In Part 1 of this article, the California portion of Interstate 5 was the focus. This article focuses on I-5 in the states of Oregon and Washington.


There are 70 primary interstate highways in the Dwight D. Eisenhower National System of Interstate and Defense Highways (commonly known as the Interstate Highway System, or IHS) is a network of freeways in the United States. The oldest parts of the interstate system date back to the 1950s, and the planning for the system began prior to World War II. To learn more about their history, read previous FreightWaves Classics articles here, here and here.

In this article and future articles, information about specific interstates will be explored. This series profiles the interstates in numeric order (Interstate 2  and Interstate 4 to date; there is no Interstate 1 and Interstate 3 is not yet active).

As most people know, interstate highways are assigned one- or two-digit route numbers (such as I-10 or I-55). Associated “auxiliary” interstate highways receive three-digit route numbers (such as I-270, I-495, etc.). 

Interstate highways whose route numbers are divisible by 5 usually represent major coast-to-coast or border-to-border routes (for example, I-10 runs from Santa Monica, California, to Jacksonville, Florida, from the Pacific to Atlantic oceans). 

This map shows the route of I-5 from the Mexican to Canadian borders. (Image:

Interstate 5 is unique

Interstate 5 (I-5) is the primary north-south interstate highway on the West Coast of the United States. It generally runs parallel to the Pacific coast in the states of California, Oregon and Washington. I-5’s total length is 1,381.29 miles.

Its southern origin is San Ysidro (San Diego), California, the nation’s busiest international border crossing; it ends at Blaine, Washington. I-5 connects all of the major population centers along or near the U.S. West Coast, including San Diego, Los Angeles, Sacramento, Portland and Seattle. I-5 also provides freeway connections to the San Francisco Bay area via I-580 and I-505.

What makes I-5 unique? It is the only continuous interstate highway that touches both the Mexican and the Canadian borders. When it reaches the Mexican border I-5 continues to Tijuana, Baja California, as Mexico Federal Highway 1. At the Canadian border, the highway continues to Vancouver as British Columbia Highway 99.

Interstate 5 in Oregon

The relatively rural terrain of extreme northern California continues as Interstate 5 enters southern Oregon in Jackson County near Ashland and enters Washington north of Portland. 

This photo shows congestion on I-5 south of Portland. (Photo: Oregon Department of Transportation)

As I-5 enters Oregon it runs northeast along a ridge in the Siskiyou Mountains, with a maximum grade of 6%, to Siskiyou Summit. At 4,310 feet, it is the highest point on the entire length of I-5; it is also one of the highest points on the Interstate Highway System. The 11-mile section of the highway is mountainous along Siskiyou Pass; there are several runaway truck ramps and chain-up areas. North of the summit, I-5 through the Rogue River-Siskiyou National Forest.

On its path through Oregon I-5 runs for 308.14 miles. The route chosen for I-5 is located to the west of the Cascade Mountains, and it connects Portland to Salem, Eugene, Medford, and other major cities in the Willamette Valley and across the northern Siskiyou Mountains. 

Interstate 5 is the second-longest freeway in Oregon and is the only interstate highway to pass through the state from north to south. The highway connects several of the state’s largest metropolitan areas, which lie in the Willamette and Rogue valleys. In addition,I-5 runs through counties with more than 80% of Oregon’s population. 

I-5 was designated in 1957 and replaced U.S. Route 99 (US 99) for most of its length. The interstate incorporated early bypasses and expressways built for US 99 in the 1950s. The Marquam Bridge in Portland was the last segment of I-5 built in Oregon. The bridge was opened in October 1966 and the highway was dedicated later that month. The highway runs  parallel or concurrent with Oregon Route 99 (OR 99) and its spur routes.

The Marquand Bridge was under construction in 1964. (Photo:

I-5 continues north into Eugene; it crosses the Whilamut Passage Bridge, a pair of concrete arch bridges that span 1,985 feet across the Willamette River west of downtown Springfield.

I-5 enters Multnomah County and Portland, Oregon’s largest city. In the South Burlingame neighborhood, I-5 has a fish hook-shaped turn through the “Terwilliger curves,” a dangerous section of the highway that changes directions five times in one mile.

I-5 continues on a northeasterly course and crosses the Willamette River on the Marquam Bridge, connecting two sides of Portland. The Marquam Bridge is double-decked; its northbound lanes are on the upper deck and southbound lanes are on the lower deck. It also is the busiest crossing in Oregon.

In North Portland the interstate spans the Columbia River on the Interstate Bridge into Vancouver, Washington. The Interstate Bridge is considered substandard and traffic delays occur daily.

Interstate 5’s Interstate Bridge spans the Columbia River and connects Oregon and Washington. (Photo: Cascade Policy Institute)

Interstate 5 in Washington

As in Oregon, I-5 is the only interstate that travels the state of Washington from north to south. It is also Washington’s busiest highway. I-5 covers 277 miles long in Washington; it runs from the Oregon border at Vancouver, through the Puget Sound region, and to the Canadian border at Blaine. 

An aerial view of freeway bridge during Interstate 5 construction in Seattle, January 1961.
(Photo: University of Washington Digital Libraries collection)

The interstate segment in downtown Seattle is among the widest highways in the U.S. It has 13 lanes, which includes express lanes that reverse direction depending on time of the day. Most of I-5 is four lanes in the state’s rural areas and six to eight lanes in its suburban areas. I-5 has three auxiliary interstates – I-205, I-405 and I-705. 

I-5 follows the path of several railroads and wagon trails that were created during the settlement of the western part of the state in the mid-to-late 19th century. In 1913, a number of local roads were incorporated into the Pacific Highway, connecting the state’s southern and northern border. In 1926 the Pacific Highway became the northernmost segment of the national U.S. Route 99.

Federal planners designated I-5 in 1957. The highway’s initial construction was completed in Washington in 1969. Interstate 5 is the primary highway for the western portion of the state. Its course goes through the most densely populated areas of the state; about 70% of the state’s population live in the nine counties served by I-5. 

The section of I-5 through downtown Seattle is Washington’s busiest highway; its daily average is nearly 300,000 vehicles. Consequently and unfortunately, I-5’s route through the Seattle metropolitan area is ranked among the worst congested U.S. highways. 

The interstate enters Washington via the Interstate Bridge. The Interstate Bridge is actually a pair of vertical-lift bridges that span the Columbia River between Portland, Oregon, and Vancouver, Washington. Because of its lifts, the bridge is the sole point on I-5 where vehicles have to stop for cross traffic.

Unlike areas in California and Oregon, there are no sections of I-5 in Washington that have major grades that impact traffic. 

Two different photos show I-5 as it passes the Tacoma Dome in Tacoma, Washington.
(Photo: Washington Department of Transportation)

Northwest of the city of Woodland, I-5’s median contains railroad tracks used by freight and Amtrak trains. East of the city of DuPont, the highway runs through Joint Base Lewis-McChord, which is a major military installation. 

In Seattle, I-5 intersects I-90, which is the state’s major east-west highway. North of the I-5/I-90 interchange, I-5 was constructed on an elevated viaduct over Seattle’s International District.

This photo shows traffic coming and going between the United States and Canada on roadways on either side of the Peace Arch. (Photo: Peace Arch News)

When I-5 reaches Blaine (the northernmost city on I-5) a state road splits away from the interstate to serve as an alternate border crossing for trucks and freight. I-5’s course is along the northeast edge of downtown Blaine; it terminates when it reaches the Canadian border at the Peace Arch.

The Peace Arch-Douglas crossing is the third-busiest port of entry on the U.S.-Canada border. In Canada the highway continues north to Vancouver; it is designated as Highway 99.