This is a concept 3-wheeler that I thought was definitely worth adding.  Designed in 2008 by student Javad Ghaffaian the Magic Trike won the Car Design News’ 2008 design contest. 

At a touch of the button the vehicle turns from a 3-wheeler into a 2-wheeler by lifting the third wheel into the air. This way it can use normal roads and then in heavy traffic turn into a motorcycle and squeeze though traffic as well as making use of  motorcycle lanes

Inside the seats in the cabin remain upright as the vehicle switches from one form into another.

At the moment it is quite a challenge for current engineering though would be amazing if such a vehicle ever did go into production.