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Poisson


Member Since September 27, 2010.

Recent Comments

"Ah, Le Poisson, casting yet more pearls before swine."
- apparently so!

"Do not give what is holy to the dogs; nor cast your pearls before swine, lest they trample them under their feet, and turn and tear you in pieces." Matthew 7:6

I don't consider myself a religious person by any means, but in this case the good book is spot on.

First, I commend you for getting input from VicRoads. However, I still don't think this type of populist dumbing-down of complex issues does you or your readers a service.

Barriers (like all road safety interventions) are a trade-off: cost v efficacy, capital cost v whole-of-life cost, danger of hitting an object v danger of hitting a barrier, cost / feasibility of removing a roadside hazard v cost / hazard of installing a barrier.

Is it more dangerous to hit a wire rope barrier or hit a tree? I'd take my chances with the barrier. A tree (sapling really) of only 100mm diameter can be fatal if hit at 110 km/h in a car. There is a famous instance in Perth where two guys were killed in a ute (Maloo, I think) which hit a tree on the Mitchell Freeway. The tree concerned was only 150mm diameter!

Barriers are rated by "test levels", ranging from TL1 to TL6. A TL1 would be a ligtweight temporary barrier used at roadworks, while a TL6 would be a two metre high reinforced concrete structure designed to restrain an out-of-control petrol tanker. Most wire rope barriers (and Armco) are TL3, which will restrain a car or SUV hitting at a given angle (don't recall off hand) at 100 km/h. Wire ropes can also be designed to TL4, but require a much greater deflection (and hence a clear space behind the barrier).

Because kinetic energy varies with the square of speed, a barrier which will contain a vehicle at 100 km/h may not contain the same vehicle at 120 (a 44% increase in KE). Again the trade-off: do we spend a lot more money on heavier duty barriers to protect speeders from themselves? Or do we not provide barriers and let them take their chances with a tree or rock face?

Some comments on the examples from your articles above...

"Two men killed in horror crash". A 16 year old driver (who may have been a learner) towing a trailer (illegal for a learner) drove off the wrong side of the road at such speed the vehicle ended two metres up a tree. Please explain how the barrier caused this crash.

"On the South Gippsland highway, there are barriers placed where there is no evident danger..." On the face of it, that barrier seems superfluous. However, are there hazards which can't be seen in the photo? Placing barriers where there is no hazard is both counter-productive and expensive.

"Which here is the greater hazard, the vegetation or a broken-down vehicle?" I won't lecture you about the irresponsibility of placing a vehicle in a hazardous situation. However in this case the "vegetation" would definitely be more hazardous than the barrier. The trees which are clearly visible in the photo are more than big enough to cause a fatality if hit. Further, the trees are there at all times - a broken-down vehicle would at most be an occasional and (hopefully) temporary occurrence. The barrier is closer to the road than desirable (3m being recommended) but it is necessary to allow sufficient deflection distance between the barrier and the object. Again, there is a trade-off: somebody did a risk assessment and concluded that a barrier a bit too close to the road was a safer situation (all things considered) than no barrier or a barrier too close to the trees.

"At night, just over a rise..." Frankly I don't see the issue here. The barrier is set well back, the car is entirely off the traffic lane and in fact almost entirely off the shoulder. I doubt it could have pulled further off the road regardless of whether the barrier was there or not. Anybody who drove into that car should not have a license and /or should be prosecuted for negligent driving.

As I said at the outset, barriers are a trade-off, and are (should be) only installed where there is no safer or more practical option. Wire rope barriers are undoubtedly a hazard for motor-cyclists, but so is any other type of barrier. And as rightly pointed out by VicRoads, it's not the ropes themselves which cause injury but the posts. What was left unsaid, is that hitting a tree or rock-face or going over a cliff on a motorbike is equally or more likely to cause injury or death.


*Typo - should read "if the road authority..."

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