2010 Plug-in Prius Prototypes – Click above for high-res image gallery

It's been two-and-a-half years since we last got behind the wheel of a plug-in Prius. The name is the same, but today's plug-in Prius is a totally different vehicle, and it was high time to see what changes Toyota has made to the plug-in hybrid (PHEV) in the ongoing effort to slowly (slowly) get the car ready for the U.S. market. Back in late 2007, for example, the prototype had a NiMH battery pack and the converted vehicle was based on the second-generation Prius. The new fleet of PHEV Priuses that are in San Diego as part of Toyota's Sustainable Mobility Seminar this week are converted 2010 third-gen models and feature upgraded lithium-ion packs.

Toyota has brought the PHEV Prius fleet to the U.S. to begin a two-year test and monitoring period. The vehicles are equipped with transmitters from Qualcomm that record not only driver behavior while in the driver seat but also how often the car is plugged in. We'll have more information soon with technical detail about these cars and an explanation of Toyota's plans to test – and finally release, in 2012 – the plug-in Prius over the next two years. Right now, we want to share what it's like to pilot one of these cars.

The short version is that driving a plug-in Prius is almost exactly like driving a standard Prius, except that the car stays quieter longer thanks to the engine being off more (during short distances). The reason for this is a bigger battery pack and improved all-electric performance. Acceleration, handling, braking – everything feels awfully familiar. Read on after the jump to find out more, including how you can now go up to 64 miles per hour without turning on the gas engine.

Photos by Sebastian Blanco / Copyright ©2010 Weblogs, Inc.

Sixty-four mph was the highest speed we managed to achieve while staying in pure EV mode, and it turns out that most of our two 10-mile loops were completed using battery power (we managed 70 percent on the highway loop, then 83 percent on the city loop when we started with a full pack). The newest PHEV Priuses have a maximum all-electric range of around 13-14 miles, compared to the seven miles in the plug-in version of the second-gen Prius.

In the new models, driving on all-electric power is indicated by a green car image that says "EV" in the driver information screen (see below). If the gas engine kicks in, then this picture turns to a simple, empty outline. This is useful, because when you're traveling at highway speeds, you can't always tell when the engine turns on. When you're driving in quiet locations, then the engine is noticeable, but other than that, the EV light is your only signal that you've moved from electrons to petroleum.

This all reinforces the impression that the new plug-in Prius is just a more advanced version of the regular Prius you can drive today. You start the car the same way (but now the button is a nice blue color) and shift and steer just like always. The car even has three driver-selectable modes – Eco, Power and standard – that are similar to the options in the third-gen Prius (there, though, the choices are Eco, Power and EV).

The main feature of Eco mode in the new PHEV Prius is that the pedal becomes physically more difficult to depress, and so the throttle is opened at a smoother rate during acceleration. In practice this makes the go pedal less responsive, which will annoy anyone who wants to speed away from a red light. But does anyone who wants to do that also want to drive a plug-in Prius? We didn't think so. In any case, when you really step down, then the charge/power bar moves all the way into the red on the right side of the screen. This is a visual that should be quite familiar to anyone who drives a standard 2010 Prius. Noticing a trend?

Except for the few seconds it takes to plug and unplug the car each day, the current version of the PHEV Prius is the regular Prius, just with better fuel economy. How much fuel does it use? Like with all plug-ins, the answer depends on how far you drive each day. For us, on our short routes, the info screens in our test cars read 99.9 mpg. If we'd driven much further, we'd have seen a serious decrease in this number because we exceeded the car's EV range, but we imagine drivers can expect to get mpg numbers in the upper 50s, easy, on most days. Thanks, batteries. By the way, those batteries take around three hours to charge from a standard 110 outlet and each vehicle comes with a charge unit that plugs into a standard outlet and feeds the car juice through a J1772 connector.

What else is different about these cars and the regular 2010 Prius? Well, these models have the PHEV-specific blue mica metallic paint color, for one. Also, the trunk floor is slightly raised up about two inches (see here) to make room for an extra 220 pounds of batteries and there are some cooling vents under the back seat. The batteries are in one pack, but are divided into three modules. One module is for the standard hybrid system while two are dedicated to the EV drive. We don't quite get why Toyota felt the need to separate the pack into three parts, but asking some questions about this set-up is one of many things at the top of our list once we get to spend some time with an engineer. Stay tuned for that, and more.

Photos by Sebastian Blanco / Copyright ©2010 Weblogs, Inc.

Our travel and lodging for this media event were provided by the manufacturer.

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