Why Did California Build Such Tall Bridges Over Its High-Speed Train Tracks?

A road passes over a high-speed train in a rendering.
High enough for ya? CHSRA

California’s flagship high-speed rail project is in trouble. The state only has enough money to complete the route’s middle segment, running through the agricultural heartland of the Central Valley, but not to connect to Los Angeles and San Francisco, the major population centers on either end. Part of the problem: The budget has soared, with the Central Valley segment alone—thought to be the easiest one to complete—leaping from $6 billion to $10.6 billion.

On Feb. 17, the HSR watchdog Elizabeth Goldstein Alexis shared an interesting observation about the beleaguered project, which is currently under construction in the Central Valley. New bridges over the train tracks—mostly roads, which cross from one side to the other every couple miles or more often—were required to clear the top of the rails by 27 feet.

A Shinkansen 700 series train car—the kind that whips passengers around Japan at 200 mph—is 12 feet and 1 inch high. The new bridges over the new California high-speed rail tracks are so high you could slide two Shinkansens beneath them, stacked on top of each other. Is it normal to build so much room between the top of a train and the bottom of a bridge?

Broadly speaking, yes, because that space will be taken up with electrical equipment—the web of wires that supplies power to the train. At the same time, California may be building the highest high-speed rail overpasses in the world, which reflects the project’s unusual structure—specifically, its designers’ relative indifference to construction costs compared to future maintenance costs.

Goldstein Alexis is a co-founder of Californians Advocating Responsible Rail Design, an advocacy group that has scrutinized the California High Speed Rail Authority for a decade and warned about some of its questionable practices—in particular the reliance on the contractor-industrial complex, wherein a handful of firms are responsible for both designing and building (not to mention lobbying for) so many U.S. rail infrastructure projects. They have been very poorly supervised by CAHSR, a November state audit concluded.

More broadly, the results of this arrangement have been disastrous by international standards. American rail is considerably more expensive than comparable projects in Europe. “We end up overbuilding everything,” Goldstein Alexis suggested. “And once you overbuild, there are knock-on effects.”

It was the world’s megacontractor-extraordinaire, WSP USA (then known as Parsons Brinckerhoff) that made the 27-foot bridge standard for the project in its 2009 design criteria. (WSP declined to speak with Slate for this story, and directed questions to the CHSRA, which runs the project.)

If you’ve been to the Central Valley recently, you might have noticed the enormous mounds of dirt that constitute the overpass foundations. Bigger bridges cost more—not just because they require bigger supports, but because the state has to buy enough land to build long, gentle ramps bringing the road up to the crossing height. (Interstate highways require 16 feet of vertical clearance, for comparison.) Land acquisition has been a problem for CAHSR. So have, in at least two instances, the design and construction of the overpasses.

Earlier studies in California had envisioned an HSR corridor with lower bridges, including a 2004 EIS that set out a vertical clearance of 21 feet. A 2013 study by the Center for Transportation Research at the University of Texas suggested high-speed rail in that state could be designed with “at least 19 feet of clearance.” France’s SNCF—whose offer of assistance was turned down by California a decade ago—manages with just over 21 feet of clearance to run its world-class TGV trains.

Still, several engineers suggested 27 feet was within the range for high-speed rail clearances. “They look very average against norms for global railways,” said Noel Dolphin, an engineer with the Swiss railway electrification firm Furrer + Frey. He said California’s bridges came out to perhaps a half-foot higher than what he would have designed, but that the difference in cost would be minimal.

“Of course [higher clearance] makes it more expensive, but the marginal increase is negligible compared to many other cost overruns,” said Roberto Illanes, an engineer working on a different stretch of the project.

On Monday, I spoke with Frank Vacca, the chief of rail operations for the California High Speed Rail Authority. The trains would draw their electricity from a contact wire 17.5 feet above the track, he said. The catenary—the collection of related electrical equipment—occupied the next five feet. There are three feet of clearance for the feeder wire. Finally, there’s a foot and change of electrical clearance.

There are ways to design overhead wires that require less space. For example: In Japan, Shinkansen trains get 25 feet of room under bridges, but by attaching the catenary to the overhead structure, the height can be lowered to 23 feet. In California, by contrast, engineers committed to have free-standing electrical equipment under overhead bridges. “A limited amount of excessive offset in the Structure Gauge is not normally a concern,” they wrote, “so in case of doubt, it is better to err in the direction of more clearance rather than less clearance.”

Does that make the bridges higher above the tracks and more expensive to build? Yes. But, says Vacca, because the bond proposal that funded the HSR project requires the system to cover operations and maintenance with ticket sales, there was a strong incentive to reduce the kind of variable design that would require more care down the road. “Our construction design requirements tend to build a system that’s optimized the use of construction one-time costs as opposed to long-term maintenance costs,” he said. Spend now, save later. Or at least that was the idea.

This post has been updated with information from the SNCF.