A little blue book holds the secrets of London's streets - hundreds of routes, landmarks and roads which help Black Cab drivers take us from A to Z. Known as 'The Knowledge', this information is a requirement for taxi drivers who must pass an exam on the 320 different routes within its pages.

Studying for this exam can take prospective taxi drivers up to four years. Drivers who pass them test will be given either a green or yellow badge depending on where they are applying to be a cab driver.

A four year stint of learning may seem like a tall-order but it is the reason why London's Black Cabs are often cited as being the best taxi service in the world.

What is included in 'The Knowledge'?

The test was introduced all the way back in 1865, after the Great Exhibition held at the Crystal

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