Ever since I saw this data I've been wondering how compacts can be so crummy.

http://ecomodder.com/blog/wp-content..._car_types.jpg
I wish they did better. I don't really want a mid-size, with the exception of the Prius mid-sizes all have 2.2-3L engines, which are blah for MPG.

Of course it is some comfort that speed is more important and slowing down, even a little, really works.

I like the diet soda with burger and fries analogy. I get really annoyed when folks with trucks and SUVs say they want a heavy vehicle to be safer. It's like they never heard of a rollover / can't believe they themselves could ever be at fault.

Because even if you buy into the weight argument, it's a zero sum arms race. Your safety (due to mass) is in proportion to your threat to others. I never hear anyone blame the parents of the drunk teen who decimated a family of six with the 4 ton nuclear weapon they let him drive.

I also really liked the analysis of speed differentials on accident probability and severity.

This part was is a mistake however; "The affect of mass gets divided by two. A 4000 lb SUV will not absorb twice as much energy as a 2000lb car, it will only absorb 50% more."

Energy is linear with mass, so doubling weight does indeed double energy. The one-half term is a scalar, but the function remains linear (and proportional).

Energy is the not exactly the right parameter for safety WRT mass anyway. The key is whether your momentum will be changed by other the vehicle, or you will change the momentum of other vehicle. This follows your percentage of the share of total mass. In the range where your adversary's weight is close to the same as yours, your ability to inflict vs receive is linear with your own mass. Outside of that range the function saturates, and so a 10 ton semi will inflict similar damage on all passenger vehicles, whether they be 2 ton compacts or 4 ton pickups, and 200lbs cyclist will take damage that depends on the height and angle of a vehicle rather than its mass, in any case the victim's final velocity will roughly equal the dominant vehicle's initial velocity.