New images released today give an intriguing insight into Europe's largest infrastructure project - the "tunnelling marathon" that is taking place beneath the streets of London.
In total, 26 miles of underground passageways are being created for Crossrail - the rail line that will eventually connect Maidenhead in Berkshire with Shenfield in Essex, via Heathrow and central London.
More than 7,000 people are now employed on the project, with work continuing round-the-clock.
Five tunnelling machines are now in operation - dubbed "Phyllis", "Ada", "Elizabeth", "Victoria" and Sophia". Together they have created more than three miles of tunnels - with 500m the current record for a week's work.
Andrew Wolstenholme, Crossrail’s Chief Executive said:
"With 26 miles of new tunnels to be built for Crossrail we are delivering our own London marathon beneath the streets of the capital. This is a huge and complex task with work underway 24 hours a day below London’s streets but our first few miles of tunnel are now completed. These new underground images show the scale of transformation taking place beneath London and the essential new transport links being created with every metre of new tunnel built.”
The £14.8 billion route - due to be completed in 2018 - will ultimately cover 73 miles, passing through 37 stations. Two twin-bore tunnels (of 13 miles each) will take the line under central London.
Transport bosses say it will increase London's railway capacity by 10 percent.