Europe's Largest Civil Engineering Project

The new rail line -- 40 years in the planning -- will stretch 70 miles across London, and is expected to carry 20 million people per year. The system is expected to help alleviate some of the pressure on London's existing rail system

NPR's Philip Reeves discusses two of the massive tunneling machines -- named Ada and Phyllis -- and the scope of the tunneling project.

The tunneling machines are "one and a half times the length of a football field," says Reeves. "They move at the pace of the average garden snail. And they generate enough force apparently to lift nearly 3,000 London taxis."

"The lines run along the northern edge of Roman and Medieval London and there's a lot of stuff down there. So Crossrail has got a team of archeologists and it says this is one of the most extensive archaeological programs ever undertaken in the U.K. And they've already started finding stuff during construction..."