Drivers should not rely too heavily on fuel economy systems in the dashboard that show the number of miles a vehicle gets per hour. Gallon and range value (how many “miles to empty”), as estimates can vary significantly over shorter trips or depend on the consistency of things that affect gas mileage, such as speed and acceleration.
These are the main findings of a new report that assessed the accuracy of fuel economy display in speed, announced Tuesday by AAA. The results, which were announced at a time when gas prices are at a seven-year high, the car group says are important as motorists often rely on display systems when making decisions about when to refuel.
The vehicle test, based on a series of simulated driving scenarios, was conducted by AAA in partnership with the Automotive Research Center of the Automobile Club of Southern California.
On average, the fuel economy of the vehicles tested showed a relatively low error of 2.3% compared to the fuel economy measured by laboratory tests. However, the individual vehicle defects varied widely, suggesting that each vehicle responded differently to changes in driving and that accuracy may be affected by driving style and conditions.
“Overall, the systems we tested were relatively accurate, but a closer examination of different driving scenarios revealed significant variation based on changes in speed, acceleration and distance,” Megan McKernan, head of the Automotive Research Center, said in a statement.
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For example, when driving conditions change, such as Going from city driving to highway driving, “the estimate is likely to lose accuracy until it adapts to the new driving conditions,” the report states. In addition, errors varied significantly over short distances, even when it was accurate over longer distances.
Testing the “miles to empty” display found similar results with accuracy fluctuating across driving scenarios. The calculation of the range at a given time is affected by the vehicle’s recent driving conditions, the researchers said.
“We drove our test vehicles through various driving situations ranging from cruising at highway speeds to getting stuck in traffic to typical city driving,” McKernan added. “Despite the irregularities our tests found, a vehicle’s fuel economy is an important tool for understanding how different driving modes affect how efficiently a vehicle uses fuel.”
The report contained a number of tips for maximum fuel economy, including: minimizing the use of air conditioning; avoid hard acceleration; always inflate tires to the recommended pressure inside the driver’s door or in the user manual; light loads; and in hot weather, parking in the shade or using a windshield sunscreen to reduce heat buildup inside the car, reducing the need for air conditioning (and thus fuel) to cool the car down.
To avoid running out of gas, AAA recommends that drivers fill up when it reaches a quarter of a tank. This will ensure that drivers have enough fuel in case of unexpected delays, but also help prevent damage to the fuel pump that can occur when a vehicle’s gas tank regularly runs down to empty.
To learn more, click here. To access the full report, click here.