Drving faster, in my experience does not make a significant change in mileage...

At roughly $1,500 per car, air bags are a very inefficient way of saving
lives. For instance, instead of air bags, investing the $1,500 per car
into increased seat belt compliance to 90% would prevent over 5,500
deaths - annually. (NHTSA estimated between 1990 and 1998 3,625 lives
were saved by air bags, and admitted 122 lives were lost in otherwise
minor i.e. low speed accidents.)

Putting $1,500 into crash prevention, such as better training of
drivers, would save far more lives than air bags ever did. For many
individuals, investing $1,500 into better tires would be a safer choice
than air bags.

Two Transport Canada studies show air bags reduce the risk of injury by
just two percent for adults who wear seat belts. On the other hand, a
car 200 pounds heavier than baseline gives you 9% greater safety in a
crash all by itself, and another 200 pounds adds another 9%.


Ivan