The believe I've read on here the average speed on the EPA highway test is 48mph with speeds up to 80mph at times, never looked to see if this is true or not. I can say with certainty that both my Cruze and Sonic get better MPG at 55mph than the EPA ratings indicate. I've gotten the highway EPA ratings with both cars from 57-70mph on trips of 80% highway or more, cold weather and AC use being the only thing that brings it down.
Take a look at your average speed on the trip computer, anything over 40mph is considered a mostly highway route. Most people actually drive a more city route than they realize with average speeds around 20mph. Anytime I've had a low MPG fill up, I can always see my average speed has dropped due to more city driving.
According to the EPA test cycle average speeds of 21 MPH for the city cycle, and 48 MPH for the highway cycle. If your car has a menu display for average speed, reset it when you fill up. At your next fill up, record the average speed for the tank, and use it to find your "true" city/hwy driving splits in the following formulas: Percentage of Highway Driving = 100*(AVG SPD - CITY)/(48 - 21) Percentage of City Driving = 100(1-(Calculated HWY%)). Any average speed under 21 MPH is 100% city, and anything over 48 MPH is 100% highway driving. For example: If at your next fill up, your average speed is 35 MPH, your city/hwy splits using the formula above are: 52% hwy, 48% city driving. Repeating this at each fill up allows you to compare your driving on Fuelly directly to the EPA estimates, rather than guesstimating your city/hwy splits. It also gives you much more consistent results than guessing does. posted by cougar435788 on January 27, 2013 Vote: