U.S. Route 101, or U.S. Highway 101 (US 101), is a north–south United States Numbered Highway that runs through the states of California, Oregon, and Washington, on the West Coast of the United States. It is also known as El Camino Real (The Royal Road) where its route along the southern and central California coast approximates the commemorative trail which links the Spanish missions, pueblos, and presidios. It merges at some points with California State Route 1 (SR 1). Though US 101 remains a major coastal north–south link along the Pacific coast north of San Francisco, it has been replaced in overall importance for transport through the West Coast states by Interstate 5 (I-5), which is more modern in its physical design, goes through more major cities, and has more direct routing due to significantly easier geography over much of the route. US 101 is a major parallel route between Los Angeles and San Francisco, and is an alternative to the Interstate for most of its length. In 1964, California truncated US 101's southern terminus in Los Angeles, as I-5 replaced it. The old road is known as County Route S21 (CR S21) or Historic Route 101 in northern San Diego County. The nearly 1,550-mile-long (2,500 km) 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.[self-published source] From Wikipedia
