Almost a year ago, General Motors launched a little marketing campaign connecting its 2011 Chevrolet Volt range-extended electric car to the figure "230 mpg."

As we pointed out at the time, they were basing that projection on a proposed formula for fuel usage patterns that made a lot of assumptions about the driving cycles that would be used.

Frankly, we think the whole exercise sowed confusion. But it sure got the Volt a lot of attention for awhile. Which was, clearly, the goal.

Now, the Environmental Protection Agency has decided not to use the formula GM based its 230-mpg number on.

The agency is still trying to work out how to provide consumers with useful, understandable information on window stickers to go into new cars with blended powertrains, which may operate sometimes on stored electricity and other times using a gasoline engine.

That issue becomes increasingly urgent as the 2011 Volt nears dealerships--first ones will arrive in November or December--with other range-extended electric cars (e.g. the 2011 Fisker Karma) and plug-in hybrids (e.g. the 2012 Toyota Prius Plug-In Hybrid) close behind.

It's a challenging topic, GM admits, meaning that talks among carmakers and regulators are likely to continue to the last possible minute.

As we've also noted before, Miles Per Gallon is a bad way to measure fuel use. It's not consumption--how much fuel you use to go a set distance--which is a linear scale. Instead, MPG is a non-linear scale that confuses people.

While the National Research Council agrees, that topic tends to generates lots of rants from readers who either don't read the full article or think we're proposing that cars use more fuel. Or something. So we're just going to ignore it for now.

As for the 2011 Volt's "gas mileage"? Stay tuned.

General Motors' mysterious 230 logo

General Motors' mysterious 230 logo

[USA Today]