Volkswagen is moving right along with its plan to put a plug-in hybrid on the road by 2011, road-testing a "Twin Drive" Golf that goes 30 miles on lithium-ion battery power alone.

The proof-of-concept test mule roaming Berlin uses a diesel-electric drivetrain, but VW says the production model will ditch the 1.4-liter turbodiesel in favor of a 1-liter turbocharged gasoline engine. Although the VW engineers discussing Twin Drive during the debut of the sixth-generation Golfcalled the engine a "range extender" – the same term GM uses for the gasoline engine in the Chevrolet Volt – it's not.

The engine in VW's Twin Drive system actually drives the wheels, whereas the engine in the Volt only charges the battery as it approaches depletion. Be that as it may, the plug-in Golf runs on electricity alone to about 30 mph, at which point the engine takes over, according to the engineers who told Motor Trend about the system.

Twin Drive ditches the transmission, a move that helps compensate for the weight of the electric motor and the 350-pound Sanyo battery pack mounted under the trunk. The electric motor provides sufficient torque to get the car moving up to 30 mph, at which point the engine takes over with a single gear ratio roughly equivalent to top gear in a conventional car. The electric motor also provides additional oomph for hard acceleration.

Regenerative braking helps keep the 12 kWh battery charged, and there's an "e-mode" for tooling around town under battery power alone. With no transmission, reverse gear is handled by the electric motor, according to Motor Trend.

Although VW is eager to put a demonstration fleet on the road, there's still no word on when, or if, the automaker will put the cars in showrooms. But as we noted when we first told you about Twin Drive, the German government is eager to see plug-in hybrids on the road ASAP and announced a $23.5 million dollar program to help automakers develop such vehicles within four years. Germany's environmental minister, Sigmar Gabriel, says there could be 1 million hybrids on the road in Germany by 2020 and 10

million a decade after that. With any luck, some of them will be VWs.

Photos by Volkswagen.