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Old 10-31-14, 07:30 AM
  #86  
wphamilton
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Originally Posted by Six jours
I doubt that you will ever find a stat about the number and severity of injuries in fatal car-bike interactions. I know that in my time as a paramedic, car-bike fatalities were usually a gigantic mess. I can't recall ever having been to the scene of one where the cyclist was pretty much okay except for the massive head injuries. I mean, when you really get tagged by a car, there's a lot of energy involved. It'd kind of be like jumping off an overpass and expecting a helmet to save you. It's possible, I suppose, but more in a theoretical kind of way.

As for the assertion that a bicycle helmet is useful in preventing traumatic head injuries, well, that's been debated for years here, and is unlikely to be settled any time soon. Let's just say that it's not exactly a settled issue.

And yes, I do know why motorcyclists wear heavier helmets than bicyclists. It's because motorcycle helmets are expected to help prevent brain injury in high-energy crashes. Kind of like those involving bicyclists and motor vehicles. If bicycle helmets were actually useful for that type of accident, then motorcyclists wouldn't have to bother with the multi-pound full-face down-to-the-neck deals they use.
I've seen plenty of hospital stats about traumatic brain injury among those in car-bike crashes.

It's not the same as jumping off a cliff - you kind of whiffed by the main thing I was trying to get across. Your head hitting the ground, the energy and impact depends on the height of the fall. Not the speed you're going, not what causes the fall, not how big or fast the car is. Your helmet is rated for 300g and will afford that same protection in every situation. When you're struck by a car, unless you are thrown up and then fall you will fall about three or four feet. When you're riding at 10 mph and slip on leaves, you will fall about three or four feet.

Your energy equation doesn't make sense from a physics viewpoint, because you're assuming that the cyclists helmet is asked to absorb the kinetic energy of the moving vehicle. If the vehicle strikes you in the head, then your head's momentum is changed as a result and you can relate that to an acceleration, but the total energy of the vehicle isn't very informative in this situation.

It's also not as useful if you're thrown or slide into an obstruction at a high velocity. This would seem to be more dependent on the cyclist's initial speed and random chance than on the motor vehicle.

Rotational TBI is the other potential danger, and IS debated here. The best we can say with any confidence is that some traumatic brain injuries cause by crashes with motor vehicles are caused by rotational forces. These may or may have a greater likelihood with motor vehicles. It would be a fallacy to represent as known or settled that helmets are useless in these accidents due to their lack of protection against rotational forces.

Last edited by wphamilton; 10-31-14 at 07:34 AM.
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