South of the transit mall, the Orange Line operates bidirectionally and terminates at Southeast Park Avenue station in Oak Grove, just outside Milwaukie proper in unincorporated Clackamas County.

As part of the PMLR project, TriMet built Tilikum Crossing, the largest "car-free" bridge in the United States, over the Willamette River.

[7][8] The proposal primarily envisioned a busway concept,[6]: 12  but also considered a light rail alternative, particularly for the corridor between Portland and Oregon City in Clackamas County.

[9] Amid pressure to identify a use for the transfer money,[10][11] as stipulated by a provision in the Federal Aid Highway Act of 1973,[6]: 7–8 [12] CRAG prioritized redeveloping the Banfield Transitway,[6]: 12 [13]: 30  a segment of I-84 connecting I-5 in downtown Portland east to I-205,[14] and put the Oregon City corridor on hold.

[16] The Banfield Transitway received the transfer funds,[17] and despite efforts from the Oregon Department of Transportation to build a busway,[6]: 13 [7] a light rail line was built.

[26][27] To settle the issue, Metro released a regional transportation plan (RTP) that reasserted the Westside Corridor's priority in January 1989.

[30][31] As the studies analyzed alternative routes, the project's advisory committee increasingly favored an alignment closer to downtown Portland along the busier I-5 and Willamette River corridors.

[32] In 1994, Metro finalized a 25-mile (40 km) light rail route from Hazel Dell, Washington through downtown Portland to Clackamas Town Center,[33] which TriMet formally called the "South/North Corridor".

[36] To fund Washington's $237.5 million share, Clark County proposed raising sales and vehicle excise taxes by 0.3 percent, also requiring voter approval.

[37][38] Planning for the South/North Corridor resumed later that year when TriMet released a revision that scaled back the line's northern half by eliminating its North Portland and Clark County segments up to the Rose Quarter.

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

[46] In August, due to the wording on the original ballot passed in 1994, which described the line extending into Clark County, the TriMet board decided to hold another vote on a new $475 million bond measure.

[49][50] In 1999, they urged TriMet to revive the northern portion of the South/North project,[51] which led to the Interstate MAX and Yellow Line opening in 2004.

[59] While planning for the second phase, alignment studies within downtown Portland showed that a fourth service along the existing tracks on Morrison and Yamhill streets, then served by the Blue, Red, and Yellow lines, would push that segment to maximum capacity.

[63][64] In July 2008, Metro adopted a locally preferred alternative (LPA) route for the second-phased Portland–Milwaukie line that began at the southern end of the Portland Transit Mall and terminated at Southeast Park Avenue in Oak Grove, just south of Milwaukie proper in unincorporated Clackamas County; the alignment was extended beyond Southeast Lake Road in downtown Milwaukie,[65]: 6  which had been the terminus in the 2003 LPA.

Metro, TriMet, Clackamas County, Portland, Milwaukie, and in-kind property donations contributed $249.3 million to the remaining local-match funds.

[13]: 95–96 On April 5, 2011, the FTA approved the start of the Portland–Milwaukie Light Rail Project's final design,[77][78] which meant TriMet could begin purchasing rights-of-way and construction materials.

[77] Construction began on June 30, initially limited to the site of the new Willamette River crossing,[70] which was temporarily named the "Portland–Milwaukie Light Rail Bridge".

[85] The agency purchased 18 new Siemens S70 light rail vehicles, designated "Type 5"; the first car arrived in Portland that September.

A petition from Senator Jeff Merkley led the FTA to approve previously eliminated project elements such as switch heaters and additional station shelters, at a total cost of $3.6 million.

[87] On May 15, 2015, the first public train ride, which carried 500 passengers including Governor Kate Brown and Senator Merkley, ran at regular operating speed along the entirety of the 7.3-mile (11.7 km) Portland–Milwaukie extension.

[88] On August 30, test trains began running along the entire Orange Line route, ahead of the following month's opening date.

[95] The viaduct carries the line over Harbor Drive and River Parkway to the South Waterfront, where tracks merge with those of the Portland Streetcar's A and B Loop.

[96] From here, the tracks leave the viaduct and again travel at-grade alongside McLoughlin Boulevard to a three-track stub terminal at Park Avenue in Oak Grove, just south of Milwaukie proper.