The upcoming Toyota Prius plug-in hybrid (PHEV) will benefit from two new tricks that will further improve efficiency. The first is a driver-controlled, electric only mode, allowing the driver to preserve the electric portion, rather than using it upfront. The second is the ability to direct the regenerative braking energy to the electric-vehicle battery, rather than the regular hybrid system battery.

Unlike plug-in hybrids thus far, the production Prius PHEV will allow you to preserve the electric energy for when you get to a city, rather than “wasting” it on a highway cruise if that happens to be the first part of the drive. Operating in this manner would allow the vehicle to run in electric mode during stop-and-go traffic, where gasoline engines are least efficient. It would also benefit the air quality and noise levels in downtown. Incidentally, the Chevrolet Volt with European specifications does just that. (This functionality is something that my colleague Gabe Shenhar suggested in a blog after driving the Prius PHEV prototype.)

The other big advance is the ability to recharge the large plug-in battery using regenerative braking. (With plug-ins, there are usually two batteries, one that gets charged from the wall and a much smaller battery that is used to store energy from the engine or brakes.)

A common complaint among early prototype testers was that they could not gain additional EV-only range by using hypermiling techniques, such as coasting on long downhills to recoup energy through regenerative braking, thus extending the pure electric range.

In driving our all-electric Nissan Leaf and other electric cars such as the Mini-E, we’ve found that regenerative braking or long coasting can be a meaningful charging source that can recover several miles worth of range.

We’ll be interested to test the production version of the plug-in Prius to see what effect these promising new features have on its mileage.

See our guide to fuel economy, as well as our guide to alternative fuels.