[4] In 1988, Portland city planners proposed a northside rail service as part of Portland's Central City and Albina Community plans;[5][6] they sought to extend the region's then-two-year-old light rail system, the Metropolitan Area Express (MAX), via Interstate Avenue, I-5, or Martin Luther King Jr. Boulevard (formerly Union Avenue).

Senators Mark Hatfield of Oregon and Brock Adams of Washington combined this proposal with a greater Vancouver–Portland–Oregon City light rail plan that Metro separately developed, for which the committee appropriated $2 million to study in 1989.

[9] Metro's Joint Policy Advisory Committee on Transportation (JPACT) identified a 25-mile (40 km) route from Hazel Dell through downtown Portland to Clackamas Town Center in 1994 that TriMet formally named the "South/North Corridor".

[14][15] Amid fears that ridership would not justify a North Portland segment if Clark County were excluded,[16] JPACT scaled back the project and released a second plan that would only build the line between the Rose Quarter and Clackamas Town Center.

[18] The Oregon Supreme Court promptly struck down this funding due to the inclusion of unrelated measures, which violated the state's constitution.

[25] Due to the wording on the original ballot passed in 1994, which described the project extending into Clark County, regional transit agency TriMet elected to reaffirm voter support by drafting a new $475 million bond measure.

[28][29] TriMet agreed and developed a proposal to build a line along the median of Interstate Avenue, between the Portland Expo Center and the Rose Quarter.

[39] In April, TriMet contracted Stacy and Witbeck to lay tracks between the Rose Quarter and Kenton and build a new vehicular overpass in Lower Albina.

[40] Meanwhile, the agency awarded the section between Kenton and the Expo Center, which included the construction of a 3,850-foot-long (1,173 m) dual-track bridge north of Argyle Street,[41] to F.E.

[39] The rapid pace of construction, which workers credited to improvements in track-laying and street reconstruction technology learned from previous MAX projects,[42] hit a halfway point in April 2002.

[44] In August 2003, with construction approximately 80 percent complete, TriMet officials announced the line's targeted opening for the following spring,[45] months earlier than the previously anticipated September commencement.

[1][48] TriMet created a new MAX service called the "Yellow Line",[49][50] which ran from Expo Center station in North Portland to the Library and Galleria stations in downtown Portland, turning around at the 11th Avenue tracks; it followed First Avenue and Morrison and Yamhill streets upon entry into downtown, serving this segment alongside the Blue and Red lines.

[47] On August 30, 2009, TriMet rerouted the Yellow Line to begin serving the light rail tracks added to the rebuilt Portland Transit Mall, with the PSU Urban Center stations as its interim southern termini.

[51][53] The agency had placed the construction of the intended PSU South termini on hold as it awaited transit-oriented development projects in the area to finish.

[57]: 6–8  The Vancouver line's tracks initially ran from the corner of First and Washington streets in downtown Portland north to Hayden Island,[58]: 73  where Vancouver-bound passengers transferred to a ferry to continue across the Columbia River.

[58]: 71 Regional planners in Oregon considered restoring rail service to Vancouver in 1974, when TriMet proposed a light rail line at the same time Governor Tom McCall's task force studied options for allocating federal assistance funds diverted from the canceled Mount Hood Freeway project.

The project would have replaced the bridge and extended MAX further north from the Expo Center through Hayden Island and across the Columbia River to downtown Vancouver and Clark College, adding seven new stations along 2.9 miles (4.7 km) of new track.

[79] A wye just south of Union Station splits the double-tracks to establish the northern end of the Portland Transit Mall on 5th and 6th avenues.

[81] Near PSU Urban Center/Southwest 6th & Montgomery station, MAX tracks cross with the Portland Streetcar, which serves a stop on Mill Street.

The line continues northward, entering Northwest Portland after passing Burnside Street, eventually reaching the north end of the transit mall at Union Station/Northwest 6th and Hoyt station.

[1][94] The drop in ridership, experienced systemwide, is attributed to crime and to lower-income riders being forced out of the inner city by rising housing prices.

[95][96] The presence of the Interstate MAX and its accompanying ICURA plan has been partly blamed for gentrifying historically black Portland neighborhoods.

[97][98][99] In an analysis conducted by The Oregonian on the 2010 United States Census, approximately 10,000 people of color have left Portland's Central City between 2000 and 2010.

[101] The 2000-adopted ICURA plan had outlined policies to prevent the displacement of existing residents—such as ensuring that affordable housing would be top priority—that the Portland Development Commission (PDC) later eliminated.

Amid mounting pressure from the community, the PDC began setting aside 30 percent of the urban renewal funds for affordable housing in 2006.