You think filling up your car is a pain in the wallet? Try being a trucker. Most big rigs get less than 10 miles to the gallon, and diesel fuel is hovering near $4 a gallon in many places. “For every one-penny increase in the price of diesel, it costs our industry $391 million,” says a trucking industry spokesperson. In response, many trucking companies are instructing their drivers to ease off the throttle. Slowing from 75 miles per hour to 65 mph can increase fuel efficiency by more than a mile per gallon. And along with burning less fuel, slowed-down trucks make highways safer for the rest of us.