Workers lower the tail shield section of a tunnel boring machine into a 45 foot deep pit, during a ceremonial naming and lowering for the Regional Connector Transit Project downtown Los Angeles in 2016.

A company owned by Elon Musk that is trying to lower the cost of building high-speed transit tunnels is nearing completion on the first tunnel, Musk said on Twitter on Sunday.

The first tunnel, under Hawthorne in the Los Angeles area, is almost done and will open on Dec. 10, Musk said. Privately held Boring Co has been promoting its plans for tunnels that would allow high-speed travel between cities.

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