Tech entrepreneur Elon Musk has unveiled his ground-breaking underground transportation tunnel, which he hopes will provide an answer to "soul-destroying traffic" across the world.
Reporters and invited guests took some of the first journeys in the revolutionary subterranean tube system beneath the surface of Los Angeles, which could eventually hit speeds of 150mph.
Guests were driven along the city's streets in a Tesla Model S electric car about a mile away from the departure point known as O'Leary Station.
The station, situated in the middle of a residential area – "basically in someone's backyard," Mr Musk said – consists of a wall-less lift which slowly took the car down a wide shaft, roughly 30ft below the surface.
After a narrow tunnel emerged, the Tesla driver sped up along the route.
The vehicle jostled significantly during the journey, which was bumpy enough to give one reporter motion sickness.
Mr Musk described his first journey as "epic".
He told reporters: "For me, it was a eureka moment.
"I was like: 'This thing is going to damn well work.'"
He said the journey is bumpy at the moment because "we kind of ran out of time", and there were some problems with the speed of his paving machine.
Of future systems, he said: "It'll be smooth as glass.
"This is just a prototype. That's why it’s a little rough around the edges."
Later, Mr Musk emerged from the tunnel himself inside one of his cars before giving a speech to reporters and guests about the technology and why it makes sense.
He said: "Traffic is soul-destroying. It's like acid on the soul."
The entrepreneur explained for the first time in detail how the system, which he simply calls "loop", could work on a larger scale beneath cities across the globe.
Autonomous, electric vehicles could be lowered into the system on the special lifts, which could be placed almost anywhere cars can go.
The cars would have to be fitted with specially designed side wheels which pop out perpendicular to the car’s regular tyres, fitted to run along the tunnel’s track.
The cost for such wheels would be about 200-300 dollars (£158-£237) per car, Mr Musk said.
A number of autonomous cars would remain inside the tunnel system just for pedestrians and cyclists. Once they are within the main arteries of the system, every car could run at top speed except when entering and exiting.
Mr Musk said the system would operate more like an underground motorway than a subway.
He added that the cars would have to be autonomous to work in the system, but not Teslas specifically, and they would have to be electric owing to the fumes that would be created otherwise.
At 40mph, the demo journeys were considerably slower than the 150mph the future system will run at, according to Mr Musk.
For the privately-funded test tunnel, Mr Musk acquired a tunnel-boring machine which had been used in a San Francisco Bay Area building project and put it down a shaft in a car park at the SpaceX headquarters.
One project Mr Musk is planning, known as the Dugout Loop, would take Los Angeles baseball fans to Dodger Stadium from one of three subway stations.
Another would take travellers from the centre of Chicago to O'Hare International Airport. Both projects are in the environmental review phase.
Mr Musk said he is hoping that an extensive network will be open in Los Angeles before the city hosts the 2028 Olympics.
He said: "Wouldn’t it be incredible if you could travel around LA, New York, (Washington) DC, Chicago, Paris, London – anywhere – at 150mph?
"That'd be phenomenal."