general good and benefit can't be used or implemented because a paltry few will abuse it.

Anyway, my views on safety barriers are well knows...waste of money, give the money to hospitals on the route instead.

mackerski

BrianD wrote:

The story about the people removing poles is hillarious. I don't doubt it happens (actually I have seen someone do a u-turn at one of these)

I was travelling north on the M1, just north of the Santry junction, at daft-O'Clock in the morning some years ago. Ahead of me, about level with a crossover point, I saw what appeared to be a vehicle pulling a very slow three-point turn. In fact the driver was reversing from a parked position on the shoulder into the median crossover, perpendicular to the traffic. For his oblivious muppetry and ignorance of correct motorway discipline I treated him to a good blast of the horn on my way by, seconds later.

Anybody who by now has guessed that this was one of our highly-trained guards, award yourselves ten points...

Dermot

jd

mackerski wrote:

Anybody who by now has guessed that this was one of our highly-trained guards, award yourselves ten points...

Dermot

what happened next ?

mackerski

jd wrote:

what happened next ?

I drove home. He probably cranked up the radio, had a snooze and eventually issued a ticket to some poor unfortunate for a minor speed limit infraction on an empty motorway. But most importantly, the public slept safely in their beds.

What could he do? It wasn't a built-up area, and it's no offence to alert another driver to your presence, especially if said driver is busy pulling a leisurely three-pointer on a motorway in front of you. As miffed as he no doubt was, he was squarely in the wrong. I'd expect better judgement from a lesson 2 learner, from a cop it's just astonishing.

Dermot

strassenwolf

Before starting this thread I looked for earlier threads but none seemed to be that closely related to this issue. On one of them there included a post with a link to a site which showed a video of a crash barrier (Flexfence) similar to the one in use on the M1, though with 4 wires instead of three. I think that site was this one http://www.ingalcivil.com.au/highway/guardrail.htm. The video is worth looking at, but this point

DubTony wrote:

It would take a very calm and collected person to figure out that the barrier will stop it so there's no need to take evasive action.

is well made, especially if there is only going to be one barrier along pretty straight stretches of the M1 and its going to be quite close to one carriageway.
This three-wire system shown at http://www.hill-smith.co.uk/wire.html also seems to be something similar to the barrier along the M1, the M50 (as shown by Victor earlier on in the thread) and perhaps other motorways. Though it doesn't look exactly like it.

The site includes the statement:
"An additional benefit of Brifen WRSF relates to the availability of emergency cross-over points which can be dismantled in minutes to allow rapid access by emergency services in the event of a complete blockage of one carriageway".

(WRSF=wire rope safety fence).

Victor

A google for "Wire Rope Safety Fence video" shows http://www.brifen.co.uk/video.html

DubTony

Victor wrote:

A google for "Wire Rope Safety Fence video" shows http://www.brifen.co.uk/video.html

Well, that just proves that the guys that fitted them and the people that told them to fit them there are all morons. In the 1500kg test video the whole car crosses the "original" fence area and then goes back in. Next time you're crawling along the northern carraigeway of the M50 near Tallaght, take a look at how close that barrier thing actually is to you.

I wonder how long it will take them to fix / replace the fence when someone does hit it.

Hotblack Desiato

The other problem with these wire rope fences is that they are lethal as far as motorcyclists are concerned. A rider will have less serious injuries hitting a smooth concrete barrier (at an acute angle, they typically glance off it) than a wire rope barrier - both the wires and the posts slice off limbs with ease. Several countries in Europe whic have wire rope installed are now removing it - at least in particular risk areas like curves. But once again the NRA goes for the bargain bucket "solution" and never mind that they'll probably have to rip it out in a few years time and replace it with something better. They were convinced chicken wire was adequate before and proven wrong, I doubt the wire rope barriers will prevent crossover accidents.

Victor

I think "solid" barriers should be used at curves, the risk of a cross-over is much higher in such locations.