 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.