National Renewable Energy Laboratory 

Innovation for Our Energy Future 

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

Office of Energy Efficiency & Renewable Energy

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

New York City Transit Hybrid 

and CNG Transit Buses: 

Interim Evaluation Results 

K. Chandler and E. Eberts 

Battelle 

L. Eudy 

National Renewable Energy Laboratory 

Technical Report 

NREL/TP-540-38843 

January 2006 
New York City Transit Hybrid 

and CNG Transit Buses: 

Interim Evaluation Results 

K. Chandler and E. Eberts 

Battelle 

L. Eudy 

National Renewable Energy Laboratory 

Prepared under Task No. FC06.3000 

Technical Report 

NREL/TP-540-38843 

January 2006 

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
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Acknowledgements 

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

Lee Slezak, within the FreedomCAR and Vehicle Technologies Program in the U.S. Department 

of Energy. All publications on the NYCT hybrid bus evaluation will be posted on DOE's Energy 

Efficiency & Renewable Energy Website. See the Medium & Heavy Duty Vehicles section of 

the following link: www.eere.energy.gov/vehiclesandfuels/avta/index.shtml 

This evaluation at New York City Transit (NYCT) would not have been possible without the 

support and cooperation of many people. The authors wish to thank each of the following: 

U.S. Department of Energy 

Lee Slezak 

New York City Transit 

Gary LaBouff 

Doug Zupo 

Danny Ilioiu 

Glenn Maerki 

Gordon Coor 

BAE Systems 

Tom Webb 

Steve Tilyou 

Orion Bus Industries 

Mark Brager 

Trillium USA 

Jennifer de Tapia 

Jan Hull 

iii
Table of Contents 

Executive Summary........................................................................................................................ 1 

Evaluation Design....................................................................................................................... 1 

Implementation Experience ........................................................................................................ 2 

Evaluation Results ...................................................................................................................... 3 

Overview......................................................................................................................................... 7 

Advanced Vehicle Testing Activity............................................................................................ 8 

Host Site Profile—NYCT........................................................................................................... 9 

Emissions Reductions Drive the Need for CNG and Hybrid Propulsion ................................. 10 

Project Design and Data Collection.......................................................................................... 12 

Vehicle System Descriptions .................................................................................................... 13 

CNG Transit Bus Propulsion .................................................................................................... 16 

BAE Systems HybriDrive® Propulsion System........................................................................ 16 

NYCT Facilities............................................................................................................................ 18 

Implementation Experience ...................................................................................................... 20 

Evaluation Results ........................................................................................................................ 26 

Route Descriptions.................................................................................................................... 26 

Bus Use ..................................................................................................................................... 27 

Fuel Economy and Cost............................................................................................................ 30 

Maintenance Analysis............................................................................................................... 33 

Roadcall Analysis ..................................................................................................................... 43 

Summary of Costs..................................................................................................................... 46 

What’s Next? ................................................................................................................................ 47 

Contacts......................................................................................................................................... 48 

References and Related Reports ................................................................................................... 50 

NYCT Related Reports............................................................................................................. 50 

Other Related Reports............................................................................................................... 50 

Appendix: Fleet Summary Statistics............................................................................................. 52 

Appendix A: Summary of Diesel, CNG, and Hybrid Results .................................................. 53 

Appendix B: CNG (Orion VII) at West Farms Depot and Hybrid (Orion VII) at Mother 

Clara Hale Depot............................................................................................................... 54 

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. DOE/NREL evaluated the original 10 prototype diesel 

hybrid buses from Orion and BAE Systems (model Orion VI buses) operated at New York City 

Transit (NYCT). That evaluation was reported in July 2002 and provided results from the 

prototype buses from 1998 through 2001. 

These DOE/NREL vehicle evaluations are a part of the Advanced Vehicle Testing Activity 

(AVTA), which supports DOE’s FreedomCAR & 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 U.S. petroleum use while improving air quality. The 

main objective of AVTA projects is to provide comprehensive, unbiased evaluations of advanced 

technologies. Data collected and analyzed include the operation, maintenance, performance, 

safety, 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 compressed natural gas (CNG) and diesel hybrid electric bus propulsion 

systems in NYCT’s transit buses. Both of these propulsion systems are alternatives to standard 

diesel buses and allow for reductions in petroleum use and emissions (usually focused on 

reductions of particulate matter and oxides of nitrogen). CNG propulsion is an alternative to 

diesel fuel use, and diesel hybrid propulsion allows for increased fuel economy, which, in turn, is 

a reduction in petroleum use. 

Evaluation Design 

This report describes the evaluation results for Orion VII low floor buses at NYCT with CNG 

propulsion (Detroit Diesel Corporation Series 50G CNG) and hybrid propulsion (BAE Systems 

HybriDrive® propulsion system). These interim results represent eight out of a planned 12-month 

evaluation of these two groups of buses. An additional evaluation of NYCT’s order of 200 Orion 

and BAE Systems hybrid buses will be reported separately. The evaluation period presented in 

this report covers October 2004 through May 2005; the final evaluation report will include data 

through September 2005. This interim report was created to expedite the release of information 

collected on these technologies. 

The CNG buses evaluated were part of an order of 260 Orion VII CNG buses that started into 

service in September 2003 at Jackie Gleason Depot and later at West Farms Depot. NYCT 

expected the buses to seamlessly replace older diesel buses after CNG fueling infrastructure was 

added and training was completed at the newly opened West Farms Depot. 

1
The hybrid buses evaluated were part of an order of 125 Orion VII hybrid buses with the BAE 

Systems series hybrid propulsion system. The buses started service in March 2004 at Mother 

Clara Hale Depot in Manhattan and later were also introduced at Queens Village Depot in 

Queens. This group of buses is the first large commercial hybrid bus delivery for Orion and BAE 

Systems. NYCT expected the 125 hybrid buses to seamlessly replace diesel buses after special 

training for high power and troubleshooting and battery conditioning activities were completed. 

The CNG evaluation presented in this report includes 10 CNG Orion VII buses (model year 

2002) chosen at random at West Farms Depot and nine diesel Orion V buses (model year 1994) 

used as a depot baseline. The baseline fleet for this evaluation is nearing the end of its useful life 

at NYCT (11 out of 12 years of planned use). The newer CNG buses have generally replaced the 

diesel buses at the depot with higher usage and lower operating costs. While comparison of 

newer technology to older diesel buses is not optimal, having a baseline is still valuable to fleets 

considering these advanced buses. In many cases, the buses being replaced are similar to those of 

NYCT: near or past their planned life. 

The hybrid evaluation presented in this report includes 10 hybrid Orion VII buses (model year 

2002) chosen at random at Mother Clara Hale Depot and nine diesel Orion V buses (model year 

1999) used as a depot baseline. Although the bus model years differ by only three years, because 

the hybrid buses did not go into service until 2004, the diesel buses are five years older in terms 

of operations experience. The newer hybrid buses have generally replaced the diesel bus fleet at 

the depot with similar usage and much higher fuel economy and better fuel cost per mile 

performance. 

One note of context for this evaluation: The DDC Series 50 engine is no longer available for new 

transit buses. Both the diesel and CNG engines are no longer available. 

The evaluation presented in this report includes comparisons of CNG and hybrid Orion VII buses 

to older diesel buses at the two depots for bus usage, fuel economy, and miles between roadcalls 

(MBRC). Because of the age difference of the diesel buses and the CNG and hybrid buses (as 

well as warranty costs), the maintenance cost per mile comparisons are only accomplished 

between the CNG and hybrid Orion VII buses. The comparison of the Orion VII CNG and 

hybrid buses includes buses that are the same age and the same bus platform. The CNG buses at 

West Farms Depot and the hybrid buses at Mother Clara Hale Depot have been operated on 

similar duty-cycles and the maintenance practices at the two depots appear to be similar. 

Implementation Experience 

The implementation experience of the CNG (260 buses) and hybrid (125 buses) fleets went well, 

and the buses were quickly put into full service. NYCT, Orion, and BAE Systems reported that 

the buses are performing well from a systems perspective. West Farms Depot built a large CNG 

compression station that has the ability to move 6,600 scfm of natural gas and fuel buses in less 

than 5 minutes. Combustible gas detection was added for the maintenance area to accommodate 

the use of natural gas buses. The hybrid buses required that adequate space be available at the 

Mother Clara Hale facility for two battery conditioning stations. 

2
The bus operators reportedly like the new buses—especially the power of the hybrid buses. 

Mileage accumulation for the 260 CNG buses through May 2005 was more than 9.5 million 

miles with a general usage rate of 2,500 monthly miles per bus. The 125 hybrid buses 

accumulated more than 2.6 million miles through May 2005 with a general usage rate of 2,500 

monthly miles per bus. Both the CNG and hybrid bus fleets experienced miles between roadcalls 

(MBRC) rates above NYCT’s required 4,000 MBRC (average 5,000 MBRC for CNG, 7,000 

MBRC for hybrid). 

Evaluation Results 

The following results and discussion focus only on the selected evaluation operating depots and 

study bus groups. 

Duty Cycle 

The general duty cycle for the CNG bus evaluation location (West Farms Depot) was an average 

speed of 6.5 mph for 2004 and 6.3 mph for 2005. The general duty cycle for the hybrid bus 

evaluation location (Mother Clara Hale Depot) was an average speed of 6.5 mph and 6.1 mph for 

2004 and 2005 respectively. The average speeds are comparable between the two evaluation 

locations. The buses at the two depots were randomly dispatched on all standard bus routes. 

Bus Use 

Bus use is intended as an indicator of reliability and availability for service. The lack of use may 

indicate downtime for maintenance or purposeful reduction of planned work for the buses. For 

the detailed study groups, the CNG buses had 15% higher bus use than the baseline diesel buses 

(CNG had 2,244 monthly miles, diesel had 1,952 monthly miles). The hybrid buses had 

essentially the same bus use compared to diesel at 3% higher for the hybrid buses (hybrid had 

2,461 monthly miles, diesel had 2,385 monthly miles). When compared across depots, the CNG 

buses had a bus use similar to the hybrid buses, with the CNG buses having a 10% lower rate. 

Fuel Economy 

The CNG buses’ average fuel economy was 25% lower than the diesel baseline buses. Average 

monthly fuel economy for the CNG and diesel baseline groups is shown in Figure ES-1. This 

fuel economy difference is typical for a low-average-speed operation for the spark-ignited 

natural gas engines. The hybrid buses’ average fuel economy was 45% higher than the diesel 

baseline buses (ranging from 32% to 52% better than the diesel baseline during the evaluation 

period), as shown in Figure ES-2. 

The diesel baseline buses for the hybrid bus evaluation have diesel engines without exhaust gas 

circulation (EGR). The addition of EGR for emissions control would tend to lower the diesel 

baseline fuel economy. The eight-month evaluation period does not include summer months, 

which could have reduced the hybrid bus fuel economy advantage from air conditioning loading 

and the ability to collect regenerative braking energy into the batteries. The summer-month fuel 

economy information will be provided in the final results report on this evaluation. The hybrid 

buses had an average fuel economy 100% higher than the CNG buses. 

3
0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

Jun04Jul-04 Aug04Sep-04 Oct-04 Nov04Dec04Jan-05 Feb05Mar05Apr05May05

Miles per Diesel Gallon (MPG)

Diesel CNG

Figure ES-1. Average Fuel Economy (MPG) for CNG and Diesel at West Farms 

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

Jun04Jul-04 Aug04Sep04Oct04Nov04Dec04Jan05Feb05Mar05Apr05May05

Miles per Gallon (MPG)

Diesel Hybrid

Figure ES-2. Average Fuel Economy (MPG) for Hybrid and Diesel at Mother Clara Hale 

Fuel Cost 

Fuel cost for the CNG buses is based on the commodity natural gas price paid by NYCT and an 

additional charge from Trillium USA to pay the operation and maintenance cost of the CNG 

fueling station. The average natural gas commodity price during the evaluation period was $0.96 

per therm and the Trillium USA charge was $0.24 per therm for a total cost of $1.32 per therm or 

$1.78 per diesel energy equivalent gallon. The average diesel fuel cost—sulfur content less than 

30 parts per million (ppm)—was $1.70 per gallon during the evaluation period. This translates 

4
into a fuel cost per mile 53% higher than the hybrid buses. The fuel cost per mile comparisons 

between CNG and diesel fuel may change considerably during the rest of the evaluation (June 

through September 2005) because of significant fuel price changes during that period. 

Total Maintenance Costs 

Total maintenance costs include mechanic labor at a standardized $50 per hour rate (this is not a 

NYCT mechanic labor rate) and parts, with no warranty costs included. The CNG buses’ 

average total maintenance cost was 8% higher than the hybrid buses during the evaluation 

period. 

It is early in the implementation process of the hybrid and CNG buses and the buses have had 

many repairs covered under warranty. Orion is in the process of completing a significant 

maintenance campaign for the entire Orion VII fleet at NYCT, which is planned to be completed 

by the end of calendar year 2005. 

Propulsion-Related Maintenance Costs

Propulsion-related maintenance costs include repairs for transmission, non-lighting electrical 

(charging, cranking, and ignition), air intake, cooling, exhaust, fuel, engine, and electric 

propulsion. The CNG buses’ average propulsion-related maintenance costs were 9% lower than 

the hybrid buses. A summary of propulsion-related maintenance cost comparisons is shown in 

Table ES-3. 

Table ES-3. Summary of Propulsion-Related Maintenance Cost per Mile Comparisons* 

System Hybrid vs. CNG 

Total Propulsion-related 9% (higher) 

Exhaust 111% (higher) 

Fuel -77% (lower) 

Engine -2% (lower or same) 

Electric Propulsion N/A 

Non-Lighting Electrical -58% (lower) 

Air Intake -38% (lower) 

Cooling -13% (lower) 

Transmission N/A 

* The cost comparisons are provided as hybrid compared to CNG as the baseline. 

((Hybrid cost per mile/CNG cost per mile) – 1) * 100% = Percent comparison 

For example, the total propulsion related entry is 9% higher, this is hybrid costs 

being 9% higher than CNG for this category. 

In this report, a roadcall (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. MBRC is the typical measure for RC performance for transit buses. NYCT 

expects transit buses to meet or exceed a rate of 4,000 MBRC for all RCs. The CNG buses had a 

rate around 5,000 MBRC compared to the diesel baseline group, which had around 2,000 

MBRC. The hybrid buses had a rate around 7,000 MBRC, and the diesel baseline group had 

around 5,000 MBRC. The diesel baseline group at West Farms is well below the NYCT 

expectations; the CNG buses and diesel baseline group at Mother Clara Hale Depot are both just 

5
above the NYCT expectations; the hybrid bus group is well above the NYCT expectations for 

MBRC. 

For RCs related only to the propulsion system, the MBRC rates are lowest for the diesel baseline 

group at West Farms at 5,000 MBRC. The CNG buses are next at around 8,000 MBRC. At just 

above 10,000 MBRC, the hybrid and diesel baseline buses have similar MBRC rates for the 

propulsion system. 

What’s Next? 

This interim evaluation report represents eight out of 12 months of evaluation planned for the 

CNG and hybrid buses (from the order of 125). The final results of these two study groups will 

be complete with data through September 2005 and should be reported in early calendar year 

2006. 

DOE/NREL also planned to evaluate hybrid buses from the order of 200 operating at 

Manhattanville Depot. Results from that evaluation will be presented separately. 

NYCT has recently announced an additional order of Orion/BAE Systems hybrid buses with 

deliveries of 216 hybrid buses for NYCT and 284 hybrid buses for MTA Buses. The price for 

these hybrid buses was reported to be a little less than $500,000 each, which is reportedly about 

$150,000 more than a new standard clean diesel bus. 

6
Overview 

This report includes results of an evaluation of the operation of new compressed natural gas 

(CNG) and diesel hybrid electric buses from Orion Bus Industries (model Orion VII buses) 

operating at New York City Transit (NYCT). This evaluation 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 with an established and documented evaluation protocol1. 

DOE/NREL evaluated the original 10 prototype diesel hybrid buses 

from Orion and BAE Systems and operated at NYCT (model Orion VI 

buses). Results from that evaluation2 were published in July 2002 and 

provided information on the prototype buses from 1998 through 2001. 

NYCT worked with Orion and BAE Systems to develop, implement, 

and test hybrid propulsion buses in an attempt to reduce emissions and 

operating costs and increase fuel economy. 

NYCT’s Clean Bus Program was created in 1992 to lower bus fleet 

emissions. In 2000, NYCT established a policy of only purchasing low 

emission buses for new bus orders. This policy, coupled with NYCT’s 

desire to achieve the best fuel economy, has resulted in NYCT’s recent purchase order for hybrid 

buses. The NYCT Clean Bus Program currently includes several activities: 

• Use of CNG buses 

• Replacement of the oldest diesel engines (two-stroke) with newer low emissions engines 

(Detroit Diesel Series 50 exhaust gas recirculation engines) 

• Use of ultra low sulfur diesel fuel for all diesel equipment (starting in 1998 with less than 

30 parts per million (ppm) sulfur, expected to be less than 15 ppm starting in 2006) 

• Addition of diesel particulate filters (DPF) to the existing and new diesel engines 

• Use of hybrid propulsion buses with engines equipped with DPFs 

Hybrid technology has generally been tested at NYCT in an effort to explore options other than 

CNG technology. This is because not all of NYCT’s operating depots are cost-effective 

candidates for CNG infrastructure due to space constraints inside buildings and the proximity of 

neighboring buildings. In early 2000, NYCT ordered 260 CNG buses in two orders from Orion 

Bus Industries (order one was 125 buses, order two was 135 buses). At the same time, NYCT 

made a commitment to purchase two orders of buses with the BAE Systems hybrid propulsion 

system from Orion Bus Industries. One order was for 125 buses, the other for 200 buses. 

 

1

 General Evaluation Plan, Fleet Test & Evaluation Projects, July 2002, NREL, NREL/BR-540-32392, 

www.nrel.gov/vehiclesandfuels/fleettest/pdfs/32392.pdf. 2

 NYCT Diesel Hybrid-Electric Buses, July 2002, NREL, NREL/BR-540-32427 

www.eere.energy.gov/afdc/pdfs/nyct_diesel_hybrid_final.pdf. 

7
Once NYCT made its commitment to purchase new CNG and hybrid buses, DOE and NREL 

started planning the next phase of evaluation work, which is reported here. The current 

DOE/NREL evaluation work is a part of DOE’s Advanced Vehicle Testing Activity (AVTA). 

The evaluation planned with NYCT is three-fold: 

• Study 10 hybrid buses from the order of 125 buses (and diesel baseline buses) 

• Study 10 CNG buses from the combined order of 260 buses (and diesel baseline buses) 

• Study 10 hybrid buses from the order of 200 buses (and diesel baseline buses) 

This evaluation report examines early evaluation results from 10 buses from the order of 260 of 

CNG Orion VII buses and 10 buses from the first hybrid order of 125 hybrid buses. The 

DOE/NREL evaluation of the hybrid and CNG buses is two-thirds of the way through the 

standard 12-month evaluation. Reporting for the full 12-month evaluation will be completed in 

2006. Evaluation of the order of 200 hybrid buses is also under way and will be reported in a 

future evaluation report. 

Advanced Vehicle Testing Activity 

The role of AVTA is to bridge the gap between research and development (R&D) and 

commercial availability of advanced vehicle technologies that reduce U.S. petroleum use while 

improving air quality. AVTA supports DOE’s FreedomCAR & Vehicle Technologies Program 

in moving these technologies from R&D to market deployment by examining market factors and 

customer requirements, evaluating performance and durability of alternative fuel and advanced 

technology vehicles, and assessing the performance of these vehicles in fleet applications. 

The main objective of AVTA projects is to provide comprehensive, unbiased evaluations of 

advanced technologies. Data collected and analyzed include the operation, maintenance, 

performance, safety, 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. 

The NREL evaluation team, which is composed of NREL and Battelle personnel, conducts 

AVTA medium- and heavy-duty vehicle evaluations. Hybrid electric and CNG transit buses are a 

few of the advanced vehicle choices available today. The evaluation team has conducted or is in 

the process of conducting several evaluations of advanced propulsion vehicles (Table 1). For 

information on other evaluations, visit www.nrel.gov/vehiclesandfuels/fleettest. 

8
Table 1. AVTA Heavy Vehicle Evaluations 

Fleet Location Vehicle Technology Evaluation Status 

Norcal San Francisco, CA Peterbilt/378, Class 

8 truck 

Cummins Westport ISXG 

high pressure direct injection 

LNG and diesel 

Complete and reported 

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

MicroTurbineTM (diesel) 

Complete, reporting in 

process 

Knoxville 

Area Transit Knoxville, TN Ebus 22-ft bus Series hybrid, Capstone MicroTurbineTM (propane) 

Complete, reporting in 

process 

King County 

Metro Seattle, WA 

New Flyer 60-ft 

articulated transit 

bus 

Parallel hybrid, GM-Allison 

EP

50 SystemTM (diesel) In progress 

New York 

City Transit 

Manhattan, 

Brooklyn, Bronx, 

Queens, NY 

Orion VII 40-ft 

transit bus 

Series hybrid, BAE Systems

HybriDrive® propulsion 

system (diesel), two 

generations; DDC S50G 

CNG engines 

In progress and interim 

results reported here 

Host Site Profile—NYCT 

NYCT is a part of the Metropolitan Transportation Authority (MTA), which is a public-benefit 

corporation chartered by New York State in 1965 (www.nyct.org/index.html). In 2004, MTA 

had an annual operating budget of $8 billion and serviced 7.7 million passengers daily through 

the operation of the seven major operating divisions: 

• New York City Transit (NYCT)—The largest division of MTA and the largest rail and 

transit bus agency in North America, NYCT serves the five boroughs (Manhattan, Bronx, 

Queens, Brooklyn, and Staten Island). 

• Long Island Rail Road (LIRR)—The largest commuter railroad in the U.S., LIRR 

operates from New York City across Long Island. 

• Long Island Bus (LI Bus)—LI Bus provides transit service in Long Island and connects 

to the LIRR and New York City. 

• Metro-North Railroad—The second largest commuter railroad in the U.S., the MetroNorth Railroad operates in New York City; Westchester, Putnam, Dutchess, Orange, and 

Rockland counties in New York and Connecticut. 

• Bridges and Tunnels—This division services and maintains the bridges and tunnels, 

including toll collection, in the New York City area. 

• Capital Construction Company—This division was formed in July 2003 to manage major 

capital expansion projects within the MTA. 

• MTA Bus—This division was created in September 2004 to consolidate the seven bus 

companies operating in New York City under franchises granted by the New York City 

Department of Transportation. 

This report focuses on the bus operations within NYCT, which operates 27 rail lines (660 track 

miles and 6,210 rail cars) and 244 bus routes (2,017 miles) with average weekday ridership of 7 

million, or more than 2 billion passengers a year. The NYCT Department of Buses operates 

4,483 buses from the following 18 operating depots in New York City. 

9
Bronx 

• West Farms 

• Gun Hill 

• Kingsbridge 

Manhattan 

• 126th Street 

• Mother Clara Hale 

• 100th Street 

• Manhattanville 

• M.J. Quill 

Staten Island 

• Castleton 

• Yukon 

Brooklyn 

• Jackie Gleason 

• East New York 

• Flatbush 

• Fresh Pond 

• Ulmer Park 

Queens 

• Jamaica 

• Queens Village 

• Casey Stengel 

This evaluation focuses on the West Farms depot in the Bronx and Mother Clara Hale depot in 

Manhattan. Other depots, including Jackie Gleason, Queens Village, Fresh Pond, and 

Manhattanville, were also involved in the activities described in this report. 

Emissions Reductions Drive the Need for CNG and Hybrid Propulsion 

The U.S. transit market, including NYCT, has been under public pressure to reduce emissions in 

large transit buses—especially those in urban areas. Since the early 1990s, emissions regulations 

have focused significant reductions of particulate matter (PM) and oxides of nitrogen (NOx) on 

heavy diesel engines. As shown in Table 2, transit bus applications have been specifically 

targeted. In the late 1990s, CNG transit bus propulsion technology emerged as the cleanest 

available emissions option for transit agencies. However, significant start-up costs and capital 

investments required to successfully operate CNG buses have kept many transit agencies looking 

for other options. Hybrid technology has created significant interest as that possible alternative. 

Diesel bus propulsion technology has also made emissions reduction improvements and is 

required to become much cleaner in the next few years. PM levels have been restricted to a low 

level of 0.05 g/bhp-hr since 1996. This level of PM has been addressed by changes in control of 

engine combustion, and, in some cases, a diesel oxidation catalyst (DOC) was added. 

Political pressure at local levels continues to lower fleet PM levels. Extremely low levels of PM 

have been achieved using a passive regenerative diesel particulate filter (DPF) in conjunction 

with ultra low sulfur diesel (ULSD) fuel. ULSD is defined to be diesel fuel with a sulfur content 

less than 15 ppm. The sulfur content of the diesel fuel must be low to keep the DPF’s catalyst 

working properly. Many transit agencies are using DPFs and ULSD for new buses and as 

retrofits to older diesel engines to minimize fleet PM levels. By the end of 2006, nearly all diesel 

fuel for on-road applications is required to be ULSD. The PM level is planned to be restricted for 

10
all on-road diesel vehicles to 0.01 g/bhp-hr starting in 2007, and DPF technology has been 

proven to reliably address this PM level3

. 

Table 2. EPA Emissions Requirements for Transit Buses 

Carbon 

Monoxide (CO) 

Hydrocarbons 

(HC) Model NOx PM 

Years g/bhp-hr g/bhp-hr g/bhp-hr g/bhp-hr 

1990 15.5 1.3 6.0 0.60 

1991-1992 15.5 1.3 5.0 0.25 

1993 15.5 1.3 5.0 0.10 

1994-1995 15.5 1.3 5.0 0.07 

1996-1997 15.5 1.3 5.0 0.05 

1998-2003 15.5 1.3 4.0 0.05 

2004-2006* 15.5 

2.4 combined or 2.5 with a limit 

of 0.5 for non-methane 

hydrocarbons 

0.05 

2007-2010 15.5 0.14** 0.2 0.01 

* The 2004 standard was moved up to 2002 as part of an agreement between the U.S. Environmental Protection 

Agency (EPA) and engine manufacturers. 

** Non-methane hydrocarbons (NMHC) 

NOx levels were reduced from 4.0 g/bhp-hr in 1998 to 2.4 g/bhp-hr combined NOx and HC in 

2004 (CNG levels are 2.5 g/bhp-hr NMHC + NOx with a limit of 0.5 g/bhp-hr NMHC). The 

2004 level was actually moved up to 2002 based on an agreement between EPA and diesel 

engine manufacturers. The emissions reduction down to 2.4 g/bhp-hr HC + NOx caused several 

diesel engine manufacturers to use EGR to help reduce NOx levels. The use of EGR has been 

reported in some locations to result in significant soot in the engine oil, caused major 

maintenance problems when combined with the use of DPF technology, and has been reported to 

have had some negative impact on fuel economy. 

NOx certification levels are to be lowered to 0.2 g/bhp-hr by 2010 with a phase-in period from 

2007 through 2009. During the phase in period, only half of the new engines (of a particular 

engine family) need to meet the 0.2 g/bhp-hr NOx level or all of the engines (of that particular 

family) must have NOx emissions levels less than 1.2 g/bhp-hr (or half the current standard). 

Most heavy diesel engine manufacturers are choosing the latter option (all engines in a family 

meeting the 1.2 g/bhp-hr NOx) during the phase-in period. The PM level is to be 0.01 g/bhp-hr 

regardless of the NOx reduction strategy. At the same time, the HC level is also being restricted 

down to 0.14 g/bhp-hr (or NMHC for natural gas) with a phase-in similar to NOx. For more 

details on this topic, see EPA’s latest public report, Highway Diesel Progress Review Report 2, 

March 2004, EPA420-R-04-004. 

For the 2010 model year and beyond, the heavy diesel engine manufacturers are exploring 

selective catalytic reduction (SCR) and NOx adsorber technologies to keep NOx emissions at 

these extremely low levels. These emissions control technologies require low sulfur levels in the 

diesel fuel for the catalysts to work effectively. These emissions reductions are expected to come 

 

3

 Emissions Reductions and Operational Experiences with Heavy-Duty Diesel Fleet Vehicles Retrofitted with 

Continuously Regenerated Diesel Particulate Filters in Southern California, 2001, SAE International, 2001-01-0512. 

11
with significant fuel economy penalties that have not yet been reported. CNG propulsion has 

already achieved the 2007 emissions certification level for NOx at 1.2 g/bhp-hr and CNG engine 

manufacturers are working to meet the 2010 certification levels early. Both Cummins and Deere 

have reported the availability of 0.2 g/bhp-hr NOx levels in their heavy natural gas engines by 

2006. 

The development of diesel hybrid bus propulsion systems is exciting for people in the transit 

industry because the systems offer improved fuel economy during a time of fuel economy 

penalties for emissions control. These systems also offer the promise of a clean propulsion 

alternative to CNG. Many transit agencies are concerned about the cost of converting a facility to 

support CNG bus operations, and are therefore, much more comfortable sticking with diesel 

fueled vehicles. 

One issue yet to be resolved for hybrid propulsion in transit is the lack of emissions reduction 

recognition by EPA. A hybrid propulsion system can significantly reduce the overall emissions 

of the vehicle simply by increasing the fuel economy. Currently, a diesel engine is certified as a 

stand-alone engine and not as part of a hybrid system. Therefore, there is no recognition of the 

emissions reduction of a hybrid propulsion system. The benefit is that the engine will be certified 

to the current emissions standard, and the bus will operate at a lower emissions level. The 

downside is that there is no way for the transit agency to get credit for the emissions reduction 

because of the hybrid propulsion system. The California Air Resources Board (CARB) has 

recognized this savings and provided hybrid bus propulsion systems with a 25% blanket 

reduction in emissions that can be used in the state implementation plan for emissions 

reductions. Currently, EPA does not recognize this benefit. 

Additional benefits gained from CNG and hybrid propulsion systems in transit applications are 

reductions in petroleum use and increased fuel economy (for hybrid propulsion). 

Project Design and Data Collection 

AVTA evaluation projects focus on using a standardized process for data collection and analysis, 

communicating results clearly, and providing an accurate and complete evaluation. The 

evaluation in this report uses diesel baseline buses operating at the CNG and hybrid depots for 

bus usage, fuel economy, and roadcall rate comparisons, but not for maintenance costs. The 

much older diesel bus maintenance costs represent maintenance outside of the warranty period 

and both the CNG and hybrid buses have warranty costs expended by the manufacturers or 

NYCT during the evaluation period (as discussed later). This evaluation also uses the CNG 

buses as the baseline for the hybrid buses for all operations and maintenance activities. 

All 40-foot buses at West Farms and Mother Clara Hale Depot were dispatched randomly on all 

routes. There were no restrictions on the CNG or hybrid Orion VII buses at the two depots in 

this evaluation report. 

NYCT expects the new CNG buses to have mature diesel-like reliability and operating costs. The 

CNG buses do not have restrictions other than only operating from the two CNG depots. The 

hybrid buses were expected to be slightly less commercial than the CNG buses due to the lack of 

12
industry experience with hybrid propulsion technology. However, NYCT operated the hybrid 

buses with the intent that they be treated just like any other diesel bus for reliability and 

operations. 

Data for this evaluation were taken from NYCT’s data system, MIDAS. Data parameters 

included the following: 

• Diesel fuel consumption by vehicle 

• CNG fuel consumption by vehicle 

• Mileage data from every vehicle 

• Preventive maintenance action work orders, parts lists, labor records, and related 

documents 

• Records of unscheduled maintenance, including roadcalls and warranty actions by 

vendors (when available in the data system) 

The data collection was designed to cause as little disruption as possible for NYCT. Data were 

sent from NYCT to Battelle electronically for analysis. 

The study design included tracking of safety incidents that affected the vehicles or occurred at 

NYCT facilities. However, no safety incidents were reported during the data collection period. 

Vehicle System Descriptions 

Table 3 shows a summary of vehicle system descriptions for the CNG, hybrid, and two baseline 

diesel study groups of buses. The following discussion includes descriptions of each of the four 

study groups of buses and detailed differences between the CNG and hybrid buses versus their 

respective diesel baseline groups of buses. 

CNG Buses at West Farms 

Ten CNG buses operating at West Farms Depot were selected from the order of 260 Orion VII 

low floor, model year 2002, CNG buses. The CNG buses use the DDC Series 50G engine. 

NYCT did not select the optional catalyst for emissions aftertreatment for these buses. 

Diesel Baseline Buses at West Farms 

Although West Farms Depot is intended to be an all-CNG bus operating depot, some diesel 

buses have been operating at West Farms. The number of diesel buses operating at the depot 

decreased as the newer CNG buses were brought into service. The evaluation in this report used 

10 Orion V high floor diesel buses as a baseline for the CNG bus evaluation of mileage usage, 

fuel economy, and roadcall rate results. 

The diesel buses are model year 1994 and close to the end of their useful life. These diesel buses 

have DDC Series 50 diesel engines. One bus (number 416) had been repowered with a newer 

DDC Series 50 EGR engine as part of a test program. This bus was removed from the evaluation 

due to its significant difference in operation; however, some comments on this vehicle are 

provided in this evaluation. 

13
Table 3. Vehicle System Descriptions 

West Farms Depot Mother Clara Hale Depot Vehicle System CNG Buses Diesel Baseline Hybrid Buses Diesel Baseline 

Number of Buses 10 9 10 9 

Bus Manufacturer and 

Model 

Orion VII, Low 

Floor Orion V, High Floor Orion VII, Low Floor Orion V, High Floor

Model Year 2002 1994 2002 1999 

Length/Width/Height 40 ft/102 in/135 in 40 ft/102 in/121 in 40 ft/102 in/132 in 40 ft/102 in/121 in 

GVWR/Curb Weight 42,540/31,400 lbs 40,000/28,500 lb 42,540/31,840 lb 40,000/28,500 lb 

Passenger Capacity 37 Seated, 

36 Standing 

39 Seated, 

36 Standing 

38 Seated, 

32 Standing 

39 Seated, 

36 Standing 

Engine Manufacturer 

and Model DDC S50G DDC S50 Cummins ISB (not EGR equipped) DDC S50 

Rated Horsepower 275 bhp @ 2,100 

rpm 

275 bhp @ 2,100 

rpm 

270 bhp @ 2,500 

rpm 

275 bhp @ 2,100 

rpm 

Rated Torque 900 lb-ft @ 1,200 

rpm 

890 lb-ft @ 1,200 

rpm 

660 lb-ft @ 1,600 

rpm 

890 lb-ft @ 1,200 

rpm 

Emissions Equipment None Retrofit DPF, 

Johnson Matthey Engelhard DPX Retrofit DPF, Johnson Matthey 

Retarder/Regenerative 

Braking Retarder Retarder Regenerative Braking Retarder 

Fuel Capacity 125 diesel 

equivalent gallons 125 gallons 100 gallons 125 gallons 

Bus Purchase Cost* $313,000 $290,000 $385,000 $290,000 

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

CNG and Diesel Baseline Vehicle Differences 

There are significant differences between the CNG and diesel baseline study groups at West 

Farms. The most important issue is the age difference between the fleets. This matters because 

the maintenance costs increase over time and significantly after five or six years of service life 

because of major repairs to components such as the transmission. Other differences include: 

• The CNG buses are low floor and the diesel buses are high floor. 

• The CNG buses have slightly higher maximum torque than the diesel buses. 

• The diesel buses have a retrofitted DPF installed and the CNG buses have no exhaust 

aftertreatment. 

• The CNG buses are heavier than the diesel buses and this slightly changed the number of 

maximum passengers allowed on the CNG buses versus the diesel buses. 

• The CNG buses were approximately $23,000 more expensive than the diesel buses. 

Hybrid Buses at Mother Clara Hale 

Ten hybrid buses from the order of 125 hybrid buses were selected from the Mother Clara Hale 

Depot. The hybrid buses are Orion VII low floor buses and use a smaller-than-standard diesel 

engine (5.9 liter versus an 8.3 or 8.9 liter engine) from Cummins Engine Company. The hybrid 

buses are equipped with an Engelhard DPXTM for exhaust aftertreatment. This DPF is actively 

monitored and regenerated (as needed) as part of the BAE Systems HybriDrive hybrid 

propulsion system. Table 4 provides descriptions of some of the electric propulsion system. 

14
Table 4. Hybrid Propulsion Systems 

Hybrid Related Systems Hybrid Buses 

Manufacturer/Integrator BAE Systems (HybridDrive® propulsion system) 

Motor and Internal Gear 

Reduction 

Type: AC Induction, high-power density 

Horsepower: 250 hp continuous (320 hp peak) 

Torque: 2,700 lb-ft @ 0 rpm 

Generator Type: Permanent magnet 

Horsepower: 160 hp continuous 

Energy Storage Type: Sealed lead acid, Hawker XT, 2 enclosures, 23 

modules each, roof mounted 

Voltage: 520-700 VDC 

Diesel Baseline Buses at Mother Clara Hale 

The diesel buses at Mother Clara Hale depot are Orion V high floor buses, but from a newer bus 

order than those at West Farms, model year 1999. The diesel buses have DDC Series 50 diesel 

engines retrofitted with a DPF. These diesel buses are approaching their six to eight year rebuild 

and two of the ten diesel baseline buses have had the rebuild. One of those buses selected for this 

study (number 6014) was essentially out of service for four of the 12 month study period. This 

vehicle has been removed from the evaluation because of this lack of usage. 

Hybrid and Diesel Baseline Vehicle Differences 

The diesel buses are a few model years older than the hybrid buses. Although the hybrid buses 

are of model year 2002 configuration, they did not go into service until 2004. The diesel buses 

are high floor and the hybrid buses are low floor. The engines in the buses are also different. The 

hybrid buses have a Cummins ISB engine and the diesel buses have a DDC Series 50 engine. 

The Cummins engine is smaller and has significantly lower peak torque. The hybrid engine is 

intended to be rebuilt at five years of service and then replaced at eight or nine years of service. 

The hybrid buses have regenerative braking and a slightly smaller diesel fuel tank. The hybrid 

buses also cost about $95,000 more than the baseline diesel buses. The next order of hybrid 

buses in NYCT had a hybrid cost approximately $150,000 more than what a “new” standard 

diesel bus might cost. 

DDC Series 50 Diesel and CNG Engine 

In 2004, DDC discontinued the Series 50 diesel and CNG engine platform. For years, the diesel 

Series 50 engine has been the workhorse of the transit industry. DDC reported to customers that 

the Series 50 diesel engine platform could not meet the next round of emissions regulations and 

was being discontinued in preference to Mercedes Benz engines provided by DDC’s parent 

company, DaimlerChrysler AG. With the removal of the Series 50 engine product, DDC 

essentially gave the U.S. transit market for 40-foot buses to Cummins and Caterpillar (and Deere 

Power Systems for CNG buses). 

15
CNG Transit Bus Propulsion 

Although the DDC natural gas engine was removed from the transit market, Cummins Westport 

Inc. and John Deere offer transit bus engine options for natural gas propulsion. Both 

manufacturers recently announced intentions to have standard-size, transit-bus, natural gas 

engines that meet the 2010 emissions certification levels available in model year 2006. 

Cummins Westport is a joint venture between Cummins Engine Company and Westport 

Innovations. It has three main natural gas engine platforms: 

• B Gas Plus (5.9 L)—Horsepower: 195, 200, 230; torque: 420, 465, 500 lb-ft 

• C Gas Plus (8.3 L)—Horsepower: 250, 275, 280; torque: 660, 750, 850 lb-ft 

• L Gas Plus (8.9 L)—Horsepower: 320, torque:1000 lb-ft 

John Deere has one commercial natural gas engine product (6081H), which has the following 

settings: 

• 6081H (8.1 L)—Horsepower: 250, 275, 280; torque: 735, 800, 900 lb-ft 

Both these natural gas engine manufacturers are working to make a life-cycle cost advantage for 

natural gas fuel use compared to equivalent diesel fuel use and diesel fuel costs. 

BAE Systems HybriDrive Propulsion System 

NYCT’s hybrid buses are built by Orion Bus Industries (a part of DaimlerChrysler Commercial 

Buses North America) and use the BAE Systems HybriDrive propulsion system (Figure 1). 

In this series hybrid electric system, a relatively small diesel engine running at an optimal 

controlled speed is connected to a generator that produces electricity for the electric drive motor 

and batteries. The electric motor drives the vehicle and acts as a generator to capture energy 

during regenerative braking. The batteries supply additional power during acceleration and hill 

climbing and store energy recovered during regenerative braking and idling. The battery 

optimization subsystem monitors and maintains the charge of each individual battery. The 

propulsion control subsystem manages the entire system and optimizes performance for 

emissions, fuel economy, and power. 

16
A: A 5.9-liter diesel engine runs at an optimal controlled speed 

and is connected to a generator to produce electrical power 

for the drive motor and batteries. 

B: The electric motor drives the vehicle and acts as a generator 

to capture energy during braking. 

C: The batteries supply power during acceleration and hill 

climbing and store energy recovered during regenerative 

braking. 

D: The propulsion control system manages the entire system 

and optimizes performance for emissions, fuel economy, and 

power. 

Figure 1. BAE Systems HybriDrive Propulsion System 

17
NYCT Facilities 

NYCT has two CNG operating depots—Jackie Gleason Depot in Brooklyn and West Farms 

Depot in the Bronx. The newly built West Farms CNG depot, shown in Figure 2, opened on 

September 7, 2003. An older depot, Coliseum Depot, was originally located where West Farms 

is now. West Farms has 157,000 square feet of office and maintenance space, outdoor parking 

for buses, and operates 256 buses including 163 CNG buses. 

CNG fueling is provided under contract from Trillium USA and is integrated into the fueling 

island as shown in Figure 3. The CNG compressor station is outside the building (Figure 4) and 

includes three 800-horsepower compressors with a total output of 6,600 scfm. The capital cost 

for the facility was $7.4 million including $2 million for construction costs to blast through solid 

rock to install the underground natural gas lines. The current cost for compression and upkeep 

for the CNG station is $0.24 per therm or $0.32 per diesel equivalent gallon (in addition to the 

base natural gas commodity price). 

Figure 2. West Farms Depot 

Figure 3. CNG Fuel Lanes at West Farms Depot 

18
Figure 4. CNG Compression Station at West Farms Depot 

The order of 125 hybrid buses was split between two operating depots—Mother Clara Hale 

Depot and Queens Village Depot. The Mother Clara Hale Depot, shown in Figure 5, has 125,690 

square feet of office and maintenance space, indoor parking for buses, and operates 125 buses 

including 62 hybrids. Every six months, the hybrid buses require a conditioning charge process 

for the traction batteries (which takes as much as 24 hours) as part of their scheduled 

maintenance routine. The conditioning is done to help extend the battery pack life to at least 

three years. The conditioning charger is shown in Figure 6. The cost of each charger unit is 

$70,000. The depots with the Orion/BAE System hybrid propulsion system are planned to 

receive at least two of the conditioner units. 

Figure 5. Mother Clara Hale Depot 

19
Figure 6. Hybrid Traction Battery Conditioning Unit 

Implementation Experience 

The discussion in this section is based on overall fleet level results of mileage accumulation and 

roadcalls (RCs) for the CNG and hybrid bus fleets—260 CNG buses and 125 hybrid buses. 

NYCT has treated both of these fleets as standard buses for service. The depots have not been 

given special treatment for meeting pullout requirements for service. 

For each study group (CNG and hybrid), several topics are covered. They include: 

• Background on NYCT expectations 

• Bus delivery 

• Total mileage accumulation from March 2003 through May 2005 for CNG and March 

2004 through May 2005 for hybrid 

• Average monthly mileage per bus 

• Miles between roadcalls (MBRC) for all RCs and for propulsion-related only 

• Fleet issues and warranty maintenance campaigns 

NYCT has three standard expectations and measures for transit bus operations. They are 

availability, reliability, and recovery time. 

• Availability—This measure, which should be 85% or above, allows for scheduled and 

some unscheduled maintenance for the bus. Buses that fall below the 85% availability 

can cause problems with having enough buses to make service. 

• Reliability—The measure should be above 4,000 MBRC for all RCs. 

• Recovery time—Buses should not be out of service for more than three days for any 

maintenance action (or anything else). 

20
Of these three topics, reliability (MBRC) is the only one covered in this report. Availability and 

recovery time were not available for this study, but are implied in bus usage levels. 

CNG Buses 

NYCT has 481 CNG buses split between the West Farms and Jackie Gleason depots. The 

addition of significantly more CNG buses would require another depot to be converted to CNG 

fueling and maintenance operations. The cost of this conversion was estimated to be higher than 

NYCT is willing to pay as long as diesel hybrid buses are a viable option in purchase and 

operations costs. 

NYCT was an early adopter of CNG transit buses. In 1995, it purchased 34 CNG buses; this 

number grew to 221 by 2001. These CNG buses were operating at Jackie Gleason Depot. As 

mentioned earlier, NYCT purchased 260 new CNG Orion VII buses. There were some delays in 

delivery of these buses due to Orion’s delays in meeting NYCT’s rigorous structural 

qualification requirements. 

The 260 CNG Orion VII buses were delivered and placed into service from March 2003 through 

approximately November 2004. Jackie Gleason Depot started its first new CNG bus in service in 

March 2003; West Farms Depot started its first new CNG bus in service in September 2003. 

Figure 7 shows total mileage accumulation at the two CNG bus depots. At the end of May 2005, 

the total Orion VII CNG fleet had reached 9.5 million miles of operation. Figure 8 shows 

average monthly mileage per CNG bus at the two CNG depots. This figure shows that the CNG 

buses were placed into service quickly and met an average usage per month of 2,300 to 2,500 

miles per month. 

0

1,000,000

2,000,000

3,000,000

4,000,000

5,000,000

6,000,000

7,000,000

8,000,000

9,000,000

10,000,000

Mar03May03Jul03Sep03Nov03Jan04Mar04May04Jul04Sep04Nov04Jan05Mar05May05

Total Miles

Jackie Gleason Depot West Farms Depot Total Mileage

Figure 7. CNG Bus Fleet Cumulative Mileage 

21
0

500

1000

1500

2000

2500

3000

Mar-03 Jun-03 Sep-03 Dec-03 Mar-04 Jun-04 Sep-04 Dec-04 Mar-05

Average Monthly Miles/Bus

Jackie Gleason West Farms

Figure 8. CNG Bus Fleet Cumulative Average Monthly Mileage per Bus 

Figure 9 shows MBRC for CNG buses at both CNG bus depots. The figure shows that for all 

RCs, the Gleason Depot CNG buses were at or above 4,000 MBRC (as expected/required by 

NYCT) by April 2004; West Farms achieved this in December 2004. The propulsion-related 

MBRC for both depots settled around 7,000 MBRC. The most common RCs for the propulsion 

system were related to the engine, no start, electrical shutdown, or problem indicator lights. 

General problems at start-up or within the first year or so of operation were mostly related to the 

Orion VII bus, rather than the propulsion system, such as axle bolts coming loose and cooling 

pump failures. Items specific to the CNG bus fleet included: 

• CNG engines were burning excessive amounts of oil—determined to be an engineering 

and design issue; cylinder kits and sleeves in the process of being changed out 

• Spark plugs were initially a reliability issue (5,000 miles between changes)—changed to 

a different spark plug; now getting the required 24,000 miles between changes 

• Fuel door switches; being changed out 

• Hydraulic cooling fan motor; changing configuration and motors 

• Had regulator problems; now resolved 

22
0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

9,000

10,000

Nov-03 Feb-04 May-04 Aug-04 Nov-04 Feb-05 May-05

Miles Between Roadcalls (MBRC)

Gleason Total MBRC Gleason Propulsion MBRC

West Farms Total MBRC West Farms Propulsion MBRC

Figure 9. CNG Bus Fleet Cumulative Average MBRC 

Hybrid Buses 

NYCT started operating prototype diesel hybrid buses from Orion and BAE Systems in 1998 

with the first of 10 prototype buses. This prototype operation led to a large purchase of hybrid 

buses to solidify commitment from NYCT and the manufacturers (Orion and BAE Systems). The 

new orders of 125 hybrid buses and 200 hybrid buses have now been delivered to NYCT. The 

order of 125 hybrid buses has been split between two NYCT operating depots—Mother Clara 

Hale and Queens Village. The order of 200 hybrid buses has been split between another two 

NYCT operating depots—Fresh Pond and Manhattanville (operating location for the original 10 

prototype hybrid buses). 

The delivery of the hybrid buses was delayed due to the acceptance of the CNG bus order 

(mostly for issues with NYCT purchasing a new platform vehicle, the Orion VII). The hybrid 

bus order of 125 buses was placed into service from March 2004 through December 2004. The 

first new hybrid bus was placed into service at Mother Clara Hale Depot in March 2004 and the 

first new hybrid bus was placed into service at Queens Village Depot in November 2004. 

Figure 10 shows total mileage accumulation at these two hybrid bus depots and a total. At the 

end of May 2005, the hybrid fleet had reached 2.6 million miles of operation. Figure 11 shows 

average monthly mileage per hybrid bus at the two hybrid depots. This figure shows that the 

hybrid buses were placed into service quickly and came up to the average usage of 2,400 miles 

per month for Mother Clara Hale and approximately 3,000 miles per month for Queens Village. 

23
0

500,000

1,000,000

1,500,000

2,000,000

2,500,000

3,000,000

Mar-04 May-04 Jul-04 Sep-04 Nov-04 Jan-05 Mar-05 May-05

Total Miles

Mother Clara Hale Queens Village Cumulative Mileage

Figure 10. Hybrid Fleet Cumulative Mileage 

0

500

1000

1500

2000

2500

3000

3500

Mar-04 May-04 Jul-04 Sep-04 Nov-04 Jan-05 Mar-05 May-05

Average Monthly Miles/Bus

Mother Clara Hale Queens Village

Figure 11. Hybrid Fleet Cumulative Average Monthly Mileage per Bus 

Figure 12 shows MBRC for hybrid buses at the two hybrid bus depots. The figure shows that for 

all RCs, the Mother Clara Hale depot hybrid buses were at or above 4,000 MBRC (as 

expected/required by NYCT) by October 2004; the buses at Queens Village achieved this in 

December 2004. The propulsion-related MBRC for Mother Clara Hale is above 6,000 and 

24
Queens Village is approaching an MBRC of 10,000. The propulsion-related MBRC for both 

depots jumped in December 2004 (this is not as noticeable for Mother Clara Hale because of the 

longer data period prior to the change). The most common RCs for the propulsion system were 

related to the engine and the hybrid control system shutdown or problem indicator lights. Many 

of the shutdown indicators for the hybrid propulsion system did not necessarily mean there was a 

repair required for the propulsion system. Problems in other systems can also be indicated by the 

propulsion control system. 

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

9,000

10,000

Apr-04 Jun-04 Aug-04 Oct-04 Dec-04 Feb-05 Apr-05

Miles Between Roadcalls (MBRC)

MCH Total MBRC MCH Propulsion MBRC

QV Total MBRC QV Propulsion MBRC

Figure 12. Hybrid Fleet Cumulative Average MBRC 

Specific maintenance items that have been worked on the hybrid buses have been: 

• Radiator baffle—surge tank overflowing 

• Water in wiring/connectors 

• Engine grid heater relay 

• Water in engine from air intake 

• Issues with the triple pump 

• Power control system (PCS) internal coolant leaks; some modification to the cooling 

system was done. 

• Software upgrades; moved some of the propulsion fault codes from the dash display to be 

on the engine compartment display; changed signal processing to be more tolerant of 

wiring intermittent signals. 

The entire Orion VII fleet (CNG and hybrid) is currently undergoing a warranty maintenance 

campaign to address the items listed above for both groups. This is a significant fleet campaign 

that is planned to be completed by the end of 2005. 

25
Evaluation Results 

In any evaluation, a starting point must be chosen. In the DOE/NREL evaluations, this starting 

point is typically called a “clean point.” The clean point is chosen to avoid some of the early and 

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

maintenance campaigns. In some cases, the clean point may require three to six months of 

operation before the evaluation can start. 

October 1, 2004 has been used as the start date for the evaluation at West Farms and Mother 

Clara Hale depots; however, this is not a clean point. As mentioned earlier, Orion has agreed to 

a significant campaign of the entire Orion VII fleet at NYCT (hybrid and CNG) to be completed 

at the end of 2005. The entire evaluation of the hybrid order of 125 and the CNG buses will be 

complete before that major campaign will be complete. The results and impact of this campaign 

is intended to be captured during the evaluation of the order of 200 hybrid buses. 

This report provides results from an eight-month evaluation period for the CNG and hybrid buses 

that ended in May 2005. The evaluation of the CNG and first order of hybrid buses will be 

complete when data through September 30, 2005, is collected, evaluated, and published in a later 

report. The start date was chosen to remove a fueling data collection problem at the fueling 

stations at both depots during the summer of 2004. The two study groups of older diesel baseline 

buses were evaluated during a 12-month period of June 1, 2004 to May 31, 2005. The diesel 

buses were being transferred out of the two study depots due to the addition of the new CNG and 

hybrid buses, so the evaluation period of the diesel baselines was selected to start a little earlier 

than the two study bus groups (CNG and hybrid). 

Route Descriptions 

West Farms Depot operates 40-foot buses on 11 to 13 Bronx routes. Buses at West Farms are 

randomly dispatched on all routes, and there are no route assignment restrictions for the CNG 

buses. As shown in Table 5, bus operations from West Farms for 40-foot standard buses had an 

overall average speed of 6.47 mph in 2004 and 6.33 mph in 2005. 

Table 5. Average Speed for All Standard Buses (40-foot) at West Farms 

Year Day of Week Miles/Day Hours Avg. Speed 

2004 Weekday 18,825.29 2,939.1 6.41 

Saturday 15,416.50 2,359.2 6.53 

Sunday 12,947.86 1,869.3 6.93 

Total 122,490.81 18,923.7 6.47 

2005 Weekday 18,522.74 2,962.4 6.25 

Saturday 14,902.57 2,319.1 6.43 

Sunday 12,499.17 1,832.2 6.82 

Total 120,015.44 18,963.3 6.33 

Mother Clara Hale Depot operates 40-foot buses on two Bronx routes and five Manhattan 

Routes. Buses at the depot are randomly dispatched on all routes, and there are no route 

26
assignment restrictions for the hybrid buses. As shown in Table 6, bus operations from Mother 

Clara Hale Depot for 40-foot standard buses had an overall average speed of 6.52 mph in 2004 

and 6.13 mph in 2005 (this reduction in average speed was the result of a high-speed route being 

moved to another depot). 

Both depots showed a general downward trend in average speed from 2004 to 2005. Much of 

these decreases in average speed are likely caused by an increase in congestion on the routes and 

some changes in NYCT’s bus scheduling. Average speeds for the West Farms and Mother Clara 

Hale depots appear to be similar and comparable. Total mileage differences are caused by the 

number of buses assigned to the depots (250 buses at West Farms and 125 buses at Mother Clara 

Hale). 

Table 6. Average Speed for All Standard Buses (40-foot) at Mother Clara Hale 

Year Day of Week Miles/Day Hours Avg. Speed 

2004 Weekday 9,722.27 1,542.4 6.30 

Saturday 8,329.96 1,180.1 7.06 

Sunday 7,201.13 951.8 7.57 

Total 64,142.44 9,843.9 6.52 

2005 Weekday 8,472.37 1,418.1 5.97 

Saturday 6,760.61 1,031.0 6.56 

Sunday 5,501.83 790.2 6.96 

Total 54,624.29 8,911.7 6.13 

Bus Use 

Bus use is intended as an indicator of reliability and availability for bus service. The lack of bus 

usage may be an indication of downtime for maintenance or purposeful reduction of planned 

work for the buses. 

Table 7 shows average monthly mileage per bus for the evaluation period for the diesel and CNG 

buses at West Farms. Figure 13 shows cumulative average monthly miles per bus. The CNG 

buses had an average of 2,244 miles per bus and the diesel buses had an average of 1,952 miles 

per bus. The evaluation period for the CNG buses was eight months; the diesel bus evaluation 

period was 12 months. However, most of the diesel buses have fewer than 12 months used 

because of in-chassis rebuilds of the engines. The usage of the CNG buses was significantly 

higher (overall 15% higher) than the diesel buses during most of the evaluation period. This 

occurred because of the age of the diesel buses and the cost of operation. NYCT tends to operate 

the more cost effective buses, which are typically the newer ones. 

Table 8 shows average monthly mileage per bus for the diesel and hybrid buses at Mother Clara 

Hale Depot. Figure 14 shows the average monthly miles per bus for the hybrid and diesel buses. 

The hybrid buses showed an average of 2,461 miles per bus; the diesel buses had an average of 

2,385 miles per bus. By the end of the evaluation period shown, these two fleets were being used 

at essentially the same rate. 

The CNG and hybrid buses also have similar usage rates with the hybrid bus usage about 10% 

higher than the CNG buses. 

27
Table 7. Monthly Mileage per Bus at West Farms 

Bus Starting 

Hubodometer 

Ending 

Hubodometer Total Mileage Months Monthly 

Average 

403 228,750 247,081 18,331 10 1,833 

407 227,496 248,486 20,990 11 1,908 

408 211,730 233,021 21,291 11 1,936 

412 228,689 247,729 19,040 10 1,904 

413 223,767 242,570 18,803 10 1,880 

428 204,180 226,368 22,188 11 2,017 

438 218,618 240,833 22,215 11 2,020 

448 222,992 247,696 24,704 12 2,059 

450 227,366 251,068 23,702 12 1,975 

Diesel 191,264 98 1,952 

7657 26,249 44,957 18,708 8 2,339 

7662 20,490 39,909 19,419 8 2,427 

7666 23,754 36,841 13,087 8 1,636 

7670 25,240 43,178 17,938 8 2,242 

7677 16,597 34,590 17,993 8 2,249 

7688 13,231 31,747 18,516 8 2,315 

7708 9,772 29,116 19,344 8 2,418 

7715 11,386 29,699 18,313 8 2,289 

7719 10,412 27,895 17,483 8 2,185 

7721 8,454 27,200 18,746 8 2,343 

CNG 179,547 80 2,244 

0

500

1000

1500

2000

2500

3000

3500

Jun-04 Jul-04 Aug04Sep-04 Oct-04 Nov04Dec-04 Jan-05 Feb-05 Mar05Apr05May05

Average Monthly Miles/Bus

Diesel Average Diesel Cumulative Average

CNG Average CNG Cumulative Average

Figure 13. Monthly Mileage per Bus at West Farms Depot 

28
Table 8. Monthly Mileage per Bus at Mother Clara Hale Depot 

Bus Starting 

Hubodometer 

Ending 

Hubodometer Total Mileage Months Monthly 

Average 

6002 143,605 172,184 28,579 12 2,382 

6004 156,587 185,787 29,200 12 2,433 

6005 163,153 193,499 30,346 12 2,529 

6006 160,513 189,600 29,087 12 2,424 

6008 163,845 193,285 29,440 12 2,453 

6011 156,097 183,498 27,401 12 2,283 

6015 159,521 186,976 27,455 12 2,288 

6018 162,137 191,639 29,502 12 2,459 

6020 161,862 188,476 26,614 12 2,218 

Diesel 257,624 108 2,385 

6367 15,224 32,036 16,812 8 2,102 

6368 16,391 33,856 18,465 8 2,308 

6369 14,081 32,626 18,545 8 2,318 

6375 12,063 33,315 21,252 8 2,657 

6378 11,328 31,862 20,534 8 2,567 

6379 8,874 29,327 20,453 8 2,557 

6380 13,320 30,283 16,963 7 2,423 

6381 10,904 30,374 19,470 8 2,434 

6382 12,889 33,932 21,043 8 2,630 

6387 11,260 32,118 20,858 8 2,607 

Hybrid 194,395 79 2,461 

0

500

1000

1500

2000

2500

3000

3500

Jun04Jul-04 Aug04Sep-04 Oct-04 Nov04Dec04Jan-05 Feb05Mar05Apr05May05

Average Monthly Miles/Bus

Diesel Average Diesel Cumulative Average

Hybrid Average Hybrid Cumulative Average

Figure 14. Monthly Mileage at Mother Clara Hale Depot 

29
Fuel Economy and Cost 

NYCT buses use Jet A diesel fuel, which is designated as aircraft fuel. NYCT and other transit 

bus operators in the area use Jet A diesel fuel because of its availability in the city. This fuel 

designation is slightly higher grade than diesel #1. As mentioned earlier, NYCT is using ultra 

low sulfur diesel fuel at less than 30 ppm sulfur content for its Jet A diesel fuel. This sulfur level 

is expected to be less than 15 ppm by 2006. 

CNG fuel is provided at West Farms by a compression station operated and serviced by Trillium 

USA. The CNG study fleet fuel consumption and economy is shown in Table 9 and Figure 15. 

The fuel economy for the CNG buses is shown in diesel gallon equivalent units based on an 

energy conversion of CNG to diesel. The CNG study group has a 25% lower fuel economy than 

the non-EGR diesel buses. Based on the duty cycle at West Farms (average speed between 6.3 

mph and 6.5 mph), this lower fuel economy is within typical expectations based on previous 

studies4. The low average speed of the operation is the key to this significantly lower fuel 

economy. Figure 15 shows the difference between the CNG and diesel study group fuel economy 

is staying generally the same over time. 

The one diesel bus that was removed from the evaluation (bus 416) is listed in the table with a 

fuel economy of 2.04 mpg. This bus had a new DDC Series 50 EGR engine installed in place of 

the original DDC Series 50 engine instead of an in-chassis rebuild. This vehicle showed a fuel 

economy that was consistently 10% lower than the rest of the diesel baseline study group at West 

Farms Depot. 

The hybrid study fleet fuel consumption and economy is shown in Table 10 and Figure 16. The 

fuel economy for the hybrid buses is 45% higher than the non-EGR diesel buses. This higher fuel 

economy for the hybrid buses is expected; however, the data period is only eight months. The 

last four months of the 12-month evaluation period are summer operation in New York, which 

requires significant load for air conditioning, and the heat may inhibit brake regeneration at 

times. As shown for the CNG and diesel baseline groups, the hybrid buses and the baseline diesel 

group have similarly shaped fuel economy curves. The hybrid bus fuel economy has fluctuated 

between 32% and 52% higher than for the diesel buses in the same time frame at Mother Clara 

Hale Depot. 

Using this data between the two study depots, the hybrid buses have fluctuated between 80% and 

120% higher fuel economy than the CNG buses based on diesel equivalent units. 

During the evaluation period, diesel fuel at NYCT was an average of $1.70 per gallon for ultra 

low sulfur diesel fuel with sulfur less than 30 ppm. The diesel fuel cost has gone up significantly 

since the end of the evaluation period for this report (currently $2.26 per gallon in September 

2005). This difference in average diesel fuel cost will be accounted for in the final results report 

for this evaluation at NYCT. 

 

4

 For example, DART’s LNG Bus Fleet, Final Results, 2000, NREL, NREL/BR-540-28739 

(www.nrel.gov/vehiclesandfuels/fleettest/pdfs/28739.pdf) and Alternative Fuel Transit Buses, Final Results,”, 1996, 

NREL, NREL/TP-425-20513 (www.eere.energy.gov/afdc/pdfs/transbus.pdf) 

30
Table 9. Fuel Use and Economy at West Farms 

Bus Mileage 

(Fuel Base) 

Gallons 

Consumed MPG 

403 17,762 7,916.7 2.24 

407 20,542 8,862.5 2.32 

408 21,064 9,195.2 2.29 

412 18,475 8,200.4 2.25 

413 18,473 8,106.6 2.28 

416* 20,488 10,053.7 2.04 

428 21,774 9,744.9 2.23 

438 21,310 9,124.7 2.34 

448 24,269 10,647.1 2.28 

450 23,013 10,221.3 2.25 

Diesel 186,682 82,019.4 2.28 

7657 16,461 9,559.6 1.72 

7662 17,793 9,505.9 1.87 

7666 12,320 7,189.5 1.71 

7670 15,641 9,249.2 1.69 

7677 15,832 9,132.7 1.73 

7688 16,683 9,993.6 1.67 

7708 18,029 11,016.5 1.64 

7715 17,547 10,099.2 1.74 

7719 16,470 10,315.6 1.60 

7721 16,987 9,588.3 1.77 

CNG 163,763 95,650.1 1.71 

* Results for bus 416 are not included in the total. 

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

Jun04Jul-04 Aug04Sep-04 Oct-04 Nov04Dec04Jan-05 Feb05Mar05Apr05May05

Miles per Diesel Gallon (MPG)

Diesel CNG

Figure 15. Average Fuel Economy (MPG) for CNG and Diesel Buses at West Farms Depot 

31
Table 10. Fuel Use and Economy at Mother Clara Hale 

Bus Mileage 

(Fuel Base) 

Gallons 

Consumed MPG 

6002 27,467 11,805.5 2.33 

6004 28,859 11,936.0 2.42 

6005 28,742 11,704.5 2.46 

6006 27,978 12,021.5 2.33 

6008 28,754 11,929.0 2.41 

6011 26,614 11,401.0 2.33 

6015 27,078 11,614.0 2.33 

6018 29,048 11,909.5 2.44 

6020 25,450 10,816.5 2.35 

Diesel 249,990 105,137.5 2.38 

6367 15,707 4,507.5 3.48 

6368 15,545 4,658.0 3.34 

6369 16,611 4,703.0 3.53 

6375 14,057 4,021.5 3.50 

6378 17,811 5,041.0 3.53 

6379 18,464 5,427.5 3.40 

6380 13,782 4,334.0 3.18 

6381 17,843 5,060.4 3.53 

6382 19,100 5,504.5 3.47 

6387 19,107 5,591.5 3.42 

Hybrid 168,027 48,848.9 3.44 

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

Jun04Jul-04 Aug04Sep04Oct04Nov04Dec04Jan05Feb05Mar05Apr05May05

Miles per Gallon (MPG)

Diesel Hybrid

Figure 16. Average Fuel Economy (MPG) for Hybrid and Diesel Buses at Mother Clara Hale Depot 

32
NYCT’s CNG cost is based on two components—the commodity price of the natural gas from 

the pipeline and the Trillium add-on to pay for the station operation. Over the evaluation period, 

this has been $0.96 per therm for the natural gas and $0.24 per therm for Trillium, which results 

in a total cost of $1.32 per therm or $1.78 per diesel equivalent gallon. 

When compared to the diesel baseline study group, the fuel cost per mile for the CNG buses was 

$1.04 per mile for CNG and $0.75 per mile for diesel—39% higher for CNG at West Farms 

Depot. The hybrid buses were 31% lower than their diesel baseline study group at $0.72 per mile 

for diesel and $0.49 per mile for hybrid buses at Mother Clara Hale Depot. Across the depots, the 

CNG buses have a fuel cost per mile 53% higher than the hybrid buses. 

Maintenance Analysis 

The maintenance analysis in this section only includes the CNG and hybrid buses. The diesel 

baseline buses at the two depots are much older and have much higher maintenance costs. The 

CNG and hybrid buses are new enough that they have much of the expensive maintenance done 

under warranty by the manufacturers and their distributor mechanics. When possible, this 

warranty maintenance cost is captured and provided in the report, but is not included in the 

maintenance cost analysis. All of the comparisons in this section are hybrid buses compared to 

CNG buses as the baseline. 

Both the CNG and hybrid buses are similar in age and the maintenance costs have been collected 

in a similar way for each study group. The duty cycle and maintenance practices at West Farms 

and Mother Clara Hale depots are similar and do allow a comparison between the CNG and 

hybrid buses. These buses are the same model (Orion VII) and have been in service about the 

same amount of time. 

For the CNG and hybrid buses, maintenance data were collected from the start of operations. 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 of October 2004 

through May 2005. 

Total Maintenance Costs

Total maintenance costs include the costs of parts and hourly labor costs of $50 per hour, and do 

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 others can change 

this rate to one more similar to their own. Also, this rate does not reflect NYCT’s current hourly 

mechanic rate. 

Table 11 shows total maintenance costs for the CNG buses at West Farms Depot and Hybrid 

buses at Mother Clara Hale Depot. Two of the CNG buses had higher total maintenance costs 

than the other eight CNG buses. These higher costs were caused mostly by brake reline 

activities. There were two hybrid buses (buses 6367 and 6379) that had total maintenance costs 

33
higher than the rest. These higher total maintenance costs were caused by significant repairs 

troubleshooting the hybrid propulsion system, hydraulic pump, PCS cooling system, doors, and 

air conditioning. Most of these significant repairs are a part of the aforementioned campaigns for 

the hybrid buses. 

The total maintenance cost for the CNG buses was 8% higher than the hybrid buses. This 

difference will be explored further in the next discussion about maintenance cost breakdown by 

vehicle systems. 

Table 11. CNG and Hybrid Bus Total Maintenance Costs 

(Evaluation Period) 

Bus Mileage Parts ($) Labor 

Hours 

Cost per 

Mile ($) 

7657 18,708 4,820.41 390.0 1.30 

7662 19,419 4,444.86 368.3 1.18 

7666 13,087 8,316.46 433.5 2.29 

7670 17,938 6,021.11 348.5 1.31 

7677 17,993 8,156.55 417.9 1.61 

7688 18,516 5,730.23 330.5 1.20 

7708 19,344 5,141.26 333.6 1.13 

7715 18,313 3,976.66 329.4 1.12 

7719 17,483 4,936.99 282.9 1.09 

7721 18,746 4,112.70 324.2 1.08 

Total CNG 179,547 55,657.23 3,558.5 1.30 

Avg. per Bus 17,955 5,565.72 355.9 -- 

6367 16,812 4,711.21 391.3 1.44 

6368 18,465 2,677.03 396.9 1.22 

6369 18,545 3,820.93 400.9 1.29 

6375 21,252 2,569.34 384.6 1.03 

6378 20,534 3,412.69 386.9 1.11 

6379 20,453 5,469.01 479.2 1.44 

6380 16,963 2,224.94 282.5 0.96 

6381 19,470 3,238.01 396.2 1.18 

6382 21,043 2,842.97 407.6 1.10 

6387 20,858 3,486.36 393.1 1.11 

Total Hybrid 194,395 34,452.49 3,919.0 1.19 

Avg. per Bus 19,440 3,445.25 391.9 -- 

Maintenance Cost Broken Down by System 

Table 12 shows maintenance costs by vehicle system and bus study group. The vehicle systems 

shown in the tables include the following: 

• Preventive maintenance inspections (PMI)—Labor for inspections during preventive 

maintenance 

• Tires 

• Propulsion-related systems—Repairs for exhaust; fuel; engine; electric motors, traction 

batteries, and propulsion control; non-lighting electrical, air intake, cooling, and 

transmission 

34
• Cab, body, and accessories—Includes body repairs following accidents, glass, and paint; 

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

hubodometers and radios 

• Frame, steering, and suspension—Includes steering and suspension repairs 

• Brakes—Excludes regenerative braking for the hybrids, which is included in propulsionrelated systems 

• Heating, ventilation, and air conditioning (HVAC) 

• Axles, wheels, and drive shaft 

• Lighting 

• Air System, general 

• Hydraulics 

Table 13 summarizes the top five maintenance cost categories from the total maintenance 

breakdown for each study group. Each of the study groups has propulsion-related, cab, body, and 

accessories, and HVAC costs in the top five. The other two categories that show up in the top 

five are brakes or frame, steering, and suspension. These categories are discussed in more detail 

in the following sections. 

Table 12. Breakdown of Vehicle System Maintenance Cost per Mile 

(Evaluation Period) 

CNG West Farms Hybrid Mother 

Clara Hale 

System Cost per 

Mile ($) 

Percent 

of Total 

(%) 

Cost per 

Mile ($) 

Percent 

of Total 

(%) 

Cab, Body, and 

Accessories 0.38 29 0.39 33 

Propulsion-related 0.27 21 0.29 25 

PMI 0.13 10 0.18 15 

Brakes 0.20 16 0.04 3 

Frame, Steering, 

and Suspension 0.05 4 0.07 6 

HVAC 0.07 5 0.09 8 

Lighting 0.05 4 0.05 4 

Air, General 0.07 5 0.04 3 

Axles, Wheels, and 

Drive Shaft 0.04 3 0.01 1 

Tires 0.04 3 0.01 1 

Hydraulics 0.00 0 0.01 1 

Total 1.30 100 1.19 100 

35
Table 13. Top 5 Maintenance Cost Categories 

Rank CNG West Farms Hybrid Mother 

Clara Hale 

1 Cab, Body, and 

Accessories 

Cab, Body, and 

Accessories 

2 Propulsion-related Propulsion-related 

3 Brakes PMI 

4 PMI HVAC 

5 HVAC Frame, Steering, 

and Suspension 

Propulsion-Related Maintenance Costs

The propulsion-related vehicle systems include the exhaust, fuel, engine, electric propulsion, air 

intake, cooling, non-lighting electrical, and transmission systems. Table 14 shows the total 

propulsion-related maintenance costs and lists the costs for the two study groups. Table 15 

summarizes the cost comparisons between the study groups. All comparison calculations are 

hybrid compared to CNG as the baseline. 

Total propulsion-related systems maintenance costs for the CNG buses was 9% lower costs than 

the hybrid buses. 

A breakdown of the propulsion-related maintenance costs included: 

• Exhaust system maintenance—The hybrid bus group had five work orders related to a 

DPF backpressure issue during the evaluation period. This problem was a result of a 

software problem in the active monitoring of the DPF in the hybrid buses. When the 

DPF was removed and cleaned or replaced, the system would recognize that there was a 

significant change in the backpressure and give a warning indicator light; however, there 

was no problem. A few exhaust backpressure sensors were replaced before this situation 

was properly resolved. A software change has been made and this is no longer an issue, 

but has shown up in the evaluation period. The hybrid buses had exhaust maintenance 

costs more than twice those of the CNG buses. The CNG buses have had a problem with 

the thermal blanket on the exhaust wear out from vibration. Five of the ten CNG buses 

had the thermal blanket replaced during the evaluation period. This issue has not yet 

been permanently resolved. 

• Fuel system maintenance— The CNG buses had fuel system maintenance costs 77% 

higher than the hybrid buses. This difference was mostly due to the extra fuel filter costs 

for the CNG buses and a few problems with the CNG fuel leak sensors. 

• Engine system maintenance costs—The CNG buses had engine system maintenance 

costs 2% higher than the hybrid buses. The CNG buses were reported to have high 

engine oil consumption. This extra cost was not captured here. The CNG engines are in 

the process of being rebuilt as a campaign with new cylinder kits along with new spark 

plugs. 

36
• Electric propulsion systems maintenance costs—These costs pertain only to the hybrid 

buses at Mother Clara Hale. Most of these maintenance issues for the hybrid buses had to 

do with troubleshooting the hybrid control system and learning to diagnose electric 

propulsion system failures. Some of the problems reported in the maintenance system 

included the PCS cooling system, triple pump, filters, traction battery, and traction motor. 

Troubleshooting work orders in this category included “won’t start” and “check” or 

“stop” hybrid electric vehicle HEV lights. 

During the evaluation period (October 2004 through May 2005), the hybrid fleet has had 

several single battery replacements including a few single battery replacements for the 

hybrid study group. This hybrid fleet of 125 has not incurred a roadcall attributable to 

the traction batteries. BAE Systems is investigating historical replacement actions to 

determine root cause and consider whether an opportunity exists to modify procedures or 

energy storage system monitoring software to improve overall system performance and 

reliability. This analysis from BAE Systems has been promised for the final evaluation 

report for the order of 125 hybrid buses. 

• Non-lighting electrical systems maintenance costs—These costs include general 

electrical maintenance other than lighting including charging, cranking, and ignition 

systems. The CNG buses had maintenance costs 58% higher than the hybrid buses. 

The CNG buses had issues with the starter, the main power control and communications 

systems. The spark plugs on the CNG buses have been an issue with failures as early as 

4,000 miles. The CNG engines now use four iridium spark plugs costing $240 for the 

set. DDC paid for the first set of these iridium spark plugs as part of the CNG engine 

campaign and now NYCT will be paying for the subsequent changes on a 24,000 mile 

interval or approximately once per year. Only one set of these new spark plugs were 

accounted for during the evaluation period, and more are expected in the final results 

report. NYCT reports that the new spark plugs are working much better so far. 

Issues for the hybrid buses in this category included the voltage regulator, alternator, and 

wiring. 

• Air intake system maintenance costs—The CNG buses had maintenance costs 38% 

higher than the hybrid buses. There were no major problems or issues for either fleet in 

this category. 

• Cooling system maintenance costs—The CNG buses had maintenance costs 13% higher 

than the hybrid buses. 

• Transmission system maintenance costs—The hybrid buses do not have a transmission. 

The CNG buses did not have any significant transmission repairs during the evaluation 

period.

37
Table 14. Propulsion-Related Maintenance Cost by System (Evaluation Period)

Maintenance System Costs CNG West 

Farms 

Hybrid Mother 

Clara Hale 

Mileage 179,547 194,395 

Total Propulsion-related Systems (Roll-Up) 

Parts Cost ($) 14,207.96 6,336.75 

Labor Hours 680.5 1,012.8 

Total Cost ($) 48,232.96 56,974.25 

Total Cost ($) per Mile 0.27 0.29 

Exhaust System Repairs 

Parts Cost ($) 659.38 624.00 

Labor Hours 37.0 102.7 

Total Cost ($) 2,509.38 5,759.00 

Total Cost ($) per Mile 0.01 0.03 

Fuel System Repairs 

Parts Cost ($) 2,744.56 753.57 

Labor Hours 99.4 24.0 

Total Cost ($) 7,714.56 1,953.57 

Total Cost ($) per Mile 0.04 0.01 

Engine System Repairs 

Parts Cost ($) 2,266.44 1,606.98 

Labor Hours 126.6 151.1 

Total Cost ($) 8,596.44 9,159.48 

Total Cost ($) per Mile 0.05 0.05 

Electric Motor, Generator, and Battery Repairs 

Parts Cost ($) 1,937.07 

Labor Hours 462.0 

Total Cost ($) 24,962.07 

Total Cost ($) per Mile 0.13 

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

Cranking, Ignition) 

Parts Cost ($) 4,101.95 622.37 

Labor Hours 263.3 143.0 

Total Cost ($) 17,266.95 7,772.37 

Total Cost ($) per Mile 0.10 0.04 

Air Intake System Repairs 

Parts Cost ($) 1,439.59 754.11 

Labor Hours 8.0 9.5 

Total Cost ($) 1,839.59 1,229.11 

Total Cost ($) per Mile 0.01 0.01 

Cooling System Repairs 

Parts Cost ($) 1,430.27 38.65 

Labor Hours 99.8 120.5 

Total Cost ($) 6,417.77 6,063.65 

Total Cost ($) per Mile 0.04 0.03 

Transmission Repairs 

Parts Cost ($) 1,565.77

Labor Hours 46.5

Total Cost ($) 3,888.27

Total Cost ($) per Mile 0.02

38
Table 15. Summary of Propulsion-Related Maintenance Cost Comparisons* 

System Hybrid vs. CNG 

Total Propulsion-related 9% (higher) 

Exhaust 111% (higher) 

Fuel -77% (lower) 

Engine -2% (lower or same) 

Electric Propulsion N/A 

Non-Lighting Electrical -58% (lower) 

Air Intake -38% (lower) 

Cooling -13% (lower) 

Transmission N/A 

* The cost comparisons are provided as hybrid compared to CNG as the baseline. 

((Hybrid cost per mile/CNG cost per mile) – 1) * 100% = Percent comparison 

For example, the total propulsion related entry is 9% higher, this is hybrid costs 

being 9% higher than CNG for this category. 

Figure 17 shows the monthly propulsion-related maintenance cost per mile for the CNG and 

hybrid buses. Each study group’s maintenance cost per mile is shown as an average for the 

month and cumulative average for the evaluation period. The cumulative average propulsionrelated maintenance cost per mile for the hybrid and CNG buses have been tracking together for 

the last three or four months of the evaluation period and end up with the hybrid buses being 9% 

higher (as mentioned above). 

0.000

0.100

0.200

0.300

0.400

0.500

Oct-04 Nov-04 Dec-04 Jan-05 Feb-05 Mar-05 Apr-05 May-05

Cost ($)/Mile

CNG CNG Cumulative Hybrid Hybrid Cumulative

Figure 17. Propulsion-Related Maintenance Cost per Mile for CNG and Hybrid Buses 

The maintenance costs of the CNG bus group have generally been decreasing for the propulsionrelated systems. There was one peak in the monthly average cost per mile around April 2005, 

which was caused by several isolated repair actions on different buses. These repair actions 

39
included the accelerator, two major engine repairs, one significant charging repair, one 

multiplexer/communications system repair, one exhaust system repair, and one significant 

transmission repair. All of these actions appear to coincidentally occur in April 2005 and do not 

appear to be related. 

For the hybrid buses, the monthly maintenance costs for propulsion-related systems steadily 

increased during the evaluation period. The maintenance issues appear to mostly involve the 

hybrid propulsion control system and the engine. In April 2005, there was a traction battery 

replacement (bus 6382) and a triple pump replaced (bus 6375). There were significant cooling 

and exhaust/DPF repairs as well. The increased propulsion-related maintenance costs were most 

likely related to an investment in mechanic time for troubleshooting and on-the-job training. This 

is an indication of the depot staff coming up to speed in how to repair the hybrid buses on their 

own. This level of mechanic time may decrease over time as the mechanics become more 

experienced with the hybrid buses. 

Cab, Body, and Accessories Systems

The vehicle systems included in this grouping are shown in Table 16. The maintenance costs 

associated with these systems are shown by bus study group. The following bullets describe each 

of the subsystem divisions chosen to break down this category. 

• Door and interlock—Includes anything that has to do with the doors and interlock system 

except for the brakes 

• Wheelchair lift/ramp—Includes all repairs for the wheelchair lift or ramp systems, except 

hydraulics 

• Body exterior—Includes all body panels and compartment doors, as well as reflectors 

• Cleaning—All cleaning activities inside and outside the bus 

• Mirrors—All inside and outside mirrors 

• General interior and seats 

• Windshield wipers—Includes the wipers, motors, and washer systems 

• Supplies and expendable items—Includes painting supplies, tools, wipes, eyeglasses, and 

coveralls assigned to a bus 

• Destination signs 

• Horn 

• Farebox 

• Fire extinguisher 

• Radio 

The CNG and hybrid bus study groups had essentially the same cost per mile for this category. 

The breakdown of the makeup of the subdivision costs is slightly different for each bus group. 

40
Table 16. Breakdown of Cab, Body, and Accessory Maintenance Cost per Mile 

(Evaluation Period) 

CNG West Farms Hybrid Mother Clara 

Hale Subsystem Cost per 

Mile ($) 

Percent 

(%) 

Cost per 

Mile ($) 

Percent 

(%) 

Doors and Interlock 0.05 13 0.11 28 

Wheelchair Lift / Ramp 0.04 11 0.04 9 

Body—Exterior 0.13 34 0.09 23 

Cleaning 0.07 18 0.06 15 

Mirrors 0.02 6 0.03 8 

General Interior and 

Seats 0.03 8 0.03 8 

Windshield Wipers 0.02 6 0.01 3 

Supplies and expendable 

items 0.00 0 0.00 0 

Destination Sign 0.00 0 0.00 0 

Horn 0.01 4 0.01 3 

Farebox 0.00 0 0.00 0 

Fire Extinguisher 0.00 0 0.01 3 

Radio 0.00 0 0.00 0 

Total 0.38 100 0.39 100 

HVAC 

This category includes all maintenance actions for heating and ventilation and the air 

conditioning system. The majority of the costs in this category are typically related to the air 

conditioning. The maintenance costs for the two study groups are shown in Table 17. The 

maintenance cost per mile for the two study groups are about the same with the CNG buses 

being 29% lower than for the hybrid buses. For the hybrid buses during the evaluation period, 

eight of the 10 buses had an inspection and repairs that took 16 hours of mechanic time each. 

Table 17. HVAC System Maintenance Costs (Evaluation Period) 

Fleet Mileage Parts 

Cost ($) 

Labor 

Hours 

Cost per 

Mile ($) 

West Farms CNG 179,547 3,715.98 182.6 0.07 

Mother Clara Hale Hybrid 194,395 1,906.13 321.5 0.09 

Brakes

The brake system maintenance costs are expected to be dramatically lower for hybrid propulsion 

systems with regenerative braking. The regenerative braking allows the electric drive motors to 

be used to slow down a bus like a transmission retarder. The energy from braking is taken into 

the electric motor and then fed back to the traction batteries. Diesel and CNG buses are expected 

to have a four-wheel reline of the brakes every 18,000 miles on average. 

Table 18 shows the maintenance costs for the brake system repairs for the two study bus groups. 

During the evaluation period, the CNG buses had 82% higher brake maintenance cost per mile 

compared to the hybrid buses. The five oldest CNG buses in the study group had at least one 

four-wheel reline of the brakes during the evaluation period. One of those five CNG buses had 

41
the four-wheel reline twice within three months. There were also some repairs for issues with the 

antilock brake system for the CNG and hybrid buses. More data is required for the hybrid buses 

to fully understand how much longer the hybrid buses can go between brake relines and what 

that cost savings might ultimately be. 

Table 18. Brake System Maintenance Costs (Evaluation Period) 

Fleet Mileage Parts 

Cost ($) 

Labor 

Hours 

Cost per 

Mile ($) 

West Farms CNG 179,547 9,571.28 536.3 0.20 

Mother Clara Hale Hybrid 194,395 1,373.64 116.9 0.04 

PMI

This category only includes labor hours for inspections of multiple bus systems during 

preventive maintenance. As shown in Table 19, the CNG buses have PMI maintenance cost per 

mile 38% lower than the hybrid buses. However, for all maintenance costs per mile for 

scheduled maintenance, the CNG and hybrid buses had exactly the same cost at $0.29 per mile. 

The scheduled maintenance costs include filters and materials used as part of scheduled 

maintenance. One note here would be that some of the preventive maintenance parts for the 

hybrid buses may have been paid for under warranty and not accounted for in this cost per mile 

measure. 

Table 19. Preventive Maintenance Inspection Maintenance Costs (Evaluation Period) 

Fleet Mileage Parts 

Cost ($) 

Labor 

Hours 

Cost per 

Mile ($) 

West Farms CNG 179,547 0.00 465.7 0.13 

Mother Clara Hale Hybrid 194,395 0.00 695.0 0.18 

Frame, Steering, and Suspension

This category includes repairs for the frame, steering, and suspension systems of the buses. As 

shown in Table 20, the CNG buses had maintenance cost per mile 25% lower than the hybrid 

buses. 

Table 20. Frame, Steering, and Suspension Maintenance Costs (Evaluation Period) 

Fleet Mileage Parts 

Cost ($) 

Labor 

Hours 

Cost per 

Mile ($) 

West Farms CNG 179,547 2,490.77 139.9 0.05 

Mother Clara Hale Hybrid 194,395 3,717.55 182.2 0.07 

Warranty Costs 

Maintenance costs that were covered under warranty were generally removed. NYCT requested 

that suppliers working on the CNG and hybrid buses enter mechanic time into the maintenance 

system. These labor hours were not included in the analyses presented in this report. The CNG 

buses had 45.2 labor hours removed from the analysis in this report and the hybrid buses had 

96.25 labor hours removed. These labor hours were from Atlantic Detroit Diesel Allison (local 

dealer), Cummins, Vapor Corporation, and Orion. 

42
There are some repairs and parts costs that are most likely included in these analyses; however, 

there was no indication in the NYCT maintenance system to make a decision to remove the data. 

As an action item for the final report, an investigation of available information on warranty 

claims will be made. If more information regarding warranty claims can be found, the confirmed 

costs claimed on warranty will be removed. 

Roadcall Analysis 

Figure 18 shows the cumulative average miles between roadcalls (MBRC) for all RCs for the 

CNG, Hybrid, and two diesel baseline fleets. With an average of 2,000 MBRC, the diesel buses 

at West Farms are well below NYCT’s expectation that all buses should meet or exceed 4,000 

MBRC. Both the diesel buses at Mother Clara Hale Depot and the CNG buses are above the goal 

at around 5,000 MBRC. The MBRC of the hybrid buses has started to settle around 7,000 

MBRC—well above the MBRC of the other three study groups. 

0

2000

4000

6000

8000

10000

12000

14000

16000

Jun04Jul-04 Aug04Sep04Oct04Nov04Dec04Jan05Feb05Mar05Apr05May05

Miles Between Roadcalls (MBRC)

Diesel WF CNG Diesel MCH Hybrid

Figure 18. Cumulative Average MBRC 

Figure 19 shows MBRC for RCs that involved the propulsion-related systems in all four of the 

study groups. Propulsion-related systems include the transmission, non-lighting electrical 

(general electrical, charging, cranking, and ignition), air intake, cooling, exhaust, fuel, engine, 

and electrical propulsion. RCs for June 2004 and July 2004 were not available for the diesel 

buses and are not included in the figure. 

The CNG buses had a RC rate 56% better than the diesel buses at West Farms Depot. The hybrid 

and diesel buses at Mother Clara Hale Depot have essentially the same rate with the hybrid group 

at 2% higher. The hybrid buses have a rate 38% higher than the CNG buses. 

43
0

5000

10000

15000

20000

25000

30000

Jun04Jul-04 Aug04Sep04Oct04Nov04Dec04Jan05Feb05Mar05Apr05May05

Miles Between Roadcalls (MBRC)

Diesel WF CNG Diesel MCH Hybrid

Figure 19. Cumulative Average MBRC, Propulsion-Related Only 

Table 21 provides a summary of the RCs for each study group of buses for the evaluation period. 

The diesel buses at West Farms had the most RCs for doors and interlock, cooling (hydraulic 

fan), and engine. The CNG buses had the most RCs for non-lighting electrical (mostly for 

problems starting), doors and interlock, and engine. The diesel buses at Mother Clara Hale had 

the most RCs for doors and interlock, non-lighting electrical, and wheelchair lift/ramp. The 

hybrid buses had the most RCs for the electric propulsion system and air system. The electric 

propulsion system RCs were mostly caused by “check” or “stop” HEV lights. 

44
Table 21. Roadcalls for Each Fleet by System (Evaluation Period) 

Diesel West 

Farms CNG West Farms Diesel Mother Clara Hale 

Hybrid Mother 

Clara Hale System 

RCs Percent 

(%) RCs Percent (%) RCs Percent (%) RCs Percent (%) 

HVAC 3 4 0 0 1 2 3 9 

Door and Interlock 16 22 7 20 10 22 3 9 

Mirrors and Sun 

Visor 1 1 0 0 0 0 0 0 

Air-General 1 1 0 0 1 2 4 14 

Brakes 2 3 0 0 0 0 1 3 

Steering 3 4 0 0 1 2 0 0 

Suspension 2 3 2 6 2 5 0 0 

Transmission* 3 4 1 3 1 2 0 0 

Non-Lighting 

Electrical* 5 7 12 35 6 13 2 6 

Lighting 0 0 1 3 2 5 0 0 

Cooling* 16 22 1 3 5 11 2 6 

Exhaust* 2 3 0 0 2 5 0 0 

Fuel* 2 3 3 9 4 9 0 0 

Engine* 10 14 6 18 4 9 2 6 

Electric Propulsion* 0 0 0 0 0 0 14 44 

Wheelchair 

Lift/Ramp 6 9 1 3 6 13 1 3 

Total 72 100 34 100 45 100 32 100 

45
Summary of Costs 

Table 22 summarizes fuel and maintenance cost per mile for the CNG and hybrid study groups. 

The hybrid buses have a cost per mile 28% lower than the CNG buses. This lower cost is due 

almost entirely to the difference in the fuel economies of the hybrid and CNG buses. 

Table 22. Summary of Cost per Mile for CNG and Hybrid Buses (Evaluation period) 

Bus Fuel Cost / Mile ($) Maintenance Cost / Mile ($) Total Cost / Mile ($) 

7657 1.03 1.30 2.33 

7662 0.95 1.18 2.13 

7666 1.04 2.29 3.33 

7670 1.05 1.31 2.36 

7677 1.03 1.61 2.64 

7688 1.07 1.20 2.27 

7708 1.09 1.13 2.22 

7715 1.02 1.12 2.14 

7719 1.11 1.09 2.20 

7721 1.01 1.08 2.09 

CNG 1.04 1.30 2.34 

6367 0.49 1.44 1.93 

6368 0.51 1.22 1.73 

6369 0.48 1.29 1.77 

6375 0.49 1.03 1.52 

6378 0.48 1.11 1.59 

6379 0.50 1.44 1.94 

6380 0.53 0.96 1.49 

6381 0.48 1.18 1.66 

6382 0.49 1.10 1.59 

6387 0.50 1.11 1.61 

Hybrid 0.49 1.19 1.68 

46
What’s Next? 

This interim evaluation report represents eight out of 12 months of evaluation planned for the 

CNG and hybrid buses (from the order of 125). The final results of these two study groups will 

be complete with data through September 2005 and should be reported in early calendar year 

2006. 

NYCT has also taken delivery of nearly all of an order of 200 more hybrid buses from Orion and 

BAE Systems. As of September 2005, 182 of the 200 buses had been delivered to NYCT for 

service. The 200 new hybrid buses are being split between Fresh Pond Depot in Brooklyn (138) 

and Manhattanville Depot in Manhattan (62). These buses will be evaluated with a selection of 

hybrid and diesel baseline buses at Manhattanville Depot. The interim report from this evaluation 

should also be available in 2006. 

NYCT has recently placed another large order of diesel hybrid buses from Orion and BAE 

Systems including 500 hybrid buses with the option to purchase up to a total of 889 buses. 

NYCT is expecting to take delivery of 216 of these hybrid buses and 284 hybrid buses are for 

their sister agency, MTA Buses. NYCT intends to add hybrid bus operations to the East New 

York and Casey Stengel depots as well as converting the entire Manhattanville Depot to only 

diesel hybrid bus operation. 

The purchase price of these hybrid buses was a little less than $500,000 each, which is reportedly 

about $150,000 more than a new standard clean diesel bus. 

47
Contacts 

U.S. Department of Energy 

Lee Slezak 

Manager, Advanced Vehicle Testing Activity 

Phone: 202-586-2335 

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

National Renewable Energy Laboratory 

Leslie Eudy 

Senior Project Leader 

Phone: 303-275-4412 

E-mail: leslie_eudy@nrel.gov 

Battelle 

Kevin Chandler 

Program Manager 

Phone: 614-424-5127 

E-mail: chandlek@battelle.org

New York City Transit 

Gary LaBouff 

Director, Research and Development 

Department of Buses 

Phone: 718-566-3535 

E-mail: galabou@nyct.com 

Orion Bus Industries 

Mark Brager 

Vice President, Sales 

Phone: 905-403-7806 

E-mail: mbrager@orionbus.com 

BAE Systems 

Tom Webb 

Business Development, Transit 

Phone: 413-253-2564 

E-mail: thomas.webb@baesystems.com 

Trillium USA 

Jennifer de Tapia 

Director of Market Services 

Phone: 800-920-1166 

E-mail: jdetapia@trilliumusa.com

48
Acronyms and Abbreviations 

AVTA—Advanced Vehicle Testing Activity 

bhp—brake horsepower 

CNG—compressed natural gas 

CO—carbon monoxide 

DDC—Detroit Diesel Corporation 

DOC—diesel oxidation catalyst 

DOE—U.S. Department of Energy 

DPF—diesel particulate filter 

EPA—U.S. Environmental Protection Agency 

EGR—exhaust gas recirculation 

g/bhp-hr—grams per brake horsepower hour 

HC—hydrocarbons 

HEV—hybrid electric vehicle 

HVAC—heating, ventilation, and air conditioning 

LIRR—Long Island Railroad 

LI Bus—Long Island Bus 

MBRC—miles between roadcalls 

MCH—Mother Clara Hale Depot 

MTA—Metropolitan Transportation Authority 

NREL—National Renewable Energy Laboratory 

NYCT—New York City Transit 

NMHC—non-methane hydrocarbons 

NOx—oxides of nitrogen 

PCS—power control system 

PM—particulate matter 

ppm—parts per million 

PMI—preventive maintenance inspection 

RC—roadcall 

R&D—research and development 

rpm—revolutions per minute 

scfm—standard cubic feet per minute 

SCR—selective catalytic reduction 

ULSD—ultra low sulfur diesel 

49
References and Related Reports 

NYCT Related Reports 

NREL, 2005, Advanced Technology Vehicles in Service: New York City Transit Drives Hybrid Electric 

Buses into the Future, National Renewable Energy Laboratory, Golden, CO, DOE/GO-102005-2009 

NREL, 2003, Advanced Technology Vehicles in Service: MTA New York City Transit, Diesel Hybrid 

Electric Buses, National Renewable Energy Laboratory, Golden, CO, NREL/FS-540-33397 

Chandler, K., Walkowicz, K., Eudy, L., 2002, New York City Transit Diesel Hybrid-Electric Buses: Final 

Results, National Renewable Energy Laboratory, Golden, CO, NREL/BR-540-32427 

Battelle/NREL, 2002, NYCT’s Diesel Hybrid-Electric Buses, Program Status Update, National 

Renewable Energy Laboratory, Golden, CO, NREL/BR-540-31668. 

Battelle/NREL, 2001, Advanced Technology Vehicles in Service, Diesel Hybrid Electric Buses, National 

Renewable Energy Laboratory, Golden, CO, NREL/FS-540-30736. 

Environment Canada, 2001, Emissions Evaluation of Orion VII Hybrid Bus with BAE Systems Controls 

HybriDriveTM Propulsion System, Environment Canada, Ottawa, Ontario, ERMD Report #01-12. 

Lanni, T., Chatterjee, S., Conway, R., Windawi, H., Rosenblatt, D., Bush, C., Lowell, D., Evans, J., 

McLean, R., 2001, Performance and Durability Evaluation of Continuously Regenerating Particulate 

Filters on Diesel Powered Urban Buses at NY City Transit, SAE International, Warrendale, PA, 2001-01-

0511. 

Clark, N., Wenwei, X., Gautam, M., Lyons, D., Norton, P., Balon, T., 2000, Hybrid Diesel-Electric 

Heavy Duty Bus Emissions: Benefits of Regeneration and Need for State of Charge Correction, SAE 

International, Warrandale, PA, 2000-01-2955. 

M.J. Bradley & Associates, 2000, Hybrid-Electric Drive Heavy-Duty Vehicle Testing Project, Final 

Emissions Report, Northeast Advanced Vehicle Consortium, Boston, MA. 

Environment Canada, 1998, Evaluation of Engine RPM on the Emissions from the Low Floor DieselElectric Hybrid Bus, Environment Canada, Ottawa, Ontario, ERMD Report #97-26771-3. 

Other Related Reports 

NREL, 2005, Advanced Technology Vehicles in Service, Knoxville Area Transit, National Renewable 

Energy Laboratory, Golden, CO, DOE/GO-102005-2085 

NREL, 2004, Advanced Technology Vehicles in Service, King County Metro Transit, National Renewable 

Energy Laboratory, Golden, CO, DOE/GO-102004-2026 

NREL, 2004, Advanced Technology Vehicles in Service, Indianapolis Public Transportation, National 

Renewable Energy Laboratory, Golden, CO, DOE/GO-102004-1986 

50
Chandler, K., Proc, K., 2004, Norcal Prototype LNG Truck Fleet, Final Results, National Renewable 

Energy Laboratory, Golden, CO, DOE/GO-102004-1920 

Chandler, K., Eudy, L., 2003, ThunderPower, Bus Evaluation at SunLine Transit Agency, National 

Renewable Laboratory, Golden, CO, DOE/GO-102003-1786 

Chandler, K., Vertin, K., Alleman, T., Clark, N., 2003, Ralphs Grocery Company EC-DieselTM Truck 

Fleet: Final Results, National Renewable Energy Laboratory, Golden, CO, NREL/BR-540-31363 

Eudy, L., Gifford, M., 2003, Challenges and Experiences with Electric Propulsion Transit Buses in the 

United States, National Renewable Energy Laboratory, Golden, CO, DOE/GO-102003-1791 

NREL, 2002, Advanced Technology Vehicles in Service, Norcal Waste Systems, Inc., National Renewable 

Energy Laboratory, Golden, CO, NREL/FS-540-32808 

NREL, 2002, General Evaluation Plan, Fleet Test & Evaluation Projects, National Renewable Energy 

Laboratory, Golden, CO, NREL/BR-540-32392 

Eudy, L., 2002, Natural Gas in Transit Fleets: A Review of the Transit Experience, National Renewable 

Energy Laboratory, Golden, CO, NREL/TP-540-31479 

Chandler, K., Norton, P., Clark, N., 2001, Waste Management’s LNG Truck Fleet, Final Results, National 

Renewable Energy Laboratory, Golden, CO, NREL/BR-540-29073 

Chandler, K., Norton, P., Clark, N., 2000, DART’s LNG Bus Fleet, Final Results, National Renewable 

Energy Laboratory, Golden, CO, NREL/BR-540-28739 

Chandler, K., Norton, P., Clark, N., 2000, Raley’s LNG Truck Fleet, Final Results, National Renewable 

Energy Laboratory, Golden, CO, NREL/BR-540-27678 

Battelle, 1999, Waste Management’s LNG Truck Fleet, Start-Up Experience, National Renewable Energy 

Laboratory, Golden, CO, NREL/BR-540-26617 

Battelle, 1997, Raley’s LNG Truck Fleet, Start-Up Experience, National Renewable Energy Laboratory, 

Golden, CO, NREL/BR-540-23402 

Battelle, 2000, DART’s LNG Bus Fleet, Start-Up Experience, National Renewable Energy Laboratory, 

Golden, CO, NREL/BR-540-28124 

Motta, R., Norton, P., Kelly, K., Chandler, K., Schumacher, L., Nigel, N., 1996, Alternative Fuel Transit 

Buses, Final Results from the National Renewable Energy Laboratory (NREL) Vehicle Evaluation 

Program, National Renewable Energy Laboratory, Golden, CO, NREL/TP-425-20513 

51
Appendix: Fleet Summary Statistics 

52
Appendix A: Summary of Diesel, CNG, and Hybrid Results 

Fleet Operations and Economics 

WF Diesel 

WF CNG 

(Eval) 

MCH 

Diesel 

MCH Hybrid 

(Eval) 

Number of Vehicles 9 10 9 10 

Period Used for Fuel and Oil Op Analysis 6/04-5/05 10/04-5/05 6/04-5/05 10/04-5/05 

Total Number of Months in Period 12 8 12 8 

Fuel and Oil Analysis Base Fleet Mileage 186,682 163,763 249,990 168,027 

Period Used for Maintenance Op Analysis 6/04-5/05 10/04-5/05 6/04-5/05 10/04-5/05 

Total Number of Months in Period 12 8 12 8 

Maintenance Analysis Base Fleet Mileage 191,264 179,547 257,624 194,395 

Average Monthly Mileage per Vehicle 1,952 2,244 2,385 2,430 

Fleet CNG/Diesel Equiv. Usage in Gal. 82,019 95,650 105,138 48,849 

 

Representative Fleet MPG (energy equiv) 2.28 1.71 2.38 3.44 

Diesel Cost per gallon 1.70 1.78 1.70 1.70 

Fuel Cost per Mile 0.75 1.04 0.72 0.49 

Total Scheduled Repair Cost per Mile 0.30 0.29 0.30 0.29 

Total Unscheduled Repair cost per Mile 1.97 1.01 1.45 0.90 

Total Maintenance Cost per Mile 2.27 1.30 1.75 1.19 

All Roadcalls 72 34 45 27 

MBRC for All Roadcalls 2,154 5,281 4,701 7,200 

Propulsion-Related Roadcalls 31 23 20 18 

MBRC for Propulsion-Related Roadcalls 5,002 7,806 10,576 10,800 

53
Appendix B: CNG (Orion VII) at West Farms Depot 

and Hybrid (Orion VII) at Mother Clara Hale Depot 

Fleet Operations and Economics

CNG (Eval) 

Hybrid 

(Eval) 

Number of Vehicles 10 10 

Period Used for Fuel and Oil Op Analysis 10/04-5/05 10/04-5/05 

Total Number of Months in Period 8 8 

Fuel and Oil Analysis Base Fleet Mileage 163,763 168,027 

Period Used for Maintenance Op Analysis 10/04-5/05 10/04-5/05 

Total Number of Months in Period 8 8 

Maintenance Analysis Base Fleet Mileage 179,547 194,395 

Average Monthly Mileage per Vehicle 2,244 2,430 

Fleet Diesel Usage in Gal. 95,650 48,849 

 

Representative Fleet MPG (energy equiv) 1.71 3.44 

Diesel Cost per gallon 1.78 1.70 

Fuel Cost per Mile 1.04 0.49 

Total Scheduled Repair Cost per Mile 0.29 0.29 

Total Unscheduled Repair cost per Mile 1.01 0.90 

Total Maintenance Cost per Mile 1.30 1.19 

 

Total Operating Cost per Mile 2.34 1.68 

Maintenance Costs

CNG (Eval) 

Hybrid 

(Eval) 

Fleet Mileage 179,547 194,395 

 

Total Parts Cost 55,657.23 34,452.49 

Total Labor Hours 3558.9 3919.0 

Average Labor Cost 177,945.00 195,950.00 

(@ $50.00 per hour) 

Total Maintenance Cost 233,602.23 230,402.49 

Total Maintenance Cost per Bus 23,360.22 23,040.25 

Total Maintenance Cost per Mile 1.30 1.19 

54
Breakdown of Maintenance Costs by Vehicle System

CNG (Eval) 

Hybrid 

(Eval) 

Fleet Mileage 257,624 194,395 

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

43, 44, 45, 46)

Parts Cost 14,207.96 6,336.75 

Labor Hours 680.5 1012.8 

Average Labor Cost 34,025.00 50,637.50 

Total Cost (for system) 48,232.96 56,974.25 

Total Cost (for system) per Bus 4,823.30 5,697.43 

Total Cost (for system) per Mile 0.27 0.29 

Exhaust System Repairs (ATA VMRS 43)

Parts Cost 659.38 624.00 

Labor Hours 37.0 102.7 

Average Labor Cost 1,850.00 5,135.00 

Total Cost (for system) 2,509.38 5,759.00 

Total Cost (for system) per Bus 250.94 575.90 

Total Cost (for system) per Mile 0.01 0.03 

Fuel System Repairs (ATA VMRS 44)

Parts Cost 2,744.56 753.57 

Labor Hours 99.4 24.0 

Average Labor Cost 4,970.00 1,200.00 

Total Cost (for system) 7,714.56 1,953.57 

Total Cost (for system) per Bus 771.46 195.36 

Total Cost (for system) per Mile 0.04 0.01 

Power Plant (Engine) Repairs (ATA VMRS 45)

Parts Cost 2,266.44 1,606.98 

Labor Hours 126.6 151.1 

Average Labor Cost 6,330.00 7,552.50 

Total Cost (for system) 8,596.44 9,159.48 

Total Cost (for system) per Bus 859.64 915.95 

Total Cost (for system) per Mile 0.05 0.05 

Electric Propulsion Repairs (ATA VMRS 46) 

Parts Cost 0.00 1,937.07 

Labor Hours 0.0 460.5 

Average Labor Cost 0.00 23,025.00 

Total Cost (for system) 0.00 24,962.07 

Total Cost (for system) per Bus 0.00 2,496.21 

Total Cost (for system) per Mile 0.00 0.13 

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

Charging, 32-Cranking, 33-Ignition) 

Parts Cost 4,101.95 622.37 

Labor Hours 263.3 143.0 

Average Labor Cost 13,165.00 7,150.00 

Total Cost (for system) 17,266.95 7,772.37 

Total Cost (for system) per Bus 1,726.70 777.24 

Total Cost (for system) per Mile 0.10 0.04 

55
Breakdown of Maintenance Costs by Vehicle System (continued)

CNG (Eval) 

Hybrid 

(Eval) 

Air Intake System Repairs (ATA VMRS 41)

Parts Cost 1,439.59 754.11 

Labor Hours 8.0 9.5 

Average Labor Cost 400.00 475.00 

Total Cost (for system) 1,839.59 1,229.11 

Total Cost (for system) per Bus 183.96 122.91 

Total Cost (for system) per Mile 0.01 0.01 

Cooling System Repairs (ATA VMRS 42)

Parts Cost 1,430.27 38.65 

Labor Hours 99.8 120.5 

Average Labor Cost 4,987.50 6,025.00 

Total Cost (for system) 6,417.77 6,063.65 

Total Cost (for system) per Bus 641.78 606.37 

Total Cost (for system) per Mile 0.04 0.03 

Hydraulic System Repairs (ATA VMRS 65) 

Parts Cost 0.00 1,599.02 

Labor Hours 5.2 17.0 

Average Labor Cost 260.00 850.00 

Total Cost (for system) 260.00 2,449.02 

Total Cost (for system) per Bus 26.00 244.90 

Total Cost (for system) per Mile 0.00 0.01 

General Air System Repairs (ATA VMRS 10)

Parts Cost 7,885.04 3,594.15 

Labor Hours 79.5 88.3 

Average Labor Cost 3,972.50 4,412.50 

Total Cost (for system) 11,857.54 8,006.65 

Total Cost (for system) per Bus 1,185.75 800.67 

Total Cost (for system) per Mile 0.07 0.04 

Brake System Repairs (ATA VMRS 13)

Parts Cost 9,571.28 1,373.64 

Labor Hours 536.3 116.9 

Average Labor Cost 26,812.50 5,842.50 

Total Cost (for system) 36,383.78 7,216.14 

Total Cost (for system) per Bus 3,638.38 721.61 

Total Cost (for system) per Mile 0.20 0.04 

Transmission Repairs (ATA VMRS 27) 

Parts Cost 1,565.77 0.00 

Labor Hours 46.5 1.5 

Average Labor Cost 2,322.50 75.00 

Total Cost (for system) 3,888.27 75.00 

Total Cost (for system) per Bus 388.83 7.50 

Total Cost (for system) per Mile 0.02 0.00 

56
Breakdown of Maintenance Costs by Vehicle System (continued)

CNG (Eval) 

Hybrid 

(Eval) 

Inspections Only - no parts replacements (101)

Parts Cost 0.00 0.00 

Labor Hours 465.7 695.0 

Average Labor Cost 23,282.50 34,750.00 

Total Cost (for system) 23,282.50 34,750.00 

Total Cost (for system) per Bus 2,328.25 3,475.00 

Total Cost (for system) per Mile 0.13 0.18 

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

Sheet Metal, 50-Accessories, 71-Body)

Parts Cost 15,426.32 14,158.72 

Labor Hours 1045.7 1237.5 

Average Labor Cost 52,282.50 61,875.00 

Total Cost (for system) 67,708.82 76,033.72 

Total Cost (for system) per Bus 6,770.88 7,603.37 

Total Cost (for system) per Mile 0.38 0.39 

HVAC System Repairs (ATA VMRS 01)

Parts Cost 3,715.98 1,906.13 

Labor Hours 182.6 321.5 

Average Labor Cost 9,130.00 16,075.00 

Total Cost (for system) 12,845.98 17,981.13 

Total Cost (for system) per Bus 1,284.60 1,798.11 

Total Cost (for system) per Mile 0.07 0.09 

Lighting System Repairs (ATA VMRS 34)

Parts Cost 2,046.57 1,623.43 

Labor Hours 146.7 172.7 

Average Labor Cost 7,332.50 8,635.00 

Total Cost (for system) 9,379.07 10,258.43 

Total Cost (for system) per Bus 937.91 1,025.84 

Total Cost (for system) per Mile 0.05 0.05 

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

Steering, 16-Suspension)

Parts Cost 2,490.77 3,717.55 

Labor Hours 139.9 182.2 

Average Labor Cost 6,995.00 9,110.00 

Total Cost (for system) 9,485.77 12,827.55 

Total Cost (for system) per Bus 948.58 1,282.76 

Total Cost (for system) per Mile 0.05 0.07 

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

Wheels, 22-Rear Axle, 24-Drive Shaft) 

Parts Cost 313.31 143.10 

Labor Hours 127.9 38.0 

Average Labor Cost 6,395.00 1,897.50 

Total Cost (for system) 6,708.31 2,040.60 

Total Cost (for system) per Bus 670.83 204.06 

Total Cost (for system) per Mile 0.04 0.01 

57
Breakdown of Maintenance Costs by Vehicle System (continued)

CNG (Eval) 

Hybrid 

(Eval) 

Tire Repairs (ATA VMRS 17)

Parts Cost 0.00 0.00 

Labor Hours 148.8 37.3 

Average Labor Cost 7,437.50 1,865.00 

Total Cost (for system) 7,437.50 1,865.00 

Total Cost (for system) per Bus 743.75 186.50 

Total Cost (for system) per Mile 0.04 0.01 

Notes 

1. The engine/fuel-related systems were chosen to include only those systems of the vehicles that could be 

directly impacted by the selection of a fuel. 

2. ATA VMRS coding is based on parts that were replaced. If there was no part replaced in a given repair, 

the code was chosen by the system being worked on. 

3. In general, inspections (with no part replacements) were only included in the overall totals (not by 

system). 101 was created to track labor costs for PM inspections. 

4. ATA VMRS 02-cab and sheet metal represents seats, doors, etc. ATA VMRS 50-accessories represents 

things like fire extinguishers, test kits, etc. ATA VMRS 71-body represents mostly windows and 

windshields. 

5. Average labor cost is assumed to be $50 per hour. 

6. Warranty costs are not included. 

58
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PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ORGANIZATION.

1. REPORT DATE (DD-MM-YYYY)

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2. REPORT TYPE

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3. DATES COVERED (From - To)

5a. CONTRACT NUMBER

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5b. GRANT NUMBER

4. TITLE AND SUBTITLE

New York City Transit Hybrid and CNG Transit Buses: Interim 

Evaluation Results 

5c. PROGRAM ELEMENT NUMBER

5d. PROJECT NUMBER

NREL/TP-540-38843 

5e. TASK NUMBER

FC06.3000 

6. AUTHOR(S)

K. Chandler, E. Eberts, and L. Eudy 

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-540-38843 

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 the evaluation of compressed natural gas (CNG) and diesel hybrid electric bus propulsion 

systems in New York City Transit’s transit buses. 

15. SUBJECT TERMS

New York City Transit (NYCT); compressed natural gas (CNG); hybrid electric; diesel; transit buses; U.S. Department 

of Energy; evaluation 

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