On those sky tracks, trains are supposed to hurtle along at speeds up to 220 mph.
Critics say it's urgent that this design feature be reconsidered before the state begins construction on the first segment of the line in the Central Valley. The recent rail disaster in China demonstrates the dangers of running bullet trains on viaducts at top speed, they say.
Meanwhile, the elevated structures add billions in construction costs to a project that increasingly seems to be seriously underfunded, even as it prepares to break ground.
"Viaducts were the (California High-Speed Rail Authority's) preferred answer to almost any alignment problem, despite known seismic and safety vulnerabilities," Richard Tolmach, president of the California Rail Foundation, wrote in a review of bullet train design issues in this month's California Rail News newsletter.
In an interview, he said putting the bullet train's tracks on solid ground could shave nearly $4 billion from the cost of building the 165-mile Central Valley line, now estimated at as much as $13.5 billion.
Those savings could be critical to a project with big money troubles.
Many experts believe Congress will never chip in the additional $15 billion the state is counting on to build the system, which would link San Francisco and Los Angeles.
At the same time, a recent study of cost overruns in public-works megaprojects suggests the final price tag on the California bullet train ? now estimated at $45 billion -- could soar to as much as $247 billion if things get out of hand.
Rachel Wall, a spokeswoman for the state High-Speed Rail Authority, acknowledged it's more costly to build viaducts but said they are a necessary design feature if California's project is to provide direct service to Central Valley cities.
In a phone interview, she said California's bullet train project is being built with safety concerns at the fore, saying, "All design options focus on avoiding collisions." In general, she said bullet trains have an exceptional international safety record. Japan has been operating high-speed rail on elevated tracks for more than 40 years without mishap, she said.
As Tolmach wrote, European bullet train projects have avoided elevated tracks whenever possible -- less than 2 percent of France's TGV network is on viaducts, and that includes river crossings.
There several reasons to avoid sky tracks, he said.
The cost difference is eye-opening. Building a mile of viaduct costs five times what it costs to lay a mile of track on the ground, he estimated. Then there's noise and blight. Viaducts have a "propensity to broadcast train noise," he wrote. Meanwhile, urban planning experts long have noted a "Chinese Wall" effect: Rail viaducts disrupt and divide established city neighborhoods.
Finally, when it comes to bullet trains, there's the safety issue. The faster you run trains on viaducts, the greater the risk that a train wreck will be catastrophic.
"Each mile of speed increase diminishes the ability to keep trains from launching off the viaduct in an accident," Tolmach wrote.
Last month's China crash unfolded after a bullet train stalled on a viaduct near Wenzhou. Authorities later said it lost electrical power because of a lightning strike. A second bullet train plowed into the first at high speed, derailing six rail cars and sending four of them plummeting 100 feet off the elevated structure. The death toll was 39. About 200 passengers suffered nonfatal injuries.
By Tolmach's count, the rail authority plans to build 42 miles of viaduct along the eastern edge of the valley between Merced and Bakersfield. Many of the structures would carry the bullet trains across watercourses that lace the area.
Almost all of those viaducts could be eliminated at enormous cost savings, Tolmach said, but it would require a rethinking of the project.
If the rail line were relocated to the western edge of the valley, on the right of way of the I-5 freeway, "you'd be building it on the ground the entire way," he said. "And it's a state right of way with plenty of room for some tracks."
But such a route would require east-west feeder rail lines to connect the bullet train to the valley cities. Wall, the rail authority's spokeswoman, said that concept was rejected early on.
"An initial focus of the high-speed rail system is, are you going to serve the growing population of the Central Valley or not?" she said. Directly connecting Central Valley cities became a "fundamental goal" of the project, and that ruled out the I-5 route, she said.
Story courtesy of our media partners at California Watch (A Project of the Center for Investigative Reporting)