As GM will tell you, over and over, almost four out of five U.S. vehicles travel less than 40 miles a day. Which means that, with a 38-mile electric range, the 2013 Chevrolet Volt could let drivers commute solely on electricity for weeks at a time.
More than that, the Volt is one of the most energy efficient cars sold in the U.S. Only a handful of battery electric vehicles--the tiny Mitsubishi i, the all-but-unavailable Honda Fit EV, and the Nissan Leaf--best its 98-MPGe rating. (That's up from the previous year's 94 MPGe, by the way.) Every one of those vehicles, however, requires several hours to recharge once the battery pack is depleted. The Volt can keep going indefinitely on its range-extending gasoline engine.
While we would rank battery electric cars higher than any car with a gasoline engine (including the Volt), it still gets our top rating of 10 because under certain circumstances, it can be driven almost indefinitely with no tailpipe emissions at all. It depends on how often you're likely to travel beyond its electric range. For certain high-mileage individuals, a 50-mpg Prius may burn less gasoline overall than a Volt running on a mix of grid power and then at 37 mpg from its range-extending engine.
Running on electricity is virtually always cheaper as an energy source than gasoline, though prices for electricity can vary by a factor of 10 across the country. In part, their efficiency is due to the fact that gasoline engines are notably inefficient at converting the energy content of their fuel into forward motion. Many studies have looked at the environmental impact of running on electricity produced from dirty coal, with most concluding that if you compare to a 50-mpg Prius, there are a few states in which that Prius is marginally cleaner on a wells-to-wheels basis. But if you compare to the average 25-mpg car, then electric running in a Volt--or any other plug-in car--is always cleaner.
It takes 7 to 10 hours to recharge a full-discharged Volt battery pack using 120-Volt household current and the standard charging cord stowed in the Volt's load bay. At a 240-Volt Level 2 charging station, whether a public unit or one installed in your private garage, that's more than cut in half. Still, if you can charge a Volt overnight reliably, that Level 2 station isn't an absolute requirement for the Volt--unlike for battery electric cars.