Surviving a car accident

Let’s say i am driving around in my cargo van and a Greyhound bus is heading my way.

The Greyhound is slamming on the brakes, but still hopelessly going to hit me.

Right now according to the laws of physics i am toast, but would i be better off actually accelerating instead of braking?

Would my added inertia cancel out some of the force the Greyhound is going to send at me?

Or would accelerating be a worse thing to do?

Ever hear the phrase “It’s not the fall, it’s the sudden stop at the bottom?”

Same story here. The damage will be done at least partly by the deceleration of your body going from X MPH to 0 MPH, or -Y MPH if the bus that’s hitting hits you hard enough to accellerate you in the other direction.

If you hit it faster going a faster speed, the total deceleration is still at least the same.

The only thing going for you is that you’ll wind up with a lower net velocity, but all that energy had to go someplace, and the initial energy input was higher in your second case, so that’s even more energy. And a significant portion of that energy will go into you.

If the bus is going to rear-end you, then yes, you want to speed up. Otherwise you want to slow down.

And better yet, swerve so the hit is as lateral as possible. Getting sideswiped will be a lot more survivable than getting hit head-on. In strict Physics terms, swerving is a form of acceleration - just not the one where your speed’s absolute value gets higher.

That would depend on where the airbags are.

Not terribly relevant. As gnoitall points out, the stopping part is what hurts. The thing about car crashes is that your body is travelling at great speed and when the car abruptly stops, your body goes bouncing around the inside of the car. The mechanism by which this stop occurs is not terribly important. Therefore, you want your body to be moving as slowly as possible. Anything that adds to your speed increases the injury.

Old cars used to be built like tanks… They were very good at surviving impacts. Problem was, this was of no benefit to the people inside because they were smacking against the inside of the vehicle. That’s why you hear about crumple zones on cars… they are sacrificing the car’s integrity to absorb some of the impact.

I hope you won’t mind if I digress to complain about one of my pet peeves. In this case, I simply want to point out that “absorbing impact” is a concept that often goes over the heads of many laymen. It took me a long to figure out why it is a good thing that modern steering wheels absorb the impact in an accident. The word people should learn is cushion, as in: Crumple zones cushion the passengers from the impact.

It’s a lot like how some people insist that there’s really no such force as “suction”, so they keep referring to “negative air pressure”. If suction doesn’t exist, then neither do financial debts (a/k/a negative cash flow).

It’s a simple case of reducing the deceleration. If the crumple zone of car deforms by, say, 3ft, then the passenger compartment is slowing down relatively gradually over that distance, rather than stopping dead with zero deformation. Therefore you don’t get the case where suddenly your body is going at 50mph inside a car going at 0mph (which is not a good situation to be in).

Translated into layman’s English:

You don’t want any sudden stops. If the steering wheel has no “give”, then it wallops you. But if it crumples, then you have a 3-foot cushion, then the stop isn’t so sudden, and you can survive it much more easily.

That would depend on your speed. If your own vehicle is stationary, you are much better off being hit head-on.

Agreed. If I’m going to have a bus hit my car I would much rather it did it from the front, where there is several feet of crumple zone between me and it, rather than from the side, where there’s a relatively thin door. Depending on the relative speeds and angles, of course, a glancing impact could be better.

If you could swerve enough that the bus hits the back of your car, that would be ideal - longer crumple zone and the force of the hit will be pushing you into the back of your seat instead of into the steering wheel/air cushion. That’s assuming you have a longer crumple zone in the back and no kids back there.

The down side is that controlling the swerve to get hit exactly from the back would be a bear. A side or diagonal hit would send you in directions that the car isn’t designed to protect you from.

Leaving Hypothetical World for a moment, being hit from behind has its own dangers, especially if we’re talking about high-speed impacts and large oncoming vehicles - cervical vertebral fractures or disk herniations, fuel tank punctures, being launched off into oncoming traffic…

If an accident is bound to happen, go limp.

I know tensing up is what your body screams to do but I survived a horrific accident by closing my eyes and just waiting.

I was rear ended in a 2 door at a standing stop by a large farm truck going 60 mph that didn’t hit the brakes. I saw it coming up fast in my rear view mirror and barely got my foot off of my brakes when he hit. The bumper took the impact nicely, had my seat belts on but still hit my forehead on the visor and found out that air bags don’t go off in a rear collision. I quickly found out why, I was thrown into oncoming traffic like rocket sled. It was the scariest part of the whole incident. Luckily the on coming cars were able to get out of the way; I walked away without just a minor knot on my head.

A similar scenario was posted about 18 months ago, albeit for a T-bone collision between two cars. I offered this analysis. Excerpt:

This is a physics question and so we let’s run some numbers.

We’ll use net change in velocity (not deceleration, because I don’t know how to determine the duration of the collision) of your van in this scenario as a measure of how fucked you are. Let’s say the bus weighs 45,000 lbs, GVW for a typical Greyhound bus. Your Ford E-Series cargo van will weigh 9,500 lbs fully loaded. This is not the typical passenger car scenario, but I’m going with the OP. If you hit the bus head-on on an undivided highway going, let’s say, 55 MPH, the momentum (which is a vector with magnitude mv) of the bus is 2,475,000 lbs-MPH in one direction, and your van has 522,500 lbs-MPH in the opposite direction. After a collision, due to conservation of momentum the fused mass now has a speed of 35.8 MPH in the same direction the bus was originally traveling. So your velocity has changed by -90.8 MPH in a very short period of time (oh, maybe a second or less). For your alternate scenario let’s say you have enough time to accelerate to 65 (pulling a number out of my ass) before impact. Now your momentum has increased to 617,500. The resulting speed of the fused mass is now 34.08 MPH. That’s slower than the first collision, but for you and your van represents a change in velocity of -99.08 MPH. So even though the net speed is slower after the collision, your increased speed just before the collision causes your net velocity change to be higher.

Braking before the collision allows you to stretch part of the deceleration over a relatively much longer period of time, reducing the forces at play when the collision happens. Hitting the gas is just suicide.

Damn. Glad you’re still with us, Si Amigo.