London, Europe's largest city, is also home to its biggest construction project: Crossrail. Scheduled for completion in 2018, it will cut journey times across the city, dramatically reduce congestion, and is estimated to boost the UK economy by around $67 billion over a 60 year period.
The sheer scale of Crossrail is vast: over 10,000 people are working on the scheme and nine new train stations are being built. Forty two kilometres of rail tunnels are being bored under the city's streets.
"It will be very much a railway of the 21st century," Terry Morgan, Chairman of Crossrail, said in a report for CNBC's Innovation Cities. "It will have brand new trains, brand new stations, and the ability to actually go across London much quicker than you're able to do today."
As well as aiming to dramatically improve the experience of London's commuters come 2018, Crossrail will be well prepared for future challenges, too.
For example, tunnels have been built to accommodate a more frequent service in the future.
"Ours will have the capacity for 12 car train sets in the middle, but we'll buy 10 initially," Morgan said. "We're building in some spare, redundant, capacity that we know we might need at some time in the future, but we don't know when…you only get one chance to build a brand new station in an underground structure."
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