Industrial Designers at Purdue University invented a new Bike design called SHIFT.

The SHIFT Bike is intended for children that just started to learn riding. The SHIFT design does not need support it balances itself. The 16" wheel bicycle looks like a tricycle, but as the child gains momentum and learns to balance, the two rear wheels shift inward to merge into one wheel.

No word yet when it will hit the market, but manufacturers are already interested.
More details on Purdue University and in a AP story on Yahoo.