LONDON, July 21: Here are key facts about London’s underground train network, which is the biggest and the oldest in the world: The London Underground, known as The Tube, opened the first line, the Metropolitan, in 1863 between Paddington and Farringdon stations. The system has 287 stations.

The Tube is one of the world’s deepest metro systems. Its deepest point is under Hampstead Heath in north London where it descends to 67 metres. The Piccadilly Line, hit by one of the July 7 blasts is among the deepest on the network, which hampered rescue efforts.

The Tube network has 253 miles (408 km) of track and consists of 12 lines. At 34 miles (55 km), the east-west Central Line is the longest.

The busiest station on the network is Victoria, closely followed by Oxford Circus, both of which are the start or end points for more than 85 million passengers each year. The next largest is King’s Cross with nearly 70 million passengers a year.

Less than half of the network is actually underground. As the track heads out to London’s sprawling suburbs it emerges to run largely above ground. —Reuters