Q: Getting poor fuel mileage lower than listed

Fuel economy has many influences on it which can raise or lower the MPG. Are you calculating fuel economy per tank or off the trip computer? The trip computer is a constant average that might be resettable (see owner manual). If so, reset it on your next long trip on the highway and see what it reads. When you are idling for any period of time, this will cause a drop in fuel economy. Fuel economy will be reduced by speed, acceleration, poor tire psi and condition, the load inside the car, weather, and terrain. For example driving 20 miles to work up a hill and never getting above 30 MPH will lower fuel economy. Highway mileage in theory means cruising at 60 MPH and during that time you will be close to what the rated MPG is. The EPA Fuel economy is measured under controlled conditions in a laboratory using a standardized test procedure specified by federal law. Manufacturers test their own vehicles—usually pre-production prototypes—and report the results to EPA. EPA reviews the results and confirms about 10%–15% of them through their own tests at the National Vehicles and Fuel Emissions Laboratory.