Piedras Blancas Highway 1 Realignment - Caltrans/San Luis Obispo
The California Department of Transportation (Caltrans) is planning to realign 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, is already experiencing increased storm damage from flooding and erosion, and these impacts are projected to increase with rising sea levels and higher storm surge caused by climate change. Realigning the highway away from the coast will reduce its vulnerability to current damage as well as to future climate impacts and will protect the highway from bluff retreat for the next 100 years.
The realignment project will involve moving the highway up to 475 feet inland of the existing route and restoring the existing alignment to natural conditions. The current alignment is threatened by erosion and damage from waves during storm events and by annual receding of the shoreline adjacent to the highway. Waves also wash 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, have the potential to accelerate this damage in the decades to come. The realignment project is designed to protect the highway from coastal erosion for 100 years; Caltrans indicates 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 current 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 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 (See Final Environmental Impact Report). Caltrans has previously successfully realigned a section of Highway 1 south of the Piedras Blancas project area as a response to coastal erosion.
Project construction began in 2015 and is expected to continue through fall of 2020. Construction will cost approximately $43.6 million with an additional $14.2 million estimated for acquiring rights-of-way. The project is being funded through the State Highway Operation and Protection Program. The project will include removing 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 will be added to the existing West Side Public Ownership Area, and portions of the abandoned roadway will be left for use as part of the California Coastal Trail rather than graded to the original ground.
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 for the next 100 years.
This Adaptation Clearinghouse entry was prepared with support from the Federal Highway Administration. This entry was last updated on March 21, 2016.
Publication Date: 2015
- California Department of Transportation (Caltrans)
- Best practice
- Case study