Sen John Warner has asked the Energy Department to look in to what the impact would be of re-imposing a national speed limit. Some very quick comments:
– With newer cars the savings are much less than they were in 1974 when this was done the first time. Most cars get maximum miles per gallon throughout a range of about 35 to 65 and then see a mileage decrease as you drive faster than this range. Graph here. For most current vehicles the improvement in gas mileage is negligible. Much greater savings can be had with purchasing more fuel efficient cars, driving slightly less (eg, combining errands, walking…), driving more consistent speeds, etc.
– Many say that the national speed limit saved lives. Reality? Likely not. Fatalities from car crashes were declining rapidly in the years leading up to the 55mph national speed limit and actually leveled off a couple of years later. The decline is attributed to huge improvements in car safety features such as seat belts, anti-lock brakes, and tires as well as more people using seat belts. Many portions of the US also implemented ‘keep right except to pass’ laws for multi-lane roads.