At a Glance

There have been four cliff collapses since August along California's Del Mar bluffs.The largest such cliff collapse was up to 50 feet wide. Coastal erosion is causing the cliffs to collapse.

A stretch of cliff-lined California coastline that's a daily route for trains has collapsed four times in the last five months, but transit officials say the routes are safe for now.

The fourth such seaside bluff collapse since August happened last week near San Diego and briefly interrupted train service.

A long-planned project to stabilize the eroding cliffs in Del Mar will break ground by summer, The plan includes reinforcing sea walls and repairing aging drainage structures.

In the meantime, transportation officials say the trains that run along the bluff are safe — barring a major earthquake.

The tracks are inspected at least twice a week and any time there is erosion, said Stephen Fordham with the North County Transit District.

For now, the landslides pose more danger to those walking on or beneath bluffs than to train operations, according to officials. Though warning signs are posted around the cliffs, pedestrians routinely ignore them.

Train traffic was halted for two hours when the rain-saturated cliff tumbled down last Monday. The collapse followed other similar landslides on Oct. 5, Sept. 27 and Aug. 22, the newspaper reported. In one case, a section of rock that broke loose was reportedly 50 feet wide.

Officials have said the main reason the bluffs are failing is that urban runoff seeps into the ground when residents and businesses irrigate their properties. Coastal erosion from waves and wind also plays a significant role.

There have been three bluff stabilizations, as well as various drainage improvements, since 1998, costing a total of about $5 million. The new round of projects, which is expected to run through 2050, has an estimated price tag of around $90 million, the Times said.

Transportation officials have said that in the long term, the 2-mile (3-kilometer) section of train track that runs through Del Mar will have to be relocated.