How a national speed limit could improve our lives.The first automotive speed limit in the United States was enacted in 1901, when the state of Connecticut declared it illegal to drive faster than 12 miles per hour on its highways. The first speeding ticket, one must imagine, followed only shortly thereafter. We freewheeling Americans don't cotton to the idea of limits, as anyone who has ever tried to actually drive 55 miles per hour on an interstate can attest.But the latest case for driving the posted speed limit, and lowering that speed limit altogether, is not about safety (though even a rudimentary understanding of physics would support that argument). Rather, it's about saving money and reducing carbon emissions. A car's gas mileage peaks at speeds around 40 miles per hour (depending on the car), and then decreases rapidly. This is because air resistance increases exponentially as a car goes faster. At high speeds, a car's engine is using the majority of its energy simply to overcome that resistance-rather than accelerating-which wastes fuel.This revelation isn't new. A 1974 law instituted a national speed limit of 55 miles per hour (a compromise between efficiency and speed). But as the oil crisis abated, the law was amended to 65 miles per hour in 1987 and finally repealed entirely in 1995, ceding the power to set speed limits back to the states. Now, many states have speed limits that exceed 70 miles per hour on interstates, and some stretches in Texas and Utah have limits as high as 80.Tim Castleman, a California native, thinks we should all slow down. He started his Drive 55 campaign in the wake of 9/11, after concluding that a reliance on foreign oil was the root cause of the disaster. Reducing our oil consumption seemed the logical step, and what easier way to do that than simply make people drive slower? This would save gas and, Castleman says, make driving a more pleasant experience. "The average driver races from red light to red light with little regard for how much energy they're consuming. It's an amazingly antisocial behavior."The Drive 55 campaign-which lobbies state and local governments to lower the speed limit and encourages drivers to maintain a self-imposed 55-mile-per-hour limit-is viewed by critics as a drop in the proverbial bucket. The Department of Energy has estimated that, at most, a national speed limit of 55 mph would save 100 million barrels of oil annually; the United States currently consumes 21 million barrels per day.But Castleman, whose original motivation was saving oil, now believes driving 55 could have broader benefits for our quality of life. A self-described "conservative person," Castleman would rather not have a law at all, but since no one wants to slow down voluntarily, it seems like the only option. "I don't want police waiting at every corner to give a ticket. I want my fellow drivers to get sane. We're all going to get there. Let's just do it in an orderly fashion."Photo by Abigail SampleLearn how to maximize your car's natural fuel economy at drive55.org.