Fixing the EPA's Fuel Economy Tests
Whether it is a consumer looking to purchase a car or truck or a lawmaker concerned with energy security and global warming, Americans rely on accurate information about their vehicles from federal agencies to make good decisions. Unfortunately, when it comes to fuel economy, we haven't always been getting accurate information. Yet, starting with the 2008 model year (MY), the Environmental Protection Agency (EPA) will use new testing and calculation methods that will provide us with gas mileage estimates that more accurately capture real-world driving.
The Old EPA Tests Overstated MPG
Prior to the new methods, the EPA's fuel economy estimates were based on the results of two laboratory tests, the Federal Test Procedure (FTP) and the Highway Fuel Economy Test (HFET). Both tests involve placing a vehicle on a dynamometer, a treadmill-like machine that allows the vehicle's wheels to rotate while the vehicle itself remains motionless. A professional driver operates the vehicle at pre-defined speeds and acceleration rates over a specified timetable. The FTP test simulates city driving conditions using an average driving speed of 20 miles per hour (mph) and a maximum speed of 56 mph. To simulate highway conditions, the HFET uses a higher average speed of 48 mph and a maximum speed of 60 mph. Automakers report the test results to the EPA, which then repeats the tests on about 10 percent of vehicle models to verify that the reported results are consistent with requirements. These test results are provided on new vehicle window stickers to help consumers compare the city and highway fuel economy of different vehicles.
Not long after the EPA created these tests, consumers began reporting that the real-world fuel economy of their cars did not measure up to the published estimates. In response, the EPA developed band-aid adjustment factors in the 1980s that lowered the city driving (FTP) test results by 10 percent and highway driving (HFET) test results by 22 percent. Despite these adjustments, the fuel economy estimates on vehicle window stickers were still overstated by an average of at least 10 percent according to data from the Energy Information Administration (EIA).
The EPA's New Fuel Economy Tests
Beginning with the MY 2011, the EPA will use new fuel economy testing and calculation procedures that take into account several factors that were missing or not fully accounted for in previous tests. The new methods will include three additional tests (in addition to the FTP and HFET) designed to replicate the three real-world conditions that can significantly affect fuel economy: air conditioning use, driving at high speeds or with rapid acceleration, and cold temperature driving. These additional tests, which are already used in the EPA emissions certification program, will help capture a broader range of real-world driving conditions and thereby, help bring the EPA estimates closer to the fuel economy consumers can expect.
In order to provide consumers with more accurate fuel economy information before the full testing regime begins in MY 2011, the EPA will use a more sophisticated adjustment factor based on preliminary results from the new testing procedure. These adjusted estimates will appear on window stickers for MY 2008 and later vehicles.
The new EPA fuel economy procedures will downgrade the gas mileage estimates for most vehicles, though nothing about the actual vehicles is changing, only the fuel economy estimates posted on new vehicle window stickers. The EPA approximates that the city fuel economy estimates of most vehicles will drop on average by about 12 percent and by as much as 30 percent. The highway fuel economy estimates will drop on average by about 8 percent and by as much as 25 percent. The impact of the new EPA tests on fuel economy estimates will vary from vehicle to vehicle as some vehicles, like hybrids, are more sensitive than others to such driving factors as air conditioning use and cold weather. Nevertheless, even with the lower fuel economy estimates, many hybrid models will remain fuel economy leaders.
Despite the test and calculation improvements, individual driving habits, traffic conditions, and other factors will continue to affect fuel mileage. Yet, the improvements are a step in the right direction, as they will provide better fuel economy information to consumers who want to make environmentally and financially sound decisions.
