A national laboratory of the U.S. Department of Energy

Office of Energy Efficiency & Renewable Energy

National Renewable Energy Laboratory 

Innovation for Our Energy Future 

Long Beach Transit: Two-Year 

Evaluation of Gasoline-Electric 

Hybrid Transit Buses 

M. Lammert 

National Renewable Energy Laboratory 

Technical Report 

NREL/TP-540-42226 

June 2008 

NREL is operated by Midwest Research Institute ● Battelle Contract No. DE-AC36-99-GO10337 
National Renewable Energy Laboratory 

1617 Cole Boulevard, Golden, Colorado 80401-3393 

303-275-3000 • www.nrel.gov 

Operated for the U.S. Department of Energy 

Office of Energy Efficiency and Renewable Energy 

by Midwest Research Institute • Battelle 

Contract No. DE-AC36-99-GO10337

Technical Report 

NREL/TP-540-42226 

June 2008 

Long Beach Transit: Two-Year 

Evaluation of Gasoline-Electric 

Hybrid Transit Buses 

M. Lammert 

National Renewable Energy Laboratory 

Prepared under Task No(s). FC08.3000 
NOTICE

This report was prepared as an account of work sponsored by an agency of the United States government. 

Neither the United States government nor any agency thereof, nor any of their employees, makes any 

warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or 

usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not 

infringe privately owned rights. Reference herein to any specific commercial product, process, or service by 

trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, 

recommendation, or favoring by the United States government or any agency thereof. The views and opinions 

of authors expressed herein do not necessarily state or reflect those of the United States government or any 

agency thereof. 

Available electronically at http://www.osti.gov/bridge

Available for a processing fee to U.S. Department of Energy 

and its contractors, in paper, from: 

U.S. Department of Energy 

Office of Scientific and Technical Information 

P.O. Box 62 

Oak Ridge, TN 37831-0062 

phone: 865.576.8401 

fax: 865.576.5728 

email: mailto:reports@adonis.osti.gov

Available for sale to the public, in paper, from: 

U.S. Department of Commerce 

National Technical Information Service 

5285 Port Royal Road 

Springfield, VA 22161 

phone: 800.553.6847 

fax: 703.605.6900 

email: orders@ntis.fedworld.gov

online ordering: http://www.ntis.gov/ordering.htm

Printed on paper containing at least 50% wastepaper, including 20% postconsumer waste
Acknowledgments 

This evaluation is funded through the Advanced Vehicle Testing Activity, which is managed by 

Lee Slezak within the U.S. Department of Energy (DOE). All publications on the Long Beach 

Transit (LBT) hybrid bus evaluation will be posted on DOE’s Energy Efficiency and Renewable 

Energy Web site. See the Medium- & Heavy-Duty Vehicles section of the following link: 

http://www1.eere.energy.gov/vehiclesandfuels/avta/index.html. 

This evaluation at LBT would not have been possible without the support and cooperation of 

many people. The author wishes to thank each of the following: 

U.S. Department of Energy 

Lee Slezak 

Long Beach Transit 

James Ditch 

Rolando Cruz 

Bryan Mills 

ISE Corporation 

Tom Bartley 

Joshua Goldman 

Harry Meyer 

Battelle 

Kevin Chandler 

iii 
List of Acronyms 

AVTA—Advanced Vehicle Testing Activity 

bhp—brake horsepower 

CARB—California Air Resources Board 

DOE—U.S. Department of Energy 

EGR—exhaust gas recirculation 

FT&E—Fleet Test and Evaluation (NREL team) 

g/bhp-hr—grams per brake horsepower hour 

GVWR—gross vehicle weight rating 

HVAC—heating, ventilation, and air conditioning 

LBT—Long Beach Transit 

MBRC—miles between road calls 

mph—miles per hour 

MY—model year 

NOx—oxides of nitrogen 

NREL—National Renewable Energy Laboratory 

PM—particulate matter 

ppm—parts per million 

RC—road call 

rpm—revolutions per minute 

SCAQMD—South Coast Air Quality Management District 

ULSD—ultra-low sulfur diesel 

VDC—voltage direct current

iv 
Executive Summary 

This report is part of a series of evaluations from the U.S. Department of Energy (DOE). 

DOE, through the National Renewable Energy Laboratory (NREL), has been tracking 

and evaluating new propulsion systems in transit buses and trucks for more than 10 years 

using an established and documented evaluation protocol. The DOE/NREL vehicle 

evaluations are a part of the Advanced Vehicle Testing Activity (AVTA), which supports 

DOE’s Vehicle Technologies Program. 

The role of AVTA is to bridge the gap between research and development and 

commercial availability of advanced vehicle technologies that reduce petroleum use in 

the U.S. while improving air quality. The main objective of AVTA projects is to provide 

comprehensive, unbiased evaluations of advanced vehicle technologies in commercial 

use. Data are collected and analyzed for operation, maintenance, performance, cost, and 

emissions characteristics of advanced technology fleets and comparable conventional 

technology fleets operating at the same site. By comparing available advanced and 

conventional technology vehicles, AVTA evaluations help fleet owners and operators 

make informed purchasing decisions. 

This report focuses on a gasoline-electric hybrid transit bus propulsion system. This 

propulsion system is an alternative to standard diesel buses and allows for reductions in 

emissions (usually focused on reductions of particulate matter and oxides of nitrogen) 

and petroleum use. Gasoline propulsion is an alternative to diesel fuel and hybrid 

propulsion allows for increased fuel economy, which ultimately results in reduced 

petroleum use. 

Evaluation Design 

This report describes the evaluation results for New Flyer low floor buses with new 

gasoline hybrid propulsion (equipped with ISE Corporation’s ThunderVolt Hybrid Drive

propulsion system) and older diesel buses at the Long Beach Transit (LBT). These final 

results represent a 24-month evaluation (July 2005 through June 2007)of these two 

groups of buses. 

The evaluation team selected 10 vehicles from the hybrid group of 47 vehicles and 10 

vehicles from the diesel group of 138 vehicles for analysis. The number of vehicles that 

comprise the study was determined sufficient to provide some degree of statistical 

significance to the results obtained. 

Evaluation Results 

The following results and related discussions focus only on selected operating depots and 

the two study bus groups. 

Bus Use and Duty Cycle 

LBT operates 228 buses out of two facilities and averages almost 40,000 miles per bus 

annually for both facilities. The average speed of the 40-ft bus fleet is 13.8 miles per hour 

(mph) with an average of 8 stops per mile. LBT currently has forty-seven 40-ft hybrid 

gasoline-electric buses. The hybrid study group had a usage rate of 31,875 miles per 

v 
month (38,250 miles per bus annually) —2.4% lower than that of the diesel study group 

buses. This small difference is not statistically significant and makes the two groups ideal 

for comparison.

Fuel Economy and Fuel Costs 

On a volumetric basis, the 24-month average fuel economy for the hybrid buses is 3.35 

miles per gallon (mpg)—4.3% lower than that of the diesel buses. This difference is 

likely due to the lower efficiency of a throttled, spark-ignited engine as well as the lower 

energy content of a gallon of gasoline versus a gallon of diesel. On an equivalent energy 

per volume basis, the hybrids had an 8.5% mpg increase. During the evaluation period, 

gasoline at LBT cost an average of $2.49 per gallon and diesel cost an average of $2.29 

per gallon. This lower fuel economy, combined with a higher fuel cost for gasoline, 

resulted in fuel costs per mile being $.74 per mile for the hybrids as compared to $.65 per 

mile for the diesels. 

2.5

3.0

3.5

4.0

4.5

Jul 05 Sep 05 Nov 05 Jan 06 Mar 06 May 06 Jul 06 Sep 06 Nov 06 Jan 07 Mar 07 May 07

Miles Per Gallon

Diesel Average MPG Diesel AVG + 95% CI Diesel AVG - 95% CI

Hybrid Average MPG Hybrid AVG + 95% CI Hybrid AVG - 95% CI

Figure ES-1. Average Monthly Fuel Economy 

Maintenance Costs 

At the beginning of the evaluation period, the hybrid buses were brand new and remained 

under warranty for the evaluation period, which accounts for the cost-per-mile difference 

with the older, out-of-warranty diesel buses. The hybrids cost $.31 per mile to maintain 

while the diesels cost $.54 per mile. Propulsion related costs were $.08 per mile for the 

hybrids and $.19 per mile for the diesels. 

Brake System Related Maintenance Costs 

In general, the brake system maintenance costs are expected to be dramatically lower for 

hybrid propulsion systems with regenerative braking, which allows use of the electric 

drive motors to slow a bus, similar to a transmission retarder. The energy from braking is 

taken into the electric motor and then fed back to the ultra-capacitors. The hybrids had 

vi 
brake system maintenance costs that were about 90% less than that of the diesel buses 

with no relines to date on the hybrids. 

Ultra-Capacitors 

LBT chose to use ultra-capacitors for energy storage instead of the traction batteries more 

commonly used in hybrid transit buses. The ultra-capacitors work well for LBT’s duty 

cycle with frequent stops per mile and slow average speeds and are able to take 

advantage of the high charge and discharge rates associated with the frequent starts and 

regenerative braking events. In addition, the ultra-capacitors have a 12-year life 

expectancy compared to three to six years for batteries. ISE offers a three-year extended 

warranty on top of their two-year standard warranty for the ultra-capacitors. 

During the evaluation period a manufacturing issue was identified; acetonitrile was 

leaking from some of the ultra-capacitors. ISE corrected the issue with a warranty 

campaign based on serial numbers of suspect batches of ultra-capacitors. 

Road Calls 

In this report, a road call (RC) is defined as an on-road failure of an in-service bus, which 

results in a bus being taken out of service or replaced on-route. RCs are a direct indicator 

of reliability for transit buses. Miles between RC (MBRC) is a typical industry 

measurement for RC performance for transit buses. The hybrid buses had 9,000 MBRC 

compared to the diesel buses with just above 11,000. 

For RCs related only to the propulsion system, the hybrid buses are 15,000 MBRC. For 

comparison, the older diesel buses have MBRC at just above 19,000. 

vii 
Table of Contents 

Executive Summary...........................................................................................................v

Evaluation Design ............................................................................................................ v 

Evaluation Results............................................................................................................ v

Overview .............................................................................................................................1

Advanced Vehicle Testing Activity ................................................................................. 1 

Host Site Profile—Long Beach Transit............................................................................ 2 

Project Design and Data Collection ................................................................................. 3 

Vehicle System Descriptions............................................................................................ 3 

Emissions ............................................................................................................................5

Evaluation Results .............................................................................................................5

Bus Use ............................................................................................................................. 5 

Fuel Economy and Cost.................................................................................................... 6 

Maintenance Cost Analysis .............................................................................................. 9 

Total Maintenance Costs ................................................................................................ 10 

Propulsion-Related Maintenance Costs.......................................................................... 10 

Brakes ........................................................................................................................... 11 

Ultra-Capacitors ............................................................................................................. 13

Road Call Analysis......................................................................................................... 14 

Summary of Costs .......................................................................................................... 15 

Status of LBT Hybrid Fleet ............................................................................................ 16 

References and Related Reports.....................................................................................18

viii 
Overview 

Advanced Vehicle Testing Activity 

The role of the Advanced Vehicle Testing Activity (AVTA) is to help bridge the gap between research 

and development (R&D) and commercial availability for advanced vehicle technologies that reduce 

petroleum use while meeting air quality standards. AVTA supports the Department of Energy’s (DOE) 

Vehicle Technologies Program by examining market factors and customer requirements and evaluating 

the performance and durability of alternative fuel and advanced technology vehicles in fleet 

applications. The National Renewable Energy Laboratory’s (NREL) Fleet Test and Evaluation (FT&E) 

team conducts evaluations primarily under support from AVTA, but also under support from other DOE 

programs focused on nonpetroleum-based and advanced petroleum-based fuels. 

The main objective of FT&E projects is to conduct comprehensive, unbiased evaluations of advanced 

technology vehicles. Data collected and analyzed include the operations, maintenance, performance, 

cost, and emissions characteristics of advanced technology vehicles and comparable conventional 

technology in fleets operating at the same site. By comparing available advanced and conventional 

technology vehicles, FT&E evaluations help fleet owners and operators make informed purchasing 

decisions. The evaluations also provide valuable data to DOE about the maturity of the technology being 

assessed. 

The FT&E team recently conducted—or is in the process of conducting—several evaluations of 

advanced propulsion heavy-duty vehicles (see Table 1). For information on these and other evaluations 

involving advanced technologies or alternative fuels such as biodiesel and Fischer-Tropsch diesel, visit 

www.nrel.gov/vehiclesandfuels/fleettest. 

Table 1. FT&E Heavy-Duty Vehicle Evaluations 

Fleet Location Vehicle Technology Evaluation Status 

Metro St. Louis, MO GILLIG 40-ft 

transit bus 

Biodiesel blend (B20) In progress; interim 

report completed 

Nov. 2007; final 

report in June 2008 

New York City 

Transit 

Manhattan, 

Bronx, NY 

Orion VII 40-ft 

transit bus 

Series hybrid, BAE Systems 

HybriDrive propulsion system 

(diesel), Order of 200 (Gen II); 

Order of 125 (Gen I); 

Completed in Jan. 

2008 

New York City 

Transit 

Manhattan, 

Bronx, NY 

Orion VII 40-ft 

transit bus 

Series hybrid, BAE Systems 

HybridDrive propulsion system 

(diesel), order of 125; DDC 

S50G CNG engines 

Completed in Nov. 

2006 

Denver RTD Boulder, CO GILLIG 40-ft 

transit bus 

Biodiesel blend (B20) Completed in Oct. 

2006 

King County 

Metro 

Seattle, WA New Flyer 60-ft 

articulated 

transit bus 

Parallel hybrid, GM–Allison 

EP

50 System (diesel) 

Completed in Dec. 

2006 

IndyGo Indianapolis, IN Ebus 22-ft bus Series hybrid, Capstone 

MicroTurbine (diesel) 

Completed in 2005 

Knoxville Area 

Transit 

Knoxville, TN Ebus 22-ft bus Series hybrid, Capstone 

MicroTurbine (propane) 

Completed in 2005 

Norcal San Francisco, 

CA 

Peterbilt/378, 

Class 8 truck 

Cummins Westport ISXG highpressure, direct- injection, 

liquefied natural gas (LNG) and 

diesel 

Completed in 2004 

1
Host Site Profile—Long Beach Transit 

Long Beach Transit (LBT) operates 228 buses out of two facilities: Anaheim and Larry Jackson, which 

are located only seven miles apart. The fleet is made up of thirty 30-ft buses, one hundred and eightyfive 40-ft buses, and thirteen articulated buses. LBT services seven cities, transports 28–29 million 

passengers per year, and averages almost 40,000 miles per bus annually. The average speed of the 40-ft 

bus fleet is 13.8 miles per hour (mph) with an average of eight stops per mile. LBT currently has fortyseven 40-ft hybrid gasoline-electric buses that arrived in June through August of 2005. The transit 

authority has taken delivery of 15 more in the third quarter of 2007 and has requested an additional 25 

for 2008. 

Because LBT operates in the South Coast Air Quality Management District (SCAQMD), SCAQMD 

regulations prevented LBT from purchasing new diesel buses after 2002. As in other California transit 

districts, the primary path toward reducing oxides of nitrogen (NOx) and particulate matter (PM) 

emissions had been using buses powered by natural gas. LBT conducted an overall cost analysis, 

though, that led the agency to try the new hybrid gasoline-electric buses instead. Like natural gas, 

gasoline was qualified as an alternative fuel for transit buses by the California Air Resources Board 

(CARB). 

LBT’s cost analysis showed that the hybrids would be more cost-effective than buses powered by 

natural gas in terms of capital costs for infrastructure, better fuel economy, and savings in maintenance 

on brake relines and transmission overhauls. In addition, replacing the gasoline engine would be less 

expensive than overhauling a diesel engine. LBT already had gasoline fueling capability on site, so for 

the first year of operation the new hybrid gasoline-electric buses used the existing facility. After the first 

year, LBT spent $1.9 million to upgrade its facilities to update the fuel island at one of the properties 

with new lines, replace aging fuel tanks, and expand the gasoline capacity for future growth. The second 

facility required no changes. 

Combining a light-duty gasoline engine in a series hybrid heavy-duty application with ultra-capacitors 

had never been done before. LBT had no official expectations for the hybrids in regards to reliability and 

durability, but did expect to have some growing pains with the new technology. The hybrids (see Figure 

1) were put into service and dispatched the same as the diesel buses with the exception of a few highspeed routes. 

Figure 1. Photo of one of LBT’s gasoline-electric hybrid transit buses. 

2
Project Design and Data Collection 

In this evaluation, the focus is on the hybrids purchased in model year (MY) 2004 and 2005 by LBT and 

their performance during the first 2 years of service (7/05/05 – 6/07/07). MY 2002 diesel buses are used 

as a baseline in this evaluation. 

Two major interests in hybrid bus operations held by the transit industry are (1) determining energy 

storage replacement frequency and costs, and (2) quantifying the benefits of regenerative braking, 

realized in reduced brake system maintenance costs. 

Ten hybrid buses and 10 diesel buses (MY 2002) were randomly chosen for this evaluation. The buses 

were spread evenly between the Anaheim and Larry Jackson depots. The depots both dispatch to all 

routes that LBT services and the study buses were assigned to routes randomly with the normal fleet of 

40-ft buses. The preventive maintenance schedules and maintenance practices are the same at each 

depot. 

Vehicle-specific data for this evaluation were taken from LBT’s maintenance and fueling data system. 

The evaluation period for buses considered in this report began in July 2005 and ended in June 2007. 

Data parameters included the following: 

• Diesel and gasoline fuel consumption 

• Mileage accumulation 

• Maintenance records, including work orders, parts costs, and labor hours 

• Road call (RC) records. 

Vehicle System Descriptions 

LBT’s hybrid buses are built by New Flyer and use the ISE Corporation’s ThunderVolt series Hybrid 

Drive propulsion system (Figure 2). 

Figure 2. Schematic of ThunderVolt series hybrid drive propulsion system. 

3
In this series hybrid electric system, a Ford 6.8 L Triton V-10 gasoline engine is connected to a 

generator that produces electricity for the electric drive motor and the ultra-capacitors. The electric 

motor drives the vehicle and acts as a generator that captures energy during regenerative braking. The 

electrolytic ultra-capacitors supplied by Maxwell supply additional power during acceleration and hill 

climbing and store energy recovered during regenerative braking and idling. 

Table 2 presents additional details on the hybrid system and Table 3 provides brief descriptions of the 

vehicle systems. 

Table 2. Hybrid Propulsion-Related Systems 

Category Hybrid Bus Description 

Manufacturer/integrator ISE Corporation, ThunderVolt Hybrid Drive propulsion 

system 

Combining Gearbox 2 AC motor input 

Peak input torque: 2x600 Nm 

Peak output torque: 4860 Nm 

Max input speed: 10,000 rpm 

Ratio: 4.05 

Weight: 100kg 

Motor Type: 3-Phase Asynchronous Motor 

Nominal power: 85 kW 

Peak power: 150 kW 

Nominal torque: 220 Nm 

Peak torque: 530 Nm 

Rated voltage DC: 650 V 

Nominal current: 142 A 

Peak current: 250 A 

Generator Type: Permanent Magnet Sync. 

Nominal power: 110 kW 

Peak power: 145 kW 

Nominal torque: 320 Nm 

Peak torque: 450 Nm 

Rated voltage DC: 650 V 

Rated current: 170 A 

Weight: 120 kg 

Energy storage Type: Ultra-capacitor, Maxwell Boostcap 

2 enclosures, 144 capacitors each, 

Roof mounted 

Voltage per enclosure: 360 VDC rated; 403 VDC peak 

Weight per enclosure: 100 kg 

Braking Resistors Two units in parallel configuration 

Capacity: 2 x 60kW continuous 

Capacity: 2 x 70kW max for 15 seconds 

4
Table 3. Vehicle System Descriptions 

Bus Specification Hybrid Gasoline-Electric 

Buses 

Diesel Buses 

Bus manufacturer New Flyer New Flyer 

Bus model low-floor GE40LF low-floor D40LF 

Model year 2004 and 2005 2002 

Length/width/height 40.8 ft/102 in./136 in. 40.8 ft/102 in./110.4 in. 

Gross vehicle weight rating 

(GVWR)/curb weight 

40,130/26,800 lb 37,920/26,800 lb 

Passenger capacity 38 seated, 19 standing 38 seated, 19 standing 

Engine manufacturer and model Ford 2004 Triton V-10 Cummins ISC (diesel particulate 

filter equipped) 

Rated horsepower 305 bhp @ 4,250 rpm 280 bhp @ 2,100 rpm 

Rated torque 405 lb-ft @ 3,250 rpm 900 lb-ft @ 2,100 rpm 

Emissions equipment Ford 3 way catalyst Johnson-Matthey CRT-2124 

Retarder/regenerative braking Regenerative braking Engine braking 

Air Conditioning Type Sutrak ACE219 Rear Mount 

Unit (electric) 

Thermo King (engine driven) 

Fuel capacity 110 gallons 119 gallons 

Bus purchase cost ($)* 462,379 268,051 

*Costs listed in the table are actual costs at the time of purchase. 

Emissions 

Original funding for the gasoline hybrid system was provided by the US DOT/FTA, the State of 

California, WestStart-CALSTART, Omnitrans, and ISE. 

The ThunderVolt gasoline hybrid system was certified by CARB to 0.6g/bHp-hr NOx and 3.7g CO; PM 

is not measured on gasoline systems; making it a very low emission 40-foot bus drive system. The 

gasoline hybrid system combines the Siemens ELFA electric drive system with the Ford ULEV rated 6.8 

L V10 engine, integrated and controlled by the ISE ThunderCan hybrid control system. Table 4 below 

compares the emissions certification levels for the Hybrid and Diesel buses. Tailpipe emissions test 

results are not available for comparison. See http://www.arb.ca.gov/msprog/onroad/cert/cert.php#6

HDE/HDV/MDE for model years 2004 and 2005. 

Table 4. Hybrid and Diesel Bus Emissions Certification 

Study Group NOx 

(g/bHp-hr)

PM 

(g/bHp-hr)

CO 

(g/bHp-hr)

Hybrid 0.6 N/A 3.7 

Diesel 4.0 0.05 0.5 

Evaluation Results 

Bus Use 

Table 5 presents the average monthly mileage per bus during the evaluation period for the two groups of 

buses. The hybrids had a usage rate 2.4% lower than that of the diesel buses. If the July ramp-up is 

removed from the hybrid group average their usage rate would only be 0.7% lower than the diesels. 

These small differences are not statistically significant (two-tailed P value = 0.3455) and make the 

5
groups ideal for comparison. This monthly mileage is also an indication of both the diesel and hybrid 

bus reliability. The hybrids were able to provide a similar number of miles of service per month as the 

conventional diesels operating on similar routes.

Table 5. Average Bus Miles Driven per Month by Study Group 

Study Group Average Miles per Month per Bus

Hybrid 3,188 

Diesel 3,266 

Figure 3 shows average monthly miles per bus for each bus group with +/- 95% confidence interval 

lines. Bus average usage did not change significantly during the evaluation period. This chart also shows 

a quick ramp-up of miles per month for the hybrids as they were implemented into the fleet in July of 

2005. After this initial ramp-up, the hybrids were driven a similar number of miles for the rest of the 

evaluation period. 

0

1000

2000

3000

4000

5000

Jul 05 Sep 05 Nov 05 Jan 06 Mar 06 May 06 Jul 06 Sep 06 Nov 06 Jan 07 Mar 07 May 07

Miles per Bus

Diesel Average Miles Diesel AVG + 95% CI Diesel AVG - 95% CI

Hybrid Average Miles Hybrid AVG + 95% CI Hybrid AVG - 95% CI

Figure 3. Hybrid gasoline-electric and diesel monthly mileage per bus. 

Fuel Economy and Cost 

LBT fuels its hybrids with standard California reformulated 87 octane gasoline. During the evaluation 

period, gasoline at LBT cost an average of $2.49 per gallon. LBT diesel buses use ultra-low sulfur No. 1 

diesel fuel at less than 30 parts per million (ppm) sulfur content. This sulfur level was required to be less 

than 15 ppm by the end of 2006. During the evaluation period, diesel fuel at LBT cost an average of 

$2.29 per gallon for ultra-low sulfur diesel (ULSD) fuel with sulfur less than 30 ppm. 

Table 6 shows the fuel consumption and economy data for each bus in each study group. The 24-month 

average fuel economy for the hybrid buses is 4.3% lower than that of the diesel buses (two-tailed P 

value = 0.0001). This statistically significant difference is likely due to the lower efficiency of a 

6
throttled, spark-ignited engine and a lower energy content per gallon of fuel. Since California 

reformulated gasoline has a lower energy content on a per gallon basis than diesel (113,824 Btu/gal vs 

128,450 btu/gal), the fuel efficiency of the buses can also be looked at from an energy equivalent basis. 

Adjusting for this difference in volumetric energy content, the hybrid buses delivered 3.78 miles per 

diesel gallon equivalent; 8.0 % higher than the diesels (two-tailed P value < 0.0001). 

Table 6. Hybrid and Diesel Bus Fuel Use and Economy 

Bus Mileage Gallons 

Consumed 

Miles per

Gallon 

Miles per 

Diesel Gallon

Equivalent 

Fuel 

Cost/Gallon ($) 

Fuel 

Cost/Mile ($)

2402 67,167 21,521 3.12 3.52 $2.49 0.80 

2404 84,224 26,577 3.17 3.58 $2.49 0.79 

2407 96,767 27,909 3.47 3.91 $2.49 0.71 

2412 58,127 18,114 3.21 3.62 $2.49 0.78 

2414 95,211 27,218 3.50 3.95 $2.49 0.71 

2421 60,704 18,713 3.24 3.66 $2.49 0.77 

2503 68,352 19,524 3.50 3.95 $2.49 0.70 

2512 80,110 23,551 3.40 3.84 $2.49 0.72 

2514 71,948 21,139 3.40 3.84 $2.49 0.73 

2519 82,389 23,904 3.45 3.89 $2.49 0.72 

Hybrid Total 764,999 228,171 3.35 3.78 $2.49 0.74 

2202 50,933 14,411 3.53 N/A $2.29 0.65 

2204 88,107 24,799 3.55 N/A $2.29 0.65 

2206 67,684 19,054 3.55 N/A $2.29 0.64 

2208 65,167 18,506 3.52 N/A $2.29 0.65 

2210 72,626 21,171 3.43 N/A $2.29 0.67 

2212 90,865 25,622 3.55 N/A $2.29 0.65 

2216 99,216 27,742 3.58 N/A $2.29 0.64 

2218 91,911 26,499 3.47 N/A $2.29 0.66 

2225 93,363 27,162 3.44 N/A $2.29 0.67 

2226 63,977 18,797 3.40 N/A $2.29 0.67 

Diesel Total 783,849 223,761 3.50 N/A $2.29 0.65 

Figure 4 shows the average monthly mpg for each bus group with +/- 95% confidence interval lines.

7
2.5

3.0

3.5

4.0

4.5

Jul 05 Sep 05 Nov 05 Jan 06 Mar 06 May 06 Jul 06 Sep 06 Nov 06 Jan 07 Mar 07 May 07

Miles Per Gallon

Diesel Average MPG Diesel AVG + 95% CI Diesel AVG - 95% CI

Hybrid Average MPG Hybrid AVG + 95% CI Hybrid AVG - 95% CI

Figure 4. Average monthly fuel economy. 

Figure 5 shows the average monthly energy equivalent mpg for each bus group with +/- 95% confidence 

interval lines.

2.5

3.0

3.5

4.0

4.5

Jul 05 Sep 05 Nov 05 Jan 06 Mar 06 May 06 Jul 06 Sep 06 Nov 06 Jan 07 Mar 07 May 07

Miles Per Energy Equivalent Gallon

Diesel Average MPG Diesel AVG + 95% CI Diesel AVG - 95% CI

Hybrid Avg En Eqiv MPG Hybrid AVG En Eqiv + 95% CI Hybrid AVG En Eqiv - 95% CI

Figure 5. Average monthly energy equivalent fuel economy. 

Figures 4 and 5 also showcase the seasonal fluctuation in fuel economy experienced by both hybrid and 

diesel buses during the 24-month evaluation period. Comparing the summer months of 2006 (June, July, 

8
August) to the winter months of 2006-2007 (December, January, February) the diesels had statistically 

significant 10.2% lower fuel economy in the summer (two-tailed P value = 0.0123) and the hybrids had 

statistically significant 12.8% lower fuel economy in the summer (two-tailed P value = 0.0259). Much of 

the summer decrease is caused by an increase in energy consumption for air conditioning; it is not clear 

why the hybrids experience a greater drop in fuel economy. The hybrids do have electric air 

conditioning, but this was not isolated as a benefit or detriment to the overall fuel economy. 

Maintenance Cost Analysis 

This evaluation focuses on bus operations spanning the first two years of the 12-year minimum life of a 

transit bus. This short evaluation period does not yield enough capital and operating costs to allow us to 

understand the full 12-year life-cycle cost of the hybrid buses. To gain a complete understanding of 

costs, we must examine the purchase cost of the buses and the costs for facility modification or addition, 

warranty, and operations. In addition, we must consider costs for longer term maintenance activities 

such as engine rebuilds or replacements and ultra-capacitor replacements. Finally, we must look at areas 

where cost savings can be achieved, as in brake repair. The intent of this evaluation, though, is to 

capture accurate actual capital and known operations costs associated with the hybrid and diesel vehicles 

for the time period selected. This analysis is not predictive of maintenance costs assumed by the transit 

agency beyond the warranty period. ISE’s standard propulsion system warranty on these hybrids is two 

years from the date of purchase and includes the ultra-capacitors. LBT opted to purchase three years of 

extended propulsion system warranty for the first 27 buses and use the standard two-year warranty for 

the remaining 20 buses. Some propulsion system components are warranted beyond two years. Hybrid 

buses in the study group fall into both warranty categories, but all remained under warranty for the entire 

study period. The exact components and warranty periods, as negotiated by LBT, ISE, and New Flyer, 

are contractual.

The hybrid buses are new enough that much of the maintenance is done under warranty. All 

maintenance for the ISE hybrid drive was done on site by ISE mechanics. These maintenance costs are 

not included in the maintenance cost analysis in this section. Not accounting for warranty repairs in the 

evaluation of total maintenance cost does offer an incomplete picture of total maintenance cost. Even 

with warranty costs absent, however, this analysis reflects the actual cost to the transit agency during the 

time period selected. 

The FT&E team collected the maintenance costs in the same way for each study group. The duty cycle 

and maintenance practices are the same for both diesel and hybrid study groups. All work orders and 

parts information available were collected for the study buses. The maintenance analysis discussions 

include only maintenance data from the evaluation period on the study group buses. 

Two major interests in hybrid bus operations held by the transit industry are (1) determining energy 

storage replacement frequency and costs, and (2) quantifying the benefits of regenerative braking. In 

addition, the benefits of regenerative braking, realized in reduced maintenance costs, are evaluated using 

data from the hybrid buses. Diesel buses are used as a baseline in this evaluation. 

9
Total Maintenance Costs 

This cost category includes the costs of parts and hourly labor costs of $50 per hour, and does not 

include warranty costs. Cost per mile is calculated as follows: 

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

The labor rate has been artificially set at a constant rate of $50 per hour so that other analysts can change 

this rate to one more similar to their own. This rate does not directly reflect LBT’s current hourly 

mechanic rate. 

Table 7 shows total and propulsion related maintenance costs for the two study groups. The total 

maintenance cost per mile was 42% less for the hybrid buses than for the diesel buses. At the beginning 

of the evaluation period, the hybrid buses were brand new and remained under warranty for the 

evaluation period, which accounts for the cost-per-mile difference with the older, out-of-warranty diesel 

buses. 

Table 7. Hybrid and Diesel Bus Total & Propulsion Maintenance Costs 

Study Group Miles Parts Cost Labor Hours Cost per Mile ($/mile)

Hybrid 764,999 $56,664 3,646 0.3124 

Hybrid Propulsion-Related 764,999 $15,050 8,96 0.0782 

Diesel 783,849 $137,287 5,707 0.5392 

Diesel Propulsion-Related 783,849 $62,508 1,739 0.1906 

Propulsion-Related Maintenance Costs 

The propulsion-related vehicle systems include the exhaust; fuel; engine, nonlighting electrical (general 

electrical, charging, cranking, and ignition); electric propulsion; and transmission systems. The ultracapacitors are discussed in the next section of this report. Table 8 summarizes the cost comparisons 

between the study groups. 

Table 8. Summary of Propulsion-Related Maintenance Cost Comparisons 

Vehicle System Hybrid 

($/mile) 

Diesel 

($/mile) 

Exhaust system 0.0059 0.0220 

Fuel system 0.0051 0.0193 

Engine 0.0392 0.0844 

Non-lighting electrical 0.0176 0.0267 

Transmission N/A 0.0382 

Total propulsion-related 0.0782 0.1906 

Figure 6 shows the cumulative average total and propulsion-related maintenance cost per mile for the 

study buses. Figure 7 shows the monthly average total and propulsion-related maintenance cost per mile 

for the study buses. 

10
0.00

0.20

0.40

0.60

0.80

Jul 05 Sep 05 Nov 05 Jan 06 M ar 06 M ay 06 Jul 06 Sep 06 Nov 06 Jan 07 M ar 07 M ay 07

Cumulative maintenance cost 

($/mile)

Diesel total Hybrid gasoline-electric total

Diesel propulsion Hybrid gasoline-electric propulsion

Figure 6. Cumulative total and propulsion-related maintenance costs. 

0.00

0.20

0.40

0.60

0.80

1.00

1.20

Average maintenance cost ($/mile)

Jul 05 Sep 05 Nov 05 Jan 06 Mar 06 May 06 Jul 06 Sep 06 Nov 06 Jan 07 Mar 07 May 07

Diesel total Hybrid gasoline-electric total

Diesel propulsion Hybrid gasoline-electric propulsion

Figure 7. Average monthly total and propulsion-related maintenance costs. 

Brakes 

In general, the brake system maintenance costs are expected to be dramatically lower for hybrid 

propulsion systems with regenerative braking, which allows use of the electric drive motors to slow a 

bus, similar to a transmission retarder. The energy from braking is taken into the electric motor and then 

fed back to the ultra-capacitors. In addition, the ISE system incorporates additional “braking resistors” to 

11
absorb energy when the ultra-capacitors are fully charged. LBT’s staff expects diesel buses to undergo a 

four-wheel brake reline every 35,000 to 40,000 miles on average. 

Table 9 shows the maintenance costs for the brake system repairs for the two study groups. During the 

evaluation period, the 10 hybrid study buses traveled 764,999 miles and required only minimal brake 

system maintenance such as adjustments for squeaking. 

Maintenance costs for the brakes on the baseline diesel buses—which had only slightly higher miles 

than the hybrids—were 10 times greater than the costs for the hybrids. All 10 buses in the diesel study 

group had at least a rear brake reline during the evaluation period. Six of the 10 had at least a four wheel 

reline during the study period, and some of the buses had an additional rear reline. 

It is important to note that the diesel buses did not have new brakes at the beginning of the study period. 

The lower brake system cost assumption, however, is supported by the extent of relines and the longerthan-average miles without a reline for the hybrids during the study period. 

Table 9. Brake System Maintenance Costs (July 2005–June 2007) 

Study Group Mileage Parts Cost 

($) 

Labor Hours Cost per Mile 

($/mile) 

Hybrid 764,999 17.11 55 0.0036 

Diesel 783,849 11,192.94 335 0.0356 

Figure 8 shows the average time to the first front and rear brake relines on the older diesel buses as 

compared to the average hybrid bus mileage at the end of the two-year study period. None of the hybrid 

buses had a reline during the study period. The first relines on the diesel buses occurred before the study 

period of this report, but are included here to provide an understanding of the brake life comparison. All 

of the hybrid buses have more miles on them than any diesel bus had by the time of its first rear reline. 

On average, the hybrid buses have doubled the mileage to first rear brake reline and are approaching the 

mileage the diesel buses averaged for their first front reline. Assuming the front brakes on the hybrids 

will last twice as long as the rears, as was the case for the diesels, this data suggests the hybrids will get 

at least twice the mileage on average between brake relines. From routine inspections, LBT anecdotally 

suggests they are only half of the way through the brake linings at this point. Measurements were not 

taken however. 

12
Brake Reline Mileage Distribution Comparison

0

20,000

40,000

60,000

80,000

100,000

120,000

140,000

Rear Front

Brake Relines

Miles to 1st Reline

(Current Mileage on Hybrid)

Diesel Average & Range Before 1st

Brake Reline

Hybrid Average & Range After 2 Yrs

WITHOUT a Brake Reline

 Figure 8. Brake reline mileage distribution comparison. 

Ultra-Capacitors 

LBT chose to use ultra-capacitors for energy storage instead of the traction batteries more commonly 

used in hybrid transit buses. The ultra-capacitors work well for LBT’s duty cycle with the frequent stops 

per mile and slow average speeds. In addition, the ultra-capacitors have a 12-year life expectancy 

compared to three to six years for batteries. ISE has a standard two-year warranty for the ultra-capacitors 

and offers a three-year extension of the warranty. LBT bought the extended warranty on the first 27 

buses, but not the remaining 20. 

During the evaluation period a manufacturing issue was identified; acetonitrile was leaking from some 

of the ultra-capacitors. ISE corrected the issue with a warranty campaign based on serial numbers of 

suspect batches of ultra-capacitors. The correction sealed them by applying an epoxy coating over the 

ultra-capacitors. Because this correction was handled as a campaign no cost was incurred to LBT and 

these repairs do not affect the maintenance analysis section of this report. Two incidents of ultracapacitor dry cell overheating were attributed to this leakage within the fleet. 

13
Figure 9 is a photo of an open ultra-capacitor pack showing the 144 individual cells. Figure 10 shows 

the installation of the two ultra-capacitor packs on the rear roof of the bus with the ultra-capacitor 

cooling system in the background. 

Figure 9. An Open ultra-capacitor pack. 

Figure 10. Two ultra-capacitor packs on the rear roof of the bus. 

Road Call Analysis 

Figure 11 shows the cumulative average miles between road call (MBRC) for all road calls (RCs) along 

with those related only to propulsion. MBRC is a good indication of the reliability of a vehicle. 

Propulsion-related systems include the exhaust; fuel; engine, non-lighting electrical (general electrical, 

charging, cranking, and ignition); electric propulsion; and transmission systems. Also note that the diesel 

study group had four months without a propulsion-related RC at the beginning of the study period. This 

heavily weighted the cumulative average very high, but it is clear the trend is coming back down over 

time to reflect propulsion MBRC similar to that of the hybrids. 

14
0

10,000

20,000

30,000

40,000

50,000

60,000

70,000

80,000

Jul 05 Sep 05 Nov 05 Jan 06 M ar 06 M ay 06 Jul 06 Sep 06 Nov 06 Jan 07 M ar 07 M ay 07

Cumulative miles between roadcalls 

(MBRC)

Diesel total Hybrid gasoline-electric total

Diesel propulsion related Hybrid gasoline-electric propulsion related

Figure 11. Cumulative miles between road call. 

The diesels had 71 road calls during the study period while the hybrids had 85; 20% more. The diesels 

had 41 propulsion related road calls during the study period while the hybrids had 51; 24% more. 

LBT’s fleet average is about 9,000 total MBRC. LBT had no official expectations for the hybrids 

because the combination of a light-duty gasoline engine in a series hybrid heavy-duty application with 

ultra-capacitors had never been done before. LBT’s staff has been happy with the MBRC performance 

of the hybrids, shown in comparison to that of the diesels in Table 10. 

Table 10. Cumulative Miles Between Road Call Comparison 

Study 

Group 

Miles Total 

Road Calls 

Total 

MBRC 

Propulsion 

Road Calls 

Propulsion 

MBRC 

Hybrid* 764,999 85 9,000 51 15,000 

Diesel 783,849 71 11,040 41 19,118 

* hybrid MBRC happened to result in even numbers. 

Summary of Costs 

Table 11 summarizes fuel and maintenance cost per mile for the two study groups. The average cost per 

mile for the hybrid buses is 11.7% lower than that of the diesel buses because the hybrids have the 

majority of their maintenance costs covered under warranty and the diesel buses are not. 

15
Table 11. Summary of Costs per Mile 

Bus Fuel 

Cost/Mile ($) 

Maintenance 

Cost/Mile ($) 

Total 

Cost/Mile ($) 

2402 0.80 0.24 1.04 

2404 0.79 0.84 1.63 

2407 0.71 0.23 0.94 

2412 0.78 0.23 1.01 

2414 0.71 0.27 0.97 

2421 0.77 0.29 1.06 

2503 0.70 0.18 0.88 

2512 0.72 0.31 1.03 

2514 0.73 0.25 0.98 

2519 0.72 0.23 0.96 

Hybrid Total 0.74 0.31 1.05 

2202 0.65 0.75 1.40 

2204 0.65 0.80 1.44 

2206 0.64 0.46 1.10 

2208 0.65 0.70 1.34 

2210 0.67 0.37 1.04 

2212 0.65 0.39 1.04 

2216 0.64 0.53 1.17 

2218 0.66 0.47 1.13 

2225 0.67 0.48 1.15 

2226 0.67 0.53 1.20 

Diesel Total 0.65 0.54 1.19 

Status of LBT Hybrid Fleet 

LBT has been happy with the performance of the original forty-seven 40-ft hybrid gasoline-electric 

buses over the first two years of service. The transit authority has taken delivery of 15 more in the third 

quarter of 2007 and has requested an additional 25 for 2008. 

Conclusions 

• Monthly miles per bus were essentially the same with the hybrids as with the diesels. This usage rate 

is one indication of reliability. 

• Fuel economy on a mpg basis was 4.3% lower than the diesel buses and fuel costs for gasoline were 

higher than diesel resulting in a higher fuel cost per mile. On an energy equivalent basis the hybrids 

had 8.5% better fuel economy than the diesels. 

• Maintenance costs were lower on the hybrids, but they are under warranty while the diesel buses are 

not. 

• Brake costs per mile were much lower on the hybrid bus group. The hybrid buses did not experience 

their first brake relines during the study period so the magnitude of the improvement could not be 

calculated. 

• MBRC was lower for the hybrids than the diesels. This indicates a lower level of reliability. 

16
Contacts

U.S. Department of Energy 

Energy Efficiency and Renewable Energy 

Vehicle Technologies Program 

Lee Slezak 

Manager, Advanced Vehicle Testing Activity 

Phone: 202-586-2335 

E-mail: lee.slezak@ee.doe.gov 

National Renewable Energy Laboratory 

Mike Lammert 

Project Engineer 

Phone: 303-275-4067 

E-mail: michael_lammert@nrel.gov 

Long Beach Transit 

Rolando Cruz 

Manager, Maintenance 

Phone: 562-599-8506 

E-mail: rcruz@lbtransit.com 

ISE Corporation 

Joshua Goldman 

Senior Project Engineer 

Phone: 858-413-1752 

E-mail: jgoldman@isecorp.com

Battelle 

Kevin Chandler 

Principal Research Scientist 

Phone: 614-424-5127 

E-mail: chandlek@battelle.org

17
References and Related Reports 

LBT Related Reports 

ARB (2002). Proposed Modifications to the Public Transit Bus Fleet Rule and Interim Certification 

Procedures for Hybrid-Electric Urban Transit Buses. Staff Report: Initial Statement of Reasons. 

Chandler, K.; Clark, N.; Zhen, F.; Wayne, S. (2007). “Hybrid-Electric Transit Bus Performance in North 

America.” Transportation Research Board Annual Meeting 2007. Paper #07-3004. 

18
F1147-E(09/2007) 

REPORT DOCUMENTATION PAGE Form Approved 

OMB No. 0704-0188

The public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, 

gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this 

collection of information, including suggestions for reducing the burden, to Department of Defense, Executive Services and Communications Directorate (0704-0188). Respondents 

should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a 

currently valid OMB control number. 

PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ORGANIZATION.

1. REPORT DATE (DD-MM-YYYY)

June 2008 

2. REPORT TYPE

TP Techical Paper 

3. DATES COVERED (From - To)

 

5a. CONTRACT NUMBER

DE-AC36-99-GO10337 

5b. GRANT NUMBER

4. TITLE AND SUBTITLE

Long Beach Transit: Two-Year Evaluation of Gasoline-Electric 

Hybrid Transit Buses 

5c. PROGRAM ELEMENT NUMBER

5d. PROJECT NUMBER

NREL/TP-540-42226 

5e. TASK NUMBER

FC08.3000 

6. AUTHOR(S)

Mike Lammert 

5f. WORK UNIT NUMBER

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

National Renewable Energy Laboratory 

1617 Cole Blvd. 

Golden, CO 80401-3393 

8. PERFORMING ORGANIZATION 

REPORT NUMBER

NREL/TP-540-42226 

10. SPONSOR/MONITOR'S ACRONYM(S)

NREL 

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

11. SPONSORING/MONITORING 

AGENCY REPORT NUMBER

12. DISTRIBUTION AVAILABILITY STATEMENT

National Technical Information Service 

U.S. Department of Commerce 

5285 Port Royal Road 

Springfield, VA 22161 

13. SUPPLEMENTARY NOTES

14. ABSTRACT (Maximum 200 Words)

This report focuses on a gasoline-electric hybrid transit bus propulsion system. The propulsion system is an 

alternative to standard diesel buses and allows for reductions in emissions (usually focused on reductions of 

particulate matter and oxides of nitrogen) and petroleum use. Gasoline propulsion is an alternative to diesel fuel and 

hybrid propulsion allows for increased fuel economy, which ultimately results in reduced petroleum use. 

15. SUBJECT TERMS

hybrid transit bus; Long Beach Transit; ultra-capacitors; diesel bus; LBT 

16. SECURITY CLASSIFICATION OF: 19a. NAME OF RESPONSIBLE PERSON 

a. REPORT 

Unclassified 

b. ABSTRACT 

Unclassified

c. THIS PAGE 

Unclassified

17. LIMITATION 

OF ABSTRACT

UL 

18. NUMBER 

OF PAGES 

19b. TELEPHONE NUMBER (Include area code)

Standard Form 298 (Rev. 8/98) 

Prescribed by ANSI Std. Z39.18