It has been more than 50 years since Japan completed the world's first dedicated high-speed rail line between Tokyo and Osaka.

It has become known around the world as the "bullet train". The Tokkaido line is by far the busiest in the world, carrying nearly 150 million passengers a year.

Now Japan Rail is about to embark on building a completely new Tokyo to Osaka line, with trains that will travel twice as fast as the old bullet train.

Our Tokyo correspondent Rupert Wingfield-Hayes has been for a ride.