I was just reading the car and driver magazine that my husband gets and always ogle the cars, then I cam upon this article which struck a cord with me as some of the items I believed to be true like have the windows open when you drive 35 mph or less and the A/C on when driving 55 MPH.
Interestingly, they say that at 55 mph with windows open you use 3.3% less than with the A/c on. Another note was taking the junk out of your car saves gas.
As a realtor I alway have "stuff" in my car if you have 100 lbs of "stuff" like potting soil you save 1.4% @ 55mph and at 75 mph you save a whopping 4.2%.
This I kind of knew if your tires are not properly inflated or deflated you use up gas. Also if you have somthing on your roof that too uses up gas.
This I was surprised about, turning off the engine saves fuel when the stops are long, but not good for short stops so when waiting for the bridge to go up and lets boats by ro waiting for a train is a good idea, however there is some discord among the exerts because it does put wear and tear on the startign system. You be the best judge of that.
Anyway I gleaned all of this information from the Dec 2008 issue and their website is www.caranddriver.com .
Have a great evening.