Why it matters: It's an ambitious project but if Elon Musk can pull it off, The Borning Company's underground tunnels could put a significant dent in traffic jams that plague major cities around the globe.

Elon Musk last month said his tunnel construction company was nearly finished with its proof-of-concept, a two-mile-long tunnel that stretches from SpaceX’s headquarters in Hawthorne, California, to an LA suburb.

Over the weekend, Musk walked the full length of the tunnel and shared video of it on Twitter.

Musk described it as “disturbingly long,” adding that the project is still on track to open on December 10. The company will be offering free rides to the public the following day.

Musk, fed up with LA’s nightmarish traffic, declared on Twitter in late 2016 that he was going to build a tunnel boring machine and “just start digging.” Many thought it was a joke but with Musk, it’s hard to know when to take him seriously. As it turns out, the plan was very real and now just two years later, we’re a month away from seeing the first prototype tunnel.

It is believed that the tunnels will use autonomous, electric “skates” to zip passengers along a track at speeds of up to 155 mph. According to reports, as many as 16 passengers could fit on a single sled. If successful, the tunnels could help to alleviate traffic headaches in LA and other large cities.