What is red but green, open but closed and old but new? Answer: London's stunning new double-decker buses.

The traditional red double-deckers are a symbol of London. Their iconic status was sealed in 2008 when one bus made the longer-than-usual trip to Beijing to collect a very special passenger: the Olympic Flame.

Now a new bus design has been unveiled and it has been wowingLondoners.

The new bus uses more efficient green technology and has two staircases and an open platform, enabling people to hop on and hop off. It also has a unique asymmetric design for the front end, which gives it afuturistic look.

Despite its innovations the design is not all new. Its exterior is veryreminiscent of London's faithful old double-decker, the Routemaster.

The new bus has a "swooshing" exterior.

In December 2005 the original Routemaster was withdrawn from general service for accessibilityand environmental reasons, but it can still be seen on two heritage routes in London.

In July 2008 a competition waslaunched by the London Mayor, Boris Johnson, to design a new Routemaster bus for the capital. There were over 700 entries, with several designers jointly winning the £25,000 (244,000 Yuan) prize.

The new double-deckers, which have three doors to speed up boarding, are expected to be in service in 2012.

Mr Johnson said: "This iconic new part of our transport system is not only beautiful, but also has a green heart beating beneath its stylish,swooshing exterior".

He expects cities around the globe to be "beside themselves with envy" for what he described as a "stunning red emblem" of 21st-century London.

However, Mr Johnson has not yet persuaded everyone to climb on board. The mayor has been criticised by some for the high cost of the new buses. A normal double-decker bus costs around £190,000 (around 1,900,000 Yuan) but it has cost £7.8m (76,000,000 Yuan) to design and build five new ones.