Gas-saving driving habits, called hypermiling, can help you achieve up to 40 percent more miles per gallon (mpg) than your car’s official fuel economy estimate. Take, for example, a 2005 Honda Accord, a best-selling sedan with a mpg rating of 24 (21 city, 31 highway). According to Wayne Gerdes — who coined the term “hypermiling” and is considered by many to be its leading expert and trainer — an Accord driver who is savvy to hypermiling can expect to get about 35 mpg. Dedicated hypermilers can achieve 50 percent or better improvement over their vehicles’ estimated mpg figures. Last year, Gerdes set a world record for distance in a gas-powered,…