A and B Loop

The A and B Loop is a streetcar circle route of the Portland Streetcar system in Portland, Oregon, United States. Operated by Portland Streetcar, Inc. and TriMet, it is made up of two separate services: the 6.1-mile (9.8 km) A Loop, which runs clockwise, and the 6.6-mile (10.6 km) B Loop, which runs counterclockwise. The route travels a loop between the east and west sides of the Willamette River by crossing the Broadway Bridge in the north and Tilikum Crossing in the south.

The A and B Loop connects Portland's downtown, Pearl District, Lloyd District, Central Eastside, and South Waterfront. It serves various landmarks and institutions, including the Rose Quarter, the Oregon Convention Center, the Oregon Museum of Science and Industry (OMSI), Oregon Health & Science University (OHSU), and Portland State University (PSU). Riders can transfer to Frequent Express (FX) and MAX Light Rail from several stations along the route.

Portland city officials considered an eastside streetcar line upon authorizing the Central City Streetcar on the west side in 1997. After several years of planning, the Portland Streetcar Loop Project was approved and held its groundbreaking in 2009. The first 3.3 miles (5.3 km) opened between the Broadway Bridge and OMSI on September 22, 2012. It was inaugurated by the Central Loop Line (CL Line) service, which ran additionally on the westside along 10th and 11th avenues. The opening of Tilikum Crossing in 2015 extended the streetcar from OMSI to the South Waterfront; this completed the loop, and the CL Line was rebranded to A and B Loop.

In 1990, a citizen advisory committee, citing the 1988 Central City Plan, convinced the Portland City Council to develop a streetcar (then referred to as "trolley") network in downtown Portland. In July 1997, the city council formally authorized the Central City Streetcar project. 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. The Hawthorne Bridge was closed in March 1998 and reopened in April 1999 with the outer-lane decks rebuilt to accommodate notches for rails. In July 2001, the Lloyd District Development Strategy proposed a separate plan that envisioned a Lloyd District transit hub, with modern streetcars complementing existing bus and MAX Light Rail service; it suggested running streetcar lines on Broadway and Weidler streets through to the west side via the Broadway Bridge, which had carried streetcars from 1913 to 1940.

In February 2003, Portland Streetcar officials, amid TriMet (Portland's regional transit agency) plans to construct a new bridge over the Willamette River for the Portland–Milwaukie Light Rail Project, proposed an inner eastside loop route using the Broadway Bridge and TriMet's proposed bridge (instead of the Hawthorne Bridge). The city council adopted the Eastside Streetcar Alignment Study that June. The study outlined a westside–eastside streetcar route that ran from the existing streetcar tracks in the Pearl District, across the Broadway Bridge to the Lloyd District, then south along Grand Avenue and Martin Luther King Jr. Boulevard to Hawthorne Boulevard. A southern crossing back to the west side depended upon whether the proposed bridge would be constructed, leaving that section undetermined at the time. 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; 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.

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, that the city council adopted in September 2007. The total cost of the project, including the cost to purchase additional vehicles, amounted to $148.8 million. Portland allocated $27 million of city funds, and $20 million from the state, $15.5 million from a local improvement district, and a combination of various other local or regional sources completed the locally sourced funding. 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. It was the first streetcar project to receive funding under the Small Starts program in part due to the Obama administration's departure from the practices of the Bush administration, which had awarded the funding to projects based on speed across long routes. The Small Starts allocation, secured in large part through the efforts of U.S. 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.

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. On July 1, 2009, its subsidiary, United Streetcar, unveiled the first prototype in Portland; it was the first U.S.-built streetcar in nearly 60 years^{[dubious – discuss]}. That August, the city signed a $20 million contract to purchase six new vehicles from United Streetcar for the eastside extension. 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. United Streetcar had relied on Czech streetcar manufacturer Škoda, which built the Portland Streetcar's first vehicles, to provide the propulsion system that eventually failed acceptance testing. 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. The changes led to higher costs and delayed the project for five months.

Groundbreaking for the Portland Streetcar Loop Project took place on June 25, 2009. Portland awarded the building contract to Stacy and Witbeck, and construction began in August. For the project route along city streets, crews laid tracks in three-to-four-block increments, with each segment completed every four weeks. Excavation for the trackbed was eight feet (2.4 m) wide and 14 to 18 inches (36 to 46 cm) deep. Workers closed the Broadway Bridge for renovation from July to September 2010. 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. In the Pearl District, sections of what had been two bidirectional streets—Lovejoy and Northrup—were converted into one-way streets after rail was installed. The Lovejoy ramp on the west end of the Broadway Bridge reopened to traffic in November 2010. In Southeast Portland, workers built a 425-foot (130 m) bridge that carried the streetcar from Southeast Stephens Street to the project's eastern terminus at OMSI. The extension's overhead lines went live in April 2012, and testing continued through to opening day.