Final answer:
The efficiency of automobiles is measured by the EPA's fuel economy rating system, expressed in MPG. This system has evolved since 1972 to better reflect real-world driving conditions and to provide consumers accurate comparisons between vehicles. The EPA also allows drivers to input their own data for comparison to these standards.
Step-by-step explanation:
The rating system used to measure the efficiency of automobiles is commonly known as the fuel economy rating, which is expressed in miles per gallon (MPG). The EPA (Environmental Protection Agency) is responsible for this rating system which was developed to help consumers compare the fuel efficiency of different vehicles.
The EPA fuel economy tests give consumers an idea of a vehicle's gas mileage under controlled conditions and aim to simulate real-world driving.
However, the initial test procedure has been revised multiple times since 1972 to better reflect changes in driving conditions and styles. For instance, in 1984, the EPA introduced adjustments to the fuel economy figures to compensate for changes in driving conditions and to better correlate with real-world driving experiences.
Over the years, additional tests like the US06 (a high-speed test) and SC03 (an air-conditioner test) have been added to the procedure, with the latest major update applied to model year 2008 vehicles.
Moreover, real-world fuel economy statistics can also be added to the EPA's 'Your MPG' database by drivers, enabling a comparison between one's own experience and the EPA's standardized test results. The importance of accurate fuel economy testing is underscored by rules that require manufacturers to use EPA test results when reporting efficiency figures, not allowing for alternative testing methods.
This is critical because fuel economy is closely linked to emissions, which the auto industry is continuously working to reduce—as seen with the Obama administration's 2009 announcement of new fuel economy standards.