Between Astoria and Portland, the highway passes through (or by) numerous Columbia River towns, such as Svensen, Knappa, Wauna, and Westport.

The highway proceeds through the towns of Warren, Scappoose, and Burlington (as well as passing by the access road to Sauvie Island) before entering Portland.

On the edge of Downtown Portland, US 30 briefly becomes a freeway, utilizing part of the route of the canceled I-505, until its interchange with I-405 at the western end of the Fremont Bridge.

Sections of the highway between The Dalles and Ontario generally follow the route of the Oregon Trail, which was used in the 19th century by U.S. settlers to reach the Willamette Valley.

[6] The Interstate Highway System, approved by the federal government in 1956, included construction of a freeway in Oregon along the US 30 corridor between Portland and Ontario; it was later numbered I-80N (now I-84).

[7][8] The Oregon state government unsuccessfully proposed an extension to cover the rest of US 30 between Astoria and Portland in the 1950s and 1960s,[9][10] which was two lanes wide and in need of funding for improvements.

[11][12] The 104-mile (167 km) Astoria–Portland section had been rebuilt with fewer curves by the 1960s but remained congested due to its use as a tourist route as well as a bypass of US 99 (and I-5) upon the removal of tolls from the Lewis and Clark Bridge near Longview, Washington.

[10][11] In 1969, the state government announced plans to widen the highway between Burlington and the Columbia County border but declined to fund further projects in favor of improvements in the Portland area.

[14] A project to widen US 30 near Scappoose and Warren in the 1970s was delayed by a decade due to disagreements between the state and local governments over its routing and an attempt to build a full bypass.

[15] The highway remained slightly more accident-prone than others in Oregon; from 1987 to 1992, a total of 22 crashes on 50 miles (80 km) of US 30 in Columbia County resulted in 26 deaths and 769 injuries.

[18] The proposed Interstate was intended to be a 3.17-mile (5.10 km) freeway spur in northwest Portland that would have connected I-405 to St. Helens Road, the latter being the original route for US 30.

Funding for the freeway was withdrawn by the city government in November 1978, as it would have required condemnation and rerouting streets on a swath of land through the Northwest Industrial neighborhood.

[19] The federal government formally approved the project's cancelation in December 1979 and reallocated funds to other transportation improvements in the area.