New research finds drivers should not rely too heavily on fuel displays like “miles-to-empty”

26 July 2021

Drivers could be taking an unnecessary risk if they over-rely on fuel economy displays.

AAA tested the accuracy of in-vehicle fuel systems that measure fuel economy and range (miles-to-empty). Collectively, the systems tested were relatively accurate, but a closer examination of different driving scenarios revealed significant variability based on changes in speed, acceleration and distance.

Read the full report here

“People want to get the most out of a tank of gas, especially when prices are higher,” said Nick Faustman, spokesman, AAA – The Auto Club Group. “Unfortunately, these systems aren’t perfect, so if drivers become so dependent on them that they run their vehicles to the last drop, they may sputter out sooner than expected.”

In 2019, AAA responded to 628,000 out-of-fuel calls and expects to respond to 109,000 this summer (period from 5/27 to 9/5).

 

According to a AAA consumer survey:

  • Nearly three quarters (74%) of drivers use their “miles-to-empty” display when getting low on gas and deciding when to fill up
  • Six in ten (62%) drivers with a gasoline vehicle believe that fuel economy estimates provided by in-vehicle systems are accurate.

 

Testing Fuel Systems

AAA used a dynamometer (essentially a treadmill for vehicle testing) to run vehicles through a series of simulated driving scenarios - ranging from city driving in heavy traffic to cruising at highway speeds on an open road.

 

Fuel Economy system

On average, the fuel economy display of the vehicles tested showed an error of 2.3%. Individually, 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.

 

Range a.k.a. “Miles to Empty” system

Testing of the "miles-to-empty” display found similar results with accuracy fluctuating across driving scenarios. While each manufacturer likely uses a unique algorithm to estimate vehicle range, it can be assumed that some historical driving data is also used to determine the vehicle’s fuel efficiency for future driving. Therefore, the range estimation, at any given point, is affected by the vehicle’s most recent driving conditions.

 

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

“To avoid running out of gas, AAA recommends drivers watch their gas gauge and fill up when it reaches a quarter of a tank,” Faustman continued. “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.”

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 vehicle whenever possible.
  • Avoid hard acceleration to maximize fuel economy.
  • 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 (and thus fuel) to cool down the car.
  • Enroll in savings programs. AAA Members who enroll in Shell’s Fuel Rewards program can save 5 cents per gallon when they fill up at Shell. Members who enroll between July 1 and August 31, 2021 can save 30 cents per gallon on their first fill up. Click here for more information.