The way the USA do fuel economy as of 2007/8 is what we should petition for here in the UK !!!!
Background / Current Tests and Methods
The city and highway MPG estimates have been provided to consumers since the 1970s as a tool to help shoppers compare the fuel economy of different vehicles. Currently, EPA relies on data from two laboratory tests to determine the city and highway fuel economy estimates. The test methods for calculating these estimates were last revised in 1984, when the fuel economy derived from the two tests were adjusted downward—10 percent for city and 22 percent for highway—to more accurately reflect driving styles and conditions.
The city and highway tests are currently performed under mild climate conditions (75 degrees F) and use acceleration rates and driving speeds that EPA believes are generally lower than those experienced by drivers in the real world. Neither test is run with the use of accessories, such as air conditioning. The highway test has a top speed of 60 miles per hour, and an average speed of only 48 miles per hour.
Since the mid-1990s, EPA's emission certification compliance regulations have required the use of three additional tests which capture a much broader range of real-world driving conditions; specifically: high-speed, fast-acceleration driving and the use of air conditioning and colder temperature operation (20 degrees F). Not only do these conditions impact the amount of air pollutants a vehicle emits, they also have a significant impact on a vehicle’s fuel economy. However, they are not currently required to be used to measure fuel economy.
The Proposed New Methods to Determine Fuel Economy
EPA is proposing to incorporate these tests into the methods used to determine the fuel economy estimates posted on the window stickers of new cars and light trucks. For the first time, the EPA fuel economy estimates will reflect vehicle-specific data from tests designed to replicate three real-world conditions that can significantly affect fuel economy: high speed/rapid acceleration driving, use of air conditioning, and cold temperature operation. Previously, these conditions were accounted for by across-the-board adjustments, rather than by vehicle-specific testing.
EPA is also proposing that the fuel economy estimates reflect other conditions that affect fuel economy, such as road grade, wind, tire pressure, load, and the effects of different fuel properties. The fuel economy for each vehicle model would continue to be presented to consumers as city and highway MPG estimates.
Auto manufacturers would be required to perform the fuel economy testing specified in EPA's proposal. In the 2008 model year, the new methods would be used to determine the estimates. In 2011, a provision would take effect that would require manufacturers to perform additional cold temperature, air conditioning and/or high speed/rapid acceleration driving tests for some vehicles that may be more sensitive to these conditions. The additional testing would ensure that the fuel economy of those vehicles is more precisely captured. EPA is proposing to delay this additional testing until 2011 in order to provide enough time for manufacturers to plan for the added testing responsibilities. Nevertheless, beginning in 2008, the fuel economy for those sensitive vehicles would still reflect enough of the above effects such that consumers can make good comparisons.