U.S. Route 101
The nearly highway's northern terminus is in Tumwater, Washington: the route remains along the Olympic Peninsula's coastal perimeter west, north, and east; the northernmost point on the highway is in Port Angeles. The southern terminus of US 101 is in Los Angeles at the East Los Angeles Interchange, the world's busiest freeway interchange.
California County Routes in zone S
The route was established in 1961.
County Route S20 (CR S20) is a former county highway in the US state of California. As the only county route in Santa Barbara County, it was merged with State Route 1 in 1988 making the southbound SR 1 freeway to go along with Country Route S20 to Vandenberg AFB.
County Route S21 is a south–north running road serving the coastal communities of northern San Diego County, running from San Diego in the south to Oceanside in the north. The route is signed in many places as "Historic Route 101" with the official Historic U.S. 101 shields. S21 follows the prior alignment of U.S. Route 101 through this region. The route is also called "Coast Highway" in some places as well. This route was originally designated in 1968 and is long.
County Route S21 begins at Interstate 5 in the north of San Diego as Genesee Avenue. After proceeding west-northwest for 3/4 mile (1.2 km) it intersects Torrey Pines Road and continues north with that name. The road then travels north into Del Mar, where it is renamed "Camino Del Mar". While in Del Mar the route passes both the historic Del Mar Racetrack and through the historic downtown of Del Mar. In Solana Beach the route moves closer to the coast. Along this stretch it is named "Highway 101" and the city has signed the route along its length with faux U.S. Highway shields that resemble the official U.S. 101 shields in use today along with the state issued Historic 101 shield. While to the north in Encinitas the route's name becomes "Coast Highway 101" also in homage to the old U.S. Route. In Carlsbad it becomes "Carlsbad Blvd". The route is named "Coast Highway" in Oceanside, and comes to an end at Interstate 5 in Camp Pendleton.