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June 2010 

3. REPORT TYPE AND DATES 

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Project Report, June 2010

4. TITLE AND SUBTITLE

National Fuel Cell Bus Program: Accelerated Testing Report #2, AC Transit

5. FUNDING NUMBERS

6. AUTHOR(S)

Kevin Chandler*, Leslie Eudy,** 

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

National Renewable Energy Laboratory, 1617 Cole Blvd., Golden, CO 80401 

Battelle, 505 King Ave. Columbus, OH 43201

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NREL/TP-560-48106-1

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Office of Research, Demonstration, and Innovation

Federal Transit Administration, 1200 New Jersey Ave, S.E., Washington, D.C. 20590

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AGENCY REPORT 

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FTA-CO-26-7004-2010.1

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*Battelle Memorial Institute 

**National Renewable Energy Laboratory

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13. ABSTRACT (Maximum 200 words)

This is an evaluation of hydrogen fuel cell transit buses operating at AC Transit in revenue service since March 20, 2006 

compared to similar diesel buses operating from the same depot. This evaluation report includes results from 

November 2007 through February 2010. Evaluation results include implementation experience, fueling station 

operation, evaluation results at AC Transit (bus usage, availability, fuel economy, maintenance costs, and roadcalls), 

and a summary of achievements and challenges encountered during the demonstration.

14. SUBJECT TERMS

Fuel cell, hydrogen, bus, transit, AC Transit, ZEBA 

15. NUMBER OF PAGES

36 

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Cover Photo Credit: L. Eudy, NREL
iii

Acknowledgments

This evaluation at Alameda-Contra Costa Transit District (AC Transit) would not have 

been possible without the support and cooperation of many people. The authors thank the 

following: 

U.S. Department of Transportation UTC Power

Federal Transit Administration Matthew Riley

Walter Kulyk Rakesh Radhakrishnan 

Christina Gikakis David Boudreau 

Sean Ricketson 

ISE Corporation 

U.S. Department of Energy Paul Scott

John Garbak Tavin Tyler

Kevin Stone 

DOE’s National Renewable Energy Laboratory 

Keith Wipke Golden Gate Transit

Gene Walker

AC Transit Steve Miller

Jaimie Levin Rich Hibbs 

Doug Byrne Greg Nordin 

Stuart Thompson Dan Lafragiola 

Joe Callaway Mike Greenfield

Craig Michels 

Mallory Nestor-Brush CALSTART

Jim Lair Lawrence Wnuk

Emilie Beusen

Steve Tracey

Stephen Reynolds 

Christina Ebojo

Jose Vega

Miguel Lopez-Vega

And many others 

Notice 

This document is disseminated under the sponsorship of the United States Department of 

Transportation in the interest of information exchange. The United States Government 

assumes no liability for its contents or use thereof.

The United States Government does not endorse products or manufacturers. Trade or 

manufacturers’ names appear herein solely because they are considered essential to the 

objective of this analysis.
iv

Executive Summary

The Alameda-Contra Costa Transit District (AC Transit) has been operating three fuel cell buses 

in revenue service since March 20, 2006. This operation has been documented in previous 

evaluation reports from the U.S. Department of Energy (DOE), the U.S. Department of 

Transportation’s Federal Transit Administration (FTA), and DOE’s National Renewable Energy 

Laboratory (NREL). This report continues the evaluation at AC Transit; the funding for NREL’s 

data collection and analysis was transitioned from DOE to the FTA. Specifically, this report 

presents the results of AC Transit’s accelerated testing of its existing three fuel cell buses as part 

of the FTA’s National Fuel Cell Bus Program (NFCBP). 

Accelerated Testing

The accelerated testing project at AC Transit includes preparation and support to maximize 

operation of the three fuel cell buses, and support of the transition to the next phase of the fuel 

cell bus program. The maximized operation will help the manufacturers further validate the 

propulsion system by identifying the weakest areas, analyzing the root causes of failure, and 

making modifications and upgrades to increase durability and reliability. 

The accelerated testing results in this report cover operation from November 2007 through 

February 2010 for the fuel cell buses, with a focus on fuel cell bus operations from the last 

installation of new fuel cell power systems (noted as the clean point). The diesel bus evaluation 

results are from January through December 2007. The evaluation results are summarized in 

Table ES-1. This report also describes the achievements and challenges from nearly 4 years of 

revenue service.

Table ES-1. Summary of Evaluation Results

Data Item Fuel Cell Diesel

Number of Buses 3 6

Data Period Clean Point – 2/10 1/07 – 12/07

Number of Months ~25 12

Total Mileage in Period 160,027 266,514

Average Monthly Mileage per Bus 2,101 3,702

Total Fuel Cell Operating Hours 16,403 N/A

Average Bus Operating Speed (mph) 9.8 N/A

Availability (85% is target) 66% N/A

Fuel Economy (miles/kg) 6.01 N/A

Fuel Economy (miles/DGEa) 6.79 4.20

Miles between Roadcalls (MBRC) – All 1,185 4,299

MBRC – Propulsion Only 1,539b 10,661

Total Maintenance ($/mile)c 0.74 0.49

Maintenance – Propulsion Only ($/mile) 0.19 0.10 a Diesel gallon equivalent. b For fuel cell propulsion only, MBRC was 10,002. c Work order maintenance cost.
v

What’s on the Horizon for AC Transit?

AC Transit is moving into the next phase of fuel cell bus development, demonstrating 12 new 

and advanced fuel cell buses. This demonstration is in response to the California Air Resources 

Board (CARB) Transit rule that requires several California agencies (including AC Transit) to

purchase new and advanced fuel cell buses as part of their zero-emission bus regulations. 

Developed by UTC Power and Van Hool, the new buses incorporate the lessons learned during 

the demonstration of the current fuel cell buses. 

AC Transit is the managing partner for a Zero Emission Bay Area (ZEBA) working group to 

respond to CARB’s advanced fuel cell bus demonstration. The ZEBA group includes several 

Bay Area transit agencies:

• AC Transit

• Santa Clara Valley Transportation Authority 

• Golden Gate Transit (GGT)

• San Mateo County Transit District 

• San Francisco Municipal Transportation Agency (SF MTA).1

AC Transit continues to work on developing hydrogen fueling infrastructure to support the new 

fuel cell buses. The Chevron station at the East Oakland Division that has been used for 

hydrogen fueling is scheduled for decommission in September 2010. AC Transit is working with 

Linde to construct new stations at East Oakland as well as its Emeryville depot (Division 2). The

new Emeryville station will be a convenient fueling location for future bus operations by ZEBA 

partner transit agencies like GGT and SF MTA.

The current evaluation of accelerated testing at AC Transit was funded by FTA in conjunction 

with their NFCBP. With the completion of this report, the evaluation funding will be transitioned 

from FTA back to DOE. The DOE evaluation plans include all 12 of the new fuel cell buses for 

the planned ZEBA/CARB demonstration. 

 

1 SF MTA is a voluntary participant. Its fleet of trolley buses already meets CARB zero-emission bus regulations.
vi

Table of Contents

Introduction and Background ......................................................................................................... 1

National Fuel Cell Bus Program ................................................................................................. 1

AC Transit Fuel Cell Bus Operation and Evaluation .................................................................. 2

Accelerated Testing at AC Transit .............................................................................................. 3

What’s in this Evaluation Report? .............................................................................................. 4

Demonstration Achievements and Challenges ............................................................................... 5

Bus Operations ............................................................................................................................ 5

Hydrogen Fueling ........................................................................................................................... 7

Facility Modifications ................................................................................................................. 7

Training ....................................................................................................................................... 8

Public Awareness ........................................................................................................................ 8

Coordination with Golden Gate Transit ...................................................................................... 8

Public Outreach ............................................................................................................................... 8

Passenger Survey Results ............................................................................................................ 9

Ridership ..................................................................................................................................... 9

Hydrogen Fueling ......................................................................................................................... 10

Fuel Cell Bus Operations—Evaluation Results ............................................................................ 13

Route Descriptions .................................................................................................................... 13

Bus Use and Availability ........................................................................................................... 14

Fuel Economy and Cost ............................................................................................................ 16

Maintenance Analysis ............................................................................................................... 18

Roadcall Analysis ...................................................................................................................... 23

What’s Next for AC Transit? ........................................................................................................ 24

Contacts......................................................................................................................................... 26

Acronyms and Abbreviations ....................................................................................................... 27

Bibliography ................................................................................................................................. 28

AC Transit ................................................................................................................................. 28

City of Burbank ......................................................................................................................... 28

General ...................................................................................................................................... 28

SunLine ..................................................................................................................................... 28

Connecticut Transit ................................................................................................................... 29

Santa Clara Valley Transportation Authority ............................................................................ 29
1

Introduction and Background

The Alameda-Contra Costa Transit District (AC Transit) has been operating three fuel cell buses 

in revenue service since March 20, 2006. The early operation was documented in three previous 

evaluation reports from the U.S. Department of Energy (DOE) and the National Renewable 

Energy Laboratory (NREL).2,3,4 In November 2007, the funding for NREL’s data collection and 

analysis transitioned from DOE to the FTA; the funding will return to DOE after publication of 

this report. This report covers the results of AC Transit’s accelerated testing of its existing three 

fuel cell buses as part of FTA’s National Fuel Cell Bus Program (NFCBP). NREL reported on 

the first half of the accelerated testing results in January 2009.5

National Fuel Cell Bus Program

The accelerated testing 

evaluation results in this report add operations from November 2008 through February 2010. 

This report completes NREL’s accelerated testing and evaluation work for this fuel cell bus 

design. Under DOE funding, NREL will continue to work with AC Transit to evaluate the nextgeneration fuel cell bus project, which is expected to start when the first of 12 new buses is 

delivered in May 2010. 

In 2006, FTA initiated the NFCBP,6 which supplied $49 

million over 4 years in competitive, 50-50 governmentindustry cost share grants to facilitate the development of 

commercially viable fuel cell bus technologies. This FTA 

program was funded as part of the Safe, Accountable, 

Flexible, Efficient Transportation Equity Act: A Legacy for Users (SAFETEA-LU)7

• Developing improved components and technologies for fuel cell buses, including fuel 

cell, energy storage, and power electronics technologies

. The 

objectives of the program include: 

• Demonstrating fuel cell buses equipped with these improved components and 

technologies 

• Understanding the requirements of market introduction, including fuel supply, fueling 

infrastructure, supplier networks, maintenance, education, safety, and insurance 

• Collaborating in developing design standards for fuel cell bus technologies. 

On October 12, 2006, at SunLine Transit Agency, FTA awarded grants to three nonprofit 

consortia—CALSTART (Pasadena, California), Center for Transportation and the Environment 

(CTE, Atlanta, Georgia), and the Northeast Advanced Vehicle Consortium (NAVC, Boston, 

 

2 Alameda-Contra Costa Transit District (AC Transit), Fuel Cell Transit Buses: Preliminary Evaluation Results, 

February 2007, NREL/TP-560-41041, http://www.nrel.gov/hydrogen/pdfs/41041.pdf 3 Alameda-Contra Costa Transit District (AC Transit), Fuel Cell Transit Buses: Evaluation Results Update, October 

2007, NREL/TP-560-42249, http://www.nrel.gov/hydrogen/pdfs/42249.pdf 4 Alameda-Contra Costa Transit District (AC Transit), Fuel Cell Transit Buses: Third Evaluation Report, July 2008, 

NREL/TP-560-43545-1, http://www.nrel.gov/hydrogen/pdfs/43545-1.pdf 5 National Fuel Cell Bus Program: Accelerated Testing Evaluation Report, January 2009, FTA-CO-26-7004-2009.1,

http://www.nrel.gov/hydrogen/pdfs/44820-1.pdf 6 FTA Bus Research and Testing Web site: http://www.fta.dot.gov/assistance/technology/research_4578.html 7 www.fhwa.dot.gov/safetealu/ 
2

Massachusetts). Over a 4-year period, these consortia were funded to lead teams that develop and 

test components, conduct outreach, and demonstrate fuel cell buses in a variety of geographic 

locations and climates across the United States. 

A portfolio of 14 projects (managed by the three consortia) was competitively selected by FTA 

to best advance fuel cell bus commercialization, including eight planned demonstration projects. 

Bus demonstration projects include both evolutionary and “clean sheet” approaches and 

incorporate multiple drive technologies and configurations, fuel cell stacks of different sizes, and 

various energy storage technologies. The buses being demonstrated incorporate components 

from four fuel cell power system manufacturers and various implementations of hybrid electric 

propulsion systems and energy storage—batteries and ultracapacitors. 

For fiscal year 2010 into 2011, additional funding for the NFCBP was appropriated. This 

additional $13.5 million will be competed among the three consortia already participating in the 

program under the same requirements as the other NFCBP projects. This new competition will 

focus on new projects that can advance project targets in the original program, contribute to the 

overall fuel cell bus research portfolio, and help further fuel cell bus commercialization in the 

near term.

Data collection, analysis, and reporting of the results of the demonstrations are all high priorities 

for FTA. As such, FTA is collaborating with DOE and NREL to ensure that data are collected on 

all fuel cell bus demonstrations in a complete and consistent manner. FTA tasked NREL as a 

third-party evaluator for the fuel cell buses developed and demonstrated under the NFCBP.

Under funding from DOE, NREL has been evaluating fuel cell buses to help determine the status 

of hydrogen and fuel cell systems in transit applications. NREL uses a standard data collection 

and analysis protocol that was established for DOE heavy-duty vehicle evaluations more than 10 

years ago. In May 2008, NREL published Hydrogen and Fuel Cell Transit Bus Evaluations: 

Joint Evaluation Plan for the U.S. Department of Energy and the Federal Transit 

Administration, which outlines the methodology and plans for both the DOE and FTA fuel cell 

bus evaluations8

AC Transit Fuel Cell Bus Operation and Evaluation

 to be performed by NREL. Appendix A is an overview of NREL’s transit bus 

evaluation activities for DOE and FTA.

AC Transit offers public transit service in the East Bay of the San Francisco, California, area, 

including Oakland. The AC Transit service area of 360 square miles includes 13 cities and 

adjacent unincorporated areas in Alameda and Contra Costa counties. Since 2000, AC Transit 

has developed and operated a fuel cell demonstration program called the HyRoad. With a goal of 

demonstrating the viability of an emission-free transit system, this program includes fuel cell bus 

and passenger car operation, on-site hydrogen production, fueling, vehicle maintenance, public 

outreach and education, and safety training. 

Golden Gate Transit (GGT), headquartered in San Rafael, California, is participating in the AC 

Transit fuel cell bus demonstration—it operated one of the fuel cell buses for nearly a month, 

from February 19 to March 21, 2008, and again in early July 2009 for an event. GGT is a part of 

 

8 Hydrogen and Fuel Cell Transit Bus Evaluations: Joint Evaluation Plan for the U.S. Department of Energy and the 

Federal Transit Administration, NREL/MP-560-42781, May 2008, http://www.nrel.gov/hydrogen/pdfs/42781-1.pdf 
3

the Golden Gate Bridge, Highway, and Transportation District, which is headquartered in San 

Francisco, and serves the North Bay area. Appendix B supplies more information about AC 

Transit and GGT. 

The fuel cell bus development is the result of collaboration between Van Hool, ISE Corporation, 

and UTC Power. The buses use the PureMotion9

The evaluation in this report also presents results from the operation of six Van Hool diesel buses 

in revenue service at the same location as the fuel cell buses. The diesel buses, which are used in 

the evaluation as a baseline, are equipped with Cummins ISL engines. Other than the fuel cell 

and hybrid electric propulsion system on the fuel cell buses, the only significant difference with 

the diesel buses is that they do not have air conditioning. This is an important detail in the fuel 

economy analysis and comparison. Appendix C gives more detail about the buses and propulsion 

technologies in this evaluation. Appendix D contains information about the hydrogen fueling 

station and facilities modified for use with hydrogen. Updated information regarding hydrogen 

dispensing into the fuel cell buses is discussed later in this report.

 120 Fuel Cell Power System manufactured by 

UTC Power in a hybrid electric drive system designed by ISE. The energy storage in this hybrid 

system consists of three ZEBRA (sodium/nickel chloride, high temperature) traction batteries. In 

addition to the three fuel cell buses at AC Transit, two other buses of the same design are 

operating at SunLine Transit Agency and Connecticut Transit (CTTRANSIT). Results from the 

operation of these two fuel cell buses are reported separately by NREL and DOE.

Accelerated Testing at AC Transit

The accelerated testing project at AC Transit continues the partnership with UTC Power and Van 

Hool for ongoing demonstration of the three fuel cell buses. As mentioned previously, the 

NFCBP introduced nonprofit consortia leads for this FTA program. The accelerated testing 

project at AC Transit is managed through CALSTART in Pasadena, California. CALSTART 

works with public and private partners to accelerate the growth of advanced transportation 

technologies, including fuel cells. CALSTART was tasked with managing 5 of the 14 projects in 

the NFCBP, including fuel cell bus demonstrations (such as the AC Transit demonstration) and 

development of advanced components related to fuel cell propulsion systems.10

The accelerated testing project at AC Transit involves preparation and support for maximizing 

operation of the three fuel cell buses and then supporting the transition to the next phase of the 

fuel cell bus program. The maximized operation includes operating the fuel cell buses in revenue 

service 15 to 19 hours per day, up to 7 days per week, and is intended to accelerate planning for 

resources and training at AC Transit to prepare to support nearly full transit operation of the fuel 

cell buses. The maximized operation is intended to help the manufacturers further validate the 

propulsion system, identifying the weakest areas, analyzing the root causes of failure, and 

making modifications and upgrades to increase durability and reliability. The resulting design 

changes are being incorporated into the next-generation systems, which will be used in AC 

Transit’s next phase of operation with 12 new fuel cell buses, with delivery starting in second 

quarter 2010. 

 

 

9 PureMotion is a registered trademark of UTC Power.

10 CALSTART Web site: www.calstart.org 
4

The 12 new fuel cell buses are a part of a multi-operator bus demonstration in the Bay Area to 

meet regulations promulgated by the California Air Resources Board (CARB). This new 

demonstration, designated the Zero Emission Bay Area (ZEBA) demonstration group, will be 

managed from AC Transit and will include participation by Golden Gate Transit (GGT), Santa 

Clara Valley Transportation Authority (VTA), San Mateo County Transit District (SamTrans), 

and San Francisco Municipal Transportation Agency (SF MTA). 

What’s in this Evaluation Report?

This accelerated testing evaluation report completes the analysis results for this fuel cell bus 

design and implementation from Van Hool, ISE Corporation, and UTC Power. These three fuel 

cell buses will be taken out of service as the first three new fuel cell buses from Van Hool and 

UTC Power arrive at AC Transit. The fuel cell power systems in the existing buses will be 

installed in the first three new fuel cell buses and will continue to operate at AC Transit. This 

transition is expected to begin in May 2010. NREL plans to evaluate these new fuel cell buses 

and will report on this transition in the first evaluation report for those new buses. 

This evaluation report starts with a summary of the overall achievements and challenges during 

this demonstration at AC Transit. AC Transit has continued to support public outreach with their 

fuel cell bus program, and - ridership is summarized. The hydrogen fueling during the 

accelerated testing is summarized along with some statistics for life-to-date operation of the 

fueling station. This hydrogen station at AC Transit will be decommissioned and torn down, and 

a new station will be built as part of the new fuel cell bus demonstration (see What’s Next for 

AC Transit?).

The bulk of this report contains summary results from the operation of the fuel cell buses from 

November 2007 through February 2010. The accelerated testing period was defined contractually 

to start with November 2007; however, the focus of the evaluation results is presented from the 

point at which the fuel cell power systems (CSAs—cell stack assemblies) were replaced for each 

of the three buses, as follows:

• Fuel Cell Bus 1 (FC1)—CSAs replaced on March 7, 2008, restarted service on March 

18, 2008 

• Fuel Cell Bus 2 (FC2)—CSAs replaced on January 31, 2008, restarted service on 

February 5, 2008

• Fuel Cell Bus 3 (FC3)—CSAs replaced on December 11, 2007, restarted service on 

December 13, 2007; the CSAs were replaced again on December 15, 2008, restarted 

service on December 31, 2008. 

UTC Power reported that this last change of the CSAs incorporates many of the lessons learned 

from the previous operation of these fuel cell buses (and from the other operating locations), and 

previous early power-loss problems are believed to be resolved. The clean point period for the 

accelerated testing evaluation is the point that these fuel cell buses restarted service (FC1—

March 2008, FC2—February 2008, FC3—December 2007) through the endpoint of February 28, 

2010. This clean point evaluation period is used throughout the Evaluation Results section. The 

diesel bus baseline evaluation period is completed and includes data from January through 

December 2007. 
5

This report concludes with a description of the next steps for the next phase of AC Transit’s 

program, including the delivery of the 12 new fuel cell buses and construction of the two new 

hydrogen fueling stations. 

Demonstration Achievements and Challenges

This section focuses on achievements during the demonstration of prototype fuel cell buses and 

fueling infrastructure at AC Transit since starting revenue service on March 20, 2006, through 

February 28, 2010. Many challenges were faced and resolved during this demonstration, and 

several challenges remain for the technology development. The lessons learned during this 

demonstration have been taken forward into an updated fuel cell bus and fuel cell power system 

design for the12 new fuel cell buses at AC Transit and the four other San Francisco Bay area 

transit agencies. Four additional new fuel cell buses of the same design are to be delivered to 

UTC Power in Connecticut for operation at CTTRANSIT and New York City Transit.

Bus Operations

The current version fuel cell buses were designed and integrated over several years, from 2001 to 

2004, and the first buses were delivered in late 2005. The specially modified Van Hool bus 

model has a fuel cell power system from UTC Power and a hybrid electric system from Siemens 

(the ELFA hybrid system). ISE Corporation completed the integration of this bus design and 

included ZEBRA high-temperature batteries for energy storage. This bus design was determined 

by a specification from AC Transit that required a bus with operational performance similar to 

that of their standard diesel buses. The main objective of the demonstration of fuel cell bus 

technology at AC Transit focused on proof of concept that a fuel cell bus could be implemented 

successfully into full transit service. Overall, this main objective of the demonstration has been 

achieved. 

Table 1 is a summary of all revenue service evaluation results achieved during this 

demonstration. The fuel cell buses went into service in March 2006. During the early 

demonstration period, the agency limited operation of the buses while the agency became 

familiar with the technology. Two buses were used in service on weekdays for 8 hours per day; 

one bus was kept for use in training, maintenance, or events. AC Transit successfully ramped up 

service of the buses during the accelerated testing period: all three buses were planned to operate 

for two shifts each weekday for up to 19 hours a day. The buses also operated on weekends as 

needed. Through February 2010 (nearly 4 years), the buses had operated for nearly 225,000 

miles and accumulated more than 22,400 hours on the fuel cell systems. Of those totals, 164,673 

miles and 16,902 hours were accumulated during the accelerated testing period. 

The age of this fuel cell bus design is important background information when considering the 

specific accomplishments of this design and implementation as well as what to expect with the 

next generation of fuel cell buses from Van Hool and UTC Power. Several of the challenges 

faced in this implementation and demonstration were resolved, and for those challenges that 

remain, the new design of the bus and propulsion system is focused on resolving these challenges 

or exploring a path to resolution.
6

Table 1. Summary of All Revenue Service Evaluation Results

Data Item Fuel Cell Buses

Number of Buses 3

Data Period 3/20/2006–2/28/2010

Number of Months 47

Total Mileage in Period 224,871

Average Monthly Mileage per Bus 1,595

Total Fuel Cell Operating Hours 22,401

Average Bus Operating Speed (mph) 10.0

Availability (85% is target) 61%

Fuel Economy (miles/kg) 6.06

Fuel Economy (miles/DGEa) 6.85

Miles between Roadcalls (MBRC) – All 1,203

MBRC – Propulsion Only 1,530b

Total Maintenance Cost, $/milec 0.70

Maintenance Cost – Propulsion Only, $/mile 0.17 a

Diesel gallon equivalent. b

For fuel cell propulsion only, MBRC was 8,031. c

Work order maintenance cost. 

• Fuel Cell System Issues—UTC Power monitors the performance of the fuel cell power 

system to analyze actual performance versus predicted performance. Early on in the 

demonstration, the cell stack assemblies (CSAs) showed power degradation during the 

operation of the buses. This early power degradation was reported with the fuel cell buses 

at other agencies as well, and UTC Power reported the problem as contamination within 

the CSAs causing the premature degradation (at about 800 to 1,200 hours of operation 

instead of the expected 4,000 hours or more). A new version of CSAs replaced the CSAs 

on the fuel cell buses at each agency. UTC Power reported that this early power

degradation was resolved for these buses. The fact that two of the new-version fuel cell 

power systems have achieved more than 5,000 hours of service with no repairs indicates 

the issues have been resolved. 

• Traction Battery Issues—Managing the ZEBRA batteries in this design has proved to 

be the biggest challenge. The hybrid design on the bus includes three traction batteries 

operating in parallel. A cell in a ZEBRA battery typically will fail in short circuit. A 

battery with failed cells has reduced voltage even though it still can operate. Because the 

batteries operate with a direct parallel connection, when the number of failed cells within 

each battery is too different among the three batteries, the difference causes an 

unbalancing of the state of charge (SOC). This imbalance makes it difficult to keep the 

batteries in the recommended operating range. The present SOC balancing algorithm will 

disconnect a battery temporarily to keep the SOC balanced. 

This situation may lead to overvolt errors in the propulsion system, causing a bus 

shutdown. UTC Power has been working closely with the battery manufacturer (MESDEA) on the issue for some time. Because failed cells are related to a stress condition 

caused by the battery use, some progress was made with controller software changes to 

improve battery operation by refining some operational limits. Options for a balancing 
7

strategy have been discussed. Additional replacement batteries are kept in stock to 

increase the number of available better-matched batteries and to reduce the amount of 

downtime of the fuel cell bus. MES-DEA also supplied training at AC Transit that was 

extremely helpful to the project team. The manufacturer also produced a manual that 

includes information and fault code definitions. This has been extremely helpful in 

understanding the battery and systems and how to troubleshoot and diagnose problems. 

To date, no permanent fix for these issues has been identified. The energy storage for the 

new design fuel cell buses has been changed to lithium ion batteries. 

• Fuel Economy—During the accelerated testing period, AC Transit’s fuel cell buses

achieved an average fuel economy of 6.0 miles per kilogram (kg), which equates to 6.8 

miles per DGE (10.4 kg hydrogen/100 kilometers [km]). AC Transit’s diesel baseline 

fleet has an average fuel economy of 4.2 miles per gallon (mpg). Using this as a baseline, 

the fuel cell buses have a fuel economy that is 61% better than the diesel buses. The 

diesel buses used for this comparison do not have air conditioning and are more than 

8,000 lbs lighter in weight. The fuel economy advantage for the new fuel cell buses is 

expected to increase, given the focus on optimization, new batteries, and use of a diesel 

baseline bus group with air conditioning. 

• Costs—Fuel cell buses are following the typical trend of all prototype technology: capital 

costs are high in the early stages and begin to fall with increased production and further 

product development. The operating costs are also higher than those of conventional 

technology. This is also the typical trend for new technology introductions. Operating 

costs can be lower than expected in the first year while the buses are under warranty and 

maintenance is handled by the manufacturer’s on-site technicians. Then costs rise as the 

transit agency staff take over more maintenance and undergo a steep learning curve. Once 

the staff becomes more familiar with maintenance, these costs are expected to drop. AC 

Transit intends to be more involved in the maintenance of the newer design fuel cell 

buses, and a better understanding of future capital and operating costs is expected. 

Hydrogen Fueling

AC Transit fuels its buses at the hydrogen station at the agency’s East Oakland Division. The 

fueling station, built and operated by Chevron, features a natural gas reformer, hydrogen storage, 

and two dispensers. During the entire demonstration, the three fuel cell buses were safely fueled 

more than 1,600 times, using more than 36,000 kg of hydrogen. This fueling station is to be 

decommissioned and demolished, and a replacement station will be constructed. AC Transit is 

installing another fueling station at its Emeryville Division to supplement fueling and operation 

at two locations and for easier use by other transit agencies in the Bay Area. Part of the new 

fueling station design is to incorporate the best way to green the hydrogen production and to 

consider what larger fleet needs will be for hydrogen production, storage, and dispensing. 

Facility Modifications

AC Transit modified one of the maintenance bays at East Oakland for fuel cell bus maintenance. 

Because the maintenance bay is in the maintenance building, the fire marshal required that 

hydrogen fuel cell buses be defueled from 5,000 psi to 600 psi before entry into the maintenance 

bay for significant work. To reduce the loss of fuel from this process, AC Transit actively works 
8

to plan service so that buses needing routine maintenance are as low on fuel as possible. In the 

future ZEBA demonstration, AC Transit has secured funding and plans are being made to

modify the bay to allow a fully fueled bus to be brought inside. 

Training

From the onset of the project, AC Transit has been proactive with its training program. AC 

Transit and its project partners organized a comprehensive training program to ensure that the 

appropriate staff gained familiarity with hydrogen as a fuel and received detailed maintenance 

and operations information for the fuel cell bus. Working with various groups such as the 

College of the Desert and Schatz Energy Research Center, the agency developed training courses 

and videos to educate the public, transit staff, and first responders about fuel cell bus technology. 

These training programs will now be expanded to include the other transit agencies in the Bay 

Area that will potentially operate the new fuel cell buses.

Public Awareness

AC Transit reports a high level of interest in the local community and the region in the fuel cell 

bus demonstration. The agency receives requests to demonstrate the bus at various events and 

accommodates as many as possible. The agency has given tours of its East Oakland Division and 

fuel cell bus demonstrations to numerous individuals and groups from the United States and 

more than 12 different countries. The agency also surveyed passengers to measure the level of 

awareness and acceptance for fuel cell bus technology in the Oakland area. The survey results 

revealed a high level of interest in the technology, and passengers ranked the fuel cell bus 

performance much higher compared with conventional diesel buses. 

Coordination with Golden Gate Transit

As an active demonstration partner, GGT wanted hands-on experience with the buses. The two 

agencies worked closely together to develop the agreements and process for allowing another 

agency to operate a bus in its service area. This was a major accomplishment and required a 

coordinated effort between the agencies. The effort involved developing a user’s agreement, 

establishing a process for a potential emergency situation, planning logistics for transfer of the 

bus, and resolving the use of equipment differences between the agencies (e.g., farebox, headsign, radios). GGT reports a positive experience in operating one of the fuel cell buses in its 

service. Because of the high average operating speed at GGT (22 miles per hour [mph]), the fuel 

economy during this operation was the highest recorded for the buses: 8.8 miles/kg or 10.0 

miles/DGE.

With the arrival of the 12 new fuel cell buses, AC Transit will be coordinating with the four 

other participating transit agencies in the ZEBA demonstration to operate, maintain, and fuel 

these fuel cell buses. 

Public Outreach

AC Transit’s hydrogen fuel cell vehicle program (HyRoad) has always had a significant focus on 

public awareness. One of the major objectives of the program has been to create opportunities to 

educate students, the general public in the Bay Area, and other interested parties such as federal 

and state government officials. Also, operating the fuel cell buses in revenue service is an 

opportunity for the public to experience hydrogen fuel cell bus technology. The agency continues 
9

to accommodate as many requests for demonstration events as possible; the number of events 

decreased over time, however, as the agency increased the in-service time to accumulate more 

miles on the buses. During 2009, AC Transit participated in 37 events, which included 

environment-themed events, educational sessions for college and high school groups, fire 

department refresher training, and tours for U.S. and foreign officials. 

Passenger Survey Results

The AC Transit passenger survey to gauge customer awareness and perceptions of the fuel cell 

bus operation received nearly 500 responses. The results are summarized in a previous report11

Ridership

for this accelerated testing at AC Transit.

AC Transit, like most transit agencies, estimates ridership by counting ridership on the routes at 

different times of the day, days of the week, and times of the year. AC Transit’s route ridership 

estimates were used to conservatively estimate the number of fuel cell bus revenue passengers 

since the buses went into service. From March 20, 2006, through the end of February 2010, each 

bus carried an average of 203,000 passengers; the total estimate is more than 609,000 

passengers. Figure 1 shows the ridership estimate by month and as a cumulative total. 

The passenger estimates were also supplemented by actual passenger counts from automated 

passenger counters installed on the buses. Actual counts on the buses started in 2008 for all three 

buses. These counts were also checked against the estimates from AC Transit to verify that they 

were consistent.

Note that the passenger count jumped significantly during the accelerated testing period 

(November 2007 through February 2010). More than three-quarters of the total passenger count 

occurred during the accelerated testing period—nearly 477,000 passengers. These data indicate 

that the bus operation during the accelerated testing is meeting the objective of significantly 

increased bus usage.

 

11 National Fuel Cell Bus Program: Accelerated Testing Evaluation Report, January 2009, FTA-CO-26-7004-

2009.1, http://www.nrel.gov/hydrogen/pdfs/44820-1.pdf 
10

Figure 1. Ridership estimates for the fuel cell buses at AC Transit

Hydrogen Fueling

The hydrogen fueling station at AC Transit was designed by Chevron Technology Ventures and 

installed at Division 4 (East Oakland) in 2005. The station includes two steam methane 

reformers that can produce 150 kg of hydrogen per day. Total storage capacity at the station is 

366 kg at up to 6,250 pounds per square inch (psi). The station was inaugurated in March 2006 

just before the start of revenue service for the fuel cell buses. Figure 2 shows one of the fuel cell 

buses at the hydrogen fueling island and the fueling connections. A more detailed description of 

the hydrogen fueling and maintenance facilities at AC Transit is in Appendix C.

Figure 3 shows average monthly hydrogen usage from the station during the accelerated testing 

evaluation period (November 2007 through February 2010) for buses only. AC Transit also has a 

fleet of seven light-duty hydrogen vehicles that uses the station as well, but that fuel 

consumption is not accounted for in this analysis and discussion. The overall average usage for

the buses during this period was 44.3 kg/day, or 988 kg/month. The calculation for this rate 

includes only the days in which hydrogen was dispensed into the buses from the station—73% of 

the calendar days during the period. In all, 27,668 kg of hydrogen was dispensed into buses 

during this period. Since the beginning of revenue service, the station dispensed 38,752 kg of 

hydrogen into buses (again excluding the light-duty fuel cell fleet).
11

Figure 2. Fueling at the Chevron hydrogen station (Photo credit: L. Eudy, NREL)

Figure 4 shows the distribution of hydrogen amounts per fill by bus. The three buses were filled 

1,160 times during the accelerated testing evaluation period, at an average fill amount of 22.6 

kg/fill. Figure 5 shows the cumulative fueling rate histogram for the AC Transit station during 

the accelerated testing period; the overall average fueling rate was 1.26 kg/minute. On average, it 

took approximately 18 minutes to fuel a bus. 

Figure 3. Average hydrogen use per month for AC Transit’s fuel cell buses
12

Figure 4. Distribution of fill amounts for the fuel cell buses

Figure 5. Fueling rate histogram for the AC Transit Hydrogen Energy Station (bus only)
13

Fuel Cell Bus Operations—Evaluation Results

For this demonstration, the fuel cell buses are considered to be prototype technology that is in the 

process of being commercialized. The analysis and comparison discussions with standard diesel 

buses serve as a baseline against which to measure the progress of the fuel cell bus technology. 

The intent of this analysis is to determine the status of this implementation and to document the 

improvements that have been made over time at AC Transit. There is no intent to consider this 

implementation of fuel cell buses as commercial (or full revenue transit service). This evaluation 

focuses on documenting progress and opportunities to improve the vehicles, infrastructure, and 

procedures. 

The evaluation periods for the buses in this report are November 2007 through February 2010 

(28 months) for the fuel cell buses and January through December 2007 (12 months) for the 

diesel buses. The accelerated testing evaluation period for the fuel cell buses focuses on a clean 

point period that starts with the last replacement of the CSAs for the fuel cell buses through 

February 2010. The start of the clean point evaluation period is as follows: 

• FC1—CSAs replaced on March 7, 2008, restarted service on March 18, 2008 

• FC2—CSAs replaced on January 31, 2008, restarted service on February 5, 2008 

• FC3—CSAs replaced on December 11, 2007, restarted service on December 13, 2007; 

the CSAs were replaced again on December 15, 2008, restarted service on December 31, 

2008. 

The diesel Van Hool buses began operation in 2003–2004 but did not start operating at Division 

4 (East Oakland) until July 2005. Data collection for these diesel buses has concluded, and a 12-

month period of operation at AC Transit’s Division 4 was chosen for a baseline comparison with 

the fuel cell buses. As mentioned earlier, one significant difference of note is that the diesel 

buses do not have air conditioning, and this affects the fuel economy results comparison. 

Route Descriptions

The fuel cell and diesel baseline buses are operated from AC Transit’s Division 4, which 

operates 15 local, 2 all-nighter, 10 transbay, and 14 school routes with a total of 179 buses (138 

buses for peak service). The average bus operating speed for weekday service from this division 

is 14.3 mph. 

At the beginning of revenue service, the fuel cell buses operated only during the week on two 

blocks of work created for testing the fuel cell and diesel baseline buses. This limited operation 

originally helped ensure that trained drivers and mechanics (and the manufacturer’s engineers) 

were available to work with the fuel cell buses when needed. Also, AC Transit decided to place 

only two of the three fuel cell buses into service on any given weekday to allow for maintenance, 

training, and special events with the third fuel cell bus. 

As AC Transit and the manufacturer partners gained experience, operating the fuel cell buses 

more aggressively became a goal. As discussed earlier, the accelerated testing project is focused 

on maximizing the operation of all three of the fuel cell buses. This effort has taken significant 

planning and work on the part of AC Transit staff and the manufacturers. To maximize the 
14

operation of the fuel cell buses, specific route blocks were defined so the fuel cell buses could 

attempt nearly full transit operation. During the accelerated testing evaluation period, the fuel 

cell buses operated on all of the route assignments shown in Table 2. 

Table 2. Route Blocks of Work Created for Fuel Cell Bus Operation

Route 

Block

Pull-Out 

Time

Pull-In 

Time

Total 

Time

Total 

Miles

Average 

Speed 

(mph)

Weekday Operation

18 6:06 a.m. 11:51 p.m. 17.8 171 9.6

18 5:22 a.m. 7:11 p.m. 13.8 140 10.1

57 7:01 a.m. 9:25 p.m. 14.4 150 10.4

Weekend Operation

57 7:51 a.m. 8:00 p.m. 12.2 129 10.6

57 5:36 a.m. 9:01 p.m. 15.4 167 10.8

As stated previously in reports on this demonstration at AC Transit, meeting the long operation 

time of the route assignments is difficult because of the need to charge the batteries overnight 

before the next pullout. During the accelerated testing, the fuel cell buses operated on longer 

hours of operation; however, this time of operation was cut back slightly over time to ensure that 

overnight charging was sufficient for the next day’s operation. A full charge for the batteries 

requires between 4 and 4.5 hours. During bus operation on the route, the batteries are kept at 

50% to 60% SOC to allow for significant energy regeneration from braking back into the 

batteries. The diesel buses were not restricted to these special blocks of work. These diesel buses 

were allowed to operate on other work blocks during the week and on weekends as well. This 

operation is reflected in the bus use, which is discussed next. 

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. This section summarizes bus 

usage and availability for the two study groups of buses.

Usage for the fuel cell buses increased nearly 50% during the accelerated testing period as 

compared with the previous revenue operations (March 2006 through October 2007). For the 

entire accelerated testing period (November 2007 through February 2010), the fuel cell buses 

averaged 1,960 miles per month (each bus). The average monthly mileage results in Table 3 

focus on the clean point periods for the fuel cell buses; the first partial month of operation after 

the last fuel cell power system replacement was removed from the calculation. The table shows 

that the average monthly mileage for the fuel cell buses was 2,129 miles per month. Compared 

with the diesel bus average mileage, the fuel cell buses have now achieved an average of 58% of 

full transit operation. 
15

Table 3. Average Monthly Mileage (Evaluation Period)

Bus Starting 

Hubodometer

Ending 

Hubodometer

Total 

Mileage Months Monthly Average Mileage

FC1 25,097 76,743 51,646 24 2,152

FC2 20,485 79,521 59,036 25 2,361

FC3 26,494 75,518 49,024 26 1,886

Fuel Cell 159,706 75 2,129

1043 111,443 155,982 44,539 12 3,712

1044 131,559 174,535 42,976 12 3,581

1045 142,518 186,774 44,256 12 3,688

1046 147,975 193,493 45,518 12 3,793

1047 128,064 173,870 45,806 12 3,817

1048 115,365 158,784 43,419 12 3,618

Diesel 266,514 72 3,702

The focus of the accelerated testing was to operate the fuel cell buses as much as the technology 

would allow. In addition, it was a key objective to operate the fuel cell power systems beyond 

4,000 hours. This objective was accomplished. In fact, as of the end of February 2010, one bus 

accumulated more than 5,000 hours and another bus accumulated more than 6,000 hours. These 

same fuel cell power systems are expected to continue to operate in new buses starting in May 

2010. The third fuel cell bus had the fuel cell power system replaced after a year of testing. The 

newer CSAs in the third bus are similar to the other two fuel cell buses.

Another measure of reliability is availability—the percentage of days that the buses are planned 

for operation compared with the days the buses are actually available. Figure 6 shows monthly 

availability for each of the three fuel cell buses and an overall average availability for the group 

during the clean point evaluation period. The low availability months were generally caused by 

the need for traction battery replacements.

Table 4 summarizes the reasons for availability and unavailability for each of the three fuel cell 

buses. During the clean point evaluation period, the average availability for the fuel cell buses 

was 66%. The overall availability percentage by bus and overall average is highlighted in blue in 

the table. The two unavailability categories with the highest percentage were issues with the 

traction batteries (36% of all unavailable days) and AC Transit maintenance (35% of all 

unavailable days). 

The traction battery issues include problems with matching SOC among the three traction 

batteries, the software to manage this SOC, and the interface between the propulsion system 

software and traction battery software. This problem improved during the evaluation period, but 

has never truly been resolved. 

AC Transit maintenance includes scheduled and unscheduled maintenance performed for the fuel 

cell buses. In addition, there were several accidents that required body repairs. There was also 

one electrical system fire that caused significant unavailability for one of the buses. This fire was 

unrelated to the fuel cell power, hydrogen storage, or hybrid propulsion systems. 
16

Figure 6. Availability for all three fuel cell buses and overall average

Table 4. Summary of Reasons for Availability and Unavailability of Buses for Service

Category FC1 FC2 FC3 Group Total

Days % Days % Days % Days %

Planned Work Days 568 620 620 1,808

Days Available 379 67 427 69 396 64 1,202 66

Available 379 100 427 100 396 100 1,202 100

On Route 355 94 406 95 357 90 1,118 93

Event/Demonstration 11 3 10 2 23 6 44 4

Training 7 2 4 1 10 2 21 2

Not Used 6 1 7 2 6 2 19 1

Unavailable 189 100 193 100 224 100 606 100

Fuel Cell Propulsion 19 10 9 5 37 16 65 11

ISE Hybrid Propulsion 15 8 35 18 6 3 56 9

Traction Battery Issues 78 41 78 40 62 28 218 36

AC Transit Maintenance 55 29 58 30 97 43 210 35

Fueling Unavailable 22 12 13 7 22 10 57 9

Fuel Economy and Cost

Hydrogen fuel is supplied by the Chevron–AC Transit Hydrogen Energy Station at the East 

Oakland Division. The hydrogen is dispensed at up to 5,000 psi for the three fuel cell transit 

buses. During the accelerated testing evaluation period, AC Transit employees performed nearly 

all fueling services for the hydrogen-fueled vehicles, and Chevron electronically reported the 

fueling amounts. 
17

Table 5 shows hydrogen and diesel fuel consumption and fuel economy for the study buses 

during the clean point evaluation period. Overall, the three fuel cell buses averaged 6.01 miles 

per kilogram of hydrogen, which equates to 6.79 miles/DGE. The energy conversion from 

kilograms of hydrogen to DGE appears at the end of Appendix E. (Appendix F contains the 

summary statistics in SI units.) It was also reported that approximately 536 kg of hydrogen were 

removed during the accelerated testing evaluation period so that the buses could be taken into the 

maintenance facility. This amount of hydrogen removed and vented equates to 2% of the 

hydrogen dispensed into the buses. AC Transit has been working to minimize the amount of 

hydrogen vented by managing the amount of bus operation and fueling before planned bus 

maintenance. The amount of hydrogen vented from the buses before maintenance has not been 

included in the fuel economy calculations. 

As mentioned earlier, the buses are plugged in each night to recharge the batteries. This energy 

added to the fuel cell buses each night is not currently accounted for in the fuel economy 

calculation. AC Transit collects monthly total charging energy for the fuel cell buses. This 

charging energy represents 5% of the total energy used by the buses (based on the average of 22 

months of data). To be accurate, the fuel cell fuel economy should be reduced by 5%, or reduced 

to 6.45 miles/DGE. This fuel economy would then be 54% higher than the fuel economy of the 

diesel buses. Note that the diesel buses do not have air conditioning, and this increases the fuel 

economy advantage of the fuel cell buses.

Table 5. Fuel Use and Economy (Evaluation Period)

Bus Mileage

(fuel base) Hydrogen (kg) Miles per kg

Diesel Equivalent 

Amount (gallon)

Miles per 

Gallon (mpg)

FC1 49,129 8,440.9 5.82 7,469.8 6.58

FC2 57,762 9,281.9 6.22 8,214.1 7.03

FC3 48,775 8,195.0 5.95 7,252.2 6.73

FCB Total 155,666 25,917.8 6.01 22,936.1 6.79

1043 43,835 10,765.1 4.07

1044 42,379 9.916.2 4.27

1045 44,256 10,381.1 4.26

1046 45,518 10,873.8 4.19

1047 45,673 10,744.5 4.25

1048 42,914 10,295.4 4.17

Diesel Total 264,575 62,976.1 4.20

Figure 7 shows monthly average fuel economy in both miles per kilogram and miles per DGE for 

the fuel cell buses as well as the baseline diesel bus average of 4.20 mpg. Note that the fuel 

economy for the fuel cell buses peaked in February and March 2008, which coincides with the 

GGT operation of one of the fuel cell buses. The GGT fuel cell bus operation and fuel economy 

were significantly higher than the AC Transit operation and influenced the overall fuel economy 

during the accelerated testing evaluation period. Also, this is a sufficiently long period of time to 

see the general degradation of the fuel cell power systems with usage (approximately 10% to 

15% degradation over the evaluation period). 

The operating cost for hydrogen production and dispensing for AC Transit is currently estimated 

at between $6 and $8/kg. This amount, which excludes capital expenses, was generated using 
18

early data (not optimized operation) and conservative maintenance and operating estimates. The 

$8/kg cost estimate for hydrogen fuel indicates a cost for the fuel cell buses of $1.33/mile. The 

average diesel fuel cost during the evaluation period is $2.29/gallon. This average indicates a 

$0.55/mile cost. The diesel cost per mile is about 41% of the fuel cost per mile for the fuel cell 

buses.

Figure 7. Average fuel economy (evaluation period)

Maintenance Analysis

The maintenance cost analysis in this section is limited to the clean point evaluation period (last 

CSA/fuel cell power system replacement through February 2010). Warranty costs are not 

included in the cost-per-mile calculations. All work orders for the study buses were collected and 

analyzed for this evaluation. For consistency, the maintenance labor rate was kept at a constant 

$50 per hour; this does not reflect an average rate for AC Transit. This section first covers total 

maintenance costs and then maintenance costs by bus system.

Total Maintenance Costs—Total maintenance costs include the price of parts and labor rates of 

$50 per hour; they do not include warranty costs. Cost per mile is calculated as follows: 

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

Table 6 shows total maintenance costs for the fuel cell and diesel buses. Note that the fuel cell 

bus maintenance was still being supported by on-site warranty work done by the manufacturer’s 

engineers at AC Transit. The AC Transit mechanics have supported the work done by the 

manufacturer’s engineers and have cleaned and maintained the bus (inside and outside). Some 
19

support has been given for responding to roadcalls, and that effort is reflected in the maintenance 

discussion that follows. During the accelerated testing evaluation period, AC Transit personnel 

essentially took over all of the maintenance and support of the fuel cell buses except for 

maintenance by the UTC Power engineer. 

Table 6. Total Maintenance Costs (Evaluation Period)

Bus Mileage Parts ($) Labor 

Hours

Cost per 

Mile ($)

FC1 51,646 18,012.21 382.3 0.72

FC2 59,036 14,943.43 390.0 0.58

FC3 49,345 20,043.71 539.3 0.95

Total Fuel Cell 160,027 52,999.35 1,311.6 0.74

Avg. per Bus 53,342 17,666.45 437.2 --

1043 44,539 10,791.13 109.0 0.37

1044 42,976 12,104.40 156.3 0.46

1045 44,256 16,832.13 154.8 0.56

1046 45,518 12,102.17 169.3 0.45

1047 45,806 15,192.03 120.1 0.46

1048 43,419 19,613.14 167.4 0.64

Total Diesel 266,514 88,635.00 877.0 0.49

Avg. per Bus 44,419 14,772.50 146.2 --

AC Transit has expressed a strong desire to have its mechanics get more involved in all 

maintenance activities for the fuel cell buses so they gain experience. AC Transit assigned one 

project manager/supervisor and two mechanic trainers to work on the fuel cell buses. This 

addition of resources for fuel cell bus maintenance was necessary based on the desired increase 

in operation along with plans for more fuel cell buses. Figure 8 shows the monthly and 

cumulative labor hours assigned for maintenance of the fuel cell buses. The chart shows the 

maintenance labor increased significantly and then was lower in the last 6 to 8 months. 

Maintenance issues for the fuel cell buses centered on problems with the traction batteries and 

fuel cell system on each of the buses. Brake relines were completed eight times, with some issues 

of smoking brakes that needed adjustment/break-in. FC3 was vandalized and needed windows 

replaced several times during the evaluation period. In addition, there were significant hours for 

accident damage body repairs and suspension repairs. 

Maintenance issues for the diesel buses were mostly related to engine problems with the 

turbocharger (two buses), injectors and pump (two buses), and coolant surge tank (five buses). 

The diesel buses also had significant brake repair costs for standard relining (eight times). The 

other major maintenance costs were for accident repair and seat and window replacement (five 

buses).

The maintenance costs for the fuel cell buses reported here are generally higher than the costs 

reported previously, an indication of the added support from AC Transit maintenance personnel. 

This higher cost is especially reflected in the number of mechanic labor hours. 
20

Figure 8. Monthly and cumulative AC Transit maintenance labor (evaluation period)

Maintenance Costs Categorized by System—Table 7 shows maintenance costs by vehicle 

system and bus study group (without warranty costs). The vehicle systems shown in the table are 

as follows:

• Cab, Body, and Accessories: Includes body, glass, and paint repairs following accidents; 

cab and sheet metal repairs on seats and doors; and accessory repairs such as 

hubodometers and radios

• Propulsion-Related Systems: Repairs for exhaust, fuel, engine, electric motors, fuel cell 

modules, propulsion control, nonlighting electrical (charging, cranking, and ignition), air 

intake, cooling, and transmission 

• Preventive Maintenance Inspections (PMI): Labor for inspections during preventive 

maintenance

• Brakes

• Frame, Steering, and Suspension

• Heating, Ventilation, and Air Conditioning (HVAC)

• Lighting

• Air System, General

• Axles, Wheels, and Drive Shaft 

• Tires
21

Table 7. Maintenance Cost per Mile by System (Evaluation Period)

System

Fuel Cella Diesel

Cost per 

Mile ($)

Percent of 

Total (%)

Cost per 

Mile ($)

Percent of 

Total (%)

Cab, Body, and 

Accessories 0.17 23 0.16 32

Propulsion-Related 0.19 26 0.10 20

PMI 0.09 12 0.07 14

Brakes 0.21 29 0.11 22

Frame, Steering, and 

Suspension 0.04 6 0.02 4 

HVAC 0.01 1 0.01 2

Lighting 0.01 1 0.01 2

Air, General 0.01 1 0.00 0

Axles, Wheels, and 

Drive Shaft 0.01 1 0.01 2 

Tires 0.00 0 0.00 0

Total 0.74 100 0.49 100

 a Excludes warranty work costs

The systems with the highest percentage of maintenance costs for the fuel cell buses were 

brakes; propulsion-related; cab, body, and accessories; and PMI. These systems were also the 

highest maintenance cost systems for the diesel buses. 

Propulsion-Related Maintenance Costs—Propulsion-related vehicle systems include the 

exhaust, fuel, engine, electric propulsion, air intake, cooling, nonlighting electrical, and 

transmission systems. 

Table 8 shows the propulsion-related system repairs by category for the two study groups during 

the evaluation period (no warranty costs). The fuel cell buses had higher maintenance costs (50% 

higher), which indicate the amount of AC Transit mechanic activity to support and maintain the 

fuel cell buses. UTC Power still has an engineer on-site to supervise and complete maintenance 

of the fuel cell power system and related systems. 
22

Table 8. Propulsion-Related Maintenance Costs by System (Evaluation Period)

Maintenance System Costs Fuel Cell Diesel

Mileage 160,027 266,514

Total Propulsion-Related Systems (Roll-up)

Parts cost ($) 2,898.40 18,794.62

Labor hours 542.0 173.1

Total cost ($) 29,996.90 27,448.12

Total cost ($) per mile 0.19 0.10

Exhaust System Repairs

Parts cost ($) 0.00 5,091.03

Labor hours 8.0 28.0

Total cost ($) 400.00 6,491.03

Total cost ($) per mile 0.00 0.02

Fuel System Repairs

Parts cost ($) 0.00 2,561.24

Labor hours 4.0 17.8

Total cost ($) 200.00 3,451.24

Total cost ($) per mile 0.00 0.01

Powerplant System Repairs

Parts cost ($) 261.16 3,549.02

Labor hours 57.5 56.4

Total cost ($) 3,136.16 6,368.52

Total cost ($) per mile 0.02 0.02

Electric Motor and Propulsion Repairs

Parts cost ($) 28.82 0.00

Labor hours 318.5 0.0

Total cost ($) 15,952.32 0.00

Total cost ($) per mile 0.10 0.00

Non-Lighting Electrical System Repairs (General Electrical, Charging, 

Cranking, Ignition)

Parts cost ($) 1,499.95 1,809.52

Labor hours 137.0 33.4

Total cost ($) 8,349.95 3,478.52

Total cost ($) per mile 0.05 0.01

Air Intake System Repairs

Parts cost ($) 1,041.15 959.66

Labor hours 0.0 0.0

Total cost ($) 1,041.15 959.66

Total cost ($) per mile 0.01 0.00

Cooling System Repairs 

Parts cost ($) 67.32 4,237.93

Labor hours 17.0 29.0

Total cost ($) 917.32 5,687.93

Total cost ($) per mile 0.01 0.02

Transmission Repairs

Parts cost ($) 0.00 451.46

Labor hours 0.0 2.5

Total cost ($) 0.00 576.46

Total cost ($) per mile 0.00 0.00
23

Roadcall Analysis

A roadcall or revenue vehicle system failure (as named in the National Transit Database12) 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.13

Table 9 shows the roadcalls and MBRC for each study bus categorized by all roadcalls and 

propulsion-related-only roadcalls. The diesel buses have much better MBRC rates for both 

categories. This lower rate is indicative of the prototype status of the fuel cell buses. The MBRC 

for the fuel cell power system, however, increased significantly over the evaluation period. 

 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 continued. They do 

not include roadcalls for things such as problems with radios or destination signs. 

Table 9. Roadcalls and MBRC (Evaluation Period)

Bus Mileage All 

Roadcalls All MBRC Propulsion Roadcalls

Propulsion 

MBRC

Fuel Cell 

only MBRC

FC1 51,646 43 1,201 28 1,845 25,823

FC2 59,036 41 1,440 33 1,789 14,759

FC3 49,345 51 968 43 1,148 4,935

Total FCB 160,027 135 1,185 104 1,539 10,002

1043 Diesel 44,539 6 7,423 2 22,270

1044 Diesel 42,976 15 2,865 5 8,595

1045 Diesel 44,256 16 2,766 6 7,376

1046 Diesel 45,518 7 6,503 3 15,173

1047 Diesel 45,806 9 5,090 4 11,452

1048 Diesel 43,419 9 4,824 5 8,684

Total Diesel 266,514 62 4,299 25 10,661

Most of the nonpropulsion roadcalls for the fuel cell buses were caused by problems with the 

brakes (13 roadcalls), air system (5 roadcalls), and suspension/leveling (5 roadcalls). When the 

brakes on the fuel cell buses are relined/replaced, there is a break-in period where the brakes give 

off a smell and “smoke,” resulting in several roadcalls. The smell and smoke come from a 

coating on the brake parts that is difficult to clean off before installation. This occurs only for a 

short period of time, but has caused some concern for the operators and passengers; however, 

this is not a safety issue.

The propulsion-related roadcalls for the fuel cell buses have been caused by problems with the 

hybrid propulsion system (49 roadcalls), traction batteries (34 roadcalls), and fuel cell power 

system (16 roadcalls). Many of the hybrid and battery roadcalls are related to a need to optimize 

the monitoring and management of the traction batteries and are not necessarily an indication of 

a component failure. 

 

12 National Transit Database web site: www.ntdprogram.gov/ntdprogram/ 13 AC Transit defines a significant delay as 6 or more minutes.
24

What’s Next for AC Transit?

AC Transit is moving into the next phase of fuel cell bus development with a demonstration of 

12 new and advanced fuel cell buses. This demonstration is in response to the CARB Transit 

rule, which requires several California agencies (including AC Transit) to purchase new and 

advanced fuel cell buses as part of its zero-emission bus regulations. Developed by UTC Power 

and Van Hool, the new buses incorporate the lessons learned during the demonstration of the 

current fuel cell buses. 

AC Transit is the managing partner for a ZEBA working group to respond to CARB’s advanced 

fuel cell bus demonstration. The ZEBA group includes several Bay Area transit agencies:

• AC Transit

• Santa Clara VTA

• GGT

• SamTrans

• SF MTA.

14

The new Van Hool fuel cell buses (purchase price is about $2.5 million each) with power 

systems from UTC Power have an improved design from the current fuel cell buses. These 

buses are 5,000 lbs lighter weight and 3 inches shorter, and have a different battery/energy 

storage design (lithium ion). The first bus was delivered to AC Transit in May 2010. 

AC Transit will own and maintain the 12 new fuel cell buses and will be responsible for 

managing the operation and demonstration; however, several of the ZEBA partners may operate 

these buses for a period of time during the demonstration. Each ZEBA transit agency is 

participating in the ongoing operations with financial and planning support. UTC Power has 

purchased an additional four new fuel cell buses from AC Transit’s bus order to be operated in 

Connecticut and other selected areas (including at least one bus at New York City Transit) under 

the FTA’s NFCBP.

AC Transit will continue to operate the three existing fuel cell buses in their accelerated testing 

project for FTA’s NFCBP until the new buses arrive. As described earlier, once the new buses 

arrive, the plan is to remove the existing three fuel cell power systems and install them into the 

first three new fuel cell buses for operation at AC Transit. The existing/older fuel cell bus gliders 

are planned to be transferred to UTC Power. The other nine remaining fuel cell buses will arrive 

at AC Transit where new fuel cell power systems will be installed. 

AC Transit continues to work on developing hydrogen fueling infrastructure to support the new 

fuel cell buses. The Chevron station at the East Oakland Division is scheduled for decommission 

in September 2010. The station was originally built to support the DOE Controlled Fleet Fuel 

Cell Vehicle Demonstration as well as the buses. Now that the DOE project is concluded, 

Chevron’s commitment is complete. AC Transit is working with Linde to construct new stations 

 

14 SF MTA is a voluntary participant. Its fleet of trolley buses already meets CARB zero-emission bus regulations.
25

at East Oakland as well as its Emeryville depot (Division 2). The Emeryville fueling station will 

be a combined facility for light-duty fuel cell vehicles and fuel cell buses. A solar-powered 

Proton Energy electrolyzer will generate up to 65 kg of hydrogen for the light-duty vehicles; 

liquid hydrogen delivery and storage will supply as many as six fuel cell buses with fuel. This 

new station will be a convenient fueling location for future bus operations by ZEBA partner 

transit agencies like GGT and SF MTA.

NREL Evaluation of AC Transit Fuel Cell Buses—The current evaluation of accelerated 

testing at AC Transit was funded by FTA in conjunction with their NFCBP. With the completion 

of this evaluation report, the evaluation funding will be transitioned from FTA back to DOE. The 

DOE evaluation plans include all 12 of the new fuel cell buses for the planned ZEBA/CARB 

demonstration. 
26

Contacts

DOT-FTA

1200 New Jersey Avenue, S.E. 

Washington, DC 20590 

Christina Gikakis, Program Manager

Phone: 202-366-2637 

E-mail: Christina.gikakis@dot.gov 

DOE

1000 Independence Ave., SW

Washington, DC 20585 

John Garbak, Technology Validation 

Manager, Vehicle Technologies Program 

Phone: 202-586-1723 

E-mail: john.garbak@ee.doe.gov

NREL

1617 Cole Boulevard 

Golden, CO 80401 

Leslie Eudy, Senior Project Leader 

Phone: 303-275-4412 

E-mail: leslie_eudy@nrel.gov 

Battelle

505 King Avenue 

Columbus, OH 43201 

Kevin Chandler, Program Manager 

Phone: 614-424-5127 

E-mail: chandlek@battelle.org

AC Transit

1700 Franklin Street 

Oakland, CA 94612 

Jaimie Levin, Director of Alternative Fuels 

Policy & Marketing

Phone: 510-891-7244 

E-mail: jlevin@actransit.org 

Joe Callaway, Director of Project 

Management

Phone: 510-891-7220 

E-mail: jcallaway@actransit.org

Doug Byrne, ZEB Program Manager 

Phone: 510-577-8821 

E-mail: dbyrne@actransit.org 

UTC Power

195 Governor’s Highway 

South Windsor, CT 06074 

Rakesh Radhakrishnan, Program Manager, 

Transportation Programs 

Phone: 860-727-2754 

E-mail: rakeshr@utcpower.com

Matthew Riley, Senior Systems Engineer

Phone: 510-628-8252 

E-mail: matthew.riley@utcpower.com 

ISE Corp

12302 Kerran Street 

Poway, CA 92064 

Tavin Tyler, Director of Prototype Programs

Phone: 858-413-1745 

E-mail: ttyler@isecorp.com 

Van Hool 

Bernard Van Hoolstraat 58 

B-2500 Lier Koningshooikt, Belgium 

Paul Jenné, Automotive Relations

Phone: +32 (3) 420 22 10 

E-mail: paul.jenne@vanhool.be
27

Acronyms and Abbreviations

AC Transit Alameda-Contra Costa Transit District

CARB California Air Resources Board

CSA cell stack assembly

CTE Center for Transportation and the Environment 

DGE diesel gallon equivalent 

DOE U.S. Department of Energy 

FTA Federal Transit Administration

GGT Golden Gate Transit 

HVAC heating, ventilation, and air conditioning

kg kilogram 

MBRC miles between roadcalls

min minutes 

mpg miles per gallon

mph miles per hour 

NAVC Northeast Advanced Vehicle Consortium 

NFCBP National Fuel Cell Bus Program 

NREL National Renewable Energy Laboratory 

PMI preventive maintenance inspection

psi pounds per square inch 

SAFETEA-LU Safe, Accountable, Flexible, Efficient 

Transportation Equity Act: A Legacy for Users 

SamTrans San Mateo County Transit District

SF MTA San Francisco Municipal Transportation Agency 

SOC state of charge

VTA Santa Clara Valley Transportation Authority

ZEBA Zero Emission Bay Area
28

Bibliography

AC Transit

Chandler, K.; Eudy, L. (2009). National Fuel Cell Bus Program: Accelerated Testing Evaluation 

Report and Appendices. NREL/TP-560-44646-1, NREL/TP-560-44646-2. Golden, CO: NREL. 

Chandler, K.; Eudy, L. (2008). Alameda-Contra Costa Transit District (AC Transit), Fuel Cell 

Transit Buses: Third Evaluation Report and Appendices. NREL/TP-560-43545-1, NREL/TP560-43545-2. Golden, CO: NREL. 

Chandler, K.; Eudy, L. (2007). Alameda-Contra Costa Transit District (AC Transit), Fuel Cell 

Transit Buses: Evaluation Results Update. NREL/TP-560-42249. Golden, CO: NREL. 

Chandler, K.; Eudy, L. (2007). AC Transit, Fuel Cell Transit Buses: Preliminary Evaluation 

Results. NREL/TP-560-41041. Golden, CO: NREL. 

NREL. (2006). AC Transit Demos Three Prototype Fuel Cell Buses. DOE/GO-102006-2286. 

Golden, CO: NREL.

City of Burbank

Eudy, L., (2010), Fuel Cell Bus Takes a Starring Role in the BurbankBus Fleet, DOE/GO102010-3035, Golden, CO: NREL. 

General

Eudy, L.; Chandler, K.; Gikakis, C. (2009). Fuel Cell Buses in U.S. Transit Fleets: Current 

Status 2009. NREL/TP-560-46490. Golden, CO: NREL. 

Eudy, L.; Chandler, K.; Gikakis, C. (2008). Fuel Cell Buses in U.S. Transit Fleets: Current 

Status 2008. NREL/TP-560-44133. Golden, CO: NREL. 

NREL. (2008). Hydrogen and Fuel Cell Transit Bus Evaluations, Joint Evaluation Plan for the 

U.S. Department of Energy and the Federal Transit Administration. NREL/MP-560-42781. 

Golden, CO: NREL.

Eudy, L.; Chandler, K.; Gikakis, C. (2007). Fuel Cell Buses in U.S. Transit Fleets: Summary of 

Experiences and Current Status. NREL/TP-560-41967. Golden, CO: NREL. 

SunLine

Chandler, K.; Eudy, L. (2009). SunLine Transit Agency, Fuel Cell Transit Bus: Fifth Evaluation 

Report and Appendices, NREL/TP-560-46346-1, NREL/TP-560-46346-2. Golden, CO: NREL. 

Chandler, K.; Eudy, L. (2008). SunLine Transit Agency, Fuel Cell Transit Bus: Fourth 

Evaluation Report and Appendices, NREL/TP-560-44646-1, NREL/TP-560-44646-2. Golden, 

CO: NREL.

Chandler, K.; Eudy, L. (2008). SunLine Transit Agency, Hydrogen-Powered Transit Buses: 

Third Evaluation Report and Appendices. NREL/TP-560-43741-1, NREL/TP-560-43741-2. 

Golden, CO: NREL.
29

NREL. (2008). SunLine Begins Extended Testing of Hybrid Fuel Cell Bus. DOE/GO12008-2610. 

Golden, CO: NREL.

Chandler, K.; Eudy, L. (2007). SunLine Transit Agency, Hydrogen-Powered Transit Buses: 

Evaluation Results Update. NREL/TP-560-42080. Golden, CO: NREL.

Chandler, K.; Eudy, L. (2007). SunLine Transit Agency, Hydrogen-Powered Transit Buses: 

Preliminary Evaluation Results. NREL/TP-560-41001. Golden, CO: NREL. 

NREL. (2006). SunLine Tests HHICE Bus in Desert Climate. DOE/GO-102006-2333. Golden, 

CO: NREL.

NREL. (2006). SunLine Expands Horizons with Fuel Cell Bus Demo. DOE/GO-102006-2287. 

Golden, CO: NREL.

Connecticut Transit

Chandler, K.; Eudy, L. (2010). Connecticut Transit (CTTRANSIT) Fuel Cell Transit Bus: Third

Evaluation Report & Appendices. NREL/TP-560-47334-1 & NREL/TP-560-47334-2. Golden, 

CO: NREL.

Chandler, K.; Eudy, L. (2009). Connecticut Transit (CTTRANSIT) Fuel Cell Transit Bus: Second 

Evaluation Report & Appendices. NREL/TP-560-45670-1 & NREL/TP-560-45670-2. Golden, 

CO: NREL.

Chandler, K.; Eudy, L. (2008). Connecticut Transit (CTTRANSIT) Fuel Cell Transit Bus: 

Preliminary Evaluation Results. NREL/TP-560-43847. Golden, CO: NREL. 

NREL. (2008). CT TRANSIT Operates New England’s First Fuel Cell Hybrid Bus. 

DOE/GO12008-2529. Golden, CO: NREL. 

Santa Clara Valley Transportation Authority

Chandler, K.; Eudy, L. (2006). Santa Clara Valley Transportation Authority and San Mateo 

County Transit District, Fuel Cell Transit Buses: Evaluation Results. NREL/TP-560-40615. 

Golden, CO: NREL.

NREL. (2005). VTA, SamTrans Look into Future with Bus Demo. DOE/GO-102005-2147. 

Golden, CO: NREL.

Reports from DOE/NREL evaluations can be downloaded via the following Web sites:

Hydrogen and fuel cell related: www.nrel.gov/hydrogen/proj_fc_bus_eval.html

Hybrid and ot her technologies: www.nrel.gov/vehiclesandfuels/fleettest/publications_bus.html