London (CNN) — Subterranean London is riddled with twisting tunnels that carry subway trains, rivers and secrets beneath the city's busy streets.

Now new video reveals that a huge addition to this underground network is almost complete as underground test runs begin on Crossrail -- a $20 billion rail line connecting east and west.

Images show the view from the driver's cabin as the first trains whoosh smoothly through the concrete chamber that will carry 200 million passengers a year when it opens December 2018.

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Installation of the overhead cables that will power the trains has allowed engineers to begin their tests. The video shows the journey as the trains slip below ground into its 26 miles of pristine tunnels resembling something from a "Star Wars" movie.

l e v a r t

Currently the biggest engineering project in Europe, Crossrail -- which will be known as the Elizabeth line in honor of Britain's queen -- has been built on a far grander scale than the city's existing "Tube" lines.

Its 60-mile length (above and below ground) will connect the commuter city of Reading, west of London, to Shenfield and Abbey Wood in the east. It'll stop at 41 stations along the way, including the main transport hubs of Paddington, Bond Street, Tottenham Court Road, Liverpool Street and Canary Wharf.

Transforming travel

The descent to the new Crossrail line at Whitechapel station. Courtesy Crossrail

Hurtling beneath the city at speeds of 60 miles per hour, it'll be faster and more efficient than London's Underground network, parts of which date back more than 150 years.

The city's transport planners hope the project will take some of the pressure off the Underground, which is showing the strain of carrying 1.37 billion passengers per year. Crossrail is expected to increase London's rail capacity by up to 10%.

"With just seven months to go until the opening of the Elizabeth line, which will transform travel across the city, it's great to see testing ramping up beneath the streets of London," says Mark Wild, managing director of London Underground and the Elizabeth line.

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A new automatic train system is currently being tested between Abbey Wood, in southeast London, and the financial center of Canary Wharf. Hundreds of test runs are expected to be completed in the run up to the line's opening.

"The brand new trains that will provide better, quicker and more comfortable journeys for hundreds of thousands of people each day are now running through the tunnels," Wild adds.