Car owners battle automakers over advertised MPG (MoneyWatch) Car buyers have become so focused on gas mileage that some are going to court when their vehicles don't get the advertised numbers Hyundai Elantra owners, joined by public interest group Consumer Watchdog, are suing the automaker over this issue. Their suit claims that Hyundai advertises that the Elantra gets 40 MPG, but does not explain that this rating is only for mileage during highway driving. Hyundai claims that its ads comply with all laws and regulations. The Hyundai suit follows a similar action against Honda regarding ads saying the Honda Civic Hybrid gets 50 MPG. A Honda Civic owner initially won her case in small claims court but then lost on appeal. Honda did settle a class action suit by 460,000 Civic Hybrid owners over gas mileage, giving each one $100 to $200. In the past, car shoppers seemed to understand that ratings published by the Environmental Protection Agency covered separate numbers for city and highway driving, while a third figure pertained to combined driving conditions. But as more cars have achieved a 40 MPG highway rating and car companies push that number in their ads, owners seem to be taking the claim more seriously. Several automotive magazines and websites have found that most new cars come close to their combined rating in normal test driving. But if you are an aggressive driver or have a daily commute filled with stop-and-go traffic, that will have a major effect on actual mileage. "So much depends on how you drive and where you drive," says Jack Nerad, executive editor of Kelley Blue Book and the kbb.com website. If you are shopping for a new car, be sure you understand all the mileage ratings and how those are likely to translate into the real world. Check the full rating of any car you are considering at the government website fueleconomy.gov. For instance, the 2013 Hyundai Elantra - in addition to that controversial 40 MPG highway rating -- also is rated at 29 MPG in city or suburban driving and 33 MPG combined. Pick a car that suits your driving habits. A hybrid like the Toyota Prius is especially good for slow driving in the city. It shuts itself off entirely at stoplights and then restarts seamlessly. In fact, the car's 51 MPG city rating is higher than the 48 MPG it gets on the highway. The combined rating is 50 MPG. On the other hand, if your work dictates constant highway driving, consider something like the Volkswagen Jetta TDI diesel, which is rated at 42 MPG on the highway and 30 MPG in the city. The combined number is 33 MPG. Take a hard look at your driving style. If you accelerate hard from a stop, tailgate other drivers, and have to brake frequently, you are hurting your gas mileage. If you care enough to shop for a high-MPG car, it's probably worth driving in a way that gets the best possible mileage.