Like transportation in the rest of the United States, the primary mode of local transportation in Portland, Oregon is the automobile. Metro, the metropolitan area's regional government, has a regional master plan in which transit-oriented development plays a major role. This approach, part of the new urbanism, promotes mixed-use and high-density development around light rail stops and transit centers, and the investment of the metropolitan area's share of federal tax dollars into multiple modes of transportation. In the United States, this focus is atypical in an era when automobile use led many areas to neglect their core cities in favor of development along interstate highways, in suburbs, and satellite cities.

Mass transit Portland has a public transportation system. The bus and rail system is operated by TriMet, its name reflecting the three metropolitan area counties it serves (Multnomah, Clackamas, and Washington). Portland's rate of public transit use (12.6% of commutes in 2008) is comparable to much larger cities like Los Angeles, and higher than in most similarly sized U.S. cities, but is lower than in some others, such as Baltimore and Seattle. Transit service between Portland and Vancouver, Washington, the second-largest city in the metropolitan area, is provided by C-Tran, with a small number of express routes.

Within the downtown area (the city center) is the Portland Transit Mall, a transit-priority corridor on which buses and light rail trains from many different parts of the region converge. First opened in 1977, and for three decades served only by buses, the transit mall underwent major changes in 2009. Tracks for light rail (MAX) were added, bus stops spaced farther apart, and the left lane opened to general traffic (but with right turns prohibited). To facilitate this major renovation and rebuilding, lasting more than two years, all bus routes using the mall were diverted to other streets (mainly 3rd and 4th avenues) starting in January 2007. The transit mall reopened to buses on May 24, 2009, and operator training runs on the new light-rail tracks took place during the late spring and summer. Light rail service on the transit mall was introduced on August 30, 2009, when the MAX Yellow Line moved to the mall from its previous routing. The new MAX Green Line opened 13 days later, on September 12, and it also serves the downtown transit mall.

From 1975 to 2010, all of downtown Portland was in Fareless Square, a fare zone within which all rides on buses, light rail and streetcars were fare-free, and starting in 2001 this zone also covered a portion of the adjacent Lloyd District. In 2010, free rides became limited to light-rail and streetcar service – no longer covering bus service – and the zone was renamed the "Free Rail Zone". In September 2012, the fareless zone was discontinued entirely, due to a $12 million shortfall in TriMet's annual budget.

Ben Holladay was the first person to offer public transportation to the city of Portland when in 1872 he opened the Portland Street Railway Company, a horsecar line on First Street extending to a garage at the end of Glisan. In 1882, a second horsecar system was built for Third Street.Labbe, p. 19 Ferries such as the O&CRR Ferry#2 were used to cross the Willamette River before the construction of the first Steel Bridge in 1888. At that point, rail expanded into Albina and East Portland. Horsecars took passengers across the river and steam trains took them further into the suburbs,Labbe, pp. 20–21 but both modes were soon replaced by electric streetcar lines, the first of which began operation on November 1, 1889, between St. Johns and Portland."Cars Running By Electricity; Formal Opening of the Portland–St. John's Line Yesterday". (November 2, 1889). The Morning Oregonian, p. 7.

Buses TriMet operates a fleet of 688 buses on a network of 79 bus routes. Twelve of the routes are designated "Frequent Service" bus routes, with more frequent schedules than other routes. Originally intended to have buses scheduled every 15 minutes or less all day, every day (including weekends and holidays), budget cutbacks in 2009 caused TriMet to change "Frequent Service" routes to have 15-minute-or-less wait times only during weekday peak usage times in the morning and afternoon. In August 2014, TriMet reintroduced 15-minutes-or-less wait times at all times during weekdays on Frequent Service routes, with the stated goal of reinstating weekend 15-minutes-or-less wait times on these routes.

TriMet's bus fleet is made up of and buses, built in 2000 or later, and all are low-floor buses, the last of the high-floor models having been retired in 2016. The last non-air-conditioned buses were retired in December 2015.

TriMet's bus routes also include express buses from downtown Portland to South Beaverton, Sherwood and Oregon City, and express buses from Marquam Hill to Beaverton, Tigard, Southwest Portland, and Milwaukie. TriMet also has several "cross-town" routes that do not serve downtown Portland. The bus network operates predominately in a hub-and-spoke network starting with the downtown Portland transit mall, and includes outlying transit centers in Portland's suburbs.

In addition to the fixed-route service, TriMet operates a paratransit service known as LIFT which operates 253 minibuses and 15 sedans offering door-to-door service for citizens who cannot access regular TriMet services.

MAX light rail

Since September 2015, Portland's light rail system, named MAX (short for Metropolitan Area Express), consists of five color-coded lines: The Blue Line is a east-west route. It begins in Hillsboro, a western suburb, passes through Beaverton and downtown Portland, then across the Willamette River, through Northeast Portland and east to the city of Gresham. The line between downtown and Gresham was the first light rail line opened in Portland, in 1986. MAX lines first became designated by colors in 2000. The Red Line incorporates a north-south addition between the airport and the Gateway Transit Center near the northeast Portland neighborhood of Parkrose. From that point the line overlaps the Blue Line, running west to downtown and beyond, terminating at the Hillsboro Airport/Fairgrounds station. From its opening in 2001 until 2003, the Red Line ended in downtown Portland before its extension along Blue Line tracks to Beaverton Transit Center and subsequently farther west to Hillsboro Airport in 2024. The Yellow Line added to the system. It connects North Portland's Expo Center with downtown. This line is often referred to as "Interstate MAX" because much of it runs along Interstate Avenue, and parallel to I-5. Until 2009, the Yellow Line followed the same mostly east-west alignment through downtown Portland as used by the Blue and Red lines, traveling along Morrison Street (westbound) and Yamhill Street (eastbound) through the core of the business district. However, on August 30, 2009, the Yellow Line shifted to a new north-south alignment through downtown that had been constructed along the Portland Mall (see Green Line). In 2015, the Yellow Line became through-routed at all times with the then-new Orange Line (see below). The Green Line runs from Clackamas Town Center, in the Clackamas area, north along I-205 for 6.5 miles (10.5 km) to the Gateway Transit Center, where it meets the Blue and Red Lines and terminates. From its opening in 2009 until 2026, the Green Line joined the Blue and Red Lines and continued westwards to downtown Portland along the 1986-opened tracks extending to the Steel Bridge. From there—a new junction on the bridge's west deck that was built for the Green Line—the line used 1.8 miles (2.9 km) of new tracks passing Union Station and running mainly along the transit mall for the remainder of its route through downtown, sharing that routing with the Yellow Line (and since 2015 the Orange Line) and terminating at Portland State University (PSU). The Orange Line added of newly constructed line, extending from the south end of the Portland Mall to Milwaukie. The project included construction of the Tilikum Crossing, the first new bridge opened across the Willamette River in Portland in 42 years (since 1973), which is also notable for being open only to transit vehicles, pedestrians and cyclists—and not private vehicles. From the PSU area in downtown, the Orange Line follows streets and a bus-and-light-rail-only viaduct to reach the South Waterfront district. After crossing the river, the line turns southward, passing through Southeast Portland along a new median on SE 17th Avenue and then mostly along or adjacent to previously existing railroad rights-of-way to downtown Milwaukie. The terminal station is at Park Avenue, just south of downtown Milwaukie. Operationally, it is linked to the Yellow Line at all times; southbound Yellow Line trains become Orange Line trains when they depart from Rose Quarter TC, and northbound Orange Line trains become Yellow Line trains when they reach the transit mall in downtown Portland.

Portland Streetcar

The Portland Streetcar is a two-line streetcar system serving the central part of Portland—downtown and the areas immediately surrounding downtown. The system's first line opened in 2001 and, with later extensions, now follows a routeMorgan, Steve. "Expansion for Portland's MAX: New routes and equipment", pp. 38-40. Passenger Train Journal, "2010:1" issue (1st quarter, 2010). White River Productions. from Legacy Good Samaritan Medical Center at NW 23rd Avenue through inner-Northwest and Southwest, including the Pearl District and Portland State University, to the new South Waterfront neighborhood, where it connects to the Portland Aerial Tram.Portland Streetcar: Streetcar History from portlandstreetcar.org In 2012, this route was given the designation North-South Line, or NS Line.

The system's second line opened in 2012 and extended service across the Willamette River to the Lloyd District and the Central Eastside. The federal share of funding for this $148-million project, a extension and fleet expansion, was approved in April 2009, and construction began in August 2009. Originally named the Central Loop Line, or CL Line, it was renamed the A Loop (clockwise) and B Loop (counterclockwise) in 2015, when it was extended from the eastside across the Tilikum Crossing bridge and also along the NS Line from South Waterfront to Portland State University. See Portland Streetcar (Eastside line) and Loop Service (Portland Streetcar) for more detail.

The Willamette Shore Trolley is a seasonal, volunteer-operated heritage streetcar service established in 1990 – after a 1987 trial run – for the purpose of preserving an approximately former Southern Pacific railroad right-of-way running south from Portland to Lake Oswego for possible future transit use. Plans to extend the Portland Streetcar along the right-of-way were mothballed in early 2012, but remain under consideration for the long term. The right-of-way was acquired by a consortium of local governmental entities in 1988 for this purpose.

An earlier streetcar began in 1871 with the introduction of eleven horse-drawn cars, which were later abandoned in 1895. The city's first electric streetcars debut in 1889 and ran over the Steel Bridge. These lines were established by private companies and later consolidated under the Portland Railway, Light and Power Company by 1906.

Commuter rail TriMet's WES Commuter Rail connects the cities of Wilsonville, Tualatin, Tigard and Beaverton. It is one of only two suburb-to-suburb commuter rail lines in the country, along with Tri-Rail in Miami. Rather than electric railcars like those of MAX, the line uses FRA-compliant diesel multiple units running on existing Portland and Western Railroad freight tracks. The first rides open to the general public took place on Friday, January 30, 2009, and regular service began on Monday, February 2, 2009.