The most congested city in all Europe is London. The traffic that chokes England's capital is legendarily bad and is only expected to get worse.
Crossrail is a £15 billion ($20.25 billion), multiyear attempt to arrest that downward spiral. The project will add a new line, the Elizabeth Line, to London's Underground. Since it began in 2009, it has been Europe's largest construction project. While London has gone about its business, giant tunnel-boring machines have been burrowing underneath the city, navigating an already crowded subterranean infrastructure to find a path for new subway tunnels.
When it's completed, Crossrail will run for 60 miles, adding 10 stations underneath London and bringing mass transit to 1.5 million additional people. The hope is that they will no longer rely on more polluting means of transportation, such as cars.
London has grappled with its traffic problem with such surface remedies as congestion pricing. As it moves into the future, the city may find that its best solutions lie underground.