The Car Connection: It's Official: SUVs Are Safer Than Cars (Well, Mostly)

F = ma,
p = mv,
J = <delta>p

Tom

 

Momentum = mass * velocity

It would be nice if there was a general comparison. I did see a website a year back that had a ton of vehicles on it and compared their overall expected fatality amounts and the Prius was pretty low. It included single vehicle accidents, but I've not seen a comparison of vehicles in different classes and how they'd fare one against the other in the same accident, like a Prius vs a Suburban.

Color is mentioned here: [ame=http://en.wikipedia.org/wiki/Automobile_safety]Automobile safety - Wikipedia, the free encyclopedia[/ame] but the benefits of white are far more modest than what you're reporting (?).

 

Right. And the energy dissipated in a inelastic collision between two cars would therefore be proportional to M(1)V(1) + M(2)V(2) (where V(x) are vectors). Therefore, everyone should be trying to minimize their Mass and their relative Velocity (and that of anyone who they might possibly collide with).

Having more mass just means that the wrecks end up more on the other side of the road.

 

See http://eetd.lbl.gov/ea/teepa/pdf/TRB_Safety_1-03.pdf for a 2003 study.

Example info: Midsize cars are slightly safer as a driver than SUVs, and much safer for other drivers.

 

You are missing an important point: the energy isn't dissipated equally by both cars and their respective occupants. The delta v of the light car ends up being much larger than the delta v of the heavy one.

For an extreme example, look at what happens with a car/train collision: the train continues at essentially the same speed, having a delta v of zero, while the car is now a hood ornament on the train. The outcome for the respective occupants is vastly different.

Tom

 

Re: The Car Connection: It's Official: SUVs Are Safer Than Cars (Well, Mostly)

Gee....ya think?
Big cars safer than little ones?

Why...I'm standing here beside myself.
Color me shocked.

Two hundred and eighty some years his death, and Sir Isaac still gets it right.

 

No, I am not. That is what the 'V is vectors' means, and is reflected in "Having more mass just means that the wrecks end up more on the other side of the road." . The crashed cars will now both be moving in the direction of the added vector velocities.

The outcome for the occupants is not based on the delta v. Take another example A man and a bullet. A man travelling at 50 mph meets a bullet travelling at 600 fps, they both end up moving at the 50 mph of the man, but the bullet could survive unscathed, the man is probably in a world of hurt.

The train passengers survive because more energy can be dissipated between them and the collision than the car passengers have. But here we are venturing far from Physics 101. Which is why the NHTSA does exhaustive tests with actual cars rather than relying on a freshman physics student to do their safety assessments.

 

See the report I cited above. Safety correlated more with resale value than weight.

 

I must disagree. While it is not the only factor, it most certainly is a contributing factor.

This example is absolutely, completely, totally irrelevant, as it is a completely different type of injury.

 

Not solely based on delta v. Better?

How fast do two cars have to be going in order to kill one of the occupants when they impact, assuming full airbags etc. and no intrusion into the driver's compartment? That would be the level at which delta v is a significant factor.

No it is not. At the level of Physics 101, they are exactly the same. If delta v were the only factor, they would be the same. Once we start talking about types of injuries we are clearly in the realm of Biology, Mechanical Engineering, and assorted other disciplines.

 

Cool link. I'll spend more time looking at it. I would rather be driver in an 18 wheeler than in a Prius if they head-on collide, though

The risk to other drivers is more or less what i'd think in that chart, though a maxima LESS risk to another driver than a Corolla surprises me.

The SUVs are definitely less safe than I expected, probably due to center of gravity. Apples to Apples, though, the small cars pose more risk to driver than heavy (e.g. corolla vs maxima) as would be expected. Not sure how the avalons numbers are so impressive. I think a lot of this is covered in the link and I want to review more!

 

Me too! But not because the 18-wheeler is heavier, but rather because a nice portion of that weight is in nicely arranged structural steel.

Which would you rather be in if it was a rock face that they hit?