Interstate 405 (Oregon)

Interstate 405
Stadium Freeway No. 61
A map of central Portland with I-405 highlighted in red
Route information
Auxiliary route of I-5
Maintained by ODOT
Length	4.25 mi[1] (6.84 km)
Existed	1958[2]–present
NHS	Entire route
Major junctions
South end	I-5 in Portland
Major intersections	US 26 in Portland US 30 in Portland
North end	I-5 / US 30 in Portland
Location
Country	United States
State	Oregon
Counties	Multnomah
Highway system
Interstate Highway System Main Auxiliary Suffixed Business Future Oregon Highways Interstate US State Named Scenic
← OR 402 → OR 410

Interstate 405 (I-405), also known as the Stadium Freeway No. 61,^[3] is a short north–south Interstate Highway in Portland, Oregon. It forms a loop that travels around the west side of Downtown Portland, between two junctions with I-5 on the Willamette River near the Marquam Bridge to the south and Fremont Bridge to the north.

The Stadium Freeway was envisioned in the 1940s and 1950s by the state government and was added to the Interstate Highway system in 1958. Construction began in 1963, utilizing a trench with extensive landscaping and frequent overpasses, and was the most expensive freeway project in state history at a cost of $121 million. Hundreds of buildings were demolished to make way for the freeway, which displaced approximately 1,100 households.

The southernmost section of I-405 opened on October 26, 1965, and was followed by extensions in 1966 and 1969. The final section, including the Fremont Bridge, opened in November 1973. Plans for a spur freeway, I-505, were cancelled in 1978 following public opposition; its interchange with I-405 was subsequently reused for a 1988 realignment of U.S. Route 30 (US 30), which runs concurrent with I-405 across the Fremont Bridge to I-5.