WASHINGTON, D. C. (Tuesday, July 27, 2021) –– It is one of the primal fears of drivers. By the same token, “running out of gas in the middle of nowhere,” it is rightly said, is also one of the easiest pitfalls of driving to avoid. AAA roadside rescuers respond to over 160,000 fuel calls during the summer months, and 24 million drivers run on empty, even though today’s vehicle fleet is equipped with in-dash fuel economy displays that estimate the number of miles a vehicle gets per gallon, including how many “miles to empty.”

To give motorists a measure of peace of mind, AAA tested the accuracy of these in-dash fuel economy and  “miles-to-empty” display systems.

The auto club also accordingly found the “miles-to-empty” warning estimates vary significantly over shorter trips, or are dependent on the consistency of things that affect gas mileage, such as speed and acceleration.

This means drivers could be taking an unnecessary risk if they over rely on these displays. This 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).

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

“People want to get the most out of a tank of gas, especially when prices are higher,” said Megan McKernan, manager of the Automotive Research Center. “Collectively, the systems we tested were relatively accurate, but a closer examination of different driving scenarios revealed significant variability based on changes in speed, acceleration and distance.”

Testing Shows Driving Habits Directly Impact Fuel Economy

AAA in collaboration with the Automotive Research Center (ARC) of the Automobile Club of Southern California, 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.

It’s road trip season and with higher gas prices, you need to know how far your car can safely go between fill ups, advises AAA Roadside Assistance. Even so, “24 million American drivers continue to drive after the low fuel warning light turns on,” a 2018 AAA survey revealed.

“Being stranded on the side of the road with an empty gas tank is not only a big inconvenience, it can also potentially leave you in harm’s way, and in an expensive predicament,” said Melvin Escobar, Car Care Manager, AAA Rockville Car Care, Insurance and Travel (CCIT) Center. “Drivers should not rely too heavily on in-dash fuel economy displays. As a good rule of thumb, a motorist should head to the gas station once one’s fuel economy display reaches a quarter of a tank. That way, you will avoid any unnecessary risk of running out of gas.”

Nationwide, AAA responds to 162,000 “fuel calls” on average in the summer. In 2019, AAA came to the rescue of 16,482 motorists in the District of Columbia, Maryland and Virginia who ran out of fuel including, 1,178 motorists in the District of Columbia, 9,421 in Maryland and 5,883 in Virginia.

While 2020 was an anomaly due to the pandemic’s impact on driving, still 11,176 total drivers in the District of Columbia, Maryland and Virginia ran out of fuel, including 705 drivers in the District of Columbia, 6,373 in Maryland and 4,098 in Virginia.

From January to July 25, 2021, numbers are looking more like 2019 with 8,180 members in the District of Columbia, Maryland and Virginia needing assistance with fuel including 592 in the District of Columbia, 4,527 in Maryland and 3,061 in Virginia.

During the shutdown of the Colonial Pipeline in mid-May, AAA responded to hundreds of calls from area motorists with empty gas tanks.

“Even worse, driving on low fuel levels may allow air to be drawn into the pump, which can cause overheating and increased wear that eventually leads to pump failure,” explained Escobar. “Replacing a fuel pump can cost $500 or more in parts and labor.”

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.

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.

“We ran our test vehicles through different driving situations ranging from cruising at highway speeds to being stuck in traffic to typical city driving,” said McKernan. “Despite the irregularities our testing found, a vehicle’s fuel economy display is an important tool to understand how different driving styles impact how efficiently a vehicle uses fuel.”

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.
• Consider minimizing your use of air conditioning. Even at highway speeds, open windows have less effect on fuel economy than the engine power required to operate the air conditioning compressor.
• 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.

While these tips will help improve fuel economy, AAA reminds drivers to always have at least one-fourth of a tank of fuel. 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.

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AAA provides automotive, travel, and insurance services to more than 62 million members nationwide and nearly 90,000 members in Washington, D.C.  AAA advocates for the safety and mobility of its members and has been committed to outstanding road service for more than 100 years.  AAA is a non-stock, membership corporation working on behalf of motorists, who can map a route, access a COVID travel restriction map, find local gas prices and electric vehicle charging stations, discover discounts, book a hotel, and track their roadside assistance service with the AAA Mobile app (AAA.com/mobile) for iPhone, iPad and Android.  For more information on joining or renewing a Membership, visit www.AAA.com..