You have completely botched this example. This example is useful to explain why airbags increase collisions. Putting a spear in cars would not make cars safer.
I don't understand your objection. Do you see a meaningful distinction between "cars are safer" and "cars are driven more safely"?
There is a major difference. The number of traffic accidents did not change significantly from 1990 to 2009, but the number of deaths from traffic accidents dropped 23%[1]. This is most likely due to cars being built in a way so that their passengers are more likely to survive accidents.