Assume someone looks into their reaview mirror 2 seconds before being rear-ended. They have just enough time to react, but the impact is inevitable. The car (automatic) is in gear and the brakes applied, would releasing the brakes have any affect on the force that each driver is subjected to by the impact? I hope that was clear.
Maybe “Im at a red light, car in gear brakes applied. I see that someone is going to rear end my car, should I release the brakes or would that just make me a danger to everything ahead of my car?”
If it’s unsafe to proceed ahead (say stopped at a red light with traffic crossing in front of you), I’d say stand on the brakes and put your head against the headrest. Brace yourself with the steering wheel (Oh, and be ready for that airbag).
Of course, the force of collision will be less if you’re not standing still, but moving in the same direction as the car that’s rear-ending you. So, if it’s safe to move ahead, do so, post haste (screeeeech!).
In addition to what Ringo said, also take speed into account. If the person is creeping up behind you (say you’re at a red light and they’re coming to a stop, or there foot slipped off the brake etc) I would just stand on the break pedal (leave the car in gear or neutral, NOT park, you could damage the tranny), if they’re just going to tap you, the impact shouldn’t be horrible. ITOH if they’re coming at you going anything over 20 or so, I’d step on the gas as to minimize the impact.
That seems fairly obvious to me, as does Ringo’s assertion that being in motion lessens the impact force. I guess what I was getting at is whether or not the friction from the brakes/tires adds an appreciable amount of impact force than if a car were in neutral. I should have said neutral in the first post, lesser combined speed equals lower impact force, or something like that. I was wondering more along the lines of inertia and its relation to increased friction, via brakes. Sorry I’m not more articulate, I’ve never taken a physics class, and am guessing at terminology.
I think bracing yourself against the steering wheel could be potentially problematic - if you are propelled forward by the impact and your arms are locked, you could end up with:
-Broken thumbs (if they are hooked inside the steering wheel rim)
-Dislocated/broken shoulders (if your arms are locked straight and the heels of your hands are against the steering wheel)
-Torn/pulled ligaments/tendons (if a sudden force is applied against your tensed muscles)
Any of these conditions could impair your ability to exit the vehicle after the impact, which could be nasty if fire is involved.
I think it would be better to take your hands off the wheel and hold them up half-flexed, but not between your and the wheel, as the airbag might cause you to punch yourself in the face.
I recently saw this exact question on the exam for a California driver’s license. It was the one question I got wrong. The question was pretty much what the OP posits. I answered that standing on the brakes is the right thing to do. Turns out that the DMV disagrees.
Of course they’re wrong, but go figure.
The idea is to minimize the acceleration of your own car. I want to get the maximum amount of kinetic energy out the collision as possible. Any left over KE is going to get transferred to the cars and occupants, and KE is what tends to hurt you. I know momentum will be conerved in any case, so what do I want: my car to receive a large transfer of KE, or the KE to be used up in insurance deductibles?
MonkeyMensch, I wouldn’t be so sure. You may indeed use the KE up in insurance deductibles, however it might turn out to be HEALTH insurance deductibles, not automotive.
The KE you speak of has to go somewhere, it won’t just dissappear. If you’re car ends up gaining KE at the end of the collision, so be it. You’ll be moving, but THEN u can use the brakes to dissapate that energy.
When you say that you want to minimize the acceleration of your own car you are correct, but standing on the brakes will not achieve this. The total time spent accelerating will probably be shorter, however the magnitude of the acceleration will be quite high - you will get a short, sharp movement. Then the suspension will complain that the car is moving when the wheels are not, and the car will experience the reverse of the initial acceleration, give or take energy dissapated by the tyres sliding along the road somewhat.
In short, the car receiving a large transfer of KE is probably a good thing, because at least it won’t be transferred into you.
BTW, this is all dependant on the fact that there is no crossing traffic in the intersection, since moving foward at such times is generally not recommended.
I was in just such a rearender. I was in a Toyota 4runner, the car that hit me was an old Honda. I was stopped with cross traffic, and a number of DOT workers on the medium. I was in the left of 2 forward lanes, and there was a car to my right. I happened to look in my mirror to see the Honda actually accelerating about 50 feet behind. The car on his right honked, but he didn’t slow down. The officer estimated his speed at about 45 mph when he hit me. I did what has been described. I held tight to the wheel, put my head into the head rest and held the brake. I was more afraid of the T-bone I’d be subjected to if pushed into the cross traffic.
My SUV moved only a few inches, and had little visible damage. There was significant unseen damage, which I was told, would not have been as extensive had I not stood on the brake. The other car was totaled. Luckily, no one was seriously hurt. I got a chipped tooth, and some spectacular bruises one my shins, one arm and A small bruise on my abdomen from my seatbelt. My airbag did not deploy. The kids in the other car were okay. The first thing the driver said upon exiting the car was “I thought you would run the light so I was going to too.” His mother arrived and varified the car was a total loss… at least to him.
His passenger was wearing a belt, but he was not. He starred the windshield, and bloodied his lip. the sister was fine.
I don’t know if standing on the brake was a good idea or not, but my 4runner moved 3 inches. I hate to think what would have happened had I been pushed into traffic.