Elon Musk to unveil underground transportation tunnel

Tech entrepreneur Elon Musk is set to unveil an underground transportation tunnel that could move people faster than subways.

Musk plans to unveil the test tunnel Tuesday, as well as the autonomous cars that will carry people through it. He's also set to show off elevators he says will bring users' own cars from the surface to the tunnel.Tuesday's reveal comes almost two years to the day since Musk announced on Twitter that "traffic is driving me nuts" and he was "going to build a tunnel boring machine and just start digging."

Since then, he's revealed a handful of photos and videos of the tunnel's progress. The tunnel, meant to be a "proof of concept," runs about 2 miles (3.2 kilometers) under Hawthorne, California, Musk's SpaceX headquarters.