NREL is a national laboratory of the U.S. Department of Energy

Office of Energy Efficiency & Renewable Energy

Operated by the Alliance for Sustainable Energy, LLC

This report is available at no cost from the National Renewable Energy

Laboratory (NREL) at www.nrel.gov/publications.

Contract No. DE-AC36-08GO28308

Strategic Partnership Project Report

NREL/TP-5400-72864

December 2018

Zero-Emission Bus Evaluation Results: 

County Connection Battery Electric 

Buses

Leslie Eudy and Matthew Jeffers

National Renewable Energy Laboratory

Produced under direction of the U.S. Department of Transportation by the 

National Renewable Energy Laboratory (NREL) under Interagency Agreement 

IAG-16-2025.
NREL is a national laboratory of the U.S. Department of Energy

Office of Energy Efficiency & Renewable Energy

Operated by the Alliance for Sustainable Energy, LLC

This report is available at no cost from the National Renewable Energy

Laboratory (NREL) at www.nrel.gov/publications.

Contract No. DE-AC36-08GO28308

National Renewable Energy Laboratory

15013 Denver West Parkway

Golden, CO 80401

303-275-3000 • www.nrel.gov

Strategic Partnership Project Report

NREL/TP-5400-72864

December 2018

Zero-Emission Bus Evaluation Results: 

County Connection Battery Electric 

Buses

Leslie Eudy and Matthew Jeffers

National Renewable Energy Laboratory

Suggested Citation

Eudy, Leslie and Matthew Jeffers. 2018. Zero-Emission Bus Evaluation Results: County 

Connection Battery Electric Buses. Golden, CO: National Renewable Energy Laboratory. 

NREL/TP-5400-72864. https://www.nrel.gov/docs/fy19osti/72864.pdf.
NOTICE

This work was authored by the National Renewable Energy Laboratory, operated by Alliance for Sustainable 

Energy, LLC, for the U.S. Department of Energy (DOE) under Contract No. DE-AC36-08GO28308, and U.S. 

Department of Transportation under Agreement IAG-16-2025. Funding provided by Department of Transportation, 

Office of Research, Demonstration and Innovation. The views expressed herein do not necessarily represent the 

views of the DOE or the U.S. Government.

This report is available at no cost from the National Renewable 

Energy Laboratory (NREL) at www.nrel.gov/publications.

U.S. Department of Energy (DOE) reports produced after 1991 

and a growing number of pre-1991 documents are available 

free via www.OSTI.gov.

Cover Photo by Leslie Eudy: NREL 54529.

NREL prints on paper that contains recycled content.
iii

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Acknowledgments

This report could not have been possible without the cooperation of the transit agencies, 

manufacturer partners, and others. Transit agency staff provided data on the zero-emission and 

baseline buses; reviewed analyses and reports; and participated in meetings to discuss the 

agency’s overall experience. Manufacturers provided selected data, reviewed reports, and 

provided feedback. The U.S. Department of Transportation’s Research, Development, and 

Technology Office provided funding for the evaluation. The authors thank the following 

individuals:

U.S. Department of Transportation Research, Development, and Technology Office

Shawn Johnson 

U.S. Department of Transportation Federal Transit Administration, Office of Research, 

Demonstration and Innovation

Sean Ricketson

Mike Baltes

County Connection

Rick Ramacier

Scott Mitchell

Ruby Horta

Rashidi Barns

Elmer Estimo

BAE Systems

Greg Marx

Marcus Jackson

Gillig

Josh Freeman

WAVE

Mike Masquelier

Marcellus Harper
iv

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Acronyms and Abbreviations

AC alternating current

ATA VMRS American Trucking Association Vehicle Maintenance Reporting 

Standards

BEB battery electric bus

Btu British thermal units

CNG compressed natural gas

dge diesel gallon equivalent

DOE U.S. Department of Energy

DOT U.S. Department of Transportation

ESS energy storage system

FCEB fuel cell electric bus

FTA Federal Transit Administration

ft feet

gal gallon

gge gasoline gallon equivalent

GPS global positioning system

hp horse power

HVAC heating, ventilation, and air conditioning

KMBRC kilometers between roadcall

kW kilowatt

kWh kilowatt hour

lb pound

Low-No Low or No Emission Vehicle Deployment Program

MBRC miles between roadcall

mi mile

mpdge miles per diesel gallon equivalent

NFCBP National Fuel Cell Bus Program

NREL National Renewable Energy Laboratory

NTD National Transit Database

OCTA Orange County Transportation Authority

OEM original equipment manufacturer

OST-R DOT’s Research, Development, and Technology Office

PMI/PM preventive maintenance inspections

RC roadcall

rpm revolutions per minute

SI International System of Units

SOC state of charge

TIGGER Transit Investments for Greenhouse Gas and Energy Reduction

ZEB zero-emission bus 
v

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Glossary

Availability: The number of days the buses are actually available compared to the days that the 

buses are planned for operation, expressed as percent availability.

Clean point: For each evaluation, NREL works with the project partners to determine a starting 

point—or clean point—for the data analysis period. The clean point is chosen to avoid some of 

the early and expected operations problems with a new vehicle going into service, such as early 

maintenance campaigns. In some cases, reaching the clean point may require 3 to 6 months of 

operation before the evaluation can start. This applies to new technology buses as well as 

conventional buses.

Deadhead: The miles and hours that a vehicle travels when out of revenue service with no 

expectation of carrying revenue passengers. Deadhead includes leaving or returning to the garage 

or yard facility and changing routes.

Miles between roadcalls (MBRC): A measure of reliability calculated by dividing the number of 

miles traveled by the total number of roadcalls, also known as mean distance between failures. 

MBRC results in the report are categorized as follows: 

• Bus MBRC: Includes all chargeable roadcalls. Includes propulsion-related issues as well 

as problems with bus-related systems such as brakes, suspension, steering, windows, 

doors, and tires. 

• Propulsion-related MBRC: Includes roadcalls that are attributed to the propulsion system. 

Propulsion-related roadcalls can be caused by issues with the transmission, batteries, and 

electric drive.

• Energy storage system (ESS)-related MBRC: Includes roadcalls attributed to the energy 

storage system only (specific to BEBs). 

• Fuel cell system-related MBRC: Includes roadcalls attributed to the fuel cell and balance 

of plant only (specific to FCEBs).

Revenue service: The time when a vehicle is available to the general public with an expectation 

of carrying fare-paying passengers. Vehicles operated in a fare-free service are also considered 

revenue service.

Roadcall: A failure of an in-service bus that causes the bus to be replaced on route or causes a 

significant delay in schedule. The analysis includes chargeable roadcalls that affect the operation 

of the bus or may cause a safety hazard. Non-chargeable roadcalls can be passenger incidents 

that require the bus to be cleaned before going back into service, or problems with an accessory 

such as a farebox or radio.
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Executive Summary

The U.S. Department of Transportation’s (DOT’s) Federal Transit Administration (FTA) 

supports the research, development, and demonstration of low- and zero-emission technology for 

transit buses. FTA funds research projects with a goal of facilitating commercialization of 

advanced technologies for transit buses that will increase efficiency and improve transit 

operations. DOT’s Research, Development, and Technology Office (OST-R) also has an interest 

in zero-emission bus (ZEB) technology deployment and commercialization. OST-R is 

coordinating and collaborating with FTA on the evaluation process and results by providing 

funding to cover additional evaluations. FTA and OST-R are collaborating with the U.S. 

Department of Energy (DOE) and DOE’s National Renewable Energy Laboratory (NREL) to 

conduct in-service evaluations of advanced technology buses developed under its programs. 

NREL uses a standard evaluation protocol for evaluating the advanced technologies deployed 

under the FTA programs.

FTA seeks to provide results from new technologies being adopted by transit agencies. The eight 

evaluations selected to date include battery electric buses (BEBs) and fuel cell electric buses 

(FCEBs) from different manufacturers operating in fleets located in both cold and hot climates. 

The purpose of this report is to present the results from Central Contra Costa Transit Authority 

(County Connection) deployment of four BEBs in Concord, California. NREL’s evaluation of 

the BEBs at County Connection was funded by OST-R.

County Connections’ service area covers more than 200 square miles in the East Bay of San 

Francisco area. In February 2017, the agency began operating a fleet of four BEBs in its service 

area. The battery buses are 29-ft trolley-replica buses built by Gillig with an electric propulsion 

system by BAE Systems. NREL is collecting data on two diesel bus fleets as baseline 

comparisons: seven model year 2014 Gillig diesel buses and three model year 2002 Gillig 

trolley-replica diesel buses. Because the older buses are operated on the same route as the BEBs, 

they are the best match in duty cycle, which is important for the fuel economy comparison. 

County Connection operates its battery fleet on a free circulator route around Walnut Creek, 

California, with a layover stop at the Bay Area Rapid Transit (BART) station. The agency 

installed two charging stations: plug-in chargers at the facility for overnight charging and a 

WAVE inductive charging pad at the BART stop for wireless charging during scheduled 

layovers.

Table ES-1 provides a summary of the results for the County Connection battery fleet and 

baseline bus fleets.
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Table ES-1. Summary of County Connection Evaluation Results

Data Item Battery Diesel Diesel (Trolley 

Replica)a

Number of buses 4 7 3

Total mileage in data period 51,550 189,068 —

Average monthly mileage per bus 1,074 2,251 —

Availability (85% is target) 76.9 85.5 —

Fuel economy (kWh/mile) 2.84 — —

Fuel economy (mpdgeb) 13.3 5.1 3.5

Average speed, including stops (mph)c 6.0 14.8 6.0

Miles between roadcalls (MBRC)—busd 4,686 63,023 —

MBRC—propulsion system onlyd 6,444 189,068 —

Total maintenance cost ($/mile)e 0.39 0.44 —

Maintenance cost—propulsion system only 

($/mile) 0.10 0.14 —

a Diesel trolley-replica buses used for fuel economy comparison only. b Miles per diesel gallon equivalent.

c Based on scheduled revenue service.

d MBRC data cumulative through May 2018.

e Work order maintenance cost.

The battery bus availability varied from 67.9% to 88.9%, with a fleet average of 76.9%. The 

availability for the diesel buses varied from 83.6% to 89.9%, with a fleet average of 85.5%. The

battery fleet experienced some early bus-side and infrastructure-side charging issues in the first 4 

months of the evaluation. The agency worked closely with the manufacturers to address these 

early issues. Availability was much higher during the last 8 months with an average availability 

of 84.7%.

The battery buses had an overall average efficiency of 2.84 kWh per mile, which equates to a 

fuel economy of 13.3 miles per diesel gallon equivalent (mpdge). The fuel economy for the 

diesel buses averaged 5.1 mpdge and for the diesel trolley buses it averaged 3.5 mpdge. The 

battery fleet’s fuel economy was 3.8 times higher than that of the diesel trolley buses operated on 

the same service route and 2.6 times higher than that of the diesel buses operated on all the 

County Connection routes.

During the data period, County Connection paid an average of $0.22/kWh for electricity for the 

battery buses and $2.01/gal for diesel fuel. The average fuel cost per mile for the battery fleet 

during the evaluation period was $0.73/mi. The per-mile fuel costs for the diesel buses showed a 

steady increase during the evaluation period, from a low of $0.32/mi in July 2017 to a high of 

$0.48/mi in May 2018. The average was $0.40/mi for the diesel buses and $0.54/mi for the diesel 

trolley buses.

NREL also analyzed work order data to provide a comparison of maintenance costs between the 

battery fleet and the baseline fleet. After removing accident- and warranty-related items for all 

fleets, the average per-mile maintenance cost for the data period was $0.39/mi for the battery 

buses and $0.44/mi for the diesel buses. During the data period, the maintenance cost for the 

battery buses was 13% less than that of the diesel buses.
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NREL analyzed the maintenance data to determine costs by vehicle system. The systems with 

the highest percentage of maintenance costs for the battery buses and diesel buses were the same: 

1) cab, body, and accessories; 2) propulsion-related; and 3) preventive maintenance inspections 

(PMI).

Issues and lessons learned for County Connection include the following.

Charger availability—When deploying a BEB fleet, availability of an on-route charger is 

critical for operation. Downtime of a charger results in downtime for the fleet. Early in this 

evaluation, County Connection experienced a couple issues with the inductive charger that 

decreased the battery fleet availability. Importantly, none of the issues were related to the 

electrical circuitry or wireless charging components; rather, the issues were related to ancillary 

cooling equipment. Investigation of the primary issue indicates that a lightning strike was likely 

the cause of the compressor failure.

Charger efficiency—During examination of the inductive charger performance, the 

manufacturer explained how the charger’s cooling system for this particular installation was 

intentionally oversized to allow for up to 100% duty cycle charging because County Connection 

had prioritized reliability and system uptime over system efficiency. The manufacturer reported 

that major improvements have been made to the cooling system design of the inductive charger 

since this first-generation product, improving the efficiency of their higher power charger to 92% 

(typical) and avoiding issues experienced in the early months of this deployment.

Added operating costs—When adding BEBs with depot charging to a fleet, an agency needs to 

plan for logistics to plug in and move the buses to and from the charger at the depot. This is 

especially true for fleets that don’t install a charger for each bus. County Connection reports that 

this adds labor costs to the project. Because the agency has two chargers to cover the fleet of four 

buses, staff are needed to stage and move the buses to ensure each one gets fully charged before 

parking overnight. Scaling up to a larger fleet will add complexity to this process. For BEBs with 

on-route charging, additional time may need to be planned into the route schedule. County 

Connection has added a half hour to the beginning and end of each operator shift to allow time 

for the BEBs to charge at the inductive charger prior to starting the route and before returning to 

the depot. This adds to the labor needs for operating BEBs. Some agencies may only experience 

one of these two impacts, but County Connection is operating both types of chargers and has 

decided to top off the charge of the buses on route and at the depot.

Maintenance costs—Because the BEBs are under warranty, some repairs were made that are not 

accounted for in the maintenance records. Labor and parts costs for repairs that are handled by 

the OEM are not typically included in maintenance data sets and NREL is unable to analyze and 

report on them. At this point in the demonstration, post-warranty maintenance costs are 

unknown. Agencies should carefully consider this when using early reported costs to plan for 

BEB fleet implementation and long-term maintenance costs.

Maintenance skill set—Deploying new technologies presents a challenge for transit staff to take 

over all maintenance responsibilities after the warranty period ends. Current staff do not have the 

skill set needed to fully maintain BEBs. Additional labor hours are incurred as staff come up to 

speed on the new technology. In addition, there is a shortage in the hiring pool of technicians 
ix

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with the desired skill sets. The industry is addressing this need by working with community 

colleges and technical schools to add the required courses for ZEB technicians. The updated 

training materials are still in the beginning stages of development, therefore current graduates do 

not yet have the needed skill set. Until these programs are fully established, hiring ZEB qualified 

technicians will be a challenge.
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Table of Contents

1 Introduction........................................................................................................................................... 1

2 County Connection BEB Evaluation Results .................................................................................... 3

2.1 Fleet Profile—County Connection................................................................................................ 3

2.2 Bus Technology Descriptions ....................................................................................................... 5

2.3 Charging Infrastructure ................................................................................................................. 6

2.4 In-Service Operations Evaluation Results..................................................................................... 8

2.4.1 Route Assignments........................................................................................................... 9

2.4.2 Bus Use ............................................................................................................................ 9

2.4.3 Availability..................................................................................................................... 11

2.4.4 Energy Use, Fuel Economy, and Cost............................................................................ 14

2.4.5 Roadcall Analysis........................................................................................................... 21

2.4.6 Maintenance Analysis.................................................................................................... 22

2.4.7 Total Work Order Maintenance Costs............................................................................ 22

2.4.8 Work Order Maintenance Costs Categorized by System............................................... 24

2.4.9 Propulsion-Related Work Order Maintenance Costs..................................................... 27

2.4.10 Total Cost....................................................................................................................... 29

2.5 Summary of Achievements and Challenges................................................................................ 29

2.5.1 Summary of Challenges................................................................................................. 30

3 County Connection Fleet Summary Statistics ................................................................................ 32

3.1 Fleet Summary Statistics—SI Units............................................................................................ 37

Appendix. Evaluation Protocol................................................................................................................ 38
xi

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List of Figures

Figure 2-1. Map of County Connection service area .................................................................................... 4

Figure 2-2. County Connection Gillig battery electric bus........................................................................... 5

Figure 2-3. Plug-in charger at the County Connection facility..................................................................... 7

Figure 2-4. WAVE inductive charging pad (left) and charging equipment (right)....................................... 8

Figure 2-5. Bus lined up to charge at the on-route WAVE charger.............................................................. 8

Figure 2-6. Cumulative miles and hours for the battery bus fleet................................................................. 9

Figure 2-7. Average monthly miles per bus for the battery and diesel fleets ............................................. 10

Figure 2-8. Monthly availability and reasons for unavailability for the battery fleet and diesel fleet........ 12

Figure 2-9. Overall availability during the evaluation period..................................................................... 13

Figure 2-10. Monthly charges and monthly energy consumption for the battery fleet............................... 14

Figure 2-11. Fraction of plug-in charges by overall time of day ................................................................ 15

Figure 2-12. Average minimum SOC for plug-in and inductive charges................................................... 16

Figure 2-13. Monthly fuel economy for the battery, diesel, and diesel trolley bus fleets........................... 17

Figure 2-14. Monthly average fuel price for electricity and diesel fuel...................................................... 19

Figure 2-15. Monthly fuel cost per mile for the battery and diesel bus fleets ............................................ 20

Figure 2-16. Monthly utility energy, bus energy, and charging efficiency................................................. 21

Figure 2-17. Cumulative bus MBRC and propulsion-related MBRC......................................................... 22

Figure 2-18. Monthly scheduled and unscheduled maintenance cost per mile for the battery and diesel 

fleets....................................................................................................................................... 24

Figure 2-19. Monthly maintenance cost per mile by system for the BEB system (battery bus fleet and 

inductive charger) .................................................................................................................. 26

Figure 2-20. Monthly maintenance cost per mile by system for the diesel bus fleet.................................. 26

Figure 2-21. Monthly operations (maintenance and fuel) cost for the battery and diesel bus fleets .......... 29
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List of Tables

Table ES-1. Summary of County Connection Evaluation Results .............................................................vii

Table 1-1. Selected Evaluation Projects ....................................................................................................... 2

Table 2-1. System Descriptions for the Battery Electric, Diesel, and Diesel Trolley Buses........................ 5

Table 2-2. Performance Metrics Analyzed for Each Fleet............................................................................ 6

Table 2-3. Average Monthly Mileage (Evaluation Period) ........................................................................ 10

Table 2-4. Summary of Availability by Bus for Battery and Diesel Buses................................................ 11

Table 2-5. Summary of Availability and Unavailability by Category ........................................................ 14

Table 2-6. Mileage, Fuel Use, and Fuel Economy...................................................................................... 18

Table 2-7. Roadcalls and MBRC................................................................................................................ 21

Table 2-8. Total Work Order Maintenance Costs....................................................................................... 23

Table 2-9. Work Order Maintenance Cost per Mile by Systema ................................................................ 25

Table 2-10. Propulsion-Related Work Order Maintenance Costs by System............................................. 28

Table 2-11. Overall Operations (Maintenance and Fuel) Cost per Mile..................................................... 29

Table 3-1. County Connection—Fleet Operations and Economics............................................................ 32

Table 3-2. County Connection—Maintenance Costs.................................................................................. 32

Table 3-3. County Connection—Breakdown of Maintenance Costs by System........................................ 33

Table 3-4. County Connection—Fleet Operations and Economics (SI)..................................................... 37

Table 3-5. County Connection—Maintenance Costs (SI) .......................................................................... 37

Table A-1. DOE/FTA Performance, Cost, and Durability Targets for FCEBsa ......................................... 38
1

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1 Introduction

The U.S. Department of Transportation’s (DOT’s) Federal Transit Administration (FTA) 

supports the research, development, and demonstration of low- and zero-emission technology for

transit buses. FTA funds a number of research projects with a goal of facilitating 

commercialization of advanced technologies for transit buses that will increase efficiency and 

improve transit operations. These programs include the following:

• National Fuel Cell Bus Program (NFCBP)—a $180 million, multi-year, cost-share 

research program for developing and demonstrating commercially viable fuel cell 

technology for transit buses.

• Transit Investments for Greenhouse Gas and Energy Reduction (TIGGER)—$225 

million for capital investments that would reduce greenhouse gas emissions and/or lower 

the energy use of public transportation systems.

• Low or No Emission Vehicle Deployment Program (Low-No)—$271.35 million in 

funding (FY13–FY18) to transit agencies for capital purchases of zero-emission and lowemission transit buses that have been largely proven in testing and demonstration efforts 

but are not yet widely deployed.

FTA understands the need to share early experience of advanced technologies with the transit 

industry. FTA is funding evaluations of a selection of these projects to provide comprehensive, 

unbiased performance results from advanced technology bus development, operations, and 

implementation. These evaluations have proved useful for a variety of groups including transit 

operators considering the technology for future procurements, manufacturers needing to 

understand the status of the technology for transit applications, and government agencies making 

policy decisions or determining future research needs. The evaluations include economic, 

performance, and safety factors. Data are collected on the operation, maintenance, and 

performance of each advanced technology fleet and a comparable baseline fleet operating at the 

same site (if available).

FTA is collaborating with the U.S. Department of Energy (DOE) and DOE’s National 

Renewable Energy Laboratory (NREL) to conduct in-service evaluations of advanced 

technology buses. For more than a decade, NREL has been evaluating advanced technology 

transit buses using a standard data collection and analysis protocol originally developed for DOE 

heavy-duty vehicle evaluations. Funding for these evaluations has come from several agencies 

including FTA, DOE, and the California Air Resources Board. NREL has evaluated fuel cell 

electric buses (FCEBs) as well as battery electric buses (BEBs) following this standard protocol. 

DOT’s Research, Development, and Technology Office (OST-R) also has an interest in zeroemission bus (ZEB) technology deployment and commercialization. OST-R is coordinating and 

collaborating with FTA on the evaluation process and results by providing funding to cover 

additional evaluations.

NREL uses a set of criteria to prioritize the available projects for selection. The criteria include 

number of buses deployed, record-keeping practices of the transit agency, commitment level of 

the bus original equipment manufacturer (OEM), and the availability of appropriate baseline 

buses for comparison. The criteria are not intended to be rigid; however, the determination of 
2

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priority is based on how many criteria are met. In consultation with FTA, NREL has selected

several projects that are in the highest priority category. Other projects will be chosen as more 

information becomes available. Table 1-1 lists the projects selected for evaluation as of the 

publication date of this report.

Table 1-1. Selected Evaluation Projects

Site 

# Transit Agency and Location Project Description Evaluation Status

1 King County Metro, Seattle, WA 3 Proterra 40-ft Catalyst buses and 1 

fast-charge station Completed

2 Long Beach Transit, Long Beach, CA 10 BYD 40-ft BEBs, overnight charging 

with 1 inductive charger on route

Initiated April 

2017

3 Central Contra Costa Transit 

Authority, Concord, CA

4 Gillig/BAE Systems 29-ft BEBs, 

overnight charging with 1 inductive 

charger on route

Completed

4 Orange County Transportation 

Authority, Santa Ana, CA

1 American Fuel Cell Bus (AFCB):

BAE Systems, Ballard Power Systems, 

and ENC

Completed

5 Stark Area Regional Transit Authority, 

Camden, OH 7 AFCBs Initiated August 2017

6 Massachusetts Bay Transportation 

Authority, Boston, MA

1 AFCB with Nuvera PowerTap system 

fueling infrastructure Completed

7 Duluth Transit, Duluth, MN 6 Proterra 40-ft Catalyst E2 BEBs Initiated May

2018

8

Southeastern Pennsylvania 

Transportation Authority, 

Philadelphia, PA

25 Proterra 40-ft Catalyst E2 BEBs Planned 

2019

The purpose of this report is to present the results from the Central Contra Costa Transit 

Authority (County Connection) deployment of four BEBs in Concord, California. NREL’s 

evaluation of the BEBs at County Connection was funded by OST-R.
3

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2 County Connection BEB Evaluation Results

In February 2017, County Connection began operating a fleet of four BEBs in its service area.

This section summarizes the evaluation results for the battery buses in comparison to a selection 

of baseline buses. The focus of the analysis is on one year of data from June 2017 through May

2018.

2.1 Fleet Profile—County Connection 

County Connection—formally known as Central Contra Costa Transit Authority—is a public 

transit agency that provides fixed-route and paratransit service in the San Francisco Bay Area. 

Headquartered in Concord, California, County Connection provides transit service to 11 

surrounding jurisdictions, including Clayton, Concord, Danville, Lafayette, Martinez, Moraga, 

Orinda, Pleasant Hill, San Ramon, Walnut Creek, and unincorporated central Contra Costa 

County. The service area covers approximately 200 square miles and contains more than 482,000 

residents. The agency operates 25 weekday routes (including 7 express routes) and 10 weekend 

routes with a fleet of 121 transit buses.

County Connection was awarded a grant from the FTA in 2012 as part of FTA’s Clean Fuels 

Grant Program. The $4.32 million grant was used to purchase four all-electric Gillig buses and 

two electric vehicle charging stations. The four trolley-replica electric buses operate on Route 

4—a free circulator route through downtown Walnut Creek with a layover stop at the Bay Area 

Rapid Transit (BART) station. The buses replaced a fleet of diesel trolley replicas that had 

reached the end of their expected service life. FTA awarded a 2016 Low-No Program grant to 

County Connection to purchase four additional electric buses to expand the service. These buses 

were delivered in May and August 2018. Figure 2-1 shows a map of the County Connection 

service area with an inset showing the Walnut Creek route.
4

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Figure 2-1. Map of County Connection service area
5

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2.2 Bus Technology Descriptions

County Connection’s battery buses are 29-ft trolley-replica buses built by Gillig with a BAE 

Systems electric propulsion system. NREL is collecting data on two diesel bus fleets as baseline 

comparisons: a fleet of seven model year 2014 Gillig diesel buses and a fleet of three model year 

2002 Gillig trolley-replica diesel buses. Table 2-1 provides selected specifications for each bus 

type. Figure 2-2 is a photo of one of the battery buses.

Table 2-1. System Descriptions for the Battery Electric, Diesel, and Diesel Trolley Buses

Vehicle System Battery Diesel Diesel Trolley

Number of buses

in evaluation 4 7 3

Bus manufacturer Gillig Gillig Gillig

Bus year and model 2016 2014 29X102 2002 29X102

Length (ft) 29 29 29

GVWR (lb) 34,500 30,000 30,000

Motor or engine BAE Systems, 

HDS200

Diesel engine, 

Cummins ISL-9

Diesel engine, 

Cummins ISL-280

Rated power 160 kW nominal, 

200 kW peak 280 hp @ 2,200 rpm 280 hp @ 2,000 rpm

Energy storage

Xalt, nickel 

manganese cobalt,

100 kWh

None None

Accessories Electric Mechanical Mechanical

Bus purchase cost $1,053,689 $459,935 $345,432

Figure 2-2. County Connection Gillig battery electric bus

One of NREL’s goals in evaluating ZEBs is to document the performance and track progress 

over time toward meeting the technical targets. NREL collects data on conventional buses at 

each demonstration site for a baseline comparison. This is important primarily because fuel 

economy is highly dependent on duty cycle, but also because maintenance practices can be 
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different from site to site. The best comparisons need to include buses operated in similar service 

at the same operating division. The most accurate comparison would be between buses of the 

same manufacturer, model, production year, and mileage. In that case, the only difference 

between the ZEB and baseline buses would be the propulsion system. This type of baseline 

comparison is not always possible.

The primary baseline comparison for this evaluation is the fleet of model year 2014 diesel buses. 

This conventional bus fleet is County Connection’s best match to the battery bus fleet with 

respect to size and age. These buses are randomly dispatched on all routes and therefore have a 

different duty cycle than the battery buses operating only on the Walnut Creek route. The older 

diesel trolley-replica buses have been operated on the Walnut Creek route since 2002 and 

therefore are the best match to the battery buses in duty cycle, which is important for the fuel 

economy comparison. Table 2-2 outlines the different fleets in the analysis and indicates which 

performance metrics are included in the results.

Table 2-2. Performance Metrics Analyzed for Each Fleet

Performance Metric Battery Diesel Diesel 

Trolley

Monthly Mileage X X

Availability X X

Fuel Economy X X X

Fuel Cost per Mile X X X

Reliability (MBRC) X X

Maintenance Cost per Mile X X

2.3 Charging Infrastructure

The agency installed two charging stations: plug-in chargers at the facility for overnight charging 

and a WAVE inductive charging pad at the BART stop on the Walnut Creek route for wireless 

charging during scheduled layovers. Figure 2-3 shows the plug-in charger installed at the County 

Connection facility. The agency typically plugs in the buses every night. The average charging 

time for the plug-in charger was 126 minutes, and each bus charged an average of less than once 

per day. There are two plug-in chargers at the facility for charging the four buses.
7

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Figure 2-3. Plug-in charger at the County Connection facility

The 50-kW WAVE charger uses inductive power transfer between a power-transmitting plate 

embedded in the road surface and a receiving plate mounted to the bottom of the bus.1 Figure 2-4

shows the inductive charging pad installed in the pavement and the WAVE charging equipment 

located nearby. The painted lines on the concrete help the operator align the bus for charging. An 

indicator in the driver’s area provides additional feedback to let the driver know when the pads 

are aligned. Figure 2-5 shows a bus aligned for charging. Drivers are not allowed to back up the 

bus at the stop—if the alignment is not within accepted tolerance, they are required to drive 

around the circle to approach the charger again. The average charging time for the inductive 

charger was 6.9 minutes per bus, and each battery bus charged an average of about 12 times per 

day. 

 1 WAVE news web page: https://waveipt.com/news/.
8

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Figure 2-4. WAVE inductive charging pad (left) and charging equipment (right)

Figure 2-5. Bus lined up to charge at the on-route WAVE charger

2.4 In-Service Operations Evaluation Results

This section focuses on the results of a full year of operation from June 2017 through May 2018

(the evaluation period). County Connection began operating the battery buses in January 2017. 

The diesel trolley fleet had been operating since 2002 and was now being replaced in service by 

the new battery fleet. 

NREL kicked off the evaluation in February 2017 and began coordinating with County 

Connection for data collection. After acquiring all necessary data files for the monthly analysis—

including utility bills for both chargers—NREL established a clean point of June 2017 for the 

evaluation.
9

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2.4.1 Route Assignments

County Connection operates the battery buses on the Walnut Creek free shuttle route (route 4), 

which is a three-mile circulator through downtown Walnut Creek with a layover at the BART 

station. Full service requires three buses. The battery buses use the wireless inductive charger 

during every scheduled layover at the BART stop. The average speed for the Walnut Creek route 

based on scheduled revenue service is 6.0 mph, which does not include deadhead or out of 

service miles. The new battery buses are replacing the old diesel trolleys, which are past their 

expected service life. The diesel trolleys are still used as substitutes for the battery buses on route 

4 if needed.

The baseline diesel buses are randomly dispatched on all routes from the County Connection 

facility, as displayed in the service map, Figure 2-1. This results in a faster average speed of 15.2 

mph. These average speeds are calculated using revenue service schedules and do not include 

deadhead or out of service miles.

2.4.2 Bus Use 

Figure 2-6 tracks the accumulated mileage and operating hours of the battery buses since they 

were placed into service. County Connection has been operating the battery buses continuously 

since January 2017, accumulating over 65,000 total fleet miles after approximately one and a 

half years. The average overall speed, including all hours of operation for the buses (revenue 

service or otherwise), is 4.0 mph.

Figure 2-6. Cumulative miles and hours for the battery bus fleet

Table 2-3 provides the evaluation period mileage for each bus and the average monthly mileage 

by bus type, which is also displayed in Figure 2-7. The battery buses averaged between 950 and 

1,300 miles per month, with an overall fleet average of 1,074 monthly miles per bus. This is 

lower than the baseline diesel bus fleet average of 2,251 monthly miles per bus. This difference 
10

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is a result of the planned operation of these fleets. The battery fleet is restricted to the Walnut 

Creek circulator route while the diesel fleet is randomly dispatched on all routes, including

commuter routes with higher speeds, which allows faster mileage accumulation.

Table 2-3. Average Monthly Mileage (Evaluation Period)

Bus # Total

Mileage Months

Average

Monthly

Mileage

1600 15,289 12 1,274

1601 11,486 12 957

1602 11,697 12 975

1603 13,079 12 1,090

Battery fleet 51,550 48 1,074

1400 23,152 12 1,929

1401 22,176 12 1,848

1402 27,834 12 2,320

1403 27,150 12 2,263

1404 29,269 12 2,439

1405 27,875 12 2,323

1406 31,612 12 2,634

Diesel fleet 189,068 84 2,251

Figure 2-7. Average monthly miles per bus for the battery and diesel fleets
11

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2.4.3 Availability

County Connection plans the BEBs for operation 7 days per week; the diesel baseline buses are 

planned for weekdays only. The availability analysis summarizes reporting from County 

Connection on the daily status of the four battery buses and seven diesel buses in the evaluation. 

The daily reports indicated whether each bus was planned for service, whether the bus was 

available for service, and, if not available, indicated a reason that the bus was unavailable. This 

analysis does not show the fraction of time the buses were actually used in revenue service, only 

whether they were available for service at the time of morning pull-out. Thus, buses could have 

been available and not used, or available but used for other purposes such as training or special 

events. In addition, availability numbers do not necessarily reflect all day operation. There may 

be instances when a bus was removed from service after being available at morning pull-out, as 

well as instances when a bus that was unavailable at morning pull-out became available for 

service later the same day and may or may not have been used. The frequency of these scenarios 

was not tracked or included in the analysis. Their impacts on the fleet availability are expected to 

be small and have the effect of offsetting each other.

NREL analyzed the primary reasons for buses being held out of service and grouped them into 

the unavailability categories shown in the availability charts below. The bus maintenance 

category applies to all general maintenance issues not specific to a powertrain. Other categories 

include preventive maintenance (PM), electric drive system, energy storage system (ESS), bus 

charging issues, inductive charger issues, transmission, and engine. Many of the categories are 

only applicable to the battery bus fleet and others are only applicable to the diesel bus fleet.

The analysis covers 12 months of data collection—June 2017 through May 2018.Table 2-4

provides a summary of the overall availability for each of the battery and diesel buses during the 

evaluation period. The availability for the diesel buses varied from 78.6% to 89.9%, with a fleet 

average of 85.5%. The battery bus availability varied from 67.3% to 88.9%, with a fleet average 

of 76.9%. 

Table 2-4. Summary of Availability by Bus for Battery and Diesel Buses

Bus # Planned

Days

Available

Days

Percent

Availability

1600 334 297 88.9%

1601 336 226 67.3%

1602 337 239 70.9%

1603 337 271 80.4%

Battery fleet 1,344 1,033 76.9%

1400 336 281 83.6%

1401 336 264 78.6%

1402 336 302 89.9%

1403 336 282 83.9%

1404 336 293 87.2%

1405 336 290 86.3%

1406 336 300 89.3%

Diesel fleet 2,352 2,012 85.5%
12

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Figure 2-8 tracks the monthly average availability for the battery bus fleet and the diesel bus 

fleets as solid lines along the top of the chart. These represent the availability for bus-related 

issues only. Also included in the chart is a dashed line for “BEB System” availability, which 

accounts for infrastructure-related downtime for the battery bus fleet as well as individual bus 

issues.

Figure 2-8. Monthly availability and reasons for unavailability for the battery fleet and diesel fleet

The battery fleet experienced some early bus-side and infrastructure-side charging issues in the 

first 4 months of the evaluation, during which the average fleet availability was 57.9%. The 

battery fleet experienced issues with the battery management system for the high-voltage 

batteries. Software updates appear to have solved the issue. Downtime for charging equipment 

can have a significant effect on availability because it limits use of the entire battery bus fleet. 

This is particularly true for a small fleet deployment that relies on a single on-route charger. 

None of the inductive charging issues experienced by County Connection were related to the 

electrical circuitry or charging pads of the inductive charger; the downtime was a result of issues 

with ancillary equipment used for cooling (discussed in more detail in the Summary of 

Achievements and Challenges section below). County Connection worked closely with WAVE 

to address the early charging issues. County Connection achieved an average availability of 

84.7% for the battery fleet during the remaining 8 months of the evaluation.

The stacked columns in Figure 2-8 show the number of days that the battery buses were 

unavailable, organized into six categories. Five of the categories—general bus maintenance, PM, 

electric drive system, ESS and bus charging issues—are all related to bus maintenance issues. 

The sixth category, inductive charger, accounts for all additional downtime from infrastructurerelated issues that caused the battery bus fleet to be unavailable. It is important to note that none 

of the infrastructure downtime was caused by issues with the charging circuitry or charging pads 

of the inductive charger; it was all related to ancillary equipment. In June and July of 2017, the 

downtime was a result of the chiller not functioning. After an inspection, it was reported to 
13

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WAVE that the failure was caused by a power surge typical of a lightning strike. In October 

2017, low coolant level caused a system shutdown and led to the replacement of an external 

cooling line. Most of the bus-side downtime during the evaluation period was due to issues in the 

ESS category, primarily with the battery management system. The battery fleet had very little 

downtime related to PM or other general maintenance issues.

The pie charts in Figure 2-9 show the percentage of days the buses in each fleet were available 

for service during the evaluation period. The fraction of unavailable days is divided into 

unavailability categories based on the reasons the buses were out of service. Downtime for the 

diesel fleet was split relatively evenly between engine maintenance (5.6%), PM (4.0%), and 

other general bus maintenance (4.6%). For the battery fleet, a large fraction of downtime—

12.0% of total planned service time—was due to issues with the ESS. The second largest 

category was bus-related charging issues, accounting for 5.5% of planned service time. 

Downtime for infrastructure-related charging issues represented 2.5% of planned service time, 

less than for general bus maintenance. Table 2-5 corresponds to Figure 2-9 and provides a fleetlevel breakdown of the availability percentages for each category.

Figure 2-9. Overall availability during the evaluation period
14

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Table 2-5. Summary of Availability and Unavailability by Category

Category

BEB

System

# Days

BEB

System

%

Battery

Fleet

# Days

Battery

Fleet

%

Diesel

Fleet

# Days

Diesel

Fleet

%

Planned days 1,344 - 1,344 - 2,352 -

Days available 1,000 74.4 1,033 76.9 2,012 85.5

Unavailable 344 - 311 - 340 -

Bus 40 11.6 40 12.9 109 32.3

PM 22 6.4 22 7.1 95 28.2

Electric drive 14 4.1 14 4.5 - -

ESS 161 46.8 161 51.8 - -

Charging issues 74 21.5 74 23.8 - -

Transmission - - - - 4 1.2

Engine - - - - 129 38.3

Inductive charger 33 9.6 - - - -

2.4.4 Energy Use, Fuel Economy, and Cost

Figure 2-10 shows the battery fleet’s monthly total number of plug-in and inductive charges as 

lines and the monthly total energy consumption by charge type as stacked columns. During the 

evaluation period, the number of inductive charges steadily increased from approximately 1,000 

charges per month to more than 1,600 charges per month for the four-bus fleet. The monthly 

energy consumption for inductive charging varied between 5,400 kWh and 10,300 kWh, with a

monthly average of 8,725 kWh. Plug-in charging behavior remained consistent throughout the 

evaluation period with averages of 105 charges per month and 2,658 kWh energy consumption 

per month. Inductive charges delivered 6.2 kWh per charge, on average, while the plug-in 

charger added 25.4 kWh back to the bus ESS. 

Figure 2-10. Monthly charges and monthly energy consumption for the battery fleet
15

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Plug-in charges could occur anytime a battery bus returned to County Connection’s facility but 

occurred most often in the evening. NREL calculated the number of charges occurring in the 

morning (anytime between midnight and noon), afternoon (noon to 5 p.m.), and evening (5 p.m. 

to midnight). The fraction of plug-in charges for each time window is shown in Figure 2-11. 

Charges that began before midnight but extended into the next day were counted as 1⁄2 charge in 

the evening and 1⁄2 charge in the morning.

Figure 2-11. Fraction of plug-in charges by overall time of day

County Connection has planned the operation of the buses to keep the battery state of charge 

(SOC) above 60% to minimize degradation. Figure 2-12 shows the average minimum SOC at the 

beginning of a charge. The beginning SOC for the plug-in charges has remained consistent over 

the data period, with an overall average of 73.8%. The beginning SOC for the inductive charging 

events has risen over time with an overall average of 73.6%. 
16

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Figure 2-12. Average minimum SOC for plug-in and inductive charges

Figure 2-13 shows the monthly average fuel economy in miles per diesel gallon equivalent 

(mpdge) for the battery and diesel bus fleets. The electrical energy used by the battery buses was 

converted to diesel gallon equivalent (dge) using a conversion factor of 37.64 kWh/dge. This 

energy conversion is detailed in the Appendix. Also plotted in Figure 2-13 is the average daily 

high temperature recorded at Buchanan Field Airport in Contra Costa County.2 The figure 

includes monthly fuel economy for both diesel baseline bus types. The standard diesel fleet is 

randomly dispatched on all routes. The overall system speed for County Connection is 14.8 mph 

including express routes. The battery buses and diesel trolley buses operate on County 

Connection’s slowest-speed route at 6.0 mph. Because it operates on the same route as the 

battery fleet (therefore at a similar speed), the diesel trolley fleet represents a better comparison 

of conventional bus fuel economy to battery bus fuel economy, despite the difference in age. 

NREL analyzed fuel economy data for the diesel trolley buses from 2002 to 2007 to ensure there 

was no significant age-related decline in average fuel economy for the fleet that would adversely 

impact this comparison. The year-to-year variation in weather is a primary factor in the 

difference in monthly average fuel economy; therefore, it is more appropriate to compare the 

diesel trolley fuel economy for the same time period than to compare the historical fuel economy 

trends.

The fuel economy for the two diesel fleets is very consistent during the evaluation period, 

averaging 5.1 mpdge for the diesel buses and 3.5 mpdge for the diesel trolley buses. The average 

fuel economy of the battery buses displays greater sensitivity to variation in ambient air 

temperature when the average high is above 80°F. The lowest monthly fuel economy for the 

battery fleet (10.8 mpdge) occurred in July 2017, corresponding with the highest average daily 

high temperature of 93.7°F. It’s important to note that the ambient temperature is only one of the 

 2 NOAA National Centers for Environmental Information–Climate Data Online, https://www.ncdc.noaa.gov/cdoweb/.
17

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major factors influencing fuel economy. Route selection (average driving speed, driving 

intensity, stops per mile), passenger loading, traffic conditions, and operator driving habits can 

all have significant impact on fuel economy. The best monthly fuel economy was 14.6 mpdge,

occurring in November 2017, and the overall average for the data period was 13.3 mpdge. The 

battery fleet’s fuel economy is 3.8 times higher than that of the diesel trolley buses operated on 

the same service route and 2.6 times higher than that of the diesel buses operated on all the 

County Connection routes. Per-bus summaries of mileage, fuel consumption, and fuel economy 

are listed in Table 2-6.

County Connection reports that because of improvements in transmission and engine 

technologies, its newer diesel buses achieve an average fuel economy that is much higher 

compared to the older diesel trolley buses. The agency estimates that if these newer buses were 

operated on the Walnut Creek route, they would be expected to have a fuel economy higher than 

3.5 mpg.

Figure 2-13. Monthly fuel economy for the battery, diesel, and diesel trolley bus fleets
18

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Table 2-6. Mileage, Fuel Use, and Fuel Economy

Bus

Mileage

(fuel 

base)

Fuel

Consumption 

(kWh)

Fuel

Consumption 

(dge)

Fuel Economy 

(kWh/mi)

Fuel Economy 

(mpdge)

1600 15,289 44,806 1190.4 2.93 12.8

1601 11,486 33,240 883.1 2.89 13.0

1602 11,697 31,778 844.3 2.72 13.9

1603 13,079 36,328 965.1 2.78 13.6

Battery fleet 51,550 146,152 3,882.9 2.84 13.3

1400 23,152 - 4,656.0 - 5.0

1401 22,176 - 4,431.3 - 5.0

1402 27,834 - 5,467.9 - 5.1

1403 27,150 - 5,486.3 - 4.9

1404 29,269 - 5,640.7 - 5.2

1405 27,875 - 5,519.1 - 5.1

1406 31,612 - 5,944.7 - 5.3

Diesel fleet 189,068 - 37,146 - 5.1

Figure 2-14 compares the average monthly price for each fleet’s transportation fuel—electricity 

for the battery fleet and diesel fuel for the baseline diesel fleet. Because these fuels use different 

native units, the chart shows the price per dge on the left axis and the equivalent price per kWh 

on the right axis. The relationship between the energy content of one gallon of diesel fuel and 

one kWh of electricity is detailed in Appendix C. The average price of diesel fuel during the 

evaluation period was $2.01/gal, compared to the average price for electricity of $0.22/kWh 

($8.39/dge). County Connection is not subject to electricity demand charges under the current

rate schedule with their electric utility, PG&E. It’s clear that the price of electricity is much 

higher—more than 4x higher—than the price of diesel fuel on an equivalent energy basis.
19

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Figure 2-14. Monthly average fuel price for electricity and diesel fuel

The corresponding cost per mile of each fleet’s fuel is compared in Figure 2-15. The per-mile 

fuel cost is a function of the unit price of the fuel (Figure 2-14) and the fuel efficiency of the 

buses (Figure 2-13).

The average fuel cost per mile for the battery fleet during the evaluation period was $0.73/mi. 

The higher fuel economy of the battery buses during the cooler winter months combined with 

lower electricity prices during those months resulted in a much lower fuel cost per mile—around 

$0.60/mi—for November through April. Conversely, high electricity prices and lower fuel 

economy during the summer led to higher per-mile fuel costs, as high as $0.99/mi in July 2017.

The per-mile fuel costs for the diesel buses were less sensitive to seasonal variations but showed 

a steady increase during the evaluation period, from a low of $0.32/mi in July 2017 to a high of 

$0.48/mi in May 2018.
20

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Figure 2-15. Monthly fuel cost per mile for the battery and diesel bus fleets

Figure 2-16 shows the overall monthly charging efficiency for the BEBs based on the total 

energy consumption of the fleet (recorded by the buses) and the total energy purchased for the 

charging stations (per the utility bills). These monthly totals are based on the utility billing 

periods and do not exactly match the calendar months. The efficiencies for each charging method 

are shown separately. The charging efficiency for the depot charging is 92.8% and the efficiency 

of the inductive charging is 85.2%. The overall charging efficiency for the system averages to 

86.9%. 
21

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Figure 2-16. Monthly utility energy, bus energy, and charging efficiency

2.4.5 Roadcall Analysis

Table 2-7 provides the miles between roadcalls (MBRC) for the BEBs and diesel buses 

categorized by bus roadcalls, propulsion-related roadcalls, and ESS-related roadcalls. Figure 2-

17 provides the cumulative MBRC for the battery buses and diesel baseline buses with total bus

roadcalls on the upper chart and propulsion-related roadcalls and ESS-related roadcalls on the 

lower chart. Propulsion-related roadcalls are a subset of bus roadcalls for all bus fleets. ESSrelated roadcalls are a subset of the propulsion-related roadcalls, specific to the ESS of the 

battery buses. The DOE/FTA target for total bus MBRC of 4,000 is included in the graph as a 

red dashed line. The BEBs currently have a total bus MBRC of 4,686, which has surpassed the 

target. 

Table 2-7. Roadcalls and MBRC

BEB Diesel

Dates 6/17–5/18 6/17–5/18

Mileage 51,550 189,068

Bus roadcalls 11 3

Bus MBRC 4,686 63,023

Propulsion-related roadcalls 8 1

Propulsion-related MBRC 6,444 189,068

ESS-related roadcalls 3

ESS-related MBRC 17,183
22

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Figure 2-17. Cumulative bus MBRC and propulsion-related MBRC

2.4.6 Maintenance Analysis

This section first covers total maintenance costs and then maintenance costs by bus system.

NREL excludes warranty repairs from the calculations. The battery buses were under warranty 

for the entire data period.

2.4.7 Total Work Order Maintenance Costs

Table 2-8 shows maintenance costs per mile for the bus fleets and includes total cost, scheduled 

cost, and unscheduled cost. Scheduled costs include PM based on the OEMs’ recommendations. 

All other maintenance is included in unscheduled costs. The warranty work—which is not 

included in the analysis—was handled by the OEMs. During the data period, the maintenance 

cost for the battery buses was 13% less than that of the diesel buses.
23

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Table 2-8. Total Work Order Maintenance Costs

Bus Fleet Mileage Parts ($) Labor 

Hours

Scheduled 

Cost per 

Mile ($)

Unscheduled 

Cost per Mile 

($)

Total Cost

per Mile

($)

1600 15,289 667.74 80.5 0.04 0.26 0.31

1601 11,486 1,129.93 87.5 0.06 0.42 0.48

1602 11,697 762.86 97.0 0.12 0.36 0.48

1603 13,079 530.92 72.5 0.09 0.23 0.32

Battery Total 51,550 3,091.45 337.5 0.08 0.31 0.39

1400 23,152 2,799.79 150.8 0.10 0.34 0.45

1401 22,176 5,266.48 169.8 0.09 0.53 0.62

1402 27,834 2,595.40 167.0 0.09 0.30 0.39

1403 27,150 2,701.37 141.0 0.10 0.26 0.36

1404 29,269 3,949.23 165.5 0.11 0.31 0.42

1405 27,875 1,996.20 145.8 0.09 0.25 0.33

1406 31,612 9,346.49 163.6 0.07 0.49 0.55

Diesel Total 189,068 28,654.96 1,103.3 0.09 0.35 0.44

The monthly scheduled and unscheduled maintenance cost per mile for both fleets of buses are 

shown as stacked columns in Figure 2-18. The high maintenance costs for the diesel buses during 

July 2017 were due to five buses reaching the mileage for a major PM and four buses 

experiencing issues with the exhaust system. The high cost in April 2018 was primarily for 

replacement of Intelligent Transportation System equipment on one bus. Issues with the battery 

management system and general bus issues increased the cost for the battery buses in November 

2017. The higher battery bus costs in May 2018 were due to cooling system issues and general 

bus issues. 
24

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Figure 2-18. Monthly scheduled and unscheduled maintenance cost per mile for the battery and 

diesel fleets

2.4.8 Work Order Maintenance Costs Categorized by System

Table 2-9 shows maintenance costs per mile by vehicle system and bus fleet (without warranty 

costs). The vehicle systems shown in the table are as follows:

• Cab, body, and accessories: Includes body, glass, cab and sheet metal, seats and doors, 

and accessory repairs such as hubodometers and radios

• Propulsion-related systems: Repairs for exhaust, fuel, engine, electric motors, battery 

modules, propulsion control, non-lighting electrical (charging, cranking and ignition), air 

intake, cooling, and transmission

• PMI: Labor for inspections during preventive maintenance

• Brakes: Includes brake pads, disks, calipers, anti-lock braking system, and brake 

chambers

• Frame, steering, and suspension

• HVAC

• Lighting

• Air system (general)

• Axles, wheels, and drive shaft

• Tires.
25

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Table 2-9. Work Order Maintenance Cost per Mile by Systema

System

BEB System

Cost per 

Mile ($)

BEB System

Percent of 

Total (%)

Diesel 

Cost per 

Mile ($)

Diesel 

Percent of 

Total (%)

Propulsion-related 0.10 25.7 0.14 31.1

Cab, body, and accessories 0.14 36.4 0.16 35.3

PMI 0.07 17.5 0.06 14.4

Brakes 0.02 6.3 0.04 9.3

Frame, steering, and suspension 0.01 3.6 0.01 2.1

HVAC 0.01 1.9 0.02 3.9

Lighting 0.02 4.5 0.00 1.0

General air system repairs 0.00 0.7 0.01 1.5

Axles, wheels, and drive shaft 0.00 0.0 0.01 1.2

Tires 0.00 0.6 0.00 0.3

Inductive charging system 0.01 2.8 — —

Total 0.39 100 0.44 100 a The top three categories for maintenance for each fleet are color coded as follows: orange—highest, green—

second highest, and purple—third highest.

The color shading denotes the systems with the highest percentage of maintenance costs: orange 

for the highest, green for the second highest, and purple for the third highest. The systems with 

the highest percentage of maintenance costs for the battery buses and diesel buses were the same:

1) cab, body, and accessories; 2) propulsion-related; and 3) PMI. Figure 2-19 shows the monthly 

cost per mile by system for the BEB system (battery bus fleet and inductive charger). Repairs 

included a coolant sensor, replacement of low-voltage batteries, electrical system, and issues 

with the battery management for the energy storage system.
26

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Figure 2-19. Monthly maintenance cost per mile by system for the BEB system (battery bus fleet 

and inductive charger)

Figure 2-20 shows the monthly cost per mile by system for the diesel fleet. The majority of 

issues with the diesel buses were in the cab, body, and accessories category. Issues included

problems with mirrors, glass, and seats. Propulsion category issues included problems with 

turbochargers, exhaust system, electrical system, and low-voltage batteries.

Figure 2-20. Monthly maintenance cost per mile by system for the diesel bus fleet
27

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2.4.9 Propulsion-Related Work Order Maintenance Costs

Propulsion-related vehicle systems include the exhaust, fuel, engine, battery modules, electric 

propulsion, air intake, cooling, non-lighting electrical, transmission, and hydraulic systems. 

These vehicle subsystems have been separated to highlight how maintenance costs for the 

propulsion system are affected by the change from conventional technology (diesel) to advanced 

technology (batteries). Table 2-10 shows the propulsion-related system maintenance costs by 

category for the two fleets during the data period. Parts for scheduled maintenance, such as 

filters and fluids, are included in the specific system categories. For example, oil and oil filters 

are included in the power plant (engine) subsystem parts costs, while air filters are included in 

the air intake subsystem parts costs.

• Total propulsion-related—The battery fleet’s total propulsion-related maintenance cost 

was 28% lower than that of the diesel buses.

• Exhaust system—Costs for the diesel buses were low. The battery buses do not have 

exhaust systems.

• Fuel system—Costs for this system for the diesel buses were low. The battery buses do 

not have a liquid fueling system.

• Power plant and electric propulsion—For the battery buses, the electric propulsion 

system accounted for 45% of the total propulsion system costs. Power plant (engine) 

repairs made up 31% of the total propulsion system costs for the diesel buses.

• Non-lighting electrical (charging, cranking, and ignition)—Costs for this system for 

the battery buses were 80% higher than for the diesel buses due to the cost for replacing 

low-voltage batteries.

• Air intake—Costs for this system for the battery and diesel buses were low.

• Cooling—Costs for this system for the battery buses were low. For the diesel buses, 

cooling system repairs made up 17% of the propulsion system costs.

• Transmission—Costs for this system were low for the diesel buses. The BEBs do not 

have a transmission.

• Hydraulic—Costs for this system were zero for both bus fleets.
28

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Table 2-10. Propulsion-Related Work Order Maintenance Costs by System

Maintenance System Maintenance Costs BEB Diesel

Mileage 51,550 189,068

Total Propulsion-Related 

Systems 

(Roll-up)

Parts cost ($) 1,515.75 12,065.48

Labor hours 72.3 279.5

Total cost ($) 5,128.25 26,040.48

Total cost ($) per mile 0.099 0.138

Exhaust System Repairs

Parts cost ($) 0.00 3,670.13

Labor hours 0.0 50.0

Total cost ($) 0.00 6,170.13

Total cost ($) per mile 0.000 0.033

Fuel System Repairs

Parts cost ($) 0.00 435.60

Labor hours 0.0 9.0

Total cost ($) 0.00 885.60

Total cost ($) per mile 0.000 0.005

Powerplant System 

Repairs (Energy Storage 

System for BEBs)

Parts cost ($) 4.78 3,300.52

Labor hours 27.8 96.3

Total cost ($) 1,392.28 8,113.02

Total cost ($) per mile 0.027 0.043

Electric Propulsion 

System Repairs

Parts cost ($) 467.47 0.00

Labor hours 37.3 0.0

Total cost ($) 2,329.97 0.00

Total cost ($) per mile 0.045 0.000

Non-Lighting Electrical 

System Repairs (General 

Electrical, Charging, 

Cranking, Ignition)

Parts cost ($) 1,043.50 1,587.46

Labor hours 5.0 21.0

Total cost ($) 1,293.50 2,637.46

Total cost ($) per mile 0.025 0.014

Air Intake System Repairs

Parts cost ($) 0.00 1,332.14

Labor hours 0.3 8.8

Total cost ($) 12.50 1,769.64

Total cost ($) per mile 0.000 0.009

Cooling System Repairs

Parts cost ($) 0.00 586.97

Labor hours 2.0 75.5

Total cost ($) 100.00 4,361.97

Total cost ($) per mile 0.002 0.023

Transmission System 

Repairs

Parts cost ($) 0.00 1,152.66

Labor hours 0.0 19.0

Total cost ($) 0.00 2,102.66

Total cost ($) per mile 0.000 0.011

Hydraulic System Repairs

Parts cost ($) 0.00 0.00

Labor hours 0.0 0.0

Total cost ($) 0.00 0.00

Total cost ($) per mile 0.000 0.000
29

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

2.4.10 Total Cost

Figure 2-21 shows the monthly total operational cost per mile, including maintenance and fuel 

cost, for the battery and diesel fleets. Energy costs dominate the battery fleet’s overall 

operational costs and are higher during the summer months when the electric rate increases. 

Diesel fuel costs are consistent over the data period. Table 2-11 summarizes the overall fuel and 

maintenance costs per mile by bus fleet. These parameters are also listed in Appendix A.

Figure 2-21. Monthly operations (maintenance and fuel) cost for the battery and diesel bus fleets

Table 2-11. Overall Operations (Maintenance and Fuel) Cost per Mile

Battery Diesel

Fuel cost per mile ($/mi) 0.73 0.40

Total maintenance cost per mile ($/mi) 0.39 0.44

Total operating cost per mile ($/mi) 1.11 0.84

2.5 Summary of Achievements and Challenges

As with all new technology development, lessons learned during this project could aid other 

agencies considering BEB technology. The team reports a number of successes that include the 

following:

• Implemented the agency’s first BEB fleet

• Fully electrified the Walnut Creek route

• Accumulated more than 51,500 miles on the battery buses in the first year of revenue 

service.
30

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

2.5.1 Summary of Challenges

Advanced-technology demonstrations typically experience challenges and issues that need to be 

resolved. Issues and lessons learned for County Connection include the following.

Charger availability—When deploying a BEB fleet, availability of an on-route charger is 

critical for operation. Downtime of a charger results in downtime for the fleet. Early in this 

evaluation, County Connection experienced a couple issues with the inductive charger that 

decreased the battery fleet availability. Importantly, none of the issues were related to the 

electrical circuitry or wireless charging components; rather, the issues were related to ancillary 

cooling equipment. The primary issue, responsible for the June/July 2017 downtime, was a 

failure of the chiller’s compressor. Subsequent investigation of the component by the 

manufacturer indicates that a power surge from a lightning strike occurred, requiring the 

compressor to be replaced. In October 2017, a slow leak in an external coolant line led to a 

shutdown of the cooling system. The coolant line was replaced with a more durable material.

Charger efficiency—During investigation of the inductive charger performance, WAVE 

provided additional information about the design of the charger’s cooling system which had an 

impact on the overall efficiency. The cooling system for this particular installation of the 50-kW 

charger was intentionally oversized to allow for up to 100% duty cycle charging in a hot 

environment because system uptime and meeting transit service requirements were the highest 

priorities for County Connection. There were also conservative settings for pre- and post-cooling 

of the water tank to ensure reliability, rather than efficiency, of the system. WAVE reported that 

major improvements have been made to the cooling system design of the inductive charger since 

this first-generation product, improving the efficiency of their higher power charger to 92% 

(typical) and avoiding issues experienced in the early months of this deployment.

Added operating costs—When adding BEBs with depot charging to a fleet, an agency needs to 

plan for logistics to plug in and move the buses to and from the charger at the depot. This is 

especially true for fleets that don’t install a charger for each bus. County Connection reports that 

this adds labor costs to the project. Because the agency has two chargers to cover the fleet of four 

buses, staff are needed to stage and move the buses to ensure each one gets fully charged before 

parking overnight. Scaling up to a larger fleet will add complexity to this process. For BEBs with 

on-route charging, additional time may need to be planned into the route schedule. County 

Connection has added a half hour to the beginning and end of each operator shift to allow time 

for the BEBs to charge at the inductive charger prior to starting the route and before returning to 

the depot. This adds to the labor needs for operating BEBs. Some agencies may only experience 

one of these two impacts, but County Connection is operating both types of chargers and has 

decided to top off the charge of the buses on route and at the depot.

Maintenance costs—Because the BEBs are under warranty, some repairs were made that are not 

accounted for in the maintenance records. Labor and parts costs for repairs that are handled by 

the OEM are not typically included in maintenance data sets and NREL is unable to analyze and 

report on them. At this point in the demonstration, post-warranty maintenance costs are 

unknown. Agencies should carefully consider this when using early reported costs to plan for 

BEB fleet implementation and long-term maintenance costs.
31

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Maintenance skill set—Deploying new technologies presents a challenge for transit staff to take 

over all maintenance responsibilities after the warranty period ends. Current staff do not have the 

skill set needed to fully maintain BEBs. Additional labor hours are incurred as staff come up to 

speed on the new technology. In addition, there is a shortage in the hiring pool of technicians 

with the desired skill sets. The industry is addressing this need by working with community 

colleges and technical schools to add the required courses for ZEB technicians. The updated 

training materials are still in the beginning stages of development, therefore current graduates do 

not yet have the needed skill set. Until these programs are fully established, hiring ZEB qualified 

technicians will be a challenge.
32

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

3 County Connection Fleet Summary Statistics

Table 3-1. County Connection—Fleet Operations and Economics

BEB Diesel

Number of vehicles 4 8

Period used for fuel and energy op analysis 6/17–5/18 6/17–5/18

Total number of months in period 12 12

Fuel and energy analysis base fleet mileage 51,550 189,068

Period used for maintenance op analysis 6/17–5/18 6/17–5/18

Total number of months in period 12 12

Maintenance analysis base fleet mileage 51,550 189,068

Average monthly mileage per vehicle 1,074 1,969

Availability 77 86

Fleet energy usage in kWh for BEB / gal for diesel 46,152.3 37,146.0

Purchased electrical energy in kWh for BEB 68,274.3 —

Roadcalls 11 3

Total MBRC 4,686 63,023

Propulsion roadcalls 8 1

Propulsion MBRC 6,444 189,068

Fleet kWh/mile 2.84 7.40

Representative fleet mpg (diesel energy equivalent) 13.28 5.09

Energy cost per kWh / diesel cost per gal 0.22 2.02

Energy/fuel cost per mile (based on purchased energy) 0.73 0.40

Total scheduled repair cost per mile 0.08 0.09

Total unscheduled repair cost per mile 0.31 0.35

Total maintenance cost per mile 0.39 0.44

Total operating cost per mile 1.11 0.84

Table 3-2. County Connection—Maintenance Costs

BEB Diesel

Fleet mileage 51,550 189,068

Total parts cost ($) 3,091.45 28,654.96

Total labor hours 337.5 1,103.3

Total labor cost (@ $50.00 per hour) ($) 16,872.50 55,165.00

Total maintenance cost ($) 19,963.95 83,819.96

Total maintenance cost per bus ($) 4,990.99 11,974.28

Total maintenance cost per mile ($/mi) 0.39 0.44
33

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Table 3-3. County Connection—Breakdown of Maintenance Costs by System

BEB Diesel

Fleet mileage 51,550 189,068

Total Engine/Fuel-Related Systems (ATA VMRS 27, 30, 31, 32, 33, 41, 42, 43, 44, 45, 

46, 65)

Parts cost 1,515.75 12,065.48

Labor hours 72.25 279.50

Average labor cost 3,612.50 13,975.00

Total cost (for system) 5,128.25 26,040.48

Total cost (for system) per bus 1,282.06 6,510.12

Total cost (for system) per mile 0.10 0.14

Exhaust System Repairs (ATA VMRS 43)

Parts cost 0.00 3,670.13

Labor hours 0.00 50.0

Average labor cost 0.00 2,500.00

Total cost (for system) 0.00 6,170.13

Total cost (for system) per bus 0.00 1,542.53

Total cost (for system) per mile 0.00 0.03

Fuel System Repairs (ATA VMRS 44)

Parts cost 0.00 435.60

Labor hours 0.0 9.0

Average labor cost 0.00 450.00

Total cost (for system) 0.00 885.60

Total cost (for system) per bus 0.00 221.40

Total cost (for system) per mile 0.00 0.00

Power Plant (Engine or ESS) Repairs (ATA VMRS 45)

Parts cost 4.78 3,300.52

Labor hours 27.8 96.3

Average labor cost 1,387.50 4,812.50

Total cost (for system) 1,392.28 8,113.02

Total cost (for system) per bus 348.07 2,028.26

Total cost (for system) per mile 0.03 0.04

Electric Propulsion Repairs (ATA VMRS 46)

Parts cost 467.47 0.00

Labor hours 37.3 0.0

Average labor cost 1,862.50 0.00

Total cost (for system) 2,329.97 0.00

Total cost (for system) per bus 582.49 0.00

Total cost (for system) per mile 0.05 0.00
34

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Table 3-3. County Connection—Breakdown of Maintenance Costs by System (continued)

BEB Diesel

Electrical System Repairs (ATA VMRS 30-Electrical General, 31-Charging, 32-

Cranking, 33-Ignition)

Parts cost 1,043.50 1,587.46

Labor hours 5.0 21.0

Average labor cost 250.00 1,050.00

Total cost (for system) 1,293.50 2,637.46

Total cost (for system) per bus 323.38 659.37

Total cost (for system) per mile 0.03 0.01

Air Intake System Repairs (ATA VMRS 41)

Parts cost 0.00 1,332.14

Labor hours 0.3 8.8

Average labor cost 12.50 437.50

Total cost (for system) 12.50 1,769.64

Total cost (for system) per bus 3.13 442.41

Total cost (for system) per mile 0.00 0.01

Cooling System Repairs (ATA VMRS 42)

Parts cost 0.00 586.97

Labor hours 2.0 75.5

Average labor cost 100.00 3,775.00

Total cost (for system) 100.00 4,361.97

Total cost (for system) per bus 25.00 1,090.49

Total cost (for system) per mile 0.00 0.02

Hydraulic System Repairs (ATA VMRS 65)

Parts cost 0.00 0.0

Labor hours 0.0 0.0

Average labor cost 0.00 0.00

Total cost (for system) 0.00 0.00

Total cost (for system) per bus 0.00 0.00

Total cost (for system) per mile 0.00 0.00

General Air System Repairs (ATA VMRS 10)

Parts cost 41.95 239.24

Labor hours 2.0 19.8

Average labor cost 100.00 987.50

Total cost (for system) 141.95 1,226.74

Total cost (for system) per bus 35.49 306.69

Total cost (for system) per mile 0.00 0.01
35

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Table 3-3. County Connection—Breakdown of Maintenance Costs by System (continued)

BEB Diesel

Brake System Repairs (ATA VMRS 13)

Parts cost 0.00 643.57

Labor hours 25.0 143.0

Average labor cost 1,250.00 7,150.00

Total cost (for system) 1,250.00 7,793.57

Total cost (for system) per bus 312.50 1,948.39

Total cost (for system) per mile 0.02 0.04

Transmission Repairs (ATA VMRS 27)

Parts cost 0.00 1,152.66

Labor hours 0.0 19.0

Average labor cost 0.00 950.00

Total cost (for system) 0.00 2,102.66

Total cost (for system) per bus 0.00 525.67

Total cost (for system) per mile 0.00 0.01

Inspections Only—No Parts Replacements (101)

Parts cost 0.00 0.00

Labor hours 69.8 242.0

Average labor cost 3,487.50 12,100.00

Total cost (for system) 3,487.50 12,100.00

Total cost (for system) per bus 871.88 3,025.00

Total cost (for system) per mile 0.07 0.06

Cab, Body, and Accessories Systems Repairs (ATA VMRS 02-Cab and Sheet Metal, 

50-Accessories, 71-Body)

Parts cost 826.60 12,998.93

Labor hours 129.0 335.0

Average labor cost 6,447.50 16,750.00

Total cost (for system) 7,274.10 29,748.93

Total cost (for system) per bus 1,818.53 7,437.23

Total cost (for system) per mile 0.14 0.16

HVAC System Repairs (ATA VMRS 01)

Parts cost 207.68 1,091.24

Labor hours 3.5 43.8

Average labor cost 175.00 2,190.00

Total cost (for system) 382.68 3,281.24

Total cost (for system) per bus 95.67 820.31

Total cost (for system) per mile 0.01 0.02
36

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Table 3-3. County Connection—Breakdown of Maintenance Costs by System (continued)

BEB Diesel

Lighting System Repairs (ATA VMRS 34)

Parts cost 499.47 237.84

Labor hours 8.0 11.3

Average labor cost 400.00 562.50

Total cost (for system) 899.47 800.34

Total cost (for system) per bus 224.87 200.09

Total cost (for system) per mile 0.02 0.00

Frame, Steering, and Suspension Repairs (ATA VMRS 14-Frame, 15-Steering, 16-

Suspension)

Parts cost 0.00 924.13

Labor hours 14.5 16.3

Average labor cost 725.00 812.50

Total cost (for system) 725.00 1,736.63

Total cost (for system) per bus 181.25 434.16

Total cost (for system) per mile 0.01 0.01

Axle, Wheel, and Drive Shaft Repairs (ATA VMRS 11-Front Axle, 18-Wheels, 22-

Rear Axle, 24-Drive Shaft)

Parts cost 0.00 591.53

Labor hours 0.0 8.5

Average labor cost 0.00 425.00

Total cost (for system) 0.00 1,016.53

Total cost (for system) per bus 0.00 254.13

Total cost (for system) per mile 0.00 0.01

Tire Repairs (ATA VMRS 17)

Parts cost 0.00 0.00

Labor hours 2.5 4.3

Average labor cost 125.00 212.50

Total cost (for system) 125.00 212.50

Total cost (for system) per bus 31.25 53.13

Total cost (for system) per mile 0.00 0.00

Inductive Charging System

Parts cost 0.00 0.00

Labor hours 11.0 0.0

Average labor cost 550.00 0.00

Total cost (for system) 550.00 0.00

Total cost (for system) per bus 137.50 0.00

Total cost (for system) per mile 0.01 0.00
37

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

3.1 Fleet Summary Statistics—SI Units

Table 3-4. County Connection—Fleet Operations and Economics (SI)

BEB Diesel

Number of vehicles 4 8

Period used for fuel and energy op analysis 6/17–5/18 6/17–5/18

Total number of months in period 12 12

Fuel and energy analysis base fleet kilometers 82,960 304,267

Period used for maintenance op analysis 6/17–5/18 6/17–5/18

Total number of months in period 12 12

Maintenance analysis base fleet kilometers 82,960 304,267

Average monthly kilometers per vehicle 1,728 3,169

Availability 76.7 85.5

Fleet fuel usage in kWh / liter equivalent 146,152.3 140,612.9

Purchased electrical energy in kWh for BEB 168,274.3 —

Roadcalls 11 3

Total KMBRC 7,542 101,422

Propulsion roadcalls 8 1

Propulsion KMBRC 10,370 304,267

Rep. fleet fuel consumption (L/100 km) 17.69 46.21

Energy cost per kWh / diesel cost per liter 0.22 0.53

Energy/fuel cost per kilometer (based on purchased energy) 0.45 0.25

Total scheduled repair cost per kilometer 0.05 0.06

Total unscheduled repair cost per kilometer 0.19 0.22

Total maintenance cost per kilometer 0.24 0.28

Total operating cost per kilometer 0.69 0.52

Table 3-5. County Connection—Maintenance Costs (SI)

Battery Diesel

Fleet mileage 82,960 304,267

Total parts cost ($) 3,091.45 28,654.96

Total labor hours 340.20 1,103.30

Average labor cost (@ $50.00 per hour) ($) 17,010.00 55,165.00

Total maintenance cost ($) 20,101.45 83,819.96

Total maintenance cost per bus ($) 5,025.36 20,954.99

Total maintenance cost per kilometer ($/km) 0.24 0.28
38

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

Appendix. Evaluation Protocol

In 2012, DOE and FTA established performance and cost targets for FCEBs.3 Interim targets 

were set for 2016 along with ultimate targets that FCEBs would need to meet to compete with 

current commercial-technology buses. DOE and FTA have not established performance targets 

specific to BEBs, but the performance targets established for FCEBs were based on typical 

conventional buses and the targets could be considered appropriate for any advanced technology.

Table A-1 shows a selection of these technical targets for FCEBs.

Table A-1. DOE/FTA Performance, Cost, and Durability Targets for FCEBsa

Units 2016 Target Ultimate 

Target

Bus lifetime years/miles 12/500,000 12/500,000

Power plant lifetimeb hours 18,000 25,000

Bus availability % 85 90

Fuel fills per day 1 (<10 min) 1 (<10 min)

Bus costc $ 1,000,000 600,000

Roadcall frequency (bus/fuel cell 

system)

miles between 

roadcalls (MBRC) 3,500/15,000 4,000/20,000

Operation time hours per day/

days per week 20/7 20/7

Scheduled and unscheduled 

maintenance costd $/mile 0.75 0.40

Range miles 300 300

Fuel economy miles per diesel 

gallon equivalent 8 8

a The cost targets for subsystems (power plant and hydrogen storage) are not included.

b The power plant is defined as the fuel cell system and the battery system.

c Cost is projected to a production volume of 400 systems per year. This production volume is assumed for 

analysis purposes only and does not represent an anticipated level of sales.

d Excludes mid-life overhaul of power plant.

NREL uses a standard evaluation protocol for evaluating the advanced technologies deployed 

under the FTA programs. Data parameters include the following:

• Bus system descriptions

• 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

 3 Fuel Cell Technologies Program Record # 12012, September 12, 2012.
39

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

For each selected fleet, NREL collects all fueling/charging, cost, and maintenance data for a 

period of 12 to 18 months to provide a full year of operation data for the analysis. For each site, 

NREL collects data on conventional technology baseline buses for comparison. For most fleets, 

the baseline buses are diesel buses. For fleets that do not operate diesel buses, the baseline buses 

are usually compressed natural gas (CNG) buses. Other technologies, such as diesel hybrid 

buses, will be included in the evaluation if they are available. The best comparisons are made 

between buses of the same make, model, production year, size, and route deployment. In that 

case, the only difference is the propulsion system. This is not always possible. NREL works with 

the transit agency to determine which vehicles the agency has in operation and selects the best 

possible baseline match for each evaluation based on what is available. The following sections 

outline the analysis approach for each parameter.

A.1 Bus System Descriptions

This category of data includes general descriptions of the buses and systems. NREL provides a 

form that the agency fills out for both the ZEBs and baseline vehicles. The form asks for 

specifications of the vehicle propulsion system and subsystems as well as accessory equipment. 

This information documents that the baseline vehicles are similar in equipment to the advanced 

technology buses. NREL collects these data at the beginning of the project; however, changes 

may be required if major systems are altered.

A.2 Operations Duty-Cycle Description

NREL collects duty-cycle descriptions from the transit agency to understand how the ZEBs are 

used compared to the baseline buses. Data collected include descriptions of the expected routes, 

operating hours during a typical work day, number of days per week that the vehicle is operated, 

the amount of fuel and range (in miles) that are expected during a given work day and between 

fueling/charging, and other information on how the vehicles are used. Transit agencies typically 

provide these data in text format. NREL uses the data to determine an average operating speed. 

Occasionally, bus OEMs provide detailed Global Positioning System (GPS) data from the onboard data collection systems. In those cases, NREL will develop specific route maps showing 

the planned use of the ZEBs. 

A.3 Bus Use and Availability

Bus use and availability are indicators of reliability. Lower bus usage may indicate downtime for 

maintenance or purposeful reduction of planned work for the buses. NREL expresses bus use as 

average miles accumulated per month. NREL uses a general target of 3,000 miles per month for 

this metric; however, the monthly miles for each agency will vary depending on the planned use 

of the buses. If a ZEB fleet does not meet this target, it does not indicate a specific limitation for 

the technology. NREL collects the mileage data for the ZEBs and baseline buses and calculates 

average monthly miles accumulated per bus. 

Availability is the number of days the buses are actually available compared to the days that the 

buses are planned for operation, expressed as percent availability. The analysis calculates

availability for morning pull-out and doesn’t necessarily reflect all-day availability. Transit 

agencies typically have a target of 85% availability for their fleets to allow time to handle 

scheduled and unscheduled maintenance. The sources for availability data vary from fleet to 

fleet. NREL works with each agency to determine the best source for the data. In addition to 
40

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

tracking the overall availability, NREL collects the reasons for unavailability. Categories for 

unavailability include issues related to general bus systems, preventive maintenance, electric 

drive, battery system, and fuel cell system. These data help indicate whether the issues are due to 

the advanced technology components or are problems with conventional bus systems. 

A.4 Energy/Fuel Consumption

Data needed for this category include records of each fueling or charging event. For liquid- and 

gas-fueled buses, NREL collects individual fueling records (amount of fuel, odometer reading, 

hour reading, date, and fueling time) and fuel prices (each fuel, each time the fuel price 

changes—price and date). For the BEBs, NREL collects daily energy use (total kWh, number of 

charges, miles traveled) and utility bills for each charging location (in depot or on-route fast

charger). NREL analyzes these data to calculate monthly fuel economy and fuel/energy cost per 

mile. For the BEBs, NREL uses the bus energy use and utility energy data to calculate the 

charging losses.

To compare the electrical energy used by the BEBs to the diesel fuel energy used by the baseline 

hybrid and diesel buses, the electrical energy is converted to diesel gallon equivalent (dge). The 

energy content of each fuel4 is used to create the conversion factor shown below:

Lower heating value for diesel fuel = 128,488 Btu/gal

U.S. average energy content of electricity = 3,414 Btu/kWh

Conversion factor = 128,488 Btu/gal / 3,414 Btu/kWh = 37.64 kWh/gal

A.5 Maintenance Cost

Maintenance data include each repair action—such as preventive (scheduled) maintenance, 

unscheduled maintenance, and roadcalls—and date of repair, labor hours, number of days out of 

service, odometer reading, parts replaced, parts cost, and descriptions of problem reported and 

actual repair performed. NREL also collects data and cost for any fluid addition (oil, 

transmission fluid, deionized water). Engine oil changes are included as part of preventive 

maintenance. The maintenance data are used to estimate operating costs (along with fuel and 

engine oil consumption costs). Because accident-related repairs are extremely variable from bus 

to bus, NREL eliminates those costs from the analysis for both ZEB and baseline bus fleets.

NREL also eliminates warranty cost data from the operating cost calculation because those costs 

are covered in the purchase price of the buses. Labor costs may be included in this analysis 

depending on the mechanic who performed the work (operator or manufacturer) and whether 

those hours were reimbursed under the warranty agreement. For consistency, NREL uses a labor 

cost of $50/hour. Cost per mile is calculated as follows:

Cost per mile = [(labor hours * $50/hr) + parts cost] / mileage

NREL calculates total cost per mile as well as scheduled and unscheduled cost per mile. To 

understand the differences between conventional and ZEB technology, NREL presents the cost 

 4 Alternative Fuels Data Center, fuel properties database, http://www.afdc.energy.gov/fuels/fuel_properties.php.
41

This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

per mile by vehicle system. The work orders are coded using vehicle maintenance reporting 

standards (VMRS) developed by the American Trucking Association to aid the industry in 

tracking equipment and maintenance using a common standard. The propulsion-related systems 

were chosen to include only those systems of the vehicles that could be affected directly by the 

selection of a fuel or advanced technology. NREL bases the VMRS coding on parts that were 

replaced. If there was no part replaced in a given repair, then NREL selects the code by the 

system being worked on. System categories include the following:

• Cab, body, and accessories: Includes body, glass, cab and sheet metal, seats and doors, 

and accessory repairs such as hubodometers and radios

• Propulsion-related systems (subsystems included):

o Engine/power plant (includes fuel cell for FCEBs)

o Electric propulsion system

o Fuel system

o Exhaust

o Non-lighting electrical system—general electrical, charging, cranking, ignition

o Air intake

o Cooling

o Transmission

o Hydraulic

• Preventive maintenance inspection (PMI): Labor for inspections during preventive 

maintenance

• Brakes: Includes brake pads, disks, calipers, anti-lock braking system, and brake 

chambers

• Frame, steering, and suspension

• HVAC

• Lighting

• Air system (general)

• Axles, wheels, and drive shaft

• Tires.

A.6 Roadcalls

All roadcalls are marked in the maintenance data collected. A roadcall, or revenue vehicle 

system failure, is defined as a failure of an in-service bus that causes the bus to be replaced on 

route or causes a significant delay in schedule. If the problem with the bus can be repaired during 

a layover and the schedule is kept, this is not considered a roadcall. The analysis described here 

includes only roadcalls that were caused by “chargeable” failures. Chargeable roadcalls include 

systems that can physically disable the bus from operating on route, such as interlocks (doors, air 

system), engine, or things that are deemed to be safety issues if operation of the bus continues. 

They do not include roadcalls for issues with components such as radios, fareboxes, or 

destination signs.

The transit industry measures reliability as mean distance between failures, also documented as 

miles between roadcalls (MBRC). MBRC is calculated by dividing the number of miles traveled 

by the number of roadcalls. NREL uses the roadcall data to calculate cumulative MBRC over 

time. MBRC results in the report are categorized as follows:
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This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

• Bus MBRC: Includes all chargeable roadcalls. This category includes propulsion-related 

issues as well as problems with bus-related systems such as brakes, suspension, steering, 

windows, doors, and tires.

• Propulsion-related MBRC: Includes roadcalls that are attributed to the propulsion system

and is a subset of the bus MBRC. Propulsion-related roadcalls can be caused by issues 

with the engine, transmission, batteries, fuel cell system, or electric drive.

• Energy storage system (ESS)-related MBRC: Includes roadcalls attributed to the ESS

only (specific to BEBs).

• Fuel cell system-related MBRC: Includes roadcalls attributed to the fuel cell and balance 

of plant only (specific to FCEBs).

Transit agencies are required to report costs and specific performance data to FTA through the 

National Transit Database (NTD). After Congress required data reporting in 1974, FTA 

developed the NTD as a repository of financial, operating, and asset condition data for American 

transit agencies. These data are published on the NTD website.5 The vehicle maintenance 

reliability metrics used by the NTD are as follows:

• Major mechanical system failure: A failure of some mechanical element of the revenue 

vehicle that prevents the vehicle from completing a scheduled revenue trip or from 

starting the next scheduled revenue trip because actual movement is limited or because of 

safety concerns.

• Other mechanical system failure: A failure of some other mechanical element of the 

revenue vehicle that, because of local agency policy, prevents the revenue vehicle from 

completing a scheduled revenue trip or from starting the next scheduled revenue trip even 

though the vehicle is physically able to continue in revenue service. Examples include a 

malfunction in the farebox or the air conditioner.

Total revenue system failures would be a sum of the two categories. The NTD categories do not 

exactly match the roadcall definitions used in the standard NREL protocol. The primary 

difference is that NTD’s other mechanical system failures category includes failures of items 

such as fareboxes and destination signs. This results in the NTD total failures being higher than 

that of the NREL analysis. Removing these failures from the NTD data would result in higher 

overall industry average MBRC. In addition, the NTD major mechanical system failure category 

includes some roadcalls that are not for the propulsion system. The NTD has no category for 

power plant failures; therefore, there is no direct comparison for fuel cell system-related or ESSrelated MBRC.

A.7 Infrastructure and Facility Modification Descriptions

At the beginning of the data collection period, NREL collects details on the fleet’s operations 

including a description of facilities and services, maintenance and fueling practices, and any 

other information needed to get a complete understanding of the fleet’s experience with the 

ZEBs. Descriptions of facilities include fueling, charging, maintenance, and vehicle storage 

facilities that may be associated with the ZEBs. 

 5 NTD website: https://www.transit.dot.gov/ntd.
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This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.

A.8 Capital Costs 

Data on capital costs include costs for any facility modifications that are required for operation 

of ZEBs. The vehicle capital costs include the costs for new vehicles and propulsion systems.

A.9 Implementation Experience

The experiences of a transit agency in implementing any new technology are an important part of 

fully understanding the current status of that technology. NREL collects data on the fleet 

implementation experience to document the background work needed for successful 

implementation of ZEBs, as well as some of the potential pitfalls and lessons learned. The types 

of information collected in support of this activity include:

• Documentation of the history that led to the agency’s decision to purchase ZEBs, its 

previous experience with alternative fuels, etc.

• Roles of important supporting organizations such as vehicle manufacturer and supplier, 

fuel suppliers, and federal, state, or local government agencies.

• Specific incentives for advanced technology vehicles, and regulations or disincentives for 

the other options that helped form the agency’s decision to purchase ZEBs.

• The driver, fleet personnel, and customer perceptions of the new technology vehicles.

• Special fleet needs such as mechanic, driver, or technician training requirements, special 

equipment, and safety issues. 

• A description of the training implementation strategy including employee orientation, 

operations and maintenance personnel, and the costs of this training. 

• What it took to bring these vehicles into revenue service, and what technical/nontechnical hurdles were overcome.