Which of the following statements is true about vehicle speed and gas mileage?

The statement that gas mileage decreases at speeds over 55 mph is true because, generally, as speed increases, the aerodynamic drag on a vehicle also increases, which in turn requires more energy (fuel) to maintain higher speeds. Many studies and real-world tests have shown that vehicles achieve better fuel efficiency at moderate speeds, typically between 45 and 55 mph. Above these speeds, the additional effort to overcome drag often leads to significantly reduced gas mileage. Therefore, it is advisable to drive within this optimal speed range to maximize fuel efficiency.