Apparently, there are three different fuel economy figures. From the National Highway Transportation Safety Administration (NHTSA):
[There are] three different sets of fuel economy values- NHTSA’s CAFE values, EPA’s unadjusted dynamometer values, and EPA’s adjusted on-road values:The NHTSA values are the law for the manufacturer, but the manufacturer's fuel economy average is computed via one of two methods:
- NHTSA’s CAFE values are used to determine manufacturers’ compliance with the applicable average fuel economy standards
- The EPA's unadjusted dynamometer values are calculated from the emissions generated during the testing using a carbon balance equation. EPA knows the amount of carbon in the fuel, so by measuring the carbon compounds expelled in the exhaust they can calculate the fuel economy.
- EPA’s adjusted on-road values are those values listed in the Fuel Economy Guide and on new vehicle labels, adjusted to account for the in-use shortfall of EPA dynamometer test values. (formatting mine)
EPA is responsible for calculating the average fuel economy for each manufacturer. CAFE certification is done either one of two ways: 1) The manufacturer provides its own fuel economy test data, or 2) the EPA will obtain a vehicle and test it...using the same laboratory test that they use to measure exhaust emissions (fuel economy standard #2 from above).This laboratory test has always been modified down to better mirror real world fuel economy (#3), so the CAFE standard has apparently been overestimating actual average fuel economy of the American fleet for years.
Bring that story up to date with this fact: the EPA estimate of on-road fuel economy has also been overestimating mpg for American cars, by as much as 50% (link discusses hybrids, but the overestimate applies to all vehicles). So, to summarize:
Actual fuel economy <>
If conserving fuel means saving fuel in the tank, not just on paper, then we need a CAFE test and a CAFE standard based on reality.
No comments:
Post a Comment