The problem isn’t that auto manufacturers are lying to us, but rather that the Environmental Protection Agency, which determines mpg ratings, was using flawed testing methods. Since the 1970s, when fuel economy estimates were introduced, the EPA has determined the figures by using two laboratory tests: one for city and one for highway driving. Both were performed at an ideal 75 degrees Fahrenheit with a top speed of 60 miles per hour, and never with accessories such as air conditioning or other equipment in operation. Those of us who have steamed along the interstate at 75 mph on a 90-degree August day with the windows down and the stereo and the air cranked will recognize the flaws inherent in this approach.