Comment Re:The real question is . . . (Score 2) 525
When moving across country (California to Florida) in 2005, I averaged 32 MPG for two consecutive tanks of gas (calculated by actual gas used at time of fill up) while driving through AZ and NM. Cruising speed was 85. Car was a '99 Grand Am (170hp 3.4L V6), EPA highway rating was 30 MPG. There was probably a tailwind.
More recently, while returning to Chicago from vacation in Colorado, I managed to average 30 MPG for a single continuous 400-mile nonstop leg while averaging 76 MPH. This car is a '05 Pontiac G6 (200hp 3.5L V6), rated at 28 MPG highway by the EPA.
Obviously, both these trips are idealized - fill up, accelerate directly to cruising speed, maintain until next fuel stop - so not representative of how the EPA tests highway mileage. Typically the G6 gets 25-28 on the highway (yes, these GM engines are woefully inefficient). Now, I know the plural of anecdote is not data, but the fact is it's possible for cars to achieve mileage better than the EPA ratings - depending on lots of things including traffic, power curve, gearing, wind, etc.