Moving toward ‘actual’ mileage
If you simply guess how many miles per gallon of fuel your vehicle gets, you might do about as well as the Environmental Protection Agency has over the last couple of decades.
Last month, the EPA announced the first major revision in its fuel economy testing procedures since 1986, aiming to create more realistic mileage comparisons among vehicles.
The EPA acknowledges that fuel economy estimates may drop by as much as 30%, an explicit admission that its prior practices were far off the mark.
A wide range of experts say the new testing regimen should provide more accurate estimates for many drivers, but that they will still fail to capture results that reflect many real-world factors in terms of road, terrain, climate and drivers.
The original method was developed in the 1960s, based on a hypothetical Los Angeles commuter who drove about 11 miles to and from work with an average speed of 21 mph and a maximum speed of 58 mph, according to the 412-page EPA report that implements the new test method. It assumed a driver would encounter no hills and a constant temperature of about 75 degrees, among many other fictions.
The EPA issued its test procedures in the mid-1970s. It updated them last in 1986. The new system will take effect in the 2008 model year.
This system introduces a number of variables, including the more aggressive acceleration and deceleration that drivers increasingly use. It also considers cold start-ups, cold temperatures, the use of air conditioning, some hills and rough road surfaces. A top speed of 80 mph is used as well.
“People’s driving behavior has really changed since 1985,” said Eric Fedewa, director of global powertrain forecasts at CMS Worldwide, a suburban Detroit consulting firm. “It didn’t reflect the way people use their vehicles with a lot of jack-rabbit starts, strong accelerations and high speeds over longer distances.”
Under the old system, few drivers have been able to meet or exceed the EPA fuel economy ratings. When the new system is in place, the ratings are supposed to fall closer to the midrange of actual fuel consumption experiences, says EPA spokesman John Millet.
Fuel economy reflects a huge range of variables, and drivers’ expectations are often flawed. One belief, for example, is that driving at higher altitudes reduces fuel economy. Not true, says Alan Weverstad, director of regulatory emissions at General Motors.
“Surprisingly, logic doesn’t always work,” he said. “Since there is less engine vacuum at any altitude, there is less pumping loss with an associated improvement in fuel economy.”
Lower atmospheric pressure at higher altitudes is compensated for by engine computers that constantly measure fuel emissions. In some cases, Weverstad said, fuel economy can actually improve at higher altitudes.
But higher altitudes are often accompanied by mountain roads that climb and drop sharply. The extra gas expended going up a hill is seldom recovered coasting downhill, because drivers have to use their brakes to slow down.
The EPA’s new model includes moderate hills, but not the mountain driving that exists across the West. It also makes assumptions about how many passengers and how much baggage a vehicle is carrying. Extra passengers or more junk in the trunk consume surprising amounts of fuel.
“For every 100 pounds of stuff you carry, you lose 2% fuel economy,” Weverstad said.
Low tire pressure, dirty air filters, poor gas quality and many other factors leave consumers disappointed in their vehicle’s actual results. And the biggest variable of all is the person in the driver’s seat. Paradoxically, drivers complain about the cost of gasoline, but pounce on their accelerators.
Millet said the EPA tests cannot accurately take into account all the variables that occur in actual driving, but that the new system will come much closer.
“It is impossible to design a perfect fuel economy test that will provide accurate, real world fuel economy estimates for every consumer,” the EPA report declares.
The tests are performed in laboratories on dynameters, similar to the ones seen at emissions-test stations in California. After getting the results, the EPA then fiddles with them, reducing them for the assumption of hills and rough road surfaces.
The new standards also will contain a significant new truth: The EPA’s fuel economy label on new cars will not contain estimates for city and highway mileage, but instead will offer an expected range of fuel economy that most drivers will get.
Once consumers realize new cars are delivering less fuel economy than they previously thought, it may lead to new political pressure to increase government-mandated fuel economy standards, Fedewa said.
“These new tests will make it harder for manufacturers to meet the current standards,” he said.
Ann Bordetsky, a policy analyst at the Natural Resources Defense Council, said the new system will provide consumers with a more accurate estimate.
But it is only “a step in the right direction,” she said. “There is still a real need for a complete overhaul of the system.”
“It might help consumers understand that the fuel economy of their vehicles is not good enough,” Bordetsky said.
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