Rising sea levels and powerful storms are eating away at the ground holding up the tracks on the second most popular Amtrak rail corridor in the U.S. The route runs 351 miles from San Diego through Los Angeles to California’s Central Coast and is also used by freight and commuter trains. 

The erosion has caused landslides that shut down the Surfliner at least a dozen times in the past six years. 

During the shutdowns, engineers have installed boulders, steel pilings and concrete walls that allow the Surfliner to operate again—but only temporarily. Despite the $140 million they have spent on repairs, officials say a more costly, permanent fix is needed because climate change is going to keep pushing up sea levels and making storms more intense.

“Ultimately, these things fail,” said Patrick Barnard, a research geologist with the U.S. Geological Survey. “The water rises and the shoreline wants to move inland.”

Around the U.S., civil engineers are fighting to save hundreds of billions of dollars of coastal infrastructure. Few places are more threatened than California, where transportation routes, homes and businesses built along the Pacific Ocean have long been part of the Golden State’s identity.

In the Central California resort town of Big Sur, officials urged residents to evacuate Wednesday as a storm threatened damage to coastal Highway 1, part of which already collapsed recently. That route has been affected by landslides about 50 times since 2009, and the frequency is growing.

Last year, the California Transportation Department moved a nearly one-mile stretch of Highway 1 in Sonoma County, north of San Francisco, inland and away from bluffs that threatened to crumble beneath it.

To get the Pacific Surfliner on safer ground for the long run, nearly everyone agrees it needs to relocate away from the ocean. Officials are considering moving several particularly vulnerable miles inland through the upscale San Diego suburb of Del Mar and the South Orange County city of San Clemente. The total cost would be billions of dollars. 

Those plans have drawn opposition, particularly in Del Mar, where proposed tunnels under homes have caused residents to worry about everything from noise to vibration to a hazardous spill from a freight train.

“We don’t want to trade off one unsafe situation for another,” said Dave Carey, a Del Mar homeowner and member of a citizens group called Coalition for Safer Trains. 

Amid the local opposition and questions about how government agencies would split costs, officials expect the track relocation process to take years or even decades. Meanwhile, the risks to the Pacific Surfliner only grow. 

“There is no easy answer,” said Chad Edison, chief deputy secretary for rail and transit of the California State Transportation Agency. “In all cases, we have to buy time…”