By then, discussions to expand streetcar service east of the Willamette River had also begun, and $200,000 was allocated to strengthen the outer lanes of the Hawthorne Bridge with the intention of having it carry a future line between OMSI and the Oregon Convention Center.

[7] The Hawthorne Bridge was closed in March 1998 and reopened in April 1999 with the outer-lane decks rebuilt to accommodate notches for rails.

A southern crossing back to the west side depended upon whether the proposed bridge would be constructed, leaving that section undetermined at the time.

[15][18] In 2008, the Portland–Milwaukie project steering committee selected a locally preferred alternative that included a new river crossing between the South Waterfront and OMSI near Caruthers Street;[19] this led to a decision to build the first phase of the eastside streetcar 3.3 miles (5.3 km) up to OMSI (farther south from Hawthorne Boulevard) until the new bridge could be completed, after which the streetcar would cross the bridge back to the west side to complete the loop.

[20][21] Metro, the Portland metropolitan area's regional government, approved the eastside streetcar extension with the selection of a locally preferred alternative on July 20, 2006,[22][23] that the city council adopted in September 2007.

[25] On April 30, 2009, U.S. Transportation Secretary Ray LaHood announced $75 million in federal funding for the project, the full amount that was requested.

Representatives Earl Blumenauer and Peter DeFazio of Oregon, was the largest and final component of the financing plan and meant the project could proceed with construction.

[26][28] In January 2007, Oregon Iron Works was awarded a $4 million contract to locally produce a streetcar prototype as provided by the Transportation Equity Act of 2005.

[34] In July 2011, the city council agreed to contractual changes that reduced the number of streetcars on order from six to five due to unanticipated costs related to production.

Project officials subsequently opted to obtain the propulsion system from Austrian manufacturer Elin, which necessitated changes to the streetcar design to accommodate a different form factor.

[39] For the project route along city streets, crews laid tracks in three-to-four-block increments,[40] with each segment completed every four weeks.

[41][42] To maintain the existing weight of the bridge after adding tracks, which was necessary to allow it to continue lifting its spans, workers replaced the deck with lighter fiber-reinforced concrete.

[51][52] Joseph Rose, writing for The Oregonian, called the streetcar the "Stumptown Slug" after he traveled quicker from OMSI to Powell's City of Books on foot.

[62] Construction of the streetcar components started in August 2013 with the installation of a turning loop on the intersection of Southeast Stephens Street, Grand Avenue, and Martin Luther King Jr.

[63] From September to October that year, crews expanded the SE Water/OMSI streetcar platform and installed the streetcar-track connection with the new bridge.

[64] From June 26 to August 17, 2015, CL Line service ceased operating as part of Multnomah County's closure of the Broadway Bridge to make way for repainting.

[66] The CL Line was formally re-branded as the "A and B Loop" on September 12, 2015,[67] when Tilikum Crossing opened to the public and began permitting streetcars to carry passengers on the route section across the bridge.

[70] In 2013, Hassalo on Eighth broke ground at the Lloyd 700 "superblock", where the eastside extension was deliberately routed to support redevelopment.

[77][78] The ongoing project aims to create red-painted dedicated lanes, remove or restrict on-street parking, and implement traffic-signal priority for buses and streetcars.

[81] In April 2022, the City of Portland filed a lawsuit in Multnomah County Circuit Court against TriMet and Stacy and Witbeck for negligence and breach of contract.

[3] Prior to the COVID-19 pandemic, which impacted public transit ridership globally, the route had served significantly more riders; the A and B Loop carried 3,612 and 3,064, respectively, on weekdays in September 2019.

[84] Each platform is equipped with a ticket vending machine, real-time display system, and line information signs,[96] and is accessible to users with limited mobility.