As of 2017, King County Metro operates the 10th largest fleet of buses in the United States, with a total of 1,540 buses.^[1]

Upon taking over transit operations on January 1, 1973, Metro used buses acquired from predecessor agencies Seattle Transit System and the Metropolitan Transit Company, still painted in their original colors.^[2] Metro acquired the 91-bus fleet of the Metropolitan Transit Company in December 1972 at a cost of $2.75 million.^[3] The first fleet of new 40-foot (12 m) buses ordered by Metro arrived in June 1976, consisting of 145 diesel coaches manufactured by AM General.^[4] In 1978, Metro became the first large transit agency in North America to introduce articulated buses to its fleet, which required some bus stops to be rebuilt to accommodate 60-foot (18 m) coaches.^[5][6][7] The fleet of 151 buses were manufactured by German maker MAN as part of a bulk order with other large U.S. transit agencies.^[8]

In 1978, Metro was the first large transit agency to order high-capacity articulated buses (buses with a rotating joint).^[9] Today, King County Metro has one of the largest articulated fleets in North America (second only to MTA New York City Transit) and articulated buses account for about 42% of the agency's fleet.^[10]

In 1979, the agency ordered some of the first wheelchair lift equipped coaches in the nation,^[11][12] promising a completely new level of independence for disabled residents. Early lifts were severely flawed, but by the mid-1980s the lifts were generally reliable and were ordered on all new buses. Metro's entire fleet has been wheelchair-accessible since 1999.

Metro was reluctant to adopt low-floor buses, not buying any until 2003. Low-floor coaches have slightly reduced seating capacity (because the wheelwells intrude further into the passenger compartment) which may have been a concern. Whatever the reason for the delay, Metro has now embraced low-floor buses and all new fleet additions since 2003 have been low-floor and the last high-floor buses were retired in March 2020.

Metro has a special fleet of more than a dozen historic motor buses and trolleybuses ranging from ones built in the late 1930s and early 1940s through to ones only recently retired. The coaches are restored, maintained and operated under an agreement with the Metro Employees Historic Vehicle Association (MEHVA), a non-profit organization formed in 1981.^[32] Metro maintains ownership of the historic fleet, providing coverage under its fleet self-insurance along with storage, work space and parts on an as available basis.

Money to operate the coaches and purchase parts not in Metro stock is generated by selling tickets to public excursions. The first trips took place in 1984, and nowadays MEHVA typically operates six to eight per year.^[32] Each excursion has a different route and a different emphasis.

MEHVA was established in 1981, as Metro prepared to retire trolleybuses that had been operating in Seattle since the 1940s. Since that time, MEHVA acquired other retired transit vehicles which were formerly operated in King County. Often these retired coaches were purchased by private citizens and left on the owner's property for many decades, leaving them in need of restoration. The collection of vehicles has gradually expanded over time, with the addition of newly retired buses when deemed historically notable and not yet represented in the collection.

These historic buses are owned by King County Metro, but are restored, maintained and operated by unpaid volunteers who are in the Metro Employee Historic Vehicle Association (MEHVA).

In addition, No. 4020, one of the MAN SG-T 310 articulated trolleybuses, was donated to and preserved at the Illinois Railway Museum (IRM) in 2008 through the efforts of MEHVA. It was part of the first fleet of articulated trolleybuses to operate in America.^[47]

See Trolleybuses in Seattle for a detailed history of Seattle's trolleybus fleet.

• Sound Transit
• Trolleybuses in Seattle