U.S. Route 101
Overview
 
U.S. Route 101, or U.S. Highway 101, is an important north–south U.S. highway that runs through the states of California, Oregon, and Washington, on the West Coast of the United States
West Coast of the United States
West Coast or Pacific Coast are terms for the westernmost coastal states of the United States. The term most often refers to the states of California, Oregon, and Washington. Although not part of the contiguous United States, Alaska and Hawaii do border the Pacific Ocean but can't be included in...

. It is also known as El Camino Real
El Camino Real (California)
El Camino Real and sometimes associated with Calle Real usually refers to the 600-mile California Mission Trail, connecting the former Alta California's 21 missions , 4 presidios, and several pueblos, stretching from Mission San Diego de Alcalá in San Diego...

 (The Royal Road) where its route along the southern and central California coast approximates the old trail which linked the Spanish missions, pueblos, and presidio
Presidio
A presidio is a fortified base established by the Spanish in North America between the sixteenth and nineteenth centuries. The fortresses were built to protect against pirates, hostile native Americans and enemy colonists. Other presidios were held by Spain in the sixteenth and seventeenth...

s. It merges at some points with California Highway 1
California State Route 1
State Route 1 , more often called Highway 1, is a state highway that runs along much of the Pacific coast of the U.S. state of California. It is famous for running along some of the most beautiful coastlines in the world, leading to its designation as an All-American Road.Highway 1 does not run...

.

According to the AASHTO
American Association of State Highway and Transportation Officials
AASHTO, the American Association of State Highway and Transportation Officials, is a standards setting body which publishes specifications, test protocols and guidelines which are used in highway design and construction throughout the United States...

's numbering scheme for U.S. Highways
United States Numbered Highways
The system of United States Numbered Highways is an integrated system of roads and highways in the United States numbered within a nationwide grid...

, three-digit route numbers are generally subsidiaries of two-digit routes.
 
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