FYI, Pop Mechanics recently ran a fuel economy test using the Elantra (and Ford Focus). You can decide for yourself how valid their test method was (described in the article).
They found that their Elantra was good for 47.6 mpg (US) @ 55 mph and 39.3 mpg (US) @ 70 mph on their highway run. In their city loop, they measured 34.1 mpg (US).
Recall city/hwy EPA ratings for the car are 29 / 40 mpg (US).
Source:
Mileage Moment of Truth - We Put 40 Mpg Claims to the Test - Popular Mechanics