[fusion210]

I recently found out that Car and Driver now includes a 75mph test for their fuel economy numbers. Some might find it useful.

Highway Fuel-Economy Test
We run all our tests at a GPS-verified 75 mph on the same 200-mile out-and-back loop on Michigan's I-94 highway. Our consistent procedure includes a methodical fill-up process, following a specific route, using cruise control, and setting the climate control to the same temperature (72 degrees auto). We also correct for odometer error, and we don't test in heavy wind or rain or with extra passengers. In the event we encounter too much traffic or unusual conditions, we abort the run and try again later.

We follow the same procedure for electric vehicles and plug-in hybrids, except for these, we have additional steps that include making sure the battery is fully charged before starting and recording the kilowatt-hours (kWh) needed to fill the battery after the drive loop. Plug-in hybrids also get a highway EV range and MPGe economy for those miles. MPGe is calculated just like miles per gallon of gas only using the EPA's equivalence factor of 1 gallon = 33.7 kWh of electricity to arrive at the result. For plug-ins that can't hit 75 mph in electric mode, we instead first drain the battery and then start the test in charge-sustaining (hybrid) mode. Since those plug-ins don't use any electricity, their results are in miles per gallon rather than MPGe. Likewise, we have to shorten our route for EVs that don't have the range to complete the entire loop. We still give them an MPGe number, though.