The main thing to understand about the Toyota Prius Plug-In Hybrid is that it's not an "electric car" as many people use the term.
Yes, it plugs in to any electric socket to recharge the 5.2-kilowatt-hour lithium-ion battery pack. And, yes, its Hybrid Synergy Drive system uses electric torque, either by itself or along with the gasoline engine, to turn the front wheels.
But in a four-day test drive over the long holiday weekend, we came to understand one fact clearly: The plug-in Prius is not an electric car in the same sense as the 2011 Nissan Leaf and or the 2011 Chevy Volt.
Still mostly gasoline
While it travels further just on electric power than a standard 2011 Prius, and can do so at higher speeds, the gasoline engine still provides most of the torque to propel the car in mixed duty cycles.
Over 424 miles, we plugged in the car to recharge the pack six times. (A 22-foot-long cable for 120-Volt charging is provided in a bag in the load bay.) Not all of those periods lasted 3 hours, which meant that twice, the pack was only partially recharged.
We were able to run locally on electric power for a few short trips--especially the downhill ones (our house is toward the end of a mountain path several hundred feet above valley level).
But the exterior temperatures of a Northeastern autumn (25 to 40 degrees F), as well as a duty cycle with almost half the miles on Interstates, cut heavily into the car's ideal electric operating range.
Bottom line? Over our entire test, the Toyota Prius Plug-In Hybrid averaged 53.9 miles per gallon.
That's better than the standard 2011 Toyota Prius hybrid, which the EPA rates at 51 mpg city, 48 mpg highway, for a blended average of exactly 50 mpg. In practice, most drivers of third-generation Priuses seem to get in the mid- to high 40s.
But the Prius Plug-In's mileage was lower than the Volt's blended 60-mpg rating under the EPA's standard test assumptions, let alone the Nissan Leaf's slightly ludicrous "99 MPGe" rating (for a car that uses no gasoline at all).
EV mode: 8 percent
And over a longer 777-mile average (which we retained in the Prius Plug-In's trip computer for comparison), the car operated in EV Mode just 8 percent of the time, and a whopping 92 percent as a standard hybrid.
That can be viewed two ways. It's an endorsement of the fundamental efficiency of Toyota's Hybrid Synergy Drive system, but it's also an indication that the Prius Plug-In's small battery pack only expands incrementally on the standard Prius electric-drive capabilities.
Our recent results also underscore the contrast with our April first test drive of the Prius Plug-In Hybrid, which took place in temperate San Diego.
There, on a 10-mile test route that included low-speed city driving, a 3-mile section of freeway where we hit 86 miles per hour, and a few hills, we obtained "99.9 mpg" and spent 63 percent of our time in EV Mode.
50 to 70 percent of EV range
Over Thanksgiving, in contrast, we achieved between 6 and 10 miles on stated electric ranges of 12.9 to 13.5 miles from a fully charged battery. And after sitting overnight in the cold, the engine switched on as soon as we powered up the car.
To maximize electric range, we used the front seat heaters but not the cabin heater, and accelerated gently. Nonetheless, the battery provided significantly less range in cold weather than it had in San Diego.
Once the EV mode switched off, the Prius Plug-In Hybrid reverted to being a standard Prius with about 100 extra pounds. Our car exhibited a few prototype aspects, including a relay that clicked whenever the brake pedal was pushed or lifted, and a trim buzz under the dash.