Caltrans Deploys Real-Time Landslide Monitoring on Highway 1 ​

Caltrans District 5 has installed a network of 85 real-time slope monitoring stations along a 40-mile stretch of Highway 1 through Big Sur, deploying inclinometers, piezometers, and surface displacement sensors on hillsides that have been enthusiastically depositing themselves onto the highway for as long as the highway has existed. The system, which cost $12 million, represents the state's most ambitious attempt yet to predict when a million cubic yards of colluvium will decide to go for a swim.

For context, Highway 1 through Big Sur has experienced 17 major landslide closures since 2010, with the most notable being the 2017 Mud Creek slide that buried a quarter-mile of road under 6 million cubic yards of debris and took 14 months to reopen. The new monitoring network aims to detect precursor movements before catastrophic failure, giving Caltrans time to close the road proactively rather than reactively. The difference being: closing the road because sensors detected 2mm/day of creep is dignified; closing the road because a mountain fell on it is not.

How It Works ​

Each station includes a ShapeAccelArray inclinometer embedded in a borehole (measuring subsurface displacement), vibrating wire piezometers (measuring pore water pressure, aka "how much rain has this hillside absorbed"), and GNSS surface monuments tracking millimeter-scale ground movement. Data transmits via cellular and satellite uplinks to Caltrans's Transportation Management Center, where algorithms flag anomalous movement patterns.

The system was calibrated using data from the 2023 and 2024 wet seasons, which were generous enough to provide several minor slope failures for validation purposes. Nature: always willing to help with research.

Early Warning Protocols ​

When monitoring thresholds are exceeded, the system triggers a three-tier response: yellow (enhanced monitoring), orange (equipment staging and public advisory), and red (road closure). Caltrans estimates the early warning capability could reduce closure response time from "well, the road is already gone" to 12-24 hours of advance notice, which is enough time for tourists to reroute and for locals to stock up on essentials.

The pilot program runs through 2028, with potential expansion to other vulnerable corridors including SR-17 through the Santa Cruz Mountains and SR-299 in Trinity County.