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 coast of the continental U.S. and U.S. Route 99 from Mexico to Canada, through the states of California, Oregon and 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 currently the only continuous 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 as British Columbia Highway 99. It is the 12th longest highway in the U.S. following Interstate 15 and the 5th longest north-south highway following Interstate 15.

Interstate 5 in Washington

Interstate 5 in Washington (I-5) is a 276.62-mile (445.18 km) highway in the U.S. state of Washington that extends from its border with Oregon to its border with Canada. Serving the cities of Vancouver, Kelso, Chehalis, Centralia, Olympia, Tacoma, Seattle, Everett, Mount Vernon, and Bellingham, it is the main route between Portland, Oregon, and Vancouver, British Columbia.

It is the only interstate to traverse the whole north–south length of Washington, but the undivided highways U.S. Route 97 and U.S. Route 395 do also. I-5 is also the only north–south primary interstate highway in Washington. The road is the busiest in the state; an estimated 240,000 motorists use the road daily. The second busiest is I-405 at 201,000.

Route description

Vancouver to Tumwater

I-5 enters Washington at the Interstate Bridge over the Columbia River between Portland and Vancouver. It initially heads north through Vancouver and intersects SR 14, the first segment of SR 501, and SR 500 until the interchange with I-205 in Salmon Creek, where the freeway begins a turn to the northeast. I-5 closely follows the alignment of old U.S. Route 99, and in some locations the US 99 alignment has become I-5. The interstate passes the Vancouver branch of Washington State University. Southeast of Ridgefield, the highway intersects SR 502 and the second segment of SR 501 before continuing north along the Columbia River to Woodland.

Interstate 5 in Oregon

In the U.S. state of Oregon, Interstate 5 traverses the state from north to south, passing through the major cities of Portland, Salem, Eugene, and Medford.

Route description

Beginning with the section about 3 miles (4.8 km) north of the California border, the highway runs from 4,310 feet (1,310 m) Siskiyou Summit, the highest point on I-5, through Oregon's southern mountains and towns such as Ashland, Medford, and Grants Pass. Past Roseburg, the mountains turn into hills, and as it reaches Eugene, the road enters the Willamette River Valley. At Eugene the highway intersects with the short Interstate 105. The interstate then heads almost due north, skirting near Albany and Corvallis, and passes through Salem. There were plans to build a spur into Salem, called Interstate 305.

In the Salem area, placed in the median near mile marker 260, are signs noting where I-5 crosses the 45th parallel. It bears the words "45th Parallel - Half Way Between the Equator and North Pole".