Trust the team over at Rinspeed to come up with an outside-the-square concept like this. It's called the Dock+Go and it is based on the Smart Fortwo with an electric powertrain.
The concept uses a connectible rear subframe, modelled like the back of a Smart Fortwo, which provides range-extending power via a combustion engine. When driving without the connecting frame, the Smart Fortwo is a zero tailpipe-emissions personal mobility tool.
Once the battery levels get a bit low, it's just a matter of reversing the Rinspeed into the third axle to obtain extra power, and a source of charge for the vehicle's on-board batteries. Without the range-extender connected, the vehicle offers a electric range of 120km. Total range is yet to be revealed.
On top of the range-extending abilities, the third axle also doubles as extra cargo space. Rinspeed envisions the space as being utilised for pizza deliveries, with space for a pizza warmer or a comprehensive tool box for mechanics and vehicle repair workers.
The Rinspeed Dock+Go concept will debut at the 2012 Geneva Motor Show in March.