Piedras Blancas Highway 1 Realignment - Caltrans/San Luis Obispo

The California Department of Transportation (Caltrans) realigned a 2.8 mile section of iconic Highway 1 to address current and anticipated impacts from coastal erosion and storm surge.  This section of Highway 1, which is north of the Piedras Blancas Lighthouse in San Luis Obispo County, was already experiencing increased storm damage from flooding and erosion, with these impacts projected to increase with rising sea levels and higher storm surge caused by climate change.  Realigning the highway away from the coast reduces its vulnerability to current damage as well as to future climate impacts and is anticipated to protect the highway from bluff retreat beyond the year 2100. The realigned section of the highway opened in 2017, allowing for the repurposing of the original alignment to add new sections of the California Coastal Trail, and for the restoration of land between the original and new alignments to provide coastal prairie and wetland habitats.

The realignment project involved moving the highway up to 475 feet inland of the original route and restoring the original alignment and adjacent lands to natural conditions. The original alignment was threatened by erosion and damage from waves during storm events and by annual receding of the shoreline adjacent to the highway. Waves also washed over the road during periods of storm activity making the highway impassable and depositing debris on the roadway. Climate change impacts, including sea level rise, were expected to accelerate this damage in the decades to come. The realignment project was designed to protect the highway from coastal erosion for 100 years (i.e., beyond 2100); Caltrans indicated that the agency considered accelerated erosion rates due to climate change impacts in establishing the 100-year erosion line.

Realignment of the road away from the coast was Caltrans’ preferred course of action to reduce the vulnerability of the highway to erosion and storm damage. Caltrans considered armoring of the bluffs to prevent erosion but rejected that option due to greater anticipated environmental impacts and inconsistency with the Local Coastal Plan and California Coastal Commission policies that call for protecting coastal resources and natural coastal processes. The San Luis Obispo County Coastal Plan prohibits the construction of permanent structures on the beach and calls for avoiding the permanent armoring of the shoreline. In addition, Caltrans found that armoring would not protect the highway from waves during high surf and could cause increased erosion in areas adjacent to the project area.

Caltrans also considered a no-build scenario in which the highway would remain in its original alignment but rejected this scenario because the agency projected continued erosion, damage to the roadway, and eventual closure of the highway. Although the no-build scenario would have had the least environmental impact, Caltrans determined that allowing closure of the road violated its mission of providing for public mobility and safety. Caltrans found the realignment option to have no significant impact and identified it as the preferred alternative in 2010 (as identified in the Final Environmental Impact Report). 

Project construction on the highway realignment began in 2015 and was completed in 2017. Construction of the new roadway cost $19.7 million and was funded through the State Highway Operation and Protection Program. The project included removing box culverts and armoring measures, previously completed in 2003 as temporary protection against erosion, to reestablish the natural dynamics of the coast line. Land on the west side of the realigned highway was added to the existing West Side Public Ownership Area and used to restore coastal prairie, lagoons, and wetlands to provide critical habitat for federally-listed plants and animals. The former road alignment was utilized to expand a new 3.5-mile section of the California Coastal Trail, which is used for pedestrian and bicycle travel. The project was enabled by a 2005 agreement between the Hearst Corporation, state agencies, and conservation partners to preserve 80,000 acres of rangeland through a conservation easement and transfer sections of privately-owned coastline for public use (through both outright ownership transfers and irrevocable public use easements).

Since the initiation of the Piedras Blancas realignment project, the State of California and Caltrans have issued requirements and guidance for the consideration of sea level rise and other climate impacts in project planning, beginning with Executive Order S-13-08, which directed state agencies to address sea level rise vulnerability. Pursuant to that Executive Order, guidance from the Coastal and Ocean Working Group of the California Climate Action Team and from Caltrans provide specific sea level rise projections and guidance for incorporating the projections into infrastructure project planning. However, since a Notice of Preparation for the Piedras Blancas realignment project had been issued prior to E.O. S-13-08, the project was exempt from requirements to consider particular sea level rise scenarios. In response to public comments that the agency did not appropriately account for future climate impacts, Caltrans indicated in the Final Environmental Impact Report that the agency considered climate-related impacts of increased erosion in setting the anticipated 100-year erosion line, to ensure that the proposed realignment would be sufficient to protect the highway beyond 2100.


This Adaptation Clearinghouse entry was originally prepared with support from the Federal Highway Administration. This entry was last updated on June 30, 2020.



Publication Date: 2017

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  • California Department of Transportation (Caltrans)

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