San Jose Mercury News columinst "Mr. Roadshow " (Gary Richards) took up a readers challenge that he wouldn't even save 20% by slowing down to 55 MPH and published the results in his column. Here are a few key quotes:

"I got 59.9 miles a gallon going 60 or under in our Prius compared with 42 mpg at speeds that would have made me prime bait for the California Highway Patrol."

"That's a staggering 42.6 percent improvement. I drove an extra 117 miles on a tank of gas by just slowing down. That's like lowering the price at the pump by more than a third - and about 10 mpg better than Prius EPA estimates."

"I calculated mileage the old-fashioned way: gallons used vs. miles traveled. The onboard computer reported slightly different results - 45.6 mpg at 75-plus vs. 58.4 mpg at 55 and under - but it's usually a little off. Still, that's a 28 percent difference."

And my favorite,

"But when I eased off the pedal and stuck to the right lane, I felt like I was sharing the road with others. Trucker merging in from my right: Here, friend, I'll slow and you can make that lane change. Driver ahead going slow? Excellent - the guy behind me may not tailgate as much."

Read the full article a http://www.mercurynews.com/ci_10032223