Real brick walls give a bunch or even collapse when hit by cars. Proverbial “brick walls” are an assumed immovable object.
Colliding head-on with an opposite-direction same-kind same-speed vehicle is about the same as hitting a truly immovable object. The KE of the other car is what delivers that functional immovability.
Hitting almost any other real world object, except for a vertical concrete bridge abutment or tunnel face, will give at least some and deliver a slower, safer deceleration profile to your car. And therefore to your body. How much safer depends on how much give there is.
Accelerating backwards does close the distance between the vehicles faster, so it reduces the amount of time and space for the rearending car to brake.
Why? If you were the same weight and going the same velocity of the guy who is going to tackle you, you double the total momentum, and you would experience double the acceleration on impact than if you were standing still. You would also double the kinetic energy to be dispersed, and kinetic energy generally correlates to collision damage.
My first job was barrier analysis at Ford Motor Co. I spent a year developing software to analyze film from test crashes. Those are not brick walls, they are huge concrete barriers. For all practical purposes it is an immovable object. My colleagues and I had to explain to people all the time that if you hit a car of the same mass in a head-on collision at 30 MPH it’s like hitting the barrier at 30 MPH.
If you think about it in terms of violence of impact, then accelerating forward is your best bet. I mean, if you can accelerate forward fast enough that you match their speed before they hit you, then there is no collision at all.
Of course that only works if nothing is obstructing your way, or potentially hitting you, but the point is to show that accelerating backwards is the worst possible option.
In that particular instance, if someone hits you, and you are stationary, then you will be thrown back and possibly take injury from the fall. In the football case, I would agree.
It’s an entirely different problem. In a collision between two football players, the padding is usually sufficient that no serious injury would take place in either case. The objective is to stay upright and “win” the collision, not to avoid injury. For that, having initial momentum against the impending collision is better.
This is interesting. It also highlights how cars are made for people of specific heights. It’s been a while since I drove regularly, but I don’t think it’s possible for me to be in the “correct” position.
I doubt it would make much difference given that the car is going to be accelerated forward so hard away from your feet, at the point of collision, that you almost certainly aren’t going to be able to keep any pressure on the pedal anyway.
I think it would take an experiment to test that, I wouldn’t be so sure. You’re trying to mitigate peak acceleration, you’ don’t so much care about the car subsequently moving forward after impact. Peak acceleration occurs very quickly upon impact, it seems quite plausible to me that it occurs before there is enough acceleration to move your foot.
You may be right. Although if the peak is that quick then it may well be that brake/no brake would make no difference because the flex in tyres and suspension would make it irrelevant as to whether the brake was on or off.
Back in August on I-17 on the way to Grand Canyon a driver in the #1 lane apparently fell asleep and slammed into the left rear corner of our car in the #2 lane knocking it to the right at about 45-degrees. After that things are a blur. I’ve done my share of driving in icy conditions so I counter steered.
I partially went into #1 lane because I remember thinking “Jeez, don’t go over the embankment!” as the opposite direction was some distance away and there was no barrier, just an eight or ten downward slope to the center of the median.
I overcorrected which took me back to the #2 lane and I continued onto the shoulder where I stopped. I don’t think I touched the brakes until I was on the shoulder but with all the skidding I had lost a lot of speed from the original 60-mph.
No airbags deployed and the G-forces were low enough we didn’t suffer any neck pains but DesertRoomie somehow had a hairline fracture of a metatarsal, from bracing I assume.
There was no time for planning anything – it was all experience and mental rehearsing.
As I stated above I was in such an accident and took my foot off of the brake just before the truck hit me from behind. I went flying and immediately slammed on the brakes. Because of the anti-lock brakes I was was able to steer and avoid oncoming traffic, so there was that. If I had been in park no steering would have been possible. Airbags do not go off in rear end collisions until you hit something in front of you because you are being thrown rearward while the car in accelerating forward, thus you are in the safest position possible as long as you are belted and not twisted around looking to see what is hitting you. I recieved my head injury from the sun visor when I went off the right side of the road and the car quickly decelerated when it plowed into the dirt.
While very scary the safety features of my car (08 Altima Coupe) worked very well. The rear bumper and trunk crumpled in an accordion type fashion, absorbing the energy. I veered into oncoming traffic and was able to steer away from oncoming cars and got back on the right side of the road where I over corrected and ran off into a soft shoulder. That’s when I abruptly stooped as the ground was fairly soft and the car dug in and I was thrust forward, hitting my forehead on the visor.
So from my vantage point getting rear ended is not nearly as bad as a front end collision, UNLESS you are thrown into another car or object. The seat and seat harness work best in rear ended scenario as it hugs you into the seat, which is the safest place to be when accident happens.
At the time I was a supplier to Nissan and worked at the tech center. I knew people in the safety department and told them about it when I returned to work and they explained that everything worked as designed., a textbook rear ending.
Interesting thread and a topic I have thought about before, nice to get some solid information on it.
It seems to me that, extending the thought process, in a lot of cases you might be able to further reduce the risk of injury by proactively driving into the car in front - this both increases the distance between you and the rear-ending vehicle, which should mean they are travelling more slowly on impact, effectively increases the size of your crumple zone if and when they do hit, and reduces the severity of the impact between your vehicle and the one in front. I wonder if this has ever been done? I guess usually there isn’t time. And you’d look a prize fool if the vehicle that was apparently about to rear-end you stopped inches from where your rear bumper was originally, and you’ve embedded the front of your car in the back of the next one - good luck explaining that to your insurer.
With no damage to the rear of your vehicle you would be 100% at fault for rear ending the guy in front of you. The guy behind you would either drive away or testify that he saw you hit the car in front of you.
It seems as though if you were right bumper to bumper with them, that would lessen the impact as you are pushed into them, but I’m not sure if hitting them would lessen things. Maybe it would work if you hit at just the same instant that you are hit, or even more to the instant, when the force of the rear ending car reaches your front bumper, but that would require more timing than I think you can do.
I spent a few years as a driver in a few different jobs, so had to take defensive driving classes. I was always told that you should have enough space between you and the car in front of you that you can see where their tires meet the road. Generally, rear impacts are not going full speed, and having enough space means that you don’t hit the car in front of you at all.
I was not sure if 1g of resistance to acceleration for the tyres really translates into a reduction of 1G in acceleration, as the tyres are just providing net resisting force, part of which is being taken up by the cars suspension , so that energy will come back to the occupants and once the friction is broken, that hit car will accelerate forwards. If the breaks are off, then the car will move forwards, but you should be absorbing less energy into the rear of the car .
Anyway I went looking to see if the NTSC or anyone had done studies
Some interesting views on peak acceleration based on the car accelerometers are here, but no indication of target vehicle breaks on or off PDF!
But I also found this paper which you have to pay for, but the abstract states there isnt any difference.
Little difference was found between vehicle kinematics for conditions in which the unaware occupant was not braking and the unaware occupant was braking “normally”. Decreased target vehicle velocity changes and increased bullet vehicle velocity changes were observed with fully or mechanically applied braking. Full or mechanical braking decreased the collision duration for the target vehicle, while bullet vehicle collision durations were not affected. Awareness of the impending impact decreased occupant head kinematic parameters and the target vehicle occupant described those impacts for which he was prepared as feeling less severe than those for which he was unaware. No differences were found in target vehicle occupant head kinematics for the unbraked and fully braked tests
Yeah, not really plausible to think it could be done in practice. Just thinking about the theory. Agree about leaving a decent gap in the first place - also gives you more room to attempt switching lanes/mounting the kerb to avoid the incoming vehicle, if that’s an option (an option that was excluded in the OP but often relevant in the real world).