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

is to bridge the gap between R&D and commercial availability of 

advanced vehicle technologies. AVTA supports DOE’s FreedomCAR 

and Vehicle Technologies Program in moving these technologies 

from R&D to market deployment by examining market factors and 

customer requirements, evaluating performance and durability of 

alternative fuel and advanced technology vehicles, and assessing 

the performance of these vehicles in fleet applications. 

The Fleet Test & Evaluation team at the National Renewable Energy 

Laboratory (NREL) supports AVTA by conducting medium- and heavyduty vehicle evaluations. The team’s tasks include recommending 

types of alternative fuel and advanced technology vehicles to test, 

identifying fleets to evaluate, designing test plans, gathering on-site 

data, preparing technical reports, and communicating results on its 

website and in print publications.

TESTING ADVANCED VEHICLES

KNOXVILLE AREA TRANSIT ◆ PROPANE HYBRID ELECTRIC TROLLEYS

Knoxville Area Transit PROPANE HYBRID ELECTRIC TROLLEYS NREL/PIX 13795

KNOXVILLE AREA TRANSIT (KAT) is recognized nationally 

for its exceptional service to the City of Knoxville, Tennessee. 

KAT received the American Public Transportation Association’s prestigious Outstanding Achievement Award in 2004. 

Award-winning accomplishments included KAT’s increase 

in annual ridership to 3.2 million passengers—the highest 

ridership in 20 years—and the advancement of its Clean 

Fuels Program. The objective of the Clean Fuels Program is 

to improve air quality in the Knoxville metropolitan area by 

reducing vehicle emissions. 

As part of the Clean Fuels Program, KAT is deploying four 

propane hybrid electric trolleys on its new Red Line Trolley 

Route. Designed to reduce downtown congestion, the Red Line 

starts at the Knoxville Civic Coliseum on the edge of downtown and continues through northern downtown, including 

Market Square, the Tennessee Valley Authority, and Gay Street. 

The route is intended primarily for downtown employees who 

take advantage of Knoxville’s Unparalleled Parking Program 

by parking at the Coliseum and using public transit to get to 

work. The Red Line circulates every seven minutes during 

peak times on weekday mornings and afternoons. Like all 

Knoxville trolley routes, it is free of charge.

More than 90% of 

KAT’s 100 vehicles 

now use alternative 

fuels. In addition to 

the hybrid electric 

trolleys, KAT’s transit 

fleet includes 16 propane vans. All of its 

diesel vehicles use a 

20% biodiesel blend 

(B20), and it has four 

light-duty hybrid 

electric vehicles.

The Clean Fuels Program also uses incentives to promote 

cleaner air and reduce congestion. All KAT services are free 

on summer ozone alert days, and free bus passes are given to 

select downtown employees to encourage public transit use.

The Clean Fuels Program is 

supported by Congestion 

Mitigation and Air Quality 

(CMAQ) grants. The CMAQ 

program, jointly administered by the Federal Highway 

Administration and the 

Federal Transit Administration, aims to alleviate traffic 

congestion and emissions in 

non-attainment air quality 

areas. The Chattanooga, 

Tennessee-based Advanced 

Transportation Technology 

Institute provided KAT 

with technical assistance in 

acquiring the hybrid electric 

trolleys.

East Church

KAT Red Line

 Trolley Stop

Gay St.

Radisson

Hotel

Tennessee

Theater

Coliseum

Parking Garage

Knoxville 

Civic Coliseum

TVA Towers

Market

Square

Mall

Union

Church

Clinch

Union

Summit Hill East Summit Hill

Clinch

State

Central

East Hill

James White Parkway

Hall of Fame Drive

Walnut

Market

Wall

Gay St.
batteries by the MicroTurbine. 

This system is charge sustaining, meaning that the batteries 

will have power as long as the 

APU has fuel. 

The trolley design also incorporates regenerative braking, 

which provides additional 

energy to recharge the battery 

pack. In this system, the 

electric motors that drive the 

trolley become generators 

during deceleration, and the 

electricity produced by the 

generators is stored in the batteries. This technology is particularly effective for routes, such as the Red Line, that encounter 

stop-and-go traffic. When the trolley is not in operation, it can 

be plugged into a fast charging station to “top off” the batteries 

in approximately one hour.

Ebus also offers this hybrid electric system with a dieselpowered APU. KAT selected propane because of this fuel’s 

low emissions and because propane infrastructure was already 

established in Knoxville.

NREL’S EVALUATION OF THE KAT RED LINE TROLLEYS

began in 2004 and will continue for approximately 6 months. 

Information being collected and analyzed includes opera-tional 

data such as vehicle use, fuel consumption, and maintenance 

performed, as well as descriptions of KAT’s experience 

implementing this new technology and the public’s perception 

of it. The objectives are to provide credible data 

and results that show the progress of these hybrid electric 

trolley and infrastructure technologies.

The final results will be published upon completion of the 

evaluation on the AVTA website, www.eere.energy.gov/

vehiclesandfuels/avta. 

Contacts

Knoxville Area Transit

Barry Greenberg, Director of Maintenance

Phone: 865-215-7834

bgreenberg@ci.knoxville.tn.us

NREL Fleet Test & Evaluation Team

Robb Barnitt, Engineer

Phone: 303-275-4489

robb_barnitt@nrel.gov

PROPANE HYBRID ELECTRIC TROLLEYS

Trolleys: Ebus, Inc. Trolley

Model Year 2003

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

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

Passenger Capacity 22 (1 wheelchair)

Maximum Forward Speed 40 mph

Service Knoxville, Tennessee

Propulsion: Series Hybrid-Electric

Motor Reliance AC Induction, 

air cooled

Energy Storage 48 NiCd, liquid-cooled, “fast 

charge” batteries, 288 V total

Opportunity Charging SAE J-2293 Fast Charging

Regenerative Braking Yes

APU: Capstone Model 330 MicroTurbine

Rating 30 kW, 250-700 V DC

Fuel Propane

Fuel Storage 50 gal

KAT SELECTED 22-FOOT, LOW-FLOOR SERIES HYBRID 

ELECTRIC trolleys manufactured by Downey, Californiabased Ebus, Inc. for the Red Line. The Ebus hybrid electric 

system propels the trolleys using 

an electric motor powered 

by a battery pack. The nickelcadmium (NiCd) batteries 

are recharged by a low-emission, 

propane-fueled Capstone 

MicroTurbineTM auxiliary power 

unit (APU), which extends the 

range of the trolleys. A digital 

power controller monitors and 

controls recharging of the 

Printed with a renewable-source ink on paper containing at least 50% wastepaper, including 20% postconsumer waste.

Neither the United States government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, 

or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply 

its endorsement, recommendation, or favoring by the United States government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States government or any agency thereof.

Websites

Ebus: www.ebus.com

KAT: www.ci.knoxville.tn.us/kat

Capstone Microturbine: www.capstoneturbine.com

NREL: www.nrel.gov/vehiclesandfuels/fleettest

AVTA: www.eere.energy.gov/vehiclesandfuels/avta

For more information contact:

EERE Information Center

1-877-EERE-INF (1-877-337-3463)

www.eere.energy.gov 

A Strong Energy Portfolio for a Strong America

Energy efficiency and clean, renewable energy will mean a stronger economy, a cleaner 

environment, and greater energy independence for America. Working with a wide array 

of state, community, industry, and university partners, the U.S. Department of Energy’s 

Office of Energy Efficiency and Renewable Energy invests in a diverse portfolio of energy 

technologies.

DOE/GO-102005-2085 • April 2005

NREL/PIX 13796

KAT fast charging station 

KNOXVILLE AREA TRANSIT ◆ PROPANE HYBRID ELECTRIC TROLLEYS

Produced by the 

National Renewable Energy Laboratory (NREL)

NREL is a U.S. Department of Energy National Laboratory

Operated by Midwest Research Institute • Battelle

Propane tank in KAT hybrid 

electric trolley

NREL/PIX 13798