State Route 1 (SR 1) is a major north–south state highway that runs along most of the Pacific coastline of the U.S. state of California. At a total of just over 659 miles (1,061 km), it is the longest state route in California.
The highway is designated as an All-American Road. In addition to providing a scenic route to numerous attractions along the coast, the route also serves as a major thoroughfare in the Greater Los Angeles Area, the San Francisco Bay Area, and several other coastal urban areas.
SR 1 was built piecemeal in various stages, with the first section opening in the Big Sur region in the 1930s. However, portions of the route had several names and numbers over the years as more segments opened. It was not until the 1964 state highway renumbering that the entire route was officially designated as SR 1. Although SR 1 is a popular route for its scenic beauty, frequent landslides and erosion along the coast have caused several segments to be either closed for lengthy periods for repairs, or re-routed inland.