The mass of a car isn't the problem with the Smart Car when it comes to a collision with a barrier. In that case, the main issue is the tiny crumple zone at the front of the car. That means that more of the impact forces of a frontal crash will be transferred to the passenger compartment. It doesn't matter if you're driving a car that weighs half a ton or a truck that weighs ten tons - if your body goes from 70mph to zero in a couple of inches, you won't survive due to massive internal injuries. The crumple zone in the front of a car is what slows the bulk of that deceleration, and the Smart Car has a very tiny one that isn't going to do much good. The frame of the car being intact is actually a catch-22 - it means that the impact forces were absorbed by the occupants of the car. The airbag and such a tiny crumple zone are not going to help with anything more than a minor fender-bender.
Like I've heard some highway safety experts say about the Smart Car, "you can't repeal the laws of physics". The small mass of that car will be a factor in collisions with larger vehicles. It's like hitting a soda can with a truck. I have a feeling that when the Smart Car is finally released in the US, it will not only get the lowest crashworthiness rating from the IIHS, but will see the highest crash/fatality ratio of any other car on the road. Certainly not a car I'd want my family to be in.
The places where I'd see this car being optimal is somewhere like downtown NYC or LA - where traffic moves slowly and space is at a premium. Everywhere else, it's going to be a death trap on wheels. I hope I'm wrong though.
