Here's how to survive a real rear-end crash … if someone is about to Liberace you, impolitely, in traffic, should you jam on the brakes and brace for impact, or not? The 'beer garden' physics of rear-end crashes is next.
A classic question from the beer garden engineer’s PhD playbook, from you:
"What’s the appropriate action to take if you are stopped at traffic lights or in a queue of traffic, and you spot that the vehicle behind you is about to crash into you at speed? Assuming you haven't either the time or space to move out of the way, what should you do to lessen the chance of injury?" - Co Flax
We’ll get to the brakes in a sec - but if you’re pressed for time, here’s the top five things you need to know about rear-end crashes.
One: These are the best crashes are the ones to have (apart from not crashing at all). Rear-enders: Typically a lot less severe than head-ons and side impacts. Certainly better than rollovers. Much more ‘walk away’ potential. In general.
Two: Adjust the headrest so that it’s at the same level as your head. People do the seatbelt, the seat, the mirrors - but they always neglect the headrest. It’s adjustable, people. If it’s got fore-and-aft adjustment, get it as far forward as possible without being uncomfortable to drive. This will minimise the neck injury potential #whiplash.
Three: Stop at least a car length from the car in front. Obviously. Bit of a buffer.
Four: If you’re turning across the oncoming traffic, keep the wheels straight if you’re awaiting a gap. That way, if you get Liberaced, it’s less likely you’ll get pushed into the oncoming traffic and be involved in a secondary head-on crash. Nobody wants that.
Five: If you are crashed into in this undignified way, straight up Main Street, take a moment in the immediate aftermath. Drive somewhere safe if you can, before getting out. If you can’t, don’t get run over, dazed and confused. Make sure the car is shut down, parking brake applied. In gear.
Head for the footpath (that’s a sidewalk - ‘Murica). Don’t get obsessed by inspecting the damage. Don’t stroll aimlessly in the traffic. Get yourself to safety. Be situationally aware.
"I have read conflicting opinions about this, with some saying to apply the brakes hard, making more use of the crumple zones to dissipate the energy, whereas others say to not apply the brakes at all, saying the impact would be lessened." - Co Flax
Injury occurs really fast in a car crash. The window of opportunity for the Grim Reaper to emerge from the green room and chalk you up is very brief. 80G for 80 milliseconds and you’re toast.
Problem #1 is that brakes can only supply in total about one G of opposing force. In the context of the 80Gs that’s going to kill you, it’s fairly insignificant. But this really doesn’t matter because there’s an even bigger problem for you, in the cabin.
Problem #2: The car’s going to accelerate forward, away from you at 20, 30, 40 G (briefly). You are going to be (subjectively) thrown violently backwards. The bottom half of your leg weighs what? 10 kilos? To keep it on the pedal you’ll have to supply 300 kilos of effort for a 30G hit. It’s not physically possible. Unless of course you can deadlift 600kg, your foot is coming off the brake whether you like it or not.
What you need for protection here is not foot on the brakes. It’s decent crumple zones. Padding. Crumpling absorbs energy over a particular distance.
Oddly enough, car crashes are exactly the same. More bent metal equals more protection for you - even though the damage looks worse - because the impact occurs over a greater distance, reducing the loads on you.
That’s why it’s so important for the engineers to do their jobs well, and for head office to give them the budget they need to get this right. Because excellence here really is the only option.
he crumple zones built into the vehicles - abutting the rigid safety cells that you and your loved ones ride in - they need to be ‘Goldilocks’ too, to limit the Grim Reaper’s window of opportunity.
"Also, some people say to brace for the impact, but others say to try and relax, citing that drunk drivers seem to come off better in a crash than their victim in the other car, because they were not tensed at impact." - Co Flax
Don’t brace. It’s really bad to put your hand out reflexively. Your arms are simply not designed to protect you, at 50Gs. If they’re locked out and they take the initial hit, it’s just going to be a significant orthopedic surgery challenge. If there’s an afterwards.
About the only thing you can do - if there’s time - is sit upright, place the back of your head firmly against the headrest, and exhale. That’s pretty much it. And don’t stress, because it’ll be over - one way or another - before you know it even happened.
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