Driving Slowly Saves Gas
"Thanks, Captain Obvious," you're thinking.
But really, foregoing the 70-mile-per-hour speed limit in favor of a leisurely 60 miles per hour really does shave about 15% off my fuel consumption. I was typically getting 23 to 25 miles per gallon with highway-heavy driving in my '92 Accord Wagon. The last tank was around 27 and a half.
The section of freeway I use most has a roughly 15-mile-long stretch where the speed limit is 70 (trucks 60). So I can shave about 2 minutes off the trip by driving at the faster speed. But that two minutes costs me the better part of a dollar in extra fuel, so it's pretty clearly not worth it unless I'm really running late.