Drivers have long known that slowing down on the highway means getting more miles to the gallon. Now airlines are trying it, adding a few minutes to flights to save millions on fuel. Southwest Airlines started flying slower about two months ago, and projects it will save $42 million in fuel this year by extending each flight by one to three minutes. On one Northwest Airlines flight from Paris to Minneapolis earlier this week alone, flying slower saved 162 gallons of fuel, saving the airline $535. It added eight minutes to the flight, extending it to eight hours, 58 minutes. That meant flying at an average speed of 532 mph, down from the usual 542 mph. "It's not a dramatic change,' said Dave Fuller, director of flight operations, which began flying slower two years ago. JetBlue adds an average of just under two minutes to each flight, and saves about $13.6 million a year in jet fuel. Adding just four minutes to its flights to and from Hawaii saves Northwest Airlines $600,000 a year. United Airlines has invested in flight planning software that helps pilots choose the best routes and speeds. In some cases, that means planes fly at lower speeds. United estimates the software will save it $20 million a year. "What we're doing is flying at a more consistent speed to save fuel,' said Megan Mc-Carthy, a United spokeswoman. United expects to pay $3.31 a gallon for fuel this year not much less than what the average American driver pays for a gallon of unleaded petrol. Southwest, which has an aggressive fuel hedging programme, expects to pay about $2.35. Fliers, already beleaguered by higher fares, more delays and long security lines, may not even notice the extra minutes. AP