1. Slow the bleep down. Driving everywhere faster does save the most precious natural resource of all: your time. That’s a pretty fair tradeoff, but just keeping up with traffic on the highway will use a lot more gas. How much? In their tests, our premium unleaded colleagues down the hall at Consumer Reports found that gas mileage dropped by anywhere from 9 to 15 miles per gallon when they sped up from 55 miles per hour to 75. Vehicles in that test included a Honda Accord, Toyota RAV4, and Ford Fusion…and they even tried it with a hybrid version of the Fusion.
2. Don’t carry stuff on the roof. Sometimes you have no choice but to carry stuff on the roof, but it will still hurt your fuel economy. Tests showed a 15 MPG decrease with a roof-top carrier on a Toyota Camry at 65 MPH.
3. Don’t run the air conditioner when it’s hot. That sounds counter-intuitive: when else are you going to run the air conditioner? The trouble is, the system works harder when the outside temperature is hotter, and does affect your mileage by maybe 1 to 4 miles per gallon. When every drop of fuel counts, crack open a window.
Gas-saving tips & myths [Consumer Reports]