> And speed matters. Nope. Delta-V, delta-t, crumple zone energy absorption and airbag/safety device deceleration capability matter. The only energy that can

> And speed matters. Nope. Delta-V, delta-t, crumple zone energy absorption and airbag/safety device deceleration capability matter. The only energy that can do damage starts with the difference in speed between vehicles. Then you have to take into account how much time it takes for the difference in speed to reach zero (that's the delta-t). This is a combination of braking (if any), grinding, sliding (tires sideways, rubbing against barriers, etc.) and crumple-zone deformation. And then you have safety devices such as airbags and seat-belts which are mostly about reducing the rate of deceleration. Of course, initial velocity is important. However, focusing on that alone, I think, is focusing on the wrong variable. Road conditions, for example, are crucial. I've ridden in taxis in Munich at 180 mph. The roads and traffic supported it. No issues. On the other hand, a couple of months ago I was on a BMW on the north-bound 5 fwy just before the Grapevine. I started a lane change when a crack/level difference between the lanes grabbed the tires. This caused a violent unintended lane change. Had my reflexes been any slower or had another car been there it could have been a horrible accident. I wasn't going much faster than 60 or 70 (I was about to get off the freeway to get gas). And, BTW, this is a section of the 5 that was repaired under the American Reinvestment (...) act. Well, they actually managed to cause more damage rather than repair the road. On this section of the 5 it feels like you could loose you kidneys even while riding in a minivan.