National Renewable Energy Laboratory 

Innovation for Our Energy Future 

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

Office of Energy Efficiency & Renewable Energy

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

Case Study: Ebus Hybrid 

Electric Buses and Trolleys 

R. Barnitt 

Technical Report 

NREL/TP-540-38749 

July 2006 
Case Study: Ebus Hybrid 

Electric Buses and Trolleys 

R. Barnitt 

Prepared under Task No. FC06.3000 

Technical Report 

NREL/TP-540-38749 

July 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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Table of Contents 

List of Figures.................................................................................................................... iv 

List of Tables ...................................................................................................................... v 

Executive Summary........................................................................................................... vi 

Objectives ...................................................................................................................... vi 

Technology .................................................................................................................... vi 

Evaluation Methods...................................................................................................... vii 

Results........................................................................................................................... vii 

IndyGo ...................................................................................................................... vii 

KAT .........................................................................................................................viii 

Both Fleets...............................................................................................................viii 

Overview: Ebus Hybrid Buses and Trolleys....................................................................... 1 

Capstone MicroTurbine APU ............................................................................................. 2 

Traction Batteries................................................................................................................ 3 

Emissions............................................................................................................................ 4 

Durability ............................................................................................................................ 4 

Project Design and Data Collection.................................................................................... 4 

Fleet Experience: IndyGo ................................................................................................... 5 

Fleet Profile..................................................................................................................... 5 

Implementation Experience ............................................................................................ 6 

IndyGo Vehicle Use and Performance ........................................................................... 8 

Duty Cycle .................................................................................................................. 8 

Fuel Economy Results .............................................................................................. 10 

Fuel Costs.................................................................................................................. 12 

Maintenance.............................................................................................................. 12 

Specific Component Issues and Resolutions ................................................................ 14 

Climate Control......................................................................................................... 15 

Electric Propulsion Motor Controls.......................................................................... 15 

Capstone MicroTurbine ............................................................................................ 15 

Traction Batteries...................................................................................................... 15 

Low SOC .................................................................................................................. 16 

Campaigns..................................................................................................................... 17 

Road Calls..................................................................................................................... 17 

Total Operating Costs................................................................................................... 19 

Summary of Results at IndyGo..................................................................................... 19 

Availability ............................................................................................................... 20 

Applicability ............................................................................................................. 20 

Reliability.................................................................................................................. 20 

Training..................................................................................................................... 20 

Fleet Experience: KAT ..................................................................................................... 21 

Fleet Profile................................................................................................................... 21 

Implementation Experience .......................................................................................... 22 

KAT Vehicle Use and Performance ............................................................................. 25 

Duty Cycle ................................................................................................................ 25 

Fuel Economy Results .............................................................................................. 26 

Fuel Costs.................................................................................................................. 28 

 iii
Maintenance.............................................................................................................. 28 

Specific Component Issues and Resolutions ................................................................ 31 

Capstone MicroTurbine ............................................................................................ 31 

Climate Control......................................................................................................... 32 

Traction Batteries...................................................................................................... 32 

Campaigns..................................................................................................................... 33 

Road Calls..................................................................................................................... 33 

Total Operating Costs................................................................................................... 34 

Summary of Results for KAT....................................................................................... 35 

Overall Summary and Comments..................................................................................... 36 

Match the Vehicle to the Duty Cycle............................................................................ 36 

Train Drivers and Maintenance Personnel.................................................................... 36 

New Technology Is Still in Development..................................................................... 37 

Contacts............................................................................................................................. 38 

Acronyms and Abbreviations ........................................................................................... 39 

References......................................................................................................................... 40 

List of Figures 

Figure 1. Ebus system block diagram (Source: Ebus)...................................................... 1 

Figure 2. Schematic of Capstone MicroTurbine (Source: Capstone Turbine 

Corporation)...................................................................................................... 3 

Figure 3. IndyGo’s headquarters in Indianapolis, IN (Source: NREL)............................ 6 

Figure 4. Ebus at IndyGo (Source: NREL)...................................................................... 6 

Figure 5. Battery tray for the electric propulsion system (Source: NREL)...................... 7 

Figure 6. Normal battery tray (left) and tray with a corroded cable (Source: NREL)..... 7

Figure 7. IndyGo’s Blue Line route (Source: IndyGo) .................................................... 8 

Figure 8. An IndyGo hybrid electric bus (Source: NREL) .............................................. 8 

Figure 9. Cumulative miles traveled during the evaluation period at IndyGo ............... 10 

Figure 10. IndyGo Fuel economy during the 6-month evaluation period........................ 11 

Figure 11. IndyGo Cumulative maintenance costs per mile ............................................ 13 

Figure 12. Maintenance cost by vehicle system (Labor + Parts) ..................................... 13 

Figure 13. Propulsion system maintenance costs (Labor + Parts) ................................... 14 

Figure 14. Capstone MicroTurbine Assembly (Source: NREL)...................................... 15 

Figure 15. IndyGo Ebus at Charging Station (Source: NREL)........................................ 16 

Figure 16. IndyGo Route Stop (Source: NREL).............................................................. 17 

Figure 17. Battery Charger Display (Source: NREL)...................................................... 18 

Figure 18. IndyGo Cumulative miles between road calls................................................ 19 

Figure 19. KAT Maintenance Facility (Source: NREL).................................................. 22 

Figure 20. KAT Ebus Trolley (Source: NREL Photo)..................................................... 23 

Figure 21. Original and upgraded LPG fueling station.................................................... 23 

Figure 22. On-board LPG storage .................................................................................... 24 

Figure 23. Original KAT charger..................................................................................... 24 

Figure 24. KAT Total mileage accumulation for the four Ebus trolleys ......................... 25 

Figure 25. Red Line and other trolley routes in Knoxville .............................................. 26 

Figure 26. KAT Average fuel economy........................................................................... 28 

Figure 27. KAT Cumulative maintenance costs per mile ................................................ 30 

 iv
Figure 28. KAT Maintenance costs by vehicle system (Labor + Parts) .......................... 31 

Figure 29. KAT Propulsion system maintenance costs (Labor + Parts) .......................... 31 

Figure 30. KAT Ebus Trolley traction battery pack (Source: NREL) ............................. 32 

Figure 31. KAT Cumulative miles between road calls (MBRC)..................................... 34 

Figure 32. KAT Cost per mile source breakdown............................................................ 35 

List of Tables 

Table 1. Ebus Series Hybrid Electric Propulsion System................................................2 

Table 2. Capstone Model 330 Hybrid Electric Vehicle (HEV) MicroTurbine 

Performance* .....................................................................................................3 

Table 3. Capstone MicroTurbine Emissions*..................................................................4 

Table 4. Vehicle Systems Overview................................................................................5 

Table 5. IndyGo Hybrid-Electric Bus Duty Cycle...........................................................9 

Table 6. IndyGo Fuel Economy Results (November 2004 through April 2005)...........11 

Table 7. IndyGo Total Maintenance Cost Comparison (November 2004 through 

April 2005).......................................................................................................12 

Table 8. IndyGo Propulsion System Costs (November 2004 to April 2005)................14 

Table 9. IndyGo Road Call Comparison (November 2004 to April 2005)...................18 

Table 10. IndyGo Overall Operating Costs .....................................................................19 

Table 11. KAT Red Line Duty Cycle Characteristics .....................................................26 

Table 12. KAT Fuel Economy Results for 6-Month Evaluation Period..........................27 

Table 13. KAT Fuel Cost Calculations............................................................................28 

Table 14. KAT Total Maintenance Cost Comparison (December 2004 to May 2005)..29 

Table 15. Campaigns........................................................................................................33 

Table 16. KAT Road Call Comparison (December 2004 to May 2005)........................34 

Table 17. KAT Total Operating Cost Comparison..........................................................35 

 v
Executive Summary 

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

provides unbiased evaluations on alternative fuel and advanced transportation 

technologies that reduce U.S. dependence on foreign oil while improving the nation’s air 

quality. AVTA’s role is to bridge the gap between research and development (R&D) and 

the commercial availability of alternative fuels and advanced vehicle technologies. 

AVTA supports DOE’s FreedomCAR & Vehicle Technologies Program by examining 

market factors and customer requirements, evaluating the performance and durability of 

alternative fuel and advanced technology vehicles, and assessing the performance of 

these vehicles in fleet applications. 

The Fleet Test & Evaluation team at the National Renewable Energy Laboratory (NREL) 

supports AVTA by conducting medium- and heavy-duty vehicle evaluations. The team’s 

tasks include selecting appropriate technologies to validate, identifying fleets to evaluate, 

designing test plans, gathering on-site data, preparing technical reports, and 

communicating results on its Web site and in print publications. One of the primary target 

audiences for AVTA evaluations is fleet operators who use or may consider using these 

advanced technologies. NREL has completed numerous light- and heavy-duty vehicle 

evaluations based on an established data collection protocol, known as the General 

Evaluation Plan,1

 developed with and for DOE. 

Objectives 

This evaluation focuses on the demonstration of hybrid electric buses and trolleys 

produced by Ebus, Inc. (www.ebus.com), of Downey, California. Ebus manufactures 22-

foot buses with a variety of optional powertrains and exterior designs. The vehicles come 

with battery electric and hybrid electric powertrain options, and purchasers can choose 

either conventional bus or antique-trolley-style exteriors. The Indianapolis Transportation 

Corporation (IndyGo) and Knoxville Area Transit (KAT) participated in a demonstration 

of the Ebus vehicles. Each fleet chose hybrid electric powertrains but selected different 

exterior designs and fuels. These vehicles were placed in revenue transit service to 

provide the following: 

• Credible data and evaluation results 

• Results that show progress and experience in using hybrid electric buses in transit 

service 

• Results from multiple operating experiences and different transit agencies. 

Technology 

Ebus’s hybrid electric vehicles are propelled by battery-powered electric motors that 

supply power to the wheels. Two nickel-cadmium (NiCd) traction battery packs are kept 

within a prescribed range of state of charge (SOC) by a generator or powerplant. The 

battery packs operate at 60% to 80% SOC and allow for the use of regenerative braking, 

which recovers energy from the braking system. The hybrid system uses a 30 kW 

 

1

 Available on the Web at www.nrel.gov/vehiclesandfuels/fleettest/pdfs/32392.pdf. 

 vi
Capstone MicroTurbineTM (www.capstoneturbine.com) auxiliary power unit (APU) as a 

primary powerplant. Onboard fuel storage supplies the APU. The APU can operate on 

several fuels, including compressed natural gas (CNG), liquefied petroleum gas (LPG), 

and diesel fuel. The hybrids are primarily designed as a charge-sustaining series hybrid, 

meaning that the batteries have power as long as the APU has fuel. The hybrids can be 

plugged into charging systems overnight to bring the batteries up to a 100% SOC for the 

morning pullout. Used in this way, they initially operate as charge-depleting series 

hybrids until SOC reduction activates the APU, and operation begins in charge-sustaining 

mode. 

Evaluation Methods 

Data were collected and evaluated for five diesel-fueled buses at IndyGo and four LPGfueled trolleys at KAT. Data included the following: 

• Fuel consumption by vehicle 

• Mileage data by vehicle 

• Preventive maintenance work orders, labor events, and parts lists 

• Records of unscheduled maintenance, such as road calls. 

Although there were some attempts to do so, data were not collected for energy gains due 

to opportunity charging of the vehicles’ traction battery packs. In addition, “selfcharging” (discussed later) and its effect on fuel economy were not quantified. 

Therefore, fuel economy calculations are based solely upon miles driven and liquid fuel 

volumes recorded. 

Results 

The following is a summary of the project results: 

• IndyGo and KAT successfully deployed diesel- and LPG-fueled Ebus hybrids in 

revenue service, collecting six months of performance and operating data for 

analysis. 

• Both agencies designed new routes for the demonstration vehicles. Route duty 

cycles differed between the fleets. 

IndyGo 

• IndyGo observed an average fuel economy of 4.37 mpg. 

• IndyGo observed a maintenance cost per mile of $0.66, a fuel cost per mile of 

$0.37, and a total operating cost per mile of $1.03. 

• IndyGo observed a hybrid propulsion maintenance cost of $0.46 per mile. 

• IndyGo used the Ebus hybrids on a 12-hour duty cycle in a downtown circulator 

route. Although the buses exhibited lower than expected availability, they were 

considered successful in terms of cost per mile and fuel economy. 

 vii
KAT 

• KAT observed an average fuel economy of 3.22 mpg (diesel equivalent gallons 

for LPG use). 

• KAT observed a maintenance cost per mile of $0.62, a fuel cost per mile of $0.35, 

and a total operating cost per mile of $0.97. 

• KAT observed a hybrid propulsion maintenance cost of $0.12 per mile. 

• KAT used the Ebus hybrids on more demanding terrain than IndyGO did, but for 

shorter periods of time each day. The agency experienced fewer hybrid systemrelated problems than IndyGo did. 

Both Fleets 

• For both fleets, there were road calls and maintenance events characterized by 

turbine fault codes and reports of low SOC. These events were caused by drivers 

accidentally shutting down turbines and by an on-road failure of the turbine to 

ignite. The events were more prevalent in IndyGo’s experience, because the 

ignitability of diesel fuel is lower than that of LPG. Corrective actions were taken 

both by Ebus and the fleet maintenance personnel. 

• Both fleets “warmed-up” their vehicles for 30 to 60 minutes before going on their 

routes. The fleets felt that they experienced fewer road calls and maintenance 

problems using this practice. 

• Each fleet cited matching vehicles to an appropriate duty cycle and training 

drivers and maintenance personnel adequately as important lessons learned. 

 viii
Overview: Ebus Hybrid Buses and Trolleys 

This report focuses on the evaluation of hybrid electric buses and trolleys produced by Ebus, 

Inc., and demonstrated by the Indianapolis Transportation Corporation (IndyGo) and Knoxville 

Area Transit (KAT). 

Ebus vehicles feature a series hybrid architecture, which means the vehicles’ auxiliary power 

unit (APU) is used with a generator to produce electricity for the battery pack and electric motor. 

In series hybrid electric systems, there is no mechanical connection between the APU and the 

wheels. Therefore, to drive the wheels, all motive power is transferred from chemical energy to 

mechanical energy, from mechanical energy to electrical energy, and from electrical energy back 

to mechanical energy. 

The Ebus hybrid electric system propels the vehicle using an electric motor powered by the 

traction battery packs. The two traction battery packs feature nickel-cadmium (NiCd) batteries 

recharged by a low-emission Capstone MicroTurbine APU. A digital power controller monitors 

and controls the recharging of the batteries by the MicroTurbine. This system is chargesustaining, meaning that the batteries will have energy as long as the APU has fuel. Figure 1 

illustrates the Ebus system. 

Figure 1. Ebus system block diagram (Source: Ebus) 

The hybrid propulsion design also incorporates regenerative braking, which provides additional 

energy to recharge the traction battery packs. In this system, the electric motor that drives the 

 1
vehicle becomes a generator during deceleration, and the energy produced from deceleration is 

stored in the batteries. This technology is particularly effective for transit applications on routes 

featuring stop-and-go traffic. A toggle switch located on the dashboard console activates or 

deactivates regenerative braking during driving. Winter driving conditions occasionally warrant 

predictable conventional braking; therefore, IndyGo requested simple deactivation of 

regenerative braking. When the vehicle is not in operation, it can be plugged into a fast-charging 

station that “tops off” the batteries in approximately 1 hour. 

Ebus offers this hybrid electric system for a range of fuels, including diesel, liquefied petroleum 

gas (LPG), and compressed natural gas (CNG). Onboard liquid fuel capacity is 50 gallons. 

Table 1 presents some general characteristics of the hybrid electric propulsion system. 

Table 1. Ebus Series Hybrid Electric Propulsion System 

APU Capstone MicroTurbine Model 330 

Motor Reliance AC Induction, air-cooled 

Energy Storage 48 NiCd, liquid-cooled, “fast charge” batteries, 288 V 

total—manufactured by Saft 

Opportunity Charging SAE J-2293 Fast Charging 

Charge Sustaining Yes 

Regenerative Braking Yes 

Capstone MicroTurbine APU 

The Capstone MicroTurbine system has several components. These include a compressor, 

recuperator, combustor, turbine, and permanent magnet generator. 

The combustion process begins as air enters the system through an intake, passing and cooling 

the generator. This approach to heat transfer eliminates the need to liquid-cool the system. Intake 

air is compressed and injected into the recuperator, where it is heated by turbine exhaust. Fuel 

enters the system through an injection port and is mixed with the heated compressed air. An 

ignition mechanism causes the air/fuel mixture to burn in the combustion chamber and, during 

this expansion through the turbine, this provides rotational power. The rotating components, 

which can reach 96,000 rpm, are mounted on a single shaft supported by low-maintenance air 

bearings. 

This advanced combustion process results in a low-emission exhaust stream, which exits the 

combustion chamber. The final result is variable voltage, variable frequency, alternating current 

(AC) power, which is converted to programmable direct current (DC) power by on-board power 

electronics. Table 2 presents Capstone MicroTurbine performance specifications, and Figure 2 is 

a schematic of the components. 

 2
Table 2. Capstone Model 330 Hybrid Electric Vehicle (HEV) MicroTurbine Performance* 

Fuel CNG (55 psig) LPG (55 psig) Diesel (5 psig) 

Overhaul Life 20,000 hr 20,000 hr 20,000 hr 

Full-Load Power 30 kW net (+/- 1 kW) 30 kW net (+/- 1 kW) 29 kW net (+/- 1 kW) 

Peak Efficiency (LHV**) 27% (+/- 2%) 27% (+/- 2%) 26% (+/- 2%) 

Fuel Flow*** 18.7 lb/hr, 8.5 kg/hr 19.0 lb/hr, 8.6 kg/hr 21.9 lb/hr, 10.0 kg/hr 

Fuel Flow, Equivalent N/A 4.5 gal/hr, 17.2 l/hr 2.9 gal/hr, 11.0 l/hr 

Exhaust Gas Temperature 500°F, 261°C 500°F, 261°C 500°F, 261°C 

Output Voltage 250-700 VDC 250-700 VDC 250-700 VDC 

*Source: Capstone Turbine Corporation 

** Lower Heating Value 

***Rated at LHV: 20,167 Btu/lbm (CNG), 19,916 Btu/lbm (LPG), 18,250 Btu/lbm (diesel) 

Figure 2. Schematic of Capstone MicroTurbine (Source: Capstone Turbine Corporation)

Traction Batteries 

Energy storage for propulsion is accomplished using 48 liquid-cooled NiCd batteries. 

Manufactured by Saft, these batteries supply 288 V at a capacity of 200 ampere-hours. The 

battery pack is located under the floor of the vehicle, in front of the rear wheels. To improve the 

battery pack’s performance and extend its life, Ebus retrofitted the battery tray with a liquidcooling system. The liquid used to cool the batteries is a 50/50 mixture of distilled water and 

Dexcool, an ethylene-glycol-based antifreeze. 

The traction batteries supply power to a single AC induction propulsion motor manufactured by 

Reliance Electrical Industrial Company. This motor provides driveshaft torque, which propels 

the vehicle. While the bus is being driven, the battery pack maintains a 60% to 80% SOC rating. 

When the SOC falls below 60%, the turbine activates, providing charge to the batteries and 

elevating the SOC. The turbine cycles off when the SOC is restored to 80%. 

 3
When garaged at night, the Ebus vehicles are plugged into a battery charging system to elevate 

the SOC to 100%. Opportunity charging of the batteries extends the vehicle’s electric-only range 

before it begins burning fuel in the APU. This system is consistent with SAE J-2293, which 

establishes requirements for electric vehicles (EV) and the off-board supply equipment used to 

transfer electrical energy to an EV from an electric utility power system in North America. 

Emissions 

The Ebus hybrid electric vehicles (HEV) emit lower amounts of four criteria air pollutants, in 

comparison to emissions from conventional diesel-fueled internal combustion engines. Table 3 

summarizes the results of HEV emission cycle testing on Capstone’s model 330 HEV 

MicroTurbine. The test is certified by the California Air Resources Board. Reported 

measurements of hydrocarbons (HC) and carbon monoxide (CO) for a diesel-fueled 

MicroTurbine are from Ebus internal test results, measured in accordance with California Air 

Resources Board (CARB) protocols.

Table 3. Capstone MicroTurbine Emissions* 

Emissions CNG LPG Diesel 

NOx** (g/bhp-hr) 0.26 0.53 0.70 

HC (g/bhp-hr) 0.42 0.42 0.30*** 

CO (g/bhp-hr) 0.41 0.18 0.40*** 

PM** (g/bhp-hr) 0.004 0.004 0.01 

*Source: www.capstoneturbine.com

**NOx is oxides of nitrogen; PM is particulate matter; bhp is brake horsepower. 

***Ebus internal test results

Durability 

An Ebus trolley powered by a diesel-fueled Capstone MicroTurbine APU was submitted for a 7-

year/200,000 mile Surface Transportation and Uniform Relocation Assistance Act (STURAA) 

test at the Pennsylvania Transportation Institute’s Bus Testing and Research Center in Altoona, 

Pennsylvania. Any bus manufacturer who intends to sell buses in the United States must submit 

its products for this required testing. This particular testing began in October 2001 and was 

completed in February 2002. 

Project Design and Data Collection 

The National Renewable Energy Laboratory’s (NREL) evaluation of the five diesel hybrid buses 

at IndyGo and four LPG hybrid trolleys at KAT began in 2004. The data collection and 

evaluation protocol used was developed by NREL and the U.S. Department of Energy (DOE). A 

limited evaluation was carried out at the two sites because of the vehicles’ application and stage 

of development. This limited evaluation focuses on 6 months of full operation of the test 

vehicles. The information collected includes operational data such as vehicle use, fuel 

consumption, and maintenance performed as well as descriptions of the fleets’ experience with 

these vehicles. 

Data for as many as 12 months were collected from the two evaluation sites. After analyzing the 

collected data, researchers identified a “clean-point” in the data for each fleet. The clean-point is 

typically the point at which a fleet clears the initial hurdles associated with implementing new 

 4
vehicles and technologies. After that point, a 6-month data collection period was identified for 

each fleet, and performance and cost calculations were based on that data collection period. 

The objective of this evaluation is to provide credible data and results in a case study that will 

help assess the progress of hybrid electric technologies, based on the experience of two fleets 

that employed slightly different versions of the Ebus technology (see Table 4). 

Technology applications and utilization varied between the two fleets. Therefore, given the 

differences in fuels used and duty cycles, a direct comparison of the fleets is not possible. NREL 

evaluations typically compare HEVs with conventional technology vehicles having the same 

duty cycle. However, neither fleet in this study included comparable conventional vehicles that 

would permit a baseline comparison. The 6-month evaluation period also differs slightly for each 

fleet because they received their Ebus vehicles and cleared initial implementation hurdles at 

different times. The evaluation period for IndyGo was November 2004 to April 2005; for KAT, 

this period was December 2004 to May 2005. 

Table 4. Vehicle Systems Overview 

Fleet KAT IndyGo 

Vehicles Purchased Four Five 

Model Trolley Bus 

Model Year 2003 2003 

Fuel LPG No. 2 Diesel 

Fuel Capacity 50 gal 50 gal 

Vehicle Cost $280,000 $280,000 

Length/Width/Height 22 ft/92 in/120 in 22 ft/92 in/103 in 

GVWR*/Curb Weight 19,500/14,500 lb 19,500/14,500 lb 

Seated Passenger Capacity 22 (one wheelchair) 22 (one wheelchair) 

Total Passenger Capacity 29 (seven standing) 29 (seven standing) 

Service Knoxville, Tennessee Indianapolis, Indiana 

 *Gross vehicle weight rating. 

Fleet Experience: IndyGo

Fleet Profile 

Indianapolis Public Transportation Corporation, or IndyGo, offers commuter services to the City 

of Indianapolis and Marion County, Indiana (www.indygo.net). Operating 28 fixed and demand 

response routes, IndyGo has 228 vehicles, including paratransit vehicles. In 2003, IndyGo 

carried nearly 11 million passengers and traveled approximately 9 million miles. 

IndyGo has 144 Gillig buses at its facilities at the edge of downtown Indianapolis. All 

operations—including scheduling, maintenance, public relations, and some training—are 

conducted at this central facility. Most vehicle maintenance is also done inside this facility, 

which has enough garage space for all the buses to be parked there at one time.

 5
Figure 3. IndyGo’s headquarters in Indianapolis, IN (Source: NREL) 

Figure 4. Ebus at IndyGo (Source: NREL) 

Implementation Experience 

As part of a technical development effort, in August 2003 IndyGo received five hybrid electric 

buses that were purchased from Ebus. Product and market availability were the deciding factors 

in purchasing the EBus buses. Negotiations between the two companies began in spring 2003. 

The procurement was intended to move IndyGo forward with new technology, enhance its 

image, and attract new events to the city. In addition, the buses would benefit the city by 

reducing air and noise pollution. Funding for the five buses came in part from The City of 

Indianapolis and in part through a Congestion Mitigation Air Quality (CMAQ) grant obtained by 

the Indiana Department of Transportation and IndyGo. The goal of the CMAQ program is to 

reduce congestion and emissions in designated nonattainment air quality areas. 

IndyGo’s Ebus diesel hybrid electric buses went in service in August 2003 and remained in 

service until early February 2004, when a setback occurred. Salt applied to the snow-covered 

 6
roads of Indianapolis began to corrode a cable and fuse that were exposed through the battery 

tray of the electric system, which is located along the lower part of the bus, as shown in Figure 5. 

The corroded cable caused a high-voltage source to ignite while the bus was parked in the bus 

garage overnight on Friday, February 6, 2004 (see Figure 6). The fire spread, damaging two of 

the hybrid-electric buses, two chargers, and part of the garage. There were no injuries. 

Ebus replaced the damaged bus approximately 5 to 6 months after the incident and repaired the 

other bus. In addition, one of IndyGo’s battery chargers had to be repaired and one had to be 

purchased because of the fire damage. To prevent further incidents, Ebus enclosed the highvoltage cable that had run through the tray and exposed a fuse. This change was made to all the 

vehicles ordered that had this system. The fire slowed down the implementation process for 

IndyGo and this evaluation, but no further problems occurred after the changes were completed. 

Figure 5. Battery tray for the electric propulsion system (Source: NREL) 

Figure 6. Normal battery tray (left) and tray with a corroded cable (Source: NREL) 

 7
Figure 7. IndyGo’s Blue Line route (Source: IndyGo) 

IndyGo Vehicle Use and Performance 

Duty Cycle 

The hybrid electric buses operate on IndyGo’s Blue Line, a circulator route connecting several 

attractions in downtown Indianapolis. The route is a 4.3-mile loop that begins and ends at the 

Indianapolis Zoo. The route makes seven additional stops at area attractions such as Victory 

Field, the Eitljorg Museum of American Indians and Western Art, the Convention Center, and 

the Circle Center Mall. Figure 7 shows this route, which was designed in August 2003 

specifically for the hybrid electric buses. Data for conventional diesel buses operating on a 

similar route were not available to provide a baseline comparison for this evaluation. 

Figure 8. An IndyGo hybrid electric bus (Source: NREL)

Three of IndyGo’s five hybrid electric buses were originally scheduled to be assigned to the Blue 

Line route each day for 7 days a week. The buses circulate the route between 9 a.m. and 9 p.m.; a 

 8
bus arrives at each stop in 10-minute intervals. Each of the three buses is scheduled to circulate 

the 4.3-mile loop 24 times a day with a 9-minute layover at the zoo (“catch-up time”) between 

runs. On this route, the average speed of a bus is 12.3 mph, and the maximum speed is 35 to 40 

mph (see also Table 5). 

Table 5. IndyGo Hybrid-Electric Bus Duty Cycle 

Terrain Flat, light city driving 

Climate (Annual, 2003) 

 Low Temperature -9°F 

 High Temperature 93°F 

 Precipitation 52.6 in. 

 Sleet or Snow 44.1 in. 

Route Blue Line (90) 

Loop Distance 4.3 miles 

Total Distance Traveled per Day 313.9 total miles for all three buses 

Time per Loop 

21 minutes, with a 9-minute layover 

between loops 

Operating Hours 9 a.m. to 9 p.m. 

Average Speed 12.3 mph 

Maximum Speed 35 mph to 40 mph 

The Blue Line is characterized by light city driving on flat terrain with marked seasonal 

differences—hot and humid in summer and cold and snowy in winter. Buses on this route 

encounter considerable stop-and-go traffic, which helps to recharge HEV battery packs. 

However, the flat terrain of downtown Indianapolis is not optimal for a regenerative braking 

system. A more hilly terrain allows a regenerative braking system to capture additional energy 

and transfer it to the battery pack when a vehicle is decelerating on an incline. 

In late spring 2005, the Blue Line was modified to assign two buses rather than three to this 

route, because three of the five HEV buses were often in the garage for repairs. IndyGo 

attempted to maintain a technician-to-bus ratio of 1:5 or less but often needed 2:5. The overall 

maintenance requirement was augmented by considerable support from Ebus. However, it often 

took a month to receive an ordered part needed to repair a bus, and this caused vehicles to be 

unavailable for service for extended periods of time. 

In spite of their reduced availability, there was a reasonably steady upward trend in the number 

of miles that the hybrid electric buses accumulated over the evaluation period. Figure 9 shows 

this upward trend, during which the hybrid electric buses logged approximately 20,000 miles of 

revenue service by April 2005.

 9
0

5000

10000

15000

20000

25000

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

Total Mileage

Figure 9. Cumulative miles traveled during the evaluation period at IndyGo

Fuel Economy Results 

IndyGo’s hybrid electric buses use diesel fuel to start and maintain the operation of the 

MicroTurbine. As noted earlier, fuel economy calculations are based solely upon miles driven 

and liquid fuel volumes recorded. The effects of opportunity charging and self-charging of the 

traction battery packs were not quantified and are not considered. A fuel economy value based 

on miles per gallon of diesel fuel used in each of the five buses over a 6-month evaluation period 

is provided in Table 6. 

Between November 2004 and April 2005, the average fuel economy of the buses was 4.37 mpg. 

During this time, bus E032 had a much lower average fuel economy than that of the other four 

buses. This can be attributed to at least two things: this bus spent less time overall running the 

route and maintained less complete fueling records than the other buses did. Figure 10 

summarizes the fuel economy of the five buses over the same 6-month evaluation period. A total 

of 20,087 revenue miles were accumulated during the evaluation period, but the mileage accrual 

was not spread evenly across all five buses. In some months, a bus would not run at all, which 

suggests that it might have been waiting for parts or had become the “spare parts” bus during that 

time. This is explained further in the section on maintenance. 

 10
Table 6. IndyGo Fuel Economy Results (November 2004 through April 2005) 

Bus 

Mileage 

Used 

Diesel 

Consumed

(gallons) 

Fuel Economy

(mpg) 

E031 4,145 888 4.67 

E032 1,883 512 3.68 

E033 5,286 1,080 4.89 

E034 4,635 1,130 4.10 

E035 3,475 830 4.19 

Total 19,424 4,440

4.37 

(average) 

During the early winter months of 2005, there was an insufficient number of chargers in the 

IndyGo garage. As a result, some buses had to be self-charged overnight to be ready for pullout 

the next morning. IndyGo performed the self-charging by running the MicroTurbine to bring the 

battery pack SOC to 100%. Self-charging the batteries overnight with diesel fuel, rather than 

charging the batteries with electricity, reduced the fuel economy of the buses. Although the buses 

could begin the route at less than 100% SOC, refueling would have been required to complete 

the route. It was not possible to measure the exact reduction in fuel economy for this study. Ebus 

replaced the chargers in March 2005 with better, more compatible chargers. 

0.00

1.00

2.00

3.00

4.00

5.00

6.00

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

mpg

Figure 10. IndyGo Fuel economy during the 6-month evaluation period 

 11
Fuel Costs 

The average price of the diesel fuel that IndyGo purchased during the 6-month evaluation period 

was $1.53 per gallon. This cost-per-gallon average is for fuel purchased between November 

2004 and April 2005. 

Maintenance 

The maintenance costs evaluation reflects the data collection period (November 2004 through 

April 2005). This evaluation also includes an expanded overview of cumulative costs per mile 

beginning in June 2004, when maintenance work orders were first collected from IndyGo. A 

standard rate of $50 per hour was applied to all labor hours. 

Table 7 is a breakdown of overall maintenance costs for each of IndyGo’s five buses. The cost 

for bus E032 is significantly higher because a DC/DC converter for the air-conditioning system 

had to be replaced. IndyGo mechanics did not charge labor hours to replace the component 

because Ebus completed this work. However, IndyGo paid for the DC/DC converter.

Table 7. IndyGo Total Maintenance Cost Comparison 

(November 2004 through April 2005)

Bus 

Total 

Mileage 

Labor 

Hours 

Parts 

Cost 

Cost/ 

Mile* 

E031 4,332 40 $73 $0.48 

E032 2,336 42 $1,790 $1.67 

E033 5,286 60 $353 $0.63 

E034 4,658 37 $646 $0.54 

E035 3,475 23 $394 $0.44 

Total 20,087 202 $3,256

$0.66 

(average) 

*At an assumed labor cost of $50/hr 

Hybrid propulsion components in this study include the batteries, on-board charging, the battery 

chiller, the electric propulsion motor, and controls for the electric propulsion motor. Figure 11 

shows the cumulative maintenance cost per mile for all vehicle systems and the cumulative 

maintenance cost of the hybrid system. There was a steep drop in both sets of costs in spring 

2004, followed by a continuing but slow decrease. 

The high cost noted in June 2004 was for the DC/DC converter replacement. The graph does not 

focus on this point ($1.58 per mile) because it was an initial startup cost. Between November 

2004 and March 2005, the cumulative cost per mile decreases by approximately 2% for both the 

overall vehicle and the hybrid system. This trend is typical when a new technology is introduced 

into a fleet. The learning curves for drivers and maintenance technicians begin to stabilize with 

time and experience. 

 12
0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

Jun-04 Jul-04 Aug-04 Sep-04 Oct-04 Nov-04 Dec-04 Jan-05 Feb-05 Mar-05 Apr-05

Cost per Mile ($/mi.)

Total

Hybrid System

Evaluation 

Period

Figure 11. IndyGo Cumulative maintenance costs per mile 

Figure 12 shows the cost of parts and labor for each vehicle system between November 2004 and 

April 2005. Repairs to the propulsion system accounted for 75% of these costs. Preventive 

maintenance inspections and parts contributed 11% to overall vehicle maintenance costs. These 

included general inspection time, filter care services for the turbine, and fuel filter replacements. 

The braking system, which incorporates regenerative braking, contributed only 7% to the overall 

costs. “Other” maintenance, which included minor repairs to the chassis and power steering, 

accounted for 2% of the costs. Detailed descriptions of the maintenance performed on the 

propulsion system follow.

Propulsion

75%

Brakes

7%

Drivetrain

1%

Other

2%

PM Inspection and Parts

11%

Cab, Body, Accessories, and 

Lighting

4%

Figure 12. Maintenance cost by vehicle system (Labor + Parts) 

 13
Specific Component Issues and Resolutions 

Before and during the evaluation period, IndyGo experienced maintenance issues with specific 

components or vehicle subsystems and performed repairs on them. Many of these components 

are unique to the Ebus hybrid system. They include the following: 

• Traction batteries 

• Battery chiller 

• Electric propulsion motor 

• Controls for the electric propulsion motor 

• MicroTurbine 

• Climate control. 

Although the electric propulsion motor is included, no repairs were performed on it during the 6-

month period and no major repairs were performed during the expanded evaluation period. A 

total cost breakdown for the propulsion system is shown in Table 8 and in Figure 13. 

Table 8. IndyGo Propulsion System Costs 

(November 2004 to April 2005) 

Bus 

Total 

Mileage 

Labor 

Hours 

 Parts 

Cost 

 Cost/ 

Mile* 

E031 4,332 27 $2 $0.31 

E032 2,336 34 $1,797 $1.50 

E033 5,286 30 $134 $0.31 

E034 4,658 30 $553 $0.44 

E035 3,475 8 $309 $0.20 

Total 20,087 129 $2,795

$0.46 

(average) 

*At an assumed labor cost of $50/hr 

Climate Control

32%

Traction Batteries

5%

Battery Chiller

1%

Controls, Electric 

Propulsion Motor

15%

MicroTurbine

15%

Low SOC (State of 

Charge)

32%

Figure 13. Propulsion system maintenance costs (Labor + Parts)

 14
Climate Control 

The climate control components that draw power from the batteries and associated labor make up 

32% of the maintenance costs for the propulsion system. The DC/DC converter for the airconditioning system (noncharging) is the major contributor to this cost, at $1,790.25; one had to 

be replaced on bus E032 during the 6-month period. An additional noncharging DC/DC 

converter was replaced in September 2004 (outside the detailed evaluation period). All of the 

DC/DC converters were replaced in fall 2003. 

Electric Propulsion Motor Controls 

Controls for the electric propulsion motor contributed 15% of the total propulsion system 

maintenance cost. Major contributors to this cost were the labor hours spent on the traction 

controls and inverters. Although replacement traction inverters were covered under the Ebus 

warranty, the mechanics at IndyGo performed the labor. 

Figure 14. Capstone MicroTurbine Assembly (Source: NREL) 

Capstone MicroTurbine 

An additional 15% of the total propulsion costs were for maintaining the MicroTurbine. A 

leading contributor was the cost of replacing parts that activate the MicroTurbine. Replacing one 

exciter and two igniters contributed $241 and $305, respectively, to the total cost. When an 

igniter fails, the MicroTurbine cannot activate to elevate the battery SOC as programmed. A 

“turbine fault” message appears on the onboard display next to the operator. If the operator is not 

aware of this message, the battery SOC will be depleted until the bus is unable to operate and the 

result is a road call. Capstone is currently developing an improved igniter design. 

Traction Batteries 

Only 5% of total propulsion costs were for maintaining traction batteries and on-board charging 

components. One Ebus NiCd battery was replaced at a cost of $133.99 during this period. 

However, IndyGo had to purchase some higher cost replacement parts outside the detailed 

 15
evaluation period. A DC/DC converter that charges the 13.5 V battery cost $1,375.20 to replace. 

One was replaced in June 2004, the other in September 2004.

Figure 15. IndyGo Ebus at Charging Station (Source: NREL)

Low SOC 

Before beginning the route each morning, mechanics started the hybrid electric buses 30 minutes 

early to allow the MicroTurbine to ignite and warm up. Early start-ups ensured that the diesel 

fuel would ignite the MicroTurbine properly. However, drivers unfamiliar with the buses and the 

early start-ups would often “start” the vehicles without knowing they were already on. When this 

happens, the MicroTurbine shuts down, but the bus continues to run. Beginning the route with 

the MicroTurbine off caused the bus to lose the ability to recharge its batteries and to shut down. 

When that happened, the buses had to be towed back to the maintenance garage to be recharged. 

Significant costs—32% of all propulsion costs—were incurred from “low SOC” reports resulting 

from having to tow the buses after batteries ran low on charge and shut down. In some cases, low 

SOC reports were the result when a driver accidentally shut down the MicroTurbine before 

beginning a route. Because the MicroTurbine operates quietly, some drivers might not have been 

aware that it was running when they rekeyed the ignition. The resulting shutdown prevented the 

batteries from reaching the required SOC. 

As noted earlier, the Capstone igniter was occasionally unable to ignite diesel fuel and activate 

the MicroTurbine. If the MicroTurbine was not activated properly when the battery SOC fell 

below 60%, the vehicle would continue to operate until the low SOC rendered it inoperable. 

 16
Low-SOC-related costs are in a separate category. They are potentially resolvable, and Ebus 

attempted to fix the associated problems by means of a computer upgrade. This is discussed 

further in the section on road calls. 

Campaigns 

As the new hybrid electric technology was implemented in the IndyGo fleet, some campaigns 

and system changes were needed to improve the comfort, safety, and maintainability of the 

buses. The DC/DC converter upgrades to the air-conditioning system were followed by two 

additional upgrades to the air-conditioning system’s communication module. In addition, a highvoltage cable and fuse exposed through the battery box was enclosed in these buses following 

the ignition incident discussed earlier. 

Another problem involved correcting the tone ring on one vehicle’s braking system in fall 2004. 

During braking, the vehicle’s speed sensor detected an incorrect number of teeth on the tone 

ring, which prevented the sensor from generating the correct voltage. Although the occurrences 

were limited, the inconsistency caused the vehicle to lose braking power randomly. Only one bus 

had this problem, but all the buses were checked as part of this campaign. 

In spring 2005, Ebus changed some software on the buses in order to make the MicroTurbine run 

all the time at a reduced level and thus constantly charge the battery pack. This upgrade—a 

significant change from the original design of the technology—was made to prevent future low 

SOC road calls. Since the turbines run on diesel fuel, running them all the time will reduce the 

fleet’s fuel economy somewhat. 

Figure 16. IndyGo Route Stop (Source: NREL)

Road Calls 

IndyGo defines a road call as a failure that needs immediate attention while the bus is in service. 

All the road calls reported during the evaluation period were related to the battery pack’s low 

SOC (see Table 9). In many cases, this could be attributed to the shutdown of the MicroTurbine, 

as noted earlier. In other cases, diesel fuel failed to reignite and fuel the MicroTurbine while on 

the route. 

 17
To alleviate this road call pattern, Ebus carried out a software upgrade campaign. The software 

upgrade, which keeps the MicroTurbine running constantly at a reduced level unless the driver 

decides otherwise, ensures that the MicroTurbine will not have to reignite while on the road. 

After the MicroTurbine is ignited and running, this software change makes it unlikely to shut 

down. 

The number of low SOC occurrences per mile of revenue service trailed off over time, and this 

helped to increase the number of cumulative miles between road calls. This trend is shown in 

Figure 18, which shows the number of cumulative miles between road calls (MBRC) over an 

expanded evaluation period and captures some early experiences with the technology at IndyGo. 

Table 9. IndyGo Road Call Comparison 

(November 2004 to April 2005) 

Low-SOC 

Bus 

Total Road 

Calls Road Calls 

E031 5 5

E032 2 2

E033 2 2

E034 7 7

E035 0 0

Total 16 16

Figure 17. Battery Charger Display (Source: NREL)

 18
0

200

400

600

800

1,000

1,200

1,400

1,600

1,800

2,000

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

MBRC

Figure 18. IndyGo Cumulative miles between road calls 

Total Operating Costs 

The overall operating costs of the Ebus fleet during the 6-month evaluation period are shown in 

Table 10. The overall costs incorporate maintenance and fuel costs for the vehicles. No 

consistent data are available on the cost of recharging the batteries overnight; therefore, they are 

not included in this analysis. 

The average cost of diesel fuel between November 2004 and April 2005 was $1.53 per gallon. 

As described in the section on maintenance, bus E032 had higher costs for parts after the 

replacement of a DC/DC converter in the air-conditioning system. The rest of the fleet 

(excluding bus E032) had an average parts cost of $0.88 per mile.

Table 10. IndyGo Overall Operating Costs 

Bus Miles Driven 

Labor 

Hours 

Parts 

Cost 

Fuel 

Cost Cost/Mile 

E031 4,145 40 $73 $1,359 $0.83 

E032 1,883 42 $1,790 $783 $2.48 

E033 5,286 60 $353 $1,652 $0.95 

E034 4,635 37 $646 $1,729 $0.91 

E035 3,475 23 $394 $1,270 $0.81 

Total 19,424 202 $3,256 $6,793 

$1.04 

(average) 

Summary of Results at IndyGo 

IndyGo implemented the Ebus hybrid electric buses as a technical development effort. The most 

significant lesson learned in this experience was that the technology was still in developmental 

 19
stages. This was the first time that diesel fuel was used with this turbine in a vehicle application. 

Comments based on availability, applicability, reliability, and training follow: 

Availability 

• It was a struggle to keep two of the five buses on the road at a time. The goal had been to 

keep three on the road 12 hours per day. 

• The desired technician-to-bus ratio during the evaluation period was 1:5 or less, but often 

a 2:5 ratio was needed. 

• Sometimes IndyGo had to let a bus sit in the garage for a month while replacement parts 

were on order. 

• The buses were available for less than one-third of the miles they had been scheduled to 

run. IndyGo found the buses to be less reliable than conventional diesel buses. 

Applicability 

• Diesel fuel is initially somewhat harder to ignite than propane. This was the first vehicle 

to use the diesel-fuel turbine combination. Capstone is currently developing an improved 

igniter for the system. 

• In spite of the reduced usage, trends indicated some successes in terms of the cost per 

mile and fuel economy of the buses. 

Reliability 

• The reliability of the buses was greatly reduced by road calls resulting from a low SOC in 

the battery bank. The battery SOC was depleted as a result of MicroTurbine shutdowns, 

which occurred for two reasons: 

o Bus operators restarted the buses with the MicroTurbine running, triggering a 

shutdown. 

o Diesel fuel failed to ignite and cycle on the MicroTurbine to elevate the SOC 

during operation. 

Although occurrences of low SOC diminished over time, it seems feasible that these road 

calls may have been eliminated following the software upgrade that causes the 

MicroTurbine to run all the time at a reduced level. This upgrade occurred after the 

evaluation period. 

Training 

• IndyGo guided the introduction and implementation of the new technology by training 

mechanics and drivers. Extensive follow-up training was necessary throughout this 

process. 

• Retaining details about operating the new technology proved to be a challenge for many 

drivers. One instance of this involved drivers who had not driven these buses for a while 

and were not aware, because of the quietness of the MicroTurbines, that the buses had 

already been running in the garage. Attempts to restart these buses caused the shutdowns 

and road call situations noted earlier. 

 20
IndyGo has continued to implement new technologies since the introduction of the Ebus hybrid 

electric buses. In 2004, two full-sized hybrid electric buses with a General Motors-Allison hybrid 

system were acquired and put into service. Although IndyGo received reasonable service from 

Ebus, there are no current plans to purchase more of these buses. 

Fleet Experience: KAT 

Fleet Profile 

The Knoxville Area Transit, or KAT (www.ci.knoxville.tn.us/KAT), operates in metropolitan 

Knoxville, Tennessee. Bus service includes 64 buses, 22 vans, and 14 trolleys. KAT provides 25 

bus and three trolley routes during peak service. In 2004, KAT provided service to 3.2 million 

passengers, the highest amount in 20 years. Figure 10 shows the KAT facility. 

KAT was recently awarded the American Public Transportation Association (APTA) Public 

Transportation System Outstanding Achievement Award for 2004 (for transit systems providing 

service to 1 million to 4 million passengers). This award was based on KAT’s increased 

ridership, Clean Fuels Program, and marketing programs. 

Because of regional air quality conditions and concerns expressed by stakeholders, KAT 

formulated and implemented a Clean Fuels Program. After analyzing the costs and 

implementation issues associated with various available alternative fuel technologies, KAT 

selected LPG as the most viable option for its fleet. LPG offered several advantages, including 

these: 

• A local supplier could maintain the fuel supply and the fueling infrastructure. 

• Costs would be lower in comparison to the cost of using diesel. 

• Noise levels would be lower than those associated with diesel. 

• LPG vehicles provided a close fit with KAT’s plan to use smaller, neighborhood-friendly 

vehicles as circulators that would feed the larger transit network. 

BAF Industries provided technical training to KAT’s maintenance staff and installed the LPG 

fueling system at KAT’s facilities while KAT maintenance personnel observed the installation. 

This training familiarized the KAT mechanics with the systems and helped to streamline later 

diagnoses and repairs of system problems. 

In addition to the four Ebus trolleys studied during the evaluation, the Clean Fuels Program at 

KAT includes five new LPG-fueled cutaway vans, several larger hybrid electric buses, and a 

grant to use B20, a biodiesel blend, in diesel vehicles. 

 21
Figure 19. KAT Maintenance Facility (Source: NREL)

Implementation Experience 

In 2002, KAT received a CMAQ grant for $900,000. Local matching funds of 20% of that 

amount brought the total to $1.1 million. These funds were originally intended for purchasing 

electric vehicles and support equipment; however, the Knoxville Regional Transportation 

Planning Organization expressed considerable interest in expanding the popular downtown 

trolley system. Therefore, the CMAQ funds were used to purchase an electric vehicle for the 

trolley system. KAT’s objectives were to comply with the requirements of the CMAQ and the 

source of the matching funds and to apply a clean fuel technology to a high-traffic route. 

The decision-making process was framed by a number of limitations, including the technologyspecific nature of the funding source, route characteristics, the fuel infrastructure and supply, and 

the time frame. Steep grades on the downtown route were deemed excessive for conventional 

battery-powered electrics, and an APU was considered necessary to manage the incline and 

range requirements. The hybrid trolley available through Ebus was designed specifically for 

diesel fuel, which was unacceptable given KAT’s commitment to lower emissions. 

KAT’s experience with LPG and the existing infrastructure made this clean fuel an appealing 

choice. Only two manufacturers of turbine APUs were available. Ebus had recently begun 

developing a hybrid electric trolley using a Capstone MicroTurbine fueled by LPG. KAT was 

interested in being an early deployer of this technology, so the transit authority volunteered to 

provide significant feedback. 

After the final vehicle design was tested, KAT purchased four hybrid electric trolleys that were 

received in December 2003. KAT continued to study route characteristics and requirements to 

ensure that the trolleys were an appropriate match. KAT found that the 22-foot trolleys were 

adept at navigating the narrow downtown streets and close quarters at turnaround points. They 

were also light enough to drive on the local viaduct. After more than four months of evaluation 

 22
and planning, KAT deployed the Ebus trolleys on its new Red Line, which serves downtown 

Knoxville during peak commuter hours. 

Figure 20. KAT Ebus Trolley (Source: NREL Photo)

KAT’s LPG fueling infrastructure was expanded during summer 2005 to accommodate the Ebus 

trolleys. Figure 21 shows the original and upgraded fueling facility. Figure 22 shows the onboard 

50-gal LPG storage tank used in the Ebus trolleys. 

Figure 21. Original and upgraded LPG fueling station 

 23
Figure 22. On-board LPG storage 

Temporary chargers provided by Ebus were also installed in the KAT maintenance facility to 

provide opportunity charging overnight. In early 2005, only one of these two chargers was 

operating because of an internal failure. Ebus replaced the two chargers with two upgraded 

models in spring 2005. Figure 23 shows the first version of charger. 

Figure 23. Original KAT charger 

 24
No other modifications were made to KAT’s maintenance facility for the LPG Ebus trolleys. 

LPG is heavier than air and therefore does not require the kind of roof ventilation employed by 

fleets using CNG or hydrogen. KAT’s maintenance facility uses lifts rather than pits, which is 

conducive to handling LPG safely. 

KAT Vehicle Use and Performance 

Figure 24 shows the mileage accumulated by the trolleys over a 12-month data-collection period. 

In August 2004, a limited number of miles were accrued because the trolleys were deactivated 

for safety reasons following a fire at IndyGo. After the trolleys were placed back in service in 

September 2004, they steadily accrued miles through the evaluation period of December 2004 to 

May 2005. The four trolleys accumulated almost 18,000 miles during the 12 months of data 

collection and nearly 11,000 miles during the 6-month evaluation period.

0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

16,000

18,000

20,000

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

Miles

Evaluation Period

Figure 24. KAT Total mileage accumulation for the four Ebus trolleys 

Duty Cycle 

The Red Line provides commuter service from new parking facilities to downtown. This new 

route was added to reduce congestion in downtown Knoxville. The route starts at the Knoxville 

Civic Coliseum on the edge of downtown and continues through the northern downtown area, 

including Market Square, the Tennessee Valley Authority, and Gay Street. The Red Line 

circulates every 7 minutes during peak commuting hours on weekday mornings and afternoons. 

Two trolleys are on the route in the morning, and two in the afternoon. Each trolley is driven 3 

hours in the morning and 2.5 hours in the afternoon, for a total of 11 daily route hours. The Red 

Line is shown in Figure 25 as part of the overall system map in Knoxville. Additional route and 

duty cycle characteristics are presented in Table 11. 

 25
Figure 25. Red Line and other trolley routes in Knoxville 

Table 11. KAT Red Line Duty Cycle Characteristics 

Terrain Hilly, light city driving 

Climate 

 Temperature (High/Low) 87°/26°F 

 Annual Rainfall 47.1 in. 

 Annual Snowfall 11.5 in. 

Route Length 2.6 miles 

Revenue Mileage/Day 82.8 

Total Mileage/Day 94 

Loops/Day 36 

Overall Average Speed 8.5 mph 

Average Passenger Load At or near capacity (29) 

Stops per Loop Four to six, depending on passenger 

needs 

Significant Grades Two 

Fuel Economy Results 

As noted earlier, fuel economy calculations are based solely upon miles driven and liquid fuel 

volumes recorded. The effects of opportunity charging and self-charging of the traction battery 

packs were not quantified and are not considered. For the evaluation period, the four trolleys 

averaged 3.22 miles per diesel gallon equivalent (DGE). Fuel records are based on the volume of 

LPG dispensed. A fuel economy value based on miles per gallon of LPG is shown in Table 12. 

 26
►Calculating Energy Equivalent Fuel Economy for LPG and Diesel 

KAT measures LPG use by volume when fuel is dispensed into the trolleys. To calculate the 

fuel economy, the gallons of LPG dispensed were converted into diesel gallon equivalents, or 

DGEs. A DGE represents the quantity of LPG that has the same energy content as one gallon 

of diesel fuel. This provides a real-world understanding of the trolley’s fuel consumption. A 

conversion factor can be determined by comparing each fuel’s energy content: 

Diesel: 129,800 Btu 

LPG: 84,300 Btu 

129,800 / 84,300 = 1.54 DGE 

This means that 1 gal of diesel has the same amount of energy as 1.54 gal of LPG (these 

energy contents are based on density at 1 atmosphere at 60°F). The fuel economy of each 

trolley can now be calculated by dividing the number of miles traveled by the LPG DGEs 

consumed by the trolley. 

Table 12. KAT Fuel Economy Results for 6-Month Evaluation Period 

Trolley 

Mileage 

Used 

Volume LPG 

Used (gallons) 

Fuel Economy 

(mpg LPG) 

Equivalent 

Volume Diesel 

Used (gallons) 

Fuel 

Economy 

(mpg diesel) 

411 1,651 851 1.94 553 2.99

412 3,391 1,719 1.97 1,116 3.04

413 3,580 1,522 2.35 988 3.62

414 2,149 1,055 2.04 685 3.14

Total 10,771 5,147 

2.09

 (average) 3,342 

3.22

(average)

Figure 26 presents average fuel economy values over 12 months. The high value for August 

2004 is based on low mileage during that month. Note the slightly increasing trend in fuel 

economy values over the evaluation period, December 2004 to May 2005. Two issues likely 

contributed to this trend: (1) the decrease in “warm-up” (idle) time as the weather warmed in 

spring (see the section on maintenance for further information) and (2) self-charging of the 

trolley battery packs during the winter while waiting for replacement chargers to arrive. In the 

absence of the chargers, KAT ran the MicroTurbine to bring the battery packs’ SOC to 100%. 

Although the trolleys could operate at less than 100% SOC, more LPG would then be required to 

complete the route. Based on the mileage demand of the route, the LPG fuel economy, and the 

onboard fuel capacity, self-charging was deemed effective insurance against running out of fuel 

on the route or being forced to refuel mid-route. This practice stopped in March 2005, however, 

when standard off-board charging became available. Both warm-up and self-charging issues add 

to fuel use but not to accumulated mileage and therefore reduce fuel economy. 

Additional factors contributing to fuel economy include these: 

• Climate control auxiliary loads: Because of the high temperatures and humidity in 

summer and relatively cold temperatures in winter, the climate control requirements for 

 27
the trolleys were significant. This issue is further addressed in the section on 

maintenance. 

• High passenger load: Because they ran during peak commute hours, the trolleys operated 

with high passenger loads constantly. 

• Significant grades: The two significant grades on the route helped to increase fuel 

consumption. 

0

1

2

3

4

5

6

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

Miles per Gallon (DGE)

Evaluation Period

Figure 26. KAT Average fuel economy 

Fuel Costs 

LPG was supplied to KAT at a fixed rate of $0.73 per gallon for the duration of the evaluation. 

Table 13 shows fuel cost calculations, which were based on total mileage and fuel volumes 

recorded during the evaluation period. 

Table 13. KAT Fuel Cost Calculations 

Trolley 

Volume LPG Used 

(gal) Fuel Cost Miles Driven 

Fuel Cost/ 

Mile 

411 943 $ 689 1,688 $0.41 

412 1,719 $ 1,255 3,460 $0.36 

413 1,530 $ 1,117 3,620 $0.31 

414 1,055 $ 770 2,149 $0.36 

Total 5,247 $ 3,830 10,917 

 $0.35

 (average) 

Maintenance 

Maintenance cost evaluations were based on the internal work orders generated by KAT during 

the evaluation period. These work orders were segregated according to vehicle subsystem. Labor 

and parts costs constitute the maintenance costs, and maintenance-cost-per-mile values were 

calculated using the miles driven by each trolley during the evaluation period. A standard labor 

rate of $50/hr was used. 

 28
Table 14 indicates the labor hours, part costs, and cost-per-mile values for each trolley during the 

evaluation period. There are no parts costs because none of the nonwarranty labor done during 

the evaluation period required parts. Labor and parts replacements done under the warranty were 

not recorded. In addition, Ebus supplied KAT with extra replacement parts for those thought to 

have a higher probability of failure. The extra parts, whether they were used or not, were not 

recorded in the maintenance records. The trolleys averaged $0.62 per mile in maintenance costs 

during the evaluation period. 

Table 14. KAT Total Maintenance Cost Comparison 

(December 2004 to May 2005)

Trolley Total Mileage Labor Hours Parts Cost Cost/Mile* 

411 1,688 29 $0 $0.86 

412 3,460 37 $0 $0.53 

413 3,620 32 $0 $0.44 

414 2,149 38 $0 $0.87 

Total 10,917 136 $0 

 $0.62

(average) 

 *At an assumed labor cost of $50/hr

With advanced technologies, it is important to determine the contribution to maintenance costs of 

vehicle systems that make up the vehicle’s advanced component. Three vehicle subsystems of 

note—the fuel system, the APU (MicroTurbine), and the electric propulsion system (EPS, 

including a digital power controller and traction batteries)—were included in the overall 

evaluation of maintenance costs but also separated for independent assessment and discussion. 

Table 15 indicates the labor hours, part costs, and cost-per-mile values for the three hybridrelated subsystems in each trolley. The 12 labor hours attributed to Trolley 414 are the result of 

three road call events, all of which involved troubleshooting a faulty APU wire harness that was 

eventually replaced under warranty. During the evaluation period, the trolleys averaged $0.12 

per mile in maintenance costs for the hybrid-related subsystems. This is approximately 19% of 

the overall maintenance cost per mile, as shown in Table 14. 

Table 15. KAT Fuel System, APU, and EPS Maintenance Cost Comparison 

(December 2004 to May 2005)

Trolley Mileage Total Labor Hours Parts Cost Cost/Mile* 

411 1,688 5 $0 $0.15 

412 3,460 2 $0 $0.03 

413 3,620 7 $0 $0.10 

414 2,149 12 $0 $0.28 

Total 10,917 26 $0 

 $0.12

(average) 

*At an assumed labor cost of $50/hr 

Figure 27 illustrates the cumulative maintenance costs per mile for the trolleys. This approach, 

summarizing cumulative costs, illustrates how a transit agency may become familiar with a new 

technology over time. In the early months of implementation, maintenance costs per mile were 

relatively high. Then, following some variability, these costs decreased and became fairly 

 29
constant during the evaluation period of December 2004 through May 2005. The upward trend 

for September 2004 to December 2004 is due in part to the troubleshooting and replacement of 

the APU wire harness, as mentioned earlier, but also to brake repairs, battery cooling system 

faults, climate control issues, and reports of low SOC. 

Figure 27 also illustrates the cumulative hybrid-related systems maintenance cost per mile for the 

trolleys. In the early months of implementation, maintenance costs per mile were relatively low. 

After increasing steadily for a while, these maintenance costs decreased and became fairly 

constant during the evaluation period. This is consistent with KAT’s observations of zero to few 

maintenance issues after receiving the trolleys, followed by a period in which the APU, fuel 

system, and controls exhibited some unreliability, and, finally, a decline and leveling of monthly 

maintenance costs related to these systems as problems were resolved. 

0.00

0.20

0.40

0.60

0.80

1.00

1.20

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

$/mile

Total Hybrid Systems

Evaluation Period

Figure 27. KAT Cumulative maintenance costs per mile 

Figure 28 illustrates how maintenance costs were allocated among all vehicle subsystems during 

the evaluation period. It is important to note that 3.5 hours per month per bus (64% of the total) 

can be attributed to KAT’s individualized battery pack preventive maintenance procedure. The 

fuel system, APU, and EPS accounted for 3%, 3%, and 12%, respectively, of the total 

maintenance costs. Propulsion-system-related maintenance costs are broken down further in 

Figure 29. The majority (87%) of propulsion-system-related maintenance costs were associated 

with reports of low SOC and turbine fault codes. As described earlier in the IndyGo section, 

drivers accidentally shutting down the APU might have contributed to low SOC events. The 

failure of the APU to activate on-route to elevate the battery SOC may have contributed as well. 

 30
Total Maintenance Costs 

(December 2004 - May 2005)

Cab, Body, 

Accessories

12%

Other

6%

PM Inspection 

and Parts

64%

Propulsion

18%

Figure 28. KAT Maintenance costs by vehicle system (Labor + Parts) 

Propulsion System Maintenance Costs 

(December 2004 - May 2005)

"Low SOC"

87%

Other

13%

Figure 29. KAT Propulsion system maintenance costs (Labor + Parts) 

Specific Component Issues and Resolutions 

Before and during the specific evaluation period, KAT experienced maintenance issues with 

specific components or vehicle subsystems and performed repairs on them. Many of these 

components are unique to the Ebus hybrid system, such as the MicroTurbine, the climate control 

system, and the traction batteries. 

Capstone MicroTurbine 

There were several problems with the Capstone MicroTurbine and associated hardware. 

According to KAT maintenance personnel, fuel injectors failed about three times and were 

 31
replaced under warranty. The DC/DC converters were problematic for all four buses, for a total 

of about eight independent failures, which were also covered by the warranty. The Capstone 

wiring harness was also replaced under warranty.

KAT noted a turbine fault code (2011) intermittently at startup, which prevented the turbine from 

firing. The solution was to cut 12 V of power to the computer, thus overriding the fault and 

allowing the turbine to start. The cause of the fault code was unknown, and so a direct fix proved 

to be elusive. 

Climate Control 

The climate control system encompasses the heating and cooling systems. Knoxville’s relatively 

wide range of temperatures and the Red Line’s large customer base together placed considerable 

demands on the climate control system. 

The trolley’s low floor, small internal volume, and large door--which opened frequently to admit 

and release customers—made it a challenge to maintain a comfortable inside temperature yearround. One complaint voiced by KAT mechanics and drivers was that the climate control system 

was too small to keep up with the fan. 

The heating unit is fueled with kerosene. One heating unit failed and was replaced under 

warranty by Ebus. 

Traction Batteries 

In general, the traction batteries performed well. However, low charge was cited as the reason for 

several road calls throughout the evaluation period. The response and actions taken by KAT 

maintenance personnel included cleaning and charging the batteries.

Figure 30. KAT Ebus Trolley traction battery pack (Source: NREL)

To reduce battery-related road calls, KAT personnel enacted an individualized preventive 

maintenance routine created specifically for the traction battery pack. This routine, which was 

 32
carried out in 2-week intervals, consisted of cleaning the batteries with a vinegar spray and then 

rinsing them with water. 

Campaigns 

Several campaigns to replace or upgrade components were conducted during the evaluation. 

Table 16 lists the campaigns that occurred during 12 months of data collection at KAT. 

Table 15. Campaigns 

Campaign Item Date Reason/Description 

AC/Heater Replacement June 2004 TransAir system prone to failure, so 

campaign carried out at several transit 

properties 

Insulate High-Voltage Wire 

and Fuse Adjacent to Battery 

Pack 

September 2004 Fire-prevention effort following incident 

at IndyGo 

Chargers and Computers April 2005, May 

2005 

Requested larger capacity charger; 

computer replacement necessary to 

interface with new charger 

Road Calls 

KAT uses a broad definition of a road call that depends primarily on the driver’s perceptions. 

When a driver makes a road call, a mechanic is dispatched to make an evaluate and repairs, if 

necessary. Some repairs can be made roadside during the time a trolley dwells at a turnaround; 

others might require towing the trolley back to the garage. 

According to KAT, the trolleys were generally reliable on the route, provided that they were 

warmed up before use. Because KAT used such a comprehensive definition for a road call, it is 

not clear how many road calls defined as such necessitated a tow back to the KAT garage. 

According to KAT maintenance personnel, only three tow-in events occurred and one of them 

was driver-related (caused by insufficient driver training rather than a legitimate problem with 

the trolley). 

The bulk of the road calls relating specifically to the EPS were triggered by a driver’s complaints 

of “low power” or “low charge.” Except for one incident in which no problem was detected, the 

action taken at all road calls was to clean and charge the batteries or check and clear codes. A 

December 2004 road call described by a driver as “low LPG” was caused by low fuel on the 

route. This event corresponded to the period when KAT had only one charger for overnight 

opportunity charging. This event prompted the implementation of self-charging, as described 

earlier. Table 17 is a summary of road calls during the evaluation period. 

 33
Table 16. KAT Road Call Comparison 

(December 2004 to May 2005) 

Trolley 

Total Road 

Calls 

Fuel, APU, EPS 

Road Calls 

411 1 1 

412 5 1 

413 5 3 

414 6 6 

Total 17 11 

Figure 31 shows the trend for the cumulative MBRC. This depiction of the frequency of road 

calls illustrates the variability of this metric in the early stages of implementing the Ebus trolleys; 

this was followed by a drop in MBRC and more stability during the evaluation period. The 

average MBRC during the evaluation period was approximately 1,000 MBRC, which, given the 

road call definition above, includes events that did not require a tow to the garage. The trend line 

begins with July 2004, because there were no road calls in May or June 2004. 

0

1,000

2,000

3,000

4,000

5,000

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

Miles

Evaluation Period

Figure 31. KAT Cumulative miles between road calls (MBRC) 

The high MBRC values are primarily the result of low-charge issues. Once KAT applied its 

personalized battery preventive maintenance practices, the number of these road calls decreased 

for all trolleys except trolley 414. 

Total Operating Costs 

The total operating cost per mile driven is an important metric to fleets, especially when they are 

evaluating a new technology. Here, total operating costs are based on the maintenance and fuel 

costs accrued during the evaluation period and are presented in Table 18. A comparison of fuel 

and maintenance costs to the overall cost per mile is shown in Figure 32. On average, the trolleys 

cost $0.97 per mile to operate during the evaluation period. The high total cost per mile values 

for trolleys 411 and 414 were driven by high maintenance cost per mile values.

 34
Table 17. KAT Total Operating Cost Comparison 

Trolley Miles Driven Labor Hours Parts Cost Fuel Cost Cost/Mile 

411 1,688 29 $0 $689 $1.27 

412 3,460 37 $0 $1,255 $0.90 

413 3,620 32 $0 $1,117 $0.75 

414 2,149 38 $0 $770 $1.23 

Total 10,917 136 $0 $3,830 

 $0.97 

(average) 

$-

$0.20

$0.40

$0.60

$0.80

$1.00

$1.20

$1.40

411 412 413 414

Fuel Cost/Mile

Maintenance Cost/Mile

Figure 32. KAT Cost per mile source breakdown 

Summary of Results for KAT 

Overall, the Ebus trolleys met KAT’s goals. KAT desired a clean-fuel, low-emissions solution to 

alleviating downtown congestion during peak commuter hours, and the LPG Ebus hybrid trolley 

met that goal. 

• Applicability: This was satisfactory and primarily the result of KAT identifying the 

application and vehicle requirements and allowing Ebus to tailor the vehicle to fit those 

requirements. 

• Availability: The Ebus trolleys met KAT’s requirements for availability, with a few 

caveats. Of KAT’s four trolleys, two could be on the route at any time and two were 

spares. This spare ratio exceeds the industry norm and far exceeds KAT’s typical ratio. 

• Reliability: With appropriate warm-ups and a short duty cycle, the vehicles were reliable 

and met KAT’s requirements. 

•

KAT learned two important lessons during the evaluation: 

• It is important to match a vehicle to an appropriate duty cycle. KAT’s thorough research 

before ordering and implementing the Ebus trolleys was validated by a relatively smooth 

experience with them. 

 35
• Frequent training of drivers and mechanics is necessary when implementing a new 

technology. Time and effort invested in training programs offset the initial increase that is 

likely in road calls and maintenance costs. 

In the future, KAT plans to expand its fleet with 30-foot LPG-fueled trolleys. There are no plans 

to purchase additional Ebus trolleys, as there are no plans to expand service for the Red Line or 

another similar route. 

Overall Summary and Comments 

To move forward with a technical development effort that would help reduce air and noise 

pollution, IndyGo and KAT independently decided to purchase several Ebus hybrid electric 

vehicles. Both agencies are relatively small in both size and resources, but they were able to 

secure partial funding for their development through CMAQ grants. Since the Ebus hybrid 

electric buses and trolleys are specialty items, downtown circulator routes were created for their 

application. 

Three overarching lessons were learned in this process. They involve matching the vehicle to an 

appropriate duty cycle, training drivers and maintenance personnel thoroughly, and 

understanding that new technologies are often still in the development stage. 

Match the Vehicle to the Duty Cycle 

When the buses and trolleys were operated for shorter blocks of time, they were more successful 

in several indicators: miles between road calls, trends in fuel economy, and repair costs incurred. 

KAT started and maintained a small-scale duty cycle for the trolleys that proved to be reasonably 

successful. KAT’s Red Line utilized two trolleys during two blocks of time for a total of 5.5 

hours per day per trolley. IndyGo chose a longer duty cycle than KAT, with 12 hours of 

operation per day per bus. It became a daily challenge for IndyGo to keep three of the five buses 

in service at one time. This limited availability caused IndyGo to reduce usage to less than onethird of the planned schedule. With reduced usage, the indicators for the IndyGo buses showed a 

reasonable amount of success. 

In general, KAT had fewer maintenance complications than IndyGo did. This can be attributed to 

both the shorter duty cycle and the different fuels used. LPG may have been a more appropriate 

fuel for the turbine technology. The diesel-turbine combination that IndyGo used had not been 

tried before. Ebus reports that diesel fuel is more difficult to ignite in the MicroTurbine. 

Capstone is therefore developing improved igniters. Also, the diesel-fueled MicroTurbine 

requires a diesel fuel pump, an additional part that is not necessary with an LPG-fueled 

MicroTurbine. 

Train Drivers and Maintenance Personnel 

Another fundamental lesson that each fleet learned was the need to expand the depth and breadth 

of training for both drivers and maintenance personnel. Both transit properties stressed that 

education was important for all employees exposed to a new technology, as the many subtle 

differences can be a cause of increases in road calls and maintenance costs. 

 36
Successful experiences at KAT and IndyGo were driven by employees’ dedication to making a 

new technology work. For instance, both transit properties had one lead mechanic who invested 

in learning new maintenance techniques for these trolleys and buses. During the early stages of 

implementation, a maintenance technician at IndyGo changed out a turbine with only phone 

assistance from Ebus. This shows a willingness to learn new things to make a technology work. 

Both transit properties were satisfied with the assistance that Ebus provided. 

The successful use of these buses at a small transit property was also largely the result of the 

adaptability of key employees who interface with advanced technology on a day-to-day basis. 

This level of dedication also extends to driver training. Not assigning drivers consistently to the 

circulator route with the Ebus buses caused some “hiccups” in the number of road calls for 

IndyGo. More consistency in driver assignments, training, and experience would have reduced 

the number of these road calls. 

New Technology Is Still in Development 

The hybrid-electric propulsion system that incorporates a MicroTurbine is a relatively young 

vehicle technology. In fact, the first application of diesel fuel in a MicroTurbine for a vehicle 

was at IndyGo. IndyGo struggled more than KAT with low-SOC road calls, which accounted for 

32% of IndyGo’s propulsion-related maintenance costs. Many of these costs were the result of a 

driver’s error, however, and some were caused by the failure of the Capstone igniter to activate 

the MicroTurbine. 

Capstone is therefore developing improved igniters, and Ebus conducted a software campaign at 

IndyGo in spring 2005 to address this issue. As noted earlier, this made the MicroTurbine run all 

the time at a reduced level rather than cycle on and off to maintain a prescribed battery SOC. 

This was a relatively significant change to the propulsion system design and was made only at 

IndyGo. 

Despite low-SOC road calls and reduced availability, the Ebus hybrid electric vehicles were 

somewhat successful. Specifically, KAT experienced a relatively successful application of the 

trolleys by using them on a short, light, duty cycle. At this stage, both agencies are using the 

vehicles in specialty applications. Both transit experiences showed the need to carefully train 

employees who interact with the technology on a day-to-day basis, as well as to monitor and not 

exceed the application of these vehicles. 

 37
Contacts 

U.S. Department of Energy 

Lee Slezak 

Manager, Advanced Vehicle Testing Activity 

202-586-2335 

lee.slezak@ee.doe.gov

IndyGo 

Morris Frye 

Director, Vehicle Maintenance 

317-614-9309 

morris@indygo.net 

KAT 

Robert Schneider 

Chief Operating Officer 

865-215-7803 

rschneider@cityofknoxville.org 

Ebus 

Andy Eklov 

562-904-3474 

eklov@ebus.com

NREL 

Robb Barnitt 

Project Engineer 

303-275-4489 

robb_barnitt@nrel.gov

 38
Acronyms and Abbreviations 

APU advanced power unit 

AVTA Advanced Vehicle Testing Activity 

bhp brake horsepower 

CARB California Air Resources Board 

CMAQ Congestion Mitigation Air Quality 

CNG compressed natural gas 

CO carbon monoxide 

DGE diesel gallon equivalent 

DOE U.S. Department of Energy 

DPF diesel particulate filter 

EPA U.S. Environmental Protection Agency 

EGR exhaust gas recirculation 

g/bhp-hr grams per brake horsepower-hour 

GVWR gross vehicle weight rating 

HC hydrocarbons 

HEV hybrid electric vehicle 

HVAC heating, ventilation, and air-conditioning 

IndyGo Indianapolis Transportation Corporation 

KAT Knoxville Area Transit 

kW kilowatt 

LPG liquefied petroleum gas 

MBRC miles between road calls 

NiCd nickel cadmium 

NREL National Renewable Energy Laboratory 

NMHC nonmethane hydrocarbons 

NOx oxides of nitrogen 

PM particulate matter 

ppm parts per million 

RC road call 

rpm revolutions per minute 

SOC state of charge 

V volt 

 39
References 

Ebus Web site, www.ebus.com. 

Eudy, L., Gifford, M., Challenges and Experiences with Electric Propulsion Transit Buses in the 

United States, DOE/GO-102003-1791, Golden, CO: National Renewable Energy Laboratory, 

2003. 

NREL, Advanced Technology Vehicles in Service, Knoxville Area Transit, DOE/GO-102005-

2085, Golden, CO: National Renewable Energy Laboratory, 2005. 

NREL, Advanced Technology Vehicles in Service, Indianapolis Public Transportation, 

DOE/GO-102004-1986, Golden, CO: National Renewable Energy Laboratory, 2004. 

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

Golden, CO: National Renewable Energy Laboratory, 2002. 

The Pennsylvania Transportation Institute, STURAA Test, 7 Year 200,000 Mile Bus from Ebus, 

Inc. Model Vintage Trolley, PTI-BT-R0121, Altoona, PA: PTI, 2002. 

 40
F1147-E(12/2004) 

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DE-AC36-99-GO10337 

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4. TITLE AND SUBTITLE

Case Study: Ebus Hybrid Electric Buses and Trolleys 

5c. PROGRAM ELEMENT NUMBER

5d. PROJECT NUMBER

NREL/TP-540-38749 

5e. TASK NUMBER

FC06.3000 

6. AUTHOR(S)

R. Barnitt 

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National Renewable Energy Laboratory 

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13. SUPPLEMENTARY NOTES

14. ABSTRACT (Maximum 200 Words)

This evaluation focuses on the demonstration of hybrid electric buses and trolleys produced by Ebus, Inc. 

(www.ebus.com), of Downey, California. Ebus manufactures 22-foot buses with a variety of optional powertrains and 

exterior designs. The vehicles come with battery electric and hybrid electric powertrain options, and purchasers can 

choose either conventional bus or antique-trolley-style exteriors. The Indianapolis Transportation Corporation 

(IndyGo) and Knoxville Area Transit (KAT) participated in a demonstration of the Ebus vehicles. Each fleet chose 

hybrid electric powertrains but selected different exterior designs and fuels. 

15. SUBJECT TERMS

Hybrid electric; buses; trolleys; Ebus Inc.; Indianapolis Transportation Corporation; IndyGo; Knoxville Area Transit; 

KAT; evaluation; U.S. Department of Energy; DOE; Advanced Vehicle Testing Activity; AVTA; National Renewable 

Energy Laboratory; NREL 

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