Confusion Hill Bypass in Mendocino County, California

The California Department of Transportation (Caltrans) completed the Confusion Hill Bypass project to reduce the vulnerability of Highway 101 in Northern California to landslides. Between 1996 and 2003, Caltrans spent a total of $14 million repairing and maintaining a 2-mile stretch of the highway. In the winter of 2002/2003, Highway 101 was closed 10 times due to landslides. Caltrans identified landslides and flooding as constant challenges in Caltrans District 1, which includes Confusion Hill in Mendocino County. Caltrans acknowledges that the frequency or severity of these phenomena may increase as the climate changes, necessitating adaptation measures.

In 2003, Caltrans characterized the hillside at Confusion Hill as unstable and predicted major slide activity every two to three years. The average cost of rectifying a catastrophic landslide at that location was estimated to be approximately $45 million. Caltrans estimated the benefits of realigning the highway and found that the project would produce $185 million in benefits from an estimated $71 million investment, producing a benefit-cost ratio of 2.6. In response, Caltrans undertook a project to relocate 1.9 miles of Highway 101 and replace two bridges to avoid the active rockslide area. The project was funded with $65 million in emergency relief funding from the Federal Highway Administration and was completed in 2009.

The realignment of Highway 101 at Confusion Hill is an example of how transportation agencies can reduce the vulnerability of transportation infrastructure to impacts from current geologic and weather phenomena while also reducing the risk to that infrastructure from future climate impacts.


This Adaptation Clearinghouse entry was prepared with support from the Federal Highway Administration. This entry was last updated on October 31, 2015.


Publication Date: 2009

Related Organizations:

  • California Department of Transportation (Caltrans)


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Resource Types:

  • Best practice
  • Case study

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