News

A329M crash barriers 'saving lives'

January 04, 2011

Crash barriers installed along a stretch of motorway in Wokingham to help protect motorists are “definitely doing their job”, highways bosses have said.

Since spending around £650,000 to have barriers installed along the A329(M) Wokingham Borough Council has said it has not received reports of any accidents where people have been injured.

Barriers were installed along a stretch of the motorway, between its junctions with the Coppid Beach Roundabout and Winnersh Triangle, last spring.

This was just weeks after Paul Payne, 23, from North Yorkshire, was killed on the A329(M) when his car crossed the central reservation and collided with a van in February.

His tragic death sparked a wave of calls from motorists, and Mr Payne’s family, for barriers to be installed along the stretch of the motorway where there was no man-made protection for drivers.

Fresh calls for A329M crash barriers

A group calling for barriers set up a page on the internet social networking website Facebook which attracted in excess of 1,500 members.

Wokingham Borough Council decided to go ahead and use its own money to install barriers after twice failing to secure around £4 million from central Government to fund them on both the A329(M) and a stretch of the A33 in Spencers Wood.

Since installing the barriers there have been several accidents where cars have collided with them, however, none have caused any injury to the occupants of the vehicles involved.

Councillor Keith Baker, executive member for highways and transport at the borough council, said the barriers are “absolutely” serving their purpose.

“Clearly the statistics are proving that point,” he said.

“No one can cross the central reservation when an accident occurs as the barriers absorb the speed of the car and deflect it back into the road. There is the chance existing traffic could hit them, but I don’t believe that has happened and the barriers are definitely doing their job.

“I am absolutely in support of anything which saves lives.”

When asked about the relative risks posed by a driver crossing the central reservation and colliding with an oncoming car, or a vehicle hitting a barrier and deflecting back into the flow of traffic, the ward member for Coronation said: “To me, I would class the risk as a lot less since the barriers absorb a lot of the speed.

“A driver would have to be really, really travelling extremely fast to have the barrier absorb the large amount of impact and speed to throw it back across the carriageway.

“I’m not saying it cannot happen but there is a much lower risk then going straight across.”

Cllr Baker said the authority intends to install more crash barriers along the stretch of the A329(M) between Winnersh Triangle and Reading.

However, he said the project has been delayed while railway incursion work is carried out on the stretch of road.

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@ Bluedoodles if 2 cars collide head on,and both cars are travelling at 70mph then the crash has a 140mph impact speed. I can confirm this be true as I worked at the TRL in 98-2001. any head on impact speed greater than 80mph will almost certainly result in a fatality regardless of vehicle (tanks excluded!) I can also confirm that these sort of impacts are very, very rare as drivers almost always have a reaction time to slow the car, so rare in fact that manufacturers are not required to test vechcles impact speed over 80mph thats 80 into a wall or 2 cars doing 40 head on.

Wagner
05/01/2011 at 17:39

*Sigh*

OLDMAN!,

why are you trying to tell me the barriers are necessary? I have stated, in plain English, that I think they are a good idea. They have probably saved lives. They will probably save lives in the future.

You won't find a comment from me suggesting otherwise but you seem to have it in your head that I need convincing.

I've been driving for years, thanks, and I know the stretch of road quite well. Please try to debate the issues on here having read what the other contributors have actually said and without trying to belittle them. It'll be easier all round.

Floater, Reading
05/01/2011 at 14:58

Floater – I may be wrong but it sounds like you have never driven or do not know this stretch of road that well

As someone who drove it on the opening week and have done so many times since I know it very well -

If you listen to the local traffic reports, especially at this time of year there are numerous report of ice / slippery road along the stretch of A329M where the barriers have now been fitted (its mostly the stretch between the Winnersh and M4 junctions)

It is a series of long sweeping bends and is very exposed with no road camber – in the dry its quite safe, wet it can get slippery at less than 70mph, in the very cold it becomes an ice rink

The cars that leave the road always tend to drift across the grass reservation and into the opposite carriageway, obviously on the opposite bend direction they drift out towards the nearside of the road, as a friend once did!

It was always a bad design that required barriers and or wind breaks to help d stop the icing of the road

All the locals plus many Reading residents know of this problem, it was WBC who seemed to ignore it for many years

OLDMAN!, Reading
05/01/2011 at 13:49

At the end of the day, the issue of barriers are a no-brainer. I don't think you need to quote statistics to prove that these barriers will so, and probably have already saved lives.

Blue Doodles, West Reading
05/01/2011 at 10:32

@ OLDMAN!

"Floater – your actual words were –

‘’would/could? How do you know that on each of the the three occasions you mention the cars would have crossed the central reservation? To regard it as a certainty would suggest that there ought to be three or four "head on" 140mph crashes every year. There weren't’’

Which seesm to imply that the bariers aren’t required"

Trust me, there's no implication. The barriers are a good idea.

However, the mere fact that three cars collided with the barrier is no indication that they would have crossed the reservation if the barrier were not there. What was the speed of the vehicles when they hit the barrier? The direction of travel? The weather conditions? etc etc.

I like that the barriers are there. I think they will (and may have) save lives.

I don't think Cllr Baker should be claiming "proof" of their success after such a short time. Clear now?

Floater, Reading
05/01/2011 at 10:02

Actually, having said that, in a "perfect" Newton's cradle (the name for the "executive toy") the two ball scenario would just end up with the balls bouncing back off the pack again and again (not stopping as I incorrectly stated), which is of course not true in a head-on car collision.

One thing that I didn't mention is the rate of change in momentum. Consider the damage done by jumping out of a two storey building onto a concrete floor compared to a big air-filled cushion. In both, you've jumped from the same height and come to a stop at the same place (ie lost the same kinetic energy), but you've done so with a different rate of change of momentum. The faster the change, the more damage done. In the head-on scenario, the change in momentum is almost instant. In the stationary car scenario, the change in momentum is cast over a longer period of time, including the rolling to a stop of the crashed vehicles. Therefore, although there is double the energy, there is more time for that energy to dissipate in road friction etc.

As I said, this is a complex discussion on many physics forums, and there are disagreements over technicalities mainly caused by the "imperfect" (from a physics point of view) nature of car collisions. That's why they use crash test dummies at TRL to work out the impact on people of such collisions. But as I said, the impact of two cars head on at 70mph is very much not the same as one car at 70 into a parked car.

@Oldman - nice post. Like it.

mavdo, Wokingham
05/01/2011 at 09:55

Sigh...

@Dormouse - this is the subject of many a discussion on physics forums. You are correct in saying that there is twice as much kinetic energy to start with (O-levels always were much better then our comparatively easy GCSEs) because the energy is proportional to velocity squared. However, to cut a long story short, you are ignoring the fact that in the stationary car scenario, the car that was stationary would end up moving after the crash, and therefore there would be kinetic energy remaining after the crash (compare this to the "executive toy" with metal balls swinging on strings).

In fact, if you use this executive toy and swing one ball into the pack, the end ball shoots off at the same speed (net KE loss = 0), whereas if you drop the two balls at either end into the pack at the same time, they both stop (net KE loss = E, ie non-zero) and all that energy will be lost in heat, with perhaps slight deformation of the balls. So, if anything, it's exactly the opposite of what you said (even going far enough the other way to prove me wrong too). But then you add in friction and crumple zones etc and you have ways of dissipating energy. However, the cars will still be moving in the stationary scenario, and the overal energy loss is therefore similar.

Whilst I will admit that the two scenarios are not entirely *identical* as a net result, the impact speed *is* 140mph in both cases, and two cars hitting head-on at 70mph is far more similar to a stationary car being hit by another at 140mph, rather than 70mph.

mavdo, Wokingham
05/01/2011 at 09:37

Before the barriers - 6 fatal / 10 seriously injured, accidents in 10 years (interestingly nearly all in the same spot / stretch) Average – 1.6 / year

After barriers – ‘0’ fatal or serious (okay that’s only over 8 months but statistically looking good)

Floater – your actual words were –

‘’would/could? How do you know that on each of the the three occasions you mention the cars would have crossed the central reservation? To regard it as a certainty would suggest that there ought to be three or four "head on" 140mph crashes every year. There weren't’’

Which seesm to imply that the bariers aren’t required

So 1.6 per years is not 3 or 4 but also not so far off and these accidents aren’t at 140mph head on for several simple reasons – speed degradation from crossing the central grass reservation / other drivers taking avoidance / and often the cars do not actually hit ‘head-on’

Also the woman who was ‘injured’ when hitting the barrier’s recently left hospital with no problems – she was taken as a precaution as she complained of neck pains, not unusual in any accident!

OLDMAN!, Reading
05/01/2011 at 09:27

@mavdo

2 cars each at 70 mph is not the same as one at 140 and one stationary. Unless they are in space perhaps. or on a frictionless road ;-)

On a real road there is resistance from the stationary car (friction between tyres and road) and twice as much kinetic energy will eventually be dissipated after the crash compared to the 70 vs 70 crash. Some of this additional energy will be dissipated as heat from the tyres etc of the stationary car, but much of it will end up deforming the structures of the 2 vehicles, either during the initial collision or as parts of each car hit the ground and eventually come to a halt.

Did you find your course notes - I can lend you my o' level maths notes if you want a read ;-)

Dormouse, Reading
04/01/2011 at 20:50

Floater, I see what you're trying to say about statistics but the fact is you can't really prove that any accident *would* end in a fatality had they not been there unless that is what actually happens. I can see that you believe a year with three non-fatal accidents is too small a data set to yield a result as yet, but you have to admit it is looking positive so far.

Vestan Pance
04/01/2011 at 14:34

@ mavdo

You said, "Two cars going head to head at 70mph each *is* the same as one car at 140mph driving into a parked car"

I don't have a masters, just a pretty shaky o-level, but I'm pretty sure that doesn't quite add up.

@ OLDMAN!

I know perfectly well how barriers work thanks. If you read what I wrote and not what you wanted to see you'll notice that I'm not suggesting the barriers won't or haven't saved lives, just that there's no (statistical) proof that they've done so.

Floater, Reading
04/01/2011 at 14:04

@Blue Doodles - well, it's proof that my degree certainly wasn't in English anyway :)

mavdo, Wokingham
04/01/2011 at 13:57

Interesting that the barrier has already saved lives, I'd have thought that people crossing quite a large grass verge like that would be a very rare event. Fair enough.

JFK
04/01/2011 at 13:45

Must've been a typo in your degree notes eh mavdo? ;)

Blue Doodles, West Reading
04/01/2011 at 13:40

'I could argue this all day, although I'd have to go and get the notes from my Masters degree in Physics to try and get you to accept the answer.'

Or you could just copy and paste the laste paragraph from the link provided:

'Now, if vehicle 2 was stationary and vehicle 1 hit it at 50 km/h, that would make a big difference compared to the rock wall. That's because now vehicle 2, having the same mass as vehicle 1 (rather than "infinite" mass, as the rock wall), is applying much less force to vehicle 1. '