Source: Consumer Watchdog
quote: The EPA highway figure is derived from a test which (except for the start and stop and some brief periods in between) is between 50-60 mph.
quote: The reason why fuel economy estimates have been coming out too high is simple: The EPA-specified testing and reporting method has not been updated since 1985. Since then, a lot has changed. For one thing, the former national speed limit of 55 mph has been abolished. So instead of topping out at 60 mph, the new highway rating test includes speeds up to 80 mph.