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

Office of Energy Efficiency & Renewable Energy

National Renewable Energy Laboratory 

Innovation for Our Energy Future 

New York City Transit (NYCT) 

Hybrid (125 Order) and CNG 

Transit Buses 

Final Evaluation Results 

R. Barnitt 

National Renewable Energy Laboratory 

K. Chandler 

Battelle

Technical Report 

NREL/TP-540-40125 

November 2006 

NREL is operated by Midwest Research Institute ● Battelle Contract No. DE-AC36-99-GO10337 
New York City Transit (NYCT) 

Hybrid (125 Order) and CNG 

Transit Buses 

Final Evaluation Results 

R. Barnitt 

National Renewable Energy Laboratory 

K. Chandler 

Battelle

Prepared under Task No. FC06.3000 

Technical Report 

NREL/TP-540-40125 

November 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
NOTICE

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Acknowledgements 

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

within the U.S. Department of Energy by Lee Slezak. All publications on the NYCT hybrid bus 

evaluation will be posted on DOE's Energy Efficiency & Renewable Energy Web site. 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 

Gordon Coor 

Danny Ilioiu 

Gary LaBouff 

Glenn Maerki 

Doug Zupo 

BAE Systems 

Tom Apalenek 

Jody Lanfranchi 

Bart Mancini 

Steve Tilyou 

Tom Webb 

Orion Bus Industries 

Mark Brager 

Trillium USA 

Mark Barton 

Jennifer de Tapia 

 iii
Table of Contents 

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

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

Implementation Experience ....................................................................................................... vi 

Evaluation Results .................................................................................................................... vii 

What’s Next? ............................................................................................................................ xii 

Changes and Additions Since the Interim Report........................................................................... 1 

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

DOE / NREL Advanced Vehicle Testing Activity..................................................................... 2 

Host Site Profile—NYCT........................................................................................................... 3 

Emissions Reductions Drive the Need for CNG and Hybrid Propulsion ................................... 4 

AVTA Project Design and Data Collection................................................................................ 5 

Vehicle System Descriptions...................................................................................................... 6 

BAE Systems HybriDrive Propulsion System............................................................................ 9 

NYCT Facilities............................................................................................................................ 10 

Implementation Experience .......................................................................................................... 12 

Evaluation Results ........................................................................................................................ 18 

Route Descriptions.................................................................................................................... 18 

Bus Use ..................................................................................................................................... 19 

Fuel Economy and Cost............................................................................................................ 21 

Maintenance Analysis............................................................................................................... 25 

Cab, Body, and Accessories Systems....................................................................................... 33 

Roadcall Analysis ..................................................................................................................... 35 

Summary of Costs..................................................................................................................... 38 

What’s Next? ................................................................................................................................ 39 

Contacts......................................................................................................................................... 40 

References and Related Reports ................................................................................................... 42 

NYCT Related Reports............................................................................................................. 42 

Appendix: Fleet Summary Statistics............................................................................................. 44 

CNG (Orion VII) at West Farms Depot and Hybrid (Orion VII) at Mother Clara Hale Depot 

Evaluation Period...................................................................................................................... 44 

 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. 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 vehicle technologies. Data are collected and analyzed for operation, maintenance, 

performance, cost, and emissions characteristics of advanced technology fleets and comparable 

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

conventional technology vehicles, AVTA evaluations help fleet owners and operators make 

informed purchasing decisions. 

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. This report focuses on 10 new compressed natural gas (CNG) and next generation 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, reduces petroleum use. 

Evaluation Design 

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

CNG propulsion (equipped with Detroit Diesel Corporation Series 50G CNG) and new hybrid 

propulsion (equipped with BAE Systems’ HybriDrive propulsion system). These final results 

represent a 12-month evaluation of these two groups of buses (October 2004 through September 

2005). 

The CNG buses evaluated were part of an order of 260 Orion VII CNG buses ($319,000 each) 

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. 

The hybrid buses we evaluated were part of an order of 125 Orion VII hybrid buses ($385,000 

each) 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 

 v
Depot in Queens. This group of buses is the first large commercial hybrid bus delivery for Orion 

and BAE Systems. 

 

The evaluation we present in this report examines 10 new CNG Orion VII buses (model year 

2002) selected at random from the West Farms Depot, and 10 new hybrid Orion VII buses 

(model year 2002) chosen at random from the Mother Clara Hale Depot. This evaluation of the 

Orion VII CNG and hybrid buses compares buses that are the same age and the same bus 

platform. The CNG and hybrid buses have been operated on similar duty-cycles and the 

maintenance practices at the two depots appear to be similar. Older (non-exhaust gas 

recirculation [EGR] engine equipped) diesel buses at both West Farms (model year 1994) and 

Mother Clara Hale (model year 1999) depots were included in this evaluation for limited 

comparisons of mileage, fuel economy, and roadcalls for standard diesel technology. The 

evaluation team selected 10 vehicles from each study group for analysis; which was determined 

to be a sufficient number to provide some degree of statistical significance to the results 

obtained. 

Implementation Experience 

NYCT reported that 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 as expected. 

Facilities: A large CNG compression station was built at West Farms Depot that has the ability 

to compress 6,600 scfm of natural gas and fuel a bus in less than 5 minutes. Combustible gas 

detection was added for the maintenance area to accommodate the use of natural gas buses. The 

total cost of facility improvements at West Farms was $7.4 million including the station, facility 

improvements, and $2 million for blasting through solid rock to bury the high pressure gas lines. 

The hybrid buses required additional space at the Mother Clara Hale facility for two battery 

conditioning stations ($70,000 each); an overhead crane was also added to enable mechanics to 

service the battery tubs on top of the hybrid buses. 

Operator comments: The bus operators reportedly like the new buses (both the hybrid and CNG 

buses)—especially the acceleration of the hybrid buses. 

Mileage accumulation: Mileage accumulation for the entire order of 260 CNG buses through 

September 2005 was nearly 12 million miles with a general usage rate of 2,400 monthly miles 

per bus. The entire order of 125 hybrid buses accumulated nearly 4 million miles through 

September 2005 with a general usage rate of 2,400 monthly miles per bus for Mother Clara Hale 

Depot and around 2,900 monthly miles per bus for Queens Village Depot. 

Reliability: Both the CNG and hybrid bus fleets experienced miles between roadcalls (MBRC) 

rates above NYCT’s required 4,000 MBRC (nearly 6,000 MBRC for CNG, and about 5,000 

MBRC for hybrid). 

 vi
Evaluation Results 

The following results and discussion focus only on the evaluated operating depots and study bus 

groups. 

Duty Cycle 

We have used average speed as an indicator of the general duty cycle for the evaluation 

locations. The average speed for the CNG buses at West Farms Depot was 6.5 mph for 2004 and 

6.3 mph for 2005. The average speed or general duty cycle for the hybrid bus evaluation 

location, Mother Clara Hale Depot, was 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 

For the detailed study groups, the CNG buses had 3% lower bus use compared to the hybrid 

buses (2,295 monthly average mileage per bus for CNG buses and 2,370 monthly average 

mileage per bus for hybrid buses). This supports the premise that these two study groups are 

being used in a similar fashion. The diesel buses studied from Mother Clara Hale Depot had an 

average monthly mileage per bus of 2,385. Also, the monthly average mileages per bus for the 

CNG and hybrid study buses are similar to the overall fleet and appear to be representative of 

typical operation. 

Fuel Economy 

• CNG Buses—The CNG study group fuel economy was 1.70 miles per diesel energy 

equivalent gallon for the 12-month evaluation period. The CNG average fuel economy is 

25% lower than the diesel study buses operating at West Farms Depot (2.28 mpg). Based on 

the duty cycle at West Farms (average speed between 6.3 mph and 6.5 mph), this lower fuel 

economy is within expectations based on previous CNG studies1

. 

Note: The NYCT bus duty cycle is a severe application for spark ignited (SI), natural gas 

engines because of the slow average speed (6.3 - 6.5 mph) and frequent stops, which 

indicates the engine is operating at a low speed and load for much of its operating time. SI 

engines typically have a lower thermal efficiency at low speed and load than compression 

ignition (CI) diesel engines. Consequently, lower natural gas fuel economy is expected in 

this type of operation. 

Both the DDC Series 50 diesel and DDC Series 50 CNG engines are no longer available for 

new transit buses. The DDC Series 50G natural gas engine, operated by NYCT is not the 

newest technology natural gas engine (fuel and electronic controls) currently available. 

Newer engines from other manufacturers may have shown better results. 

 

1

 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) 

 vii
• Hybrid Buses—The hybrid study group 12-month average fuel economy was 3.19 mpg, 

which was 34% higher than the non-EGR diesel buses (average 2.38 mpg for a 12-month 

period) operating at Mother Clara Hale Depot and 40% higher than the non-EGR diesel buses 

(average 2.28 mpg for a 12-month period) operating at West Farms Depot. 

The hybrid bus average fuel economy for the 12-month evaluation period fluctuated between 

60% and 120% higher than the CNG buses based on diesel gallon equivalent units. Figure 

ES-1 shows 12 months of average monthly fuel economy for the two diesel study groups, 

CNG, and hybrid buses. The two diesel study groups have similar average fuel economy 

results for the evaluation period shown. The hybrid bus fuel economy has fluctuated 

generally between 26% and 52% higher than for the diesel buses (in the same time frame) at 

Mother Clara Hale Depot; however, during the summer months (June 2005-September 

2005), this positive difference dipped as low as only 12% (better compared to diesel average) 

for one month during the summer. 

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

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

Miles per Diesel Gallon

WF Diesel MCH Diesel CNG Hybrid

Figure ES-1. Average Fuel Economy (MPG) 

The hybrid bus average fuel economy had a much larger decrease/fluctuation in fuel economy in 

the summer months (June through September) than any of the other three study bus groups 

shown. According to BAE Systems, much of this decrease is due to an increase in energy 

consumption for air conditioning. Although air conditioning load is similar for all four study bus 

groups, this is compared as a percentage to a much lower overall fuel consumption for the hybrid 

buses (see Figure ES-2). Additional factors such as different engine sizes, CNG engine thermal 

efficiency changes with loading, and others likely contribute to the magnitude of the summer 

versus winter fuel economy differences between the three different propulsion types. In other 

words, all four study bus groups have a significant increase of energy consumption for air 

 viii
conditioning in the summer months, but this increase represents a much larger percentage of 

overall fuel consumption for the hybrid buses, resulting in a larger penalty in fuel efficiency. 

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

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

Fuel Consumption (gal/mile)

MCH Diesel WF Diesel CNG Hybrid

Figure ES-2: Average Fuel Consumption (Diesel Equivalent Gallons per Mile) 

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 $1.00 

per therm and the Trillium USA charge was $0.25 per therm for a total cost of $1.25 per therm or 

$1.74 per diesel energy equivalent gallon. The average diesel fuel cost—sulfur content less than 

30 parts per million (ppm)—was $1.78 per gallon during the evaluation period. This translates 

into a CNG bus study group fuel cost per mile 45% higher than the hybrid buses and 31% higher 

than the diesel study group at West Farms Depot. 

Total Maintenance Costs 

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

life of a transit bus. This short evaluation period does not provide enough of the capital and 

operating costs to understand the full 12-year life cycle cost of the CNG, or hybrid buses. In 

order to gain a complete understanding of costs, one must examine the purchase cost of the 

buses, cost of facility modification or addition, warranty cost, operations cost (and savings), and 

longer term maintenance costs (such as engine rebuilds or replacements, traction battery 

replacements, brake repair savings, etc.). However, the intent of this evaluation is to provide 

accurate actual capital and known operations costs experienced for hybrid and CNG vehicles for 

the time period selected. 

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

NYCT mechanic labor rate) and parts, but do not include warranty costs. 

The hybrid and CNG buses have had many repairs covered under warranty which are not 

included in this analysis. The cost of warranty repairs is accounted for in the bus purchase price 

set by the bus manufacturer. Not accounting for warranty repairs in the evaluation of total 

maintenance cost offers an incomplete picture of true maintenance cost. However, the 

maintenance cost reported with the absence of warranty costs does reflect the actual cost to the 

transit agency for the time period evaluated. Therefore, the maintenance cost analysis presented 

here does not include warranty repairs, but is limited to labor and parts costs associated with 

repair work performed by NYCT mechanics. This analysis is not predictive of maintenance 

costs which will be assumed by the transit agency beyond the warranty period. The general 

warranty on these particular hybrids is two years from date of purchase, with some drivetrain 

components warranted beyond two years. The exact components and warranty periods are 

negotiated by NYCT and Orion, and are contractual. 

The CNG buses’ average total maintenance cost was $1.29/mile which was 5% higher than the 

hybrid buses ($1.23/mile) during the evaluation period. Diesel baseline vehicle maintenance 

costs were not compared due to the older age of the diesels relative the CNG and hybrid vehicles. 

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, electric propulsion, 

and hydraulics. The CNG buses’ average propulsion-related maintenance costs per mile were 5% 

lower than the hybrid buses. A summary of propulsion-related maintenance costs is shown in 

Table ES-2. 

Table ES-2. Summary of Propulsion-Related Maintenance Cost per Mile Comparisons* 

System CNG ($/mile) Hybrid ($/mile) Hybrid vs. CNG 

Total Propulsion-Related 0.349 0.367 5% (higher) 

Exhaust 0.020 0.024 22% (higher) 

Fuel 0.058 0.015 -74% (lower) 

Engine 0.064 0.061 -5% (lower) 

Electric Propulsion/Transmission 0.036 0.181 403% (higher) 

Non-Lighting Electrical 0.101 0.042 -58% (lower) 

Air Intake 0.012 0.006 -53% (lower) 

Cooling 0.053 0.031 -41% (lower) 

Hydraulic 0.005 0.007 62% (higher) 

* 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 

Other Important Maintenance Costs 

In addition to the above measured maintenance costs, this report includes additional information 

on four maintenance cost topics because of their relevance to hybrid propulsion technology. 

• Engine—NYCT plans to replace the smaller than standard transit bus diesel engine used in 

the hybrid buses at approximately year six out of the 12-year life. A standard diesel or CNG 

 x
bus would typically have one engine overhaul during the 12-year life without any planned 

engine replacements. 

• Traction Batteries—The traction batteries for the NYCT hybrid buses are sealed gel leadacid batteries in two separate tubs of 23 batteries each or 46 battery modules total. These 

batteries (based on recommendations from the manufacturer), are expected to last at least 

three years, and then they will need to be replaced (or three sets of traction batteries during 

the 12-year life of the bus). A total of 22 traction batteries were replaced for the 10 study 

buses during the evaluation period. This translates into a 4.8% per year replacement rate. 

BAE Systems reports that analysis shows that none of those 22 traction batteries had failed, 

and they rolled out a software change in April 2006 (after this evaluation ended) to reduce 

the number of unnecessary traction battery replacements. While this software change could 

potentially improve battery life, it may also affect fuel economy; however, this software 

change occurred after the end of this evaluation period and the impact on fuel economy is 

unknown. 

• PMI—this is preventive maintenance inspection labor time spent on the buses. Based upon 

the data collected during this evaluation, the hybrid buses had 50% more labor spent on 

scheduled maintenance time. However, due to the way in which the NYCT mechanics record 

their time, additional unscheduled activities are included in what is defined as PMI. No 

difference in PMI labor is expected between the CNG and hybrid buses. Recognizing this, 

but reporting the unmodified data collected on PMI costs, total PMI labor costs are: CNG—

$0.12/mile vs. hybrid—$0.18/mile. 

• Brakes—brake repairs and reline activities are a large expense for transit bus operations. 

The study’s hybrid buses use regenerative braking, which converts energy back into the 

electric propulsion generator to slow down the vehicle instead of using only the mechanical 

brakes. This braking energy is then stored in the traction batteries for later use, and provides 

increased fuel efficiency for the hybrid buses. Hybrid buses are expected to have reduced 

brake reline and repair costs because they use regenerative braking. During this evaluation, 

the hybrid buses had brake repair costs that were 79% lower than for the CNG buses (CNG—

$0.18/mile vs. Hybrid—$0.04/mile). CNG buses had nine four-wheel relines (planned at 

approximately 18,000 miles), and the hybrid buses had none as of the end of the evaluation. 

Roadcalls 

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. Miles between RC (MBRC) is a typical industry measurement 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 nearly 6,000 MBRC. The hybrid buses had around 

5,000 MBRC. 

For RCs related only to the propulsion system, the hybrid buses are around 8,000 MBRC, and 

the CNG buses are just above that at nearly 9,000 MBRC. For comparison, the older diesel buses 

at Mother Clara Hale Depot have the highest MBRC of the groups at just above 10,000. 

 xi
What’s Next? 

DOE/NREL has started evaluating the EGR equipped hybrid buses from the order of 200 

operating at Manhattanville Depot. This new evaluation provides an opportunity to look at 

newer MY2004 diesel engine technology to be utilized in the hybrid buses, improvements in the 

BAE electric propulsion system, and traction battery replacement experience. Results from this 

evaluation will be available in 2007. 

NYCT recently announced an additional order of 500 Orion/BAE Systems hybrid buses. The 

price for this additional hybrid bus purchase was reported to be a little less than $500,000 each, 

which is reportedly about $150,000 more than a similar, new standard diesel bus. The hybrid 

buses in this evaluation were reported to cost $385,000 or about 25%-30% higher than a similar 

new standard diesel bus. 

 xii
Changes and Additions Since the Interim Report 

This final evaluation report updates the New York City Transit Hybrid and CNG Transit Buses: 

Interim Evaluation Results, January 2006, NREL/TP-540-38843. The interim report covered the 

first eight months of a 12-month evaluation (October 2004 through September 2005) at New 

York City Transit of their Orion VII CNG and hybrid (from the order of 125) buses. This report 

completes the 12 months of data evaluation with the addition of the summer months (June 2005 

through September 2005). This update also includes updates in average diesel fuel costs, which 

increased significantly by the end of the evaluation period. Additional maintenance information 

and analysis have been provided in this report including more attention to missing parts costs and 

work orders as well as describing the experience to date with traction battery failures. 

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 completed by 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 protocol2. 

DOE/NREL previously evaluated the original 10 prototype diesel 

hybrid buses from Orion and BAE Systems operated at NYCT (

Orion VI buses). Results from that evaluation

model 

 

3

 were published in July 

2002 and provided information on the prototype buses from 1998 

through 2001. 

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 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. 

2

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

www.nrel.gov/vehiclesandfuels/fleettest/pdfs/32392.pdf. 3

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

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

 1
Hybrid technology was 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. 

Once NYCT made this 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). 

This evaluation report examines evaluation results from 10 buses from the order of 260 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 now complete through the standard 12-month 

evaluation. Evaluation of 10 buses from the order of 200 hybrid buses is also under way and will 

be reported in a future evaluation report. 

NYCT and MTA Bus (both a part of Metropolitan Transportation Authority) recently made a 

joint order for an additional 500 Orion VII/BAE Systems diesel hybrid buses — 216 buses for 

NYCT and 284 buses for MTA Bus. This order of hybrid buses also allows for 389 additional 

hybrid buses in options. 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. 

DOE / NREL Advanced Vehicle Testing Activity 

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

commercial availability for advanced vehicle technologies that reduce petroleum use while 

meeting air quality standards. AVTA supports DOE’s FreedomCAR & Vehicle Technologies 

Program by examining market factors and customer requirements and evaluating performance 

and durability of alternative fuel and advanced technology vehicles in fleet applications. 

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

advanced technology vehicles. Data collected and analyzed include the operation, maintenance, 

performance, cost, and emissions characteristics of advanced technology vehicles and 

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

advanced and conventional technology vehicles, AVTA evaluations help fleet owners and 

operators make informed purchasing decisions and also provide valuable data to DOE regarding 

the maturity of the technology being assessed. 

In this evaluation at NYCT, the CNG bus study group was used as the baseline group. The CNG 

bus propulsion technology has been available since the early 1990s and has been used by many 

 2
transit agencies. For the last six years, CNG bus purchases have accounted for up to 24% of all 

new transit bus purchases each year in the United States4. 

The AVTA team recently conducted or is in the process of conducting several evaluations of 

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

evaluations, visit www.nrel.gov/vehiclesandfuels/fleettest. 

Table 1. AVTA Heavy Vehicle Evaluations 

Fleet Location Vehicle Technology Evaluation Status 

New York City 

Transit 

Manhattan, Bronx, 

NY 

Orion VII 40-ft 

transit bus 

Series hybrid, BAE Systems 

HybriDrive propulsion system 

(diesel), Order of 125; DDC 

S50G CNG engines 

Interim report for CNG 

and Hybrid (order of 

125) 

New York City 

Transit Manhattan, NY Orion VII 40-ft transit bus 

Series hybrid, BAE Systems 

HybriDrive propulsion system 

(diesel), Order of 200 (next 

generation) 

Just under way, Interim 

Report due by end of 

2006 

King County 

Metro Seattle, WA 

New Flyer 60-ft 

articulated transit 

bus 

Parallel hybrid, GM-Allison 

EP

50 System (diesel) 

Interim report 

completed in 2006; 

Final report planned for 

fall 2006 

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

MicroTurbine (diesel) Completed in 2005 

Knoxville 

Area Transit Knoxville, TN Ebus 22-ft bus Series hybrid, Capstone MicroTurbine (propane) Completed in 2005 

Norcal San Francisco, CA Peterbilt/378, Class 

8 truck 

Cummins Westport ISXG 

high pressure direct injection 

LNG and diesel 

Completed in 2004 

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 

seven major operating divisions: 

• New York City Transit (NYCT) 

• Long Island Rail Road (LIRR) 

• Long Island Bus (LI Bus). 

• Metro-North Railroad 

• Bridges and Tunnels 

• Capital Construction Company 

• MTA Bus 

This report focuses on the bus operations within the NYCT division, 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 

 

4

 Based on data from the American Public Transportation Association (APTA) Fact Books for 2000 through 2005. 

 3
operates 4,483 buses from the following 18 operating depots in the five boroughs of New York 

City. 

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 Division and Mother Clara Hale 

Depot in the Manhattan Division. 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 and EPA pressure to reduce 

emissions from large transit buses—especially those in urban areas (see Table 2). 

Conventional diesel bus propulsion technology (non-hybrid) 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 and are being regulated even lower 

starting in 2007. Future PM regulations are forcing the use of diesel particulate filters (DPFs) 

and will require ultra low sulfur diesel fuel (less than 15 ppm sulfur). This level of PM has been 

addressed by changes in control of engine combustion, and, in a few cases, a diesel oxidation 

catalyst (DOC) was added. 

 4
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 requirement of 2.4 g/bhp-hr HC + NOx caused 

several diesel engine manufacturers to use EGR to help reduce NOx levels. The use of EGR will 

have some effect on durability and fuel economy compared to non-EGR engines. The buses in 

this study did not utilize EGR equipped engines. The next order of 200 (which will be evaluated 

by NREL) will have EGR equipped Cummins engines. 

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

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

penalties for diesels engines with added emissions control systems. These systems may also offer 

an alternative to CNG which offer improved emissions over conventional diesels, but suffer from 

a fuel economy penalty. 

AVTA 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 is focused on hybrid buses from NYCT’s first commercial purchase of 

125 Orion VII hybrid buses and new CNG buses from an order of 260 Orion VII CNG buses as 

the baseline propulsion technology. These hybrid and CNG buses have been operated at two 

different depots at NYCT, which have similar average speeds as discussed later. In order to 

explore the standard baseline at each of these two depots, the operations of older diesel buses 

were included to compare to the hybrid and CNG buses at their respective depots. This 

extension of the evaluation looked at bus usage, fuel economy, and roadcall rate comparisons 

only. 

The AVTA evaluations focus on data collection and analyzing advanced propulsion systems 

compared to baseline propulsion systems. The results from these evaluations are a snapshot of 

 5
experience and actual capital and operating costs at a given location and for a given period of 

time. At this time, the AVTA evaluations do not include an attempt at life-cycle cost modeling. 

AVTA evaluations also track multiple vehicles within a fleet in order to provide enough data 

samples to ensure some level of statistical significance. In this case, 10 vehicles of each 

technology were chosen for data analysis and the AVTA team felt that this number of vehicles 

should provide accurate and statistically valuable data. 

All 40-foot buses at the two depots included in this evaluation (West Farms and Mother Clara 

Hale Depots) 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 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 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). 

Vehicle System Descriptions 

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

comparison 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 buses. 

CNG Buses at West Farms Depot 

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 purchase the optional catalyst for emissions aftertreatment for these buses. 

 6
Table 3. Vehicle System Descriptions 

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

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 

Diesel Extended Comparison Buses at West Farms Depot 

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

buses have been operating there. 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 for a limited comparison to 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. 

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, Inc. The hybrid buses are 

equipped with an Engelhard DPX for exhaust aftertreatment. This DPF is actively monitored and 

regenerated (as needed) as part of the BAE Systems HybriDrive hybrid propulsion system. Table 

4 describes major components of the electric propulsion system. 

 7
Table 4. Hybrid Propulsion-Related Systems 

Category Hybrid Bus Description 

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 Extended Comparison Buses at Mother Clara Hale Depot 

The diesel buses at Mother Clara Hale depot are model year 1999 Orion V high floor buses, but 

from a newer bus order than those at West Farms Depot. 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 use. 

DDC Series 50 Diesel and CNG Engine 

Both the DDC Series 50 diesel and DDC Series 50 CNG engines are no longer available for new 

transit buses. 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 after limited refinements in the last few years. Thus, the 

DDC Series 50G natural gas engine, operated by NYCT is not the newest technology natural gas 

engine (with fuel and electronic controls) currently available. Newer engines from other 

manufacturers may have shown better results. 

Hybrid and CNG Baseline Vehicle Differences 

The hybrid and CNG baseline buses are the same model buses and essentially the same age 

(model year 2002). Both bus types met the NYCT performance requirements. Some of the 

differences between the two bus study groups follow. 

• CNG buses are taller (3 inches) 

• Hybrid buses are heavier (440 lbs) 

• Hybrid buses have a smaller size engine (5.9 liter diesel versus a 8.5 liter natural gas) 

• Hybrid buses have a DPF, the CNG buses did not have additional emissions control 

• Hybrid buses have regenerative brakes and CNG buses have a retarder 

• Hybrid buses have a smaller fuel capacity (100 gallons for hybrid and 125 gallons diesel 

equivalent for CNG) 

• These hybrid buses (order of 125) were reported to be only $72,000 more per unit than a 

CNG bus; however, the recent purchase of 500 hybrid buses at NYCT show the 

incremental hybrid price will exceed $100,000 compared to CNG and $150,000 

compared to new diesel buses. 

 8
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 down-sized 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. Orion and BAE Systems currently (June 2006) have 325 Orion VII diesel hybrid 

buses in service at NYCT. 

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 

 9
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. West Farms Depot 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 (it met all local New York building codes and requirements) 

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 $0.25 per 

therm or $0.35 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 

 10
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, each hybrid bus requires a conditioning charge process 

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

maintenance routine; the charger is shown in Figure 6. The conditioning is done to help extend 

the battery pack life to at least three years. The battery conditioner performs a slow controlled 

charge of the batteries, while monitoring each battery for specific voltage changes that indicate 

the conditioning cycle is complete. Without this battery conditioning, the traction batteries will 

exhibit a hysteresis effect of lower and lower energy storage capacity over time. The depots with 

the Orion/BAE System hybrid propulsion system have received or will receive at least two of the 

conditioner units, which cost $70,000 each. 

Figure 5. Mother Clara Hale Depot 

 11
Figure 6. Hybrid Traction Battery Conditioning Unit 

Implementation Experience 

The discussion in this section is based on overall fleet-level results (260 CNG buses and 125 

hybrid buses) of mileage accumulation and roadcalls (RCs) for the CNG and hybrid bus fleets. 

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 in this section. 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 buses 

• Average monthly mileage per bus 

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

 12
Of these three topics, reliability (MBRC) is the only one directly covered in this report. 

Availability and recovery time were not available for this study. Availability is collected in 

NYCT’s system, but is not archived, so it was not available for this evaluation. Recovery time 

was not readily available from NYCT’s system. 

CNG Buses 

NYCT currently has 481 CNG buses split between two depots—the West Farms and Jackie 

Gleason Depots. 

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

number grew to 221 by 2001, all operating at Jackie Gleason Depot. As mentioned earlier, 

NYCT purchased 260 new CNG Orion VII buses. 

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

approximately November 2004. West Farms Depot started its first new Orion VII CNG bus in 

service in September 2003. Figure 7 shows total mileage accumulation at the two CNG bus 

depots. At the end of September 2005, the total Orion VII CNG fleet had reached nearly 12 

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

2,000,000

4,000,000

6,000,000

8,000,000

10,000,000

12,000,000

14,000,000

Mar03May03Jul03Sep03Nov03Jan04Mar04May04Jul04Sep04Nov04Jan05Mar05May05Jul05Sep05

Total Miles

Jackie Gleason Depot West Farms Depot Total Mileage

Figure 7. CNG Bus Fleet Cumulative Mileage (260 Buses) 

 13
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 Jun-05 Sep-05

Average Monthly Miles/Bus

Jackie Gleason West Farms

Figure 8. CNG Bus Fleet Cumulative Average Monthly Mileage per Bus (260 Buses) 

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 was between 7,000 and 8,000 MBRC by the end of the data period. 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. A few 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 are in the process of being changed out. 

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

changed to a different spark plug and is now getting the required 24,000 miles between 

changes. 

• Fuel door switches were changed out. 

• Hydraulic cooling fan motor; changing configuration and motors 

• Regulator problems; now resolved. 

 14
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 Aug-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 (260 Buses) 

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 was split between Mother Clara Hale and Queens Village Depots. The 

order of 200 hybrid buses was split between the Fresh Pond and Manhattanville Depots 

(Manhattanville was the operating location for the original 10 prototype hybrid buses). 

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 September 2005, the hybrid fleet had reached nearly 4 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. 

 15
0

500,000

1,000,000

1,500,000

2,000,000

2,500,000

3,000,000

3,500,000

4,000,000

4,500,000

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

Total Miles

Mother Clara Hale Queens Village Cumulative Mileage

Figure 10. Hybrid Fleet Cumulative Mileage (125 Buses) 

0

500

1000

1500

2000

2500

3000

3500

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

Average Monthly Miles/Bus

Mother Clara Hale Queens Village

Figure 11. Hybrid Fleet Cumulative Average Monthly Mileage per Bus (125 Buses) 

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 Depot achieved this 

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

 16
and Queens Village Depot is approaching an MBRC of 10,000. The propulsion-related MBRC 

for both depots jumped in December 2004. 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 bus systems can also be 

indicated by the propulsion control system. 

0

2,000

4,000

6,000

8,000

10,000

12,000

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

Miles Between Roadcalls (MBRC)

MCH Total MBRC MCH Propulsion MBRC

QV Total MBRC QV Propulsion MBRC

Figure 12. Hybrid Fleet Cumulative Average MBRC (125 Buses) 

A few items specific for 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 (the triple pump has been eliminated from subsequent orders) 

• 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) underwent a warranty maintenance campaign to 

address the items listed above for both groups and several other items. This is a significant fleet 

campaign that was completed at the end of 2005. 

 17
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 (and their 

suppliers) agreed to a significant campaign of the entire Orion VII fleet at NYCT (hybrid and 

CNG) completed at the end of 2005. The entire evaluation of the hybrid order of 125 and the 

CNG buses was completed before that major campaign finished. We intend to capture the results 

and impact of this campaign (for the hybrid buses) during the evaluation of the order of 200 

hybrid buses. 

The evaluation results shown in this section of the report are focused on a 12-month evaluation 

period for the selected ten CNG and ten hybrid buses (October 2004 through September 2005). 

The evaluation 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 buses 

(nine diesel buses in each group) 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 

started a little earlier than the two study bus groups (CNG and hybrid) to ensure that the study 

buses would not be transferred during this study. 

Route Descriptions 

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

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 Depot 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 

 18
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. 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 

(approximately 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 

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

hybrid buses. The overall 12-month average monthly miles per bus are essentially the same for 

the CNG and hybrid buses, with the hybrid buses having a 3% higher average. This supports the 

premise that these two study groups are being used in a similar fashion. One other aspect of the 

table is the end hubodometer reading for these two study groups. The average end hubodometer 

for the CNG study group (average of 44,103 miles) is an average of 3,000 miles higher than the 

hybrid study group (average 40,978 miles). This would be a mileage difference of about one 

preventive maintenance work order cycle. This also supports the premise that these two study 

groups should be similar for maintenance cost per mile comparisons. 

Figure 13 shows cumulative average monthly miles per bus for the CNG and hybrid buses. The 

average monthly mileage for the hybrid buses went down over time as the number of hybrid 

buses at the depot increased, and therefore the need for higher usage went down. The CNG bus 

average usage did not change much during the evaluation period, and the two study fleets 

essentially had the same average usage by the end of the evaluation period. 

 19
Table 7. CNG and Hybrid Monthly Mileage per Bus 

Bus Starting 

Hubodometer 

Ending 

Hubodometer Total Mileage Months Monthly 

Average 

7657 26,249 53,732 27,483 12 2,290 

7662 20,490 51,042 30,552 12 2,546 

7666 23,754 44,607 20,853 12 1,738 

7670 25,240 52,118 26,878 12 2,240 

7677 16,597 45,229 28,632 12 2,386 

7688 13,231 41,131 27,900 12 2,325 

7708 9,772 39,947 30,175 12 2,515 

7715 11,386 39,684 28,298 12 2,358 

7719 10,412 37,793 27,381 12 2,282 

7721 8,454 35,746 27,292 12 2,274 

CNG 275,444 120 2,295 

6367 15,224 41,607 26,383 12 2,199 

6368 15,391 43,378 27,987 12 2,332 

6369 14,081 40,244 26,163 12 2,180 

6375 12,063 41,799 29,736 12 2,478 

6378 11,328 42,212 30,884 12 2,574 

6379 8,874 37,684 28,810 12 2,401 

6380 13,320 40,480 27,160 12 2,263 

6381 10,904 39,269 28,365 12 2,364 

6382 12,889 42,003 29,114 12 2,426 

6387 11,260 41,101 29,841 12 2,487 

Hybrid 284,443 120 2,370 

0

500

1000

1500

2000

2500

3000

3500

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

Average Monthly Miles/Bus

CNG Avg Mi/Bus CNG Cumulative Mi/Bus

Hybrid Avg Mi/Bus Hybrid Cumulative Mi/Bus

Figure 13. CNG and Hybrid Monthly Mileage per Bus 

Table 8 summarizes the two diesel study bus groups’ monthly mileage per bus. The diesel bus 

study group at West Farms Depot had an overall average mileage per bus of 1,952 and the diesel 

 20
buses at Mother Clara Hale Depot had 2,385 miles per bus average (both for a 12-month period 

between June 2004 to May 2005). The diesel buses at West Farms Depot have a much lower 

average mileage per bus, and this has most likely occurred because of the age of the buses. The 

older buses are typically used less than newer buses (especially compared to buses under 

warranty). Comparing the diesel buses from Mother Clara Hale Depot with the CNG and hybrid 

buses, the CNG buses had an average monthly mileage per bus 4% lower and the hybrid buses 

were 1% lower (or essentially the same). 

Table 8. Diesel Study Bus Monthly Mileage per Bus 

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 

West Farms 

Diesel 191,264 98 1,952 

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 

Mother Clara 

Hale Diesel 257,624 108 2,385 

Fuel Economy and Cost 

NYCT buses use ultra low sulfur No. 1 diesel fuel at less than 30 ppm sulfur content. This sulfur 

level is required to be less than 15 ppm by the end of 2006. 

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

Trillium USA. The CNG study group fuel consumption and economy is shown in Table 9 and 

Figure 14. The fuel economy for the CNG buses is shown in diesel gallon equivalent units based 

on an energy conversion of CNG to diesel equivalent at the dispenser. With a fuel economy of 

1.70 miles per diesel equivalent gallon, the CNG study group has a 25% lower fuel economy 

than the diesel buses operating at West Farms. Based on the duty cycle at West Farms Depot 

(average speed between 6.3 mph and 6.5 mph), this lower fuel economy is within typical 

 21
expectations based on previous studies.5

 A more recent study from DOE/NREL showed that 

newer technology CNG engines might show only a 16%-18% penalty compared to diesel.6 The 

low average speed of the NYCT operation is the key to this significantly lower fuel economy. 

Compared to the diesel buses operating in a similar duty cycle at Mother Clara Hale Depot, the 

CNG buses had a 28% lower fuel economy. 

The NYCT bus duty cycle is a severe application for spark ignited (SI) natural gas engines 

because of the slow average speed (about 6 mph) and frequent stops, which indicates the engine 

is operating at a low speed and load for much of its operating time. SI engines typically have a 

lower thermal efficiency at low speed and load than compression ignition (CI) diesel engines. 

Consequently, lower natural gas fuel economy is expected in this type of operation. 

The hybrid study fleet fuel consumption and economy is also shown in Table 9 and Figure 14. 

The 12-month average fuel economy for the hybrid buses (average of 3.19 mpg) is 34% higher 

than the diesel buses (average 2.38 mpg for a 12-month period, June 2004 to May 2005) 

operating at Mother Clara Hale Depot and 40% higher than the diesel buses (average 2.28 mpg 

for a 12-month period, June 2004 to May 2005) operating at West Farms Depot. Compared to the 

average diesel fuel economy between both depots, the hybrid study fleet achieved 37% higher 

fuel economy. The hybrid bus study fleet also exhibited 88% higher fuel economy than the CNG 

study fleet. 

Figure 14 shows 12 months of average monthly fuel economy for the two diesel study groups, 

CNG, and hybrid buses. The two diesel study groups have data shifted four months prior to the 

start of data for the CNG and hybrid study groups. The two diesel study groups have similar 

average fuel economy results for the evaluation period shown. The hybrid bus fuel economy has 

fluctuated generally between 26% and 52% higher than for the diesel buses in the same time 

frame at Mother Clara Hale Depot; however, during the summer months this positive difference 

dipped as low as only 12% for one month during the summer. 

 

5

 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) 6

 Washington Metropolitan Area Transit Authority: Compressed Natural Gas Transit Bus Evaluation, 2006, NREL, 

NREL/TP-540-37626 (http://www.nrel.gov/vehiclesandfuels/ngvtf/pdfs/37626.pdf). 

 22
Table 9. CNG and Hybrid Bus Fuel Use and Economy 

Bus Mileage 

(Fuel Base) 

Gallons 

Consumed MPG 

7657 25,236 14,737.1 1.71 

7662 28,795 15,384.0 1.87 

7666 20,086 12,213.5 1.64 

7670 24,581 14,667.8 1.68 

7677 26,370 15,240.0 1.73 

7688 26,067 15,686.0 1.66 

7708 28,860 17,508.8 1.65 

7715 27,187 15,509.1 1.75 

7719 26,368 16,619.8 1.59 

7721 25,533 14,449.9 1.77 

CNG 259,083 152,016.0 1.70 

6367 25,278 8,035.0 3.15 

6368 24,989 8,025.5 3.11 

6369 24,229 7,416.5 3.27 

6375 22,541 6,951.5 3.24 

6378 28,161 8,535.5 3.30 

6379 26,744 8,497.5 3.15 

6380 23,979 8,042.0 2.98 

6381 26,738 8,196.9 3.26 

6382 27,171 8,239.5 3.30 

6387 28,090 8,844.5 3.18 

Hybrid 257,920 80,784.4 3.19 

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

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

Miles per Diesel Gallon

WF Diesel MCH Diesel CNG Hybrid

Figure 14. Average Fuel Economy (MPG) 

 23
The hybrid bus average fuel economy had a much larger decrease/fluctuation in fuel economy in 

the summer months (June through September) than any of the other three study bus groups 

shown. According to BAE Systems, much of this decrease is due to an increase in energy 

consumption for air conditioning. Although air conditioning load is similar for all four study bus 

groups, this is compared as a percentage to a much lower overall fuel consumption for the hybrid 

buses (see Figure 15). Additional factors such as different engine sizes, CNG engine thermal 

efficiency changes with loading, and others likely contribute to the magnitude of the summer 

versus winter fuel economy differences between the three different propulsion types. In other 

words, all four study bus groups have a significant increase of energy consumption for air 

conditioning in the summer months, but this increase represents a much larger percentage of 

overall fuel consumption for the hybrid buses, resulting in a larger penalty in fuel efficiency. 

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

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

Fuel Consumption (gal/mile) 

MCH Diesel WF Diesel CNG Hybrid

Figure 15. Average Fuel Consumption (Diesel Equivalent Gallons per Mile) 

Table 10 shows fuel consumption and economy results for the two diesel study groups of buses. 

There is one diesel bus from West Farms Depot listed (and shaded) that is not included in the 

total because this bus had a new DDC Series 50 EGR engine installed in place of the original 

DDC Series 50 engine. This bus showed a fuel economy (2.04 mpg) that was consistently 10% 

lower than the rest of the diesel study group from West Farms Depot (2.28 mpg). This would 

indicate that for this repower, the fuel economy effect of having the newer, lower emissions 

engine was a 10% loss of fuel economy. 

 24
Table 10. Diesel Bus Fuel Use and Economy 

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 

West Farms 

Diesel 186,682 82,019.4 2.28 

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 

Mother Clara 

Hale Diesel 249,990 105,137.5 2.38 

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

The hybrid bus average fuel economy for the 12-month evaluation period fluctuated between 

60% and 120% higher fuel economy than the CNG buses based on diesel equivalent units. 

During the evaluation period, diesel fuel at NYCT cost an average of $1.78 per gallon for ultra 

low sulfur diesel fuel with sulfur less than 30 ppm. The diesel fuel cost went up significantly by 

the end of the evaluation period for this report ($2.26 per gallon in September 2005). 

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 an average of $1.00 per therm for the natural gas and $0.25 per therm for Trillium, 

which results in a total cost of $1.25 per therm or $1.74 per diesel equivalent gallon. 

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

$1.02 per mile for CNG ($0.78 per mile for diesel)—31% higher for CNG at West Farms Depot. 

The fuel costs for hybrid buses were 25% lower than their diesel baseline study group at $0.75 

per mile for diesel and $0.56 per mile for hybrid buses at Mother Clara Hale Depot. Across both 

depots, the CNG buses have a fuel cost per mile 45% higher than the hybrid buses. 

Maintenance Analysis 

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

life of a transit bus. This short evaluation period does not provide enough of the capital and 

 25
operating costs to understand the full 12-year life cycle cost of the CNG, or hybrid buses. In 

order to gain a complete understanding of costs, one must examine the purchase cost of the 

buses, cost of facility modification or addition, warranty cost, operations cost (and savings), and 

longer term maintenance costs (such as engine rebuilds or replacements, traction battery 

replacements, brake repair savings, etc.). However, the intent of this evaluation is to provide 

accurate actual capital and known operations costs experienced for hybrid and CNG vehicles for 

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

transit agency beyond the warranty period. The general warranty on these particular hybrids is 

two years from date of purchase, with some drivetrain components warranted beyond two years. 

The exact components and warranty periods are negotiated by NYCT and Orion, and are 

contractual. 

The maintenance analysis in this section provides a comparison of hybrid buses to CNG buses. 

The diesel buses at the two depots are older, and are therefore an inappropriate comparison due 

to their higher maintenance costs. The CNG and hybrid buses are new enough that much of the 

maintenance is done under warranty by the manufacturers and their distributor mechanics. When 

possible, this warranty maintenance cost is captured and provided separately in the report, but is 

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

evaluation of total maintenance cost offers an incomplete picture of true maintenance cost. 

However, this analysis, with the absence of warranty costs, does reflect the actual cost to the 

transit agency during the time period selected. 

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 (as discussed above in Bus Usage). 

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

through the end of the evaluation period (September 2005). 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 September 

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 other analysts can 

change this rate to one more similar to their own. Also, this rate does not directly 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. One of the CNG buses had higher total maintenance costs 

 26
than the other CNG buses. These higher costs were caused mostly by brake reline activities. 

There was also one hybrid bus (bus 6379) that had total maintenance costs 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. 

There was one significant accident in June 2005 for this bus as well. Several of these significant 

repairs are a part of the aforementioned campaigns for the hybrid buses. 

The total maintenance cost per mile for the CNG buses was 5% higher than the hybrid buses, 

parts costs on average were 40% higher for the CNG buses, and labor hours were 13% higher for 

the hybrid buses. These differences will be explored further in the next discussion about 

maintenance cost breakdown by vehicle systems. 

Table 11. CNG and Hybrid Bus Total Maintenance Costs 

(October 2004—September 2005) 

Bus Mileage Parts ($) Labor 

Hours 

Cost per 

Mile ($) 

7657 27,483 9,524.10 609.5 1.46 

7662 30,552 9,245.59 504.1 1.13 

7666 20,853 12,510.57 619.7 2.09 

7670 26,878 10,097.71 482.5 1.27 

7677 28,632 13,169.32 582.0 1.48 

7688 27,900 12,678.36 581.9 1.50 

7708 30,175 9,562.91 454.6 1.07 

7715 28,298 6,155.98 422.1 0.96 

7719 27,381 9,638.15 433.7 1.14 

7721 27,292 7,397.03 442.8 1.08 

Total CNG 275,444 99,979.72 5,132.8 1.29 

Avg. per Bus 27,544 9,997.97 513.3 -- 

6367 26,383 8,172.50 591.4 1.43 

6368 27,987 4,856.74 479.9 1.03 

6369 26,163 6,109.25 604.5 1.39 

6375 29,736 6,009.55 649.1 1.29 

6378 30,884 4,901.92 556.2 1.06 

6379 28,810 9,240.45 761.1 1.64 

6380 27,160 5,070.21 419.3 0.96 

6381 28,365 5,092.11 556.2 1.16 

6382 29,114 5,591.24 572.0 1.17 

6387 29,841 5,433.59 602.8 1.19 

Total Hybrid 284,443 60,477.56 5,792.5 1.23 

Avg. per Bus 28,444 6,047.76 579.3 -- 

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 only for inspections during preventive 

maintenance 

• Tires—This only includes tire repairs; costs for the replacement of the tires themselves 

are not collected or presented in the maintenance analysis 

 27
• Propulsion-related systems—Repairs for exhaust, fuel, engine, electric motors, traction 

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

and hydraulics 

• 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 

• 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. 

Table 12. Breakdown of Vehicle System Maintenance Cost per Mile 

(October 2004—September 2005) 

CNG West Farms Hybrid Mother Clara 

Hale 

Vehicle System Cost per 

Mile ($) 

Percent 

of Total 

(%) 

Cost per 

Mile ($) 

Percent 

of Total 

(%) 

Cab, Body, and 

Accessories 0.33 26 0.39 32 

Propulsion-related 0.35 27 0.37 30 

PMI 0.12 9 0.17 14 

Brakes 0.18 14 0.04 3 

Frame, Steering, 

and Suspension 0.06 5 0.07 6 

HVAC 0.07 5 0.08 6 

Lighting 0.05 4 0.05 4 

Air, General 0.05 4 0.03 2 

Axles, Wheels, and 

Drive Shaft 0.04 3 0.02 2 

Tires 0.04 3 0.01 1 

Total 1.29 100 1.23 100 

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. 

 28
Table 13. Top 5 Maintenance Cost Categories 

Rank CNG West Farms Hybrid Mother 

Clara Hale 

1 Propulsion-related Cab, Body, and 

Accessories 

2 Cab, Body, and 

Accessories 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, transmission, and hydraulic 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 per mile for the CNG buses were 5% lower 

than the hybrid buses. 

A breakdown of the propulsion-related maintenance costs included: 

• Exhaust system maintenance—The hybrid and CNG buses had essentially the same 

maintenance costs for this system. The hybrid bus group had troubleshooting issues 

involving the DPF backpressure sensor and a few exhaust backpressure sensors were 

replaced. The rest of the maintenance costs for this system were related to inspections of 

the exhaust piping and clamps. All 10 hybrid buses appeared to have undergone the 

yearly cleaning for the DPF. The CNG buses have had a problem with the thermal 

blanket on the exhaust wearing out from vibration. The thermal blanket insulation was 

replaced 19 times during the evaluation period. This issue has not yet been permanently 

resolved. 

• Fuel system maintenance—The CNG buses had fuel system maintenance costs 74% 

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 5% 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 

also in the process of being rebuilt as part of a campaign with new cylinder kits along 

with new spark plugs, which is not reported here as a cost as it is covered under warranty. 

The hybrid bus diesel engine is smaller than the CNG engine and parts costs for standard 

preventive maintenance are lower for the hybrid buses. 

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

buses evaluated at Mother Clara Hale Depot. Most of the 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 

 29
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 lights. 

Table 14. Propulsion-Related Maintenance Cost by System (October 2004—September 2005)

Vehicle System CNG West 

Farms 

Hybrid Mother 

Clara Hale 

Mileage 275,444 284,443 

Total Propulsion-related Systems (Roll-Up) 

Parts Cost ($) 37,080.52 10,880.98 

Labor Hours 1181.5 1870.1 

Total Cost ($) per Mile 0.349 0.367 

Exhaust System Repairs 

Parts Cost ($) 3,058.60 879.07 

Labor Hours 48.0 120.2 

Total Cost ($) per Mile 0.020 0.024 

Fuel System Repairs 

Parts Cost ($) 8,226.37 1,845.80 

Labor Hours 154.2 48.8 

Total Cost ($) per Mile 0.058 0.015 

Engine System Repairs 

Parts Cost ($) 3,320.92 2,477.86 

Labor Hours 288.2 295.8 

Total Cost ($) per Mile 0.064 0.061 

Electric Motor, Generator, and Battery Repairs 

Parts Cost ($) 2,922.96 

Labor Hours 972.9 

Total Cost ($) per Mile 0.181 

Non-Lighting Electrical System Repairs (General Electrical, 

Charging, Cranking, Ignition) 

Parts Cost ($) 10,890.80 849.89 

Labor Hours 340.6 220.7 

Total Cost ($) per Mile 0.101 0.042 

Air Intake System Repairs 

Parts Cost ($) 2,342.26 922.20 

Labor Hours 20.5 13.8 

Total Cost ($) per Mile 0.012 0.006 

Cooling System Repairs 

Parts Cost ($) 2,920.49 361.91 

Labor Hours 232.6 169.0 

Total Cost ($) per Mile 0.053 0.031 

Transmission Repairs 

Parts Cost ($) 6,213.90

Labor Hours 75.0

Total Cost ($) per Mile 0.036

Hydraulic Repairs 

Parts Cost ($) 107.18 621.29 

Labor Hours 22.5 29.0 

Total Cost ($) per Mile 0.005 0.007 

 30
Table 15. Summary of Propulsion-Related Maintenance Cost Comparisons* 

Vehicle System CNG ($/mile) Hybrid ($/mile) Hybrid vs. CNG 

Total Propulsion-Related 0.349 0.367 5% (higher) 

Exhaust 0.020 0.024 22% (higher) 

Fuel 0.058 0.015 -74% (lower) 

Engine 0.064 0.061 -5% (lower) 

Electric Propulsion/Transmission 0.036 0.181 403% (higher) 

Non-Lighting Electrical 0.101 0.042 -58% (lower) 

Air Intake 0.012 0.006 -53% (lower) 

Cooling 0.053 0.031 -41% (lower) 

Hydraulic 0.005 0.007 62% (higher) 

* 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 5% higher; this is hybrid costs being 5% higher than 

CNG for this category. 

During the evaluation period (October 2004 through September 2005), the hybrid study 

bus group had 11 incidents involving seven of the 10 buses that required at least one 

traction battery to be replaced; a total of 22 traction batteries. This translates into a 4.8% 

per year failure rate taking into account that each of the 10 hybrid buses has 46 traction 

batteries and the evaluation period is one year long. Two of these incidents caused a 

roadcall as well. On average, each of these incidents required 13 hours of mechanic time 

to troubleshoot, remove, and replace the affected traction batteries. 

NYCT reported some concern about the amount of labor required and the number of 

these incidents. BAE Systems has been investigating the situation including having the 

traction battery manufacturer (Hawker/EnerSys) inspect and report on the removed 

traction batteries. The results from this investigation showed that none of the traction 

batteries failed, a few had manufacturing defects, and a few had mechanical damage 

(maybe from installation). Hawker/EnerSys reported changes in procedure to improve 

the manufacturing process. BAE Systems released a software change in April 2006 for 

the hybrid propulsion system to make identifying faulty batteries a little less aggressive 

and reduce the overall number of traction batteries removed with no true failure. This 

may have a small effect on fuel economy; however, BAE Systems did not expect any 

measurable difference in fuel economy. 

These batteries are approaching their three-year life expectancy in another year. The 

competing traction battery technology (nickel metal hydride—NiMH) for this application 

is currently reported to be three to four times more expensive than the lead-acid 

technology in use now with only a two times life expectancy increase. NYCT and BAE 

Systems are planning the first traction battery changeouts for the order of 125 hybrid 

buses. 

During the evaluation, all 10 hybrid buses had the traction batteries conditioned with the 

on-site chargers at Mother Clara Hale Depot. The conditioning charge is needed to help 

extend the life of the traction batteries and was completed twice (every six months) 

during the evaluation period (first around 10-11/2004 and second around 6-7/2005). 

Although there was a work order created for this traction battery conditioning, there was 

 31
essentially no mechanic time charged to this activity. NYCT spent time making sure that 

the traction battery conditioning is scheduled as part the preventive maintenance. 

• 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 $261 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. Four of the 10 CNG buses received these new 

spark plugs during the evaluation period. 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 53% 

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

this category. The hybrid bus diesel engine is smaller than the CNG engine and parts 

costs for standard preventive maintenance are lower for the hybrid buses. 

• Cooling system maintenance costs—The CNG buses had maintenance costs 41% higher 

than the hybrid buses. The hybrid bus diesel engine is smaller than the CNG engine and 

parts costs for standard preventive maintenance are lower for the hybrid buses. 

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

The CNG buses had six oil coolers replaced at approximately $900 each plus labor. 

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

and hybrid buses. The hybrid propulsion maintenance cost starts out low and comes up above 

$0.40 in February 2005 and then climbs slowly up to $0.48 per mile by the end of the evaluation 

period. This is most likely due to the added maintenance costs of the NYCT mechanics taking 

over some of the unscheduled warranty-related troubleshooting and maintenance of the hybrid 

buses from the BAE Systems technicians. 

The CNG propulsion maintenance cost starts high in the first month (four transmission oil 

coolers and three natural gas regulators), peaks in April 2005 (electrical, exhaust blanket 

insulation, and transmission), drops significantly below the hybrid line, and then comes back up 

to the level of the hybrid costs at the end of the evaluation period (electrical, exhaust blanket 

insulation, and fuel system). 

The CNG propulsion maintenance costs for parts are more than three times those reported for the 

hybrid group, which most likely had many of the more expensive parts covered under warranty; 

warranty costs are not included here. The comparison of labor hours shows the opposite—the 

hybrid propulsion maintenance has 57% more labor hours than for the CNG propulsion 

 32
maintenance. This is most likely due to NYCT learning how to troubleshoot the more complex 

hybrid electric propulsion system. 

0.000

0.100

0.200

0.300

0.400

0.500

0.600

0.700

0.800

Oct-04 Nov04Dec04Jan-05 Feb05Mar05Apr05May05Jun05Jul-05 Aug05Sep-05

Propulsion Maintenance Cost ($)/Mile

CNG Hybrid

Figure 16. Propulsion-Related Maintenance Cost per Mile for CNG and 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 and are generally independent of the 

advanced technology being evaluated in this study. It is included to give some perspective to the 

various bus maintenance costs. 

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

(October 2004—September 2005) 

CNG West Farms Hybrid Mother Clara 

Hale Vehicle Subsystem Cost per 

Mile ($) 

Percent 

(%) 

Cost per 

Mile ($) 

Percent 

(%) 

Doors and Interlock 0.05 15 0.10 25 

Wheelchair Lift / Ramp 0.04 12 0.05 13 

Body—Exterior 0.11 34 0.12 31 

Cleaning 0.04 12 0.04 10 

Mirrors 0.02 6 0.02 5 

General Interior and 

Seats 0.03 9 0.03 7 

Windshield Wipers 0.02 6 0.01 3 

Supplies and 

expendable items 0.01 3 0.00 0 

Horn 0.01 3 0.01 3 

Fire Extinguisher 0.00 0 0.01 3 

Total 0.33 100 0.39 100 

 33
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 related to the air conditioning. 

Both study groups of buses utilized the same HVAC system. The maintenance costs for the two 

study groups are shown in Table 17. The maintenance cost per mile for the CNG buses was 11% 

lower than for the hybrid buses. 

Table 17. HVAC System Maintenance Costs (October 2004—September 2005) 

Fleet Mileage Parts 

Cost ($) 

Labor 

Hours 

Cost per 

Mile ($) 

West Farms CNG 275,444 7,097.42 241.2 0.070 

Mother Clara Hale Hybrid 284,443 4,202.86 361.4 0.078 

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, similar to a transmission retarder. The energy from braking is taken 

into the electric motor and then fed back to the traction batteries. Non-hybrid buses are expected 

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

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 79% higher brake maintenance cost per mile 

compared to the hybrid buses. The six oldest CNG buses in the study group had at least one fourwheel reline of the brakes during the evaluation period. Three of those six CNG buses had the 

four-wheel reline twice during the evaluation period. There were also some repairs for issues 

with the antilock brake system for the CNG and hybrid buses. Brake maintenance costs for CNG 

buses were consistently around 80% higher for CNG for the entire 12-month evaluation period. 

Table 18. Brake System Maintenance Costs (October 2004—September 2005) 

Fleet Mileage Parts 

Cost ($) 

Labor 

Hours 

Cost per 

Mile ($) 

West Farms CNG 275,444 12,517.92 725.1 0.177 

Mother Clara Hale Hybrid 284,443 1,797.66 171.9 0.037 

PMI 

This is preventive maintenance inspection labor time spent on the buses. Based upon the data 

collected during this evaluation, the hybrid buses had 50% more labor spent on scheduled 

maintenance time. However, due to the way in which the NYCT mechanics record their time, 

additional unscheduled activities are included in what is defined as PMI. No difference in PMI 

labor is expected between the CNG and hybrid buses. This reporting discrepancy must be 

recognized when considering the apparent difference in PMI labor for CNG and hybrid buses. 

However, in keeping with our intent of reporting unbiased data, but applying the appropriate 

caveats, PMI costs are presented in Table 19, below. 

 34
Table 19. Preventive Maintenance Inspection Maintenance Costs (October 2004—September 2005) 

Fleet Mileage Parts 

Cost ($) 

Labor 

Hours 

Cost per 

Mile ($) 

West Farms CNG 275,444 0.00 646.8 0.117 

Mother Clara Hale Hybrid 284,443 0.00 996.2 0.175 

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 19% lower than the hybrid 

buses. 

Table 20. Frame, Steering, and Suspension Maintenance Costs (October 2004—September 2005) 

Fleet Mileage Parts 

Cost ($) 

Labor 

Hours 

Cost per 

Mile ($) 

West Farms CNG 275,444 5,324.46 244.9 0.064 

Mother Clara Hale Hybrid 284,443 8,175.53 267.7 0.076 

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. During the evaluation period, the CNG buses had 19.5 labor hours and $5,575.09 in parts 

costs removed from the analysis in this report. The hybrid buses had 13 labor hours and 

$13,651.82 in parts costs removed from the evaluation period analysis in this report. The 

reported labor hours were from Atlantic Detroit Diesel Allison (local dealer), Cummins, Vapor 

Corporation, and Orion. These figures do not include all warranty costs experienced at NYCT 

and are not included in the previous maintenance cost sections. Many repair actions were 

performed for both study fleets by the manufacturer service representatives on site at NYCT and 

not captured in the maintenance tracking system or this evaluation. 

Roadcall Analysis 

Figure 18 shows the cumulative average 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 Depot 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 

for the MCH diesel buses and just under 6,000 MBRC for the CNG buses. The MBRC of the 

hybrid buses has started to settle below 6,000 MBRC for the evaluation period. 

 35
0

2,000

4,000

6,000

8,000

10,000

12,000

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

Miles Between All Roadcalls (MBRC)

WF Diesel CNG MCH Diesel Hybrid

Figure 17. Cumulative Average MBRC 

Figure 19 shows cumulative average MBRC over the evaluation periods 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 diesel buses at West Farms Depot had the lowest propulsion-related MBRC at around 5,000. 

The CNG buses had a propulsion-related MBRC that steadily rose over the evaluation period to 

around 8,800. The diesel buses at Mother Clara Hale had the highest propulsion-related MBRC 

at the end of the evaluation period at just over 10,000. The hybrid buses started the evaluation at 

a high propulsion-related MBRC that has leveled out a little lower than the CNG buses (8,100). 

 36
0

5,000

10,000

15,000

20,000

25,000

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

Miles Between Roadcalls (MBRC)

WF Diesel CNG MCH Diesel Hybrid

Figure 18. 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 Depot 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 

Depot 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. 

 37
Table 21. Roadcalls for Each Fleet by System (October 2004—September 2005) 

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 1 2 1 2 5 9 

Door and Interlock 16 22 9 19 10 22 5 9 

Mirrors and Sun 

Visor 1 1 0 0 0 0 0 0 

Air-General 1 1 0 0 1 2 4 7 

Brakes 2 3 0 0 0 0 1 2 

Steering 3 4 1 2 1 2 1 2 

Suspension 2 3 3 6 2 5 2 4 

Transmission* 3 4 2 4 1 2 0 0 

Non-Lighting 

Electrical* 5 7 13 27 6 13 4 7 

Lighting 0 0 1 2 2 5 0 0 

Cooling* 16 22 1 2 5 11 5 9 

Exhaust* 2 3 0 0 2 5 0 0 

Fuel* 2 3 6 13 4 9 2 4 

Engine* 10 14 9 19 4 9 2 4 

Electric Propulsion* 0 0 0 0 0 0 22 39 

Wheelchair 

Lift/Ramp 6 9 2 4 6 13 2 4 

Total 72 100 48 100 45 100 55 100 

* These systems represent the propulsion-related vehicle systems. 

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 23% 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. 

 38
Table 22. Summary of Cost per Mile for CNG and Hybrid Buses (October 2004—September 2005) 

Bus Fuel Cost / Mile ($) Maintenance Cost / Mile ($) Total Cost / Mile ($) 

7657 1.02 1.46 2.48 

7662 0.93 1.13 2.06 

7666 1.06 2.09 3.15 

7670 1.04 1.27 2.31 

7677 1.01 1.48 2.49 

7688 1.05 1.50 2.55 

7708 1.05 1.07 2.12 

7715 0.99 0.96 1.95 

7719 1.09 1.14 2.23 

7721 0.98 1.08 2.06 

CNG 

avg. 

1.02 1.29 2.31 

6367 0.57 1.43 2.00 

6368 0.57 1.03 1.58 

6369 0.54 1.39 1.93 

6375 0.55 1.29 1.84 

6378 0.54 1.06 1.60 

6379 0.57 1.64 2.21 

6380 0.60 0.96 1.56 

6381 0.55 1.16 1.71 

6382 0.54 1.17 1.71 

6387 0.56 1.19 1.75 

Hybrid 

avg. 

0.56 1.23 1.79 

What’s Next? 

This is the final report for the 12-month evaluation of NYCT’s hybrid buses from the order of 

125 and the CNG Orion VII buses. NYCT has also taken delivery of all of an order of 200 more 

hybrid buses from Orion and BAE Systems. The order of 200 new hybrid buses are model year 

2004 buses and include a Cummins ISB engine with EGR and some of the electric propulsion 

equipment and controls have been refined. The 200 new hybrid buses are being split between 

Fresh Pond Depot in Brooklyn (138) and Manhattanville Depot in Manhattan (62).A selection of 

10 of these new hybrid buses from the Manhattanville depot will be evaluated. The evaluation of 

the order of 200 hybrid buses is intended to document improvements and experience at NYCT. 

NYCT recently placed another large order for 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. Currently, NYCT has no plans to 

purchase more CNG buses; however, NYCT still considers CNG buses a potential option for 

future purchases. 

 39
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 

Robb Barnitt 

Project Engineer 

Phone: 303-275-4489 

E-mail: robb_barnitt@nrel.gov 

Battelle 

Kevin Chandler 

Principal Research Scientist 

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

 40
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 

 41
References and Related Reports 

NYCT Related Reports 

Chandler, K., Eudy, L., Eberts, E., 2006, New York City Transit (NYCT) Hybrid and CNG Transit Buses: 

Interim Evaluation Results, National Renewable Energy Laboratory, Golden, CO, NREL/TP-540-38843. 

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. 

Environment Canada, 2004, Orion VII Transit Bus Equipped with BAE Systems HybriDrive Propulsion 

System Emissions and Fuel Economy Test Report, Environment Canada, Ottawa, Ontario, ERMD Report 

#2004-18. 

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. 

The Pennsylvania Transportation Institute, 2003, Partial STURAA Test, Orion Bus Industries, Inc., Model 

Orion VII, PTI, Altoona, PA, PTI-BT-R0327-P. 

The Pennsylvania Transportation Institute, 2003, Partial STURAA Test, Orion Bus Industries, Inc., Model 

Orion VII, PTI, Altoona, PA, PTI-BT-R0304-P. 

The Pennsylvania Transportation Institute, 2002, STURAA Test, Orion Bus Industries, Inc., Model Orion 

VII, PTI, Altoona, PA, PTI-BT-R0113. 

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 

HybriDrivePropulsion 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. 

 42
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. 

 43
Appendix: Fleet Summary Statistics 

CNG (Orion VII) at West Farms Depot and Hybrid (Orion VII) at Mother Clara Hale 

Depot Evaluation Period 

Fleet Operations and Economics 

CNG Hybrid 

Number of Vehicles 10 10 

Period Used for Fuel and Oil Op Analysis 10/04-9/05 10/04-9/05 

Total Number of Months in Period 12 12 

Fuel and Oil Analysis Base Fleet Mileage 259,083 257,920 

Period Used for Maintenance Op Analysis 10/04-9/05 10/04-9/05 

Total Number of Months in Period 12 12 

Maintenance Analysis Base Fleet Mileage 275,444 284,443 

Average Monthly Mileage per Vehicle 2,295 2,370 

Fleet Diesel Usage in Gal. 152,016 80,784 

Representative Fleet MPG (energy equiv) 1.70 3.19 

Diesel Cost per gallon 1.74 1.78 

Fuel Cost per Mile 1.021 0.558 

Total Scheduled Repair Cost per Mile 0.287 0.279 

Total Unscheduled Repair cost per Mile 1.008 0.952 

Total Maintenance Cost per Mile 1.295 1.231 

 

Total Operating Cost per Mile 2.316 1.788 

Maintenance Costs 

CNG Hybrid 

Fleet Mileage 275,444 284,443 

Total Parts Cost 99,979.72 60,477.56 

Total Labor Hours 5132.8 5792.5 

Average Labor Cost 256,642.00 289,625.00 

(@ $50.00 per hour) 

Total Maintenance Cost 356,621.72 350,102.56 

Total Maintenance Cost per Bus 35,662.17 35,010.26 

Total Maintenance Cost per Mile 1.295 1.231 

 44
Breakdown of Maintenance Costs by Vehicle System

CNG Hybrid 

Fleet Mileage 275,444 284,443 

Total Engine/Fuel-Related Systems (ATA VMRS 27, 30, 31, 32, 33, 

41, 42, 43, 44, 45, 46, 65)

Parts Cost 37,080.52 10,880.98 

Labor Hours 1181.5 1870.1 

Average Labor Cost 59,073.50 93,507.00 

Total Cost (for system) 96,154.02 104,387.98 

Total Cost (for system) per Bus 9,615.40 10,438.80 

Total Cost (for system) per Mile 0.349 0.367 

Exhaust System Repairs (ATA VMRS 43)

Parts Cost 3,058.60 879.07 

Labor Hours 48.0 120.2 

Average Labor Cost 2,400.00 6,010.00 

Total Cost (for system) 5,458.60 6,889.07 

Total Cost (for system) per Bus 545.86 688.91 

Total Cost (for system) per Mile 0.020 0.024 

Fuel System Repairs (ATA VMRS 44)

Parts Cost 8,226.37 1,845.80 

Labor Hours 154.2 48.8 

Average Labor Cost 7,707.50 2,437.50 

Total Cost (for system) 15,933.87 4,283.30 

Total Cost (for system) per Bus 1,593.39 428.33 

Total Cost (for system) per Mile 0.058 0.015 

Power Plant (Engine) Repairs (ATA VMRS 45)

Parts Cost 3,320.92 2,477.86 

Labor Hours 288.2 295.8 

Average Labor Cost 14,407.50 14,792.00 

Total Cost (for system) 17,728.42 17,269.86 

Total Cost (for system) per Bus 1,772.84 1,726.99 

Total Cost (for system) per Mile 0.064 0.061 

Electric Propulsion Repairs (ATA VMRS 46) 

Parts Cost 2,922.96 

Labor Hours 972.9 

Average Labor Cost 48,645.00 

Total Cost (for system) 51,567.96 

Total Cost (for system) per Bus 5,156.80 

Total Cost (for system) per Mile 0.181 

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

Charging, 32-Cranking, 33-Ignition) 

Parts Cost 10,890.80 849.89 

Labor Hours 340.6 220.7 

Average Labor Cost 17,030.00 11,033.50 

Total Cost (for system) 27,920.80 11,883.39 

Total Cost (for system) per Bus 2,792.08 1,188.34 

Total Cost (for system) per Mile 0.101 0.042 

 45
Breakdown of Maintenance Costs by Vehicle System (continued) 

CNG Hybrid 

Air Intake System Repairs (ATA VMRS 41) 

Parts Cost 2,342.26 922.20 

Labor Hours 20.5 13.8 

Average Labor Cost 1,025.00 687.50 

Total Cost (for system) 3,367.26 1,609.70 

Total Cost (for system) per Bus 336.73 160.97 

Total Cost (for system) per Mile 0.012 0.006 

Cooling System Repairs (ATA VMRS 42)

Parts Cost 2,920.49 361.91 

Labor Hours 232.6 169.0 

Average Labor Cost 11,631.00 8,450.00 

Total Cost (for system) 14,551.49 8,811.91 

Total Cost (for system) per Bus 1,455.15 881.19 

Total Cost (for system) per Mile 0.053 0.031 

Hydraulic System Repairs (ATA VMRS 65) 

Parts Cost 107.18 621.29 

Labor Hours 22.5 29.0 

Average Labor Cost 1,125.00 1,450.00 

Total Cost (for system) 1,232.18 2,071.29 

Total Cost (for system) per Bus 123.22 207.13 

Total Cost (for system) per Mile 0.005 0.007 

Transmission Repairs (ATA VMRS 27) 

Parts Cost 6,213.90

Labor Hours 75.0

Average Labor Cost 3,747.50

Total Cost (for system) 9,961.40

Total Cost (for system) per Bus 996.14

Total Cost (for system) per Mile 0.036

General Air System Repairs (ATA VMRS 10)

Parts Cost 10,150.20 3,429.39 

Labor Hours 111.5 116.9 

Average Labor Cost 5,572.50 5,846.00 

Total Cost (for system) 15,722.70 9,275.39 

Total Cost (for system) per Bus 1,572.27 927.54 

Total Cost (for system) per Mile 0.057 0.033 

Brake System Repairs (ATA VMRS 13)

Parts Cost 12,517.92 1,797.66 

Labor Hours 725.1 171.9 

Average Labor Cost 36,254.00 8,592.50 

Total Cost (for system) 48,771.92 10,390.16 

Total Cost (for system) per Bus 4,877.19 1,039.02 

Total Cost (for system) per Mile 0.177 0.037 

 46
Breakdown of Maintenance Costs by Vehicle System (continued)

CNG Hybrid 

Inspections Only - no parts replacements (101)

Parts Cost 0.00 0.00 

Labor Hours 646.8 996.2 

Average Labor Cost 32,341.50 49,811.50 

Total Cost (for system) 32,341.50 49,811.50 

Total Cost (for system) per Bus 3,234.15 4,981.15 

Total Cost (for system) per Mile 0.117 0.175 

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

and Sheet Metal, 50-Accessories, 71-Body)

Parts Cost 24,184.50 28,491.44 

Labor Hours 1315.8 1647.0 

Average Labor Cost 65,789.50 82,350.50 

Total Cost (for system) 89,974.00 110,841.94 

Total Cost (for system) per Bus 8,997.40 11,084.19 

Total Cost (for system) per Mile 0.327 0.390 

HVAC System Repairs (ATA VMRS 01)

Parts Cost 7,097.42 4,202.86 

Labor Hours 241.2 361.4 

Average Labor Cost 12,059.00 18,071.00 

Total Cost (for system) 19,156.42 22,273.86 

Total Cost (for system) per Bus 1,915.64 2,227.39 

Total Cost (for system) per Mile 0.070 0.078 

Lighting System Repairs (ATA VMRS 34)

Parts Cost 3,092.94 2,634.10 

Labor Hours 197.8 233.9 

Average Labor Cost 9,891.00 11,695.00 

Total Cost (for system) 12,983.94 14,329.10 

Total Cost (for system) per Bus 1,298.39 1,432.91 

Total Cost (for system) per Mile 0.047 0.050 

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

15-Steering, 16-Suspension)

Parts Cost 5,324.46 8,175.53 

Labor Hours 244.9 267.7 

Average Labor Cost 12,245.00 13,384.50 

Total Cost (for system) 17,569.46 21,560.03 

Total Cost (for system) per Bus 1,756.95 2,156.00 

Total Cost (for system) per Mile 0.064 0.076 

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

Wheels, 22-Rear Axle, 24-Drive Shaft) 

Parts Cost 531.76 865.60 

Labor Hours 227.2 69.6 

Average Labor Cost 11,362.00 3,481.50 

Total Cost (for system) 11,893.76 4,347.10 

Total Cost (for system) per Bus 1,189.38 434.71 

Total Cost (for system) per Mile 0.043 0.015 

 47
Breakdown of Maintenance Costs by Vehicle System (continued)

CNG Hybrid 

Tire Repairs (ATA VMRS 17)

Parts Cost 0.00 0.00 

Labor Hours 241.1 57.7 

Average Labor Cost 12,054.00 2,885.50 

Total Cost (for system) 12,054.00 2,885.50 

Total Cost (for system) per Bus 1,205.40 288.55 

Total Cost (for system) per Mile 0.044 0.010 

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 

represent 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. 

 48
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PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ORGANIZATION.

1. REPORT DATE (DD-MM-YYYY)

November 2006 

2. REPORT TYPE

Technical Report 

3. DATES COVERED (From - To)

 

5a. CONTRACT NUMBER

DE-AC36-99-GO10337 

5b. GRANT NUMBER

4. TITLE AND SUBTITLE

New York City Transit (NYCT) Hybrid (125 Order) and CNG Transit 

Buses: Final Evaluation Results 

5c. PROGRAM ELEMENT NUMBER

5d. PROJECT NUMBER

NREL/TP-540-40125 

5e. TASK NUMBER

FC06.3000 

6. AUTHOR(S)

R. Barnitt and K. Chandler 

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-540-40125 

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 describes the evaluation results for new Orion VII buses at NYCT with CNG propulsion and new hybrid 

propulsion. 

15. SUBJECT TERMS

AVTA; NYCT; New York City Transit; Orion; BAE; HybriDrive; hybrid bus 

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

a. REPORT 

Unclassified 

b. ABSTRACT 

Unclassified

c. THIS PAGE 

Unclassified

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OF ABSTRACT

UL 

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OF PAGES 

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