King County trolley bus wired for success

Evaluating King County Metro's trolley bus service

King County Department of Transportation Metro Transit Division | Seattle, WA, USA | 2012

About 18 percent of Seattle commuters ride trolley buses
89 percent of Metro riders own a car, but commute by bus
Over 57 million commuters use Metro Transit per year


  • Metro needed to evaluate several vehicle alternatives to its aging trolley bus fleet ahead of its procurement of replacements.
  • Primary replacement options included electric trolley buses (taking power from the overhead contact system), fuel-cell powered electric buses, hybrid diesel-electric buses, and motor buses burning compressed natural gas.
  • Because of Seattle's steep terrain, a full-scope capability assessment was needed to determine the most effective candidate vehicle.


  • Surveyed six systems that continue to operate trolley bus fleets in North America: Boston, Philadelphia, Dayton, San Francisco, Seattle, and Vancouver.
  • Prepared an extensive vehicle system and bus technology assessment, evaluating trends and further developments in multiple technologies including diesel-generator and battery based auxiliary power units (APUs).
  • Compiled all research and analysis into a project report detailing environmental comparisons, consideration of federal funding sources, and a total life-cycle cost analysis of vehicle alternatives.
  • Concluded two technologies merited further study: electric trolley buses equipped with battery APUs and hybrid diesel-electric buses (which may require modification to the drive train system to climb steep hills).


  • Leveraged insights from the project report to inform Metro’s procurement of new electric trolley buses, generating significant environmental advantages of electric propulsion in a region largely dependent on hydropower.
  • Successfully mitigated risk of using wireless buses on Seattle’s steeply graded transit lines.
  • Based on the study results, Metro ordered 141 battery-powered New Flyer Xcelsior trolley buses in June of 2013, rolling out the first in its fleet to have a low-floor design, wheelchair ramps (instead of lifts), air conditioning, and auxiliary power units.

Project numbers

  • 141 battery-powered New Flyer Xcelsior trolley buses procured
  • 69 miles of parallel overhead trolley wire in Seattle
  • 174 trolley buses in Seattle
  • 15 years: the typical lifespan of a trolley bus

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