[Big Dave]

Maybe the metric should be gallons per year instead of miles per gallon.

This iswhy I always use the same route for my MPG tests. If road construction forces me off my route I abort the test.

There's other ways to "cheat". Cut your errand driving by shopping over the Internet and let them deliver to your door. Of course, UPS burns the fuel instead of you.

I've always thought that honest MPG testing is possible only on a speedway. A dyno doesn't get aero right, and "real world" testing is subject to traffic and weather. If one rented one of these mile-and-a-half tri-ovals you could put a couple or three cars on the track at a set speed (say 70 MPH) and let them make 100 km actual runs. Use highly accurate fuel weighing devices to arbitrate fuel usage. Viola! Accurate MPG.