NREL is a national laboratory of the U.S. Department of Energy, Office of Energy 

Efficiency & Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.

Contract No. DE-AC36-08GO28308

FedEx Express Gasoline Hybrid 

Electric Delivery Truck 

Evaluation: 12-Month Report

R. Barnitt

Technical Report

NREL/TP-5400-48896

January 2011 
NREL is a national laboratory of the U.S. Department of Energy, Office of Energy 

Efficiency & Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.

National Renewable Energy Laboratory

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Golden, Colorado 80401

303-275-3000 • www.nrel.gov

Contract No. DE-AC36-08GO28308

FedEx Express Gasoline 

Hybrid Electric Delivery Truck 

Evaluation: 12-Month Report

R. Barnitt

Prepared under Task No. FC08.3000

Technical Report

NREL/TP-5400-48896

January 2011 
NOTICE

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iii

Executive Summary

This final report presents results of a technology evaluation of gasoline hybrid electric parcel 

delivery trucks operated by FedEx Express in and around Los Angeles, California. FedEx 

Express is a large commercial fleet that operates more than 30,000 motorized vehicles and has 

hybrid electric (diesel and gasoline) vehicles currently in service. FedEx Express has deployed 

20 gasoline hybrid electric vehicles (gHEVs) on parcel delivery routes in the Sacramento and 

Los Angeles areas. This report presents the results of parcel delivery drive cycle data collection 

and analysis activities, 12-month in-use fuel economy and maintenance costs, and emissions and 

fuel economy results of chassis dynamometer testing of a gHEV and a comparative diesel truck 

at the National Renewable Energy Laboratory’s (NREL’s) Renewable Fuels and Lubricants 

(ReFUEL) laboratory. 

The drive cycle data collection and analysis effort framed the selection of study vehicles and 

routes and structured the measurement of vehicle emissions and fuel economy on the chassis 

dynamometer at NREL’s ReFUEL laboratory. Tailpipe emissions from the gHEV were 

substantially lower across all three tested drive cycles than emissions from the diesel baseline 

vehicle. Notably, the gHEV exhibited 75–89% lower oxides of nitrogen (NOx) and over 99% 

lower particulate matter. Laboratory-measured diesel-equivalent fuel economy was similar 

between the gHEV (7.3 – 11.4 mpg) and diesel vehicle (6.1 – 11.7 mpg). On the most 

kinetically intensive drive cycle tested in the laboratory, the hybrid exhibited 21% higher fuel 

economy than the diesel. There was no statistical difference in calculated on-road diesel 

equivalent fuel economy for the gHEV (7.5 mpg) and diesel (7.9 mpg) study groups. The fuel 

economy findings are encouraging considering that gasoline engines in general have lower fuel 

economy than diesel engines. These gHEV’s were able to provide similar or improved fuel 

economy while also providing significantly reducing emissions.

Six similar trucks were selected for this in-use evaluation project. Three of the trucks are gHEVs,

and three are conventional diesel trucks that serve as a control group. Comparison data were 

collected and analyzed for in-use fuel economy and fuel costs, maintenance costs, total operating 

costs, and vehicle uptime. Based upon the data collected during this study, there was no 

statistically significant difference in fuel cost per mile or maintenance cost per mile between the 

gHEV and diesel groups. As a result, there was no statistically significant difference in total 

operating cost per mile between the gHEV ($0.63/mile) and diesel ($0.59/mile) groups.

The gHEVs experienced a smooth integration and deployment into commercial service. During 

the study period, the gHEVs performed as expected, experienced a minimum of unscheduled 

maintenance, and met the expectations of FedEx Express. 

This technology evaluation was part of a collaborative effort co-funded by the U.S. Department 

of Energy’s (DOE’s) Vehicle Technologies Program and the South Coast Air Quality 

Management District (SCAQMD) via CALSTART. The in-use technology evaluation was 

conducted by NREL and primarily sponsored by DOE. The chassis dynamometer testing was 

conducted by NREL and primarily funded by SCAQMD via CALSTART.
iv

Acronyms and Abbreviations

AC alternating current

ATA American Trucking Association

AZD Azure Dynamics, Inc. 

CAN Controller Area Network

CO carbon monoxide

CoV coefficient of variance

DC direct current

DOE U.S. Department of Energy

FE fuel economy

FT&E Fleet Test and Evaluation 

g gram

gHEV gasoline hybrid electric vehicle

GPS global positioning system

HC hydrocarbons

HP horsepower

J joule

KI kinetic intensity

lb-ft foot-pounds

mpg miles per gallon

NOx oxides of nitrogen

NREL National Renewable Energy Laboratory

NYCC New York City Cycle

OC Bus Orange County Bus

PM particulate matter

ReFUEL Renewable Fuels and Lubricants 

RPM revolutions per minute 

SCAQMD South Coast Air Quality Management District 

THC total hydrocarbons

V volt

VMT vehicle miles traveled
v

Table of Contents

Executive Summary................................................................................................................................... iii

Acronyms and Abbreviations ................................................................................................................... iv

Table of Contents........................................................................................................................................ v

List of Figures ............................................................................................................................................ vi

List of Tables ............................................................................................................................................. vii

1 Background........................................................................................................................................... 1

2 Introduction........................................................................................................................................... 1

3 Approach............................................................................................................................................... 3

3.1 Route / Drive-Cycle Selection .............................................................................................3

3.2 Vehicle Descriptions............................................................................................................6

3.3 Laboratory Vehicle Emissions and Fuel Economy Measurement.......................................6

3.4 In-Use Vehicle Refueling Data Collection ..........................................................................7

3.5 Vehicle Maintenance and Data Collection ..........................................................................8

3.5.1 Vehicle Warranty Repairs...........................................................................................9

3.6 Vehicle Uptime ....................................................................................................................9

4 Results................................................................................................................................................... 9

4.1 Laboratory Vehicle Emissions and Fuel Economy Measurement.......................................9

4.1.1 Vehicle Emissions Comparison ..................................................................................9

4.1.2 Vehicle Fuel Economy Comparison .........................................................................11

4.2 In-Use Fuel Economy and Costs........................................................................................12

4.3 Maintenance Costs.............................................................................................................14

4.3.1 Vehicle Warranty Repairs.........................................................................................19

4.4 Total Operating Costs........................................................................................................20

4.5 Vehicle Uptime ..................................................................................................................21

5 Summary ............................................................................................................................................. 23

Appendix: ReFUEL Test Report .............................................................................................................. 25

Objectives ................................................................................................................................27

General Lab Description and Methods....................................................................................27

Chassis Dynamometer .......................................................................................................27

Fuel Storage and Blending.................................................................................................28

Fuel Metering & Conditioning...........................................................................................29

Air Handling & Conditioning ............................................................................................29

Emissions Measurement ....................................................................................................29

Project Specific Setup and Methods........................................................................................31

Test Vehicles......................................................................................................................32

Fuel ....................................................................................................................................32

Air and Exhaust..................................................................................................................32

Vehicle Simulation.............................................................................................................33

Test Description and Results ...................................................................................................33

State Of Charge Considerations.........................................................................................34

ReFUEL Test Report Appendix A. Test Cell Instrumentation................................................35

ReFUEL Test Report Appendix B. Fuel Analysis...................................................................37

ReFUEL Test Report Appendix C. Coast Down Data ............................................................39

ReFUEL Test Report Appendix D. Test Results.....................................................................40
vi

List of Figures 

Figure 1. FedEx Express gHEV (Photo courtesy of Sam Snyder, FedEx Express) ....................... 2

Figure 2. Study routes..................................................................................................................... 5

Figure 3. Comparison of drive cycle kinetic intensities ................................................................. 7

Figure 4. Criteria emissions by drive cycle .................................................................................. 10

Figure 5. Influence of route kinetic intensity on fuel economy.................................................... 11

Figure 6. Fuel economy results..................................................................................................... 13

Figure 7. Fuel and fuel cost per mile results................................................................................. 13

Figure 8. Total maintenance cost and maintenance cost per mile results..................................... 15

Figure 9. gHEV maintenance costs by system.............................................................................. 17

Figure 10. Diesel maintenance costs by system............................................................................ 17

Figure 11. Lower-tier maintenance costs per mile by system ...................................................... 18

Figure 12. Total operating costs.................................................................................................... 21

Figure 13. Vehicle uptime............................................................................................................. 22

Figure A-1. Chassis dynamometer schematic............................................................................... 28

Figure A-2. Pierburg fuel metering system................................................................................... 29

Figure A-3. Venturi nozzles.......................................................................................................... 30

Figure A-4. Gaseous and PM sampling benches.......................................................................... 30

Figure A-5. Class 1000 clean room, filter housing, and microbalance......................................... 31

Figure A-6. Chassis cell with test vehicle..................................................................................... 32

Figure A-7. Process and instrumentation diagram........................................................................ 35

Figure A-8a. HEV track coast down curves ................................................................................. 39

Figure A-8b. Coast down comparison – conducted at ReFUEL .................................................. 39

Figure A-9. NYCC drive cycle ..................................................................................................... 40

Figure A-10. Orange County Bus drive cycle .............................................................................. 40

Figure A-11. HTUF4 drive cycle.................................................................................................. 41
vii

List of Tables

Table 1. AZD Balance Hybrid System ........................................................................................... 3

Table 2. Drive Cycle Data Collection by Truck-Days.................................................................... 4

Table 3. Parcel Delivery Study Routes........................................................................................... 5

Table 4. FedEx Express Delivery Truck Basic Information........................................................... 6

Table 5. Summary of Emissions Results ........................................................................................ 9

Table 6. gHEV Criteria Emissions Reductions by Drive Cycle ................................................... 10

Table 7. gHEV Fuel Economy Comparison by Drive Cycle........................................................ 11

Table 8. Fuel Economy and Costs from Retail Fueling Records.................................................. 12

Table 9. CAN Fuel Economy Results........................................................................................... 14

Table 10. Relative Ages of Study Vehicles.................................................................................. 14

Table 11. Maintenance Costs by System...................................................................................... 16

Table 12. Vehicle Warranty Repairs............................................................................................. 20

Table 13. Total Operating Costs................................................................................................... 21

Table 14. Vehicle Uptime ............................................................................................................. 22

Table A-1. Test Vehicle Information............................................................................................ 32

Table A-2. Instrumentation List.................................................................................................... 36

Table A-3. CARB Diesel Fuel Analysis....................................................................................... 37

Table A-4. CARB Phase II Gasoline ............................................................................................ 38

Table A-5. Conventional Test Results.......................................................................................... 42

Table A-6. Hybrid Test Results.................................................................................................... 43
1

1 Background

The Fleet Test and Evaluation (FT&E) team at the National Renewable Energy Laboratory 

(NREL) provides unbiased evaluations of alternative fuel and advanced transportation 

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

The FT&E team’s role is to bridge the gap between research and development and the

commercial availability of alternative fuels and advanced vehicle technologies. FT&E supports 

the U.S. Department of Energy’s (DOE’s) 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 FT&E team supports vehicle research activities at NREL 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. NREL has 

completed numerous medium- and heavy-duty vehicle evaluations based on an established data 

collection protocol, known as the General Evaluation Plan,1

This technology evaluation was part of a collaborative effort co-funded by the DOE’s Vehicle 

Technologies Program and CALSTART via funding from the South Coast Air Quality 

Management District (SCAQMD). The in-use technology evaluation was conducted by NREL 

and primarily sponsored by DOE. The chassis dynamometer testing was conducted by NREL 

and primarily funded by CALSTART via funding from SCAQMD. 

developed with and for DOE. This 

project supports DOE’s Advanced Vehicle Testing Activity. 

2 Introduction 

This document presents the final results of a technology evaluation of gasoline hybrid electric 

parcel delivery trucks operated by FedEx Express in and around Los Angeles, California. FedEx 

Express is a large commercial fleet that operates more than 30,000 motorized vehicles and has 

hybrid electric (diesel and gasoline) vehicles currently in service. FedEx Express has deployed 

20 gasoline hybrid electric vehicles (gHEVs) on parcel delivery routes in the Sacramento and 

Los Angeles areas. These gHEVs (Figure 1) are built upon a Ford E-450 strip chassis, and each 

vehicle is powered by a Ford 5.4L gasoline engine and Azure Dynamics, Inc. (AZD) Balance 

Hybrid System. Additional vehicle information is discussed in subsequent sections, while the 

specifics of the hybrid system evaluated are presented in Table 1. FedEx Express was the 

domestic launch customer for the AZD Balance Hybrid electric product. FedEx Express chose 

this vehicle platform for several reasons:

1. It represented a gHEV solution for use in California.

2. It provided an engine off at idle feature.

3. It offered a projected improvement in fuel economy over the gasoline engine W700.

 1 Available on the Web at http://www.nrel.gov/docs/fy02osti/32392.pdf. 
2

4. It would provide a platform comparison to the diesel hybrid electric W700 platform.

FedEx Express’s expectation for gHEV deployment was a successful launch of the technology.

Figure 1. FedEx Express gHEV (Photo courtesy of Sam Snyder, FedEx Express)
3

Table 1. AZD Balance Hybrid System

Model Year 2008 

Model Balance Hybrid Electric (parallel hybrid) 

Motor 100 kW AC induction w/regenerative braking 

Motor Controller 120 kW inverter 

Transmission Elect. 5-spd. Torqshift auto. O/D transmission 

Battery 

Cobasys 288 V, 60 kW, 8.5 Ah, nickel metal hydride

Automatic high-voltage disconnect in case of vehicle 

collision 

System Voltage 288 VDC nominal 

Power Steering/Brakes Engine on – standard engine-driven pump 

12V System Alternator supplemented by DC/DC converter 

Cooling 

Engine – Ford cooling system with electrified radiator 

cooling fans

Hybrid system – Separate low temp cooling loop 

This final report presents the results from a 12-month in-use evaluation comparing in-use fuel 

economy and maintenance costs of gHEVs and comparative diesel parcel delivery trucks. In 

addition, this report presents the results of the parcel delivery drive cycle data collection and 

analysis activities as well as emissions and fuel economy results of chassis dynamometer testing 

of a gHEV and a comparative diesel truck at NREL’s Renewable Fuels and Lubricants 

(ReFUEL) laboratory.

3 Approach

3.1 Route / Drive-Cycle Selection

Matching gHEV and diesel trucks to similar routes is important for accurate comparison of inuse fuel economy and maintenance costs. In addition, grouping well-matched gHEV and diesel 

truck routes aids in truck-truck comparisons as well as group-group comparisons. Finally, 

knowledge of in-use driving characteristics, including intensity, speed, and stops per mile allows 

for the selection of similar industry drive cycles for chassis dynamometer testing. The relevance 

of chassis dynamometer-derived emissions and fuel economy is dependent upon selecting test 

cycles that are similar to drive cycles driven in the field.

Global positioning system (GPS)-based data loggers were used to collect drive cycle information 

from several FedEx Express parcel delivery trucks. This drive cycle data collection effort was 

conducted in two phases. First, in order to identify three well-matched gHEVs and routes, eight 

gHEVs deployed from three FedEx Express depots in southern California were instrumented 

with GPS-based data loggers, and spatial speed-time data were collected over 61 valid route-days 

(Table 2). These route data were filtered, visualized using Google Earth, and analyzed according 

to 58 drive cycle metrics to analyze daily route consistency and to characterize each route. Data 
4

filtering and analysis were performed using the NREL Duty Cycle Analysis and Custom Test 

Generation Tool.2

Table 2. Drive Cycle Data Collection by Truck-Days

Truck Depot Days 

Logged

Days 

Valid 1 2 3 4 5 6 7 8 9 10 11

D286 EMT 4 3 OFF ON ON ON NM NM NM NM NM NM NM 

D288 EMT 11 8 ON ON ON ON OFF OFF ON ON ON ON OFF

D289 SPQ 8 6 ON ON ON ON OFF OFF ON ON NM NM NM 

D290 SPQ 10 8 ON ON ON ON OFF OFF ON ON ON ON NM 

H292 POC 10 9 ON ON ON ON ON ON ON ON ON OFF NM

H293 POC 10 9 OFF ON ON ON ON ON ON ON ON ON NM

H294 POC 9 9 ON ON ON ON ON ON ON ON ON NM NM

H295 POC 9 9 ON ON ON ON ON ON ON ON ON NM NM

Totals 71 61

OFF: Vehicle not in service

ON: Vehicle in service

NM: Data were not measured

Our goal was to assemble a group of three similar routes being driven by gHEVs from a single 

depot. These three similar gHEV-served routes would be the focus of this 12-month in-use 

evaluation and would provide average drive cycle metrics to aid in chassis dynamometer test 

cycle selection. Two depots had been assigned only two gHEVs each. The third depot (POC) 

was assigned four gHEVs and was subsequently decided upon as the focus of this analysis. 

Based upon a statistical comparison of key drive cycle characteristics (Table 3), three of the four 

gHEV-served POC routes were selected as three of the six total study routes for the in-use 

evaluation. These routes (A1, A2, and A3) were initially served by trucks H292, H294, and 

H295. 

In the absence of initial GPS-derived route data, diesel vehicles driving similar routes in terms of 

daily vehicle miles traveled (VMT) and traffic patterns were suggested by the POC depot 

manager. These routes (B1, B2, and B3) were initially served by trucks D670, D896, and D830. 

In the second phase of drive cycle data collection, the three routes served by diesel vehicles were 

instrumented with GPS data loggers. Data were collected, filtered, and analyzed using the same 

process. The key drive cycle characteristics of these routes (A1, A2, A3, B1, B2, and B3), 

anonymized at the request of FedEx Express, are presented in Table 3 and are visualized in 

Figure 2. 

 2 NREL Vehicle Drive Cycle Tool, User Guide. Copyright © 2009 Alliance for Sustainable Energy, LLC. All Rights 

Reserved.
5

Table 3. Parcel Delivery Study Routes

Drive Cycle 

Characteristic

Route and Group Statistics

A1 A2 A3 Mean 

A

CoV 

A B1 B2 B3 Mean B

CoV 

B

Average Driving 

Speed (mph) 16.8 16.9 16.3 16.7 2% 18.9 20.9 18.8 19.5 6%

Daily VMT 

(miles) 43.8 47.3 21.4 37.5 37% 38.7 36.1 49.3 41.4 17%

Stops per Mile 3.85 3.79 4.22 3.96 6% 2.97 2.66 3.38 3.00 12%

Average 

Acceleration 

(ft/s2)

2.27 2.11 2.09 2.16 4% 2.26 2.13 2.03 2.14 6%

Average 

Deceleration 

(ft/s2)

-2.59 -2.55 -2.52 -2.55 1% -2.44 -2.31 -2.56 -2.43 5%

Accelerations 

per Mile 20.80 20.78 22.82 21.46 5% 21.37 18.12 18.32 19.27 9%

Decelerations 

per Mile 20.26 19.71 22.63 20.87 7% 20.13 18.21 18.03 18.79 6%

Kinetic Intensity 

(ft-1) 0.00059 0.00055 0.00074 0.00063 16% 0.00037 0.00030 0.00039 0.00035 14%

Figure 2. Study routes

While each of the two groups is made up of relatively well-matched routes, there is some 

variability between A and B groups. While the differences are small for most statistics, there is a 

larger A versus B difference in kinetic intensity. In order to partially account for this route 

variability, the vehicle groups exchanged routes after 6 months of evaluation. Thus, the 12-

month averages for gHEV and diesel groups are comparable. 
6

Fuel economy can vary due to driving style. In general, FedEx Express assigns one driver to a 

given vehicle operating on a given route. However, due to vacations and illness, as well as 

occasional scheduling needs, other drivers may operate a vehicle on a route for a day or more. As 

a result, in-use fuel economy results include some uncontrolled driver and driving style 

variability. Drivers did not follow vehicles when the vehicle-route swaps were conducted but 

instead continued to serve the same route using a different vehicle.

3.2 Vehicle Descriptions

Based upon the activities outlined in Section 3.1 and based upon the FedEx Express fleet 

composition and usage of vehicles within their fleet, six similar trucks were selected for this inuse evaluation project. Three of the trucks are gHEVs and three are conventional diesel trucks 

that serve as a control group. Although these truck groups are not identical, they represented the 

best possible match for an evaluation based on vocational usage, size, and age. Both groups of 

trucks provided the same functionality for FedEx Express. Basic vehicle attributes are presented 

in Table 4. 

Table 4. FedEx Express Delivery Truck Basic Information

Vehicle Information gHEV Diesel

Asset Numbers H292, H294, H295 D670, D896, D830

Chassis Manufacturer/Model Ford E-450 Strip Chassis Freightliner MT-45

Chassis Model Year 2008 2006

Engine Manufacturer/Model Ford 5.4L EFI Triton V-8 Cummins 5.9L ISB 200 I-6

Engine Model Year 2008 2006 (EPA 04)

Engine Ratings

Max. Horsepower

Max. Torque

255 HP @ 4,500 RPM

350 lb-ft @ 2,500 RPM

200 HP @ 2,300 RPM

520 lb-ft @ 1,600 RPM

Fuel Capacity 55 gallon - Gasoline 45 gallon - Diesel

Transmission Manufacturer/Model Ford 5R110 5-spd. auto. Allison 1000 5-spd. auto.

Curb Weight 9,300 lb 9,700 lb

Gross Vehicle Weight Rating 14,050 lb 16,000 lb

Cabin Air Conditioning Yes Yes

3.3 Laboratory Vehicle Emissions and Fuel Economy Measurement

One representative gHEV and one representative diesel vehicle were tested at the ReFUEL 

laboratory, which is operated by NREL and located in Denver, Colorado. The ReFUEL 

laboratory utilizes a heavy-duty vehicle (chassis) test cell with emissions and fuel consumption 

measurement capability. Additional information relative to the ReFUEL laboratory’s capabilities 

and experimental setup is included in the appendix. A gHEV being used by FedEx Express at the 

POC depot in southern California was transported to ReFUEL, and a representative MY2006 

(2004 engine certification) diesel truck was obtained from the Denver FedEx Express fleet for 

testing. The goal of testing at the ReFUEL laboratory was to quantify the reduction in emissions 

realized with the gHEV and to compare the fuel economy of a gHEV and a diesel vehicle.
7

To select the appropriate chassis dynamometer test cycles, calculated kinetic intensity3

Figure 3

was used 

to compare real, collected drive cycle data (section 3.1) to industry drive cycles. Drive cycle 

kinetic intensity is derived from the classic road load equation for power. Kinetic intensity is a 

calculated “macro-characteristic” that represents the transient intensity (accelerations and 

decelerations) of a particular drive cycle. At the time chassis dynamometer testing was 

performed, drive cycle data had only been collected for the A group described in the previous 

section. Based upon the observed group A drive cycle kinetic intensities, the Orange County Bus 

cycle (OC Bus) was selected as a cycle that best approximated the average of the routes driven 

by the initial three routes. The New York City Cycle (NYCC) and HTUF4 cycles were selected 

as upper and lower boundaries for kinetic intensity with the intention of demonstrating the 

expected range of fuel economy. NYCC and HTUF4 were also selected based upon usage in 

previous tests of similar vehicles. presents kinetic intensity values for the industry drive 

cycles and the measured A and B routes along with the average kinetic intensity of all six study 

routes. Figure 3 also includes cycle average driving speed, as it is a common basic metric for 

cycle comparison.

Figure 3. Comparison of drive cycle kinetic intensities

3.4 In-Use Vehicle Refueling Data Collection

The purpose of collecting and analyzing truck in-use fuel records is to calculate and compare inuse fuel economy. Three in-use fuel economy evaluation methods were used for corroboration 

due to potential reliability and accuracy issues inherent in each. Collection of truck fueling 

records took two forms:

 3 O’Keefe, M. Duty Cycle Characterization and Evaluation Towards Heavy Hybrid Vehicle Applications. Society of 

Automotive Engineers Paper No. 2007-01-0302, 2007.
8

1. Fuel logs were located in each truck, and drivers were instructed to fill in fields at each 

fueling event. Each week, depot management faxed a completed fuel log to NREL.

2. Retail fuel purchases required the entry of mileage and asset number. Although a 

transaction receipt is an option, a monthly statement associated with the fuel card 

provided the required data. These fuel records were transmitted electronically to NREL, 

reviewed for accuracy, and analyzed to compare fuel economy for the gHEV and diesel 

vehicle groups. 

A third method was also implemented:

3. Controller Area Network (CAN) bus-derived fuel consumption was measured with 

ISAAC brand data loggers. Fuel consumption data were downloaded periodically by 

AZD personnel and transmitted to NREL. These data were not inclusive of all study 

vehicles for all study months; they were intended merely as a spot check of methods 1 

and 2.

This overlap and cross-indexing will allow for higher confidence in in-use fuel economy 

calculations. 

3.5 Vehicle Maintenance and Data Collection

Scheduled and unscheduled maintenance is performed by FedEx Express personnel at the POC 

depot. Preventive maintenance is conducted in accordance with the California requirement of 90-

day intervals, and the scope is identical for gHEV and diesel trucks. 

Repair orders in the form of labor hours and parts costs are cataloged by American Trucking 

Association code and are captured electronically. Evaluation truck repair orders were transmitted 

electronically to NREL by FedEx Express, reviewed for accuracy, and analyzed for a 

maintenance cost per mile comparison of the gHEV and diesel groups. Because several vehicle 

systems differ between gHEV and diesel groups, or because the common systems may 

experience different operating conditions, specific maintenance cost per mile figures are

calculated and reported for each of these systems. 

These systems and specific components of interest include:

• Vehicle systems

o Engine

o Hybrid propulsion system

o Brakes

• Vehicle components

o Brake rotors, pads

o Spark plugs

o Exhaust aftertreatment (three-way catalyst and diesel particulate filter)
9

3.5.1 Vehicle Warranty Repairs

Data on warranty repairs are collected in a similar manner to data on normal maintenance 

actions. However, the warranty cost data are not included in the operating cost calculation. Labor 

costs may be included depending on the mechanic (operator or manufacturer) and on whether 

those hours were reimbursed under the warranty agreement. (Warranty maintenance information 

is collected primarily for an indication of reliability and durability.)

The MY2006 diesel trucks and pre-production gHEVs were under warranty during the 

evaluation period.

3.6 Vehicle Uptime

gHEV availability or uptime is tracked by AZD and reported to FedEx Express in a weekly, 

monthly, and quarterly format. AZD included NREL in the distribution of this reporting metric. 

Diesel evaluation truck availability data were transmitted electronically to NREL by FedEx 

Express, reviewed for accuracy, and analyzed for comparison of the gHEV and diesel vehicle 

groups. 

4 Results

4.1 Laboratory Vehicle Emissions and Fuel Economy Measurement

A detailed description of experimental setup, vehicle coast down curves, test fuels (California 

certification gasoline and diesel), tested drive cycles, and gHEV battery state of charge 

considerations are included in the appendix. It is worthwhile to note two things related to the 

drive cycles tested. First, the NYCC drive cycle is relatively short, so to collect adequate 

particulate matter (PM) mass this cycle was run three times in sequence. Second, reported results 

for the HTUF4 cycle are specific to an NREL modification of the HTUF Class 4 PDDS drive 

cycle. The HTUF Class 4 PDDS drive cycle has three distinct phases totaling 55 minutes in 

duration. Due to scheduling and cost constraints, this cycle was shortened to include only phases 

1 and 3 and was designated HTUF4. These modifications to HTUF4 are detailed in the appendix.

4.1.1 Vehicle Emissions Comparison

A summary of results is presented in Table 5. Distilled results and discussion are provided in the 

subsections below.

Table 5. Summary of Emissions Results

Drive 

Cycle Vehicle NOx(g/mile)

CO

(g/mile)

THC

(g/mile)

PM

(g/mile)

NYCC gHEV 3.24 0.84 NDa 0.0016

Diesel 12.70 7.60 0.80 0.7930

OC Bus gHEV 1.05 0.29 NDa 0.0004

Diesel 7.60 2.90 0.60 0.3000

HTUF4 gHEV 0.57 1.03 0.04 0.0006

Diesel 5.20 2.50 0.40 0.2820

a Measured below laboratory detection limit. Note error bars in Figure 4.
10

As expected, tailpipe emissions were considerably lower across all drive cycles for the gHEV 

than for the diesel vehicle. This hybridized, gasoline-fueled vehicle is equipped with a three-way 

catalyst, which results in very low tailpipe gaseous emissions. The diesel baseline vehicle was 

not equipped with a diesel particulate filter. For this project, precise measurement of nitrogen 

oxides (NOx) and PM were essential. The laboratory dilution ratio was calibrated to optimize 

NOx measurement precision at the expense of some hydrocarbon analyzer precision in measuring 

carbon monoxide (CO) and total hydrocarbons (THC). Thus, there is higher variability in the CO 

and THC data than would otherwise occur. Criteria emissions reductions are presented in Table 

6.

Table 6. gHEV Criteria Emissions Reductions by Drive Cycle

Drive Cycle gHEV Emissions Reductions (%)

NOx CO THC PM

NYCC 74.5 88.9 100 99.8

OC Bus 86.2 90.0 100 99.9

HTUF4 89.0 58.6 89.9 99.8

Figure 4 visually illustrates the emissions reductions realized with the gHEV. Furthermore, the 

relationship between drive cycle kinetic intensity and tailpipe emissions is demonstrated. With 

decreasing kinetic intensity, characterized by fewer stops and accelerations per mile, tailpipe 

emissions are typically lower.

Figure 4. Criteria emissions by drive cycle
11

4.1.2 Vehicle Fuel Economy Comparison

To allow for normalization of volumetric fuel economy, NREL measured the energy content of 

both gasoline (42,372 J/g) and diesel (46,048 J/g) fuels. Volumetric fuel economy was measured 

for each vehicle over three drive cycles. These results, as well as the normalized gHEV fuel 

economy advantage by drive cycle, are presented in Table 7 and Figure 5.

Table 7. gHEV Fuel Economy Comparison by Drive Cycle

Drive Cycle gHEV Fuel 

Economy

gHEV Diesel 

Equivalent Fuel 

Economy

Diesel Fuel 

Economy

gHEV 

Advantage

(diesel equivalent 

basis)

(mpg) (mpg) (mpg) (%)

NYCC 6.75 7.34 6.08 20.6

OC Bus 8.61 9.36 9.52 -1.7

HTUF4 10.45 11.36 11.66 -2.6

Figure 5. Influence of route kinetic intensity on fuel economy
12

The gHEV is statistically equivalent to the diesel vehicle with respect to normalized fuel 

economy for the HTUF4 and OC Bus test cycles. While there is slight overlap in fuel economy 

error bars for the NYCC test cycle, the average fuel economy difference between gHEV and 

diesel is more pronounced. While the hybrid electric element imparts higher efficiency, this 

advantage is offset in part by the lower liquid fuel energy content (gasoline compared with 

diesel) and lower thermal efficiency (spark ignition compared with compression ignition). The 

NYCC drive cycle exhibits the highest kinetic intensity, characterized by many acceleration and 

deceleration events. gHEV acceleration demands are shared by the gasoline engine, the battery,

and the electric motor, while the diesel vehicle relies solely on its diesel engine. The electric 

power train is a higher-efficiency option for these transient events. gHEV deceleration events 

allow for the recapture of energy via regenerative braking, while this energy is unrecoverable 

and lost by the diesel vehicle. For these reasons, high kinetic-intensity drive cycles are a better 

application for gHEVs than for diesel vehicles.

These results highlight the need to match the most appropriate drive cycles to hybrid power train 

vehicles. Drive cycles with higher kinetic intensity are better candidates for hybrid vehicle 

application due to the improved fuel economy. In addition, route distance and daily VMT are 

important metrics to consider in order to maximize hybrid vehicle return on investment.

4.2 In-Use Fuel Economy and Costs

In-use fuel data were collected via retail fuel data supplied by FedEx Express and via on-board 

fuel logs completed by vehicle drivers and faxed to NREL. Due to occasional gaps in on-board 

fuel log data, the more comprehensive retail fuel data set was analyzed. Fuel data for the study 

period are presented below (Table 8, Figure 6, Figure 7). There is no statistically significant 

difference (two-tailed P value of 0.45) in diesel equivalent fuel economy values for the gHEV 

and diesel groups.

Table 8. Fuel Economy and Costs from Retail Fueling Records

Vehicle 

Type Asset # Start Date

End 

Date Miles

Fuel 

Volume 

(gallons)

Fuel 

Economy 

(mpg)

Diesel 

Equivalent 

FE (mpg)

Fuel 

Cost

($)a

Fuel Cost 

per Mile

($/mile)

gHEV

H292 04/21/09 04/12/10 10,693 1,540.8 6.94 7.54 4,468 0.42

H294 04/21/09 04/14/10 11,843 1,744.7 6.79 7.38 5,119 0.43

H295 04/23/09 04/22/10 7,214 1,001.5 7.20 7.83 3,010 0.42

Total 29,750 4,287.0 6.94 7.54 12,597 0.42

Diesel

D670 04/21/09 04/23/10 13,099 1,822.43 7.19 7.19 5,254 0.40

D830 04/22/09 04/26/10 11,344 1,321.50 8.58 8.58 3,893 0.34

D896 04/28/09 04/26/10 11,124 1,350.82 8.23 8.23 3,899 0.35

Total 35,567 4,494.8 7.91 7.91 13,046 0.37

a Average fuel costs for the study vehicles during the study period were $2.94/gallon (gasoline) and $2.90/gallon 

(diesel). 
13

Figure 6. Fuel economy results

Figure 7. Fuel and fuel cost per mile results

-

1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

H292 H294 H295 D670 D830 D896

gHEV Diesel

Miles per Gallon

Miles Fuel (gallons) FE (mpg)

-

0.05 

0.10 

0.15 

0.20 

0.25 

0.30 

0.35 

0.40 

0.45 

0.50 

-

1,000 

2,000 

3,000 

4,000 

5,000 

6,000 

H292 H294 H295 D670 D830 D896

gHEV Diesel

$/mile

Fuel (gallons) Fuel Cost ($) Fuel cost/mile
14

AZD personnel downloaded CAN data from the ISAAC data loggers during scheduled visits to 

POC. These data, consisting of distance traveled and fuel consumed since the last download, 

were collected from the gHEVs during the first 6 months of the study period. Table 9 compares 

fuel economy values calculated using the ISAAC data with values calculated using retail fuel 

logs during the same 6-month period. AZD reports a ± 3% error in CAN-derived fuel 

consumption during simultaneous chassis dynamometer testing. A similar difference between 

CAN-derived and in-use data is shown in the table. The relatively small difference between these 

types of data imparts confidence to the retail fuel log-derived fuel economy results.

Table 9. CAN Fuel Economy Results

Vehicle 

Type

Asset 

#

Start 

Date

End 

Date

CAN 

Miles

CAN Fuel 

Volume 

(gallons)

CAN 

FE 

(mpg)

Retail 

Fuel Log 

FE

(mpg)

% 

Difference

gHEV

H292 04/22/09 09/03/09 4,507 650.0 6.93 6.78 2.2%

H294 04/22/09 09/03/09 3,180 423.3 7.51 7.29 3.0%

H295 04/22/09 09/03/09 2,410 345.8 6.97 6.78 2.7%

4.3 Maintenance Costs

Maintenance costs and maintenance costs per mile driven can be a function of vehicle age. Table 

10 presents the odometer readings of the study vehicles at the beginning and at the end of this 

study period. 

Table 10. Relative Ages of Study Vehicles

Vehicle Type Asset # Start Miles End Miles

gHEV

H292 10,807 21,500

H294 11,190 23,033

H295 7,868 15,082

Average 9,955 19,872

Diesel

D670 37,643 50,742

D830 40,130 51,474

D896 42,245 53,369

Average 40,006 51,862

The diesel group is generally older and has been driven farther than the gHEV group, which 

suggests that maintenance costs could be higher. These diesel vehicles were chosen for the study 

because they were the newest comparable vehicles available from this fleet at the time of the 

study. However, the gHEV group represents a new technology, and additional maintenance 

procedures and/or lack of familiarity on the part of the maintenance personnel could lead to 

higher maintenance costs. Regardless, in their current usage pattern of approximately 10,000 

miles/year per vehicle, the diesel vehicles are on average three truck-years older than the gHEVs. 
15

In-use maintenance data were supplied by FedEx Express and transmitted to NREL for analysis. 

NREL removed warranty items and associated costs from this comparison. During the study 

period, the gHEVs had labor and parts warranted, while the diesel vehicles did not. Had warranty 

costs been included, the total gHEV maintenance costs for the study period would have been 

$6,815, or $0.229/mile. Maintenance data for the study period are presented below (Figure 8 and 

Table 11). There is no statistically significant difference (two-tailed P value of 0.637) in 

maintenance cost per mile between the gHEV and diesel groups.

Figure 8. Total maintenance cost and maintenance cost per mile results 

$-

$0.05 

$0.10 

$0.15 

$0.20 

$0.25 

$0.30 

0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

H292 H294 H295 D670 D830 D896

gHEV Diesel

Miles Maintenance cost ($) Maintenance cost/mile
16

Table 11. Maintenance Costs by System

ATA Code(s) Description

gHEV Diesel

Total Cost 

($)

Cost per Mile 

($/mile)

Total Cost 

($)

Cost per Mile 

($/mile)

000 Preventive 

Maintenance 1,416.37 0.048 2,580.71 0.073

001

Air 

Conditioning, 

Heating, and 

Ventilation

258.46 0.023 71.67 0.002

002 Cab 274.22 0.009 328.88 0.009

003

Instruments, 

Gauges, 

Meters

82.26 0.003 246.01 0.007

013 Brakes - - 220.04 0.006

014 Frame 46.28 0.002 - -

017 Tires 1,520.25 0.051 1,458.70 0.041

031, 032 Charging 

System 127.30 0.007 442.12 0.012

034 Lighting 

System 151.37 0.005 27.43 0.001

035 Multi-Function 

Electronic 67.03 0.002 491.94 0.014

041 Air Intake 

System - - 35.69 0.001

042 Cooling

System - 0.002 360.63 0.010

043 Exhaust 51.79 0.002 81.52 0.002

044 Fuel System - - 830.20 0.023

045 Power Plant 30.46 0.001 54.84 0.002

048

Electric 

Propulsion 

System

252.88 0.012 - -

053 Expendable 

Items 613.03 0.021 18.28 0.001

066, 071, 072 Body, Doors 524.54 0.018 202.57 0.006

075 Manholes 18.28 0.001 - -

078 Trim 70.88 0.002 - -

092

Bulk Product 

Transfer 

(Compressor)

- - 9.14 0.000

102 Special Body 

Codes 161.48 0.005 109.69 0.003

153 Misc. Shop 

Supplies 107.26 0.004 169.71 0.005

156 Back-Up 

Camera 362.12 0.012 193.61 0.005

Total 6,136.26 0.206 7,933.38 0.223
17

Maintenance costs are dominated by preventive maintenance activities and tire replacements 

(Figure 9 and Figure 10). These two dominant maintenance categories are removed in Figure 11, 

allowing for better visualization of lower-tier maintenance costs for each study group.

Figure 9. gHEV maintenance costs by system

Figure 10. Diesel maintenance costs by system
18

Figure 11. Lower-tier maintenance costs per mile by system

Upon examination of Figure 11, there are several obvious differences between the gHEV and 

diesel groups. Some of them (air conditioning and heating, ventilation and cooling, body, 

lighting, and various expendable items used to engineer solutions to minor problems) are likely 

due to “shakedown” activities when integrating the pre-production gHEVs. Key vehicle systems 

for comparison are the electric propulsion system, exhaust, power plant, brakes, and fuel system; 

these systems exhibit design or usage differences between the study groups.

During the study period, there were records of electric propulsion system maintenance for each 

of the gHEVs. This non-warranty maintenance was limited to inspections and road tests. 

Warranty events involving the electric propulsion systems are discussed in Section 4.3.1 below.

During the study period, no brake repairs were performed on the hybrid vehicles; this was an 

expected result due to their low mileage and regenerative braking capability. Diesel trucks D670 

and D830 had two-wheel brake replacements during the study period, for a total cost of $220.04. 

FedEx Express examines brakes every time preventive maintenance is performed and replaces 

them as necessary. Quantifying any differences in brake maintenance costs between the gHEV 

and diesel vehicle groups may require a study period in excess of 12 months. At the time of this 

study, FedEx Express did not provide a brake life metric for their W700 fleet.
19

Exhaust and power plant system maintenance cost differences between the two groups were 

insignificant during the study period. The diesel group exhibited a higher fuel system cost per 

mile. Vehicle D896 had on-road fuel system problems, requiring a tow, fuel-water separator 

maintenance, and fuel tank cleaning, which totaled $821.06. The diesel group exhibited a higher 

multifunction electronic/electric system cost per mile. Vehicle D896 had two incidents in five 

days during December 2009; each required an inspection and tow, which totaled $491.94. No 

additional information was available in the FedEx Express maintenance data provided. The 

diesel group also exhibited a higher cooling system cost per mile. Vehicle D830 experienced a 

cracked radiator, and required a tow and radiator replacement.

4.3.1 Vehicle Warranty Repairs

There were several warranty repairs for the gHEVs during the study period and none for the 

diesel group. These warranty repairs were mainly related to the heating, ventilating, and air 

conditioning; cooling; and electric propulsion systems. The electric propulsion system repairs 

included a campaign to replace the 200A traction battery fuses in each gHEV and the 

replacement of the integrated starter generator and digital motor operational controller in vehicle 

H295. These warranty repairs with associated costs (reimbursed by AZD) are summarized in 

Table 12. 
20

Table 12. Vehicle Warranty Repairs

Asset 

# Mileage System Assembly Part Item Description Warranted Cost ($)

H292 11,334 001 001 049 Valve Assembly

Expansion 

Inspection 18.28

H292 11,596 031 000 000 Charging System Inspection 36.56

H292 11,596 031 001 000 Generator/Alternator

Other 

Maintenance 6.09

H292 11,596 031 001 000 Generator/Alternator

Other 

Maintenance 24.37

H292 11,596 032 000 000 Cranking System Inspection 9.14

H292 11,858 048 001 000 Power Train Assembly

Hybrid 

Exchange New 36.56

H292 11,858 048 001 000 Power Train Assembly

Hybrid Burned 

Out –

H292 18,280 042 004 031

Pulley - Idler, Water 

Pump Inspection 15.23

H294 19,597 042 004 031

Pulley - Idler, Water 

Pump Inspection 15.23

H294 20,036 048 001 000

Power Train Assembly -

Hybrid Exchange New 18.28

H294 20,036 048 001 000

Power Train Assembly -

Hybrid Burned Out –

H294 20,036 048 001 000

Power Train Assembly -

Hybrid Road-Test 12.19

H294 20,101 048 000 000 Hybrid Power Train Exchange New 45.70

H294 20,101 048 000 000 Hybrid Power Train Worn –

H294 20,911 001 001 052 Core - Evaporator Exchange New 48.75

H294 20,911 001 001 000

Air Conditioning 

Assembly

Other 

Maintenance 42.65

H294 20,911 001 001 000

Air Conditioning 

Assembly

Other 

Maintenance 67.03

H294 20,911 001 001 052 Core - Evaporator Broken 176.55

H294 20,911 001 001 049

Valve Assembly -

Expansion

Standard 

Practice 29.44

H294 20,911 001 001 065

Receiver - Dehydrator 

Assembly

Standard 

Practice 36.00

H294 20,911 053 999 021

Refrigerant - Air 

Conditioner

Standard 

Practice 13.00

H294 20,911 153 997 000 Misc. Shop Supplies

Standard 

Practice 12.75

H295 12,161 042 004 031

Pulley - Idler, Water 

Pump Inspection 15.23

Total 679.03

4.4 Total Operating Costs

Total operating costs include fuel and maintenance costs. These costs for the study period are 

summarized and presented in Table 13 and Figure 12. 
21

Table 13. Total Operating Costs 

Vehicle 

Type Asset # Miles Fuel Cost ($) 

Maintenance 

Cost 

($) 

Total 

Operating 

Cost ($) 

Total Operating 

Cost per Mile 

($/Mile) 

gHEV 

H292 10,693 4,468 1,451 5,919 0.55 

H294 11,843 5,119 3,065 8,218 0.69 

H295 7,214 3,010 1,620 4,630 0.64 

Total 29,750 12,597 6,136 18,767 0.63 

Diesel 

D670 13,099 5,254 2,422 7,676 0.59 

D830 11,344 3,893 2,386 6,279 0.55 

D896 11,124 3,899 3,126 7,024 0.63 

Total 35,567 13,046 7,933 20,979 0.59 

Figure 12. Total operating costs

4.5 Vehicle Uptime 

Vehicle uptime is calculated as: 

ሿ݅ܿ݁ݒݎܵ݁ ݂݋ ݐݑܱ ݏݕܽܦ ݈ܽ݊݊݁݀݌ܷ݊ ൅ ݅ܿ݁ݒݎܵ݁ ݅݊ ݏݕܽܦሾ/ሿ݅ܿ݁ݒݎܵ݁ ݅݊ ݏݕܽܦሾ

Vehicle and study group uptime percentages for the study period are presented in Table 14 and 

Figure 13 and represent both warranty and non-warranty related maintenance. The uptime goal 

of 98% is shown as a red dashed line in Figure 13. 

-

0.10 

0.20 

0.30 

0.40 

0.50 

0.60 

0.70 

0.80 

0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

H292 H294 H295 D670 D830 D896

gHEV Diesel

Miles Fuel Cost ($)

Maintenance cost ($) Fuel cost/mile

Maintenance cost/mile Total Operating cost/mile
22

Table 14. Vehicle Uptime

Vehicle 

Type Asset #

Unplanned 

Days Out of 

Service

Total Days

in Period

Days in 

Service Uptime %

gHEV

H292 4 366 362 98.9

H294 23 366 343 93.7

H295 19 366 347 94.8

Total 46 1098 1052 95.8

Diesel

D670 3 366 363 99.2

D830 5 366 361 98.6

D896 10 366 356 97.3

Total 18 1098 1080 98.4

Figure 13. Vehicle uptime

It is important to note that only four of the 46 unplanned days out of service for the gHEVs were 

related to hybrid propulsion system-related maintenance issues. These four days were specific to 

vehicle number H295, due to the replacement of an integrated starter generator and digital motor 

operational controller. Thus, the vehicle uptime related to hybrid system performance was 

99.6%. 

90%

92%

94%

96%

98%

100%

H292 H294 H295 Total D670 D830 D896 Total

gHEV Diesel
23

5 Summary

A robust drive cycle data collection and analysis effort framed the selection of study vehicles and 

routes and provided the data to accurately select test cycles for the measurement of vehicle 

emissions and fuel economy on the chassis dynamometer at NREL’s ReFUEL laboratory. The 

testing completed on the chassis dynamometer proved to be an accurate assessment of the range 

of fuel economy that could be expected during on-road operation, as the 12-month, on-road fuel 

economy averages were shown to fall within the tested range documented in the lab. Realizing 

the primary goal of this gHEV deployment in the FedEx Express fleet, tailpipe emissions from 

the tested gHEV were proven to be substantially lower across all tested drive cycles than 

emissions from the diesel baseline vehicle. Fuel economy results observed both in the lab and on 

the road were similar between the gHEV and the diesel vehicle, except for the highest kinetic 

intensity drive cycle tested in the laboratory, where the hybrid exhibited ~20% higher fuel 

economy. These results highlight the need to match the most appropriate drive cycles to hybrid 

power train vehicles. As observed, drive cycles with higher kinetic intensity are better candidates 

for hybrid vehicle application due to the improved fuel economy. In addition, route distance and 

daily VMT are important metrics to consider in order to maximize hybrid vehicle return on 

investment.

Based upon the data collected during this study, there was no statistically significant difference 

in fuel cost per mile or maintenance cost per mile between the gHEV and diesel groups. As a 

result, there was no statistically significant difference in total operating cost per mile between the 

gHEV and diesel groups. 

The gHEVs experienced a smooth integration and deployment into commercial service. During 

the study period, the gHEVs performed well, experienced a minimum of unscheduled 

maintenance, and met the expectations of FedEx Express. 
24

Acknowledgments

The author wishes to thank Lee Slezak, U.S. Department of Energy Vehicle Technologies 

Program, for his financial support in conducting this project. Partial funding for this project was 

provided by CALSTART via the SCAQMD. In addition, the author wishes to recognize the 

valued and significant contributions of the following individuals:

• Sam Snyder, Cathy Thomas, Raul Diosdado, Doug Evans, Ralph Hemrick, Raquel 

Moreno – FedEx Express

• Jim Mancuso, Dave Alef – Azure Dynamics, Inc.

• Jeff Cox – South Coast Air Quality Management District

• Jasna Tomic – CALSTART

• Adam Duran, John Ireland, Robert Moore, Kevin Walkowicz, Scott Walters – NREL
25

Appendix: ReFUEL Test Report

This appendix provides additional information related to the ReFUEL Laboratory capabilities 

and experimental setup. 
26

PROJECT SUMMARY REPORT 

Dynamometer Testing of FedEx Express Fleet Hybrid Electric 

Vehicle

October 2, 2009

ReFUEL Laboratory

National Renewable Energy Laboratory

1980 31st Street

Denver, CO 80216

Test Participants:

Name Organization

John Ireland ReFUEL Lab, NREL

Dan Pedersen ReFUEL Lab, NREL

Aaron Williams ReFUEL Lab, NREL

Robb Barnitt ReFUEL Lab, NREL

Kevin Walkowicz ReFUEL Lab, NREL

Jasna Tomic CALSTART

Sam Snyder FedEx Express
27

Objectives

This work comprises chassis dynamometer testing of two medium-duty FedEx Express delivery 

vehicles, a gasoline hybrid electric vehicle (GHEV) and a conventional diesel (baseline) vehicle. 

Testing was performed to compare the benefits of the GHEV with the baseline vehicle as well as 

to gather data for model validation, with the primary focus on fuel economy. The remainder of 

this report serves to describe the experimental setup, outline the test procedures, present the data, 

and summarize the results from dynamometer testing of each vehicle.

General Lab Description and Methods

The vehicles were tested at the ReFUEL laboratory, operated by NREL and located in Denver, 

Colorado. The lab includes a heavy-duty vehicle (chassis) test cell and an engine dynamometer 

test cell with emissions measurement capability. The laboratory is designed for the challenge of 

measuring a variety of engines and vehicles with a range of emissions levels. Regulated 

emissions measurements are performed using procedures consistent with the Code of Federal 

Regulations applicable to heavy-duty engine certification for 2007. Extensive data acquisition 

and combustion analysis equipment can be used to relate the effects of different fuel properties 

and engine settings to performance and emissions. Other capabilities of the laboratory include 

power analyzer equipment to perform hybrid-electric research, systems for sampling and 

analyzing unregulated emissions, on-site fuel storage and fuel blending equipment, high-speed 

data acquisition hardware and software to support in-cylinder measurements, altitude simulation 

system, and fuel ignition quality testing. Instrumentation and sensors at the laboratory are 

maintained with NIST-traceable calibration.

Chassis Dynamometer

The ReFUEL Chassis Dynamometer is installed in the main high-bay area of the laboratory. The 

roll-up door to the high bay is 14 ft x 14 ft, high enough to accept all highway-ready vehicles 

without modification. The dynamometer is installed in a pit below the ground level, such that the 

only exposed part of the dynamometer is the top of the 40-in. diameter rolls. Two sets of rolls are 

used so that twin-axle tractors can be tested. The distance between the rolls can be varied 

between 42 in. and 56 in. The dynamometer will accommodate vehicles with a wheelbase 

between 89 in. and 293 in. The dynamometer can simulate up to 80,000 lb vehicles at speeds up 

to 60 mph. 

The chassis dynamometer is composed of three major components: the rolls, which are in direct 

contact with the vehicle tires during testing; the direct current (DC) electric motor (380 hp 

absorbing/360 hp motoring) dynamometer; and the flywheels. 

The rolls are the means by which power is absorbed from the vehicle. The rolls are attached to 

gearboxes that increase the speed of the central shaft by a factor of 5. The flywheels, mounted on 

the back of the dynamometer, provide a mechanical simulation of the vehicle inertia. 

The electric motor is mounted on trunnion bearings and therefore is used to measure the shaft 

torque from the rolls. The absorption capability of the dynamometer is used to apply the “road 

load,” which is a summation of the aerodynamic drag and friction losses that the vehicle 

experiences in use, as a function of speed. The road load may be determined experimentally, if 
28

data are available, or estimated from standard equations. The electric dynamometer is also used 

to adjust the simulated inertia, either higher or lower than the 31,000-lb base dynamometer 

inertia, as the test plan requires. The inertia simulation range of the chassis dynamometer is 

8,000–80,000 lb. The electric motor may also be used to simulate grades and provide braking 

assist during decelerations. 

The truck is secured with the drive axles over the rolls. A driver’s aid monitor in the cab is used 

to guide the vehicle operator in driving the test trace. A large fan cools the vehicle radiator 

during testing. The chassis dynamometer is supported by 72 channels of data acquisition in 

addition to the emissions measurement, fuel metering, and combustion analysis subsystems. 

The dynamometer is capable of simulating vehicle inertia and road load during drive cycle 

testing. With the vehicle jacked up off of the rolls, an automated dynamometer warm-up 

procedure is performed daily, prior to testing, to ensure that parasitic losses in the dynamometer 

and gearboxes have stabilized at the appropriate level to provide repeatable loading. An unloaded 

coast down procedure is also conducted to confirm that inertia and road load is being simulated 

by the dynamometer control system accurately.

Figure A-1. Chassis dynamometer schematic

Fuel Storage and Blending

Buildings designed specifically for safely storing and handling fuels are installed at the ReFUEL 

facility. The fuel storage shed is 8 ft x 26 ft and holds 48 drums (55 gal each). Features include 

heating/cooling, secondary containment to 25% of its capacity, continuous ventilation, 

explosion-proof wiring/lighting, and a dry chemical fire suppression system. 

The fuel blending shed is 8 ft x 14 ft, and it has a nominal storage capacity of 24 drums. It has all 

of the features of the storage shed, with the addition of an explosion-proof electrical outlet for 

powering accessories. The fuel blending may be performed on a gravimetric or a volumetric 

basis and may involve both large-scale (L/kg) and small-scale (cc/g) measurements. A fuel line 

inside of a sealed conduit delivers the fuel from the supply drum to the fuel 

metering/conditioning system inside the ReFUEL laboratory, eliminating the need for bulk fuel 

storage inside the laboratory. Another fuel line in the same conduit delivers waste fuel back to 

the fuel blending shed for storage (waste fuel is generated only when a fuel changeover requires 

a flush of the system). 
29

Fuel Metering & Conditioning

The fuel metering and conditioning system supports both engine and chassis dynamometers. The 

meter measures volumetric flow to an accuracy of +/- 0.5% of the reading, with a reproducibility 

of 0.2%. A sensor measures the density at an accuracy of +/- 0.001 g/cc, allowing an accurate 

mass measurement in real time even if the density of the fuel blend is not known prior to testing. 

Figure A-2. Pierburg fuel metering system

Air Handling & Conditioning

Dilution air and the air supplied to the engine or vehicle for combustion are derived from a 

common source, a roof-mounted system that conditions the temperature of the air and humidifies 

as needed to meet desired specifications. This air is then passed through a HEPA filter, in 

accordance with the (2007) CFR specifications, to eliminate background particulate matter as a 

source of uncertainty in measurements. 

Engine intake air flow is metered with a Laminar Flow Element (LFE) that measures air flow to 

within +/- 0.72% of reading. Inlet and exhaust restrictions can be adjusted with inline valves to 

meet manufacturers’ specifications or testing requirements.

Emissions Measurement

The ReFUEL laboratory’s emissions measurement system supports both the chassis and engine 

dynamometers. It is based on the full-scale dilution tunnel method with a Constant Volume 

Sampling (CVS) system for mass flow measurement. The system is designed to comply with the 

requirements of the 2007 Code of Federal Regulations, title 40, part 86, subpart N. Exhaust from 

the engine or vehicle flows through insulated piping to the full-scale 18-in. diameter stainless 

steel dilution tunnel. A static mixer ensures thorough mixing of exhaust with conditioned, 

filtered, dilution air prior to sampling of the dilute exhaust stream to measure gaseous and 

particulate emissions.

A system with three Venturi nozzles is employed to maximize the flexibility of the emissions 

measurement system. Featuring 500 cfm, 1,000 cfm, and 1,500 cfm Venturi nozzles and gastight valves, the system flow can be varied from 500 cfm to 3,000 cfm flow rates in 500 cfm 

increments. This allows the dilution level to be tailored to the engine size being tested (whether 

on the engine stand or in a vehicle), maximizing the accuracy of the emissions measurement 

equipment. 
30

Figure A-3. Venturi nozzles

The gaseous emissions bench is a Pierburg model AMA-2000. It features continuous analyzers 

for total hydrocarbons (HC), oxides of nitrogen (NOx), carbon monoxide (CO), carbon dioxide 

(CO2), and oxygen (O2). The system features auto-ranging, automated calibration, zero check, 

and span check features as well as integrating functions for calculating cycle emissions. It 

communicates with the ReFUEL data acquisition systems through a serial interface. There are 

two sample trains for gaseous emissions measurement: one for HC/NOx and another for the other 

gaseous emissions. The HC and NOx sample train is heated to prevent sample loss and water 

condensation. Both sample probes are in the same plane of the dilution tunnel. 

Figure A-4. Gaseous and PM sampling benches

The particulate matter sample control bench is managed by the ReFUEL data acquisition system 

through a serial connection. It maintains a desired sample flow rate through the particulate matter 

(PM) filters in proportion to the overall CVS flow, in accordance with the CFR. Stainless steel 

filter holders, designed to the 2007 CFR requirements, house 47-mm diameter Teflon membrane 

filters through which the dilute exhaust sample flows. The PM sampling system is capable of 

drawing a sample directly from the large full-scale dilution tunnel or utilizing secondary dilution 

to achieve desired temperature, flow, and concentration characteristics. A cyclone separator, as 
31

described in the CFR requirements, may be employed for ultra-clean vehicles equipped with PM 

aftertreatment.

A dedicated clean room/environmental chamber is installed inside the ReFUEL facility. It is a 

Class 1000 clean room with precise control over the temperature and humidity (+/- 1°C for 

temperature and dew point). This room is used for all filter handling, conditioning, and weighing.

The microbalance for weighing PM filters features a readability of 0.1 μg (a CFR requirement) 

and features static control, a barcode reader for filter identification and tracking, and a computer 

interface for data acquisition. The microbalance is installed on a specially designed table to 

eliminate variation in the measurement due to vibration. The microbalance manufacturer 

(Sartorius) was consulted on the design of the clean room to ensure that the room air flow would 

be compatible with the microbalance. 

Figure A-5. Class 1000 clean room, filter housing, and microbalance 

Project Specific Setup and Methods

The test vehicles were installed on the chassis dynamometer as shown in Figure A-6. A process 

and instrumentation diagram of the test setup is included in Appendix A along with detailed 

information regarding sensor description and placement. All sensors shown were monitored and 

recorded continuously by the ReFUEL data acquisition system throughout each test cycle run, 

unless otherwise noted. Additional data from the engine control unit, including state of charge 

details for the HEV, were also recorded using a data logger connected via CAN interface. 
32

Figure A-6. Chassis cell with test vehicle

Test Vehicles

The hybrid electric and baseline vehicles were both tested for fuel economy and emissions on the 

chassis dynamometer. The baseline vehicle incorporated a 5.9 Liter, 6 cylinder diesel engine. 

The hybrid vehicle featured a 5.4 Liter, V8 gasoline engine with a 100 kW electric motor. Other 

vehicle information is outlined in Table A-1. 

Table A-1. Test Vehicle Information

Vehicle Information gHEV Trucks Diesel Trucks

Chassis Manufacturer/Model Ford E-450 Strip. Chassis Freightliner MT-45

Chassis Model Year 2008 2006

Engine Manufacturer/Model Ford 5.4L EFI Triton V-8 Cummins 5.9L ISB 200 I6

Engine Model Year 2008 2006 (EPA 04)

Engine Ratings

Max. Horsepower

Max. Torque

255 HP @ 4,500 RPM

350 lb-ft @ 2,500 RPM

200 HP @ 2,300 RPM

520 lb-ft @ 1,600 RPM

Fuel Capacity 55 Gallon - Gasoline 45 Gallon - Diesel

Transmission Manufacturer/Model Ford 5R110 5-Spd. Auto. Allison 1000 5-Spd. Auto.

Curb Weight (Mfg.) 9,300 lb 9,700 lb

Gross Vehicle Weight Rating 14,050 lb 16,000 lb

Fuel

Tests run on the conventional diesel were run using a California certification diesel. The hybrid 

gasoline vehicle was tested on CARB phase II certification gasoline. Certificates of analysis for 

both fuels are included in Appendix B. The fuel supplied to the engine of each test vehicle was 

conditioned and metered. All fuel measurements for reported fuel economy were from the 

Pierburg fuel meter.

Air and Exhaust

Intake air was conditioned and supplied to each test vehicle by the ReFUEL system with 

continuous recorded measurements of ambient pressure, inlet restriction, air flow rate, humidity, 

and temperature of the inlet air. 
33

Approximately 20 ft of 6-in. diameter, insulated, stainless steel tubing connected the test vehicle 

exhaust pipe to the dilution tunnel, with temperatures measured at the outlet of the vehicle 

exhaust pipe, at the entrance to the dilution tunnel, and at the plane of the emissions sampling 

probes. 

Vehicle Simulation

The simulated vehicle inertia test weight for the conventional vehicle was set at 11,500 lb. The 

11,500-lb test weight was calculated from the vehicle curb weight plus one half of the usual 

FedEx Express payload of 2,000 lb. Since no coast down data for the conventional vehicle was 

available, ReFUEL conducted crude coast down tests locally to compare the two vehicles (see 

Figure A-8b in Appendix C). Note: the coast downs provide by Azure and those taken at 

ReFUEL are not directly comparable due to road surface and grade differences. These data, 

along with previously published coefficients for this vehicle type, were compared to data for 

similar vehicles in the ReFUEL software from previous tests and used to derive the road load 

curve and the following coefficients: 

A = 147.70 lb

B = -1.35 lb/mph

C = 0.100 lb/mph2

.

Simulated test weight for the hybrid vehicle was also curb weight plus 1,000 lb (half of the 2,000 

lb payload). This sum yielded a 10,860 lb test weight for the hybrid vehicle. Coast down data 

was delivered with the vehicle (Appendix C, Figure A-8a) and road load curves were generated 

from this data. The coefficients of the road load curve for the hybrid vehicle are the following: 

A = 198.55 lb

B = -3.9389 lb/mph

C = 0.13690 lb/mph2

.

The appropriate chassis dynamometer road load settings were then derived to simulate the road 

load for both test vehicles on the rolls to match the track data. 

Test Description and Results

Initially, on each test day the chassis dynamometer was run through a standard automated warmup procedure to ensure that dynamometer parasitics had stabilized. Periodic unloaded and loaded 

coast downs were also performed to ensure that inertia and road load were being simulated 

correctly according to the set inputs.

Each vehicle was driven through a variety of test cycles, including repeated hot-start runs: 1) 

New York City Cycle, 2) Orange County Bus, and 3) HTUF Class 4 Parcel Delivery drive cycles 

(shown in Appendix D, figures A-9, A-10, and A-11). Both trucks were keyed off during 

predetermined idle portions of the HTUF Class 4 drive cycle. 

The hybrid electric vehicle (HEV) was tested from April 16–24, 2009. The conventional 

(baseline) vehicle was tested from May 12–18, 2009. Tables A-5 and A-6 in Appendix D 
34

summarize the results for testing both vehicles on the New York City (NYCC X3), Orange 

County Bus, and HTUF Class 4 drive cycles. 

The data demonstrates better fuel economy on the Orange County and HTUF Class 4 cycles for 

the conventional vehicle and a fuel economy penalty on the more aggressive New York City 

Cycle. Due to the hybrid’s gasoline engine with three-way catalyst, NOx and particulate matter 

emissions were significantly lower for the hybrid than for the diesel powered vehicle. These 

values are in comparison to a representative vehicle from the FedEx Express diesel fleet. 

However, it is important to note that diesel vehicles built following the 2007 and 2010 model 

years will have additional emissions equipment and will have significantly lower PM and NOx

emissions, respectively.

State Of Charge Considerations

State of charge was recorded and noted at the start and end of each test drive cycle for the HEV 

runs. The SAE Recommended Practice J2711 is established to provide an accurate, uniform, and 

reproducible procedure for simulating use of heavy-duty hybrid-electric vehicles (HEVs) and 

conventional vehicles on dynamometers for the purpose of measuring emissions and fuel 

economy. The recommended practice provides a description of state of charge (SOC) correction 

for charge-sustaining HEVs.

The basic premise of the procedure is to ensure that fuel economy and emissions data for a 

hybrid-electric vehicle are not unduly increased or decreased due to significant changes in 

energy storage levels over a single drive cycle. The procedure determines the percent change in 

state of charge (or energy storage) over each individual test cycle run. The basis for this is the net 

energy change (change in stored energy) divided by the total energy used during the test cycle

run, calculated from the fuel calorific content. If the percentage is < 1% no correction factor is 

applied; if the percentage is > 5% the results are deemed invalid; and for percentage changes 

between 1% and 5% a correction factor may be applied to provide the corrected figures for fuel 

economy and emissions through basic interpolation. The recommendation is to perform this 

correction if the interpolation relationship can be described by linear regression with an R2 > 0.8.

A current clamp was used to measure current during all cycles at 1 Hz. When the total energy 

was calculated it was found that all cycles had a less than 1% change in the state of charge, so no 

correction was required. All calculations were done per SAE J2711.
35

ReFUEL Test Report Appendix A. Test Cell Instrumentation

Figure A-7. Process and instrumentation diagram
36

Table A-2. Instrumentation List

 
37

ReFUEL Test Report Appendix B. Fuel Analysis

Table A-3. CARB Diesel Fuel Analysis
38

Table A-4. CARB Phase II Gasoline
ReFUEL Test Report Appendix C. Coast Down Data 

Figure A-8a. HEV track coast down curves 

Figure A-8b. Coast down comparison – conducted at ReFUEL 

-20

0

20

40

60

80

100

120

0 50 100 150 200

Vehicle Speed (km/h)

Time (s)

Coastdown Test: Vehicle Speed vs. Time

FWD1

FWD2

FWD3

REV1

REV2

REV3

39
ReFUEL Test Report Appendix D. Test Results 

Figure A-9. NYCC drive cycle 

Figure A-10. Orange County Bus drive cycle 

0

5

10

15

20

25

30

0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560 1680 1800 1920

Speed (mph)

Time (sec)

NYCC X3

-5

0

5

10

15

20

25

30

35

40

45

0 120 240 360 480 600 720 840 960 1080 1200 1320 1440 1560 1680 1800 1920

Speed (mph)

Time (sec)

Orange County Bus

40
Figure A-11. HTUF4 drive cycle 

 

41
42

Table A-5. Conventional Test Results

Date Cycle Run # NOx CO THC CO2 PM

Fuel 

Economy Distance

g/mile g/mile g/mile g/mile g/mile mpg miles

05/13/09 NYCC X3 2056 12.3 7.08 0.94 1430 0.719 6.18 3.55

05/18/09 NYCC X3 2065 13.1 8.01 0.57 1507 0.821 5.93 3.53

05/18/09 NYCC X3 2066 12.6 7.77 0.75 1470 0.839 6.13 3.53

avg 12.7 7.6 0.8 1468.9 0.793 6.08 3.5

stdev 0.42 0.48 0.19 38.92 0.064 0.13 0.01

cov 3% 6% 25% 3% 8% 2.2% 0%

Date Cycle Run # NOx CO THC CO2 PM

Fuel 

Economy Distance

g/mile g/mile g/mile g/mile g/mile mpg miles

05/14/09 OC Bus 2059 7.4 2.87 0.52 956 0.275 9.59 6.57

05/14/09 OC Bus 2060 7.5 3.03 0.60 955 0.319 9.45 6.60

05/14/09 OC Bus 2061 7.8 2.85 0.60 952 0.305 9.53 6.58

avg 7.6 2.9 0.6 954 0.300 9.52 6.6

stdev 0.18 0.10 0.05 2 0.022 0.07 0.02

cov 2% 3% 9% 0% 7% 0.8% 0%

Date Cycle Run # NOx CO THC CO2 PM

Fuel 

Economy Distance

g/mile g/mile g/mile g/mile g/mile mpg miles

05/13/09 HTUF4 2057 5.2 2.38 0.43 759 0.273 11.86 7.34

05/13/09 HTUF4 2058 5.4 2.43 0.40 781 0.292 11.42 7.34

05/13/09 HTUF4 2053 5.1 2.74 0.43 761 N/M 11.68 7.34

avg 5.2 2.5 0.4 767 0.282 11.66 7.3

stdev 0.14 0.20 0.02 13 0.01 0.22 0.00

cov 3% 8% 4% 2% 5% 1.9% 0%
43

Table A-6. Hybrid Test Results

Date Cycle Run # NOx CO THC CO2 PM

Fuel 

Econ Distance SOC

g/mile g/mile g/mile g/mile g/mile mpg miles %

04/22/09 NYCC X3 2037 NM 0.81 NM 1114 N/M 7.03 3.49 -0.64

04/22/09 NYCC X3 2038 3.5 2.25 0.127 1219 0.0016 6.43 3.53 0.96

04/22/09 NYCC X3 2039 3.4 0.16 0.042 1190 0.0017 6.61 3.54 -0.54

04/22/09 NYCC X3 2040 2.8 0.16 0.057 1122 0.0014 6.92 3.51 -0.27

avg 3.2 0.8 0.0 1160.9 0.0016 6.75 3.5

stdev 0.39 0.99 0.21 51.39 0.0002 0.28 0.02

cov 12% 117% -800% 4% 9% 4.1% 1%

Date Cycle Run # NOx CO THC CO2 PM

Fuel 

Econ Distance SOC

g/mile g/mile g/mile g/mile g/mile mpg miles %

04/23/09 OC Bus 2041 1.2 0.29 NM 928 0.0003 8.40 6.54 0.33

04/23/09 OC Bus 2042 0.6 0.17 NM 912 0.0006 8.51 6.49 0.55

04/23/09 OC Bus 2043 1.4 0.41 0.016 872 0.0004 8.92 6.50 -0.47

avg 1.0 0.3 0.0 903.8 0.0004 8.61 6.5

stdev 0.44 0.12 0.08 28.57 0.0002 0.28 0.03

cov 42% 42% -189% 3% 37% 3.2% 0%

Date Cycle Run # NOx CO THC CO2 PM

Fuel 

Econ Distance SOC

g/mile g/mile g/mile g/mile g/mile mpg miles %

04/23/09 HTUF4 2045 0.6 0.58 0.053 770 0.0005 10.22 7.27 0.44

04/23/09 HTUF4 2046 0.5 1.28 0.036 760 0.0008 10.46 7.32 -0.04

04/23/09 HTUF4 2047 0.6 1.24 0.032 745 0.0005 10.66 7.34 -0.25

avg 0.6 1.0 0.0 758.6 0.0006 10.45 7.3

stdev 0.02 0.40 0.01 12.44 0.0002 0.22 0.04

cov 4% 38% 28% 2% 25% 2.1% 0%
F1147-E(10/2008)

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1. REPORT DATE (DD-MM-YYYY)

January 2011

2. REPORT TYPE

Technical Report

3. DATES COVERED (From - To)

4. TITLE AND SUBTITLE

FedEx Express Gasoline Hybrid Electric Delivery Truck Evaluation: 

12-Month Report

5a. CONTRACT NUMBER

DE-AC36-08GO28308

5b. GRANT NUMBER

5c. PROGRAM ELEMENT NUMBER

6. AUTHOR(S)

R. Barnitt

5d. PROJECT NUMBER

NREL/TP-5400-48896

5e. TASK NUMBER

FC08.3000

5f. WORK UNIT NUMBER

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

National Renewable Energy Laboratory

1617 Cole Blvd.

Golden, CO 80401-3393

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REPORT NUMBER

NREL/TP-5400-48896

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National Technical Information Service

U.S. Department of Commerce

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13. SUPPLEMENTARY NOTES

14. ABSTRACT (Maximum 200 Words)

This report summarizes the data obtained in a 12-month comparison of three gasoline hybrid electric delivery 

vehicles with three comparable diesel vehicles. The data show that there was no statistical difference between 

operating cost per mile of the two groups of vehicles. As expected, tailpipe emissions were considerably lower across 

all drive cycles for the gHEV than for the diesel vehicle. 

15. SUBJECT TERMS

Gasoline hybrid electric truck; gHEV; Evaluation; ReFUEL; fuel economy; diesel

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