Detailed engineering plans were released Friday that inject a dose of reality into Elon Musk’s futuristic, but heretofore vague vision of a new “express” high-speed underground public-transportation system that could rival LA Metro’s light rails.

The three-dimensional tunnel network, called Loop, would run from Long Beach Airport to Sherman Oaks, parallel to the 405 Freeway. Short complementary routes from Los Angeles International Airport to Dodger Stadium, and out to the beaches in Santa Monica and the South Bay beach cities, also are in the plans.

Passengers would speed through the all-electric system inside rectangular pods attached to autonomous skates that are affixed to a track more than 30 feet below ground. Musk’s Boring Co., which already is digging a tunnel beneath Hawthorne streets adjacent to the tech titan’s SpaceX headquarters, is currently seeking permits from the city of Los Angeles to extend the tunnel to the San Fernando Valley.

At the heart of the system are electric-powered skates.

“The electric skate is a platform on wheels propelled by multiple electric motors which can be used to transport between 8 and 16 passengers,” according to the excavation permit, released by Los Angeles’ Department of Engineering. “The skate’s top speed within Los Angeles of between 125 and 150 mph is well below the skate’s maximum capabilities and is a standard operating speed used routinely in The Boring Company’s testing facility in Hawthorne.”

Entry and exit points to the network would be through “side tunnels,” so the pods can speed through the network without significant slowing.

A 2-mile test track is now under construction from Musk’s rocket-manufacturing company SpaceX, west under 120th Street toward the 405 Freeway. It would connect to the main part of the tunnel network, according to the plans.

Meanwhile, a separate track from LAX to Union Station and Dodger Stadium near downtown Los Angeles would be constructed.

The Hawthorne tunnel has a vehicle elevator that can deliver electric cars and passenger pods into the underground track. But the proposed public-transit system does not include the use of cars inside the tunnel.

The first phase of the project would be a 6.5-mile, privately funded “proof of concept” tunnel in Silicon Beach, connecting Santa Monica, Playa del Rey, Marina del Rey, Playa Vista and Culver City along the freeway.

“Phase 1 would not be utilized for public transportation until the proof-of-concept tunnel is deemed successful by county government, city government, and The Boring Company,” the plans state. “Phase 2 would be developed separately from this permit application and in cooperation with Los Angeles County, the city of Los Angeles, city governments in the greater Los Angeles area, and the general public.”

This initial route would be used to test the system’s safety, operational procedures, and demonstrate line-switching capabilities.

“If Phase 1 is successful, TBC would submit additional permit applications to construct a large, three-dimensional tunnel network for public use,” the plans state. “The Loop would create a significant public benefit as a result of decreases in urban congestion, decreases in driving commute times, increases in public safety, decreases in public transit trip times, decreases in transportation cost/fares, and decreases in greenhouse gas emissions.”

On Wednesday, Musk announced that The Boring Co. will bid on its first government contract to construct a high-speed rail route between downtown Chicago and O’Hare International Airport. The company also is working on a tunnel connecting Baltimore to Washington, D.C.