Elon Musk unveils prototype high-speed LA transport tunnel
How will it work?
The plan envisages modified cars being lowered into the tunnel network by lifts and then slotted into tracks on the "loop".
"The profound breakthrough is very simple: it's the ability to turn a normal car into a passively stable vehicle by adding the deployable tracking wheels, stabilising wheels, so that it can travel at high speed through a small tunnel," Mr Musk said.
"The way the loop will work is you will have main arteries that are travelling at 150mph and when you want to go to an exit, you will have an off ramp," he added.
"So you can travel the vast majority of your journey without stopping at 150mph and only slow down when you get to your exit, and then automatically transfer from one tunnel to another. It's like a 3D highway system underground basically."