Created in 1969 by the Oregon legislature, the district replaced five private bus companies that operated in the three counties: Multnomah, Washington, and Clackamas.

TriMet began operating a light rail system, MAX, in 1986, which has since been expanded to five lines that now cover 59.7 miles (96.1 km).

In 2018, the entire system averaged 310,000 rides per weekday and operates buses and trains between the hours of approximately 5 a.m. and 2 a.m. TriMet's annual budget for FY 2018 is $525.8 million, with 30% of resources coming from a district-wide payroll tax and 10% from fares.

[2] The TriMet district serves portions of the counties of Multnomah, Washington, and Clackamas; it extends from Troutdale to Forest Grove east to west, and from Sauvie Island to Oregon City and Estacada north to south.

For more than 30 years the agency called itself Tri-Met, but it formally dropped the hyphen from its name in 2002, as part of a new corporate identity strategy involving a redesigned logo and new color scheme for its vehicles and other media.

[14] As of January 2024, TriMet operates a total of 695 buses on 84 routes,[citation needed] 145 MAX light rail cars on five lines, and 253 LIFT paratransit vehicles.

[15] TriMet connects to several other public transit systems:[16] TriMet also links to various local shuttle services operated by the following: Ride Connection, which serves Banks, Gaston, King City and North Plains; the Swan Island Transportation Management Association; the Tualatin Transportation Management Association; Intel; Nike; and Oregon Health & Science University, including the Portland Aerial Tram.

Metro also has statutory authority to take over the day-to-day operations of TriMet, but has never exercised that power, as past studies of such a merger have found it to be problematic.

Incidents of violence on the system have led to calls for more security,[19] and some have argued that more thorough checking of fares would improve riders' overall feeling of safety.

[20] Additionally, TriMet is partnering with Google Maps to install Bluetooth low energy beacons on MAX platforms, allowing nearby Android device users to directly receive schedule and alert information.

TriMet buses began carrying bicycles on the front in 1992, on a trial basis on eight routes;[28] the experiment was judged a success and within three years the entire bus fleet had been fitted with bike racks.

[29] TriMet added a temporary free shuttle service connecting between Rose Quarter Transit Center and a temporary bottle redemption facility in industrial district in Northwest Portland specifically to address people redeeming empty containers while grocers have been relieved from the Oregon Bottle Bill during the COVID-19 pandemic.

[32] TriMet uses a flat fare system, with a single price (for each category of rider: adult, youth, senior or disabled) regardless of the distance of the trip.

Single-fare tickets permit unlimited transfers to other routes within 2½ hours, and passes are valid until end of the service day.

[38] Developed by INIT (Innovations in Transportation)[39] for TriMet, the City of Portland, and C-Tran, at a cost estimated (in 2015) to be about $30 million,[40] the new Hop Fastpass system enables riders to pay with a fare card, using card readers on buses and train platforms and, as of August 2017, using a smartphone equipped with NFC (near field communication) via a digital wallet.

[40] As of July 2022[update], TriMet's fleet included 696 buses, in lengths of either 40 or 30 feet (12 or 9 meters) for use on traditional fixed-route services.

[63] The Frequent Express service operates a fleet of 60-foot (18.3 m) articulated buses;[64][65] they were manufactured by Nova Bus in Plattsburgh, New York.

The agency's first paint scheme, adopted in April 1970,[87] featured a tangerine (or orange) base with silver (unpainted metal) along the middle portion of the lower half and a white stripe below and above the windows.

[94] TriMet works with local jurisdictions and agencies to identify and recommend priority transit projects to include in Metro's Regional Transportation Plan (RTP).

The 2018 RTP is Metro's latest iteration, and it lists three funding scenarios that divide the region's proposals into three priority levels.

stations opening Cost TriMet has indicated that other extensions and improvements have been studied or discussed with Metro and cities in the region.

A state law that went into effect on October 1, 1987, enabled communities with a population of less than 10,000 to petition to leave the TriMet district.

[140] The first three areas to make use of the law and withdraw from the TriMet district, effective January 1, 1989, were Damascus, Molalla, and Wilsonville.

TriMet also partners with the Transportation Security Administration, which provides a canine unit to detect explosives and deter acts of terrorism.

Riders are encouraged to alert TriMet employees using on-board intercoms or to dial 9-1-1 when witnessing crime or suspicious activity.

According to the audit, PPB's management "led to some adverse outcomes with community members when they have a negative encounter with a transit officer and learn that accountability is elusive.

[148][149][150] In response, the agency adopted a new policy restricting the number of hours a driver is permitted to work within a 24-hour period.

[151] An investigation by several local Portland news outlets found that several of the MAX Light Rail ticket machines have extremely high failure rates.