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 

King County Metro Transit 

Hybrid Articulated Buses: 

Final Evaluation Results 

K. Chandler 

Battelle 

K. Walkowicz 

National Renewable Energy Laboratory

Technical Report 

NREL/TP-540-40585 

December 2006 

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

Hybrid Articulated Buses: 

Final Evaluation Results 

K. Chandler 

Battelle 

K. Walkowicz 

National Renewable Energy Laboratory

Prepared under Task No. FC07.3000 

Technical Report 

NREL/TP-540-40585 

December 2006 

National Renewable Energy Laboratory

1617 Cole Boulevard, Golden, Colorado 80401-3393 

303-275-3000 • www.nrel.gov 

Operated for the U.S. Department of Energy 

Office of Energy Efficiency and Renewable Energy 

by Midwest Research Institute • Battelle 

Contract No. DE-AC36-99-GO10337
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Acknowledgements 

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

Lee Slezak within the FreedomCAR & Vehicle Technologies Program in the U.S. Department of 

Energy (DOE). All publications on the King County Metro Transit hybrid bus evaluation will be 

posted on the DOE Office of Energy Efficiency and Renewable Energy Web site. Please see 

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

This evaluation conducted at King County Metro Transit (KC Metro) would not have been 

possible without the support and cooperation of many people. Therefore, the authors wish to 

thank each of the following: 

U.S. Department of Energy 

Lee Slezak 

NREL 

Leslie Eudy 

KC Metro 

Jim Boon 

Colleen Duke 

Bernie Durant 

Todd Gibbs 

Ann Gonzales 

Wayne Hom 

Lynn Matteoni 

Jo Merrick 

George Stites 

GM Allison 

Peter Chiang 

Paul Nama 

New Flyer Industries 

Rick Brandenburg 

Paul Zanetel 

Caterpillar 

Dave Bradshaw 

NC Power 

Bill Hofer 

Craig Johnson

iii
Table of Contents 

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

Project Design and Data Collection............................................................................................ v 

Hybrid and Diesel Buses............................................................................................................ vi 

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

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

Emissions Testing ...................................................................................................................... ix 

Future Work............................................................................................................................... ix 

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

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

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

Host Site Profile—KC Metro Transit ......................................................................................... 2 

Description of the KC Metro Hybrid Transit Bus Project .......................................................... 2 

Project Design and Data Collection............................................................................................ 8 

Vehicle System Descriptions...................................................................................................... 9 

Facility Descriptions..................................................................................................................... 14 

Implementation Experience .......................................................................................................... 16 

Evaluation Results (12 Months).................................................................................................... 18 

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

Bus Usage ................................................................................................................................. 19 

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

Maintenance Cost Analysis....................................................................................................... 24 

Road Call Analysis ................................................................................................................... 34 

Summary of Costs..................................................................................................................... 35 

Laboratory Emissions Testing .................................................................................................. 36 

Future Work.................................................................................................................................. 38 

Contacts......................................................................................................................................... 39 

Acronyms and Abbreviations ....................................................................................................... 40 

Bibliography ................................................................................................................................. 42 

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

iv
Executive Summary 

This is the final report to evaluate and compare new diesel and diesel hybrid electric articulated 

buses operated as part of the King County Metro Transit (KC Metro) fleet in Seattle, 

Washington. It concludes a 12-month evaluation at KC Metro. The evaluation was completed 

through the U.S. Department of Energy’s (DOE) Advanced Vehicle Testing Activity (AVTA) by 

the National Renewable Energy Laboratory (NREL). 

KC Metro operates bus-only transit service in the 2,134-square-mile Seattle/King County, 

Washington, area. Its fleet consists of 1,400 standard and articulated buses, trolley buses, and 

streetcars. KC Metro recently began using 235 new hybrid electric articulated buses that replace 

an older fleet of 236 dual-mode Breda articulated buses. The Breda buses were specially 

developed for use in the 1.3-mile Seattle downtown transit tunnel since its opening in 1990. This 

tunnel was built with light rail in mind but had been used only by the Breda dual-mode buses 

until the hybrid buses were introduced. The Breda dual-mode buses allowed zero-emission, fully 

electric propulsion operation inside the tunnel, and diesel engine propulsion outside the tunnel or 

when the buses were not connected to the electric catenary system.1 

Both the diesel and diesel hybrid electric articulated buses at KC Metro were manufactured by 

New Flyer Industries. The hybrid buses include General Motors’ (GM) Allison EP

50 System

parallel hybrid propulsion system. This fleet is the largest application of the GM Allison hybrid 

propulsion system to date. 

Project Design and Data Collection 

This evaluation focused on diesel and hybrid diesel buses selected from three of KC Metro’s 

seven operating depots or bases (see Table ES-1). All 30 of the new diesel articulated buses 

currently operate from the Ryerson Base depot; they are identical to the hybrid buses except for 

the hybrid electric propulsion systems. Ten diesel buses were selected from Ryerson Base for 

detailed evaluation, and 10 hybrid buses were selected from Atlantic Base for comparison. The 

Ryerson diesel buses and the Atlantic hybrid buses have similar service and duty cycles—

downtown service at an average speed of 12.4 mph for Ryerson and 11.6 mph for Atlantic during 

the first six months of the evaluation period, and 12.3 mph for Ryerson and 10.5 mph for 

Atlantic during the second six months. This difference is attributed to route changes during the 

evaluation period. During the first six months of the demonstration, the hybrid buses were 

operating in the downtown transit tunnel, while during the second six months, the tunnel was 

closed and all buses drove the surface streets in downtown Seattle. 

 

1

 A catenary system features electricity-carrying wires strung above a roadway. Buses and trolley vehicles can 

obtain access to electric power via poles that touch the catenary wires and provide electricity directly to the electric 

propulsion system in the bus. Many light rail systems also use a catenary system to provide the light rail vehicle with 

access to electricity and power for propulsion. 

v
Table ES-1. Summary of Evaluation Sites and Buses

Topic Ryerson Base Atlantic Base South Base 

Number of Buses in Evaluation 10 10 10 

Bus Type Diesel Only Diesel Hybrid Diesel Hybrid 

Evaluation Period April 1, 2005—March 31, 2006

South Base hybrid buses (10 buses) were also selected for study, because that depot was the first 

to receive the new hybrid vehicles. South Base provided an opportunity to study an early 

implementation experience with the new technology at KC Metro, as well as to look at longer 

term potential maintenance and reliability issues that might arise in these oldest of the fleet 

buses. South Base has a higher operating average speed (19.5 mph for articulated buses in the 

first six months and then 18.1 mph for the second six months) than the other two depots and 

should not be used in direct comparison. Data from this depot are therefore provided for 

reference only. The South Base evaluation results appear in gray type in this report as a reminder 

that the information is not intended to be directly compared with results from the other two 

depots. 

Hybrid and Diesel Buses 

The New Flyer diesel and diesel-hybrid articulated buses are identical except for the GM Allison 

EP

50 parallel hybrid system. Both types of buses are equipped with Caterpillar (CAT) engines 

(C9-330 brake horsepower [bhp] maximum, 1,150 ft-lb torque and diesel particulate filters or 

DPF). The hybrid buses weigh approximately 1,100 lb more than the diesels, but this does not 

make a difference in the number of passengers that can be carried because there is not enough 

standing space on either one to take the bus to the gross vehicle weight rating (GVWR). 

The GM Allison EP50 parallel electric propulsion system has a drive unit that contains two 

motors and fits where a standard-size transmission would normally be placed in the bus. Each 

motor, which can also act as a generator, is capable of 75 kW continuous power and up to 150 

kW peak power. This parallel hybrid propulsion system blends both the CAT engine power and 

the electric motor power to provide propulsion power. The energy storage system for the hybrid 

electric system consists of nickel metal hydride batteries, and the system operates with 

regenerative braking (i.e., braking energy is captured back through the motor/generator set and 

used later for propulsion along with the energy saved in the battery pack). The CAT engine is 

also capable of charging the energy storage system along with the regenerative braking energy. 

Implementation Experience 

New diesel and diesel-hybrid articulated buses were delivered to KC Metro at nearly the same 

time in May 2004. The 30 diesel buses were onsite and in service at Ryerson Base depot by July 

2004. All 235 hybrid buses were delivered and put into service at Atlantic Base and South Base 

as well as two other depots by early December 2004. 

KC Metro reported that there were no significant issues in placing the buses into service. It took 

only a few weeks after each bus was delivered to Seattle. As the new articulated buses were 

placed in service, the older Breda buses were retired. CAT used a local dealer for warranty 

support and in troubleshooting problems with these buses. New Flyer made one 

vi
mechanic/technician available on site for KC Metro’s needs. GM Allison also provided onsite 

technical support as needed. The buses are reportedly doing well; through March 2006, the 235 

hybrid buses had operated for 13 million miles and the 30 diesel buses for 1.7 million miles. 

The hybrid and diesel buses have been operating with only a few significant issues. There have 

been a few “fleet defects” and “campaigns” of warranty repairs as the manufacturers gained 

more experience with the KC Metro operation and environment, as well as specific design issues 

concerning the integration of the bus systems. A “fleet defect” is defined in the contract between 

the transit agency and the manufacturer as “failures of the same type occurring on multiple buses 

in an order.” A “campaign” is a repair (typically covered under warranty) that is applied to an 

entire (or significant portion) of an order of buses. The following list summarizes some of the 

significant (major) campaigns for the propulsion system of these buses (some of which occurred 

during the evaluation period of this project): 

1. Axle planetary snap rings (8/2004) 

2. Allison software upgrade for issues with the inverter and CAT engine software changes 

(9/2004) 

3. Proheat auxiliary coolant heater software change (1/2005) 

4. Relocation of the DPF and change of the thermal blanket (2/2005) 

5. Allison software upgrade for additional CAT engine software changes and HUSHTM

mode hybrid thermal protection (5/2005) 

6. Allison software upgrade for removing HUSH mode and a few software enhancements 

(10/2005) - removal of HUSH mode was at the request of KCM due to 2-year Transit 

Tunnel shutdown for remodeling. It will be re-activated again in 2007. 

7. Voltage regulator retrofit (11/2005) 

8. Replacement of turbocharger, heavier usage than expected, using titanium turbocharger 

parts (1/2006). 

The problem in item eight above, includes a warranty campaign for the CAT engine 

turbocharger. This problem, caused by heavier than expected usage, has resulted in a few 

turbocharger failures and, ultimately, associated DPF failures because of engine oil leaking into 

the exhaust through the damaged turbocharger. CAT has replaced the turbocharger compressor 

wheels with components made with titanium to alleviate this issue. 

April 1, 2005, was chosen as a “clean point” for the evaluation because by then the major 

campaigns listed above were completed. The evaluation period selected for this report is April 

2005 through March 2006. 

Evaluation Results 

The evaluation results presented in this report focus on the diesel buses operating from Ryerson 

Base and hybrid buses operating from Atlantic Base. These two depots were chosen for the 

evaluation because of their similar duty cycles, as noted earlier. South Base hybrid buses are 

included in the evaluation only to note some experiences in implementing the first hybrids at KC 

Metro. The duty cycle of the South Base hybrid buses was significantly different from those at 

the other two depots. It is not directly comparable and is included in this report for reference 

only. 

vii
Table ES-2 summarizes the evaluation results presented in greater detail later in this report. Note 

that South Base hybrid data are presented but not included in the comparison discussion. 

Regarding maintenance costs, mechanic labor was kept constant at $50 per hour, which is not the 

actual labor rate at KC Metro. Data in the table column titled “Hybrid Difference” was calculated 

in this manner: (Result Hybrid Atlantic Base / Result Diesel Ryerson Base—1)* 100% 

A positive result (+) indicates that the hybrid Atlantic Base result was higher than the diesel 

Ryerson Base result. A negative result (-) indicates that the hybrid Atlantic Base result was lower 

than the diesel Ryerson Base result. 

Table ES-2. Summary Evaluation Results (12-month evaluation period)

Category 

Diesel 

Ryerson 

Base 

Hybrid 

Atlantic 

Base 

Hybrid 

Difference 

Hybrid 

South Base 

Monthly Average Mileage per Bus 2,949 3,096 +5% 3,957 

Fuel Economy (mpg) 2.50 3.17 +27% 3.75 

Fuel Cost per Mile ($) (@$1.98/gal) 0.79 0.62 -22% 0.53 

Total Maintenance Cost per Mile ($) 0.46 0.44 -4% 0.41 

Propulsion-Only Maintenance Cost 

per Mile ($) 

0.12 0.13 +8% 0.13 

Total Operating Cost per Mile ($) 1.25 1.06 -15% 0.94 

Miles Between All Road calls 5,896 4,954 -16% 4,696 

Miles Between Propulsion Road 

calls 

12,199 10,616 -13% 8,547 

• Bus Usage—The diesel buses at Ryerson Base and hybrid buses at Atlantic Base had 

essentially the same monthly average mileage per bus; average mileage for the Atlantic 

Base hybrid buses was only 5% higher. 

• Fuel Economy—The hybrid buses at Atlantic Base had on average 27% higher fuel 

economy than the diesel buses at Ryerson Base. This difference ranged from 24% up to 

30% during the evaluation period (0.67 mpg difference). 

• Fuel Cost per Mile—The diesel buses at Ryerson Base used a biodiesel blend of 5% 

biodiesel (B5) and 95% ultra-low-sulfur diesel (ULSD) costing an average of $2.01 per 

gallon during the evaluation period. The hybrid buses at Atlantic Base used only ULSD 

costing an average of $1.98 per gallon during the evaluation period. The fuel cost and 

fuel economy combined resulted in a fuel cost per mile that was 22% lower (assuming 

only the ULSD cost of $1.98 per gallon for both) for the hybrid buses at Atlantic Base 

than that of the diesel buses at Ryerson Base ($0.17 per mile difference). 

• Total Maintenance Cost per Mile—The hybrid buses at Atlantic Base and the diesel 

buses at Ryerson Base had similar total maintenance cost per mile; this cost for hybrid 

buses was 4% lower ($0.02 per mile difference). 

• Propulsion Only Maintenance Cost per Mile—The propulsion-related systems are 

transmission, nonlighting electrical (charging, cranking, and ignition), air intake, cooling, 

exhaust, fuel, engine, electric propulsion, and hydraulics. The hybrid buses at Atlantic 

Base and the diesel buses at Ryerson Base had similar cost per mile for this category with 

the hybrid buses being 8% higher ($0.01 per mile difference). 

• Total Operating Cost per Mile—This category is the sum of the fuel cost per mile and the 

total maintenance cost per mile. Total operating costs for the hybrid buses at Atlantic 

viii
Base were 15% lower than those of the diesel buses at Ryerson Base ($0.19 per mile 

difference). 

• Miles Between All Road Calls—The definition of road call is taken from the Federal 

Transit Administration (FTA) National Transit Database (NTD). A road call, or revenue 

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

replaced on its route or that causes a significant schedule delay. The hybrid buses at 

Atlantic Base had a 16% lower rate of miles between all road calls than that of the diesel 

buses at Ryerson Base. 

• Miles Between Propulsion Road Calls—The rate for hybrid buses at Atlantic Base in this 

category was 13% lower than that of the diesel buses at Ryerson Base. 

Emissions Testing 

Two buses were tested at NREL’s ReFUEL laboratory in Golden, Colorado, in May and June 

2005. One bus (vehicle 2899) was from the conventional diesel fleet (from Ryerson Base Depot), 

and another bus (vehicle 2709) was from the hybrid fleet (one of the 235 hybrids ordered). Both 

vehicles were tested for fuel economy and emissions performance on identical cycles. Four 

cycles were tested to determine the variability of fuel economy and emissions: Central Business 

District 14 (CBD), Manhattan, the Orange County Transit Authority (OCTA), and a custom 

cycle made up of various King County runs (KCM). Each vehicle was tested multiple times on 

each run to ensure some level of statistical accuracy. Fuel economy, carbon dioxide (CO2), 

carbon monoxide (CO), nitrogen oxides (NOx), and particulate matter (PM) were measured. 

Differences in measurements between the hybrid and the conventional bus are shown in Table 

ES-3. 

Table ES-3. Hybrid Bus vs. Conventional Bus Test Results

Manhattan OCTA CBD KCM 

In-use: 

Atlantic Base

Fuel Economy (mpg, % increase) 74.6% 50.6% 48.3% 30.3% 26.8% 

Fuel Consumption (gram/mi, % reduction) 42.9% 33.7% 32.8% 23.4% 21.2% 

NOx (gpm, % reduction) 38.7% 28.6% 26.6% 17.8% - 

PM (gpm, % reduction) 92.6% 50.8% 97.1% Ns - 

CO (gpm, % reduction) ns 32.0% 48.0% 59.5% - 

THC (gpm, % reduction) ns ns 75.2% 56.3% - 

Note: gpm = gallons per mile; mpg = miles per gallon; ns = not statistically significant at 95% 

confidence level or not enough data to determine; THC = total hydrocarbon. 

Detailed information on this testing is available later in this report. It will also be available online 

in the report KCM Transit Emissions (www.nrel.gov/vehiclesandfuels/ahhps/publications.html).

Future Work 

All the new diesel and hybrid articulated buses ordered from New Flyer have been in service 

since at least December 2004. This final evaluation report provides results from a 12-month 

evaluation period. The first six months covered in this report included operation of the hybrid 

buses in the downtown transit tunnel. The second six months of operation were with the transit 

tunnel closed. The HUSH mode feature of the hybrid buses was deactivated via software in 

ix
October 2005 to coincide with the closure of the tunnel. The tunnel is planned to reopen in 2007 

and HUSH mode will be reactivated at that time. 

KC Metro has just issued an RFP to add 20 more hybrid buses to its fleet. The RFP also includes 

an additional 60-month supply option for up to 340 more hybrid and conventional powered 

articulated low floor buses.

x
Changes and Additions Since the Interim Report 

This final evaluation report updates the King County Metro Transit Hybrid Articulated Buses: 

Interim Evaluation Results, April 2006, NREL/TP-540-39742. The interim reported covered six 

months of a 12-month evaluation (April 2005 through September 2005) of the New Flyer 

articulated 60-foot hybrid and diesel buses at King County Metro Transit (KC Metro). This 

report completes the full 12 months of data evaluation—April 2005 through March 2006 and 

includes updates in diesel fuel costs, fuel economy, and maintenance information. Extensive 

effort has been made to complete the evaluation of warranty repairs and costs, which are 

presented separate from the maintenance cost analysis. 

Overview 

This report includes the results of an evaluation of new diesel hybrid electric buses featuring 

General Motors (GM) Allison EP50 System parallel hybrid propulsion system and standard diesel 

articulated buses from New Flyer Industries. The buses operate in the KC Metro fleet in Seattle, 

Washington. The evaluation was completed through the U.S. Department of Energy’s (DOE) 

Advanced Vehicle Testing Activity (AVTA) by the National Renewable Energy Laboratory 

(NREL), which has been tracking and evaluating new propulsion systems in transit buses and 

trucks for more than 10 years using a well-established and documented evaluation protocol.2 

Advanced Vehicle Testing Activity 

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

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

consumption. AVTA supports DOE’s FreedomCAR & Vehicle Technologies Program by 

evaluating the performance and durability of alternative fuel and advanced technology vehicles 

and assessing the performance of these vehicles in fleet applications. 

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

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

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

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

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

operators make informed purchasing decisions. 

The AVTA team conducts medium- and heavy-duty vehicle evaluations. Hybrid electric transit 

buses are one of the advanced vehicle choices available today. The evaluation team has 

conducted or is in the process of conducting several evaluations of advanced propulsion vehicles 

(see Table 1). For information on other evaluations, visit 

www.nrel.gov/vehiclesandfuels/fleettest. 

 

2 General Evaluation Plan, Fleet Test and Evaluation Projects, NREL/BR-540-32392, National Renewable Energy 

Laboratory, July 2002; www.nrel.gov/vehiclesandfuels/fleettest/pdfs/32392.pdf. 

1
Table 1. AVTA Heavy Vehicle Evaluations 

Fleet Location Vehicle Technology Evaluation Status 

King County 

Metro Seattle, WA 

New Flyer 60-ft 

articulated transit 

bus 

Parallel hybrid, GM-Allison 

EP

50 System (diesel) 

In progress; interim 

results reported here 

New York City 

Transit 

Manhattan, 

Brooklyn, Bronx, 

Queens, NY 

Orion VII 40-ft 

transit bus 

Series hybrid, BAE Systems 

HybriDrive propulsion system 

(diesel), two generations; 

DDC S50G CNG engines 

Final results for the 

order of 125 hybrid and 

CNG reported in 

August 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 

Note: CNG = compressed natural gas; LNG = liquefied natural gas 

Host Site Profile—KC Metro Transit 

KC Metro (http://transit.metrokc.gov) operates bus-only transit service in the 2,134-square-mile 

Seattle/King County, Washington, area. KC Metro operates a fleet of about 1,400 vehicles, 

standard and articulated buses, trolley buses, and streetcars that make a total of about 100 million 

trips annually. KC Metro also operates the largest publicly owned vanpool program in the 

country—more than 600 vans in the program make more than 2.9 million trips per year. 

Like most large transit agencies, KC Metro has been committed to supplying environmentally 

responsible transportation through several initiatives, including the following: 

• Retrofits of the existing diesel bus fleet with diesel particulate filters (DPF) and the use of 

ultra-low sulfur diesel (ULSD) fuel. ULSD is a specially refined fuel with significantly 

lower sulfur content (less than 15 parts per million) than regular highway diesel. 

• Continued use of zero-emission electric trolley buses to supply clean and quiet 

transportation on some of the busiest routes. 

• Use of biodiesel blends at B5 levels (or 5% biodiesel by volume in diesel fuel) at two 

operating depots (Bellevue and Ryerson bases). 

• Use of new hybrid electric articulated buses from New Flyer and GM Allison. 

KC Metro also provides bus service in King County under contract to Sound Transit. Sound 

Transit is a regional transit operator serving multiple counties. KC Metro and Sound Transit are 

cooperating to install light rail in the Seattle downtown transit tunnel, as discussed later in this 

report. 

Description of the KC Metro Hybrid Transit Bus Project 

One of the latest transit improvements introduced at KC Metro is the use of new hybrid electric 

articulated buses to replace a fleet of dual-mode Breda articulated buses. The Breda buses were 

specially developed for use in the Seattle downtown transit tunnel (see the map in Figure 1) since 

it opened in 1990. The Breda dual-mode buses allowed zero-emission electric propulsion 

2
operation in the tunnel and diesel engine propulsion outside the tunnel or when the buses are not 

connected to the electric catenary system. 

In a catenary system, electricity-carrying wires strung above a roadway provide buses and trolley 

vehicles with electric power. Poles touch the catenary wires and provide electricity directly to the 

bus’s electric propulsion system. Many light rail systems also use a catenary system to provide 

the light rail vehicle with access to electricity and power for propulsion. 

Experiences with the Breda Dual-Mode Buses. KC Metro has been operating a fleet of 236 

Breda dual-mode buses (one is shown in Figure 2) that are at the end of their useful life—more 

than 14 years, in contrast to their 12-year expected lifetime. The 1.3-mile Seattle downtown 

tunnel was built with light rail in mind but had been used exclusively by the Breda dual-mode 

buses until the hybrid buses were placed in service. The bus tunnel was built under 3rd Avenue 

through the downtown area. This has helped to reduce congestion in downtown Seattle and helps 

KC Metro to keep buses on schedule with this exclusive right-of-way. One of the tunnel stations 

is shown in Figure 3. 

Figure 1. Seattle Downtown Transit Tunnel 

3
Figure 2. Breda Dual-Mode Bus in Yard 

Figure 3. Hybrid Bus in Seattle Downtown Tunnel at International Station 

The Breda dual-mode buses (Figure 2) were originally a unique application. This 60-foot (ft) 

articulated bus has two operating modes, a diesel engine mechanical power train, and an electric 

propulsion system powered by a catenary system. While it is in the tunnel, the bus is propelled 

by the electric drive system via the catenary poles for electricity and power. When the bus is 

outside the tunnel, the catenary poles are retracted, and the diesel engine drives a separate 

mechanical drive train to operate the bus. Other North American cities that have used a similar 

type of dual-mode bus include Vancouver, Dayton, and Boston. 

KC Metro has had a somewhat difficult and expensive experience with the Breda dual-mode 

buses. In 1988, the Breda buses were purchased for $450,000 each, and the Italian manufacturer 

4
did not provide much onsite support. Troubleshooting and maintaining the Breda buses required 

a significant amount of time and dedication on the part of the KC Metro staff. Some operating 

problems with the Breda dual-mode buses required KC Metro staff to come up with unique 

solutions so the bus’s operation would be acceptably reliable. One of the major issues was the 

unavailability of replacement parts. Some of these parts were available only through the 

manufacturer, who used small suppliers in Italy. In some cases, these parts had to be purchased a 

year in advance and in large quantities. Some parts were therefore analyzed and redesigned so 

that local U.S. shops could be used for procurements. 

In KC Metro’s experience through 2004, the last full year of the Breda fleet’s operation, about 

25% of the fleet needed to have an engine rebuilt each year and 33% needed to have a 

transmission rebuilt each year, on average. These measures were causing significant increases in 

maintenance costs. The engine in the Breda buses was an older DDC 6V92 diesel engine that 

needed an emissions waiver to be operated because it was not certified at the required 310-hp 

level required for an articulated bus. 

The use of the Breda buses was discontinued in early 2005 to reduce operating and maintenance 

costs. The last date of operation for those buses was January 24, 2005; however, 59 of the buses 

were refurbished as trolley buses (electric only) and were put back in service on the catenary 

system (one is shown in Figure 4). Many of the remaining Breda dual-mode buses will be used 

for parts to help keep the 59 Breda trolley buses operating. 

Figure 4. Refurbished Breda Dual-Mode Bus to Electric-Only Trolley-Bus Operation 

Investigation of the GM Allison Hybrid. At around the same time that the transit company 

began investigating replacements for the Breda dual-mode buses, KC Metro and Sound Transit 

were putting plans together to add light rail to the downtown tunnel operation. The light rail 

operation requires a 1,500 VDC (volts, direct current) catenary, and the dual-mode bus catenary 

is 700 VDC. If both the light rail and dual-mode bus fleet were to operate in the tunnel at the 

same time, both catenary systems would need to coexist in the tunnel. The company decided that 

there would be a significant benefit to removing the 700 VDC catenary system and discontinue 

the use of the dual-mode buses. 

KC Metro looked into replacing the Breda dual-mode buses not just because of their age but also 

because those buses had always been expensive to operate and maintain. New dual-mode buses 

5
were expected to be an expensive purchase; for example, Boston recently purchased new dualmode buses at an average cost of $1.6 million each. However, new dual-mode buses were no 

longer desirable to KC Metro because of the light rail situation in the tunnel. A replacement bus 

technology needed to be found that could meet the following objectives: 

1. Operate in the tunnel with low tailpipe and noise emissions, preferably without the 

catenary system 

2. Have significantly reduced operation and maintenance costs, compared with those of the 

Breda dual-mode buses 

3. Ideally, operate on routes other than the tunnel route. 

The search for a bus technology that would replace the dual-mode buses started in early 2000, 

around the same time that a division of GM known as Allison Electric Drives 

(www.allisontransmission.com/product/electricdrive/index.jsp) began investigating potential test 

fleets for its new hybrid bus propulsion system. After viewing a conference presentation by 

Allison, KC Metro and Allison began discussions. Allison demonstrated its technology at KC 

Metro using a 40-ft bus with a trailer to simulate the operation of an articulated bus. 

The result of this testing was enough to move KC Metro to the next stage, which was to 

demonstrate the technology by purchasing one bus (number 2599). New Flyer Industries 

(www.newflyer.com) was the only builder to respond to KC Metro’s request for proposals (RFP) 

for the one hybrid articulated demonstrator bus. Bus number 2599 was received in October 2002 

and immediately put into service shadowing another in-service bus. The goal was to put a year’s 

worth of operation on the bus as soon as possible. It was loaded to 130% seated load weight and 

operated in mock revenue service (known as “shadow service”) from November 2002 through 

February 2003 for 7 days a week from noon to 8 a.m. the next morning. The bus was serviced 

between 8 a.m. and noon each day. It operated a total of 37,000 miles during the four-month 

testing period. This test was documented in a GM Allison video, “Allison Electric Drives King 

County Seattle Phases 1 & 2 Test.” 

This first hybrid articulated bus used a Cummins engine (ISL-330 hp, 8.9 liter). In December 

2002, Cummins notified KC Metro that it could not meet the emissions requirement for a model 

year 2004 bus with a 330-hp engine and pulled out of the project. Soon afterward, Caterpillar 

(CAT) expressed an interest in providing high-horsepower engines for the transit bus industry. 

CAT had a C9 (8.8 liter) diesel engine that was already certified for emissions at 330 hp for a bus 

model year 2004 engine. This was the exact size needed for the hybrid articulated bus. Therefore, 

the project team—which included New Flyer, GM Allison, and KC Metro—switched to CAT as 

the engine supplier at that time. 

Purchase of 235 New Flyer/GM Allison Hybrid Buses. In April 2003, KC Metro released an 

RFP for 265 buses—including 213 hybrid 60-ft articulated buses for KC Metro, 22 hybrid 60-ft 

articulated buses for Sound Transit, plus 30 conventional diesel 60-ft articulated buses for KC 

Metro. The RFP included only standard performance criteria, because KC Metro wanted to allow 

the manufacturer some flexibility, and the CAT engine was specified in the RFP as a powerplant 

acceptable to KC Metro just before release. A contract was signed in October 2003 with New 

Flyer that included the GM Allison electric drive and CAT C9 engine. The intent of this order 

was to replace the Breda fleet of buses entirely; the 235 new hybrid buses plus the demonstrator 

6
replaced the 236 Breda dual-mode buses. The new hybrid articulated buses cost $645,000 each. 

The diesel articulated buses, which were essentially identical to the hybrid buses without the 

electric propulsion system, cost $445,000 each. 

The new hybrid and diesel articulated buses (shown in Figures 5 and 6) were delivered to five 

operating bases at KC Metro in the following order: 

1. South Base—75 hybrid buses 

2. Ryerson Base—30 diesel buses 

3. East Base—38 hybrid buses 

4. North Base—48 hybrid buses 

5. Atlantic Base—52 hybrid buses 

KC Metro took final delivery of all the new hybrid articulated buses in early December 2004. 

Expectations of the Hybrid Bus Project. KC Metro and the hybrid bus project team expected 

significant cost savings for the hybrid buses when compared with the Breda dual-mode buses for 

operation and maintenance. The reasons that KC Metro implemented this hybrid project were as 

follows: 

• The buses are capable of tunnel operation. 

• Maintenance costs will be lower (when compared with costs for the Breda buses). 

• Fuel economy will increase (when compared with that of the Breda buses; hybrid electric 

technology reduces emissions further when compared with the Breda buses by converting 

energy that is normally wasted in braking into electricity used to help the bus accelerate, 

i.e., regenerative braking). 

• Intervals between brake relinings should be longer (~70,000 miles). 

• There is potential to extend the engine oil drain interval (based on oil sampling, the 

Cummins engine in the demonstration bus extended the oil drain interval from 6,000 

miles to 24,000 miles with no problems; the CAT engine was expected also to extend this 

interval, and a sampling program was planned to determine the appropriate interval; the 

company is also looking at using a synthetic engine oil). 

• The engines of the hybrid buses are expected to last the entire 12-year life of the bus. 

• The drive train is not expected to require fluid changes during its lifetime. 

Figure 5. New Flyer 60-Ft Articulated Diesel Bus at Ryerson Base 

7
Figure 6. New Flyer 60-Ft Articulated Hybrid Bus 

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 

information in this report utilized data based on 10 selected new baseline diesel buses operating 

at Ryerson Base and 10 new hybrid buses operating at Atlantic Base as well as 10 new hybrid 

buses at South Base. The Ryerson and South Base buses went into service about the same time 

(June-July 2004) and the Atlantic Base buses went into service around November 2004. This 

evaluation omits warranty costs from the maintenance cost analyses; the warranty costs are 

analyzed separately. 

South Base was the first depot to receive hybrid buses, and this provided an opportunity to 

evaluate the early operation of the hybrid buses at KC Metro as well as to look at the longer term 

operation of this hybrid technology for potential maintenance and reliability issues. Ryerson 

Base was the only depot with the diesel version of the new articulated buses, and the hybrid 

buses at Atlantic Base were selected for evaluation because of the similar operating cycles of 

Ryerson and Atlantic. Therefore, all cost and fuel economy comparisons in this report focus on 

the buses at the Ryerson and Atlantic bases, because they allow an ‘apples-to-apples’ 

comparison. South Base was used for reference only. The evaluation strategy is discussed again 

in the section on evaluation results. 

All the articulated buses at the three depots were dispatched randomly on all routes designated 

for articulated bus operation. There were no restrictions on the diesel or hybrid articulated buses. 

The data collection activity was designed to disrupt KC Metro operations as little as possible. 

Data were sent electronically from KC Metro to Battelle for analysis. Data collected for the study 

included the following (vehicle, dates, and odometer readings were recorded for each): 

• Fluids—fuel, oil, coolant, transmission, and any others 

• Maintenance—repair history, including all work orders 

• Warranty—all warranty costs from KC Metro, New Flyer, GM Allison, and CAT 

• Road calls—from the Work Order Cost Report 

• Route assignment. 

Fleet-level summary data for the 30 new diesel and 235 new hybrid articulated buses were also 

collected, including mileage accumulations and road calls. The study was designed to include 

8
tracking of safety incidents that affected the vehicles or occurred at KC Metro facilities; 

however, no safety incidents were reported during the data collection period. 

Vehicle System Descriptions 

Table 2 summarizes the vehicle system descriptions for the diesel and hybrid articulated groups 

of buses studied. The diesel and hybrid articulated buses are essentially identical except for the 

hybrid propulsion system. The hybrid buses weigh approximately 1,100 lb more than the diesels; 

this does not make a difference in the number of passengers because there is not enough standing 

space to take the bus to the gross vehicle weight rating (GVWR). Table 3 provides some details 

about the GM Allison EP50 parallel electric propulsion system. 

Table 2. Vehicle System Descriptions

Vehicle System Diesel Hybrid Hybrid 

Operating Location Ryerson Atlantic South 

Number of Buses 10 10 10 

Bus Manufacturer and 

Model 

New Flyer D60LF New Flyer DE60LF New Flyer DE60LF 

Model Year 2004 2004 2004 

Length/Width/Height 60.7 ft/102 in/132 in 60.7 ft/102 in/132 in 60.7 ft/102 in/132 in 

GVWR/Curb Weight 66,790 lb/43,500 lb 66,790 lb/44,600 lb 66,790 lb/44,600 lb 

Passenger Capacity 58 Seated 

Standees Space Limited

58 Seated 

Standees Space Limited 

58 Seated 

Standees Space Limited

Engine Manufacturer 

and Model 

Caterpillar C9 (8.8L) Caterpillar C9 (8.8L) Caterpillar C9 (8.8L) 

 Rated Horsepower 330 hp @ 2100 rpm 330 hp @ 2100 rpm 330 hp @ 2100 rpm 

 Rated Torque 1150 ft-lb @ 1400 rpm 1150 ft-lb @ 1400 rpm 1150 ft-lb @ 1400 rpm 

Emissions Equipment Engelhard DPX Engelhard DPX Engelhard DPX 

Retarder/Regenerative 

Braking 

Retarder Regenerative Braking Regenerative Braking 

Fuel Capacity 125 gallons 125 gallons 125 gallons 

Bus Purchase Cost $445,000 $645,000 $645,000 

Table 3. Hybrid Propulsion Systems 

Hybrid-Related System Hybrid Buses 

Manufacturer/Model GM Allison Electric Drives EP50 

Hybrid Type Parallel 

Motor/Generator 75 kW continuous, 150 kW peak 

Drive Unit EV50 Drive: 246 kW input rating, 1,050 ft-lb torque 

Controls Allison (proprietary) 

Energy Storage Nickel metal hydride batteries, 6 modules, 600 VDC 

(nominal) 

Inverter Dual Power Inverter Module (DPIM), 430-900 VDC, 

160 kW continuous 3-phase AC 

Regenerative Braking Yes 

Caterpillar C9 Engine. The diesel engine used in each of the new diesel and hybrid articulated 

buses is the Caterpillar (CAT) C9 engine (see https://ohe.cat.com/cda/layout?m=37285&x=7). 

The U.S. Environmental Protection Agency (EPA) engine emissions certification data results for 

the CAT C9 engine are shown in Table 4. 

9
Table 4. EPA Emissions Certification Levels for Model Year 2004 (g/bhp-hr)

Model Year Fuel HC + NOx CO PM Engine Family 

Certification 

Levels Diesel 2.4 15.5 0.05 All 

2004 CAT C9 Diesel 2.4 0.6 0.00 4CPXH0537H3K 

GM Allison Electric Drives EP

50. The parallel hybrid propulsion system blends both the CAT 

engine power and the electric motor power to provide propulsion power. The energy storage 

system supplies electricity to the motor and stores the energy generated during regenerative 

braking events. The system is also recharged via the diesel engine and generator in the drive unit. 

Figure 7 provides some details about the operation of this hybrid propulsion system. Figure 8 

shows a static display of the electric propulsion drive unit, which is designed to replace a 

standard transmission and to go where a standard transmission is usually placed. Figure 9 shows 

the Dual Power Inverter Module (DPIM) with the cover open. Each bus has one DPIM that is 

used to convert electrical energy into alternating current (AC) and direct current (DC) for storage 

and use. 

This electric propulsion system has several advantages over conventional propulsion systems. It 

allows the engine to operate more efficiently and allows for regenerative braking, both of which 

increase fuel economy. For example, electric power dominates when the bus accelerates from a 

stop, helping to eliminate the exhaust cloud typically produced by the higher transient load on 

the engines in conventional buses. The added electric power also allows the bus to accelerate 

faster, which is beneficial in city driving. 

The hybrid buses have a feature unique to KC Metro’s operation: HUSHTM mode. HUSH mode 

fills the need for an operating mode to minimize noise and engine emissions while a bus is in 

Seattle’s downtown transit tunnel. The hybrid buses operate in an electric-only mode in the 

station areas of the tunnel and in a reduced engine power mode in between stations. 

10
The Allison EP

50 System 

Courtesy of Allison Transmission, a Division of General Motors

The energy storage system supplies electricity to the EV50 Drive’s electric motors. It stores electricity 

during normal operation and regenerative braking. 

The dual power inverter module converts electricity into alternating or direct current. This enables transfer, 

storage, and use of energy between the EV50 Drive, which uses and produces alternating current, and the 

energy storage system, which can only store direct current. 

The hybrid control modules process information from system components and driver inputs. They control 

vehicle propulsion and energy production and include diagnostic and reprogramming features. 

The engine produces power, which is used to propel the bus and to produce electricity that is stored in the 

energy storage system. 

The EV50 Drive converts electricity from the energy storage system into power to propel the bus, and it 

converts power from the engine and regenerative braking into electricity that is stored in the energy storage 

system.

Figure 7. GM Allison EP50 System Description 

During the first six months of the evaluation, KC Metro’s operation in the 1.3 mile long 

downtown tunnel posed a unique challenge for GM Allison engineers. KC Metro wanted the 

hybrid buses to be able to operate in the tunnel only on electric power, without any engine 

operation, to reduce tailpipe and noise emissions in the tunnel. The Allison engineers determined 

that the hybrid buses could operate in the tunnel on battery power only, but this would severely 

reduce battery life, so a compromise was needed. 

11
Figure 8. GM Allison Electric Drive Unit 

Figure 9. Dual-Power Inverter Module 

This need for low tailpipe and noise emissions and adequate battery life resulted in the 

development of HUSH mode for the hybrid buses. As previously mentioned, HUSH mode 

operation allows the use of both all-electric operation and a combination of diesel and electric 

operation. This operation has the following characteristics: 

• Before entering the tunnel, the batteries are precharged to maximum state of charge 

(SOC); the driver pushes a button on the dashboard to start this process. 

• The driver initiates HUSH mode by pushing the precharge button one more time before 

the bus enters the tunnel. 

• The tunnel has two types of areas—the big, open station areas and the tunnel tubes 

between stations. 

• The hybrid buses operate in an all-electric mode while in the station areas, but while in 

the tunnel tube areas, the diesel engine is allowed to operate in reduced-power mode to 

allow for charging of the batteries (about 110 hp). 

• The timing of the switch between all-electric operation and reduced-power diesel mode is 

based on vehicle speed once it is in HUSH mode (15 mph or more for reduced-power 

mode). 

12
• While in the station area, the bus operates on battery power; however, the engine still 

rotates to operate auxiliary loads such as the air compressor; when the doors open at a 

station boarding area, the engine stops until the doors are closed again. 

• HUSH mode is automatically de-activated by distance traveled or manually by the driver. 

Originally, if a driver break was required, the batteries were precharged by parking the hybrid 

buses in staging areas at each end of the tunnel until the precharge was complete, which took 

about 5 minutes. When light rail operation in the tunnel starts, precharging at the staging areas 

will not be possible. Allison and KC Metro have identified a place at each end of the tunnel 

where the precharge is now initiated to ensure that the batteries are sufficiently charged before 

entering the tunnel. In this way, the buses did not need to stop for the precharge, and is now 

accomplished en route. 

The Seattle downtown transit tunnel closed on September 24, 2005, for the addition of light rail. 

The bus catenary in the tunnel is being removed. According to the plan, the tunnel will be closed 

for two years, so bus traffic has been moved up onto 3rd Avenue. Routes were changed to 

accommodate the use of the city street instead of the tunnel. HUSH mode was then deactivated 

in the hybrid buses in early October 2005 (see campaign item #6 in the next section). 

13
Facility Descriptions 

KC Metro operates seven depots for 1,420 standard, articulated, and trolley buses. This 

evaluation covers diesel and hybrid articulated buses from three of the seven depots. The new 

diesel articulated study buses operate only from Ryerson Base, and the hybrid articulated study 

buses operate from South and Atlantic bases. No special facilities or equipment are used for the 

new diesel and hybrid articulated buses. 

South Base is located in Tukwila, 10 miles south of Seattle, and serves mainly intercity routes in 

the south end and service from southern outlying suburbs into Seattle. The majority of South 

Base routes are interurban and involve service at relatively high average speeds. Approximately 

270 buses operate from South Base. Figure 10 shows the South Base maintenance and office 

building. Figure 11 shows a hybrid bus leaving South Base for peak evening service. 

Figure 10. South Base Maintenance and Office Building 

Figure 11. Hybrid Articulated Bus Leaving South Base 

The Ryerson and Atlantic bases are both within one mile of the downtown Seattle area and serve 

mainly downtown-area riders. Some of the routes move outside the Seattle city limits, but most 

are in and around downtown. The average-speed service for routes from these two bases is 

similar and lower than the average-speed service for South Base buses. Average speeds and 

routes will be discussed further in the section on evaluation results in this report. Figures 12 and 

13 show Ryerson Base. Figure 14 shows Atlantic Base. 

14
Figure 12. Ryerson Base Maintenance and Office Building 

Figure 13. Bus Parking at Ryerson Base, with Part of Seattle Skyline in Background 

Figure 14. Bus Parking at Atlantic Base with Central Base Depot in Background 

15
Implementation Experience 

This section discusses overall fleet-level results for mileage accumulations and significant 

campaign issues associated with the fleet of 213 KC Metro and 22 Sound Transit hybrid buses 

and 30 KC Metro diesel buses. KC Metro has treated them as standard articulated buses for 

service. No special treatment was given to the operating bases for pullout requirements. 

The hybrid and diesel articulated buses were delivered to KC Metro between May 2004 and 

early December 2004 and placed in service within a few weeks of delivery. Preparation of a bus 

only required adding KC Metro equipment, checking the bus’s operation for safety, and placing 

the bus into service. KC Metro’s experience overall has been better than expected. The bus 

operators like the new buses and do not want the old Breda dual-mode buses back. KC Metro 

reports that vendor support has also been better than expected. Caterpillar and New Flyer each 

have one technical person available in the Seattle area to help KC Metro place the new buses in 

service and keep them in service. 

As these new diesel and hybrid articulated buses were received and placed in service, the Breda 

dual-mode buses were removed from the fleet on a one-for-one basis. Figure 15 shows 

cumulative mileage for all the new hybrid and diesel buses from June 2004 through March 2006. 

As of March 2006, the 235 hybrid buses had accumulated approximately 13 million miles. The 

30 diesel buses had accumulated nearly 1.7 million miles through March 2006. 

0

2,000,000

4,000,000

6,000,000

8,000,000

10,000,000

12,000,000

14,000,000

Jun-04 Sep-04 Dec-04 Mar-05 Jun-05 Sep-05 Dec-05 Mar-06

Total Miles

Diesel (30 Buses) Hybrid All (235 Buses)

Figure 15. Cumulative Mileage for the Hybrid and Diesel Bus Fleet 

Figure 16 displays average monthly mileage per bus for the hybrid and diesel buses. This figure 

shows that, in general, the buses have been used at a similar rate and have averaged between 

16
2,500 and 3,000 monthly miles per bus. In the last three months of the data period shown, the 

diesel buses experienced lower usage as a result of engine problems, which are discussed later. 

0

500

1,000

1,500

2,000

2,500

3,000

3,500

Jun04Aug04Oct04Dec04Feb05Apr05Jun05Aug05Oct05Dec05Feb06

Average Monthly Miles/Bus

Diesel (30 Buses) Hybrid All (235 Buses)

Figure 16. Average Monthly Mileage per Bus for Entire Hybrid and Diesel Bus Fleet 

The hybrid and diesel buses have gone into service with only a few significant issues. There 

have been a few “fleet defects” and “campaigns” of warranty repairs as the manufacturers 

gained experience with the KC Metro operation and environment and addressed specific 

design issues involving the integration of the bus systems. A “fleet defect,” as defined in the 

contract between the transit agency and manufacturer, refers to failures of the same type on 

multiple buses in an order. A “campaign” is a repair, typically covered under warranty, 

applied to an entire order of buses or significant portion of one. The following list 

summarizes information about some of the significant campaigns for these buses. 

1. Axle planetary snap rings (8/2004) 

2. Allison software upgrade for issues with the inverter and CAT engine software changes 

(9/2004) 

3. Proheat auxiliary coolant heater software change (1/2005) 

4. Relocation of the DPF and change of the thermal blanket (2/2005) 

5. Allison software upgrade for additional CAT engine software changes and HUSH mode 

hybrid thermal protection (5/2005) 

6. Allison software upgrade for removing HUSH mode and a few software enhancements 

(10/2005) - removal of HUSH mode was at the request of KCM due to 2 year Transit 

Tunnel shutdown for remodeling. It will be re-activated again in 2007.

7. Voltage regulator retrofit (11/2005) 

8. Replacement of turbocharger, heavier usage than expected, using titanium turbocharger 

parts (1/2006). 

17
There were also minor campaigns for other bus systems, but those listed were the major changes 

to the propulsion system. April 1, 2005, was chosen as the “clean point” for the evaluation 

because the major campaigns were completed and the reliability of the buses was stabilized after 

January-February 2005. As discussed in the next section, the evaluation period for this report is 

April 2005 through March 2006. 

Evaluation Results (12 Months) 

This evaluation started April 1, 2005 and ran for 12 months through March 31, 2006. The study 

buses for this evaluation were 10 diesel articulated buses operating from Ryerson Base (Diesel 

Ryerson Base) and 10 hybrid articulated buses operating from Atlantic Base (Hybrid AB). The 

10 hybrid articulated buses operating from South Base (Hybrid SB) are included to describe 

early implementation experiences and for reference only. One of the hybrid buses at South Base 

had a turbocharger failure and was incorrectly repaired in March 2005. This caused the engine to 

be damaged beyond repair, so it was replaced in April 2005. This bus, number 2646, was 

removed from the evaluation summary results. 

As discussed earlier, this evaluation focused on comparing results for diesel buses from Ryerson 

with those for the hybrid buses from Atlantic. This was done because of the similar duty cycles 

at Ryerson and Atlantic, but not at South Base. South Base hybrid buses are included in this 

evaluation report to increase our understanding of the technology, since this was the first 

operating base to receive hybrid buses at KC Metro. The South Base hybrid buses also allowed 

us to look into near-term hybrid bus maintenance and reliability issues, since they are the oldest 

of the hybrid bus fleet studied. Results for the South Base hybrid buses are shown in gray type to 

distinguish them from other results. 

Route Descriptions 

Table 5 shows an average week’s work planned for the new articulated buses (hybrid and diesel) 

at Ryerson, Atlantic, and South Base (note that the results here are slightly different from the 

Interim Report). These data are based on route assignments as of September 2004 and are valid 

to the point when the Seattle downtown tunnel was closed in September 2005. As discussed 

earlier, average speeds were similar at Ryerson and Atlantic: 12.4 mph for Ryerson and 11.6 

mph for Atlantic. South Base is significantly different, with an average speed of 19.5 mph. 

Table 6 shows the same information for Ryerson, Atlantic, and South Base for routes operated 

after September 2005 when the tunnel closed. 

18
Table 5. Average Speed for Articulated Buses at Bases with Study Buses 

(April 2005-September 2005) 

Base Day of Week Miles/Day Hours Avg. Speed (mph) 

Weekday 4,650 379.00 12.3 

Saturday 1,006 75.05 13.4 

Sunday 1,006 75.10 13.4 

Ryerson 

Weekly Total 25,262 2,045.10 12.4 

Weekday 4,856 415.84 11.7 

Saturday 2,806 258.13 10.9 

Sunday 

Atlantic 

Weekly Total 27,096 2,337.33 11.6 

Weekday 11,212 567.00 19.8 

Saturday 5,204 282.79 18.4 

Sunday 4,180 235.93 17.7 

South 

Weekly Total 65,444 3,353.32 19.5 

Table 6. Average Speed for Articulated Buses at Bases with Study Buses 

(September 2005-April 2006) 

Base Day of Week Miles/Day Hours Avg. Speed (mph) 

Weekday 3,895 320.00 12.2 

Saturday 1,024 77.30 13.2 

Sunday 1,077 77.43 13.9 

Ryerson 

Weekly Total 21,576 1,752.88 12.3 

Weekday 6,032 575.16 10.5 

Saturday 3,505 328.50 10.7 

Sunday 1,837 192.57 9.6 

Atlantic 

Weekly Total 35,502 3,394.87 10.5 

Weekday 11,381 625.00 18.2 

Saturday 5,042 302.22 16.7 

Sunday 4,190 236.31 17.7 

South 

Weekly Total 66,137 3,662.73 18.1 

Bus Usage 

Bus usage is one indicator of the reliability and availability of bus service. The lack of usage may 

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

Figure 17 shows cumulative average monthly mileage per bus for the three study groups since 

they began operating. The general mileage trend for each of the three study groups is slightly 

higher over time, leveling off toward the end of the data period. The hybrid buses at Atlantic and 

the diesel buses at Ryerson Base have similar cumulative average monthly mileage—3,096 and 

2,948 miles per bus, respectively, during the evaluation period. The hybrid buses at South Base 

have a usage of just under 4,000 miles per bus, which reflects the higher speed and route mileage 

duty cycle compared with Ryerson and Atlantic Base operation, which highlights why the data 

are not comparable. 

Table 7 shows average monthly mileage per bus for the study buses during the evaluation period. 

Usage for the hybrid buses at Atlantic and the diesel buses at Ryerson Base is approximately the 

same—that for the hybrid buses is 5% higher. These usage rates support the decision to focus the 

19
evaluation on the study buses at the Ryerson and Atlantic Base. The hybrid buses at South Base 

are used in a significantly different manner, averaging 3,957 monthly miles per bus, which is 

34% higher than the mileage for the diesel buses. 

0

500

1000

1500

2000

2500

3000

3500

4000

4500

Jul-04 Sep-04 Nov-04 Jan-05 Mar-05 May-05 Jul-05 Sep-05 Nov-05 Jan-06 Mar-06

Average Monthly Miles/Bus

Diesel RB Hybrid AB Hybrid SB

Evaluation Period

April 2005 - March 2006

Figure 17. Cumulative Average Monthly Miles per Bus 

20
Table 7. Monthly Mileage per Study Bus 

(12-month evaluation period)

Bus Starting 

Mileage 

Ending 

Mileage 

Total 

Mileage Months Monthly Average 

Diesel Ryerson Base 

2880 22,078 54,917 32,839 12 2,737 

2881 22,178 55,313 33,135 12 2,761 

2882 24,569 57,025 32,456 12 2,705 

2883 21,108 57,264 36,156 12 3,013 

2884 24,068 59,065 34,997 12 2,916 

2885 21,764 57,595 35,831 12 2,986 

2886 22,508 58,484 35,976 12 2,998 

2887 22,775 62,674 39,899 12 3,325 

2888 18,259 55,395 37,136 12 3,095 

2889 21,932 57,292 35,360 12 2,947 

353,785 120 2,948

Hybrid AB 

2780 6,791 45,560 38,769 12 3,231 

2781 7,439 41,597 34,158 12 2,847 

2782 6,243 38,296 32,053 12 2,671 

2783 7,450 44,525 37,075 12 3,090 

2784 7,626 47,703 40,077 12 3,340 

2785 4,134 42,455 38,321 12 3,193 

2786 6,615 46,563 39,948 12 3,329 

2787 6,224 39,126 32,902 12 2,742 

2788 7,111 45,220 38,109 12 3,176 

2789 5,938 46,074 40,136 12 3,345 

371,548 120 3,096

Hybrid SB 

2640 37,180 83,119 45,939 12 3,828 

2641 41,580 91,093 49,513 12 4,126 

2642 34,009 79,845 45,845 12 3,820 

2643 35,419 80,193 44,774 12 3,731 

2644 31,062 77,696 46,634 12 3,886 

2645 36,879 82,253 45,374 12 3,781 

2647 35,343 86,997 51,654 12 4,305 

2648 36,025 85,330 49,305 12 4,109 

2649 36,548 84,841 48,293 12 4,024 

427,331 108 3,957

Fuel Economy and Cost 

KC Metro buses use ULSD fuel, which has a sulfur content less than 15 ppm. Instead of ULSD, 

Ryerson Base diesel buses use a 5% biodiesel blended with ULSD (B5), which has virtually the 

same energy content (<1% difference). Table 8 summarizes fuel economy results for the 30 

study buses. The hybrid buses from Atlantic Base had a 27% higher fuel economy on average 

compared with that of diesel buses at Ryerson Base (26% higher for the first six months of the 

evaluation period, as stated in the interim report). This comparison is the most applicable 

because of the similar usage and duty cycles, as discussed earlier. The South Base hybrid buses 

have operated in a higher average speed duty cycle and have a fuel economy that is 50% higher 

21
on average than that of the diesel buses at Ryerson Base and 18% higher than that of the other 

hybrid buses at Atlantic Base. 

Figure 18 shows average fuel economies for the Ryerson and Atlantic study groups since the 

beginning of their operation at KC Metro (the evaluation period is indicated). The diesel buses at 

Ryerson Base had an average fuel economy that started at around 2.2 mpg and increased to 

around 2.5 mpg from August-October 2004. This increase was accomplished through a software 

change in the CAT engine. The diesel buses have operated at around 2.5 mpg since the first three 

months of operation. All of the CAT engines (diesel and hybrid) received this software update. 

Table 8. Fuel Use and Economy 

(12-month evaluation period) 

Bus Mileage 

(Fuel Base) 

Gallons 

Consumed

Miles per 

Gallon 

Diesel Ryerson Base 

2880 32,773 12,836 2.55 

2881 32,118 12,921 2.49 

2882 31,999 12,785 2.50 

2883 36,079 14,564 2.48 

2884 34,997 14,389 2.43 

2885 35,514 13,637 2.60 

2886 35,620 14,549 2.45 

2887 39,408 15,818 2.49 

2888 36,699 14,258 2.57 

2889 35,361 14,240 2.48 

350,567 139,996 2.50 

Hybrid AB 

2780 37,465 11,876 3.15 

2781 33,521 10,438 3.21 

2782 31,409 10,268 3.06 

2783 36,629 11,653 3.14 

2784 39,768 12,069 3.30 

2785 37,512 11,856 3.16 

2786 37,962 11,737 3.23 

2787 31,341 10,107 3.10 

2788 36,699 11,527 3.18 

2789 39,753 12,523 3.17 

362,049 114,054 3.17 

Hybrid SB 

2640 41,908 11,343 3.69 

2641 41,005 10,921 3.75 

2642 41,708 11,065 3.77 

2643 39,400 10,562 3.73 

2644 43,036 11,627 3.70 

2645 39,319 10,850 3.62 

2647 47,374 12,652 3.74 

2648 43,217 11,148 3.88 

2649 42,361 11,007 3.85 

379,328 101,174 3.75 

22
0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

Jul-04 Oct-04 Jan-05 Apr-05 Jul-05 Oct-05 Jan-06

Miles per Gallon (MPG)

Diesel RB Hybrid AB

Evaluation Period

Apr 2005 - Mar 2006

RB Avg. 2.50 mpg

AB Avg. 3.17 mpg

AB/RB +27%

Figure 18. Average Fuel Economy (mpg)

For a controlled, detailed, direct fuel economy comparison of similar routes, KC Metro 

recommended Route 120 operated from Ryerson Base and Route 106 operated from Atlantic 

Base (which initially operated in the downtown tunnel). For the study buses at these two 

operating bases, route and fuel consumption data were used to compare fuel economies 

calculated from operation on the two bus routes. During the first 6 months of the evaluation 

period (April-September 2005), the hybrid buses operated in the Seattle downtown bus tunnel 

using HUSH mode showed a 21% higher fuel economy. During the second 6 months of the 

evaluation period (October 2005 to March 2006), the hybrid buses were not operated in the 

tunnel (HUSH mode was not used), and the hybrid buses showed a 22% higher fuel economy 

than the diesel buses. Table 9 shows the results of this comparison for the evaluation period. 

Table 9. Fuel Economy Comparison for Route 120 and Route 106 

(Six-month evaluation period) 

Timeframe Buses Route Average 

Speed Fuel Economy 

4/05-9/05 Diesel 

Ryerson 

Base 

120 12.9 2.54 

(In Tunnel) Hybrid AB 106 12.3 3.08 

Percent Difference (Hybrid/Diesel) 21% 

10/05-3/06 Diesel 

Ryerson 

Base 

120 12.9 2.53 

(Out of Tunnel) Hybrid AB 106 12.1 3.09 

Percent Difference (Hybrid/Diesel) 22% 

Actual fuel costs during the evaluation period were $1.98 per gallon for the ULSD at KC Metro. 

The diesel buses at Ryerson Base used a biodiesel blend of 5% by volume biodiesel in diesel fuel 

23
(B5). The use of the B5 blend at Ryerson Base was not a technical requirement for the diesel 

buses but it was used 100% of the time at that depot. This use of biodiesel caused the fuel cost 

per gallon at Ryerson Base to be $0.03 to $0.05 per gallon higher than for just diesel fuel use; 

however, this additional cost has not been used. Costs per mile for each of the three study bus 

groups with diesel fuel at $1.98 per gallon average are as follows: 

• Diesel RB = $0.79 per mile 

• Hybrid AB = $0.62 per mile 

• Hybrid SB = $0.53 per mile. 

This translates to a cost per mile 22% lower for the Atlantic Base hybrid buses when compared 

with the Ryerson Base diesel buses. 

Maintenance Cost Analysis 

The maintenance cost analysis in this section focuses on the evaluation period (April 2005-

March 2006). However, some of the analyses compare results from the time prior to the 

evaluation period, typically back to the start of operation for the study buses. The data period is 

clearly indicated for each figure in this section. Warranty costs are not included in this section 

but are analyzed separately later. All work orders since the beginning of the operation of the 

study buses were collected and analyzed for this evaluation. The labor rate for maintenance was 

kept at a constant $50 per hour, and this does not reflect an average rate at KC Metro. This 

section first discusses total maintenance costs and then maintenance costs broken down by bus 

system. 

Total Maintenance Costs. Total maintenance costs include the actual cost of parts and hourly 

labor costs at $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. 

Table 10 shows total maintenance costs during the evaluation period for the diesel and hybrid 

study buses at the two depots. The two study groups of buses had similar total maintenance cost 

for the evaluation period (4% lower for the hybrid buses at Atlantic Base compared to the diesel 

buses at Ryerson Base). South Base depot results are shown in Table 10 for reference only. 

The Ryerson diesel study group had one bus with higher maintenance costs (bus 2889), which 

were caused by significant heating, ventilation, and air-conditioning (HVAC) repairs in January 

2006 along with soot filter repairs. The Atlantic hybrid study group also had one bus with higher 

maintenance costs (bus 2781), which were caused by significant repairs to the steering system in 

November 2005, repairs for vandalism in February 2006, minor accident repairs in March 2006, 

and significant repairs for the differential in March 2006. 

24
Table 10. Total Maintenance Costs 

(12-month evaluation period)

Bus Mileage Parts 

Cost ($) 

Labor 

Hours 

Cost per 

Mile ($) 

Diesel Ryerson Base 

2880 32,839 3,382.66 257.7 0.50 

2881 33,135 2,368.47 270.5 0.48 

2882 32,456 3,517.79 214.0 0.44 

2883 36,156 3,467.79 241.0 0.43 

2884 34,997 3,448.13 255.4 0.46 

2885 35,831 3,323.60 260.1 0.46 

2886 35,976 2,836.40 239.2 0.41 

2887 39,899 3,292.13 241.2 0.39 

2888 37,136 2,841.93 304.4 0.49 

2889 35,360 4,076.15 332.1 0.59 

Avg. 35,379 3,255.51 261.5 0.46 

Hybrid Atlantic Base 

2780 38,769 4,279.80 283.0 0.48 

2781 34,158 5,419.23 322.3 0.63 

2782 32,053 1,969.08 274.1 0.49 

2783 37,075 2,834.53 229.1 0.39 

2784 40,077 4,535.76 252.7 0.43 

2785 38,321 2,654.11 251.2 0.40 

2786 39,948 3,548.54 231.4 0.38 

2787 32,902 4,442.49 239.2 0.50 

2788 38,109 5,676.97 238.5 0.46 

2789 40,136 3,959.38 193.0 0.34 

Avg. 37,155 3,931.99 251.4 0.44

Hybrid South Base 

2640 45,939 2,585.81 392.1 0.48 

2641 49,513 4,757.51 366.1 0.47 

2642 45,845 2,453.56 267.6 0.35 

2643 44,774 2,056.86 266.8 0.34 

2644 46,634 3,467.61 337.9 0.44 

2645 45,374 2,425.35 348.9 0.44 

2647 51,654 3,716.83 362.3 0.42 

2648 49,305 4,105.09 333.7 0.42 

2649 48,293 2,612.92 271.6 0.34 

Avg. 47,481 3,131.28 327.4 0.41

Figure 19 shows cumulative total maintenance costs for the Ryerson and Atlantic study bus 

groups from the start of operation through March 2006. In general, the Ryerson Base diesel 

buses and Atlantic Base hybrid buses had similar total maintenance costs for most of the period 

shown, and the costs trended slightly higher at the end of the evaluation period. 

25
0.000

0.100

0.200

0.300

0.400

0.500

0.600

Jul-04 Oct-04 Jan-05 Apr-05 Jul-05 Oct-05 Jan-06

Maintenance Cost ($) per Mile

Diesel RB Hybrid AB

Evaluation Period

April 2005 - March 2006

Figure 19. Cumulative Maintenance Cost per Mile (All data) 

Maintenance Cost Breakdown by System. Table 11 shows maintenance costs by vehicle 

system and bus study group. The vehicle systems shown in the table include the following: 

• Air system, general 

• Axles, wheels, and drive shaft 

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

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

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

hubodometers and radios 

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

• HVAC 

• Lighting 

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

maintenance 

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

traction batteries, and propulsion control; nonlighting electrical (charging, cranking, and 

ignition); air intake, cooling, hydraulics, and transmission 

• Tires. 

The four highest-cost repair categories for all three bus study groups were cab, body, and 

accessories; propulsion-related; HVAC; and PMI. There were no major brake repairs in the three 

study groups. 

26
Table 11. Breakdown of Vehicle System Maintenance Cost per Mile 

(12-month evaluation period) 

Diesel Ryerson Hybrid Atlantic Hybrid South 

System 

(in order of cost) 

Cost per 

Mile ($) 

Percent of 

Total (%) 

Cost per 

Mile ($) 

Percent of 

Total (%) 

Cost per 

Mile ($) 

Percent 

of Total 

(%) 

Cab, Body, and 

Accessories 0.16 35 0.19 43 0.14 34 

Propulsion-Related 0.12 26 0.13 30 0.13 32 

HVAC 0.07 16 0.04 10 0.04 10 

PMI 0.05 11 0.05 11 0.04 10 

Frame, Steering, and 

Suspension 0.01 2 0.01 2 0.01 2 

Lighting 0.01 2 0.00 0 0.00 0 

Air, General 0.01 2 0.00 0 0.01 2 

Axles, Wheels, and 

Drive Shaft 0.02 4 0.01 2 0.01 2 

Brakes 0.00 0 0.01 2 0.00 0 

Tires 0.00 0 0.00 0 0.00 0 

Articulation Joint 0.01 2 0.00 0 0.03 8 

Total 0.46 100 0.44 100 0.41 100 

Cab, Body, and Accessories Maintenance Costs. The maintenance costs associated with these 

systems are shown by bus study group. The following describes each subsystem in this category. 

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

• Destination signs 

• Cleaning—All cleaning activities inside and outside the bus 

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

except the brakes 

• Farebox 

• Fire extinguisher 

• General interior and seats 

• Horn 

• Mirrors—All inside and outside mirrors 

• Radio 

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

coveralls assigned to a bus 

• Wheelchair ramp—Includes all repairs for the wheelchair ramp system except hydraulics 

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

The maintenance costs for the hybrid buses at Atlantic Base in this category were slightly higher 

than those for the diesel buses, and the costs for the hybrid buses at South Base were slightly 

lower than those of the diesel buses. The highest-cost subsystems in this category were cleaning, 

farebox, body-exterior, and general interior and seats. 

Propulsion-Related Maintenance Costs. The propulsion-related vehicle systems include the 

exhaust, fuel, engine, electric propulsion, air intake, cooling, nonlighting electrical (charging, 

cranking, and ignition), transmission, and hydraulic systems. The cooling system also includes 

27
an auxiliary coolant heater (manufactured by Proheat) to ensure that the engine coolant warms up 

quickly at startup. At other times, this auxiliary coolant heater is used in conjunction with the 

HVAC system of the bus. 

Table 12 shows the total propulsion-related maintenance costs and lists each of the system 

maintenance costs that make up propulsion-related maintenance for the three study groups of 

buses. All comparison calculations are for the hybrid compared with the diesel buses from 

Ryerson Base. 

The propulsion-related maintenance cost per mile for the Atlantic Base hybrid buses are nearly 

the same ($0.01 per mile higher or 5% higher) as that for the Ryerson Base diesel buses. The cost 

per mile for the South Base hybrid buses are essentially the same as that of the diesel buses. The 

following list is a breakdown of propulsion-related maintenance costs during the evaluation 

period and focused on the study buses at Ryerson and Atlantic Bases (as shown in Table 12). 

• Air intake system maintenance—These costs were low and similar for the two study 

groups. 

• Cooling system maintenance—These costs were lower for the hybrid bus study group 

than for the diesel buses. The diesel buses had higher labor hours spent on repairs for this 

system (mostly for the auxiliary coolant heater). 

• Electric propulsion maintenance (reference only)—When comparing the two depots with 

hybrids (which have different duty cycles), costs were lower in this category for the 

Atlantic Base hybrid buses, and those of the South Base hybrid buses were higher at 

$0.04 per mile. The higher cost for the South Base hybrid buses was caused by a high 

number of labor hours spent to troubleshoot problems with the propulsion system 

(perhaps because South Base was the first to receive hybrids). For two of the hybrid 

buses in the South Base study group, labor hours were significant and included 

investigating a problem with the cooling lines for the DPIM. Four DPIMs were replaced 

in the South Base hybrid buses, and two were replaced in the Atlantic Base hybrid buses 

during the evaluation period. No battery replacements were reported since the beginning 

of operation for any of the hybrid buses; however, a few of the main fuses have been 

replaced. 

• Engine system maintenance—For both the Atlantic and Ryerson Base groups of buses 

costs for the engine system were similar. 

• Exhaust system maintenance—The repair costs for the hybrid buses were the highest in 

this category, because of higher parts costs. 

• Fuel system maintenance—The maintenance costs for this system were essentially the 

same for study buses with the hybrid buses being slightly higher. 

• Hydraulic system maintenance—Costs for this system were low and the same for both 

study groups. Only costs for hydraulic fluid replacements for scheduled maintenance 

were reported for both study groups. 

• Nonlighting electrical systems maintenance—The costs for this category for the two 

study groups were essentially the same; those for the hybrid buses at Atlantic Base were 

only slightly higher than those in the other study group. 

• Transmission maintenance—These costs were very low and similar for both groups. 

28
Table 12. Propulsion-Related Maintenance Cost by System 

(12-month evaluation period) 

Maintenance System 

Costs 

Diesel 

Ryerson 

Hybrid 

Atlantic 

Hybrid South 

Mileage Base 353,785 371,548 427,331 

Total Propulsion-Related Systems (Roll-Up) 

Parts Cost ($) 13,010.39 15,456.05 11,901.59 

Labor Hours 600.0 643.9 868.7 

Total Cost per Mile ($) 0.12 0.13 0.13 

Exhaust System Repairs 

Parts Cost ($) 1,727.33 4,380.21 578.20 

Labor Hours 65.7 60.5 27.0 

Total Cost per Mile ($) 0.01 0.02 0.01 

Fuel System Repairs 

Parts Cost ($) 732.51 896.16 1,079.67 

Labor Hours 10.1 15.0 19.6 

Total Cost per Mile ($) 0.00 0.01 0.00 

Engine System Repairs 

Parts Cost ($) 3,721.11 3,529.57 4,437.85 

Labor Hours 251.9 247.0 271.2 

Total Cost per Mile ($) 0.05 0.04 0.04 

Electric Motor, Generator, and Battery Repairs 

Parts Cost ($) 534.44 24.31 

Labor Hours 90.5 332.9 

Total Cost per Mile ($) 0.01 0.04 

Nonlighting Electrical System Repairs (General Electrical, Charging, 

Cranking, Ignition) 

Parts Cost ($) 2,302.21 1,497.78 1,997.27 

Labor Hours 131.5 141.7 105.3 

Total Cost per Mile ($) 0.03 0.03 0.02 

Air Intake System Repairs 

Parts Cost ($) 823.00 341.63 146.25 

Labor Hours 20.0 14.0 13.2 

Total Cost per Mile ($) 0.00 0.00 0.00 

Cooling System Repairs 

Parts Cost ($) 293.28 1,656.52 330.78 

Labor Hours 113.0 62.3 91.1 

Total Cost per Mile ($) 0.02 0.01 0.01 

Transmission Repairs 

Parts Cost ($) 0.76 62.10 238.08 

Labor Hours 8.0 12.5 8.5 

Total Cost per Mile ($) 0.00 0.00 0.00 

Hydraulic Repairs 

Parts Cost ($) 3,410.20 2,557.65 3,069.18 

Labor Hours 0.0 0.0 0.0 

Total Cost per Mile ($) 0.01 0.01 0.01 

Figure 20 shows monthly propulsion-related maintenance costs for the Ryerson and Atlantic 

Base study groups for the evaluation period. Costs per mile for the diesel buses at Ryerson Base 

were between $0.10 and $0.15 per mile, except in January 2006 when the cost spiked above 

$0.20 per mile. Early problems had to do with the auxiliary coolant heater. Later problems for 

29
the diesel buses had to do with the engine, turbocharger, and DPF. The costs for the hybrid buses 

at Atlantic Base started low then jumped in August 2005 and again from January-March 2006. 

These higher costs were caused by problems with the engine, standard batteries, voltage 

regulator for the alternator, DPF, and auxiliary coolant heater. Most repairs related to the 

propulsion system (hybrid and conventional) were covered under warranty and were not included 

in this cost. The warranty repair costs are covered separately in this report. 

0.00

0.05

0.10

0.15

0.20

0.25

0.30

Apr05May05Jun05Jul-05 Aug05Sep-05 Oct05Nov05Dec05Jan06Feb06Mar06

Propulsion Maintenance Cost ($) / Mile

Diesel RB Hybrid AB

Figure 20. Propulsion-Related Maintenance Cost per Mile (12-month evaluation period) 

HVAC Maintenance Costs. 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 system. Maintenance costs for the study groups of buses are shown in 

Table 13. 

These costs were lowest for the hybrid buses. The parts costs for all the study groups were for 

major repairs for the air-conditioning system. The diesel buses at Ryerson Base had significantly 

more HVAC repair costs than the two hybrid groups. For all three study groups, troubleshooting 

work orders for the heating system were most likely the result of an issue with the auxiliary 

coolant heater. However, the work order descriptions were not specific enough to indicate the 

root cause of the “no heat” problem. 

 Table 13. HVAC System Maintenance Costs 

(12-month evaluation period)

Study 

Group Mileage Parts 

Cost ($) 

Labor 

Hours 

Cost per 

Mile ($) 

Diesel 

Ryerson 

Base 

353,785 8,373.29 330.6 0.07 

Hybrid AB 371,548 4,965.71 208.5 0.04 

Hybrid SB 427,331 4,964.15 220.9 0.04 

30
PMI Maintenance Costs. This category only includes labor hours for scheduled inspections of 

multiple bus systems during preventive maintenance. As shown in Table 14, the maintenance 

cost per mile for this category was essentially the same for the study groups. This indicates that, 

in general, the three study groups featured similar preventive maintenance practices even though 

they operate from three separate locations. 

Table 14. PMI Maintenance Costs 

(12-month evaluation period)

Study 

Group Mileage Parts Cost ($) 

Labor 

Hours 

Cost per 

Mile ($) 

Diesel 

Ryerson 

Base 

353,785 0.00 320.0 0.05 

Hybrid AB 371,548 0.00 367.0 0.05 

Hybrid SB 427,331 0.00 383.5 0.04 

Warranty Items. Warranty costs listed in this section are costs covered by the manufacturer(s) 

of the vehicle, such as providing parts at no cost to the fleet, and for labor costs that were 

incurred by the fleet and reimbursed by the manufacturer under the warranty period associated 

with the new purchase. There is a one- to two-year warranty period for many systems on the 

buses; the warranty period for some systems is determined by mileage or calendar time. The 

Allison hybrid system has a 2-year warranty. Most transit bus operators also have a fleet defect 

clause that covers maintenance beyond the standard warranty period. The maintenance analysis 

in the previous section does not include any of the costs presented here. 

The KC Metro maintenance system tracks most part replacements, including those provided by 

the manufacturers. The cost summary in Table 15 shows warranty parts and associated labor 

costs in the KC Metro maintenance tracking system. Parts that were covered by warranty (and 

were initially listed as $0.01) use the actual invoice price of the parts listed, with the exception of 

the major hybrid system replacement parts that were replaced (DPIMs) because costs are not yet 

available from the manufacturer. Labor costs shown are hours reimbursed multiplied by $50 

($50/hr is an estimated labor rate used throughout this report). 

Table 15 shows the warranty parts costs for all three depots for the evaluation period. 

For the diesel buses, the highest warranty costs were for exhaust (DPF replacements), fuel, and 

engine (turbocharger replacements) systems. The diesel buses experienced relatively higher 

warranty costs early on that were caused by DPF replacements (for a manufacturing defect) and 

early campaigns. In July 2005, costs for the Atlantic Base hybrid buses jumped because of the 

campaigns for the multiplexing modules and alternators. The costs for the diesel buses were 

generally low until September 2005. Beyond that, especially in November 2005, the diesel buses 

experienced significant turbocharger and DPF problems. There were also a few campaigns that 

were completed during that timeframe, including one for an alternator mounting bracket. 

For the hybrid buses, all warranty costs are shown with the exception of the major electric 

propulsion system components that were replaced under warranty, which consisted of two 

DPIMs at Atlantic Base and 4 DPIMs at South Base. At the time of this report, the replacement 

31
costs for these components were not available and therefore are not included in the total. Also 

note that KCM is currently in the process of replacing improper cooling lines and fittings to the 

DPIMs on some South Base buses. These improper cooling lines were delivered with the earlier 

South Base deliveries only. The Atlantic Base hybrids had the correct fittings installed on the bus 

when delivered. Three of the six DPIMs failed with the improper cooling line installed and this 

may have been a contributing factor in these three DPIM failures (the other three had correct 

fittings installed prior to failure). The warranty costs for hybrid drive batteries and electrical 

drive units totaled approximately $1,000 for the Atlantic Base buses and approximately $6,200 

for the South Base buses during the evaluation period. The Atlantic Base hybrid buses reported 

lower engine warranty costs than the nonhybrid Ryerson Base buses. 

High warranty costs were reported for each of the three study groups for the nonlighting 

electrical category, which was caused by issues with the voltage regulators, alternators, and 

starters. Some additional warranty costs in the nonlighting electrical category were incurred for 

campaign activities for the multiplexing modules. 

Both the hybrid buses at South Base and the diesel buses at Ryerson Base were placed into 

service months before the Atlantic Base hybrid buses were. This allowed the manufacturers to 

troubleshoot and resolve several warranty/campaign issues before the Atlantic Base hybrid buses 

were placed into service. Figure 21 shows average monthly warranty costs (excluding DPIM 

replacement) from the beginning of operation through March 2006 for the study buses. 

32
Table 15. Warranty Costs by Bus System for Evaluation Period ($)

System Diesel Ryerson Base Hybrid AB Hybrid SB 

Parts Labor Total Parts Labor Total Parts Labor Total 

HVAC 4,606.20 605.00 5,211.20 2,813.73 255.00 3,068.73 3,423.11 1,000.00 4,423.11

Cab, Body, 

Accessories 2,784.70 380.00 3,164.70 25.78 675.00 700.78 99.88 700.00 799.88

Air, General 0.00 0.00 0.00 70.86 80.00 150.86 70.86 75.00 145.86

Suspension 0.00 0.00 0.00 133.32 125.00 258.32 0.00 0.00 0.00

Axles 763.42 375.00 1,138.42 4,688.57 45.00 4,733.57 5,605.25 1,745.00 7,350.25

Brakes 0.77 25.00 25.77 0.00 0.00 0.00 0.00 250.00 250.00

Steering 504.79 825.00 1,329.79 1,912.35 350.00 2,262.35 0.00 0.00 0.00

Transmission 137.94 102.50 240.44 493.26 0.00 493.26 24.84 75.00 99.84

Lighting 0.00 0.00 0.00 8.37 25.00 33.37 0.00 0.00 0.00

Nonlighting 

Electrical 8,703.44 2,475.00 11,178.44 29,203.43 2,537.50 31,740.93 20,160.62 2,587.50 22,748.12

Air Intake 524.16 550.00 1,074.16 116.48 150.00 266.48 349.44 450.00 799.44

Cooling 14,826.79 1,625.00 16,451.79 3,483.75 1,800.00 5,283.75 3,844.50 1,475.00 5,319.50

Exhaust 18,711.26 525.00 19,236.26 5,776.11 0.00 5,776.11 12,062.85 325.00 12,387.85

Fuel 5,121.79 735.00 5,856.79 0.00 300.00 300.00 8,906.51 1,760.00 10,666.51

Engine 14,028.34 3,515.00 17,543.34 2,672.15 1,155.00 3,827.15 22,677.09 2,638.50 25,315.59

Electric 

Propulsion* 0.00 0.00 0.00 1,625.86* 500.00 2,125.86 7,126.74* 1,375.00 8,501.74

DPIMs Replaced N/A - - 2 - - 4 - - 

Battery Packs 

Replaced N/A - - 0 - - 0 - - 

Drive Units 

Replaced N/A - - 0 - - 0 - - 

Articulation 

Joint 946.46 0.00 946.46 946.46 0.00 946.46 1,419.69 0.00 1,419.69

Total 71,660.06 11,737.50 83,397.56 53,970.48* 7,997.50 61,967.98 85,771.38* 14,456.00 100,227.38

* costs are not available for major electric propulsion components replaced (DPIMs) 

0.0

5000.0

10000.0

15000.0

20000.0

25000.0

30000.0

35000.0

40000.0

45000.0

Jul-04 Sep-04 Nov-04 Jan-05 Mar-05 May-05 Jul-05 Sep-05 Nov-05 Jan-06 Mar-06

Warranty Cost ($) Total

SB Warranty RB Warranty AB Warranty

Evaluation Period

April 2005-March 2006

Figure 21. Monthly Total Warranty Cost ($) 

(excluding DPIM replacements) 

33
Road Call Analysis 

A road call (RC) or revenue vehicle system failure (so named for the National Transit Database3) 

is defined as a failure of an in-service bus that causes the bus to be replaced in route or results in 

a significant schedule delay. If the problem can be repaired during a layover and the schedule is 

not affected, this is not considered an RC. This analysis includes only RCs that were caused by 

“chargeable” failures. Chargeable RCs involve systems that can physically disable the bus from 

operating en route, such as interlocks (doors), the engine, etc. The analysis does not include RCs 

for things such as radios or destination signs. 

Figure 22 shows cumulative miles between road calls (MBRC) and Table 16 breaks down the 

RCs by vehicle system for all three study groups for the evaluation period. There are two lines 

for each study group; one is for the MBRC for all RCs and the other is for the MBRC only for 

propulsion-related RCs. The MBRC for all RCs for the Ryerson and Atlantic study groups were 

nearly the same by the end of the evaluation period—4,954 MBRC for the hybrid buses and 

5,896 MBRC for the diesel buses. The propulsion-related MBRC for the Atlantic Base hybrid 

buses was 10,616; for the diesel buses it was 12,199, or 13% higher. 

0

5000

10000

15000

20000

25000

30000

35000

Apr-05 Jun-05 Aug-05 Oct-05 Dec-05 Feb-06

Miles Between Roadcalls (MBRC)

Diesel RB Cumulative MBRC Diesel RB Cumulative Propulsion MBRC

Hybrid AB Cumulative MBRC Hybrid AB Cumulative Propulsion MBRC

Figure 22. Total and Propulsion-Only Cumulative MBRC (12-month evaluation period) 

 

3

 Revenue vehicle system failures are defined for the FTA’s National Transit Database in the Reporting Manual 

Resource Module, which can be found at 

www.ntdprogram.com/NTD/ReportingManual/2005/Annual/PDFFiles/2005%20Resource%20Module.pdf. 

34
As shown in Table 16, the top three system categories for the most RCs for the diesel buses were 

engine, doors and interlock, and cooling problems (in that order). The top three system 

categories with the most RCs for the hybrid buses at Atlantic Base were doors and interlock, 

engine, and a tie for third (lighting, cooling, fuel, and wheelchair ramp). The top three system 

categories with the most RCs for the hybrid buses at South Base were the electric propulsion, 

engine, and doors and interlock. The RCs for electric propulsion were related to early problems 

with the cooling of the DPIM. 

 Table 16. Summary of Road Calls by System 

(12-month evaluation period) 

Diesel RB Hybrid AB Hybrid SB 

System 

Road 

Calls 

Percent 

(%) 

Road 

Calls 

Percent 

(%) 

Road 

Calls 

Percent 

(%) 

HVAC 3 5 12 16 9 10 

Doors and Interlock 6 10 8 11 13 15 

Wipers 2 3 1 1 3 3 

Air, General 2 3 0 0 2 2 

Brakes 2 3 5 7 3 3 

Steering 6 10 3 4 0 0 

Suspension 1 2 2 3 2 2 

Axles 2 3 2 3 1 1 

Transmission* 1 2 0 0 0 0 

Nonlighting Electrical* 11 18 10 13 10 11 

Lighting 4 7 4 5 2 2 

Cooling* 6 10 7 10 6 7 

Exhaust* 1 2 1 1 1 1 

Fuel* 0 0 3 4 2 2 

Engine* 10 17 10 13 15 16 

Electric Propulsion* 0 0 4 5 16 18 

Wheelchair Ramp 2 3 3 4 3 3 

Articulation Joint 1 2 0 0 4 4 

Total 60 100 75 100 91 100 

All MBRC 5,896 4,954 4,696 

Propulsion MBRC 12,199 10,616 8,547 

*=Propulsion System Related Groups

Summary of Costs 

Table 17 summarizes fuel and maintenance costs per mile for the study groups. The table shows 

the costs for each bus and the group average. The total cost for the hybrid buses at Atlantic Base 

were 15% lower than those of the diesel buses ($0.19 per mile difference). 

35
Table 17. Summary of Costs per Mile

Bus 

Fuel Cost per 

Mile ($) 

Maintenance Cost 

per Mile ($) 

Total Cost per 

Mile ($) 

Diesel RB

2880 0.78 0.50 1.28 

2881 0.80 0.48 1.28 

2882 0.79 0.44 1.23 

2883 0.80 0.43 1.23 

2884 0.81 0.46 1.27 

2885 0.76 0.46 1.22 

2886 0.81 0.41 1.22 

2887 0.80 0.39 1.19 

2888 0.77 0.49 1.26 

2889 0.80 0.59 1.39 

Avg. 0.79 0.46 1.25 

Hybrid AB

2780 0.63 0.48 1.11 

2781 0.62 0.63 1.25 

2782 0.65 0.49 1.14 

2783 0.63 0.39 1.02 

2784 0.60 0.43 1.03 

2785 0.63 0.40 1.03 

2786 0.61 0.38 0.99 

2787 0.64 0.50 1.14 

2788 0.62 0.46 1.08 

2789 0.62 0.34 0.96 

Avg. 0.62 0.44 1.06 

Hybrid SB

2640 0.54 0.48 1.02 

2641 0.53 0.47 1.00 

2642 0.53 0.35 0.88 

2643 0.53 0.34 0.87 

2644 0.54 0.44 0.98 

2645 0.55 0.44 0.99 

2647 0.53 0.42 0.95 

2648 0.51 0.42 0.93 

2649 0.51 0.34 0.85 

Avg. 0.53 0.41 0.94 

Laboratory Emissions Testing 

Tests were performed on one hybrid bus (of the 235) and one conventional bus (of the 30) during 

May-June 2005 to determine the emissions and fuel economy benefits of the hybrid electric 

powertrain being evaluated on site in King County. The tests were conducted over four driving 

cycles: Central Business District (CBD), Orange County (OCTA), Manhattan, and a custom test 

cycle developed from in-use data on the King County Metro (KCM) fleet’s operation. To 

evaluate the effects of additional engine and vehicle loading due to grade, select cycles were 

repeated with and without this added load. Vehicle exhaust emissions, fuel consumption, and 

state of charge of the energy storage system were measured for repeated test conditions. 

36
The vehicles were tested at NREL’s ReFUEL Laboratory in Denver, Colorado. The laboratory 

includes a heavy-duty vehicle (chassis) test cell and an engine dynamometer test cell with 

emissions measurement capability. Regulated emissions measurements are performed using 

procedures consistent with the Code of Federal Regulations (CFR) title 40, section 86, subpart N. 

Instrumentation and sensors at the laboratory are maintained with National Institute of Standards 

and Technology-traceable calibration. Test procedures, 

calibrations, and measurement accuracies are maintained to 

meet requirements outlined in the current CFR title 40, 

section 86, subpart N. 

Figure 23. Chassis Cell with Test 

The test vehicles were installed on the chassis dynamometer, 

shown in Figure 23. All sensors shown were monitored and 

recorded continuously by the ReFUEL data acquisition 

system throughout each test cycle run, unless otherwise 

noted. Detailed results of this testing are included in the 

report, “KCM Transit Emissions”, which is available at 

www.nrel.gov/vehiclesandfuels/ahhps/publications.html.

Fuel economy results for the buses are shown in Table 18. Emissions results (for NOx, PM, CO, 

and CO2) are shown in Table 19. 

Table 18. Fuel Economy of Buses on Various Cycles on Chassis Dynamometer

 Manhattan OCTA CBD KCM 

KCM, 

no grade

Conventional Bus Fuel Economy (mpg) 1.46 2.15 2.19 2.90 3.03 

Hybrid Bus Fuel Economy (mpg) 2.56 3.24 3.25 3.78 3.98 

Fuel Economy (mpg) % Increase w/Hybrid Bus 74.6% 50.6% 48.3% 30.3% 31.4% 

Table 19. Average Values for Emission Results of Buses on Specified Cycles*

Manhattan OCTA CBD KCM 

 Diesel Hybrid Diesel Hybrid Diesel Hybrid Diesel Hybrid 

NOx 

(gram/mile) 29.58 18.12 18.91 13.51 19.67 14.44 14.74 12.11 

PM 

(gram/mile) 0.380 .003 0.050 0.024 0.101 0.003 .108 0.187 

CO 

(gram/mile) 3.13 2.81 2.29 1.55 1.77 1.55 0.66 0.27 

THC 

(gram/mile) 0.04 0.05 0.03 0.03 0.12 0.03 0.04 0.02 

CO2 

(gram/mile) 6714 3771 4579 3001 4587 2991 3446 2614 

*Average of at least three runs; see detailed report for measured variation between runs. 

37
Future Work

All the new diesel and hybrid articulated buses from New Flyer have been delivered and have 

been in service since at least December 2004. This final evaluation report provides results from a 

12-month evaluation period. The first six months covered in this report included operation of the 

hybrid buses in the downtown transit tunnel. The tunnel is now closed, and the second 6 months 

of operation were completed outside the transit tunnel. The HUSH mode feature of the hybrid 

buses was deactivated via software in October 2005 to coincide with the tunnel closure. The 

tunnel is planned to reopen in 2007 and HUSH mode will be reactivated. 

KC Metro has just issued an RFP to add 20 more hybrid buses to its fleet. The RFP also includes 

an additional 60-month supply option for up to 340 more hybrid and conventional powered 

articulated low floor buses. 

38
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 

Kevin Walkowicz 

Senior Project Engineer 

Phone: 303-275-4492 

E-mail: kevin_walkowicz@nrel.gov 

King County Metro Transit 

Todd Gibbs 

Senior Program Administrator 

Phone: 206-684-2878 

E-mail: todd.gibbs@metrokc.gov 

GM Allison Electric Drives 

Peter Chiang 

Vehicle/Field Engineering 

Phone: 317-915-2748 

E-mail: peter.chiang@gm.com 

New Flyer Industries 

G. Paul Zanetel 

Chief Technical Advisor 

Phone: 204-982-8180 

E-mail: paul_zanetel@newflyer.com 

Caterpillar Inc. 

Dave Bradshaw 

Truck Engine District Manager, Northwest Region 

Phone: 425-562-9659 

E-mail: bradshaw_david_G@cat.com 

Battelle 

Kevin Chandler 

Program Manager 

Phone: 614-424-5127 

E-mail: chandlek@battelle.org 

39
Acronyms and Abbreviations 

AB Atlantic Base 

AVTA Advanced Vehicle Testing Activity 

B5 biodiesel blend at 5% 

bhp brake horsepower 

CAT Caterpillar 

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 

DPIM dual-power inverter module 

EPA U.S. Environmental Protection Agency 

EGR exhaust gas recirculation 

ft feet 

ft-lb foot-pounds 

FTA Federal Transit Administration 

g/bhp-hr grams per brake horsepower-hour 

GM General Motors 

GVWR gross vehicle weight rating 

HC hydrocarbons 

HEV hybrid electric vehicle 

hp horsepower 

HVAC heating, ventilation, and air-conditioning 

in. inches 

KC Metro King County Metro Transit 

kW kilowatts 

L liter 

lb pounds 

LNG liquefied natural gas 

MBRC miles between road calls 

mpg miles per gallon 

mph miles per hour 

NREL National Renewable Energy Laboratory 

NMHC nonmethane hydrocarbons 

NOx oxides of nitrogen 

NTD National Transit Database 

PM particulate matter 

ppm parts per million 

PMI preventive maintenance inspection 

RB Ryerson Base 

RC road call 

R&D research and development 

40
RFP request for proposals 

rpm revolutions per minute 

SB South Base 

THC total hydrocarbon 

ULSD ultra-low-sulfur diesel 

V volts 

VDC volts direct current 

41
Bibliography 

Barnitt, R., 2006, Case Study: Ebus Hybrid Electric Buses and Trolleys, National Renewable Energy 

Laboratory, Golden, CO, NREL/TP-540-38749 

Battelle, 1997, Raley’s LNG Truck Fleet, Start-Up Experience, National Renewable Energy Laboratory, 

Golden, CO, NREL/BR-540-23402 

Battelle, 1999, Waste Management’s LNG Truck Fleet, Start-Up Experience, National Renewable Energy 

Laboratory, Golden, CO, NREL/BR-540-26617 

Battelle, 2000, DART’s LNG Bus Fleet, Start-Up Experience, National Renewable Energy Laboratory, 

Golden, CO, NREL/BR-540-28124 

Battelle/NREL, 2001, Advanced Technology Vehicles in Service, Diesel Hybrid electric Buses, National 

Renewable Energy Laboratory, Golden, CO, NREL/FS-540-30736. 

Battelle/NREL, 2002, NYCT’s Diesel Hybrid electric Buses, Program Status Update, National Renewable 

Energy Laboratory, Golden, CO, NREL/BR-540-31668 

Chandler, K., 2006, Ten Years of Compressed Natural Gas (CNG) Operations at SunLine Transit Agency, 

National Renewable Energy Laboratory, Golden, CO, NREL/SR-540-39180 

Chandler, K., Eudy, L., 2003, ThunderPower, Bus Evaluation at SunLine Transit Agency, National 

Renewable Laboratory, Golden, CO, DOE/GO-102003-1786 

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

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

Chandler, K., Norton, P., Clark, N., 2000, DART’s LNG Bus Fleet, Final Results, National Renewable 

Energy Laboratory, Golden, CO, NREL/BR-540-28739 

Chandler, K., Norton, P., Clark, N., 2000, Raley’s LNG Truck Fleet, Final Results, National Renewable 

Energy Laboratory, Golden, CO, NREL/BR-540-27678 

Chandler, K., Norton, P., Clark, N., 2001, Waste Management’s LNG Truck Fleet, Final Results, National 

Renewable Energy Laboratory, Golden, CO, NREL/BR-540-29073 

Chandler, K., Proc, K., 2004, Norcal Prototype LNG Truck Fleet, Final Results, National Renewable 

Energy Laboratory, Golden, CO, DOE/GO-102004-1920 

Chandler, K., Vertin, K., Alleman, T., Clark, N., 2003, Ralphs Grocery Company EC-Diesel Truck Fleet: 

Final Results, National Renewable Energy Laboratory, Golden, CO, NREL/BR-540-31363 

Chandler, K., Walkowicz, K., 2006, King County Metro Transit Hybrid Articulated Buses: Interim 

Evaluation Results, National Renewable Energy Laboratory, Golden, CO, NREL/TP-540-39742 

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 

42
Chandler, L., Barnitt, R., 2006, New York City Transit (NYCT) Hybrid and CNG Transit Buses: Final 

Evaluation Results, National Renewable Energy Laboratory, Golden, CO, NREL/TP-540-40125 

Eudy, L., 2002, Natural Gas in Transit Fleets: A Review of the Transit Experience, National Renewable 

Energy Laboratory, Golden, CO, NREL/TP-540-31479 

Eudy, L., Gifford, M., 2003, Challenges and Experiences with Electric Propulsion Transit Buses in the 

United States, National Renewable Energy Laboratory, Golden, CO, DOE/GO-102003-1791 

Motta, R., Norton, P., Kelly, K., Chandler, K., Schumacher, L., Nigel, N., 1996, Alternative Fuel Transit 

Buses, Final Results from the National Renewable Energy Laboratory (NREL) Vehicle Evaluation 

Program, National Renewable Energy Laboratory, Golden, CO, NREL/TP-425-20513 

NREL, 2002, Advanced Technology Vehicles in Service, Norcal Waste Systems, Inc., National Renewable 

Energy Laboratory, Golden, CO, NREL/FS-540-32808 

NREL, 2002, General Evaluation Plan, Fleet Test & Evaluation Projects, National Renewable Energy 

Laboratory, Golden, CO, NREL/BR-540-32392 

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 

NREL, 2004, Advanced Technology Vehicles in Service, Indianapolis Public Transportation, National 

Renewable Energy Laboratory, Golden, CO, DOE/GO-102004-1986 

NREL, 2004, Advanced Technology Vehicles in Service, King County Metro Transit, National Renewable 

Energy Laboratory, Golden, CO, DOE/GO-102004-2026 

NREL, 2005, Advanced Technology Vehicles in Service, Knoxville Area Transit, National Renewable 

Energy Laboratory, Golden, CO, DOE/GO-102005-2085 

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 

43
Appendix: Fleet Summary Statistics 

King County Metro (Seattle, WA) Fleet Summary Statistics 

Evaluation Period Only 

Fleet Operations and Economics 

Diesel Hybrid Hybrid 

Ryerson Atlantic South 

Number of Vehicles 10 10 9

Period Used for Fuel Analysis 4/05—3/06 4/05—3/06 4/05—3/06

Total Number of Months in Period 12 12 12

Fuel Analysis Base Fleet Mileage 350,567 362,049 379,328

Period Used for Maintenance Op Analysis 4/05—3/06 4/05—3/06 4/05—3/06

Total Number of Months in Period 12 12 12

Maintenance Analysis Base Fleet Mileage 353,785 371,548 427,331

Average Monthly Mileage per Vehicle 2,948 3,096 3,957

Fleet Fuel Usage in Gal. 139,996 114,054 101,174

Representative Fleet MPG 2.50 3.17 3.75

Hybrid compared to Diesel 27% 50%

Average Fuel Cost as Reported 1.98 1.98 1.98

per Gal D2 per Gal D2 per Gal D2

Average Fuel Cost per Energy Equivalent 1.98 1.98 1.98

Fuel Cost per Mile 0.791 0.624 0.528

Number of Total Road Calls 60 75 91

MBRC All Road Calls 5,896 4,954 4,696

Number of Propulsion System Road Calls 29 35 50

MBRC Propulsion System Road Calls 12,199 10,616 8,547

Total Scheduled Repair Cost per Mile 0.154 0.140 0.118

Total Unscheduled Repair cost per Mile 0.308 0.304 0.293

Total Maintenance Cost per Mile 0.462 0.444 0.411

Total Operating Cost per Mile 1.252 1.068 0.939

Maintenance Costs 

Diesel Hybrid Hybrid 

Ryerson Atlantic South 

Fleet Mileage 353,785 371,548 427,331

Total Parts Cost 32,555.04 39,319.89 28,181.55

Total Labor Hours 2615.4 2514.2 2946.9

Average Labor Cost 130,770.00 125,707.50 147,346.00

(@ $50.00 per hour) 

Total Maintenance Cost 163,325.04 165,027.39 175,527.55

Total Maintenance Cost per Mile 0.462 0.444 0.411

44
Breakdown of Maintenance Costs by Vehicle System 

Diesel Hybrid Hybrid 

Ryerson Atlantic South 

Fleet Mileage 353,785 371,548 427,331

Total Propulsion-Related Systems 

(ATA VMRS 27, 30, 31, 32, 33, 41, 42, 43, 44, 45, 46, 65)

Parts Cost 13,010.39 15,456.05 11,901.59

Labor Hours 600.0 643.9 868.7

Average Labor Cost 30,000.00 32,192.50 43,433.50

Total Cost (for system) 43,010.39 47,648.55 55,335.09

Total Cost (for system) per Mile 0.122 0.128 0.130

Exhaust System Repairs (ATA VMRS 43)

Parts Cost 1,727.33 4,380.21 578.20

Labor Hours 65.7 60.5 27.0

Average Labor Cost 3,285.00 3,025.00 1,350.00

Total Cost (for system) 5,012.33 7,405.21 1,928.20

Total Cost (for system) per Mile 0.014 0.020 0.005

Fuel System Repairs (ATA VMRS 44)

Parts Cost 732.51 896.16 1,079.67

Labor Hours 10.1 15.0 19.6

Average Labor Cost 505.00 750.00 980.00

Total Cost (for system) 1,237.51 1,646.16 2,059.67

Total Cost (for system) per Mile 0.004 0.004 0.005

Power Plant (Engine) Repairs (ATA VMRS 45)

Parts Cost 3,721.11 3,529.57 4,437.85

Labor Hours 251.9 247.0 271.2

Average Labor Cost 12,592.50 12,350.00 13,558.50

Total Cost (for system) 16,313.61 15,879.57 17,996.35

Total Cost (for system) per Mile 0.046 0.043 0.042

Electric Motor, Generator, and Battery Repairs (ATA VMRS 46) 

Parts Cost 534.44 24.31

Labor Hours 90.5 332.9

Average Labor Cost 4,525.00 16,642.50

Total Cost (for system) 5,059.44 16,666.81

Total Cost (for system) per Mile 0.014 0.039

Electrical System Repairs (ATA VMRS 30-Electrical General, 

31-Charging, 32-Cranking, 33-Ignition)

Parts Cost 2,302.21 1,497.78 1,997.27

Labor Hours 131.5 141.7 105.3

Average Labor Cost 6,572.50 7,085.00 5,262.50

Total Cost (for system) 8,874.71 8,582.78 7,259.77

Total Cost (for system) per Mile 0.025 0.023 0.017

45
Breakdown of Maintenance Costs by Vehicle System (continued) 

Diesel Hybrid Hybrid 

Ryerson Atlantic South 

Air Intake System Repairs (ATA VMRS 41)

Parts Cost 823.00 341.63 146.25

Labor Hours 20.0 14.0 13.2

Average Labor Cost 997.50 700.00 660.00

Total Cost (for system) 1,820.50 1,041.63 806.25

Total Cost (for system) per Mile 0.005 0.003 0.002

Cooling System Repairs (ATA VMRS 42)

Parts Cost 293.28 1,656.52 330.78

Labor Hours 113.0 62.3 91.1

Average Labor Cost 5,647.50 3,112.50 4,555.00

Total Cost (for system) 5,940.78 4,769.02 4,885.78

Total Cost (for system) per Mile 0.017 0.013 0.011

Hydraulic Repairs (ATA VMRS 65)

Parts Cost 3,410.20 2,557.65 3,069.18

Labor Hours 0.0 0.0 0.0

Average Labor Cost 0.00 0.00 0.00

Total Cost (for system) 3,410.20 2,557.65 3,069.18

Total Cost (for system) per Mile 0.010 0.007 0.007

Transmission Repairs (ATA VMRS 27)

Parts Cost 0.76 62.10 238.08

Labor Hours 8.0 12.5 8.5

Average Labor Cost 200.00 625.00 425.00

Total Cost (for system) 200.76 687.10 663.08

Total Cost (for system) per Mile 0.001 0.002 0.002

Cab, Body, and Accessories Systems Repairs 

(ATA VMRS 02-Cab and Sheet Metal, 50-Accessories, 71-Body) 

Parts Cost 7,503.07 16,134.94 6,797.54

Labor Hours 1002.4 1072.3 1039.3

Average Labor Cost 50,120.00 53,612.50 51,962.50

Total Cost (for system) 57,623.07 69,747.44 58,760.04

Total Cost (for system) per Mile 0.163 0.188 0.138

Inspections Only - no parts replacements (101)

Parts Cost 0.00 0.00 0.00

Labor Hours 320.0 367.0 383.5

Average Labor Cost 16,000.00 18,350.00 19,175.00

Total Cost (for system) 16,000.00 18,350.00 19,175.00

Total Cost (for system) per Mile 0.045 0.049 0.045

46
Breakdown of Maintenance Costs by Vehicle System (continued) 

Diesel Hybrid Hybrid 

Ryerson Atlantic South 

HVAC System Repairs (ATA VMRS 01)

Parts Cost 8,373.29 4,965.71 4,964.15

Labor Hours 330.6 208.5 220.9

Average Labor Cost 16,527.50 10,422.50 11,045.00

Total Cost (for system) 24,900.79 15,338.21 16,009.15

Total Cost (for system) per Mile 0.070 0.041 0.038

Brake System Repairs (ATA VMRS 13)

Parts Cost 8.93 27.77 4.64

Labor Hours 14.5 48.5 37.3

Average Labor Cost 725.00 2,425.00 1,862.50

Total Cost (for system) 733.93 2,452.77 1,867.14

Total Cost (for system) per Mile 0.002 0.007 0.004

Air System Repairs (ATA VMRS 10)

Parts Cost 1,034.53 547.40 489.19

Labor Hours 35.0 25.4 43.3

Average Labor Cost 1,750.00 1,270.00 2,162.50

Total Cost (for system) 2,784.53 1,817.40 2,651.69

Total Cost (for system) per Mile 0.008 0.005 0.006

Lighting System Repairs (ATA VMRS 34)

Parts Cost 622.59 383.61 274.55

Labor Hours 35.0 34.8 18.5

Average Labor Cost 1,750.00 1,737.50 925.00

Total Cost (for system) 2,372.59 2,121.11 1,199.55

Total Cost (for system) per Mile 0.007 0.006 0.003

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

Suspension) 

Parts Cost 950.97 929.63 1,390.21

Labor Hours 81.5 56.3 55.0

Average Labor Cost 4,075.00 2,812.50 2,750.00

Total Cost (for system) 5,025.97 3,742.13 4,140.21

Total Cost (for system) per Mile 0.014 0.010 0.010

Axle, Wheel, and Drive Shaft Repairs (ATA VMRS 11-Front Axle, 12-Middle Axle, 

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

Parts Cost 989.84 529.51 646.79

Labor Hours 109.5 41.2 50.7

Average Labor Cost 5,472.50 2,060.00 2,535.00

Total Cost (for system) 6,462.34 2,589.51 3,181.79

Total Cost (for system) per Mile 0.018 0.007 0.007

47
Breakdown of Maintenance Costs by Vehicle System (continued) 

Diesel Hybrid Hybrid 

Ryerson Atlantic South 

Tire Repairs (ATA VMRS 17)

Parts Cost 0.00 0.00 0.00

Labor Hours 3.0 4.0 32.0

Average Labor Cost 150.00 200.00 1,600.00

Total Cost (for system) 150.00 200.00 1,600.00

Total Cost (for system) per Mile 0.000 0.001 0.004

Articulation Repairs (ATA VMRS 59) 

Parts Cost 6.30 345.26 1,712.89

Labor Hours 84.0 12.5 197.9

Average Labor Cost 4,200.00 625.00 9,895.00

Total Cost (for system) 4,206.30 970.26 11,607.89

Total Cost (for system) per Mile 0.012 0.003 0.027

Notes 

1. The engine and fuel-related systems were chosen to include only those systems of the vehicles that could be 

directly a part of the propulsion system. 

2. ATA VMRS coding is based on parts that were replaced. If there was no part replaced in a given repair, then the 

code was chosen by the system being worked on. 

3. In general, inspections (with no part replacements) were only included in the overall totals (not by system). 

101 was created to track labor costs for PM inspections. 

4. ATA VMRS 02-Cab and Sheet Metal represents seats, doors, etc.; ATA VMRS 50-Accessories represents 

things like fire extinguishers, test kits, etc.; ATA VMRS 71-Body represent mostly windows and windshields. 

5. Average labor cost is assumed to be $50 per hour. 

6. Warranty costs are not included.

48
F1147-E(12/2004) 

REPORT DOCUMENTATION PAGE Form Approved 

OMB No. 0704-0188

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PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ORGANIZATION.

1. REPORT DATE (DD-MM-YYYY)

December 2006 

2. REPORT TYPE

Technical Report 

3. DATES COVERED (From - To)

May 2005-May 2006 

5a. CONTRACT NUMBER

DE-AC36-99-GO10337 

5b. GRANT NUMBER

4. TITLE AND SUBTITLE

King County Metro Transit Hybrid Articulated Buses: 

Final Evaluation Results 

5c. PROGRAM ELEMENT NUMBER

5d. PROJECT NUMBER

NREL/TP-540-40585 

5e. TASK NUMBER

FC07.3000 

6. AUTHOR(S)

K Chandler and K. Walkowicz 

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-540-40585 

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 evaluation focused on diesel and hybrid diesel buses selected from three of KC Metro’s seven operating depots 

or bases. All 30 of the new diesel articulated buses currently operate from the Ryerson Base depot; they are identical 

to the hybrid buses except for the hybrid electric propulsion systems. Ten diesel buses were selected from Ryerson 

Base for detailed evaluation, and 10 hybrid buses were selected from Atlantic Base for comparison. 

15. SUBJECT TERMS

Evaluation; diesel buses; hybrid electric diesel buses; King County Metro; U.S. Department of Energy; Advanced 

Vehicle Testing Activity; AVTA; transit agency 

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

a. REPORT 

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