The Environmental Protection Agency reports Smart Car gasoline ratings at 34 mpg in the city, 38 mpg on the highway and 36 mpg forcombined driving, as of 2015. Several factors affect actual mpg, such as individual driving styles, vehicle maintenance and variations in fuels.
Speeding, hard accelerations and driving on difficult roads make the motor work harder, which uses more gas. Running the air conditioner increases gas consumption. Failing to keep the car tuned up and driving on tires that are worn or improperly inflated use more gas. Different brands of fuel can diminish mpg by as much as 1 to 3 percent.