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Guard Rails And Crash Barriers

Car-lamp-postOne of the hazards of losing control when travelling at speed is that you’re going to hit something. What usually springs to mind if you dare to let your imagination linger on this is hitting another vehicle. However, this isn’t the only thing that you can hit – there is a reason why they do the lamppost test while crash testing, after all. Sometimes, if you lose control and/or let your attention wander (or, in most accident cases, first letting attention wander and then losing control), you don’t end up on the other side of the road but going off the edge of it. This might be somewhat better for the people in the oncoming vehicle but it’s definitely not good news for you. In fact, according to ARRB Transportation Ltd., 30–40% of all serious and fatal crashes in Australia are caused by someone going off the road and colliding with a fixed object such as a lamppost, rock or similar.

Let’s just say that hitting a rock, lamp-post or similar in real life is nothing like hitting one in a computer game, where these obstacles simply disappear after being struck while your virtual car carries on at 200 km/h.  Need For Speed games have a lot to answer for… (though I kind of like the special Porsche edition of the game with the nice scenery).

Vehicles come with a range of systems to stop the car drifting off the side of the road.  Traction control and ABS braking help to prevent skidding. ESC (electronic stability control) kicks in to prevent oversteer or understeer. Lane departure warnings detect that you’re drifting towards the side of the road where treacherous gravel lurks (in the case of rural roads). If things do go to custard, many cars have side impact protection beams, curtain or side airbags and pretensioned seatbelts to keep you safe, while the car itself usually has crumple zones to absorb the impact.

Absorbing the impact is key in any crash. It’s the shock of impact where all the force of Object A (the vehicle) gets transferred to Object B (a lamppost), so if Object B is hard and unforgiving, Object A takes the forces and gets damaged. If Object A is also hard and tough, all that force has to go somewhere and often gets transferred to the occupants of the vehicle… and humans tend to be soft and easily broken. There are heaps of examples in everyday life where we apply the principle of absorbing impact to prevent damage. We wear shoes with nice thick soles to protect our feet when walking or running (or at least we should). We lie down on mattresses rather than bare boards. We use mats when exercising on the floor and boxing gloves if we like slightly more aggressive forms of exercise. And there’s a reason why a scrum machine is padded like heck.

Guard RailIt’s not just the cars that have to absorb impact, either. Guard rails are becoming quite a common sight around many roads in Australia, especially in high-risk areas where the amount of traffic and/or the design of the road is likely to lead to a car going off the road. You also see them in places where going off the road is going to lead to something much worse than hitting a lamppost. You can miss a lamppost if you go off the road and may end up hitting a nice forgiving bush instead. You can’t, however, miss a cliff very easily…

Guard rails and crash barriers will stop your car going off a cliff or skidding onto the wrong side of the road and into an oncoming B-train if you hit a patch of ice or oil. However, you may have spotted the wee problem looming here: if they haven’t been designed right, they become hard, rigid objects in their own right and also cause problems when you hit them.

Road designers and road safety buffs are not stupid and are aware of this problem. People around the world are thinking up ways to make guard rails and crash barriers even safer. It’s a bit of a balancing act. Make the barriers too soft and flimsy and you’ll just plough through them and end up going through into that rock or off the cliff.  Make them too hard and they’ll have the same effect as hitting a lamppost but with less chance of missing it.  Make them springy (e.g. piles of old tyres like you sometimes see at car races, or tyres strung along like very ugly Christmas tree decorations like you see on the side of docks for big ships) and you get the problem of being bounced back in the other direction far too quickly.

What the designers like to do is to make a crash barrier that’s soft enough to slow you down but tough enough to stop you going off the road… and will allow you to slide along it so that you come to rest somewhere safe (and free from lampposts). Those fences made of very thick “wires” (more like metal cables) can do the trick, but they’re pretty nasty if a motorbike hits them, so some road safety experts don’t like them much. W-beams are “semi-rigid” structures that tend to the job a lot better.

However, there’s more to guardrails and crash barriers than just the actual barrier itself. The post the rail is attached to plays a role, as do the bolts holding the rails to the posts. The soil that the post is stuck into also affects how much energy the barrier will absorb for you.  Designers have also started thinking about putting things between the rail and the post – kind of like a washer sort of thing – to add an extra crumple zone.  They also have to think about what happens at the beginning and the end of the rail, and how easily a crashing car or motorbike can snag on the rail instead of sliding along to a safer place.

Public-Domian-W-Beam-4-1024x768It would be nice if they thought about making them look a bit more attractive, too.

Of course, it’s much better for everyone if you don’t get a very close acquaintance with a guard rail or crash barrier at all.  Let’s stop to think how you are most likely to whack into one. Cornering is usually involved, as is speed. Ice or other slippery substances can also play a role. On straighter bits, wandering attention is usually to blame.  The moral? Go back to basics and drive properly, rather than relying on driver aids, active safety systems, passive safety systems and crash barriers to save you.  This means that you need to slow down in the wet and cold, and don’t thrash your car at speed around the corner.  And for goodness sake, don’t try to play Pokemon Go while driving!