There is very little public transportation to common trailheads outside of urban areas, but here are some options:

• Portland International Airport ground transportation Shuttles that will transport you to/from Cascade Locks, Timberline Lodge, and other locations.
• Sasquatch Shuttle Shuttles between eight stops in the western Oregon Gorge: Portland Women's Forum, Vista House, Latourell Falls, Bridal Veil, Angel's Rest, Wahkeena Falls, Multnomah Falls, Horsetail Falls.
• Columbia Gorge Express runs buses seven days a week between the Gateway Transit Center (Portland) and Hood River. The bus stops five times daily at Multnomah Falls.
• Gorge WET bus from Vancouver to North Bonneville, Stevenson, Carson, and Dog Mountain.
• Sandy Area Metro Goes from Portland Gresham Max station to Timberline Lodge. Stop at Zigzag and you could walk over to the West Zigzag Trail or up Hunchback Mountain. Stop at Mt Hood Village and hike over to the Wildwood Recreation Site and up the Boulder Ridge Trail into the Salmon-Huckleberry Wilderness.

• NW Connector lists public transport in Clatsop, Tillamook, Lincoln, Columbia, and Benton counties.
• Point Transit has several long routes, including Portland to Astoria via Cannon Beach and Portland to Eugene.

• Eugene Airport Ground Transportation Several possibilities.
• Lane Transit District Transit goes from Eugene as far East as McKenzie Bridge which is about 21 miles from the PCT and the Three Sisters.
• Horse Creek Lodge shuttle from one end of McKenzie trail to the other.

• Central Oregon Breeze Goes between Portland and Bend. They will make stops at Government Camp if you pre-arrange.
• Pacific Crest Bus Lines runs from Eugene to Bend, crossing the PCT.
• Cascades East Transit connects Central Oregon cities like Bend, Prineville, Redmond, and Madras.

• Clallam Transit runs on the north side of Olympic National Park: Forks, Neah Bay, Lake Crescent, Port Angeles, Sequim, Port Townsend, Bainbridge Island Ferry.
• Backpacking by Bus Website about places you can backpack by bus. Seattle-centric.

• Make a request on oregonhikers.org and maybe you can get someone to give you a ride, especially from Portland to closer locations like Cascade Locks or Timberline Lodge.

• Public Transit Hikes Hikes in the Oregon Hikers Field Guide accessible by public transportation, usually in urban areas.