In-dash fuel economy displays estimate the number of miles a vehicle gets per gallon, including how many “miles to empty” a motorist has. AAA tested the accuracy of these systems and found their estimates vary significantly over shorter trips and can depend heavily on speed and acceleration. This means drivers could be taking an unnecessary risk if they over-rely on these displays, which is especially true for the 74% of drivers who use their “miles-to-empty” display when they are low on gas to decide when to fill up (according to a AAA consumer survey).

“While motorists have fuel economy on their minds, they shouldn’t push their vehicles too close to the ‘E’ mark,” said Mike Hoshaw, vice president of automotive services, AAA East Central. “While the systems tested were fairly accurate, changes in speed, acceleration and distance produced noticeable fluctuations in the systems’ accuracy.”

Testing Shows Driving Habits Directly Impact Fuel Economy

In collaboration with the Automotive Research Center (ARC) of the Automobile Club of Southern California, AAA used a dynamometer (essentially a treadmill for vehicle testing) to run selected vehicles through a series of simulated driving scenarios to determine the accuracy of the fuel economy estimation and range value (aka “miles-to-empty”) systems.

On average, the fuel economy display of the vehicles tested showed a relatively low error of 2.3% as compared to the fuel economy measured by the dynamometer. However, individual vehicle error varied greatly, ranging from −6.4% to 2.8%. The negative number indicates that one test vehicle overestimated fuel economy by 6.4% or 2.2 mpg, while another underestimated it by 2.8% or 0.9 mpg. These specific results suggest that each vehicle reacted to changes in driving differently, and that the accuracy can be impacted by driving style and conditions.

The information displayed by these systems can give drivers a clearer picture of how their specific driving habits influence their fuel economy. To do this, drivers should reset their vehicle’s trip data after filling up, and then watch how their fuel economy display changes as driving conditions change.

Maximizing Fuel Economy is Key as Gas Prices Reach 7-year High

In recent weeks, gas prices have reached their highest point in seven years. To offset some of this additional cost, AAA recommends drivers do the following:

Plan ahead and run multiple errands in one trip, and whenever possible avoid times of day when traffic is heavier.

If you own more than one car, use the most fuel-efficient model whenever possible.

Avoid hard acceleration to maximize fuel economy, and always inflate your tires to the recommended pressure found inside the driver’s side door or owner’s manual.

Remove unnecessary and bulky items from your car. Minimize your use of roof racks and remove special carriers when not in use. Smaller cars weighed down by heavy cargo will have a greater reduction in fuel economy than larger models designed to carry more weight.

In hot weather, park in the shade or use a windshield sunscreen to lessen heat buildup inside the car. This reduces the need for air conditioning to cool down the car.

While these tips will help improve fuel economy, AAA reminds drivers it’s best to always have at least a quarter of a tank of gas. This will ensure drivers have enough fuel in case of unexpected delays but also helps to prevent fuel pump damage that can occur when a vehicle’s gas tank is regularly run down to empty.

AAA East Central is a not-for-profit association with 73 local offices in Kentucky, New York, Ohio, Pennsylvania and West Virginia serving 2.7 million members. Past news releases are available at news.eastcentral.aaa.com. Follow us on Twitter and Facebook.