Interstate 5

Interstate 5 (I-5) is the main Interstate Highway on the West Coast of the United States, running largely parallel to the Pacific Ocean and U.S. Highway 101 along the coastline from Mexico to Canada (California to Washington). It serves some of the largest cities on the U.S. West Coast, including Seattle, Portland, Sacramento, Los Angeles, and San Diego, and also links the capital cities of Washington (Olympia), Oregon (Salem), and California (Sacramento) together. The highway's southern terminus is the Mexico – United States border and its northern terminus is the Canada – United States border; it is the only Interstate highway to touch the U.S. borders with both Canada and Mexico. Upon crossing the Mexican border at its southern terminus, Interstate 5 continues to Tijuana, Baja California as Mexico Federal Highway 1. Upon crossing the Canadian border at its northern terminus, it continues to Vancouver, British Columbia as British Columbia Highway 99.

Interstate 5 links to control cities in California (San Diego, Santa Ana, Los Angeles, Oakland, San Francisco, Sacramento, Redding, Mount Shasta, Weed, and Yreka), Oregon (Ashland, Medford, Grants Pass, Roseburg, Eugene, Salem, and Portland), and Washington (Tacoma, Seattle, Everett, Mount Vernon, and Bellingham). Vancouver, British Columbia becomes the highway's control city north of Seattle; it is signed as "Vancouver B.C." in order to avoid confusion with Vancouver, Washington.

One notable control city that Interstate 5 does not directly reach is San Francisco, which is about 80 miles (130 km) west of the highway. To the south, in the Tracy area, Interstate 580 splits from I-5 towards San Francisco, while to the north, near Vacaville, Interstate 505 cuts south to Interstate 80, which serves that city. That routing, via I-580, I-80, and I-505, was planned originally as Interstate 5W.