Lighter cars means less energy at high speeds when crashing into a wall like during the crash test. But Heavier cars are safer during a head on collision when hitting a lighter car. Larger cars also have a bigger survival zone vs a smaller car during a crash. So would a really safe car be something based on the rolls royce phantom for example. But with Carbon Fiber Wheels, and a plastic engine(actually possible but hasn't been done since a car race in 1980's) and other weight savings in none critical areas. Take the weight savings to scale the vehicle up slightly(2 to 3%) and put the remaining weight savings back into the vehicle with enhancements done to structurally integrity of the cabin as well as crumple zones?