Fuel
economy is measured under controlled conditions in a laboratory
using a standardized test procedure specified by federal law.
Manufacturers test their own vehicles—usually pre-production
prototypes—and report the results to EPA. EPA reviews the
results and confirms about 10-15 percent of them through their
own tests at the National
Vehicles and Fuel Emissions Laboratory.
In the laboratory, the vehicle's drive wheels are placed
on a machine called a dynamometer that simulates the
driving environment—much like an exercise bike
simulates cycling.
The energy
required to move the rollers can be adjusted to account
for wind resistance and the vehicle's weight.
On the
dynamometer, a professional driver runs the vehicle
through a standardized driving routine, or schedule,
which simulates “typical” trips in the city
or on the highway.
