Environmental Economics and The Energy Collective are among the many voices recently advising consumers they could save gasoline by driving more slowly. I was curious to take a look at the evidence behind such claims. Source: U.S. Dept. of Energy. Air resistance increases the faster you travel, which might lead you to think that higher speeds always require more fuel. However, your car's engine is designed for maximal efficiency in converting fuel into motion when you drive at higher speeds. As a result, the typical car gets much better gas mileage if you drive it at 45 mph instead of 15. However, at speeds above 60 mph, the wind resistance becomes a dominant factor, and miles per gallon for most cars starts to decline significantly if you drive faster than 60. The basis for the graph above and many of ...