Battery-Electric Buses piloted in Seattle reduced maintenance costs per mile by 44.1 percent compared to their diesel bus counterparts.

Study presents evaluation results for the Battery Electric Buses in comparison to a selection of baseline diesel hybrid buses, standard diesel buses, and electric trollies.


Summary Information

The Federal Transit Administration (FTA) in partnership with the U.S. Department of Energy (DOE) National Renewable Energy Laboratory (NREL) conducted a year-long study of battery electric buses in service with King County Metro from April 2016 through March 2017.

The electric buses were compared to diesel hybrid buses, standard diesel buses, and electric trollies that King County Metro also has in service. All buses in the study were 40-foot buses, model year 2015, but from three different manufacturers. The electric buses were in service for 83,128 miles during the evaluation period, or 27,709 miles per bus. The electric buses accumulated more miles then the standard diesel buses and trollies because of the route assignments. The electric buses were only used on two routes, the hybrid buses were randomly distributed which included longer commuter routes of longer distance and faster speeds. The diesel buses were only used on one route and only on weekdays, and the trollies were limited to downtown Seattle routes with the catenary electric system which are slower routes.


NREL developed a standardized evaluation process for evaluation advanced technologies deployed under FTA programs. This process has/will be applied to several alternative fuel bus evaluations. The data parameters included in the evaluation include:
  • Bus System Description
  • Operations Duty-cycle Description
  • Bus Use and Availability
  • Energy/Fuel Consumption and Cost
  • Maintenance Cost
  • Roadcalls
  • Infrastructure and Facility Modification Descriptions
  • Capital Costs
  • Implementation Experience
NREL looks to have 12-18 months of service data for the evaluation of electric buses with comparisons to baseline buses fleets that are generally diesel, Compressed Natural Gas (CNG), or hybrid.

  • While the electric buses had a slightly lower availability then the other vehicles, most of the downtime was associated with general maintenance issue, but they also experience down time for electric drive issues.
  • The electric buses did have the best fuel economy measured in miles per diesel gallon equivalent for comparisons. For maintenance costs, overall the electric buses were 17.8 percent cheaper than the hybrid buses, 44.1 percent cheaper than the diesel buses, and 43.2 percent cheaper than the trolley buses. All the data can be seen in the table below, with additional information in the full report.
Data Items Battery-
Hybrid Diesel Trolley
Number of buses 3 10 3 10
Total mileage in data period 83,128 435,552 69,329 180,554
Average mileage per bus 27,709 43,555 23,110 18,055
Average monthly mileage per bus 2,309 3,630 1,926 1,505
Availability (85% is target) 80.6 90.5 86.4 84.9
Fuel economy (kWh/mile) 2.36 - - 2.57
Fuel economy (miles/dgea) 15.9 6.3 5.3 14.7
Average speed, including stops (mph)b 14.8 15.2 14.6 9.0
Miles between roadcalls (MBRC) – busc 2,771 7,641 17,332 1,641
MBRC – propulsion system onlyc 6,927 29,037 34,665 2,960
Total maintenance cost ($/mile)d 0.26 0.32 0.46 0.46
Maintenance – propulsion system only ($/mile) 0.05 0.12 0.13 0.17
a Diesel gallon equivalent.
b Based on scheduled revenue service.
c MBRC data cumulative through March 2017.
d Work order maintenance cost.

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Zero-Emission Bus Evaluation Results: King County Metro Battery Electric Buses

Author: Eudy, Leslie and Matthew Jeffers

Published By: National Renewable Energy Laboratory

Source Date: 02/01/2018

Other Reference Number: FTA Report No. 0118



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Benefit ID: 2019-01361