No wonder the EPA estimates are so far off. If you look at the city/hwy
schedules, they are very misleading.
http://www.fueleconomy.gov/feg/fe_test_schedules.shtml

What do you think of when you see "highway"? I think of cruising down
the freeway at 65 mph. Well, the EPA thinks that highway means average
speed of 48 mph and top speed of 60 mph. I can't think of any driving
situation that matches that.

What do you think of when you see "city"? I think of stop and go
between 0-30 mph. The EPA's city test is mostly stop and go, but the
top speed during the test is 56 mph! How can the top speeds for city
and hwy test only differ by 4 mph?!!

Also, the EPA tests on a "treadmill".
http://www.fueleconomy.gov/feg/how_tested.shtml

Supposedly, they account for drag: "The energy required to move the
rollers can be adjusted to account for aerodynamic forces and the
vehicle's weight." But do they actually vary the simulated drag
differently for each vehicle's drag coefficient? Do they increase the
simulated drag when speed increases? I'm very skeptical of the realism
of the test because drag is a huge component of fuel efficiency at
higher speeds.