Toyota has been testing their plug-in Prius and it's looking good so far. Initial trials show the plug-in getting 65 mpg (3.6L/100km) in mixed driving. In comparison, the next generation 2010 Toyota Prius is getting 50 mpg in the same cycle.
"That is real-world driving," said Bill Reinert, Toyota Motor Sales U.S.A.'s national alternative-fuel vehicle manager. "I ask my guys to drive them as you drive your normal Prius."
Those figures are in line with what other testers are seeing. Google, for instance, was getting similar numbers from their plug-in testing as part of their non-profit testing of various hybrids and plug-in hybrids, at least until they decided to work at increasing their numbers. After deciding to do some testing, google found they could get 100 mpg out of their plug-in fleet.
But what does 65 mpg vs 50 mpg in mixed driving mean? About 55 gallons a year if you drive 12,000 miles a year. Around 70 gallons if you drive 15,000 miles. If you look at 40 mpg as the lower value (say, what the new Honda Insight will likely get), you're still only saving 115 gallons a year at 12,000 miles.
That's not much, and it's definitely a consideration when you look at the likely price differential between the new Prius (or Honda Insight, for that matter) and the likely price of a plug-in Prius.
But, if you're interested in doing anything you can to reduce oil imports or gasoline emissions, the plug-in that gets 65 mpg is definitely a big step in the right direction. Besides, if you really tried to enhance the way you drive, and not just 'drive your normal' way, you can probably kick the fuel economy way up with a plug-in.
The Chevy Volt, on the other hand, may be getting better numbers because of the way it's designed. The EPA rating may not be available, but some people could see their mpg's in the 100 mpg range if they keep their driving distance down. That's because the Volt won't use the gas engine until it's used up the juice in it's battery pack. After that, your fuel economy is going to go way down, but given how hard they've worked on the design, you're probably still likely to get very good mpgs even when the gas engine is being fully employed.
(A little side-note: going from 65 mpg to 100 mpg only saves you another 65 gallons a year.)
The Plug-in Prius, on the other hand, has been designed to use the battery pack and the gas engine in tandem. Depending on your driving situation, either method could be better.
In case you're interested, here's a quick and dirty conversion from mpg to gallons per year when you drive 12,000 miles a year
|MPG||Gallons per Year|