F U E L C O N S U M P T I O N

CLIMATE CHANGE

e m e r g i n g t e c h n o l o g i e s

t r u c k e m i s s i o n s reducing green house gas emissions

Prepared by:

NESCCAF

Northeast States Center for a Clean Air Future

ICCT 

International Council on Clean Transportation

Southwest Research Institute

TIAX, LLC

R E D U C I N G

Heavy-Duty Long Haul Combination 

Truck Fuel Consumption and CO2

 Emissions

Final Report

October, 2009

i

Prepared by:

NESCCAF

Northeast States Center for a Clean Air Future

ICCT 

International Council on Clean Transportation

Southwest Research Institute

TIAX, LLC

Final Report

October, 2009

R E D U C I N G

Heavy-Duty Long Haul Combination 

Truck Fuel Consumption and CO2

 Emissions

iii

Principal Contributors:

Coralie Cooper, NESCCAF

Fanta Kamakaté, ICCT

Thomas Reinhart, SwRI

Matthew Kromer, TIAX, LLC

Robert Wilson, TIAX, LLC

Editor:

Paul Miller, NESCCAF

Report

R E D U C I N G

Heavy-Duty Long Haul Combination 

Truck Fuel Consumption and CO2

 Emissions
iv

R E D U C I N G Heavy-Duty Long Haul Combination Truck Fuel Consumption and CO2 Emissions

ACKNOWLEDGMENTS

NESCCAF and ICCT gratefully acknowledge the generous support provided by The 

William and Flora Hewlett Foundation, The Energy Foundation, the ClimateWorks 

Foundation, the California Air Resources Board, and the California Energy 

Commission. Their vision and support made this study possible. 

Many people assisted with information during the simulation modeling and cost 

analysis done for this report. We are indebted to the members of the project 

Research Steering Committee - listed on the following page - who provided 

technical advice throughout the study and reviewed the draft final report. We 

owe thanks to additional experts who provided technical input to the study team, 

including Fritz Marinko of the Auto Research Center, Kambiz Salari and Rose 

McCallen of Lawrence Livermore National Laboratory, and Scott McBroom 

formerly of Southwest Research Institute. We would like to acknowledge the work 

of Ashok Nedungadi who conducted the vehicle and hybrid system simulation 

modeling at Southwest Research Institute, and David Branyon and Nicholas Badain 

who were responsible for the engine modeling at Southwest Research Institute. In 

addition, Ray Schubert of TIAX developed costs for the truck technologies in this 

study. We appreciate their contributions.

Finally, a number of people reviewed the draft report and we are indebted to those 

individuals for their advice and comments. We are particularly grateful to the International Council on Clean Transportation participants who have reviewed this 

report and support its findings and recommendations. We also appreciate the advice 

provided by members of the NESCCAF Board who reviewed the draft report and 

provided valuable input.
v

Project Steering Committee Members: 

Bill Van Amburg, Senior Vice President 

WestStart-CALSTART

Don Anair, Senior Analyst 

Union of Concerned Scientists

Steve Antcliff, Director of Public Strategy

Cummins, Inc.

Cheryl Bynum, Group Manager, SmartWay Transport Partnership

U.S. Environmental Protection Agency

Brian Coe, Powertrain Engineering Technical Steward, On Highway Power Systems 

Caterpillar

David Deppe, Principal 

Fuel Technologies

Jack W. Gehring, Director, Global Regulatory Policy, Power Systems

Caterpillar

Daniel Hawelti, On-Road Heavy-Duty Diesel Section

California Air Resources Board

Günter Hörmandinger, Environment Directorate-General, Clean Air & Transport

European Commission

Ken Howden, Director, 21st Century Truck Partnership, Vehicles Technologies Program

U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy

Mitch Greenberg, former Group Manager, SmartWay Transport Partnership

U.S. Environmental Protection Agency

Anthony Greszler, Vice President of Advanced Engineering

Volvo Powertrain North America

Steve Jarosinski,

Schneider National, Inc.

Therese Langer, Transportation Program Manager

American Council for an Energy Efficient Economy

Michael Ogburn,

Energy Engineering

Michael Roeth,

formerly of Navistar International Corporation

Tom Stover,

Eaton Corporation

Luke Tonachel, Vehicles Analyst 

Natural Resources Defense Council

NESCCAF and ICCT Express Our Sincere Appreciation to the 

Project Steering Committee Members
Board of Directors: 

Steven P. Suttle, NESCCAF, Chair

Cormetech, Inc.

Michael J. Bradley

M.J. Bradley & Associates, Inc.

James P. Brooks, Director

Maine Department of Environmental Protection, Bureau of Air Quality Control

Anne Gobin, Director

Connecticut Department of Environmental Protection, Bureau of Air Management

Carolyn L. Green

EnerGreen Capital Management, LLC

Jason Grumet, Executive Director

National Commission on Energy Policy

Christopher J. Hessler

AJW Inc.

John Higgins

New York Department of Environmental Conservation, Division of Air Resources

Adele Hurley

University of Toronto, Munk Centre for International Studies

Timothy V. Johnson

Corning, Inc.

Barbara Kwetz, Director

Massachusetts Department of Environmental Protection, Bureau of Waste Prevention

Professor Morton Lippmann

New York University School of Medicine

Douglas L. McVay

Rhode Island Department of Environmental Management, Office of Air Resources

Professor Mario Molina

University of California, San Diego, Department of Chemistry & Biochemistry

William O’Sullivan

New Jersey Department of Environmental Protection, Division of Air Quality

Robert Scott

New Hampshire Department of Environmental Services, Air Resources Division

Eric Svenson

PSEG

Susan Tierney, Ph.D.

The Analysis Group

Richard Valentinetti, Director

Vermont Department of Environmental Conservation, Air Pollution Control Division

NORTHEAST STATES CENTER FOR A CLEAN AIR FUTURE

vi

R E D U C I N G Heavy-Duty Long Haul Combination Truck Fuel Consumption and CO2 Emissions
vii

INTERNATIONAL COUNCIL ON CLEAN TRANSPORTATION

The goal of the International Council on 

Clean Transportation (ICCT) is to dramatically reduce conventional pollution and 

greenhouse gas emissions from personal, 

public, and goods transportation in order 

to improve air quality and human health, 

and mitigate climate change. The Council 

is made up of leading government officials 

and experts from around the world 

that participate as individuals based on 

their experience with air quality and 

transportation issues.

The ICCT promotes best practices and 

comprehensive solutions to improve vehicle 

emissions and efficiency, increase fuel 

quality and sustainability of alternative 

fuels, reduce pollution from the in-use fleet, 

and curtail emissions from international 

goods movement.

R E D U C I N G

Heavy-Duty Long Haul Combination 

Truck Fuel Consumption and CO2

 Emissions

TABLE OF CONTENTS

ix

TABLE OF CONTENTS

t a b l e o f c o n t e n t s

t a b l e o f c o n t e n t s table of contents

Table of Contents

Acknowledgments.............................................................................................................................. iv

Executive Summary ........................................................................................................................... 1

Introduction ................................................................................................................................... 9

Purpose of the Study .................................................................................................................... 9

The Importance of the Transportation Sector................................................................................. 9

Political and Regulatory Context in the U.S. and Internationally .................................................... 11

 International Context .......................................................................................................... 11

 Climate Change Action by the U.S. Federal Government...................................................... 13

 State Actions to Reduce the Impacts of Climate Change ....................................................... 15

Overview of the Study Method........................................................................................................... 19

Selecting and Defining a Baseline Class 8 Truck ............................................................................ 20

Validating Simulation Modeling Results for the Representative Class 8 Long-Haul Truck ................ 22

 Engine Model...................................................................................................................... 22

 Adjusting the Baseline Engine to 2010 NOx Emissions Requirements ................................... 24

 Vehicle Model ..................................................................................................................... 24

Selecting a Drive Cycle................................................................................................................. 26

Identifying Discrete Vehicle Technology Options for Evaluation ..................................................... 28

 Downselection of Technologies Included in this Analysis ...................................................... 28

 Transmission System Technologies ....................................................................................... 32

 Vehicle Technologies............................................................................................................ 33

 Future Developments in Heavy-Duty Truck Technology........................................................ 38

Assembling Technology Packages for Model Simulation....................................................................... 39

Method of Estimating Cost of Technology Package.............................................................................. 42

Method of Cost-Benefit Analysis......................................................................................................... 44

Fleet-Wide Emissions Benefit Analysis Methodology............................................................................ 46

 Fleet Characterization.......................................................................................................... 46

 Fleet Model Validation ......................................................................................................... 46

 Technology Adoption Methodology ...................................................................................... 47

Results ................................................................................................................................... 49
x Ta b l e o f C o n t e n t s

R E D U C I N G Heavy-Duty Long Haul Combination Truck Fuel Consumption and CO2 Emissions

Overview ................................................................................................................................... 49

Emission and Fuel Consumption Reduction Results....................................................................... 49

CO2 Emission and Fuel Consumption Reduction Potential for Individual Technologies................... 50

Modeled CO2 Emission and Fuel Consumption Reduction Potential Individual Technologies and 

Technology Combinations............................................................................................................. 50

 Package 1 – Baseline Vehicle and Weight Reduction Evaluation ........................................... 50

 Package 2 – 2007 SmartWay Aerodynamic Improvement Plus Wide Base Single Tires........... 51

 Package 3 – Advanced Aerodynamic Drag and Rolling Resistance Improvements .................. 53

 Package 4 – Hybrid Electric System...................................................................................... 53

 Package 5 – Mechanical Turbocompound............................................................................. 54

 Package 6 – Electric Turbocompound................................................................................... 55

 Package 7 – Variable Valve Actuation (VVA)......................................................................... 55

 Package 8 – Bottoming Cycle............................................................................................... 55

 Package 9 – Longer/Heavier Vehicle Combinations.............................................................. 56

 Package 10 – Lower Road Speed.......................................................................................... 60

 Package 11 – Advanced EGR Cooling .................................................................................. 62

Maximum Reduction Combinations.............................................................................................. 63

 Package 12 – Standard Trailer Maximum Technology Combination ...................................... 63

 Package 13 – Longer/Heavier Truck Lower Cost Maximum Technology Combination.......... 64

 Package 14 – Longer/Heavier Truck Higher Cost Maximum Technology Combination ......... 64

Maximum Technology Combination Results ................................................................................. 65

Estimate of Fuel Consumption and Emissions Reduced from Idling Reduction................................ 65

Cost Analysis................................................................................................................................ 66

 Cost Benefit Analysis ........................................................................................................... 68

Fleet-Wide Fuel Consumption and CO2 Emissions Benefit Analysis ............................................... 71 

 Fleet Wide Analysis Assuming 15 Year Payback Requirement................................................ 72

 Fleet Wide Analysis Assuming 3 Year Payback Requirement.................................................. 72

 Fleet Wide Analysis Assuming Maximum Technology Case................................................... 72

Conclusions ................................................................................................................................. 74

APPENDIX A: Description of Heavy-Duty Technologies and Modeling Approach ................................. 77

APPENDIX B: Summary of Incremental Costs for Technology Packages............................................... 95
Ta b l e o f C o n t e n t s xi

APPENDIX C: Detailed Information on TIAX Cost Analysis................................................................. 99

APPENDIX D: Detailed Information on the Fleet Model Analysis ........................................................ 123

APPENDIX E: References................................................................................................................... 131

Figures

Figure 1. Potential Fuel Savings in the U.S. Long Haul Box Trailer Fleet......................................... 7

Figure 2. 2006 U.S. GHG inventory.............................................................................................. 10

Figure 3. Fuel Consumption by Medium and Heavy-duty Vehicle Class.......................................... 11

Figure 4. SmartWayTM equipment standards (US EPA 2008).......................................................... 14

Figure 5. Potential Timeline for a US DOT medium- and heavy-duty fuel economy regulation ........ 15

Figure 6. BSFC Comparison of Simulation Model and Engine Test Data ......................................... 23

Figure 7. Heavy Truck Line-haul Drive Cycle ................................................................................ 27

Figure 8. Grades on Heavy Truck Line-haul Drive Cycle................................................................ 27

Figure 9. 2008 EIA Long-term Energy Outlook Diesel Price Scenarios ........................................... 45

Figure 10. Historical vs. Modeled Fuel Use in U.S. Combination Class 8 Trucks............................. 47

Figure 11. Baseline Vehicle Fuel Economy and Sensitivity to Vehicle Mass..................................... 51

Figure 12. Results From Moderate Drag and Rolling Resistance Reduction..................................... 52

Figure 13. Results From Advanced Drag and Rolling Resistance Reduction..................................... 52

Figure 14. Efficiencies for Longer/Heavier Vehicles Evaluated ....................................................... 57

Figure 15. Results for Longer/Heavier Trucks with Increased Engine Power at Differing Freight 

Densitities ................................................................................................................................... 60

Figure 16. Impact of Lower Road Speed on Fuel Consumption ...................................................... 61

Figure 17. 15 Year Net Cost of Ownership for Technology Packages.............................................. 68

Figure 18. 3 Year Net Cost of Ownership for Technology Packages................................................ 69

Figure 19. Net Vehicle Costs Assuming 3 and 15 Years of Ownership ............................................ 70

Figure 20. Breakdown of Fuel Consumed in Class 8 Trucks........................................................... 71
xii Ta b l e o f C o n t e n t s

R E D U C I N G Heavy-Duty Long Haul Combination Truck Fuel Consumption and CO2 Emissions 

Figure 21. 15 Year Payback Requirement Fleet Analysis................................................................. 73

Figure 22. 3 Year Payback Requirement Fleet Analysis................................................................... 73

Tables

Table 1. Technologies and Measures Combined in the Modeled Packages...................................... 3 

Table 2. Heavy-duty Long Haul CO2 and Fuel Consumption Reduction and Cost Results for 

Analyzed Packages ....................................................................................................................... 5

Table 3. Summary of Japanese heavy-duty vehicle fuel economy regulation.................................... 12

Table 4. The 21st Century Truck Program Technology Goals......................................................... 13

Table 5. Summary of Northeastern State Climate Legislation/Plans................................................ 17

Table 6: Comparison of Vehicle and Model Results........................................................................ 25

Table 7. Vehicle Technologies Evaluated for Possible Inclusion in this Study................................... 28

Table 8. Aerodynamic Improvements Considered.......................................................................... 35

Table 9. Description of Technologies Simulated by SwRI................................................................ 40

Table 10. Scenario Summary......................................................................................................... 48

Table 11. Parallel Hybrid System Modeling Results........................................................................ 54

Table 12. Mechanical Turbocompound System Results.................................................................. 54

Table 13. Electrical Turbocompound System Results...................................................................... 54

Table 14. Bottoming Cycle System Results .................................................................................... 56

Table 15. Summary for Longer / Heavier Vehicles Evaluated ......................................................... 56

Table 16. CO2 and Fuel Consumption Reductions for Longer / Heavier Vehicles ........................... 58

Table 17. Results for Longer/Heavier Trucks with Higher Engine Power........................................ 59

Table 18. Maximum Technology Combination Modeling Results................................................... 65

Table 19. Fuel Consumption and CO2 Reductions from Idle Reduction Technologies...................... 66

Table 20. Summary of Costs Estimated for Each of the Technology Packages.................................. 67
E X E C U T I V E S U M M A RY

1

EXECUTIVE SUMMARY

e x e c u t i v e s u m m a r y e x e c u t i v e s u m m a r y

executive summaryExecutive Summary

R E D U C I N G

Heavy-Duty Long Haul Combination 

Truck Fuel Consumption and CO2

 Emissions

Overview

This study provides an assessment of available and emerging technologies that could be used to reduce CO2

 emissions and lower fuel consumption from new heavy-duty 

long haul combination trucks in the United States in the 

2012 to 2017 timeframe. Its findings are drawn from the 

results of original cost and technology analyses conducted 

for this study, together with information obtained from 

previous studies and reports.

In 2006, transportation sources emitted approximately 40 

percent of all GHG emissions in the United States. 

Medium- and heavy-duty vehicles (above 8,500 gross 

vehicle weight rating) represent about 22 percent of the 

transportation emissions, up from 15 percent in 1990 (EPA 

2009). Trucking is energy-intensive and accounted for 

69 percent of freight energy use, consuming 2.35 million 

barrels of oil per day in 2008 and generating 363 million 

metric tons of carbon dioxide (EIA, 2009). Hence trucks 

are an important place to look for energy savings and 

climate change mitigation in the transportation sector. 

There were over 11 million medium- and heavy-trucks 

(those over 10,000 pounds GVWR, Class 3 through 8) on 

U.S. roads in 2008 and 684,000 new medium and heavy 

trucks were sold into the market in that year (Polk, 2008). 

Sales of individual models number in the hundreds or 

thousands, in contrast to the tens or hundreds of thousands 

for car models. While truck owners and operators are more 

affected than passenger vehicle users by fuel expenses, 

the demand for fuel economy has historically not been 

sufficient to bring all cost-effective efficiency technologies 

into the market. Manufacturer risk, low fuel prices, lack 

of fuel economy information on individual models, and 

undervaluation of fuel economy all limit the introduction of 

fuel saving technologies.

Among medium- and heavy-trucks, Class 8 trucks are the 

largest CO2

 emitters and fuel users, consuming two-thirds 

of all truck fuel, or 1.57 million barrels per day. Current 

fuel economy for Class 8 trucks is estimated by the US 

Department of Energy at 6.0 mpg and projected to rise 

modestly to 6.8 mpg by 2025 (EIA, 2009). Substantial 

improvements could be made to truck efficiency through 

a variety of existing and emerging technologies, including 

engine improvements, transmission enhancements, better 

aerodynamics and changes in systems and logistics. This 

study finds that fuel consumption for new tractor-trailers 

could be lowered by 20 percent starting in 2012 and as 

much as 50 percent beginning in 2017, while providing 

net savings for the owner based on lifetime fuel savings 

paying for the incremental vehicle, operation, and maintenance costs.

Method

The project was directed by an expert steering committee 

composed of representatives from major truck and powertrain manufacturers, government agencies, trucking fleets, 

and fuel economy and heavy-duty experts from non-profit 

organizations. The core of the analysis consisted of a 

series of modeled simulations to predict the fuel saved by 

incorporating various technology and operational measure 

combinations in new trucks. Southwest Research Institute 

(SwRI) was engaged to perform vehicle and engine simulation modeling, which provides detailed information on the 

acceleration, braking, power, fuel economy, and emissions 

performance of different heavy-duty vehicle designs, 

including advanced powertrain designs. The technologies 

and operational measures selected are further discussed in 

Chapter 2, and in Appendix A. TIAX LLC (TIAX) assembled cost information for each package modeled, assessed 

the net cost of these packages over two time horizons and 
2 E x e c u t i v e S u m m a r y

R E D U C I N G Heavy-Duty Long Haul Combination Truck Fuel Consumption and CO2 Emissions

estimated the United States fleet-wide fuel savings impact 

of various technology adoption scenarios. 

The baseline vehicle should be a vehicle representative 

of the average Class 8 truck in today’s fleet for which 

sufficient data has been collected to serve as inputs to 

the simulation models. NESCCAF, SwRI and the Steering 

Committee selected a Kenworth T-600 Class 8 tractor, a 

Volvo D13 engine and an Eaton Fuller 10-speed manual 

transmission as the study’s representative vehicle. This 

baseline truck and powertrain, although not a combination 

available on the market, fulfilled the criteria for a good 

baseline vehicle. It has aerodynamic and rolling resistance 

characteristics that approximate the average performance 

of the current truck fleet. It has a 2007 emission standards 

compliant engine that can be upgraded to meet 2010 

emissions requirements. And it has a manual transmission 

that has a high market share among fuel economy cost 

sensitive fleets.

Once the baseline truck and engine was determined, two 

simulation models were used to allow the evaluation of 

various packages: GT-POWER for engine cycle simulation 

and RAPTOR to model the vehicle, including the transmission and driveline. An important benefit of simulating the 

performance of technology packages, rather than individual 

technologies, is that it eliminates the possibility that the 

reductions will be “double counted”. The benefits associated with various options are not necessarily additive when 

these improvements are combined in a single vehicle, 

particularly to the extent that many technologies target the 

same sources of mechanical or thermodynamic inefficiency. 

The simulation modeling conducted for this analysis avoids 

this problem. Both models were validated by comparing 

predicted fuel economy results to actual on-road vehicle 

fuel economy measurements, or to test cell engine fuel 

consumption results.

The test cycle used in this study was based on the California Heavy-Duty Diesel Truck Drive Cycle. The California 

cycle was created from analysis of a statistical study of line 

haul truck operations in California. The following changes 

were made to the California cycle for this study, based on 

input from the experts on the Steering Committee:

The portion of high speed driving was increased to 

reflect longer average travel distances nationwide.

The speeds used in the California cycle were increased 

by 8 percent to reflect current typical truck operating 

speeds on long-haul routes nationwide.

Two segments with grade were added. One segment 

includes positive and negative 1 percent grades, and a 

second segment has positive and negative 3 percent 

grades.

The total duration of the cycle is 6,830 seconds (one hour 

and 54 minutes), and the total distance traveled is 103.3 

miles. It is important to note that the drive cycle chosen for 

this study is specific to long-haul trucks. Thus, the results 

are specific to long-haul trucks and cannot necessarily 

be extrapolated to other heavy-duty trucks, even Class 8 

An important benefit of simulating the 

performance of technology packages, 

rather than individual technologies, is 

that it eliminates the possibility that the 

reductions will be “double counted”.
E x e c u t i v e S u m m a r y 3

trucks, operating on different drive cycles such as regional 

haul, pickup and delivery, or drayage.

Technology and Operational Measures 

A total of 32 technologies and operational measures were 

identified and considered for inclusion in this project. 

The complete list of the individual vehicle technologies 

considered in this study for purposes of evaluating future 

Class 8 heavy-duty truck fuel consumption and CO2

emissions reduction potential is available in Appendix A. 

The list includes a brief description of each of the technologies and an explanation of how each option might reduce 

CO2

 emissions. Some of the technologies selected for 

evaluation in this study are fully commercialized. Others, 

such as bottoming cycle, are not and may present technical 

challenges that could result in delayed introduction or 

lower performance than projected in this study.

SwRI did not consider fuel consumption and CO2

reduction technologies that are not currently in production 

or for which a design specification is not available in the 

literature. As such, the study findings do not represent the 

total available potential to reduce heavy-duty vehicle fuel 

consumption and CO2

 emissions – the results only estimate 

what can be done given known technologies. Going 

forward, more advanced technologies to improve engine, 

vehicle, and transmission technologies could and will likely 

be developed that would further reduce truck fuel consumption and CO2

 emissions beyond the 2017 timeframe. 

Using the most promising individual technologies that 

emerged from the initial screening evaluation described 

above, in combination with cost estimates for the 

individual technologies, a series of technology packages 

was assembled for modeling. Generally, these packages 

were designed to span the full range of CO2

 reduction 

potential (i.e., from modest to substantial reductions), so 

they necessarily reflect a range of impacts (and costs). 

Table 1 presents the technology packages modeled in 

three groups: (1) Building block technologies, 

(2) Operational measures, and (3) Maximum reduction 

combination packages.

1

TABLE

TECHNOLOGIES AND MEASURES COMBINED IN THE MODELED PACKAGES

PACKAGE NAME PACKAGE # DETAILED PACKAGE DESCRIPTION

Baseline 1 Volvo D13 (2010 emissions), Kenworth T600, 10-speed manual transmission

Building Block Technologies 

SmartWay 2007 (SW1) 2

Additional aero streamlining to the cab and the trailer sufficient to reduce the 

coefficient of drag from 0.63 to 0.5. Fully aerodynamic mirrors, cab side extenders, integrated sleeper cab roof fairings, aerodynamic bumper, and full fuel tank 

fairings. Trailer streamlining includes a side skirt fairing, and either a trailer gap 

fairing or a rear-mounted trailer fairing such as a boat tail. RR of 0.0055. Wide 

base single tires and aluminum wheels. Idle reduction, improved lubricants

Advanced SmartWay (SW2) 3

Package #2 plus advanced aero and rolling resistance package. Includes 

continued streamlining of the cab, a reshaped trailer, boat tail, full skirting of cab 

and trailer, tractor-trailer gap fairing, and very low rolling resistance tires 

Parallel hybrid-electric

powertrain (HEV) 4 Parallel hybrid system 
4 E x e c u t i v e S u m m a r y

R E D U C I N G Heavy-Duty Long Haul Combination Truck Fuel Consumption and CO2 Emissions

PACKAGE NAME PACKAGE # DETAILED PACKAGE DESCRIPTION

Mechanical turbocompound 5 Mechanical turbocompound plus Package #7

Electrical turbocompound 6 Electrical turbocompound plus Package #7

Variable Valve Actuation 

(VVA) 7 Variable valve actuation

Bottoming cycle 8 Bottoming cycle 

Advanced EGR 11 Advanced exhaust gas recirculation 

Operational Measures

Rocky Mountain Double 

(RMD) trailers 9 Longer/heavier trailer (rocky mountain doubles – 48’ and 28’ trailers) 

60 mph speed limit 10 Slower road speed (60 mph) 

Maximum Reduction Combination Packages

Maximum reduction 

combination 1 12 Standard trailer w/advanced aero and rolling resistance tires, hybrid, bottoming cycle, 60 mph (Packages #3, #4, #8, #10)

Maximum reduction 

combination 2 13 Longer and heavier trailer w/advanced aero and rolling resistance tires, hybrid, electric turbocompound, VVA, 60 mph (Packages #3, #4, #6, #7, #9, #10)

Maximum reduction 

combination 3 14 Longer and heavier trailer w/advanced aero and rolling resistance tires, hybrid, bottoming cycle, 60 mph (Packages #3, #4, #8, #9, #10)

1

TABLE (continued)

TECHNOLOGIES AND MEASURES COMBINED IN THE MODELED PACKAGES

Results

The results from the simulation modeling demonstrated 

a broad range of emission reductions and fuel savings for 

the 14 technology packages modeled. Table 2 provides the 

results obtained for each package. The individual measures 

are compared to the baseline vehicle. Table 2 provides the 

incremental vehicle cost, which is the modeled package 

additional capital cost compared to the baseline (Package 

1). The table also includes the net cost of the technology 

package, defined as the incremental technology package 

cost minus 15 years of fuel savings discounted at a rate of 

7 percent.1

 Note that a negative net cost means that 

fuel savings more than offset the incremental cost of the 

emissions reduction technologies being modeled. In other 

words, it equates to projected consumer savings over 

the lifetime of the vehicle. The net cost analysis assumes 

an average price of $2.50 per gallon of diesel fuel, and 

assumes that the annual mileage declines as the vehicle 

ages. Results from an additional net cost analysis assuming 

3 years of fuel savings at a different fuel price is presented 

in Chapter 3. Finally, the table provides the length of time 

required for the fuel savings to payback the investment in 

technology.

The eight building block technologies considered in this 

study reveal a range of potential reductions from a modest 

improvement for variable valve actuation and advanced 

exhaust gas recirculation to almost 28 percent for a host 

of aerodynamic, friction and rolling resistance technologies listed as Advanced Smartway (See Table 1 for list of 

Advanced SmartWay technologies). When combined, these 

existing and emerging technologies are capable of improving baseline fuel consumption up to 50 percent. 

1

 The analysis assumes a truck is driven 1.2 million miles over the 15 year period. It also includes operation and maintenance costs.
E x e c u t i v e S u m m a r y 5

2

TABLE

HEAVY-DUTY LONG HAUL CO2 AND FUEL CONSUMPTION REDUCTION AND COST 

RESULTS FOR ANALYZED PACKAGES

The technology costs range from several hundred dollars 

(variable valve actuation and ERG) to moderate ($6,600 

for electric turbo compounding) to expensive ($23,000 

for SmartWay and hybrid-electric powertrain packages), to 

2 Includes idle reduction benefits from a diesel-fired APU

3 Includes idle reduction benefits from battery storage; the modeled on-road fuel consumption improvement was 5.6%

4 Includes credit for an auxiliary power unit (APU), which is included in the SmartWay package, but is not needed in a hybrid vehicle. 

5 The lifetime cost of ownership figures are calculated using fuel savings averaged between grossed out and cubed out trucks.

6 Includes idle reduction benefits from battery storage.

a Calculations based on year 2022 high volume technology costs, EIA 2022 fuel price ($2.50/gal), a 7% discounted cash flow; time to payback assumes a 

constant 120,000 miles per year; the cost of ownership calculation assumes annual mileage declines over the life of the vehicle with a total mileage of 

1.2 million miles in 15 years.

very expensive (nearly $45,000 for Advanced Smartway). 

Despite the wide range in costs, most of these technologies 

pay for themselves in the first few years of ownership with 

the exception of the hybrid electric powertrain.

PACKAGE NAME FUEL CONSUMPTION/ 

CO2 REDUCTION (%)

INCREMENTAL 

VEHICLE COST ($)a

LIFETIME COST 

OF OWNERSHIP 

(15 YEARS, 7%)a

TIME TO 

PAYBACK 

a

(YEARS)

Baseline n/a n/a n/a n/a

Building Block Technologies 

SmartWay 2007 (SW1) 17.8% 2 $22,930 -$23,600 3.1

Advanced SmartWay (SW2) 27.9%2 $44,730 -$55,800 3.8

Parallel hybrid-electric powertrain 

(HEV) 10%3 $23,0004 $100 7

Mechanical turbocompound 3.0% $2,650 -$5,500 2.0

Electric Turbocompound 4.5% $6,650 -$5,500 3.5

Variable Valve Actuation (VVA) 1.0% $300 -$2,500 0.6

Bottoming cycle 8.0% $15,100 -$4,800 5.2

Advanced EGR 1.2% $750 -$2,600 1.4

Operational Measures 

Rocky Mountain Double (RMD) 

trailers

16.1% (grossed out)

21.2% (cubed out) $17,500 -$34,1005 2.1

60 mph speed limit 5.0% $0 -$13,900 n/a

Maximum Reduction Combination Packages 

Maximum reduction combination 

1 (standard 53’ trailer, hybrid, BC, 

SW2, 60 mph) 

38.6% (grossed out) 6

40.2% (cubed out)6 $71,630 -$27,3005 4.8

Maximum reduction combination 

2 (RMD, hybrid, electric turbocompound, VVA, SW2, 60 mph)

48.7% (grossed out)6

46.2% (cubed out)6 $80,380 -$41,6005 4.3

Maximum reduction combination 3 

(RMD, BC, hybrid, SW2, 60 mph)

50.6% (grossed out)6

48.3% (cubed out)6 $89,130 -$37,2005 4.7
6 E x e c u t i v e S u m m a r y

R E D U C I N G Heavy-Duty Long Haul Combination Truck Fuel Consumption and CO2 Emissions

According to this analysis, combinations of technologies 

already used in some production heavy-duty long haul 

trucks can reduce CO2 emissions by approximately 5-18 

percent. Examples of these technologies include hybrid 

vehicle systems, turbocompounding, and the SmartWay 

package of modest aerodynamic, tire, and idle-reduction 

improvements. Reductions beyond this level will require 

the introduction of more advanced technologies such as a 

bottoming cycle and advanced aerodynamic or tire rolling 

resistance improvements. For example, a package including 

advanced aerodynamic components and improved tires can 

provide a 28 percent CO2 and fuel consumption reduction 

for an incremental vehicle cost of $44,730. Even greater 

CO2 and fuel consumption reductions can be achieved – 

up to 39 percent - using a combination of bottoming 

cycle, slower road speed, advanced aerodynamics, and 

hybridization. 

Operational measures include slowing the speed of Class 

8 trucks and increasing the size and weight of truck-trailer 

combinations. Assuming a longer and heavier trailer design 

alone, CO2 and fuel consumption reductions ranging from 

16-21 percent are feasible for an incremental vehicle cost 

of $17,500. This result is for a combination of one 48’ 

trailer with one 28’ trailer (Rocky Mountain Double or 

“RMD”). Additional results for other types of longer and 

heavier trailer designs are detailed in Chapter 3. Greater 

reductions can be achieved by combining longer and 

heavier truck trailers with advanced technologies such as 

bottoming cycle and hybridization. There are, however, 

limitations to the routes that these longer and heavier 

combination vehicles can safely operate. The technology 

package that provides the greatest CO2

 and fuel 

consumption reduction – 50 percent from the baseline 

vehicle – includes advanced aerodynamics and rolling 

resistance technology, a longer and heavier trailer 

combination, a hybrid electric drivetrain, and a bottoming 

cycle. This package represents both an impressive 

improvement in fuel savings and a very complex 

technology combination.

It is critical to recognize that while the costs of using 

advanced technologies are greater than the cost of conventional long haul truck technologies, fuel-cost savings in 

many cases outweigh additional technology costs for the 

technology packages. Assuming a 15-year period, fuel cost 

savings far outweigh the additional technology costs for 12 

of the 13 advanced technology packages. Table 2 shows 

net costs of most of the technology packages that produce 

up to 50 percent CO2

 and fuel consumption reductions is 

negative. Truck owners save between $2,500 and $55,800 

over the life of the vehicle due to avoided fuel purchases.

As noted in Table 2, the emission reduction packages evaluated in this study include a range of individual technologies 

with a range of CO2

 and fuel consumption reduction 

potential and a range of costs in an effort to provide a 

robust overview of the benefits and costs of candidate 

CO2-reduction technologies. Given that future technology 

advances could reduce costs for these technologies, the 

costs presented could be overstated. Consequently, the 

complete set of technology packages does not constitute a 

low-cost solution to any particular CO2

-reduction scenario, 

but rather presents a host of possible solutions across a 

range of reductions and costs.

Figure 1 depicts the total potential fuel and CO2 emissions 

saved in the U.S. heavy-duty long haul combination truck 

fleet, assuming penetration of technologies modeled by 

SwRI in this study. The top line represents fuel consumption in the U.S. fleet in a business as usual case. In the 
E x e c u t i v e S u m m a r y 7

business as usual case, approximately 18 billion gallons of 

fuel are used in the entire U.S. fleet in 2030. The second 

line, with an arrow indicating “3-year payback” shows 

one scenario for introduction of technologies into the 

U.S. heavy-duty long haul fleet between now and 2022. 

According to this scenario, approximately 3 billion gallons 

of fuel are saved from the introduction of technologies 

into the U.S. heavy-duty long haul fleet. In the “3-year 

payback” scenario, only technologies that provide a net 

cost savings over three years are introduced into the fleet. 

The third line, indicated with an arrow and text saying “15 

year payback,” represents the amount of fuel that could be 

saved with more aggressive introduction of technologies 

to reduce fuel consumption and CO2

 emissions into the 

U.S. heavy-duty long haul fleet between now and 2030. 

In the “15-year payback” scenario, technologies which pay 

for themselves within 15 years of purchase are adopted 

into the U.S. heavy-duty fleet. As the lower line indicates, 

assuming aggressive introduction of the technology 

combinations modeled in this study into the U.S. fleet, 

approximately 7 billion gallons or 39 percent of total U.S. 

heavy-duty long haul fleet fuel consumption could be 

avoided. This represents 39 percent of heavy-duty long 

haul CO2 emissions as well. Assuming maximum technology penetration (the lowest line in the graph), the use of 

approximately 8 billion gallons of fuel and 44 percent of 

heavy-duty long haul truck CO2 emissions could be avoided 

in the U.S. in 2030.

1

FIGURE

POTENTIAL FUEL SAVINGS IN THE U.S. LONG HAUL BOX TRAILER FLEET

Business as Usual

0

2

4

6

8

10

12

14

16

18

20

2007

2008

2009

2010

2011

2012

2013

2014

2015

2016

2017

2018

2019

2020

2021

2022

2023

2024

2025

2026

2027

2028

2029

2030

Line-Haul Box Trailer Fleet Fuel Use (B Gal)

3-Yr Payback

15-Yr Payback

Max Technology

Business as Usual

3-Yr Payback

15-Yr Payback

Max Technology
8 E x e c u t i v e S u m m a r y

R E D U C I N G Heavy-Duty Long Haul Combination Truck Fuel Consumption and CO2 Emissions 

The analysis does not assume that any existing vehicles are 

retrofitted with technologies and as such, could underestimate the total potential emissions and fuel use avoided 

from heavy-duty technologies evaluated in this study. In 

addition, the analysis does not assume the introduction of 

any new technologies after 2015, and could therefore 

underestimate the benefits realized from advances in 

science and engineering. There are also downside risks, 

where some of the modeled technologies may not reach 

production maturity with the expected fuel savings or cost. 

Many controls, reliability, durability, and packaging issues 

remain to be overcome to implement all of the modeled 

technologies, and some of these issues may prove difficult. 

Conclusions

The results of the analysis suggest that existing and emerging vehicle, engine, and transmission technologies can 

achieve substantial and cost-effective reductions in heavyduty vehicle CO2

 emissions and fuel consumption in the 

2012 to 2017 timeframe. Coupled with operational measures, the benefits could even be larger. Specifically, CO2

and fuel consumption emissions from heavy-duty vehicles 

can be reduced up to 50 percent in this timeframe. Over 

a three year period and with a diesel fuel price of $2.50 

per gallon, this study found that five of the technology 

packages would result in a net cost savings to the truck 

owner, taking into account both incremental technology 

costs and fuel savings. The analysis shows that most of the 

technology combinations that provide the greatest 

reductions would not be adopted into the fleet assuming 

a three-year payback requirement. This indicates that 

given the short payback period demanded by the trucking industry, a number of these technologies will not be 

adopted into the U.S. fleet absent regulation. With a longer 

payback period of 15 years estimated lifetime net savings 

are between $30,000 and $42,000 for owners of vehicles 

achieving CO2

 and fuel consumption reductions of up to 

50 percent. 

Introduction of all the technologies and strategies modeled

in this study into the U.S. heavy-duty long haul fleet 

between now and 2030 would lead to an estimated 8 

billion gallons of diesel fuel saved annually beginning 

in 2030, with lesser reductions being achieved as soon 

as 2012. The 8 billion gallons of fuel saved annually 

represents approximately 44 percent of the total projected 

business as usual fuel consumption in the heavy-duty long 

haul fleet. Cumulative fuel savings between now and 2030 

would equal approximately 90 billion gallons of diesel fuel. 

Approximately 97 million metric tons of annual CO2

emissions would be reduced beginning in 2030. This 

would be equivalent to a 44 percent reduction in annual 

CO2

 emissions beginning in 2030 from business as usual 

projections. Cumulative CO2 emissions avoided between 

now and 2030 would equal approximately 1.1 billion 

metric tons. 

The results of the analysis suggest that 

existing and emerging vehicle, engine, 

and transmission technologies can 

achieve substantial and cost-effective 

reductions in heavy-duty vehicle CO2

emissions and fuel consumption in the 

2012 to 2017 timeframe.
I N T R O D U C T I O N

9

INTRODUCTION

i n t r o d u c t i o n i n t r o d u c t i o n

i n t r o d u c t i o n Introduction

R E D U C I N G

Heavy-Duty Long Haul Combination 

Truck Fuel Consumption and CO2

 Emissions

Purpose of the Study

This study provides an assessment of available and 

emerging technologies that could be used to reduce carbon 

dioxide (CO2) emissions and fuel consumption from heavyduty long-haul vehicles in the United States in the 2012 to 

2017 timeframe.7 Its findings are drawn from the results 

of original cost and technology analyses conducted for this 

study, together with information obtained from other available reports. An impetus for this study was the establishment of climate change action plans in the northeastern 

United States, California, and countries outside of the U.S. 

that will require substantial reductions in motor vehicle 

CO2

 emissions if the climate goals are to be met. Another 

impetus for this study was the development of a regulation 

adopted by the Japanese government to reduce heavy-duty 

vehicle fuel consumption. After this study began, the U.S. 

Congress passed the Energy Independence and Security 

Act of 2007. This act directed the U.S. Department of 

Transportation (US DOT) to begin regulation of mediumand heavy-duty vehicle fuel consumption. Any regulations 

resulting from this act should also have the effect of reducing CO2

 emissions. Also, in early 2009, the EPA reached 

a finding that CO2 is a danger to human health. The EPA 

may soon begin the process of regulating CO2 emissions 

from heavy-duty vehicles. CO2 is the only GHG included in 

this assessment.

The goal of this assessment is to help define CO2

-reducing 

heavy-duty vehicle technologies and strategies that are 

expected to be feasible, commercially available, and 

cost-effective in the 2012 and 2017 timeframe. The study 

did not evaluate regulatory changes that would likely be 

necessary to allow for widespread use of some operational 

changes. For example, changes in state or federal law 

would likely be necessary to reduce road speeds, however 

an analysis of this and other necessary policy changes was 

not included in this study. A wide range of technologies 

were evaluated, both individually and in packages, for their 

potential to reduce CO2

 emissions and fuel consumption 

from heavy-duty vehicles. The technologies examined fall 

into five primary categories: 

(1) off-the-shelf aerodynamic improvement technologies;

(2) off-the-shelf drivetrain technologies; 

(3) emerging drivetrain technologies; 

(4) emerging aerodynamic improvement technologies; and 

(5) operational measures. 

The study also includes an assessment of the potential CO2

emissions and fuel consumption avoided by the introduction of these technologies and operational measures into 

the U.S. heavy-duty vehicle fleet.

The results presented in this report have significant 

implications for states, provinces, and countries that share 

the commitment to reducing transportation-related CO2

emissions as part of a broader effort to address the risks 

posed by global climate change.

The Importance of the Transportation 

Sector

In 2006, transportation sources emitted approximately 40 

percent of all CO2 emissions in the United States. Figure 2

on page 10 provides a breakdown of the contribution of 

different sources to total U.S. greenhouse gas emissions. 

As can be seen in the figure, electricity generation is the 

largest source of CO2

 emissions in the U.S., followed by 

CO2 emissions from transportation sources.

7

 CO2 was the only greenhouse gas evaluated in this study.
10 I n t r o d u c t i o n

R E D U C I N G Heavy-Duty Long Haul Combination Truck Fuel Consumption and CO2 Emissions

2

FIGURE

2006 U.S. GHG INVENTORY

CO2 Electricity Generation

CO2

 Commercial

CH4

 Enteric Fermentation

CH4

 Landfills

0 500 1000 1500 2000 2500

CO2

 Non-Energy Use of Fuels

CO2

 Wood Biomass and Ethanol Consumption b

CO2

 Transportation

CO2

 Residential

N2

O Agricultural Soil Management

CO2

 Industrial

Source: EPA 2006

EPA’s 2006 GHG inventory provides a breakdown of the 

contribution of different mobile sources to total 

transportation GHG emissions. According to the 

inventory, medium- and heavy-duty vehicles (above 8,500 

gross vehicle weight rating (GVWR)) represented about 

22 percent of the transportation emissions, up from 15 

percent in 1990 (EPA 2008). The majority of medium- and 

heavy-duty truck GHG emissions come from diesel-fueled 

commercial vehicles and among these commercial vehicles, 

Class 8 trucks emit the majority – more than two thirds – 

of GHG emissions from medium- and heavy-duty trucks.

Figure 3 provides a breakdown of fuel consumption in 

medium- and heavy-duty trucks and, as can be seen, Class 

8 trucks are by far the largest consumers of fuel. Class 8 

consists of trucks with GVWR above 33,000 lbs. The most 

common type of Class 8 truck is the tractor-trailer combination truck. These vehicles are primarily employed in freight 

transportation over long distances or long-haul trucking. 

Approximately 70 percent of fuel used by Class 8 trucks 

is used in long-haul service with trips over 200 miles long 

and regional freight transport – trips that are under 200 

miles long. Class 8 tractor trailer trucks’ large share of the 

sector’s fuel use is due to their high usage rate compared to 

other heavy-duty vehicles. The remainder of fuel consumed 

by Class 8 vehicles is used in other types of trucks such as 

refuse, dump, and cement trucks. The type of truck evaluated in this study; long haul, tractor trailer trucks consume 

approximately 45 percent of total Class 8 fuel annually.

Clearly, significantly reducing heavy-duty truck CO2

 emissions is an important part of a comprehensive approach 

to address CO2 emissions from the transportation sector 

and ultimately reverse the impacts of climate change, in 

the United States and globally. This study builds on and 

complements the substantial research being conducted 

by the U.S. Department of Energy’s 21st Century Truck 

Program, the U.S. EPA’s (Environmental Protection Agency) 
I n t r o d u c t i o n 11

3

FIGURE

FUEL CONSUMPTION BY MEDIUM AND HEAVY-DUTY VEHICLE CLASS

2.30%

1.10%

3.80%

13.50%

4%

75.30%

Class 3 (10,001 to 14,000 lb)

Class 4 (14,001 to 16,000 lb)

Class 5 (16,001 to 19,500 lb)

Class 6 (19,501 to 26,000 lb)

Class 7 (26,001 to 33,000 lb)

Class 8 (33,001 lb and over)

Source: DOE 2001 

SmartWay program, research by truck and engine 

manufacturers, and trucking fleet research and 

demonstration projects.

The following sections provide additional information 

on the political and regulatory context in the United 

States and abroad within which heavy-duty CO2 and fuel 

economy regulation are to be developed.

Political and Regulatory Context in 

the U.S. and Internationally

International Context

As early as 1992, international awareness of the many 

potential risks associated with global warming led 160 

countries, including the United States, to adopt a Framework Convention on Climate Change with the stated 

objective of achieving “stabilization of greenhouse gas 

concentrations in the atmosphere at a level that would 

prevent dangerous anthropogenic interference with the 

climate system.”[UN 1992]

Toward this objective, signatories pledged to work to 

stabilize greenhouse gas emissions. A number of industrialized countries, again including the United States, adopted 

the specific near-term goal of returning year 2000 CO2

emissions to 1990 levels. It subsequently became evident 

that most countries, including the United States, were not 

on track to meet this objective. In response, parties to the 

Framework Convention adopted the Kyoto Protocol in 

1997, which included targets and timetables for reducing 

GHG emissions to specific levels for each country. As of 

early 2003, 102 countries had ratified or acceded to the 

Protocol. However, the United States – citing economic 

concerns – has not ratified the Kyoto Protocol. 
12 I n t r o d u c t i o n

R E D U C I N G Heavy-Duty Long Haul Combination Truck Fuel Consumption and CO2 Emissions

Internationally, Japan was the first and remains the only 

country to have adopted mandatory fuel economy 

standards for heavy-duty vehicles. Japan adopted the 

standards in 2005 and they will come into force with 

model year 2015.

Japanese Heavy-Duty Fuel Economy Standards

In November 2005, the Japanese government introduced 

the first of their kind fuel economy standards for new 

medium- and heavy-duty diesel vehicles, which were 

estimated to be responsible for approximately one-quarter 

of all CO2

 emissions from motor vehicles in 2002 in Japan. 

Those standards affect commercial trucks with a gross 

vehicle weight (GVW) in excess of 3.5 metric tons (about 

7,700 lbs) and buses with a carrying capacity above 11 

passengers. 

Relative to the fuel economy standards required for 

passenger vehicles,8 the heavy-duty standards require 

modest improvements in fuel economy [ANRE/MLIT 

2007]. Table 3 summarizes the average 2015 fuel economy 

target by vehicle type and class, along with the relative 

improvement over the 2002 baseline, required by the 

standards.

3

TABLE

SUMMARY OF JAPANESE HEAVY-DUTY VEHICLE FUEL ECONOMY REGULATION

VEHICLE 

TYPE

VEHICLE 

CLASS

FUEL ECONOMY (KM/L) IMPROVEMENT (%) 2002 BASELINE 2015 TARGET

Truck

Tractor 2.67 2.93 9.7

Other truck 6.56 7.36 12.2

Total 6.32 7.09 12.2

Bus

Urban 4.51 5.01 11.1

Other bus 6.19 6.98 12.8

Total 5.62 6.30 12.1

The 2015 average target and relative improvement assume a constant 2002 vehicles sales mix

Compliance with the model year 2015 fuel economy 

targets is to be measured by reference to individual 

standards disaggregated by vehicle class, gross vehicle 

weight, and, for lighter trucks, rated cargo load. Each 

manufacturer is required to meet the fuel economy target 

for each type of vehicle based upon a sales-weighted 

average for that category. Fuel economy is measured 

through a combination of engine-only fuel consumption 

testing and simulation modeling of gear shifting and vehicle 

resistance loads.

The Japanese standards explicitly take into account the 

trade-off between emissions and fuel consumption. The 

reason stated for the relatively modest improvement 

required over a 15 year span is because the standard 

recognizes that a significantly larger improvement must 

be made to overcome fuel economy losses inherent in the 

implementation of more stringent emissions regulations.

8 Japan’s aggressive light-duty fuel economy standards finalized in February 2007 require a 23.5 percent improvement in the fuel economy of passenger vehicles

from 2004 to 2015.
I n t r o d u c t i o n 13

4

TABLE

THE 21ST CENTURY TRUCK PROGRAM TECHNOLOGY GOALS

Climate Change Action by the U.S. Federal 

Government

In 2007, the U.S. Congress passed the Energy Independence and Security Act (EISA) that requires the U.S. 

Department of Transportation (US DOT) to set fuel 

economy standards for medium- and heavy-duty vehicles. 

The standards are to be applicable no earlier than the 2016 

model year and the form and stringency of the standard(s) 

have yet to be determined. In 2008, EPA issued an 

Advance Notice of Proposed Rulemaking that requested 

comment on the feasibility of requiring GHG standards for 

medium- and heavy-duty vehicles. Also at the federal level, 

two voluntary programs aimed at improving the efficiency 

and GHG emissions of heavy-duty vehicles are underway. 

These are the Department of Energy’s 21st Century Truck 

Program and the EPA’s SmartWay Transport Partnership.

The 21st Century Truck

Since 2000, the 21st Century Truck Program has sought 

to significantly improve the fuel efficiency, safety, and 

pollutant emissions of trucks and buses by funding 

public-private partnerships for technology research and 

development as well as demonstration. The program’s 

16 industry partners and four government agencies have 

worked to meet specific goals in five areas: engine systems 

(fuel, engine, and after-treatment), heavy-duty hybrid drive 

trains, parasitic losses (aerodynamic drag, rolling resistance, 

drivetrain losses, and auxiliary loads), idle reduction, and 

safety. Table 4 summarizes the goals in each of these areas.

ENGINE SYSTEMS HD HYBRIDS PARASITIC LOSSES IDLE REDUCTION SAFETY

• Increase thermal efficiency 

 from 42% to 50% by 2010

• Stretch goal of 55% 

 thermal efficiency in 

 prototype engines by 2013

• 10% gain in over-the-road 

 fuel economy by 2013, 

 compared to 2010 goal

• By 2012 develop 

 drive unit with 15 

 year design life that 

 costs <$50/kw

• By 2012 develop 

 energy storage 

 system with 15 year 

 design life that costs 

 <$25/ peak kw

• Achieve 60% 

 increase in fuel 

 economy on urban 

 drive cycle

• Reduce aero drag on 

 Class 8 combination 

 truck by 20%

• Reduce auxiliary 

 loads on Class 8 

 combination truck 

 by 50%

• Develop materials and 

 manufacturing that 

 can reduce Class 

 8 combination truck 

 weight by 15-20%

• By 2009 demonstrate 

 add-on idle reduction 

 devices with <2 yr 

 pay back

• By 2012 produce 

 a truck with fully 

 integrated idle 

 reduction system

• By 2015 demonstrate 

 5-30 kw fuel cell APU

• Reduce stopping 

 distance from 

 operational 

 speeds by 30%

• Reduce

 incidences of 

 HDV roll over

• Develop driver 

 aid systems 

 to provide 360° 

 visibility and 

 that promote 

 safe following 

 distance and 

 in-lane tracking

Source: MJ Bradley & Associates 2008
14 I n t r o d u c t i o n

R E D U C I N G Heavy-Duty Long Haul Combination Truck Fuel Consumption and CO2 Emissions

A recent review by the National Academy of Sciences 

published in 2008 found that many of the program’s goals 

had not been met either because they were not feasible 

from an engineering standpoint, or because they were not 

adequately funded, or again because planned technologies 

were not implemented (NAS 2008). However, the review 

highlighted the program’s importance in accelerating the 

development of technologies leading to cleaner, safer, and 

more efficient vehicles. The review provided a number of 

recommendations aimed at a restructuring and refocusing 

the program. Finally, it warned that the program’s declining funding would further impede its ability to meet its 

important goals. 

The SmartWay Transport Partnership

Initiated by the US EPA in 2004, the SmartWay Transport 

Partnership brings together fleets, technology providers, 

and retailers to implement fuel savings and GHG reducing 

strategies. The program aims to reduce fuel consumption 

by 150 million barrels of oil per year and 33 to 66 million 

tons of CO2

 as well as conventional pollutants. The more 

than 1,200 partners account for about an estimated quarter 

of all goods moved in the United States (EPA 2008). The 

program has focused on identifying and promoting products and practices that reduce conventional and climate 

change emissions. The program has certified vehicles and 

equipment such as tractors, trailers, idle reduction, and 

aerodynamic retrofit kits that meet SmartWay goals. The 

certification is not performance based, rather the SmartWay 

certified vehicles and equipment have a number of required 

features that are expected to enhance their environmental 

performance. Figure 4 shows the features in a SmartWay 

tractor and trailer.

SmartWay has also developed a draft heavy-duty vehicle 

GHG emission and fuel-efficiency test protocol to assist 

in the evaluation of technologies and vehicle designs 

including hybrid drivetrain technologies. Once finalized, 

this protocol will be used to certify SmartWay vehicles and 

equipment. 

The Energy Independence and Security Act of 2007

Signed into law in December 2007, the Energy Independence and Security Act (EISA) of 2007 is primarily known 

4

FIGURE

SMARTWAYTM EQUIPMENT STANDARDS (EPA 2008)
I n t r o d u c t i o n 15

5

FIGURE

POTENTIAL TIMELINE FOR A US DOT MEDIUM- AND HEAVY-DUTY FUEL 

ECONOMY REGULATION

2008

NAS Study

Regulations first

take effect in 2016

or 2017 model year

First update

possible in 2019 or

2020 modl year

DOT Study

DOT Regulatory Development

Manufacture Lead Time

2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021

for improving the Corporate Average Fuel Economy (CAFE) 

standards for light-duty cars and trucks. It also established 

a mandatory Renewable Fuel Standard for fuel producers. 

The EISA also puts forth a timeline for the US DOT to 

develop and implement a fuel economy standard for “work 

trucks” (8,500 to 10,000 lbs. GVWR) as well as mediumand heavy-duty trucks. It is expected that the earliest 

model year that might be required to meet fuel economy 

limits would be model year 2016 or 2017. Figure 5 depicts 

the possible sequence of steps described in the EISA, 

beginning with a National Academy of Sciences (NAS) 

study of medium and heavy-duty fuel economy. The NAS 

study results will inform the development of medium and 

heavy-duty vehicle standards required by EISA. The NAS 

committee began its activities in late 2008 and is expected 

to deliver its final report in March 2010.

Potential EPA Heavy-Duty Vehicle GHG Regulation

In the EPA 2008 Advance Notice of Proposed Rulemaking on regulating GHG emissions, the Agency presents 

its assessment of the potential to address climate change 

under the Clean Air Act and discusses the regulatory 

options the Agency is considering for each major mobile 

Source: MJ Bradley & Assoc., 2008

and stationary source type. EPA identified three approaches 

to reduce GHG emissions from heavy-duty vehicles. The 

Agency asked for comment on the feasibility of reducing 

heavy-duty vehicle GHG emissions 40 percent by 2015 and 

achieving subsequent, greater reductions beyond 2015. 

The first approach is setting an engine CO2 or GHG standard in a process similar to the current criteria pollutant 

emissions standards. The second approach would require 

each vehicle model to meet a CO2 or GHG standard 

expressed either in grams/mile or grams/ton-mile. The 

last approach considers the potential for in-use emission 

reduction strategies such as idling reduction to generate 

credits. 

State Actions to Reduce the Impacts of 

Climate Change

In the United States, many state and local leaders had 

become sufficiently concerned about the issue of climate 

change by the end of the 1990s and set out to adopt a 

range of measures aimed at reducing GHG emissions 

within their jurisdictions. This trend began with a few 

leading states in the early 1990s, but accelerated in the 

following decade. In 2001 and 2002, approximately 
16 I n t r o d u c t i o n

R E D U C I N G Heavy-Duty Long Haul Combination Truck Fuel Consumption and CO2 Emissions

one-third of the states passed new legislation or executive 

orders specifically aimed at addressing climate change 

[Rabe 2002].9 These policies ranged from comprehensive 

state action plans with quantitative GHG reduction targets 

to regulations or laws limiting emissions from a specific 

sector such as electric power generation or transportation. 

In the Northeast, the Regional Greenhouse Gas Initiative 

requires power plants to reduce total GHG emissions 10 

percent by 2020. In California, Assembly Bill AB 32 “The 

Global Warming Solutions Act of 2006” requires reducing 

the state’s GHG emissions to 1990 levels by 2020. The 

scoping plan adopted by the implementing agency, the 

California Air Resources Board (ARB), in December 2008 

includes measures targeting emissions from a wide range of 

sectors, including heavy-duty vehicles.

The California Global Warming Solutions Act

The California Global Warming Solutions Act of 2006 

(AB 32) established a program of regulatory and market 

mechanisms to achieve quantifiable and cost-effective 

reductions of GHGs. The goal is to achieve 1990 emission 

levels by 2020 (an estimated 30 percent reduction) and 

an 80 percent reduction below 1990 levels by 2050. The 

ARB was required to adopt a plan indicating how emission 

reductions will be achieved from significant GHG sources 

via regulations, market mechanisms, and other actions. 

This plan, named the Climate Change Scoping Plan, was 

adopted in December 2008. The scoping plan further 

develops the three interrelated components contributing to 

emissions in the transportation sector: (1) vehicle technology, (2) fuels, and (3) vehicle use. Most of the regulations 

in the scoping plan must be adopted by January 1, 2011. In 

addition, the ARB has identified some early action measure 

to be enforced by January 1, 2010. 

The scoping plan includes two regulations targeting 

heavy-duty vehicle GHG emissions. The first is an early 

action measure, adopted in December 2008, requiring new 

and in-use trucks with 53 foot or longer trailers operating 

in California to achieve aerodynamic drag and rolling 

resistance improvements through SmartWay certified new 

equipment and retrofits. New tractors and trailers must 

meet the requirements starting with model year 2011, 

in-use tractors must comply by 2012, and in-use trailers 

by 2014. The second regulation, which is the early phases 

of development, would promote hybridization in mediumand heavy-duty vehicles 

Northeast States 

In 2001, the Conference of New England Governors 

and Eastern Canadian Premiers (NEG/ECP) adopted 

the regional “Climate Change Action Plan.” The plan 

establishes targets for stabilizing aggregate GHG emissions 

in New England, Quebec, New Brunswick, Nova Scotia, 

Newfoundland, and Prince Edward Island, at 1990 levels 

by 2010, 10 percent below 1990 emissions levels by 2020, 

and substantial further reductions (as much as 75 to 80 

percent) in subsequent years.

In recent years, other northeastern states have developed 

state-specific plans and/or reduction targets, and New 

England states have formalized the NEG/ECP targets 

by signing them into law or establishing more stringent 

targets. These are summarized in Table 5.

9

 Additionally, other states adopted measures that were not expressly aimed at climate change but clearly were driven at least in part by the issue of global warming.
I n t r o d u c t i o n 17

STATE LEGISLATION 

OR PLAN

YEAR 

SIGNED

REDUCTION TARGETS

2010 2020 2050

CT

Act Concerning CT 

Global Warming 

Solutions

2008 10% below 

1990 levels 80% below 1990 levels

ME

Act to Provide Leadership in Addressing 

the Threat of Climate 

Change

2003 1990 levels 10% below 1990 levels 75-80% below 1990 

levels

MA Global Warming Solutions Act 2008 10-20% below 1990 

levels 80% below 1990 levels

NH NEG/ECP Climate Change Action Plan Targets

NJ Global Warming 

Response Act 2008 1990 levels 80% below 2006 levels

NY State Energy Plan and 

Final Impact Statement 2002 5% below 1990 levels 10% below 1990 levels

PA Climate Change

Roadmap 2007 25% below 2000 emissions by 2025

80% below 2007 

emission levels by 2050

RI Global Warming Solutions Act Pending 20% below 1990 levels 80% below 1990 levels

VT NEG/ECP Climate Change Action Plan Targets

In response to the expected increase in emissions attributable to the transportation sector, states in the region have adopted the 

California motor vehicle GHG standards, are exploring the adoption of a low carbon fuel standard, and are evaluating mechanisms 

to reduce vehicle miles traveled (VMT).

5

TABLE

SUMMARY OF NORTHEASTERN STATE CLIMATE LEGISLATION/PLANS

Denotes non-legislative action

OVERVIEW OF THE STUDY METHOD

19

OVERVIEW OF THE STUDY METHOD

o v e r v i e w o f t h e s t u d y m e t h o d o v e r v i e w o f t h e s t u d y m e t h o d o v e r v i e w o f t h e s t u d y m e t h o d Overview of the Study Method

R E D U C I N G

Heavy-Duty Long Haul Combination 

Truck Fuel Consumption and CO2

 Emissions

This chapter provides an overview of the method used 

to estimate CO2 reductions that could be achieved by 

introducing advanced technologies and operational changes 

into new Class 8 heavy-duty10, long haul combination 

trucks in the U.S. in the 2012-2017 timeframe. The core 

of this analysis consists of a series of modeled simulations 

to predict the emissions impacts of incorporating various 

technology combinations in new trucks. It is important to 

note that this study did not quantify the effect of retrofits 

to existing trucks and trailers, nor was an attempt made 

to predict the impact of technologies that may be invented 

and commercialized in the future. Appendix A provides 

a more detailed description of the specific methods and 

assumptions used in this analysis.

All simulation modeling for this study was performed 

by Southwest Research Institute (SwRI) using publicly 

available RAPTOR and GT-POWER software. GT-POWER 

was used to model the performance, fuel consumption and 

CO2

 emissions of the engine with a range of alternative 

technologies applied. RAPTOR was used to simulate the 

performance of the entire vehicle, using the output of the 

GT-POWER model as an input. RAPTOR provides detailed 

information on the acceleration, braking, and emissions 

performance of different truck designs. The modular 

structure of the models can accommodate a variety of 

vehicle configurations – including trucks, buses, cars, and 

motorcycles – and allows for the detailed specification of a 

wide range of individual vehicle components. This enables 

the user to investigate – at the vehicle level of detail – how 

modifying or replacing certain components, either individually or in combination, affects truck performance across a 

number of parameters, over standardized driving cycles; in 

terms of climbing performance; steady-state and top speed 

performance; maximum acceleration and traction force; 

and braking performance.11

The following sections of this chapter describe each basic 

step of the analysis method. In brief, these steps consist of:

1. Defining a representative “baseline” long-haul heavyduty Class 8 truck and modeling the baseline truck, 

using simulation modeling.

2. Validating baseline truck model simulation results 

against actual performance of representative 2008 

model year vehicles, and adjusting the baseline engine 

to meet the 2010 nitrogen oxides (NOx) emission 

standard.

3. Developing a list of specific technology and operational 

options and assessing the costs and potential CO2-

reducing benefits of each option in isolation using 

publicly available data.

4. Performing GT-POWER and RAPTOR model 

simulations for the representative engine and truck 

technology packages selected for this analysis to assess 

fuel consumption and emissions reduction impacts of 

the technologies.

5. Assessing the incremental and net costs of different 

technologies and technology combinations.

6. Assessing the impacts to the U.S. fleet of heavy-duty 

Class 8 long-haul trucks of widespread introduction 

of advanced technologies to reduce fuel consumption 

and CO2 emissions.

10 Consistent with the classifications used in most existing state and federal regulations, Class 8 heavy-duty vehicles are defined in this study as vehicles with a 

GVWR more than 33,000 lbs.

11 The range of components that can be individually specified in RAPTOR and GT-POWER includes; vehicle and trailer; engine and engine components; clutches; 

transmission elements; control elements; shafts (rigid or torsion-elastic); wheel/tire; electrical components; hybrid components; brakes and auxiliaries (such as 

water pump, air conditioning or power steering). In addition the software allows for modification of assumptions about the driver and about environmental 

driving conditions (such as shift points and road grade (hills)).
20 O v e r v i e w o f t h e S t u d y M e t h o d

R E D U C I N G Heavy-Duty Long Haul Combination Truck Fuel Consumption and CO2 Emissions

Selecting and Defining a Baseline 

Class 8 Truck

Because the focus of this study is long-haul, Class 8 tractor 

trailers, trucks in this category were first evaluated for 

major utility distinctions. The existing heavy-duty truck 

fleet exhibits a wide range of fuel efficiency and design 

features from one vehicle to another. Some of the differences in truck fuel efficiency are driven by necessity. For 

example, some trailer configurations such as bulk haulers 

or flatbeds are less amenable to aerodynamic improvement 

than the standard box van trailers. Operators who go 

off-road or who pull unusually heavy loads generally need 

to use overdrive transmissions that are slightly less efficient 

in top gear than direct drive transmissions. They do this 

to get an adequate gear ratio spread for their applications. 

Operators who run 80,000 pounds or less on highway 

often use overdrive transmissions as well, because an 

overdrive transmission will provide better overall gearing 

for their application. Operators who go off-road or operate 

frequently in low friction conditions also may need to use 

tires with higher traction and thus higher rolling resistance. 

Some operators may find aerodynamic upgrades to be 

cost-effective, while other operators may run into operational issues or may lack the money to pay for upgrades 

even if the payback interval is relatively short. Widespread 

introduction of wide-base single tires, which can provide a 

significant rolling resistance reduction, has been delayed by, 

among other issues, perceived downtime concerns.

A portion of the variation in fuel economy of existing 

heavy-duty vehicles fuel economy is driven not by variation 

in vehicle applications or by practical necessity, but by 

buyer preference. Square nose conventional tractors with 

external air cleaners and dual vertical exhausts mounted 

on the side of the cab are the traditional image of trucking. 

These trucks typically have very high aerodynamic drag. 

Many truckers, especially owner-operators and small fleets, 

persist in buying traditional style trucks, even though 

they use significantly more fuel than more aerodynamic 

tractor designs. They do this because driver satisfaction and 

retention is a big issue for truck fleets, especially smaller 

fleets. The recent spike in fuel prices has reduced sales of 

traditional style trucks, but they have not disappeared from 

the market.

The study team selected an older model of aerodynamic 

truck - the Kenworth T-600 – to be the baseline for this 

study. This was done in part for purposes of practical 

necessity and in part because this truck is representative of 

many trucks on the road today. The reasons for selecting 

this vehicle include:

• Measured drag and rolling resistance coefficients for the 

T-600 are available from a previous SwRI project. 

• The T-600 is more aerodynamic than a traditional 

truck, but not competitive with the latest aerodynamic 

trucks. This truck can be expected to roughly match 

the overall trucking fleet average for aerodynamic and 

rolling resistance performance. 

• The baseline T-600 tractor / trailer combination used 

tires with a rolling resistance typical of current product 

offerings. Dual wheels were used on every axle except 

the steering axle, as is typical on current trucks.

After the baseline vehicle was chosen, a baseline powertrain was selected. The requirements were to select an 

engine that could be modeled with reasonable accuracy at 

the future 2010 emissions standards, and a transmission 

that is typical for long-haul service. SwRI had available to 
O v e r v i e w o f t h e S t u d y M e t h o d 21

them extensive test data from the SwRI Heavy-Duty Engine 

Benchmarking program for three 2007 model year engines: 

a CAT C15, a Cummins ISX, and the Volvo D13. These 

data allowed the calibration of a GT-POWER simulation 

model, which could then be used to explore a range of 

technology options. The engine selected was a 2007 model 

Volvo D13 engine for the following reasons:

• This engine has technical characteristics in common 

with most heavy-duty truck engines that meet 2007 

emissions requirements. High pressure loop cooled 

exhaust gas recirculation (EGR) is used to control NOx 

emissions, while a diesel particulate filter (DPF) system 

is used to control PM.

• The Volvo exhaust emission control approach is 

shared with engines from Cummins, Detroit Diesel, 

Mack, and Mercedes. The only high volume heavyduty truck engines that do not follow this technical 

approach for 2007 emissions are from Caterpillar. 

Because Caterpillar recently announced that it will 

withdraw from the heavy-duty truck market, its 

technical approach is unlikely to be used in future 

heavy-duty trucks. Thus, the Volvo D13 is 

representative of nearly all current heavy-duty engines.

• The Volvo D13 is not offered in the Kenworth T-600 

truck, but it has very similar performance, fuel 

economy, and emissions characteristics to the engines 

that are offered.

An Eaton Fuller 10-speed manual transmission was paired 

with the baseline vehicle for the following reason:

• This transmission offers a very efficient direct drive 

 top gear, and it is widely used in fleets where fuel 

 economy is a priority. The efficiency of a heavy-duty 

 truck transmission in top gear is important to the 

 overall vehicle fuel economy because long-haul 

 trucks typically spend most of their time in top gear.

The representative truck selected for this study has 

aerodynamic and rolling resistance characteristics that 

approximate the average performance of the current truck 

fleet. The representative truck also has a 2007 emissions 

engine that can be upgraded to meet 2010 emissions 

requirements. Finally, the representative truck has a 

manual transmission that has a high market share among 

fuel economy sensitive fleets.

 

The representative truck selected for 

this study has aerodynamic and rolling 

resistance characteristics that approximate the average performance of the 

current truck fleet. The representative 

truck also has a 2007 emissions engine 

that can be upgraded to meet 2010 

emissions requirements. Finally, the 

representative truck has a manual 

transmission that has a high market share 

among fuel economy sensitive fleets.
22 O v e r v i e w o f t h e S t u d y M e t h o d

R E D U C I N G Heavy-Duty Long Haul Combination Truck Fuel Consumption and CO2 Emissions

Validating Simulation Modeling 

Results for the Representative Class 8 

Long-Haul Truck 

As described in the foregoing section, the specifications 

used to describe a representative or “average” truck for 

simulation purposes were based on actual 2007 vehicle 

characteristics. To validate model simulations of the 

vehicle, it was necessary to compare real world data and 

other data for the drivetrain and vehicle with the simulation modeling results for the baseline vehicle and the 

baseline engine adjusted to 2010 emissions performance.

Engine Model

Once the baseline truck and powertrain was determined, 

simulation models were created to allow the evaluation 

of various alternative technologies. The engine simulation 

was done using GT-POWER, which is a commercial code 

widely used for engine cycle simulation. Volvo supplied the 

GT-POWER model used in this project, and SwRI calibrated 

the model using 2007 D13 data measured at SwRI in the 

Heavy-Duty Engine Benchmarking Program. Combustion 

(heat release) data from 12 engine operating conditions 

were evaluated and used to tune the GT-POWER model to 

provide an accurate estimate of actual engine performance 

and fuel consumption. Figure A-1 in Appendix A shows the 

GT-POWER model of the Volvo D13 engine in its baseline 

configuration. 

GT-POWER provides an option for automatic control of 

certain parameters. The automatic control is set up to use 

a selected input, such as fuel quantity, to control a selected 

output quantity, such as engine torque. The initial model 

created for the baseline engine included a torque control to 

match the torque curve of the production engine, and an 

EGR control to match the EGR flow rate measured on the 

production engine. It is required that the model match the 

power and torque of the actual engine. Matching EGR rate 

is also important, because it means that the NOx characteristics of the simulated engine will match those of the actual 

engine. The variable geometry (VG) turbocharger also had 

a controller set to maintain the boost level and control air/

fuel ratio.

In order to determine if the simulation model provides a 

good match to the actual engine, several parameters were 

evaluated. Brake specific fuel consumption (BSFC), exhaust 

temperature, and air/fuel ratio were selected for model 

validation in this study. The goal was for the simulation 

model to be within 4 percent of the actual engine BSFC, 

within 30o C of the actual exhaust temperature, and within 

1 ratio of the actual air/fuel ratio. Figure 6 shows the 

match between the model and experimental engine data 

for BSFC. 

The goal was for the simulation model to 

be within 4 percent of the actual engine 

BSFC, within 30o C of the actual exhaust 

temperature, and within 1 ratio of the 

actual air/fuel ratio.
O v e r v i e w o f t h e S t u d y M e t h o d 23

6

FIGURE

BSFC COMPARISON OF SIMULATION MODEL AND ENGINE TEST DATA

BSFC ERROR

RPM

% Load

100 % Error

 -6.00

 -4.00

 -3.00

 -2.00

 -1.00

 0.00

 1.00

 2.00

 3.00

 4.00

 6.00

800 1000 1200 1400 1600 1800 2000 2200

Max: 5.50

>Range

<Range

Min: -5.90

90

80

70

60

50

40

30

20

The tan and light gray areas of Figure 6 show areas where 

the model comes within 2 percent of the test data. These 

colors dominate most of the area between 1,000 and 

1,900 revolutions per minute (RPM), which is where the 

engine operates for the majority of the time. There is an 

area around 1,500 RPM from 40 percent to 90 percent 

load where the model over-predicts the BSFC by more 

than 2 percent, but less than 3 percent. At 1,200 RPM, the 

model under-predicts BSFC by more than 3 percent from 

40 percent to 80 percent load. Figure 6 shows that BSFC 

predicted by the simulation model is within 4 percent 

of the actual engine data except at very low speed, high 

load (below 1000 RPM) and at 2000 RPM, high load. In 

actual operation, the engine will spend little or no time 

operating at these points, so the match between the engine 

and model was judged successful. Because the truck 

cruise operation is in the 1,300 to 1,500 RPM range, it is 

likely that the engine model will slightly over-predict fuel 

consumption. 

The exhaust temperature predicted by the simulation was 

found to be always within 30o C of the actual engine test 

data, so the match between the engine and test data was 

considered successful. Typical air/fuel ratios at high load 

are as low as 19 or 20. It is important to maintain air/fuel 

ratios at or above the minimum values used on the actual 
24 O v e r v i e w o f t h e S t u d y M e t h o d

R E D U C I N G Heavy-Duty Long Haul Combination Truck Fuel Consumption and CO2 Emissions

engine, to control PM emissions. This is normally only an 

issue at lower speeds and high load. At light load, values as 

high as 60 can be found. For most of the operating range 

of the engine, less than half a ratio error in the prediction 

of air/fuel ratio was found between the modeled and real 

world data. For a small area of the operating range, a 1⁄2 to 

1 ratio underestimate of air/fuel ratio was found. Only at 

800 RPM and 20 percent engine load is the error greater 

than 2 ratios. These results meet the 1 ratio target for 

simulation accuracy in the heart of the operating map. 

Given the results discussed in this section, the engine 

simulation model was determined to be accurate enough to 

use for the baseline 2007 engine.

Adjusting the Baseline Engine to 2010 NOx 

Emissions Requirements

Once the 2007 model year engine data had been validated, 

SwRI adjusted the GT-POWER model so that the baseline 

engine would meet 2010 NOx emissions limits. The model 

year 2007 emission limit for NOx is 1.2 grams per brake 

horsepower-hour (g/bhp-hr). In 2010, the limit will be 

lowered to 0.2 g/bhp-hr. Because heavy-duty powertrain 

and vehicle technologies to reduce vehicle fuel consumption and CO2

 emissions in this study were evaluated for the 

years 2008 and 2017, it was imperative that the baseline 

engine meet 2010 NOx emission standards in the modeling exercise. The Volvo D13 baseline engine uses EGR to 

control NOx, and a DPF to control particulate. For 2010, 

the engine will also use a selective catalytic reduction 

system (SCR) in addition to EGR to control NOx. The 

development of the 2010 engine is not complete, so actual 

test results for the 2010 engine are not available yet. 

Because it is not known exactly how much of the NOx 

will be controlled by the EGR versus the SCR system, SwRI 

estimated the NOx conversion efficiency of the two 

components for the 2010 engine. If it is assumed that the 

EGR system removes most of the NOx emissions, this 

would result in a fuel consumption penalty compared to 

a 2007 engine. Conversely, a very high NOx conversion 

efficiency in the SCR system would allow high engine-out 

NOx, which would reduce fuel consumption. For the 

purposes of this study, SwRI made the assumption of a 

conversion efficiency in the 85 percent range for the SCR 

system, which would allow the engine to maintain 2007 

levels of engine-out NOx. This assumption means that the 

2010 engine is projected to have identical fuel consumption and engine-out NOx to the baseline 2007 version.

It is likely that 2010 engines will have a different engineout NOx level than was assumed by SwRI for this study. 

The error caused by the SwRI estimate that 2007 engineout levels will carry into 2010 unchanged is likely to result 

in an error in fuel consumption and CO2

 emissions of less 

than ±3 percent. Recent comments by engine manufacturers to the National Academy of Sciences committee entitled 

Assessment of Fuel Economy Technologies for Medium and 

Heavy Duty Vehicles indicate that 2010 engines are likely 

to have slightly lower fuel consumption than 2007 engines. 

SwRI did not estimate the additional CO2 emissions that 

will result from the use of urea in the SCR system.

Vehicle Model

A commercial code developed by SwRI called RAPTOR was 

used to model the vehicle, including the transmission and 

driveline. This program has capabilities similar to GT-Drive 

and other commercially available vehicle simulation codes. 

Once the vehicle model was created, it was validated by 

comparing the predicted fuel economy on three drive 

cycles to actual on-road vehicle fuel economy measured 
O v e r v i e w o f t h e S t u d y M e t h o d 25

using the T-600 truck (but with a different 2004 emissions 

engine). For this validation test, drive cycles were created 

to match actual driving cycles of the test truck for which 

data are available. The “Hwy_65_Drive_Sch” uses a 

65 miles per hour (MPH) cruise speed, but the truck 

frequently slows to 30 MPH and then accelerates back to 

65 MPH. This cycle is intended to simulate traffic congestion. The “Line_Haul_Drive_Sch” is not the schedule 

used in this project, but it has similar characteristics. One 

significant difference is lower cruising speeds in the drive 

cycle used for the comparison. The “constant_65_sch” is a 

steady state cruise schedule. In all cases shown in Table 6, 

the vehicle GVW was 80,000 pounds. 

Note that the engine used in the vehicle testing is not the 

same as that used in our modeling. The vehicle has an 

engine that meets 2004 emissions requirements. However, 

the performance and fuel economy characteristics of the 

two engines are very similar. For the model runs, actual 

measured engine data for the 2007 Volvo D13 engine were 

provided as inputs. The results of the vehicle tests and 

model simulations match very well, especially considering 

the fact that the engines are not the same. Differences 

range from less than 1 percent to a maximum of 2.2 

percent on the simulated line haul schedule. Because the 

vehicle model was created using data from the test truck, 

this close match is not unexpected. Table 6 provides a 

comparison of test truck and model results.

Next, a comparison was made between the predicted fuel 

economy using two different sets of input data for the 

vehicle model:

• Measured Volvo D13 engine data from the Heavy-Duty 

Diesel Benchmarking program

• Predicted Volvo D13 engine data from the 

GT-POWER model

Using the baseline engine and vehicle configurations at a 

GVW of 65,000 pounds, a comparison was made between 

measured engine and model results. With the measured 

engine data, the predicted fuel economy on the line haul 

cycle was 5.82 miles per gallon (MPG), while it was 5.66 

MPG using the GT-POWER simulated engine. The GTPOWER model gave results 2.8 percent lower than the 

actual engine data when both were compared using the 

same vehicle model. This is within our target of predicting 

the actual engine performance within 3 percent over a 

driving cycle.

To provide confidence in the engine and vehicle simulations, two levels of comparison were completed successfully. First, the RAPTOR vehicle model was validated 

by comparison to actual truck test results. Second, the 

GT-POWER engine model was validated by comparison 

to actual engine test results. In both cases, the program 

targets for model validation were achieved.

6

TABLE

COMPARISON OF VEHICLE AND MODEL RESULTS

DRIVING CYCLE MODEL MPG VEHICLE MPG DIFFERENCE (%)

Hwy_65_Drive_Sch 4.78 4.83 1.0%

Line_Haul_Drive_Sch 5.69 5.57 2.2%

constant_65_sch 5.54 5.57 0.5%
26 O v e r v i e w o f t h e S t u d y M e t h o d

R E D U C I N G Heavy-Duty Long Haul Combination Truck Fuel Consumption and CO2 Emissions

Selecting a Drive Cycle

As mentioned previously, the target market segment of this 

study is line haul heavy-duty trucking, which accounts for 

about 70 percent of the fuel burned by heavy-duty vehicles. 

Line haul trucking typically involves extended time at high 

speeds. In addition, some time is spent in congested traffic, 

which introduces more variation in vehicle speed. Some 

time is spent getting from the loading dock to the highway 

and back in urban or suburban type driving. This portion 

of the driving cycle may have frequent stops and speed 

variation.

The test cycle used in this study was based on the California Heavy-Duty Diesel Truck Drive Cycle. The California 

cycle was created from analysis of a statistical study of line 

haul truck operations in California. The following changes 

were made to the California cycle for this study, based on 

input from industry experts:

• The portion of high speed driving was increased to 

reflect longer average travel distances

• The speeds used in the California cycle were increased 

by 8 percent to reflect current typical truck operating 

speeds on long-haul routes

• Two segments with grade were added. One segment 

includes positive and negative 1 percent grades, and 

a second segment has positive and negative 3 percent 

grades

Figure 7 shows the drive cycle used in the study. The total 

duration of the cycle is 6,830 seconds (one hour and 54 

minutes), and the total distance traveled is 103.3 miles. 

The average speed over the cycle, including the urban/

suburban portions, is 54.4 miles per hour. The first high 

speed segment reaches a cruising speed of 70 MPH, while 

the remaining high speed cruise segments are at speeds 

ranging from 65 to 67 MPH. The first steady speed cruise 

segment is with no grade. The second steady speed cruise 

segment has an alternating ±1 percent grade. The third 

steady speed cruise segment has an alternating ±3 percent 

grade for a portion of the segment. On portions with a 

positive 3 percent grade, the vehicle will not be able to 

maintain the desired cruise speed. The minimum speed 

achieved by the vehicle on the 3 percent grade will provide 

a measure of the performance penalty or gain from any 

given technology package. The final two steady speed 

segments are run with no grade.

Figure 8 on page 27 shows the grades and elevations on 

the drive cycle used for this study. The x-axis on this figure 

shows distance in miles, rather than time in seconds. In 

Figure 7, the 1 percent grade segment runs from 1,740 to 

2,700 seconds, and the 3 percent grade section runs from 

2,870 to 3,700 seconds. Note that this is a simulation of 

rolling hills, not of mountains.

It is important to note that the drive cycle chosen for 

this study is specific to long-haul trucks. Thus, the results 

described in Chapter 3 are specific to long-haul trucks and 

cannot necessarily be extrapolated to other heavy-duty 

trucks operating on different drive cycles.
O v e r v i e w o f t h e S t u d y M e t h o d 27

7

8

FIGURE

FIGURE

HEAVY TRUCK LINE-HAUL DRIVE CYCLE

GRADES ON HEAVY TRUCK LINE-HAUL DRIVE CYCLE

0

10

20

30

40

50

60

70

80

0 1000 2000 3000 4000 5000 6000 7000

Time (sec)

Vehicle Speed (mph)

-4

-3

-2

-1

0

1

2

3

4

0 20 40 60 80 100 120

Distance (miles)

Grade (%)
28 O v e r v i e w o f t h e S t u d y M e t h o d

R E D U C I N G Heavy-Duty Long Haul Combination Truck Fuel Consumption and CO2 Emissions

Identifying Discrete Vehicle 

Technology Options for Evaluation

A total of 32 technologies were identified and considered 

for inclusion in this project. Table 7 lists the individual 

vehicle technologies considered in this study for purposes 

of evaluating future Class 8 heavy-duty truck fuel consumption and CO2

 emissions reduction potential. A complete 

description of each of the technologies – including an 

explanation of how each option might reduce CO2

emissions – is provided in Appendix A.

Downselection of Technologies Included in 

this Analysis

As a first step toward identifying technology options for 

inclusion in this study, the potential CO2 emissions impact 

of each of the options listed in Table 7 were evaluated. 

The purpose of the evaluation was to identify promising 

technologies and then to identify a select group of 

technologies to be included in a set of “maximum 

reduction” technology combination simulations conducted 

later in the analysis. Technology analysis varied, including 

both literature-based and model-based methods. 

An overview of each technology and the approach used to 

incorporate it into the analysis follows:

Improved SCR Conversion Efficiency

Exhaust after-treatment systems capable of converting a 

high percentage of NOx into N2

 and O2 may yield higher 

powertrain efficiency in the future. This improvement 

would be made possible by permitting different balances 

between engine efficiency and after-treatment efficiency, if 

the durability of such systems is proven by the considerable 

work now going on within the industry.

Depending on how much conversion efficiency can be 

achieved from an advanced SCR system, an improvement 

of up to 3 percent could be achieved in fuel consumption 

and CO2

 emissions. Since it is not clear what increase in 

SCR system performance will prove possible over the next 

few years, and there are no published data that provide 

7

TABLE

VEHICLE TECHNOLOGIES EVALUATED FOR POSSIBLE INCLUSION IN THIS STUDY

ENGINE POWERTRAIN AERODYNAMICS

Improved SCR Efficiency Automated Manual Transmission Fully aerodynamic mirrors

Engine Friction Reduction Moderate Hybrid Systems Cab side extenders

Mechanical Turbocompound Aggressive Hybrid Systems Integrated sleeper cab roof fairings

Electric Turbocompound Aerodynamic front bumper

Dual Stage Turbocharging OTHER TECHNOLOGIES Full fuel tank fairings

EGR Pump Mass Reduction Trailer side skirt fairings

Variable Valve Actuation (VVA) Component Friction Improvements Trailer gap fairing

Advanced VVA Reduced Rolling Resistance Rear-mounted trailer fairing

Alternative Combustion Modes Auxiliary Power Unit Undercarriage Flow Device

Insulated Exhaust Ports Advanced tractor-trailer gap seal

Bottoming Cycle OPERATIONAL CHANGES Advanced rear-mounted trailer fairing

Accessory electrification Lower Road Speed

Increased Vehicle Size and Weight
O v e r v i e w o f t h e S t u d y M e t h o d 29

good guidance on this topic, SwRI did not make projections

based on improved SCR performance. Therefore, the model 

of the 2010 engine matches the efficiency and CO2

emissions of the 2007 engine exactly. 

Engine Friction Reduction

Development of engine main and rod bearings is under 

way to allow the use of lower viscosity engine oils. The 

lower viscosity oil will in turn reduce engine friction in the 

bearings and between the piston, rings, and liner. About a 

10 percent reduction in engine friction is expected if the 

current standard 15W40 engine lube oil can be replaced by 

a 5W30 grade. A more expensive synthetic oil is expected 

to be required in order to allow the use of a lower viscosity. 

For this study, we made the assumption that a 10 percent 

reduction in friction could be achieved, which results in a 1 

percent improvement in fuel efficiency and CO2

 emissions. 

This effect was judged to be small enough to leave out of 

the rest of the study.

Improved Air Handling Efficiency

Almost all turbocharged heavy-duty diesel engines sold 

in North America today use high pressure loop EGR for 

control of engine-out NOx levels. To get EGR to flow from 

the exhaust manifold to the intake manifold, the pressure 

in the exhaust manifold must be higher than the pressure 

in the intake manifold, whereas the opposite condition 

is the result of a higher efficiency engine/turbocharger 

system. To achieve the “negative delta-p” required to cause 

EGR flow, turbocharger efficiency is intentionally sacrificed. Some potential ways of avoiding this and achieving 

improved air handling efficiency are to use high efficiency 

turbocharging in combination with: mechanical or electric 

turbocompounding, an EGR pump, dual stage turbocharging with an EGR pump, or variable valve actuation. 

This technology was evaluated as part of the two 

turbocompound packages.

Mechanical Turbocompound

A power turbine is added to the exhaust system after the 

normal turbocharger. The backpressure created by the 

power turbine allows the use of a very efficient conventional turbo, while still providing the negative delta-p 

required to support EGR flow and harvesting useful work 

from the exhaust stream. The power turbine is geared to 

put power back into the crankshaft through a fluid coupling 

that allows control of turbine speed and isolates the power 

turbine from engine crankshaft torsional vibration. 

Electric Turbocompound

This is the same concept as the mechanical turbocompound, except the power is fed into an electrical machine. 

Electric turbocompound is ideal as a power source for a 

hybrid system, and will in fact require a hybrid system or 

some type of electric propulsion system to utilize the power 

generated by the turbine. Independent control of engine 

speed and turbine speed makes electric turbocompounding 

slightly more efficient than mechanical turbocompounding.

Dual Stage Turbocharging with Intercooling

Achieving the high pressures required by modern engines 

can be done more efficiently with two turbos, where each 

achieves half of the required pressure ratio, and intercooling 

is used between the two turbos and before the intake 

manifold. This approach requires an EGR pump, turbocompound system, or other device to facilitate EGR flow. 

Packaging two turbocharger stages with a turbocompound 

power turbine was judged to be very difficult from a cost 

and mechanical feasibility standpoint, so this approach was 

not evaluated. This technology has a potential benefit of 1 

to 2 percent.
30 O v e r v i e w o f t h e S t u d y M e t h o d

R E D U C I N G Heavy-Duty Long Haul Combination Truck Fuel Consumption and CO2 Emissions

EGR Pump

An EGR pump can facilitate EGR flow and help control 

the flow rate to achieve the desired level of EGR. This 

device makes EGR flow independent of the engine’s 

delta-p, which allows the use of high efficiency air handling 

systems. Energy used by an EGR pump partially cancels the 

efficiency gain from the high efficiency turbocharger we 

pair it with. Based on simple spreadsheet calculations, the 

EGR pump proved less attractive than turbocompound as a 

way of providing the negative delta-p required to drive EGR 

flow. This technology was not included in the analysis.

Variable Valve Actuation

In gasoline engines, variable valve actuation (VVA) can 

have a huge impact on engine performance and fuel 

economy. VVA can be used to improve engine breathing 

over wide engine speed ranges, thus increasing power 

and/or reducing the pumping losses caused by throttling 

the intake. In heavy-duty diesel engines, the potential 

benefits of VVA are much more limited, in part due to their 

narrower range of operating speeds as compared to gasoline 

engines. VVA allows flexibility to operate a turbocharger 

at a more efficient point on the compressor map, but with 

consideration to maintain adequate SCR temperature at 

low loads to prevent an increase in NOx emissions. VVA 

can also be used to improve the power output of a turbocompound system by leaving more energy (temperature/

pressure) in the exhaust stream. Variable valve actuation 

was extensively modeled in GT-POWER, both as a standalone feature and in combination with turbocompounding 

and the bottoming cycle. SwRI results show that the ability 

of VVA to improve diesel engine efficiency as a stand-alone 

feature is rather limited, which agrees with past results 

from several engine makers. 

Advanced VVA:

There are examples in the literature where dramatic 

improvements are claimed from modified engine operating 

cycles that VVA can enable, such as the Sturman “Digital 

Engine” combustion cycle. This cycle is claimed to be 

revolutionary in its ability to inject air during a combustion 

event in ways that are impossible in conventional engine 

arrangements. According to Sturman, this ability opens 

up significant possibilities for efficiency improvement and 

in-cylinder emissions control. Unfortunately, the available 

literature does not provide enough details to allow SwRI to 

attempt to duplicate the claimed results for this study.

Alternative Combustion Modes: LTC / HCCI / PCCI

Low temperature combustion (LTC), homogeneous charge 

compression ignition (HCCI), and premixed charge compression ignition (PCCI) are all “alternative” combustion 

modes that can be used in place of standard diesel combustion. All of these modes have been developed in an effort 

to reduce NOx output, and in the case of HCCI, Particulate 

matter (PM) output as well. If NOx is not an issue, these 

Electric turbocompound is ideal as a 

power source for a hybrid system, and 

will in fact require a hybrid system or 

some type of electric propulsion system 

to utilize the power generated by the 

turbine. Independent control of 

engine speed and turbine speed 

makes electric turbocompounding 

slightly more efficient than 

mechanical turbocompounding.
O v e r v i e w o f t h e S t u d y M e t h o d 31

alternative combustion modes generally suffer from lower 

thermal efficiency than conventional diesel combustion. 

However, conventional diesel combustion suffers substantial thermal efficiency degradation at low engine-out NOx 

levels, so these alternative modes can become attractive. 

The performance of these alternative combustion modes 

is duty cycle dependent: most of the potential is at low 

load. Typically, alternative combustion modes can be used 

up to 30 percent or 40 percent load. Therefore, alternative combustion modes will have little impact on the fuel 

economy or CO2 emissions of an engine that operates most 

of the time at higher loads, such as in a long-haul truck 

application. These modes do not offer a fuel consumption 

or CO2 benefit over standard diesel combustion combined 

with SCR, so the decision was made not to pursue alternative combustion modes for this project. 

Engine Thermal Management Improvements

The goal of thermal management features is to retain 

energy in the gas flow through the engine rather than allow 

heat to be lost along the way. Examples include insulated 

exhaust ports and a bottoming cycle, discussed below.

Insulated Exhaust Ports

Increased exhaust temperature was calculated for an 

engine outfitted with ports insulated using ceramic coatings 

or inserts with air gaps. The retained energy can then be 

used in an energy recovery device, such as a turbocompound system or a bottoming cycle. The energy potential of 

insulated ports and is better at high load, but there can also 

be a benefit from higher temperature into an SCR system 

for improved NOx conversion efficiency. In practice, the 

potential from features such as insulated exhaust ports 

is small.

Bottoming Cycle

A bottoming cycle is a heat engine that uses waste heat 

from the primary engine, in this case the heavy-duty diesel, 

to produce additional work. There are many concepts available for use in a bottoming cycle, including steam turbines. 

Heat sources for a bottoming cycle include exhaust gas 

flow, EGR flow, charge air flow, and engine coolant. The 

great advantage of a bottoming cycle is that it uses “free” 

energy – energy that is otherwise thrown away by the 

primary engine. The great disadvantage of a bottoming 

cycle is that its efficiency is limited by the amount (flow 

rate) and quality (temperature) of waste heat sources, 

further disadvantaged by variability in heat sources linked 

to varied driving conditions. Bottoming cycles have been 

used for many years in stationary power plants, yet so far, 

they have not found application in vehicles because of cost, 

weight, packaging, reliability, and performance challenges. 

The great advantage of a bottoming cycle 

is that it uses “free” energy – energy that 

is otherwise thrown away by the 

primary engine. The great disadvantage 

of a bottoming cycle is that its efficiency 

is limited by the amount (flow rate) 

and quality (temperature) of waste 

heat sources, further disadvantaged by 

variability in heat sources linked to varied 

driving conditions.
32 O v e r v i e w o f t h e S t u d y M e t h o d

R E D U C I N G Heavy-Duty Long Haul Combination Truck Fuel Consumption and CO2 Emissions

After studying the available literature, SwRI decided to 

model a steam turbine bottoming cycle using water as the 

working fluid. Water has well understood properties and a 

boiling temperature favorable for bottoming cycle applications. Disadvantages include risk of freezing, difficulty 

in packaging, surviving on-road vibration, and more, all 

requiring careful engineering design consideration to 

develop a successful system. A sophisticated spreadsheet 

simulation of the bottoming cycle was created in order 

to evaluate alternative designs, taking into account many 

parameters and assumptions, and calculating temperatures, 

pressures and flow rates through the system. 

In the evaluation performed by SwRI, by far the best 

performance was obtained by heating the bottoming cycle 

fluid first with the exhaust gas stream, and then adding 

additional heat from the EGR stream. This approach 

provided much better results than using either of the two 

sources alone. Only about 25 to 30 percent of the exhaust 

flow is devoted to EGR, but it is taken from the exhaust 

manifold before the turbocharger, therefore offering the 

highest quality (temperature) of the available waste-heat 

streams. 

The amount of energy available from a bottoming cycle 

is strongly dependent on engine speed and load. At high 

speed and load, the highest temperatures and exhaust flow 

rates are achieved, which allows a high bottoming cycle 

power. At average loads such as 1400 RPM and 40 percent 

load, the modeled bottoming cycle still contributes 7.5 

percent of total engine crankshaft power, which translates 

into a 7.5 percent reduction in fuel consumption and CO2

emissions.

Transmission System Technologies

Automated Manual Transmission

Most heavy-duty trucks use manual transmissions with 8 

to 18 ratios available. The most common transmissions for 

line haul applications have 10 ratios with an overdrive top 

gear. Torque-converter automatic transmissions, similar 

to those used in passenger cars, are used in some stop/go 

truck applications but are more expensive do not have an 

efficiency advantage in line-haul applications. Automated 

manual transmissions have been available on the market 

for over 10 years now and are increasing in market share. 

Automated manuals have a computer to decide when 

to shift and use pneumatic or hydraulic mechanisms to 

actuate the clutch and hidden shift levers. An automated 

manual can shift as quickly as the best driver, and the 

shift schedule can be tailored to match the characteristics 

of the engine and vehicle. This reduces variability of fuel 

consumption and CO2

 emissions between drivers, with all 

drivers achieving results closer to those of the best drivers. 

An Eaton 10 speed manual transmission was selected as 

the baseline transmission for the project and was simulated 

with a model driver using good shifting practices. The shifting practices chosen for the automated manual transmission were identical, meaning that the automated manual 

showed no CO2/fuel economy benefit. Therefore, the 

automated manual transmission was not included in this 

analysis. In the real-world, there would be a fuel economy 

improvement proportional to the number of non-fuelconscious drivers in a fleet.

Moderate Hybrid Systems

These systems are similar in concept to the mild hybrids 

used in light-duty applications using an integrated starter/

generator, often mounted between the engine flywheel and 
O v e r v i e w o f t h e S t u d y M e t h o d 33

the transmission. Engine start/stop capability is included, 

along with limited duration auxiliary power unit (APU) 

capability using battery power, electrified accessories, 

launch assist, and regenerative braking to recharge the 

battery. The battery size is modest to control cost and 

weight. A moderate hybrid system was not modeled for 

this project. The Steering Committee agreed that a more 

powerful “aggressive hybrid” offered much more potential 

fuel savings for heavy-duty trucks.

Aggressive Hybrid Systems

These systems are similar in concept to the full hybrids 

used in light-duty applications. Both a parallel-hybrid and a 

series-hybrid approach were considered in this study. 

The first approach has a 50kW motor/generator on the 

transmission with a battery, all-electric engine and vehicle 

accessories, and APU-capability using the battery. The 

second hybrid approach modeled for this study was a series 

hybrid in combination with a 2-speed transmission. At 

very low speeds, a 10kWh battery pack drives the wheels 

through a 200kW electric motor without starting the 

engine. At medium speeds, the engine drives a generator 

that drives the wheels using a 200 kW electric motor. The 

special 2-speed transmission is used to directly connect 

engine to the drive wheels only at highway speeds. 

The parallel hybrid was chosen for use in this study. The 

series hybrid model displayed large energy conversion 

losses making this system unattractive. The series hybrid 

approach allows the engine to operate at more efficient 

speed/load points, but this is not enough to overcome the 

energy conversion losses in the electric machines. As a 

result, the series hybrid was not able to provide an 

advantage over the fuel efficiency of the baseline manual 

transmission and was not considered in this study. There 

may be ways of operating the series hybrid that would 

provide better results, but we were not able to get enough 

detail from any company developing a series hybrid system 

to accurately model their approach. 

Vehicle Technologies

Accessory Electrification

The use of a hybrid system or electric turbocompound 

provides a large source of electrical energy that can be 

used to drive accessories that are engine-driven on today’s 

vehicles. Given the availability of significant electric power, 

the following accessories can be converted to electric drive: 

electric power steering (EPS), electric water pump (EWP) 

electric a/c compressor, and an electric air compressor. 

If over 30 kW of electric power is available, the engine 

Given the availability of significant electric 

power, the following accessories can be 

converted to electric drive: electric power 

steering (EPS), electric water pump (EWP) 

electric a/c compressor, and an electric 

air compressor. If over 30 kW of electric 

power is available, the engine cooling fan 

can also be converted to electric drive, 

though in line haul applications the 

efficiency savings from an electric 

cooling fan is normally not required at 

higher vehicle speeds.
34 O v e r v i e w o f t h e S t u d y M e t h o d

R E D U C I N G Heavy-Duty Long Haul Combination Truck Fuel Consumption and CO2 Emissions

cooling fan can also be converted to electric drive, though 

in line haul applications the efficiency savings from an 

electric cooling fan is normally not required at higher 

vehicle speeds. Fan-on time tends to be very low except 

during low speed vehicle operation, since ram air provides 

adequate cooling under most higher speed conditions.

If electric power is not available, there are still some 

technologies that can be applied to reduce the parasitic 

power consumption of accessories. Increased component 

efficiency is one approach, and clutches can be used to 

disengage the alternator and air compressor when they 

are not required. Air compressors that are rotating but not 

creating pressure absorb about half the power of a pumping 

compressor, and compressors normally only pump a small 

percentage of the time in long-haul trucks.

For this study, the accessory power demand of a baseline 

truck was modeled as a steady state power draw of 5 kW, 

and 3 kW for more electrical accessories in individual 

vehicle configurations that included electric turbocompounding and/or hybridization. This 2 kW savings versus 

average engine power of 100 to 200kW over a drive cycle 

nets roughly 1-2% savings compared to a baseline vehicle. 

Component Friction Improvements

Engine friction reduction is described in Appendix A. 

Lower viscosity lubricants, and lubricants whose viscosities are less temperature sensitive, can also be applied in 

transmissions, differentials, and axles. In many cases, these 

components need to be designed to be compatible with 

low friction lubricants. The benefits of friction reduction 

on these components are sensitive to ambient temperature 

with larger benefits found in cold weather. Due to the complexity of modeling friction reductions, realistic reduction 

estimates were included in the overall rolling resistance 

values that are used in Package 2, Package 3, and all subsequent packages, which use the Package 3 values. Package 

2 assumes no change in component friction, while Package 

3 assumes a 10 percent reduction in component friction.

Aerodynamic Drag Reduction

There are many technical features that are available or 

under development to reduce the coefficient of drag (Cd) of 

a heavy-duty truck. Because reliable data are not universally available from independent sources on the effects of 

individual features and because modeling the effects of 

individual features was beyond the scope of this project, we 

modeled the effect of changes in overall Cd from “off-theshelf” and “emerging” technologies on the fuel economy 

and CO2

 emissions of the truck.

A long list of aerodynamic features initially discussed was 

used as a starting point to down-select technologies for 

the study. That list included: reduced tractor to trailer gap, 

trailer side skirts and undercarriage skirts, a boat tail, boat 

tail plates, integrated tractor roof fairings, a tractor “eyebrow,” frontal area reduction (not implemented, in order 

to keep carrying capacity constant), trailer edge rounding, 

vortex generators, guide vanes, active and passive pneumatics, aerodynamic mirrors, replacement of mirrors with 

cameras, a trailer underbody wedge, fuel tank fairings, 

bumper fairings, and hidden vertical exhaust stacks.

Aerodynamic improvements considered for this study were 

broken into two groups, as shown in Table 8.
O v e r v i e w o f t h e S t u d y M e t h o d 35

“OFF-THE-SHELF” IMPROVEMENTS 

Fully aerodynamic mirrors Mirrors shaped and positioned to minimize drag.

Cab side extenders Designed to reduce the tractor-trailer gap.

Integrated sleeper cab roof fairings Large fairings to match the roof height of a truck to the height 

of the trailer.

Aerodynamic front bumper For smoother airflow around the hood and wheels.

Full fuel tank fairings To smooth airflow over fuel and air tanks.

Trailer side skirt fairings To deflect air away from the trailer undercarriage.

Trailer gap fairing Mounted to the trailer to reduce the tractor-trailer gap.

Rear-mounted trailer fairing Sometimes called a 'boat tail,' used to reduce drag at the 

rear of the trailer.

“EMERGING” IMPROVEMENTS 

Undercarriage Flow Device (UFD) To further deflect air away from the trailer's undercarriage.

Advanced tractor-trailer gap seal

A device that creates a nearly-complete closure of the tractortrailer gap. This will require redesign of the tractor and trailer 

shape.

The baseline Kenworth T-600 truck with a standard 53 

foot van trailer is known to have a Cd of 0.63, a value that 

can be expected to roughly match the overall trucking fleet 

average. From the baseline, two packages of aerodynamic 

improvements were considered.

The off-the-shelf improvements were incorporated into a 

group known as Package 2, representing a full implementation of technologies currently recommended by EPA Smart 

Way. This package assumed a drag coefficient of 0.5. A 

second, more aggressive aerodynamic package called 

Package 3 looked at a feasible drag coefficient for 2017. 

After much discussion in the Steering Committee, a drag 

coefficient of 0.4 was selected, based on available data 

regarding emerging aerodynamic improvements. To reach 

a value of 0.4, vehicle design changes that go well beyond 

those listed above, and which have some effect on the 

operation of the truck are likely to be required. Since the 

technology is not mature at this time, the impact of these 

operational changes has not yet been determined. This 

means that some risk is inherent in the assumption that a 

Cd of 0.4 is achievable within the time frame of this study.

Mass Reduction

Reduced mass can benefit fuel efficiency and CO2

 emissions 

in two ways. If a truck is running at its gross vehicle weight 

limit with high density freight, more freight can be carried 

on each trip, increasing the trucks ton-miles per gallon. If 

8

TABLE

AERODYNAMIC IMPROVEMENTS CONSIDERED
36 O v e r v i e w o f t h e S t u d y M e t h o d

R E D U C I N G Heavy-Duty Long Haul Combination Truck Fuel Consumption and CO2 Emissions

the truck is carrying lower density freight and is below the 

GVW limit, the total vehicle mass is decreased, reducing 

rolling resistance and the power required to accelerate or 

climb grades.

Weight reduction can be achieved by making components 

with lighter materials (high strength steel, aluminum, 

composites) or by eliminating components from the 

truck. A common component-elimination example is to 

use wide-base single tires and aluminum rims to replace 

traditional dual tires and rims, eliminating 8 steel rims and 

8 tires. Many of the features being added to modern trucks 

to benefit fuel economy, such as additional aerodynamic 

features or idle reduction systems, have the effect of 

increasing truck weight.

Reduced Rolling Resistance

Lowering the rolling resistance of tires through improved 

design and inflation reduces the power required to move 

the truck down the road, directly reducing fuel consumption and GHG emissions. A well designed wide-base single 

tire has lower rolling resistance than traditional dual tires 

and manufacturers also offer low rolling resistance versions 

of dual tires. Automatic tire inflation and tire monitoring 

systems also lower the rolling resistance by helping drivers 

operate their tires at optimum pressure. Actual vehicle testing yielded baseline rolling resistance data, while improved 

values used in the technology packages were provided by 

EPA SmartWay and Michelin. An important consideration 

with lower rolling resistance is that traction and braking performance often suffer as the rolling resistance is 

reduced. A balance must be achieved that provides the 

lowest practical rolling resistance without too great of an 

effect on vehicle performance or safety.

Lower Road Speed

Since aerodynamic drag is a function of speed squared, 

reducing speed can improve vehicle fuel economy and 

CO2

 emissions. Limits to this approach include delivery 

time requirements for certain cargo or an increase in the 

number of trucks on the road to deliver a given amount 

of freight. Any possible increase in the number of trucks 

caused by lower speeds could be eliminated by a proportional increase in truck size and weight. To model the 

impact of speed alone, a speed limit of 65, 60 and 55 MPH 

was imposed on the chosen drive cycle.

Increased Vehicle Size and/or Weight

Trucks that travel at maximum weight or with a maximum 

volume of cargo could deliver more freight if heavier 

or larger longer trailer combinations, respectively, were 

allowed. A truck is said to be “cubed-out” when it is full 

of low density freight, while a truck at the GVW limit is 

Lowering the rolling resistance of tires 

through improved design and inflation 

reduces the power required to move the 

truck down the road, directly reducing 

fuel consumption and GHG emissions. 

A well designed wide-base single tire 

has lower rolling resistance than 

traditional dual tires and manufacturers 

also offer low rolling resistance versions 

of dual tires.
O v e r v i e w o f t h e S t u d y M e t h o d 37

said to be “grossed out” when it is full of high density 

freight. Maximum operating efficiency is achieved if a 

trucking company is able to load the truck until one or 

both of the limits are reached. Increase in the permitted 

size and weight of trucks could reduce fuel consumption 

on a ton-mile basis and lead to lower CO2 emissions for the 

fleet provided that concerns including infrastructure are 

addressed. This study considered a 3-axle 53’ trailer and 

a variety of Long Combination Vehicles (LCVs) but settled 

on one LCV known as a Rocky Mountain Double (RMD) 

that consists of a standard 45-48’ trailer towing a second 

28’ foot trailer with a maximum GWVR of 120,000lb. 

Modeling accounted for these changes by adjusting Cd 

and rolling resistance to represent larger, heavier vehicles. 

Real and publicly perceived safety considerations of larger 

and heavier trucks could be addressed by mandating driver 

training, vehicle performance characteristics such as braking performance and crash compatibility, and by requiring 

technologies such as stability control, crash avoidance, and 

more.

Idle Reduction

Line haul truck engines use a significant amount of fuel 

meeting overnight “hotel loads” for drivers. These hotel 

loads include heating, cooling, and electricity to power appliances (televisions, computers, etc). A typical truck uses 

hotel loads that range from 3 to 5 kW (U.S. DOE 2000). 

Trucks frequently idle their engines throughout the evening 

to meet these loads. Because truck engines are sized for 

much higher on-highway power requirements, the engine 

operates very inefficiently to provide these small amounts 

of power. EPA (SmartWay 2009) estimates that an idling 

engine consumes 0.8 to 0.9 gallons of diesel per hour. The 

amount of time that a truck spends idling is estimated to 

run as high as 2,400 hours per year (nominally 8 hours 

per day, 300 days per year) (SmartWay, 2009). Sodolsky 

(2002) estimates the average idle time for long haul trucks 

to be 1,800 hours per year. These estimates suggest that a 

typical line haul truck without idle reduction technology 

uses 1,500 to 1,600 gallons per year; total on-road fuel use 

for a truck that travels 120,000 miles at 6 MPG is 20,000 

gallons, so overnight idling can consume 7 to 8 percent of 

the truck’s fuel.

There are several approaches for powering hotel loads 

more efficiently. These include shore power systems, which 

plug in to an off-board electricity source; direct fire heaters, 

which burn diesel fuel directly to meet heating loads; 

automatic engine idle control systems, which intelligently 

power the engine on and off throughout the evening; battery powered systems, which use energy stored in a battery 

pack charged by the engine; and auxiliary power units, 

which are small, highly efficient diesel generators. These 

idle reduction technologies are all currently available either 

through third party vendors or as add-on options to trucks 

directly through manufacturers. 

Our analysis focused on the potential for achieving idle 

reduction using an APU, included in the SmartWay technology (package 2); and a battery-based system, included as 

part of the hybrid package (package 4). We did not evaluate 

shore power systems, as this represents an infrastructure 

challenge that lies outside the scope of the study. We 

selected an APU rather than a battery based system as 

part of the SmartWay package because these systems are 

capable of providing hotel loads for longer periods; battery 

based systems require that the engine be powered on 

frequently (a few minutes per hour) to recharge the battery. 
38 O v e r v i e w o f t h e S t u d y M e t h o d

R E D U C I N G Heavy-Duty Long Haul Combination Truck Fuel Consumption and CO2 Emissions

The hybrid package uses a battery-based system because 

all of the tertiary systems are already included in standard 

hybrid vehicle, so idle reduction is realized for “free.” Both 

of these systems are estimated to reduce fuel use to 0.2 

gallons per hour (SmartWay 2009), which reduces fuel use 

by approximately 6 percent on a line-haul truck.

In addition to estimating the emission reduction potential 

of each of the individual technology options described 

above and listed in Table 7, rough cost estimates were 

developed for each option to gauge the relative cost-effectiveness of employing one CO2

 reduction technology versus 

another. In most cases, costs available in the literature were 

reported as retail costs. In two cases, discussed in more detail on page 43 of this chapter, factory component hardware 

costs were converted to retail costs using a markup factor 

of 2.0 by TIAX.

Overall, the study encompassed technologies that are 

already in production for the U.S., European, or Japanese 

truck markets, or that are known to be under development 

for production in these markets. These technologies were 

identified by SwRI, by other members of the NESCCAF 

study team, or by the Research Steering Committee formed 

to provide advice during this project. SwRI performed the 

fuel consumption and CO2

 analysis, while TIAX assembled 

functional definitions of each of the CO2 reduction technologies as they were modeled by SwRI, gathered industry 

information on specific technologies using interviews and 

technical papers, and performed a cost and impact study 

using adoption-rate estimates. The results of TIAX’s analysis 

were reported in the form of a matrix of the truck-level 

difference in hardware costs (relative to a baseline truck) 

for any given package of technologies. The cost matrix is 

summarized in Appendix B.

Future Developments in Heavy-Duty 

Truck Technology

As mentioned above, SwRI did not consider fuel 

consumption and CO2 reduction technologies unless 

they are currently in production or for which a design 

specification is available in the literature. As such, the 

study findings do not represent the total available potential 

to reduce heavy-duty vehicle fuel consumption and CO2

emissions – the results only estimate what can be done 

given known technologies. Going forward, more advanced 

technologies to improve engine, vehicle, and transmission 

technologies could and will likely be developed that would 

further reduce truck fuel consumption and CO2

 emissions 

beyond the 2017 timeframe. Engine manufacturers and 

others are currently working on advanced approaches to 

improve truck efficiency. Some of these technologies could 

include: 

• Improvements in thermal efficiency. The 21st Century 

Truck Program has established a target of reaching a 

55 percent thermal efficiency for heavy-duty vehicles. 

An efficiency similar to that level was not evaluated 

because a technical path to achieve this goal has yet to 

be identified or demonstrated

• Further reductions in engine friction

• Advanced variable valve actuation that is used to create 

a new type of engine cycle (Sturman Digital Engine)

• Alternative combustion modes (HCCI, PCCI, LTC, 

others to be invented)

• Advanced bottoming cycles and exhaust thermalto-power schemes that extend beyond the steam 

bottoming cycle concept modeled in this study
O v e r v i e w o f t h e S t u d y M e t h o d 39

Modeling technologies such as those described in the list 

above was beyond the scope of this project for two reasons: 

first, some of the technologies require very sophisticated 

and expensive modeling, and second, in several cases it is 

not clear from the literature exactly what to model. Additional strategies are also available to reduce fuel consumption and GHG’s from transporting freight that were outside 

the scope of this analysis including intermodal shipping, 

improved logistics to avoid congestion and reduce empty 

hauls, driver training and driver aid technologies (real-time 

fuel economy monitors, GPS systems for anticipating road 

grade changes), improved efficiency for refrigerated cargo, 

amongst others. 

Assembling Technology Packages for 

Model Simulation

Using the most promising individual technologies that 

emerged from the initial screening evaluation described 

above, in combination with cost estimates for the individual technologies, a series of technology packages was 

assembled for modeling. Generally, these packages were 

designed to span a wide range of CO2 reduction potential 

so they necessarily reflect a wide range of impacts 

and costs. 

Package 2 represents a suite of technologies recommended 

by the EPA Smart-Way program and available for purchase 

today, including aerodynamic improvements, low rolling 

resistance tires, and an APU. Package 2 goes one step 

beyond Smart-Way by including the rolling resistance 

benefits of the best currently available wide-base single 

tires. Package 3 represents a further improvement of 

aerodynamics and tires, based on estimates of the capability 

of emerging technologies. 

Most of the remaining packages have been modeled in 

comparison to the baseline Package 1 and Package 3. 

Packages 4 through 8 and Package 11 were each modeled 

to determine their ability to reduce fuel consumption of an 

otherwise baseline truck. These powertrain-focused options 

were evaluated separately to provide a clearer understanding to the team about how they might be combined in the 

final “maximum reduction” packages.

Packages 9 and 10 are unique, in that they involve operational changes to trucks and do not require new technologies. Introducing these changes broadly might, however, 

require regulatory changes. The effect of speed on fuel 

economy is well understood and a variety of types of Long 

Combination Vehicles that carry more freight are already in 

use in most states in the US and in Canada. 

Packages 12-14 use differing combination of technologies 

and operational changes to demonstrate various paths to 

achieve a maximum reduction in CO2

 using the technologies included in the study available for incorporation into 

trucks prior to 2017.

A full GT-POWER and RAPTOR simulation was then 

performed for each technology package, using the performance constraints identified for 2017 models. For all 

packages except for Package 9 (the longer / heavier vehicle 

combinations), engine performance (power and torque) 

remained the same as the 2007 baseline vehicle. Engine 

power was increased in Package 9 to accommodate the 

higher vehicle weight. The specific packages evaluated, 

along with model simulation results for each package, are 

presented in Chapter 3.
40 O v e r v i e w o f t h e S t u d y M e t h o d

R E D U C I N G Heavy-Duty Long Haul Combination Truck Fuel Consumption and CO2 Emissions

9

TABLE

DESCRIPTION OF TECHNOLOGIES SIMULATED BY SWRI

PACKAGE PACKAGE NAME DETAILED PACKAGE DESCRIPTION

1 Baseline Volvo D13 (2010 emissions), Kenworth T600, 10-speed 

manual transmission

BUILDING BLOCK TECHNOLOGIES

2 SmartWay 2007 (SW1)

Additional aero streamlining sufficient to reduce the coefficient of drag from 

0.63 to 0.5 to the cab and the trailer. Fully aerodynamic mirrors, cab side 

extenders, integrated sleeper cab roof fairings, aerodynamic bumper, and 

full fuel tank fairings. Trailer streamlining includes a side skirt fairing, and 

either a trailer gap fairing or a rear-mounted trailer fairing such as a boat 

tail. RR of 0.0055. Wide-base singles and aluminum wheels. Idle reduction, 

improved transmission and axle lubricants

3 Advanced SmartWay (SW2)

Package #2 plus advanced aero and rolling resistance package. Includes 

continued streamlining of the cab/trailer combination, a reshaped trailer, 

boat tail, full skirting of cab and trailer, tractor-trailer gap fairing, and very 

low rolling resistance tires 

4 Parallel hybrid-electric powertrain 

(HEV) Parallel hybrid system 

5 Mechanical Turbocompound Mechanical turbocompound plus package #7

6 Electrical Turbocompound Electrical turbocompound plus package #7

7 Variable Valve Actuation (VVA) Variable valve actuation

8 Bottoming Cycle Bottoming cycle 

11 Advanced EGR Advanced exhaust gas recirculation 

OPERATIONAL MEASURES

9 Rocky Mountain Double 

Trailers (RMD) Longer/heavier trailer (Rocky Mountain doubles – 48’ and 28’ trailers) 

10 60 mph speed limit Slower road speed (60 mph) 

MAXIMUM REDUCTION COMBINATION PACKAGES

12 Maximum Reduction Combo 1 Standard 53’ trailer, hybrid, bottoming cycle, advanced aero and rolling 

resistance package, 60mph speed limit (packages #3, #4, #8, #10)

13 Maximum Reduction Combo 2 

Longer heavier trailer, bottoming cycle, hybrid, electric turbocompound, 

VVA, advanced aero and rolling resistance package, 60 mph speed limit 

(packages #3, #4, #6, #7, #9, #10)

14 Maximum Reduction Combo 3 Longer heavier trailer, hybrid, bottoming cycle, advanced aero and rolling 

resistance package, 60 mph speed limit (packages #3,#4,#8,#9, #10)
O v e r v i e w o f t h e S t u d y M e t h o d 41

An important benefit of simulating the performance of 

technology packages, rather than individual technologies, 

is that it eliminates the possibility that CO2 reductions will 

be “double counted.” The emissions benefits associated 

with various options do not necessarily add when these 

improvements are combined in a single vehicle, particularly 

to the extent that many technologies target the same 

sources of mechanical or thermodynamic inefficiency. The 

simulation modeling conducted for this analysis avoids 

this problem. At the core of each simulation is an engine 

map that defines CO2 emissions over a full range of engine 

speed and load points. Each map reflects the contribution 

of all engine technologies incorporated in the vehicle and 

therefore accounts for their composite impact on CO2

emissions. Engine maps were completely replaced for each 

engine technology package simulated in this analysis; they 

were not added or otherwise manipulated. In the case of 

technologies that do not directly affect the engine map 

but rather the point on the map at which a vehicle is 

operating (e.g., rolling resistance or aerodynamic drag), 

the simulation model ascribes benefits to those technologies in accordance with their cumulative effect on engine 

operation. Thus, at any given point in time, the vehicle is 

simulated as operating at one speed/load point as determined by the combination of technologies present; in turn, 

the specific CO2 emissions rate for that point in time is 

simply read from the underlying engine map. 

The following example briefly illustrates how this process 

works. As described above, combinations of technologies are modeled as a complete vehicle system. Take, for 

example, a technology package consisting of a combination 

of improved aerodynamic drag and reduced vehicle speed. 

These improvements will reduce the power demand on 

the engine. However, when modeled in combination, the 

package provides a reduction in fuel consumption that is 

somewhat less than the sum of the individual technology 

benefits. The reason for this is that the relative benefit of 

aerodynamic drag improvements changes with speed, since 

aerodynamic drag is proportional to the square of speed.

In our example, one could measure or simulate at 65 MPH 

the improvement in fuel consumption caused by moving 

from a baseline aerodynamic package to a new aerodynamic package. Next, one could measure or simulate 

the reduction in fuel consumption caused by slowing the 

baseline truck from 65 MPH to 60 MPH. Unfortunately, 

the two improvements cannot be simply added together to 

determine the benefit caused by both improving aerodynamics and lowering vehicle speed. A more aerodynamic 

truck will have a lower drag force, and therefore it will not 

benefit from lower speed to the same extent as a higher 

drag truck. There are two correct paths to determine the 

benefit of combining these two technologies, and one path 

that gives the wrong answer:

1. Correct: first simulate the benefit of improved 

aerodynamics at 65 MPH, and then calculate the 

benefit of lower speed, using the new, lower coefficient 

of drag (Cd) value. These two improvements can be 

added together. 

2. Correct: first calculate the benefit of lowering speed 

from 65 to 60 MPH, and then determine the benefit 

of improved aerodynamics at 60 MPH. These two 

benefits can be added together. 

3. Incorrect: calculate the benefit of improved 

aerodynamics at 65 MPH and calculate the benefit of 

lower speed using the baseline Cd. These two benefits 

are not fully additive.
42 O v e r v i e w o f t h e S t u d y M e t h o d

R E D U C I N G Heavy-Duty Long Haul Combination Truck Fuel Consumption and CO2 Emissions

Note that changes in drag coefficient and speed may result 

in a change in required engine power that is different from 

the fuel economy benefit that is realized. For example, a 

given set of changes might reduce the power requirement 

by 30 percent. If all things remain equal, a reduction in 

power required should translate directly into a 30 percent 

fuel savings. However, if the engine then has to operate at a 

less efficient point on its map, the overall fuel savings might 

be less, for example only 28 percent. Conversely, if the 

changes in vehicle power demand put the engine at a more 

efficient point on its operating map, the fuel savings will be 

larger than the reduction in power demand. The simulation 

technique used in this project accounts for these situations.

Some technologies tend to interfere with each other’s 

performance. This interference may be so large that one 

would not consider combining the two technologies. An 

example of this is a combination of low temperature EGR 

and a bottoming cycle or a turbocompound system. Low 

temperature EGR by itself reduces fuel consumption, 

but if it is combined with a system that extracts energy 

from the exhaust, the two technologies work against 

each other. Low temperature EGR reduces the exhaust 

stream temperature, which will lower the performance of 

a turbocompound system or a bottoming cycle. Thus, the 

benefits of low temperature EGR and either turbocompound or a bottoming cycle cannot be added together. 

Similarly, turbocompound and a bottoming cycle cannot be 

combined without substantially degrading the performance 

of one of these systems. Because both systems work to 

extract energy from the exhaust, they cannot be added 

together to provide a benefit even close to the sum of the 

two individual benefits.

Method of Estimating Cost of 

Technology Packages

For each of the technology combinations listed in Table 9, 

TIAX developed net cost estimates from direct published 

quotes and pricing guidelines such as those published by 

the EPA SmartWay program. Net hardware costs in this 

context include system and component costs, as well as 

applicable credits in instances where the use of a particular 

technology would reduce other component or system costs. 

For example, the entire cost of lightweight tires is not 

added to the cost of a truck because the lightweight tire 

purchase is partially offset by the avoided cost of standard 

tires. 

When more than one value was found, the estimated 

cost was calculated by averaging all values. Key reference 

sources for most of the cost estimations are listed in 

Appendix C. Input from industry experts was also 

incorporated, particularly when the technologies were not 

currently available for purchase. Cost assessments were 

based on the assumption of reasonable volume production 

for the Class 8 line haul truck industry and corresponding 

market penetration. 

Once costs for individual technologies 

were developed, TIAX integrated these 

values to arrive at cost estimates for the 

technology packages modeled by SwRI. 

Total package costs were calculated based 

on the assumption that for each tractor 

equipped with new technologies, three 

trailers would need to be equipped. 
O v e r v i e w o f t h e S t u d y M e t h o d 43

For certain pre-commercial technologies (such as bottoming cycle), the estimated costs were developed from a 

typical bill of materials assuming design and development 

costs would be fully amortized. Once costs for individual 

technologies were developed, TIAX integrated these values 

to arrive at cost estimates for the technology packages 

modeled by SwRI. Total package costs were calculated 

based on the assumption that for each tractor equipped 

with new technologies, three trailers would need to be 

equipped. This was based on the industry average ratio of 

existing in-use trailers to tractors. Because the packages 

included technologies affecting different aspects of the 

vehicle (engine, transmission, aerodynamics, etc.), in 

most cases the costs were additive. However, there were 

some cases (e.g., hybridization combined with electricturbo-compounding) for which double-counting had to 

be avoided to arrive at an estimated system cost. TIAX 

addressed these situations by developing a bill of materials 

for each technology package, and from this bill of materials

duplicative components were removed. All of the 

technology packages were compared to the 2007 

baseline (Package 1).

As described above, rough cost estimates were developed 

for each option to gauge the relative cost-effectiveness of 

employing one CO2

 reduction technology versus another. 

This task was performed using available information on 

incremental system and component hardware costs. TIAX 

obtained incremental system and component hardware 

costs as retail costs. In the case of two technologies – 

bottoming cycle and hybridization – costs were calculated 

as incremental factory manufacturing cost to truck and 

engine manufacturers. For these two technologies, the 

impact on the retail price of the trucks from a consumer 

perspective was then estimated by applying a factor of 2.0 

representing “Retail Price Equivalent” (RPE). The basis 

for this factor is a series of U.S. Department of Energy 

reports published on hybrid electric and automotive fuel 

cell system manufacturing cost. Although these reports are 

based on the light-duty automotive sector, we assume that 

roughly the same market dynamics apply to the heavy-duty 

vehicle manufacturing sector (i.e., many of the same Tier 

One suppliers serve both light-duty and heavy-duty original 

equipment manufacturers (OEMs), and have high-volume 

manufacturing and relatively low margins). Therefore, 

the 2.0 factor is a reasonable factor for estimating RPE for 

heavy-duty vehicle technologies. The ratio of retail price 

to ex-factory cost was taken at 2.0 assuming that for these 

line haul packages, first tier suppliers would provide most 

components to the OEM truck builder. A lower ratio would 

be appropriate only if all the technology components were 

manufactured from raw materials by the OEM.

The retail price equivalent includes:

• Actual cost of materials, parts and assembly labor, 

including facilities, factory tooling (amortized), 

equipment maintenance, depreciation cost of operating 

capital and utilities, and other process costs

• Factory overhead or mark-up of the OEM and/or Tier 

One supplier includes items such as warranty, research 

and development, engineering, depreciation, legal, 

marketing and sales, corporate overhead, retirement 

and health benefits, accounting, shipping and 

distribution, corporate taxes, and dealer support

• Dealer discount or mark-up

• Profit
44 O v e r v i e w o f t h e S t u d y M e t h o d

R E D U C I N G Heavy-Duty Long Haul Combination Truck Fuel Consumption and CO2 Emissions

TIAX’s cost estimates attempt to capture all costs to the 

manufacturer of incorporating new technologies, and 

include an estimate of cost impact at the consumer level 

as reflected in the purchase price of a new vehicle.

All costs are presented in 2007 U.S. dollars and assume 

the subject technologies will be manufactured in a highly 

competitive environment using flexible and lean manufacturing methods. Costs are estimated for the year 2012 

and beyond assuming that each manufacturer will produce 

between 2,000 and 10,000 units per year, thereby 

achieving full economies of scale. Importantly, TIAX 

did not assume future cost reductions due to currently 

unknown advances in either technology design or manufacturing – future costs reflect fully learned, high-volume 

production of current technology designs. To the extent 

that basic science advances in design or manufacturing do 

occur, future costs may be lower than estimated. To the 

extent that development may require additional features 

or improvements to achieve the expected performance 

with adequate reliability and durability, future costs may be 

higher than estimated.

Method of Cost-Benefit Analysis

As described above, for each of the technology packages 

an incremental and retail price equivalent cost was 

determined and is presented in the cost results section of 

Chapter 3. Using the incremental vehicle costs and 

operations & maintenance (O&M) costs, the net cost 

of ownership was calculated for each of the technology 

packages. This analysis takes into account the savings 

realized through reduced fuel use over two time periods: 

(1) a 15-year time horizon; and (2) a three-year time 

horizon.12 The 15-year vehicle life is a good proxy for 

determining societal benefit from adopting a new technology, and hence may be used to justify regulation. However, 

experience suggests that truck operator use a far shorter 

time horizon in making their vehicle purchase decisions. 

The basic elements of these calculations are described 

below. A more detailed description of the cost-benefit 

analysis is provided in Appendix C.

The TIAX analysis weighs the fuel savings against capital 

costs and any change in the yearly maintenance cost, such 

as impacts on brake maintenance, major overhaul intervals 

and other operation and maintenance costs. Future costs 

and benefits are discounted at a rate of 7 percent per year. 

The 7 percent figure has been used in regulations such as 

the EPA’s Tier 2 [1999] and Heavy-Duty Vehicle Regulations 

[1997]. Cost of ownership is defined as follows:

Cost of ownership = (Capital Cost) - Σ(Fuel saved – O&M)/(1+r)t

Where r is the discount rate (7 percent), t is the age of the 

vehicle, and the fuel savings and O&M costs are expressed 

in dollars per year, and are summed (Σ) over either a 

three-year or a fifteen-year time horizon. A negative cost of 

ownership implies that a given technology saves the buyer 

money.

The fuel savings accrued over the life of the vehicle, and 

hence ownership costs, are very sensitive to a truck’s 

annual mileage, which varies as a function of vehicle age. 

This age dependence was estimated using data from the 

12 The 15-year vehicle life is a good proxy for determining societal benefit from adopting a new technology. However, experience suggests that truck operator use 

a far shorter time horizon in making their vehicle purchase decisions . Several industry sources have suggested payback periods of 18 to 24 months to justify an 

investment in fuel saving technology. There may be extreme cases where fleets run tractors for a 15-year period, however, this would be extremely rare. Over the 

road operators typically run 4 years and then sell or trade the vehicle. Because of this an owner of a heavy-duty long haul truck will not realize a cost benefit from 

introduction of technologies that have a payback period longer than 2 years, even though over the life of the vehicle the technologies could be cost effective. 

Thus, without regulation or subsidies, many of the technologies evaluated would not likely be introduced into the market.
O v e r v i e w o f t h e S t u d y M e t h o d 45

2002 Vehicle Inventory and Use Survey [VIUS 2002], a 

wide-ranging survey of the commercial trucking industry; 

additional confirmation was provided by discussions with 

industry stakeholders. Over the first three to four years of 

the vehicle life, trucks operate in long-haul service, which 

is characterized by upwards of 100,000 miles traveled 

per year, primarily, long-range trips (a radius greater than 

several hundred miles), and travel primarily over interstate 

highways at highway speeds. This type of duty-cycle 

typically dominates the first five to seven years of a tractor’s 

life. As trucks age, they tend to migrate into local and regional applications, and a growing fraction get retired from 

service altogether. Regional operators tend to drive much 

shorter distances (on the order of 50,000 miles per year); 

operate within a confined region; and travel a significant 

number of miles in urban or exurban areas at lower speeds 

with more frequent stops. The median age of trucks in 

regional operation is on the order of 18 to 20 years. In 

sum, the long-haul portion of a truck’s service life accounts 

for 60 percent to 70 percent of the total tractor-trailer fuel 

use [VIUS 2002].

The cost of ownership calculations account for this age 

dependence by treating mileage as a function of age. In the 

case of calculations over a 3-year time horizon, mileage 

is assumed to remain constant at 120,000 miles per year. 

Over a 15-year time horizon, the annual mileage for a 

typical truck on long-haul duty cycles declines dramatically 

9

FIGURE

2008 EIA LONG-TERM ENERGY OUTLOOK DIESEL PRICE SCENARIOS

$0.00

$0.50

$1.00

$1.50

$2.00

$2.50

$3.00

$3.50

$4.00

2005 2010 2015 2020 2025 2030

Diesel Price ($/Gal)

Reference

Low

High
46 O v e r v i e w o f t h e S t u d y M e t h o d

R E D U C I N G Heavy-Duty Long Haul Combination Truck Fuel Consumption and CO2 Emissions

to less than 20,000 miles per year13. Our cost of ownership 

analysis focuses only on the long-haul portion of a truck’s 

service life. This means that fuel savings accrued during 

regional operation are not accounted for. These unaccounted for savings from regional service may be significant for 

certain technologies that were considered, such as hybrids; 

but fairly small for others, such as aerodynamic improvements or 60 MPH speed governors. In addition, the long 

trailer or double trailer configurations that were considered 

are not feasible for regional haulers. A more detailed 

discussion of this issue is presented in Appendix D.

Fuel price scenarios were a critical element of the analysis 

of fuel-savings benefits, and we relied on DOE Energy 

Information Administration (EIA) forecasts from their 2008 

long-term energy outlook, shown in Figure 9 [EIA 2008]. 

As additional forecasts are released by EIA these can be 

readily used to update the analysis. 

Fleet-Wide Emissions Benefit 

Analysis Methodology

The last step in the heavy-duty CO2 analysis was to 

estimate the amount of fuel and CO2 reduced through 

widespread adoption of heavy-duty technologies into the 

U.S. fleet of heavy-duty Class 8 long-haul trucks. This work 

is described below.

Fleet Characterization

To project the fleet-wide effect of the technology packages 

described above, TIAX developed a spreadsheet-based 

heavy-duty fleet model. The fleet model uses estimates of 

new truck sales, scrap rates, vehicle miles traveled, and 

fuel economy to develop a bottom-up estimate of fleet-wide 

13 This mileage estimate represents long-haul miles for a typical truck. Included in this “average” data is the fact that some trucks are scrapped, and that most miles 

are driven on regional routes. Analysis of a regional duty-cycle was not conducted for this study.

characteristics, such as fleet fuel use, fleet VMT, and truck 

population. The model uses historical data to estimate 

the size, composition, duty cycle, and turnover of the 

long-haul truck fleet, and an estimated fleet growth rate 

to extrapolate these data into the future. Because many 

of the technology packages under consideration, such as 

moderate and aggressive improvements to aerodynamics, 

apply specifically to “box” or “van” type trailers, the fleet 

model calculates benefits only for those tractor-trailer 

(“combination”) trucks that primarily tow van trailers. 

Based on data from the 2002 Vehicle Inventory and Use 

Survey [VIUS 2002], we estimate that these types of trailers 

account for 60 percent of the combination truck population. In addition, miles accrued on a regional duty-cycle 

were not included. A more detailed description of the data 

sources and assumptions used to develop this fleet model is 

included in Appendix D.

Annual mileage assumptions are based on appropriate 

averages for tractor-trailers as a function of vehicle age, 

including the effects of vehicle age on annual mileage, 

the migration to regional service, and the retirement rate 

of older trucks. When the combined impacts of declining 

VMT, increasing vehicle retirements, and discounted future 

cash flow are considered, fuel savings beyond 15 years 

are negligible, so the calculations assume a 15 year truck 

lifetime. 

Fleet Model Validation

In order to validate the fleet model, TIAX compared the 

bottom-up fleet model estimates for fuel use with actual 

historical data. Figure 10 illustrates how the modeled fuel 

consumption in millions of gallons per year for all Class 8 
O v e r v i e w o f t h e S t u d y M e t h o d 47

14 The primary source of inconsistency between the modeled and actual data comes from differences between historical and modeled estimates of the truck 

population. Historical data have inherent inaccuracies, particularly with regard to truck sales and scrappage, and as a result, truck populations fluctuate from year 

to year to a greater extent than is predicted by the data, primarily due to macroeconomic factors such as economic growth. 

combination trucks compares with historical data from the 

Federal Highway Administration [TEDB 2007]. As shown, 

the modeled data match fairly well with the historical 

data.14 Given that the focus of this study was on the effect 

of technology introduction on the future fleet, the bottomup model is a reasonable foundation on which to estimate 

the impact of technology penetration on a fleet-wide basis.

Technology Adoption Methodology

The next step in the fleet assessment was to estimate the 

adoption rate of specific technologies into the U.S. fleet. 

The TIAX fleet model estimates rates of adoption as a 

10

FIGURE

HISTORICAL VS. MODELED FUEL USE IN U.S. COMBINATION CLASS 8 TRUCKS

0

5,000

10,000

15,000

20,000

25,000

30,000

1980 1985 1990 1995 2000 2005 2010

Total Fuel Used (M Gal)

Hist

Modeled

Source: TEDB 2007

function of an individual technology’s cost, benefit, and 

year of introduction. Within the model, each individual 

technology is allowed to compete based on net present 

value (NPV) against other similar technologies for market 

share within the fleet. Because it is impractical to individually model every combination of technologies that could 

be adopted, it was necessary to disaggregate the results 

of simulation modeling results generated by SwRI and 

make reasonable judgments about what combinations of 

technologies would plausibly be adopted by the fleet. For 

example, the fleet model is structured to allow only a single 

waste heat recovery technology (e.g., bottoming cycle, 
48 O v e r v i e w o f t h e S t u d y M e t h o d

R E D U C I N G Heavy-Duty Long Haul Combination Truck Fuel Consumption and CO2 Emissions

turbo-compounding, or advanced EGR) to be adopted into 

a vehicle at a time. This approach is described in greater 

detail in Appendix D.

Two different technology adoption scenarios were modeled 

for this analysis. The two scenarios differ in the assumed 

rate of adoption. These were compared against a reference 

case scenario in which the fuel economy and CO2

 emissions of the fleet remains constant, but the fleet grows at 

a constant rate. The first scenario (“Scenario A”) assumes 

maximum penetration of fuel consumption and CO2

reducing technologies into the heavy-duty long-haul fleet. 

Under this scenario, the most aggressive technologies that 

have a negative cost of ownership over a fifteen-year time 

horizon are fully adopted, subject to technology availability 

and assumed production capacity technologies. The second 

technology adoption scenario (“Scenario B”) uses a rational 

buyer model in which the rate of adoption for a given 

technology is calculated as a function of time to payback. 

Both technology introduction scenarios assume that it 

takes several years for new technologies to ramp up to 

10

TABLE

SCENARIO SUMMARY

SCENARIO A – MAXIMUM TECHNOLOGY 

ADOPTION SCENARIO SCENARIO B – MARKET DRIVEN

Net-positive NPV technologies are fully adopted 3-year payback is used to estimate market-based 

technology adoption

EIA Ref & High fuel price cases EIA Ref & High fuel price cases

7-year ramp for new technologies 10-year ramp for new technologies

These scenarios and the assumptions used to develop them are described in more detail in Appendix D.

full production and fully penetrate new vehicle sales. 

This phase-in period is based on EIA projections for the 

introduction of incremental vehicle technology options in 

the light-duty sector [EIA 2008], which typically require 

five to 10 years to fully penetrate new vehicle sales. The 

model also assumes that technology costs decline from 

the time of technology introduction until full deployment. 

For mature technologies, such as moderate aerodynamic 

improvements (Package 2), a faster phase-in period with no 

cost reduction is assumed. In the case of Rocky Mountain 

doubles, implementation will require buy-in from many 

stakeholders, regulatory changes in a number of states, and 

some infrastructure changes. In addition, they are not

feasible in urban areas and may not offer benefits for lessthan-truckload (LTL) carriers. Due to these complexities, 

we have capped the maximum market penetration at 

60 percent of the long-haul tractor-trailer fleet, or 

approximately 40 percent of the entire tractor-trailer fleet. 

The next chapter provides results for the fuel consumption 

and CO2

 emissions reduction analysis, cost analysis, costbenefit analysis, and fleet-wide CO2

 and fuel consumption 

reduction analysis.
RESULTS

49

RESULTS

r e s u l t s r e s u l t sR E S U L T S

r e s u l t s Results

R E D U C I N G

Heavy-Duty Long Haul Combination 

Truck Fuel Consumption and CO2

 Emissions

Overview

The methods described in Chapter 2 and detailed in 

Appendices A through C were used to predict the CO2

emissions and fuel consumption impacts and costs associated with deploying a variety of automotive technologies 

on future heavy-duty long-haul trucks. In this report, 

fuel consumption results, CO2 emissions, and costs are 

presented for one representative long-haul vehicle.

A total of 32 engine, vehicle, drivetrain, load reducing technologies, and truck configuration or speed modifications 

were evaluated in this analysis to quantify associated CO2

reduction potential. Currently available heavy-duty engine 

technologies such as aerodynamic drag improvements and 

improved tires were evaluated as well as more advanced 

technologies such as bottoming cycle and variable valve 

actuation. Turbocompounding and hybridization were also 

considered. The emissions and fuel consumption benefits 

of individual technologies and packages or combinations 

of these technologies were analyzed. The study relies on a 

systems analysis approach that avoids the “double counting” that could occur by simply combining the emission 

reduction benefits of individual technologies. In some 

cases, benefits of individual technologies are not additive. 

Examples of this issue are presented in the method overview to illustrate the impact of a systems analysis approach 

on emission benefit projections.

This chapter first discusses the CO2

 reduction potential 

of individual technologies. Vehicle results are presented 

in miles per gallon and ton mile per gallon (ton MPG) 

units, but all percent changes are presented in terms of 

percent change in total fuel consumed (gallons per mile) 

and percent change in total CO2 emissions. In many cases, 

MPG and percent savings in fuel consumption are plotted 

on the same graph, with MPG on the left hand y-axis, and 

percent reduction in fuel consumption and CO2

 emissions 

presented on the right hand y-axis. The overall CO2 impact, 

retail price equivalent, and net cost estimates are then 

presented for each of the technology packages evaluated. 

The technologies evaluated in this study are described in 

Appendix A. Finally, an analysis of the potential CO2 and 

fuel consumption reductions that could be achieved in 

the U.S. fleet of heavy-duty long-haul vehicles with introduction of technologies to reduce fuel consumption and 

emissions is presented. Appendix D describes in detail the 

method used to estimate the fleet-wide fuel consumption 

and CO2 emissions reductions associated with the 

introduction of heavy-duty vehicle technologies.

Emission and Fuel Consumption 

Reduction Results

As described in Chapter 2, the emission benefit analysis 

conducted for this study involved several steps. The first 

step was a literature survey and engineering assessment to 

identify potential CO2 reduction technologies and assess 

their likely emission reduction capabilities. These included 

both stand-alone technologies and those appropriate for 

inclusion with other technologies in combination packages. Second, an actual vehicle model from the U.S. fleet 

was selected to represent a Class 8 long-haul truck. Third, 

SwRI’s RAPTOR and commercially available GT-POWER 

software were used to assess the CO2 and fuel consumption impacts of individual or combinations of technologies 

for the Class 8 long-haul truck. A systems analysis was 

subsequently conducted for the selected technology 

packages. The results of these analyses are presented in the 

following sections.
50 R e s u l t s

R E D U C I N G Heavy-Duty Long Haul Combination Truck Fuel Consumption and CO2 Emissions

CO2 Emission and Fuel Consumption 

Reduction Potential for Individual 

Technologies

Individual technologies were first evaluated to aid in the 

selection of options for inclusion in technology packages or 

combinations which were then subjected to more in-depth 

evaluation using GT-POWER and RAPTOR simulation code 

(as described in the method section). This initial evaluation 

was designed to provide approximate CO2 reduction 

estimates for use solely in the context of selecting technologies for further investigation. Because this first part 

of the study served a preliminary screening function, no 

technologies were evaluated using full model simulations. 

All technologies were evaluated using data from published 

literature.

From the published literature, individual technologies 

were found to produce a broad range of projected CO2

reductions. The analysis indicates that evolutionary engine 

and drivetrain technologies generally provide reductions 

ranging from 1 to 10 percent. The technologies offering 

the most significant CO2 reductions are aerodynamic drag 

improvements (10 percent to 26 percent), bottoming cycle 

(up to 10 percent with the configuration evaluated), trailer 

weight and size increases (up to 30 percent), and reduced 

road speed (up to 10 percent). Other technologies showing significant reduction potential over a long-haul cycle 

include mechanical and electrical turbocompounding and 

hybridization.

The only GHG considered in this study was CO2

. Some 

evaluation was done of the potential to reduce hydrofluorocarbons (HFCs) from air conditioning systems and also to 

reduce CO2 emissions associated with the additional load 

of running the air conditioning system. However, these 

approaches were not analyzed in the simulation modeling given the small relative contribution of HFC leakage, 

and given the fact that CO2

 emissions from powering air 

conditioning represent a very small share of heavy-duty 

vehicle CO2 emissions from fuel consumption. For the 

same reason, approaches to reduce N2O or other tailpipe 

GHG emissions from long-haul trucks were not evaluated. 

Finally, approaches to reducing carbon black from long-haul 

trucks were not evaluated as part of this study.

Modeled CO2 Emission and Fuel 

Consumption Reduction Potential 

for Individual Technologies and 

Technology Combinations

The following sections describe the results of the 

simulation modeling conducted by SwRI.

Package 1 – Baseline Vehicle and Weight 

Reduction Evaluation

Figure 11 shows the fuel economy of the baseline vehicle 

in MPG. The baseline vehicle on the highway duty cycle 

described in Chapter 2 achieved a fuel economy of 5.4 

MPG. In addition to evaluating the baseline vehicle fuel 

economy in this simulation, the potential to reduce fuel 

consumption and CO2 emissions by reducing weight from 

the baseline weight of 80,000 pounds was evaluated. For 

the purpose of this calculation, the weight reduction could 

come either from carrying lighter freight or from a reduction in the empty weight of the truck. If the vehicle mass is 

reduced to 65,000 pounds, the fuel economy improves to 

5.9 MPG. The fuel savings and CO2 reduction on the 

baseline vehicle amount to about 0.5% per 1,000 pounds 

of mass reduction. This result suggests that efforts to 

reduce the empty vehicle mass will have only a modest 

benefit on fuel economy, at least on a long haul route.
R e s u l t s 51

11

FIGURE

BASELINE VEHICLE FUEL ECONOMY AND SENSITIVITY TO VEHICLE MASS

Package 1: Fuel Economy vs GVW

5

5.5

6

6.5

7

7.5

8

8.5

9

65,000 70,000 75,000 80,000 85,000

GVW (lbs)

Fuel Economy, MPG 

0

5

10

15

20

25

30

35

40

Percent Fuel Saved

Fuel Economy (mpg)

Percent Fuel Saved

Package 2 – 2007 SmartWay Aerodynamic 

Improvement Plus Wide Base Single Tires

Figure 12 shows the fuel economy of the truck with tractor 

and trailer aerodynamic improvements that comply with 

the 2007 EPA SmartWay program. The rolling resistance 

has been reduced to represent the improvement offered by 

the best currently available wide base single tires. Figure 

12 also shows the sensitivity of the results to changes in 

aerodynamic drag. If the value of the coefficient of drag 

(Cd) = 0.6298 at the far right of the plot is taken, this 

result shows the fuel savings from the rolling resistance 

reduction alone. All results shown in this figure are for a 

vehicle mass of 80,000 pounds.

The results presented in Figure 12 show that the reduction 

in rolling resistance coefficient from 0.0068 to 0.0055 

provides a fuel savings and CO2

 gas reduction of 6 percent, 

while the reduction in the coefficient of drag from 0.6298 

to 0.5 provides an additional 8 percent fuel savings. 

The combined benefit due to aerodynamics and rolling 

resistance improvements of Package 2 is a 14 percent fuel 

savings and CO2 reduction. This package represents the 

best currently available aerodynamic and rolling resistance 

technology. This package also includes a diesel powered 

APU to provide power for heating, cooling, and electrical 

accessories while the truck is shut off (also called “hotel 

load”). The benefits of reducing the idling of the truck 

engine were calculated separately, and are shown in 

Table 19. 
52 R e s u l t s

R E D U C I N G Heavy-Duty Long Haul Combination Truck Fuel Consumption and CO2 Emissions

12

13

FIGURE

FIGURE

RESULTS FROM MODERATE DRAG AND ROLLING RESISTANCE REDUCTION

RESULTS FROM ADVANCED DRAG AND ROLLING RESISTANCE REDUCTION

Package 2: Cd Sweep: Crr=0.0055, GVW = 80klbs 

5

5.5

6

6.5

7

7.5

8

8.5

9

0.35 0.4 0.45 0.5 0.55 0.6 0.65

Coefficient of Drag (-)

Fuel Economy, MPG 

0

5

10

15

20

25

30

35

40

Percent Fuel Saved

Fuel Economy (mpg)

Percent Fuel Saved vs Package 1

Package 2 Cd = 0.5

Coefficient of Drag (-)

Fuel Economy, MPG 

Percent Fuel Saved

Package 3: Cd Sweep with Crr=0.0045, GVW = 80klbs 

5

5.5

6

6.5

7

7.5

8

8.5

9

0.3 0.35 0.4 0.45 0.5 0.55 0.6 0.65

0

5

10

15

20

25

30

35

40

Fuel Economy (mpg)

Percent Fuel Saved

vs Package 1

Package 3 Cd = 0.4
R e s u l t s 53

Package 3 – Advanced Aerodynamic Drag and 

Rolling Resistance Improvements

The next set of technologies evaluated included advanced 

technologies to improve aerodynamic drag such as sealing 

the gap between the cab and the trailer and significantly 

improved tires with lower rolling resistance. 

Package 3 includes a reduction in the aerodynamic 

drag coefficient to 0.4 from the original value of 0.63 

(Package 1) and 0.5 (Package 2). Interviews with engineers 

responsible for aerodynamic design of trucks indicate that 

a reduction in drag coefficient to 0.4 will not be possible by 

adding new features to current designs of trucks and trailers. A complete redesign of the truck/trailer combination 

vehicle will probably be required, and this is likely to have 

significant impacts on the operational characteristics of the 

vehicle. The coefficient of rolling resistance is reduced to 

0.0045 from the original value of 0.0068 and the Package 

2 value of 0.0055. Figure 13 shows the results in terms of 

MPG and percent fuel savings for an 80,000 pound truck.

The results presented in Figure 13 show that the reduction 

in rolling resistance coefficient from 0.0068 to 0.0045 

provides a fuel savings and CO2 reduction of 10.6 percent, 

while the reduction in aerodynamic drag coefficient from 

0.63 to 0.4 provides an additional 14.1 percent fuel 

savings. The overall benefit of Package 3 is a 24.7 percent 

fuel savings and CO2

 reduction compared to the baseline 

truck.

It is interesting to note that a long/heavy combination 

vehicle with Package 3 characteristics and a GCW of 

140,000 pounds provides nearly identical fuel consumption 

and GHG emissions to a Package 1 (baseline) vehicle at 

80,000 pounds GCW. In other words, a turnpike double 

combination vehicle with Package 3 aerodynamic and 

rolling resistance features can deliver nearly twice the 

freight of a baseline Package 1 vehicle at approximately 

equal fuel consumption. 

This package also includes a diesel powered APU which 

reduces idling. The emissions and fuel consumption 

reductions associated with reduced idling for the package 

are shown in Table 19.

Package 4 – Hybrid Electric System

Two hybrid systems were evaluated in combination with 

Package 3, the aggressive aero and rolling resistance 

improvements. Each version of the hybrid drivetrain also 

includes electrification of engine accessories, which is 

assumed to reduce total engine-driven accessory load from 

5 kW to 3 kW. The first hybrid system to be evaluated was 

a series hybrid. Despite several iterations in the modeling effort, favorable fuel consumption results were not 

achieved. There is a commercial series hybrid system under 

development, but the control strategy being developed for 

this system was not available for evaluation during the time 

of this study. 

Results are presented here for the second hybrid system 

evaluated - a parallel hybrid similar in concept to those 

used in many passenger cars. A 50 kW motor/generator 

was installed along with a battery storage system. At first, 

the motor/generator was coupled to the engine flywheel. 

Later, the motor/generator was moved to the transmission input, on the other side of the clutch. This allowed 

the engine to be disconnected from the driveline during 

regenerative braking, increasing the energy that can be 

recaptured. Putting the electric motor on the transmission 

side of the clutch also allows the truck to move at low 

speeds on electric power alone.
54 R e s u l t s

R E D U C I N G Heavy-Duty Long Haul Combination Truck Fuel Consumption and CO2 Emissions

Initially, a 10 kW-hr battery pack was used with the parallel 

hybrid system. Later, a 4 kW-hr battery pack was simulated 

in order to reduce the system cost and weight. The fuel 

economy penalty for the smaller battery pack was small, 

so the smaller 4 kW-hr battery pack was chosen for the 

final configuration. The results for the final parallel hybrid 

system are shown in Table 11.

If the hybrid system is applied to the baseline Package 1 

vehicle, the savings will be 5.5 percent. In addition to the 

improvement in fuel economy during the long-haul drive 

cycle, a hybrid can be used to handle hotel loads such 

as heating, cooling, and electricity when the vehicle is 

stationary. Instead of idling all night, the engine can be run 

for a few minutes each hour to charge the battery pack. 

This hotel load reduction nearly doubles the fuel consumption benefit of hybridizing a tractor-trailer, increasing its fuel 

consumption benefit to 10 percent. An APU is not included 

in Package 4, since the battery storage of power takes care 

of idle reduction.

Package 5 – Mechanical Turbocompound

A mechanical turbocompound system was added to 

the GT-POWER engine model in this study. The vehicle 

model includes Package 3, the aggressive aero and rolling 

resistance package. Variable valve actuation was added to 

11

12

13

TABLE

TABLE

TABLE

PARALLEL HYBRID SYSTEM MODELING RESULTS

MECHANICAL TURBOCOMPOUND SYSTEM RESULTS

ELECTRICAL TURBOCOMPOUND SYSTEM RESULTS

VEHICLE MASS BASELINE MPG 

(PKG. 3) HYBRID MPG % REDUCTION IN FUEL CONSUMPTION & CO2

 EMISSIONS

65,000 lbs. 7.95 8.46 6.0%

80,000 lbs. 7.18 7.61 5.6%

140,000 lbs. 5.20 5.50 5.5%

VEHICLE MASS BASELINE MPG 

(PKG. 3)

MECHANICAL TURBOCOMPOUND MPG% REDUCTION IN FUEL 

CONSUMPTION & CO2

 EMISSIONS

65,000 lbs. 7.95 8.15 2.4%

80,000 lbs. 7.18 7.36 2.4%

140,000 lbs. 5.20 5.35 2.9%

VEHICLE MASS BASELINE MPG 

(PKG. 3)

ELECTRICAL TURBOCOMPOUND MPG% REDUCTION IN FUEL 

CONSUMPTION & CO2

 EMISSIONS

65,000 lbs. 7.95 8.30 4.2%

80,000 lbs. 7.18 7.49 4.1%

140,000 lbs. 5.20 5.43 4.2%
R e s u l t s 55

help provide more exhaust energy to the power turbine 

within the constraints of maintaining the efficiency of the 

base engine. The results are summarized in Table 12.

The performance of a turbocompound system is sensitive 

to engine load, so better results are achieved with heaver 

truck combinations. If mechanical turbocompound is 

applied to the 80,000 pound baseline Package 1 vehicle, 

the reduction in fuel consumption and GHG emissions will 

be 2.9 percent.

Package 6 – Electric Turbocompound

An electrical turbocompound system was added to the 

GT-POWER engine model in this study. The vehicle 

model includes Package 3, the aggressive aero and rolling 

resistance package. Electric turbocompound also includes 

electrification of engine accessories, which is assumed 

to reduce the total accessory load from 5 kW to 3 kW. 

Variable valve actuation was added to help provide more 

exhaust energy to the power turbine within the constraints 

of maintaining the efficiency of the base engine. The results 

are summarized in Table 13.

Most of the difference in performance between the 

mechanical and electrical turbocompound is due to the 

conversion of accessories from mechanical to electric drive. 

Another factor is that the electric generator allows the 

power turbine to run at a speed independent of the engine 

crankshaft speed, which slightly improves the efficiency 

of the turbocompound system itself. If electric turbocompound is applied to the baseline Package 1 vehicle, the fuel 

and CO2

 savings will be 4.2 percent.

Package 7 – Variable Valve Actuation

VVA was explored in the GT-POWER engine model 

within the constraints of maintaining the baseline diesel 

combustion cycle. Maintaining both baseline EGR flow 

rates and high load air/fuel ratios was also a requirement, 

in order to maintain baseline NOx and PM emissions. 

Within these constraints, only about a 1 percent reduction in fuel consumption could be obtained with VVA, 

regardless of the performance of the baseline vehicle. One 

percent reductions were found both against a Package 

1 baseline, as well as against a Package 3 baseline. This 

result is consistent with results achieved by diesel engine 

manufacturers who have evaluated VVA. Alternative 

engine cycles were not evaluated because there is not 

enough information available in the literature to allow 

modeling of the alternative cycles.

Package 8 – Bottoming Cycle

This technology is described in Appendix A along with a 

detailed description of the modeling approach used in this 

study. The GT-POWER model of the engine was combined 

with a spreadsheet-based bottoming cycle model to create 

an engine fuel map. In the vehicle model, the bottoming 

cycle fuel map was combined with the aggressive aero and 

rolling resistance improvements of Package 3. In addition, 

the bottoming cycle includes electric accessories, since the 

bottoming cycle expander is connected to a generator. As 

in other packages using electrically powered accessories, 

it was assumed that the accessory power demand on the 

engine is reduced from an average of 5 kW to 3 kW.

Because the bottoming cycle relies on EGR and exhaust 

heat, anything that reduces exhaust temperature will 

reduce the performance of the bottoming cycle. Therefore, 

features such as turbocompound, VVA, and low temperature EGR should not be combined with a bottoming cycle. 

These features were all evaluated in combination with a 

bottoming cycle, and they all provided reduced bottoming 
56 R e s u l t s

R E D U C I N G Heavy-Duty Long Haul Combination Truck Fuel Consumption and CO2 Emissions

cycle performance. The performance of the bottoming 

cycle with an otherwise standard engine is summarized in 

Table 14.

The bottoming cycle provides a significant improvement in 

fuel consumption and CO2

 emissions, and the sensitivity to 

vehicle load is small. However, see Appendix A regarding 

difficulties that are expected in developing a bottoming 

cycle for heavy truck applications. Also, the bottoming 

cycle will probably have to be combined with a hybrid 

system in order to address the fact that the bottoming 

cycle does not have acceptable transient response (see 

Appendix A). For the cost / benefit analysis performed 

later, a reduced scope bottoming cycle was used. The 

14

15

TABLE

TABLE

BOTTOMING CYCLE SYSTEM RESULTS

SUMMARY OF LONGER / HEAVIER VEHICLES EVALUATED 

VEHICLE MASS BASELINE MPG 

(PKG. 3)

BOTTOMING CYCLE 

MPG

% REDUCTION IN FUEL 

CONSUMPTION & CO2

 EMISSIONS

65,000 lbs. 7.95 8.83 9.9%

80,000 lbs. 7.18 8.01 10.3%

140,000 lbs. 5.20 5.84 10.3%

VEHICLE 

CONFIGURATION

EMPTY 

WEIGHT (LB)

MAX. 

GCW (LB)

FREIGHT 

VOLUME (FT3

)

VOLUME 

INCREASE 

(%)

MAX. 

FREIGHT 

(LB)

LOAD 

INCREASE 

(%)

Baseline 53’ trailer 32,000 80,000 4040 N/A 48,000 N/A

53 Foot Three 

Axle Trailer 35,000 97,000 4040 0 62,000 29.2%

28 Foot Doubles 35,500 80,000 4200 4% 44,500 -7.3%

33 Foot Doubles 37,000 97,000 4950 22.5% 60,000 25%

Rocky Mountain 

Doubles 43,500 120,000 5750 42.3% 76,500 59%

28 Foot Triples 47,500 120,000 6300 56% 72,500 51%

Turnpike Doubles 50,000 137,000 7300 81% 87,000 81%

maximum power of the system was limited from 57 kW 

down to 30 kW, and more conservative assumptions were 

made for the condenser outlet pressure and temperature. 

With these more conservative assumptions, the fuel savings 

on the drive cycle dropped from 10 percent to 8 percent. 

The more conservative bottoming cycle was not put into 

the vehicle model for a complete evaluation, and thus the 

8 percent figure is an approximation based on spreadsheet 

analysis of the bottoming cycle performance.

Package 9 – Longer / Heavier Vehicle 

Combinations

If trucks are able to carry a higher volume or heavier 

weight of freight, there is potential to carry the same total 
R e s u l t s 57

amount of freight using less fuel. There is also a potential 

of reducing the number of trucks required to move a given 

amount of freight. This offers the potential for congestion 

reduction in locations where truck traffic makes up a 

substantial portion of overall traffic. 

This study evaluated a number of existing truck combinations that are used in some areas of the United States today. 

This approach allowed for a direct comparison with the 

efficiency of existing vehicle combinations. The range of 

vehicle combinations modeled is presented in Table 15. 

All of the combinations listed in the table use a standard 

tandem axle tractor. The Rocky Mountain double is a 

combination of a 48 foot trailer with a second 28 foot 

trailer. A turnpike double is a combination of two 48 foot 

trailers. In the summer of 2009, the Canadian province of 

Ontario started a one year pilot program to evaluate the 

safety and performance of combination vehicles consisting 

of one tractor with two 53 foot trailers. This 53 foot double 

is larger than any vehicle evaluated in this study.

Some of the trailer configurations shown in Table 15 

provide significant increases in either freight volume, 

maximum freight load, or both. Each configuration was 

evaluated on the long-haul vehicle cycle described in 

Chapter 2 with a range of freight densities (and thus a 

range in GCW). Results are presented in terms of ton-miles 

per gallon in Figure 14 for varying freight densities. On the 

sloped portion of each curve, the vehicle load is volume 

limited. In other words, the trailer is completely full, 

14

FIGURE

EFFICIENCIES FOR LONGER/HEAVIER VEHICLES EVALUATED

Package 9 Trailer Configurations at 500 HP

100

150

200

250

6 7 8 9 10 11 12 13 14 15 16

Freight Density (lb/ft3)

Tons-Miles / Gallon Fuel x

Std 53 ft 5 Axle 28 ft Double

33 ft Double 28 ft Triple

Rocky Mntn Double Turnpike Double

53 ft 6 Axle
58 R e s u l t s

R E D U C I N G Heavy-Duty Long Haul Combination Truck Fuel Consumption and CO2 Emissions

without reaching the maximum allowed vehicle weight. 

The fuel efficiency of each truck combination increases 

with increasing freight density, since more tons of freight fit 

into the truck as freight density increases. Adding weight 

to the truck causes MPG to go down, but the ton-MPG 

values increase. This is a paradox when considering truck 

operations. A more heavily loaded or longer/heavier truck 

will get worse fuel economy (lower MPG) and a higher fuel 

consumption (gallons per mile), but it will be more efficient 

(higher ton-miles per gallon, or lower gallons per ton-mile). 

This is because a larger/heavier or more fully loaded truck 

can do more work for a given amount of fuel.

The flat part of each curve in Figure 14 represents the 

situation where the vehicle is at maximum GCW. As the 

freight density increases beyond the point where maximum 

GCW is reached, the truck weight remains constant, but it 

is no longer possible to completely fill the trailer. Figure 14 

shows that there is significant potential to increase truck 

efficiency by going to longer / heavier vehicle combinations with all of the configurations evaluated. 

The reductions in fuel consumption and CO2

 for longer/

heavier vehicles run over the duty cycle selected for this 

study as compared with the baseline vehicle are summarized in Table 16. The combination that shows the greatest 

benefit on the cycle was the turnpike double, which 

provides a 25 to 28 percent reduction in fuel consumption 

and CO2 emissions, depending on freight density. Rocky 

Mountain doubles and 28 foot triples both achieved the 

second best reduction, with a range of 17 to 21 percent 

improvement. The triples are more favorable for low 

density freight, while the Rocky Mountain doubles are 

better with high density freight. The widely used 28 foot 

double combination is slightly worse than the standard 53 

foot trailer baseline. It appears that operational convenience 

for the shipper is the only reason to use this configuration. 

Adding an extra axle to a standard size 53 foot trailer 

provides a slight penalty with low density freight, but for 

high density freight there is a 15.3 percent benefit.

One issue that results from increases in vehicle weight or 

size is a reduction in the vehicle power/weight ratio. As 

16

TABLE

CO2 AND FUEL CONSUMPTION REDUCTIONS FOR LONGER / HEAVIER VEHICLES 

VEHICLE 

CONFIGURATION

TON-MPG @ 

6.93 LB/FT3

 DENSITY

% REDUCTION IN 

FUEL AND CO2

TON-MPG @ 

MAX. GCW

% REDUCTION IN 

FUEL AND CO2

Baseline 53’ trailer 115 N/A 172 N/A

53 Foot Three 

Axle Trailer 113 -1.7% 203 15.3%

28 Foot Doubles 114 -0.9% 158 -8.1%

33 Foot Doubles 128 10% 192 10%

Rocky Mountain 

Doubles 138 16% 218 21%

28 Foot Triples 145 21% 207 17%

Turnpike Doubles 160 28% 229 25%
R e s u l t s 59

17

TABLE

RESULTS FOR LONGER/HEAVIER TRUCKS WITH HIGHER ENGINE POWER

VEHICLE 

CONFIGURATION

BASELINE 

ENGINE 

POWER (HP)

HIGHER ENGINE 

POWER (HP)

% FUEL AND CO2

 PENALTY 

FOR HIGHER POWER

6.93 LB/FT3 HI DENSITY

53 Foot Three Axle 

Trailer 500 600 3.6% 3.8%

Turnpike Doubles 500 700 6.7% 4.8%

the power/weight ratio declines, the vehicle can suffer 

from a decrease in acceleration capability, and the speed 

that can be maintained on hills will decline. This could 

result in trucks becoming more of an impediment to light 

vehicle traffic, particularly where there are limited opportunities for cars to pass slower trucks. One way to deal with 

this issue is to increase engine power to make up for some 

or all of the loss in power/weight ratio.

A concern with higher engine power is the potential to 

reduce the fuel savings achieved by the longer / heavier 

vehicle combination. To address this concern, SwRI 

modeled two vehicle configurations with higher engine 

power. The two selected configurations were the three axle 

53 foot trailer and the turnpike doubles. For the three axle 

50 foot trailer, the maximum GCW is 97,000 pounds, a 

21 percent increase over the standard 80,000 pounds. 

The GT-POWER engine model was scaled up to 600 horsepower (HP), 20 percent more than the standard model, to 

match the higher GCW.

For the turnpike doubles vehicle combination, the maximum GCW is 137,000 pounds, a 71 percent increase over 

the standard GCW of 80,000 pounds. It is not practical to 

increase engine power to this extent, so the GT-POWER 

engine model was scaled up to 700 HP, a 40 percent 

increase. This power level will still suffer some acceleration and hill climbing performance penalty compared to 

the baseline truck. Table 17 shows the effect of increased 

power on the efficiency of the two truck combinations. 

Increasing engine power to limit vehicle performance losses 

does increase fuel consumption, but the penalty is much 

smaller than the benefit in overall fuel consumption that 

can be achieved with larger / heavier vehicle combinations. Even if power/weight ratios are held constant to 

maintain vehicle performance, the longer/heavier vehicles 

do save fuel and reduce CO2

 emissions. The results in Table 

17 can also be used to evaluate the potential savings of 

engine downsizing. A downsizing of 20 percent results in 

less than a 4 percent fuel savings, and even a 40 percent 

downsizing only saves 5 to 6 percent. 

The fuel consumption and CO2

 emissions increases that 

result from moving to higher horsepower engines are 

depicted graphically in Figure 15. In Figure 15 the results 

for the longer/heavier trucks with the baseline engine are 

shown in the solid orange and dotted gray lines. The results 

for the longer/heavier trucks with the higher horsepower 

engines are shown in the solid gray and dotted orange 

lines. The graph in Figure 15 shows the penalty in ton 

miles of freight moved per gallon of fuel that results from 
60 R e s u l t s

R E D U C I N G Heavy-Duty Long Haul Combination Truck Fuel Consumption and CO2 Emissions

the use of higher horsepower engines in these two trucks. 

In this analysis, several simulations using the longer/

heavier truck settings were run over the drive cycle with 

several different assumptions about freight densities.

All of the results reported in this section for longer/

heavier combination vehicles include Package 3 rolling and 

aerodynamic features as a baseline. If long/heavy combinations are built using baseline Package 1 technology, the fuel 

economy (MPG) and ton-miles per gallon numbers will be 

lower, and fuel consumption will be higher. However, the 

basic relationships regarding percent fuel and CO2

 saved 

for each variation compared to the baseline will be almost 

identical. All of the longer heavier truck configurations 

15

FIGURE

RESULTS FOR LONGER / HEAVIER TRUCKS WITH INCREASED ENGINE POWER AT 

DIFFERING FREIGHT DENSITIES

1 0 0

1 5 0

2 0 0

2 5 0

6 7 8 9 1 0 1 1 1 2 1 3 1 4 1 5 1 6

Tons Miles per Gallon Fuel 

Turnpike Do uble a t 7 0 0 Hp

Turnpike Do uble a t 5 0 0 Hp

5 3 ft, 6 Axle a t 6 0 0 Hp

5 3 ft, 6 Axle a t 5 0 0 Hp

Package 9: Penalty for Higher Power Engines

Freight Density (lb/ft^3

)

assume the use of additional safety features in the cost 

analysis, including anti lock disk brakes, vision assists, and 

stability controls. 

Package 10 – Lower Road Speed

Road speed reduction is a well known method for improving vehicle fuel economy. In this study, the standard engine 

model was combined with the vehicle model of Package 

3, the aggressive aero and rolling resistance improvements. 

The drive cycle was modified by imposing a range of speed 

limits onto the cycle: no limit, 65 MPH, 60 MPH, and 

55 MPH. As the cruise road speed is reduced, the vehicle 

specification normally will be changed to match. The rear 

axle ratio will be increased numerically to provide higher 
R e s u l t s 61

engine RPM at a given road speed. This is done to 

maintain the ability to climb a grade without the need for 

downshifting.

The study looked at two scenarios for lower road speed. 

In the first scenario, the road speeds were reduced, but no 

vehicle changes were made to compensate. In the second 

scenario, the final drive ratio (rear axle ratio) was modified 

to match the reduction in road speed for the 60 and 55 

MPH routes. This is done to maintain the match between 

engine and road speeds. Figure 16 summarizes the results 

for the two vehicle scenarios.

On the driving cycle evaluated, this package yielded only a 

1 percent benefit for reducing road speed to 65 MPH. This 

is because the drive cycle includes only a small portion at 

speeds above 65 MPH. The step down from 65 to 60 MPH 

provides an additional improvement of almost 3 percent. 

This step influences all of the cruise portions of the drive 

cycle. There is no evident penalty for matching the final 

drive ratio to maintain engine RPM at 60 MPH. At 55 

MPH, fuel consumption improves by an additional 3.6 to 

4.4 percent from 60 MPH. The overall fuel savings caused 

by reducing maximum route speed from 70 MPH to 55 

MPH is 7.3 to 8.1 percent, depending on whether or not 

the final drive ratio is adjusted. The improvement would be 

larger if the baseline vehicle route included more time at 

70 miles per hour.

Overall, a benefit of about 0.7 percent per MPH speed 

reduction is seen. This is less than the 1 percent per MPH 

figure often quoted in the literature. There are two reasons 

16

FIGURE

IMPACT OF LOWER ROAD SPEED ON FUEL CONSUMPTION Percent Fuel Saved

Package 9: Fuel Savings vs Speed Limit

Speed Limit (mph)

0

1

2

3

4

5

6

7

8

9

5 0 5 5 6 0 6 5 7 0 7 5

wrt P a cka ge 3 - no cha nge in FD

wrt P a cka ge 3 - with cha nge in FD
62 R e s u l t s

R E D U C I N G Heavy-Duty Long Haul Combination Truck Fuel Consumption and CO2 Emissions

that may explain the discrepancy. The figures quoted in the 

literature are normally for steady state operation on level 

ground. The drive cycle used in this study included some 

suburban type driving at speeds below 55 MPH, as well as 

some driving on grades. The differences in drive cycle will 

tend to reduce the benefit of lower road speed. In addition, 

the vehicle model used for this study included aggressive 

aerodynamic and rolling resistance reductions, which also 

tends to reduce the benefit of lower road speed. If the same 

analysis was performed on a Package 1 baseline vehicle, 

the benefit is expected to be closer to 0.9 percent per MPH 

speed reduction.

One issue must be dealt with in considering lower road 

speed limits for trucks. As the speed limit goes down, the 

travel time will increase. If the lower speed only applies 

to a small portion of the route, the increase in travel time 

will be minimal. This is the case for situations where traffic 

or road conditions often limit the truck’s speed to a value 

below the road speed limit. Vehicles in this situation will 

also experience little savings in fuel. However, on long-haul 

routes where traffic density is relatively low, a reduction 

in cruise speed will translate directly into increased trip 

time. These vehicles will experience a significant fuel 

consumption and CO2

 reduction. To some extent, this will 

also mean that more trucks are required to deliver a given 

amount of freight over a given distance per day. Overly 

aggressive road speed limits will increase truck traffic 

density and will impede traffic flow in areas where passing 

is difficult.

Package 11 – Advanced EGR Cooling

By reducing the temperature of the EGR stream, lower 

NOx can be achieved. If NOx is held constant, the timing 

can be advanced to improve engine’s brake specific fuel 

consumption in g/kW-hr. In this study, an auxiliary EGR 

cooler was added to the GT-POWER engine model to drop 

the EGR stream temperature by about 60o C from the 

standard engine values. For example, at 1400 RPM and 

60 percent load, the EGR temperature coming out of the 

EGR cooler was reduced from 167o C down to 104o C. In a 

vehicle, this would be accomplished with a secondary EGRto-air heat exchanger at the front of the vehicle. There are 

some significant practical concerns about condensation that 

need to be resolved in order to use this approach in vehicle 

applications. It is important not to have condensation 

coming into the turbocharger compressor inlet, in order to 

avoid corrosion of the compressor wheel.

According to the GT-POWER engine model, fuel consumption and CO2

 emissions can be reduced by 1 to 1.2 percent 

using advanced EGR. The performance advantage is largest 

for lightly loaded trucks, since the brake specific fuel 

consumption benefit is largest at light loads.

The drive cycle used in this study 

included some suburban type driving 

at speeds below 55 MPH, as well as 

some driving on grades. The differences 

in drive cycle will tend to reduce the 

benefit of lower road speed. In addition, 

the vehicle model used for this study 

included aggressive aerodynamic and 

rolling resistance reductions, which 

also tends to reduce the benefit of lower 

road speed.
R e s u l t s 63

Because low temperature EGR going into the cylinder also 

reduces the temperature of the exhaust coming out of the 

cylinder, low temperature EGR does not work well with 

systems that extract energy from the exhaust, such as 

turbocompound or a bottoming cycle.

Maximum Reduction Combinations

To determine the potential benefit of combining several 

vehicle and engine technologies, additional simulation runs 

were made using selected combinations of technologies 

evaluated in Packages 1 through 11. Three combinations 

were selected for the maximum reduction packages. One 

combination was built to evaluate the maximum benefit 

that could be obtained within the constraint of current 

vehicle size and weight limits. This becomes Package 

12. The second configuration added a longer / heavier 

vehicle combination to Package 12 and substituted electric 

turbocompound for the bottoming cycle to reduce cost and 

technical risk. This is Package 13. Finally, a version was 

created to represent a maximum technology version of 

Package 13. This is Package 14, which also includes 

the bottoming cycle and the longer / heavier vehicle 

combination.

Several of the technologies evaluated did not provide 

enough benefit to be included in the maximum technology 

combinations. The Package 2 aerodynamic and rolling 

resistance improvements were left out in favor of the more 

advanced Package 3, which is expected to be available by 

2017. Mechanical turbocompound (Package 5) was left out 

in favor of the higher performing electric turbocompound. 

Advanced EGR (Package 11) was not used, because it 

reduced the energy available for the exhaust energy 

recovery systems. 

VVA was used in combination with turbocompound, but 

not with the bottoming cycle. This is due to the tendency 

to reduce exhaust temperature available to the bottoming cycle system. VVA is used with the turbocompound 

system, where it can be tuned to help the overall system 

performance. From Package 10 (reduced road speed) a 60 

mph speed was chosen. The 60 MPH speed was selected 

to minimize the potential increase in traffic density that 

a low road speed could cause, as well as to minimize the 

disruption to normal traffic flow that slow-moving trucks 

would cause. In addition, the 60 MPH speed would not 

require such a large re-gearing of the trucks as would 

be necessary with the 55 MPH option. These three 

combination packages, along with the modeling results 

are provided below.

Package 12 – Standard Trailer Maximum 

Technology Combination 

Package 12 includes the following technologies in a 

standard 80,000 pound GCW, standard 53 foot trailer 

vehicle combination:

• Aggressive aero and rolling resistance reduction, 

without the APU (idle reduction is achieved using the 

hybrid system) (Package 3)

• Parallel electric hybrid drivetrain with electrified 

accessories (Package 4)

• Bottoming cycle (Package 8)

• 60 MPH road speed governor (Package 10)

This configuration represents the maximum improvement 

in fuel consumption and CO2 emissions that is technically 
64 R e s u l t s

R E D U C I N G Heavy-Duty Long Haul Combination Truck Fuel Consumption and CO2 Emissions

feasible within the 2017 timeframe of the study for a 

standard 53 foot, 80,000 pound GCW truck. This 

conclusion was based on conversations with experts in 

industry, Steering Committee members, and experts at 

national laboratories.

Package 13 – Longer/Heavier Truck Lower Cost 

Maximum Technology Combination

Package 13 includes a Rocky Mountain double vehicle 

configuration. The Rocky Mountain double is a combination of one 48 foot trailer with one 28 foot trailer. This 

approach is more conservative than the use of turnpike 

doubles (two 48 foot trailers), but the safety and political 

implications of going to such a large vehicle combination 

could be a considerable challenge. Package 13 includes:

• Aggressive aero and rolling resistance reduction, 

without the APU (idle reduction is achieved using the 

hybrid system) (Package 3)

• Parallel electric hybrid drivetrain with electrified 

accessories (Package 4)

• Turbocompound (Package 6)

• VVA (Package 7)

• Rocky Mountain doubles (Package 9)

• 60 MPH road speed governor (Package 10)

This configuration represents the maximum improvement 

in fuel consumption and CO2 emissions in the 2017 timeframe at a lower cost and technical risk than package 14.

Package 14 – Longer/Heavier Truck Higher 

Cost Maximum Technology Combination

This configuration is a modification of Package 13. The 

bottoming cycle is regarded as having a high technical risk, 

higher cost, and having other difficult issues to overcome 

before a production feasible system could be made 

available. Package 14 replaces the electric turbocompound 

system and VVA modeled in package 13 with a bottoming 

cycle. Otherwise, Package 14 matches 13:

• Aggressive aero and rolling resistance reduction, 

without the APU (idle reduction is achieved using the 

hybrid system) (Package 3)

• Parallel electric hybrid drivetrain with electrified 

accessories (Package 4)

• Bottoming cycle (Package 8)

• Rocky Mountain doubles (Package 9)

• 60 MPH road speed governor (Package 10)

This configuration represents the maximum improvement in fuel consumption and CO2

 emissions that can be 

achieved with reasonable technical risk within the 2017 

time frame of the study. This package is basically a long/

heavy version of Package 12. 
R e s u l t s 65

Maximum Technology Combination Results

Fuel and CO2 savings have been calculated for vehicles 

operating at several freight densities. First, calculations 

were run at a freight density of 8.17 lb/ft3

. This density 

results in a GCW of 65,000 pounds in a standard 53 foot 

tractor/trailer combination vehicle. The results were 

also calculated for freight density greater than 13.3 lb/

ft3, which will result in all vehicles evaluated running at 

their maximum legal GCW. The low density calculation is 

typical of “cubed out” applications (the trailer is completely 

full with low density freight, and the vehicle is under the 

GCW limit), while the high density calculation represents 

“grossed out’ applications (the trailer is not filled, but the 

truck is at the GCW limit). The results are summarized in 

Table 18.

Package 14 provides the best results of all the simulated 

packages. Package 14 includes both the longer / heavier 

vehicle combination and a bottoming cycle. According to 

the simulation results, a maximum of 50 percent reduction 

in fuel consumption and CO2 emissions is possible. Package 

13, which substitutes a less technically risky turbocompound system for the bottoming cycle, also provides 

impressive results, only 3.1 to 3.3 points less than Package 

18

TABLE

MAXIMUM TECHNOLOGY COMBINATION MODELING RESULTS

TECHNOLOGY PACKAGE

FUEL SAVINGS / CO2

 REDUCTION

GROSSED OUT 

DENSITY > 13.3 LB/FT3

CUBED OUT 

DENSITY = 8.17 LB/FT3

12 – 53 foot trailer, bottoming cycle 36.9% 38.6%

13 – Turnpike doubles, electric turbocompound 46.9% 44.2%

14 – Turnpike doubles, bottoming cycle 50% 47.5%

14. Package 12 offers less potential benefit, but the overall 

savings are still over 36 percent compared to the baseline 

vehicle. These results make it clear that by combining 

several fuel saving technologies, a dramatic improvement 

in vehicle fuel efficiency is possible.

Estimate of Fuel Consumption 

and Emissions Reduced from Idling 

Reduction 

The potential reductions in CO2 and fuel consumption that 

result from the use of idling reduction technologies were 

not estimated as part of the simulation modeling, since the 

drive cycle used in the simulation modeling did not include 

an idle segment. Idling reduction benefits were calculated 

outside of the simulation model. Total gallons of fuel used 

on road per year per truck was estimated to be 20,000 gallons of fuel, a typical value for a long haul truck that travels 

120,000 miles per year. Next, the idle fuel consumption 

rate in gallons per hour was multiplied by an assumed 

1,800 hours of idling per year per truck. For the purposes 

of this analysis, the total fuel consumption per truck 

per year was calculated by summing the fuel consumed 

annually during idling and driving. The reduction in fuel 

consumption attributable to idling reduction technologies 
66 R e s u l t s

R E D U C I N G Heavy-Duty Long Haul Combination Truck Fuel Consumption and CO2 Emissions

was estimated by assuming all of the 1,800 hours of engine 

idling would be replaced by a more efficient auxiliary 

power unit or, in the case of the hybrid, a battery that is 

periodically recharged by the engine. The results of this 

analysis are shown in Table 19. The table shows results 

only for those technology packages that include idle reduction technology such as a diesel APU or a hybrid system. 

These are packages 2, 3, 4, 12, 13, and 14. 

The next sections describe the results of the package cost 

and cost benefit analyses conducted by TIAX using the 

SwRI modeled results for the different technology 

combinations. In addition, results from the TIAX fleet 

19

TABLE

FUEL CONSUMPTION AND CO2 REDUCTIONS FROM IDLE REDUCTION TECHNOLOGIES

PACKAGE # DESCRIPTION

% FUEL CONSUMPTION 

AND CO2 REDUCTION 

COMPARED TO PACKAGE 1

% FUEL CONSUMPTION AND CO2

REDUCTION COMPARED TO PACKAGE 

1 - WITH IDLING REDUCTION 

2 SmartWay 14% 17.8%

3 Advanced 

SmartWay 24.7% 27.9%

4 Hybrid 5.5% 10%

12

Maximum 

reduction 

combination 1

36.9% grossed out

38.6% cubed out

38.6% grossed out

40.2% cubed out

13

Maximum 

reduction 

combination 2

46.9% grossed out

44.2% cubed out

48.7% grossed out

46.2% cubed out

14

Maximum 

reduction 

combination 3

50% grossed out

47.5% cubed out

50.6% grossed out

48.3% cubed out

model analysis estimating the amount of fuel use and 

CO2

 emissions that could be avoided with introduction of 

heavy-duty efficiency improving technologies is provided.

Cost Analysis

As described in Chapter 2, TIAX estimated costs for each 

of the technology packages modeled by SwRI. Appendix 

B provides detailed costs for components in each of the 

technology packages and Appendix C presents a detailed 

explanation of how these costs were developed. Table 20 

presents a summary of these costs.
R e s u l t s 67

20

TABLE

SUMMARY OF COSTS ESTIMATED FOR EACH OF THE TECHNOLOGY PACKAGES

PACKAGEPACKAGE 

NAME DESCRIPTION

CAPITAL COST INTRO 

YEAR

O&M

COMMENTS

INITIAL FLOOR ($/MI)

1 Baseline – – – – – –

2 SmartWay

Improved aero &

tires, idle reduction,

and advanced 

lubricants

$22,930 $22,930 2009 ($0.004)

Cost information from EPA’s 

SmartWay website. Costs are 

based on three trailers and 

one tractor and include an 

APU.

3 Advanced 

SmartWay

Generation 2 aero 

& tires $66,530 $44,730 2015 ($0.004)

Estimates based on feedback 

from experts and TIAX cost 

estimates

4 HEV Parallel hybrid $35,000 $23,000 2012 ($0.006)

Based on component-level 

estimates with assumed 

RPE of 2.0, and early-stage 

demonstration vehicles.

5 Mech. Turbo 

(MTC) Includes VVA $5,300 $2,650 2010 ($0.003) Based on industry experience with small turbines

6 Elec. Turbo 

(ETC)

Includes accessory 

electrificaiton & 

VVA

$13,100 $6,550 2012 ($0.007)

Component-level 

estimates similar to 

those used for the 

HEV and mechanical 

turbocompounding.

7 VVA Var. valve actuation $600 $300 2009 $0.000 $50 incremental cost per 

cylinder 

8 Bottoming Cycle 

(BC)

Steam cycle, ~30 

kW $30,200 $15,100 2015 ($0.003)

TIAX bottom-up estimate 

based on prospective bill-ofmaterials and assumed RPE 

of 2.0.

9 Rocky Mt 

Double

48’ trailer + 

28’ trailer $25,000 $17,500 2015 ($0.002)

TIAX estimate based on 

assumed engine, safety, 

and brake upgrades, and 

increased number of trailers.

10 60 MPH 60 MPH speed limit $0 $0 2010 $0.000 Assumes no additional cost

11 Adv. EGR Low-temp EGR 

system $1,500 $750 2010 $0.000 Estimated cost of added cooling and pumps.

12 Max Tech, Std. 

trailer

SW2 + 60 MPH + 

HEV + BC $117,330 $71,630 2015 ($0.013) Sum of individual packages

13 Low Cost Tech. 

Combination

SW2 + 60 MPH + 

HEV + ETC + RMD $124,830 $80,380 2015 ($0.012) Sum of individual packages

14 Max Tech, Long 

trailer

SW2 + 60 MPH + 

HEV + BC + RMD $142,330 $89,130 2015 ($0.015) Sum of individual 

packages
68 R e s u l t s

R E D U C I N G Heavy-Duty Long Haul Combination Truck Fuel Consumption and CO2 Emissions

Cost Benefit Analysis

As described in Chapter 2, TIAX calculated the net cost 

of ownership over a 3 year and a 15 year time horizon. 

They assumed two fuel costs: 1) $2.50 per gallon of diesel 

fuel; and 2) $3.53 per gallon of diesel fuel. TIAX used a 7 

percent discount rate for the analysis. Figure 17 summarizes the results of the cost benefit analysis for the 15 year 

ownership case assuming a $2.50 per gallon price of diesel 

fuel and a $3.53 per gallon price of diesel fuel. Negative 

numbers indicate a cost savings for the vehicle owner. As 

can be seen from Figure 17, at both $2.50 per gallon of 

diesel fuel and at $3.53 per gallon of diesel fuel, for 12 of 

the 13 technology packages, owners will recoup the entire 

incremental vehicle purchase price in fuel savings; the 

exception is the hybrid package when evaluated at $2.50 

per gallon, which has a slightly positive lifetime cost of 

ownership.

17

FIGURE

15 YEAR NET COST OF OWNERSHIP FOR TECHNOLOGY PACKAGES

-$100

-$80

-$60

-$40

-$20

$0

$20

$40

Smartway

Adv. Smartway

HEV (Incl. Idle reduction)

Mech. Turbo

Elec. Turbo

VVA

Bottoming Cycle

Rocky Mt Double

60 MPH

Adv. EGR

Tech. Combo 1

Tech. Combo 3

Tech. Combo 2

Net Cost of Ownership (1000 $)

EIA Low Fuel Price ($2.50/gal)

EIA High Fuel Price ($3.53/gal)

The technology packages that provide the greatest savings 

over the 15 year period are Advanced SmartWay, Rocky 

Mountain double, and the three maximum technology 

combination packages shown at the far right of the graph. 

Figure 18 summarizes the results for the 3 year ownership scenario assuming both a cost of $2.50 per gallon of 

diesel and $3.53 per gallon of diesel. As can be seen from 

Figure 18, the net cost of ownership is much higher than 

in the 15 year case, since the vehicle owner recoups only 

the amount of money saved from lower fuel consumption 

over a period of 3 years instead of a 15 year period. Over 

a period of 3 years at $2.50 a gallon, 5 technology packages pay for themselves. The remaining 8 do not. The five 

include: mechanical turbocompounding, variable valve 

actuation, Rocky Mountain doubles, 60 MPH speed, and 

advanced EGR. In the 3 year net cost of ownership case at 

a diesel price of $3.53 per gallon, 9 technology packages 

are cost effective and 4 are not.
R e s u l t s 69

18

FIGURE

3 YEAR NET COST OF OWNERSHIP FOR TECHNOLOGY PACKAGES Net Cost of Ownership (1000 $)

-$25

-$15

-$5

$5

$15

$25

$35

Smartway

Adv. Smartway

HEV (Incl. Idle reduction)

Mech. Turbo

Elec. Turbo

VVA

Bottoming Cycle

Rocky Mt Double

60 MPH

Adv. EGR

Tech. Combo 1

Tech. Combo 2

Tech. Combo 3

EIA Low Fuel Price ($2.50/gal)

EIA High Fuel Price ($3.53/gal)

A more detailed discussion of these results is included in 

Appendix C. 

Figure 19 depicts the relative benefits and costs of each 

of the evaluated technology packages for the 3 year and 

15 year ownership period at $2.50 per gallon of diesel 

fuel. As this figure suggests, for both ownership scenarios, 

the technology packages span a broad range of reduction 

potential and costs. For example, in the three year cost of 

ownership scenario, packages providing CO2

 reductions 

from 2.5 percent to 28 percent encompass a net cost range 

from approximately negative $10,000 (i.e., net consumer 

savings) to positive $10,000. Clearly, a least-cost solution 

would favor the technology packages in the lower end of 

this cost range. Nevertheless, for purposes of this study, we 

have assumed a technology supply curve1 that includes all 

of the evaluated technology packages. This allows for the 

fact that least-cost technologies may not be viable for some 

segments of the market and that vehicle manufacturers 

may therefore choose not to implement specific CO2

reduction solutions across the entire vehicle class. For 

example, because approaches such as longer and heavier 

trailers or technologies such as turbocompounding may be 

limited to a subset of heavy-duty vehicles, a supply curve 

constructed solely on the basis of least-cost solutions may 

understate the actual cost of class-wide CO2 reduction 

solutions. Including all of the evaluated technology 

packages in the development of the supply curve provides 

a more robust indication of likely class-wide impacts. 

The diamonds in Figure 19 represent the CO2

reduction supply curve for long-haul trucks assuming a 

1 A supply curve indicates the relationship between CO2

 emissions reduction potential and cost.
70 R e s u l t s

R E D U C I N G Heavy-Duty Long Haul Combination Truck Fuel Consumption and CO2 Emissions

3 year ownership period from the time of initial purchase. 

The net cost is equal to the additional purchase price of 

the truck minus the fuel cost savings over three years, 

discounted at 7 percent. Each point represents the net 

cost of ownership for a different technology or technology 

combination. Presumably, a rational fleet operator would 

adopt technologies that offer net negative ownership. As 

indicated, at least one technology provides CO2 and fuel 

consumption reductions of about 20 percent are obtainable 

for a net negative cost (i.e., three year fuel savings exceed 

incremental technology costs). The figure also includes 

a second set of cost of ownership calculations to show 

the results of a sensitivity analysis in which the assumed 

time of ownership is 15 years rather than three. With the 

longer vehicle life (shown as squares in Figure 17), most 

technology packages reflect negative net costs. The package 

which fails to pay back over 15 years is the parallel hybrid 

system. The hybrid system can only be made to pay back in 

combination with other more cost-effective or with higher 

fuel costs; for example, it may interact synergistically with 

electrified waste-heat recovery systems, such as electric 

turbocompounding. The economics of the hybrid system 

are hampered both by the duty cycle used in the study, 

which offers only modest benefits; and battery replacement, which is assumed to be required every six years2

.

In the 15 year ownership scenario, estimated lifetime cost 

savings can be as high as $56,000 for a vehicle achieving 

approximately a 28 percent reduction in CO2

 and fuel 

consumption. Assuming a three year ownership scenario, 

costs are estimated to be $10,000 for the same level of 

emission reduction.

19

FIGURE

NET VEHICLE COSTS ASSUMING 3 AND 15 YEARS OF OWNERSHIP Net Cost of Ownership (1,000 $)

-$60

-$50

-$40

-$30

-$20

-$10

$0

$10

$20

$30

$40

0% 10% 20% 30% 40% 50% 60%

% Reduction in CO2 and Fuel Consumption

3-Yr Cost of Ownership

15-Yr Cost of Ownership

2 At this point, battery replacement intervals and strategy are highly speculative as there is not any operational data by which to judge.
R e s u l t s 71

20

FIGURE

BREAKDOWN OF FUEL CONSUMED IN CLASS 8 TRUCKS

0

5,000

10,000

15,000

20,000

25,000

30,000

35,000

40,000

45,000

Fuel use (M gallons)

2007 2010 2013 2016 2019 2022 2025 2028

Other Class 8

Regional Haul Combination

Long Haul Combination

Fleet-Wide Fuel Consumption and 

CO2

 Emissions Benefit Analysis

The last step in the study was to estimate the potential to 

reduce CO2 emissions and fuel consumption in the U.S. 

heavy-duty long haul fleet from the introduction of existing 

and emerging technologies. A detailed discussion of these 

results, as well as fuel price sensitivity analysis, is included 

in Appendix D. TIAX conducted this analysis using a 

propriety fleet model. In the fleet model, technologies are 

adopted as they become cost effective. 

The analysis includes that portion of the fuel consumed 

by long haul tractors hauling dry box van trailers. A 

breakdown of fuel use in different types of Class 8 trucks 

is shown in Figure 20 to illustrate the fraction of Class 8 

fuel consumed in long haul tractor trailer trucks. As can 

be seen from the figure, approximately 45 percent of total 

Class 8 truck fuel is consumed in the long haul box trailer 

fleet segment – shown in the gray wedge. The TIAX fleet 

model focuses on this fleet segment because many of the 

technologies modeled by SwRI would not offer the same 

benefits over a regional duty cycle, and many aerodynamic 

devices cannot be implemented on irregularly shaped 

trailer bodies.

The red wedge shows the amount of fuel consumed 

annually by regional and local heavy-duty trucks hauling 

combination trucks. The yellow wedge represents the 

combined fuel use of all remaining combination trucks, 

such as flatbed or lowboy trailers. 

In the next section, the TIAX analysis of potential CO2

 and 

fuel consumption reductions that could be realized with 
72 R e s u l t s

R E D U C I N G Heavy-Duty Long Haul Combination Truck Fuel Consumption and CO2 Emissions

introduction of efficiency improving technologies into the 

U.S. fleet of long haul combination vehicles is presented. 

Results for the analysis are shown for a 15 year payback 

case, a 3 year payback case, and a maximum technology 

penetration case.

Fleet Wide Analysis Assuming 15 Year Payback 

Requirement

Figure 21 depicts the total potential fuel and CO2 emissions 

savings in the U.S. heavy-duty long-haul box trailer fleet, 

assuming penetration of technologies modeled by SwRI in 

this study. The analysis estimates the technology adoption 

that could occur over a 20 year timeframe, assuming that 

all technologies which offer a 15 year payback are fully 

adopted by the fleet. Each wedge in the graphic represents 

a different technology modeled by SwRI and the benefit 

associated with adoption of that technology into the U.S. 

heavy-duty long-haul fleet. The analysis does not assume 

that any existing vehicles are retrofitted with technologies, 

with the exception of a 60 MPH speed limit.3 As such, the 

figure could underestimate the total potential emissions 

and fuel use avoided from heavy-duty technologies 

evaluated in this study.

In this scenario, by 2022, 30 percent of total U.S. heavyduty long-haul combination truck CO2

 and fuel consumption could be avoided. By 2030, the fuel savings grows to 

39 percent of the total for this fleet segment. 

Fleet Wide Analysis Assuming 3 Year Payback 

Requirement

The second fleet-wide analysis evaluated the fuel consumption and CO2

 emission reductions that would be 

achieved using the assumptions described for Scenario B 

in Chapter 2. In this scenario, technologies are adopted by 

an increasing fraction of the fleet as the time to payback 

decreases; if the time to payback is three years, 50 percent 

of the fleet will adopt a technology. Figure 22 graphically 

presents the results of this scenario. In this case, fuel use 

and CO2

 emissions from the long-haul truck fleet are 

reduced by 11 percent, or by 1.8 billion gallons, by 2022 

and by 3 billion gallons by 2030. In contrast to the 15 year 

payback scenario, the year-by-year fuel reductions projected 

in the 3 year payback case slow the growth in total fleet 

fuel use, but do not appreciably reduce consumption below 

present-day levels. 

In both the scenarios described above, fleet fuel use begins 

to grow again starting in 2022 to 2024 due to the lack of 

new technology after 2017. This is due to the constraints 

of this study that required a design specification for 

technologies evaluated.

Fleet Wide Analysis Assuming Maximum 

Technology Case

In the maximum technology case, TIAX used a diesel price 

of $4.40 per gallon and a 15 year payback requirement. 

At this diesel price, all of the technologies evaluated by 

SwRI were adopted by the fleet model, resulting in CO2

and fuel consumption reductions even greater than the 

15 year payback case. In this case, 44 percent of U.S. long 

haul combination truck fuel use and CO2 emissions were 

reduced in 2030. The higher fuel price allowed for the 

hybrid technology to be adopted into the fleet model.

Impact on Regional Heavy-Duty Trucks and 

Alternative Tractor-Trailer Configurations

As discussed in Chapter 2, our analysis focused on longhaul combination trucks. The fuel used by Class 8 long 

haul trucks represents a subset of total, lifetime Class 8 

3 Speed governors are already widely deployed, but are typically fixed to a higher speed limit.
R e s u l t s 73

21

22

FIGURE

FIGURE

15 YEAR PAYBACK REQUIREMENT FLEET ANALYSIS 

3 YEAR PAYBACK REQUIREMENT FLEET ANALYSIS

SW1 60 MPH R.M. Double

SW2

M Turbo

E Turbo

0

2

4

6

8

10

12

14

16

18

20

2007

2008

2009

2010

2011

2012

2013

2014

2015

2016

2017

2018

2019

2020

2021

2022

2023

2024

2025

2026

2027

2028

2029

2030

Fuel Used/Avoided (B Gal)

HEV+B. Cycle

HEV+ETurbo

Bottoming Cycle

E Turbo

M Turbo

SW2

R.M. Double

60 MPH

SW1

Fuel Used

2022: 4.7B Gallons of Fuel Saved

(30% below the base case)

SW1

60 MPH

SW2 R.M. Double

M Turbo

E Turbo

2022: 1.8B Gallons of Fuel Saved

(11% below the base case)

0

2

4

6

8

10

12

14

16

18

20

2007

2008

2009

2010

2011

2012

2013

2014

2015

2016

2017

2018

2019

2020

2021

2022

2023

2024

2025

2026

2027

2028

2029

2030

Fuel Used/Avoided (B Gal)

HEV+B. Cycle

HEV+ETurbo

Bottoming Cycle

E Turbo

M Turbo

SW2

R.M. Double

60 MPH

SW1

Fuel Used
74 R e s u l t s

R E D U C I N G Heavy-Duty Long Haul Combination Truck Fuel Consumption and CO2 Emissions

combination truck fuel usage since long-haul trucks are 

typically sold into regional service after several years. As 

such, our analysis does not attempt to account for fuel 

savings benefits that accrue once the same truck migrates 

from long-haul operation to regional service. Nor does it 

attempt to account for technology adoption in the 

approximately 40 percent of the Class-8 heavy-duty fleet 

that does not pull van-type trailers (e.g., tankers, flat beds, 

etc). These two fleet segments can leverage many of the 

approaches that have been analyzed for long-haul trucking, 

but also present unique challenges that are expected to 

reduce the potential benefits.

The main challenges with transferring technologies from 

the long-haul trucking fleet to trucks operating in regional 

service include: different duty cycles and the greater variety 

of trailers in the regional fleet. For example, in the case of 

the non-van trailer segment of the fleet, the non-uniformity 

of the trailer would prevent full implementation of the 

aerodynamic improvements specified in Packages 2 and 

3. As such, the projected benefits of the improved aerodynamic packages would be lower in these applications than 

in a long-haul truck. However, some other technologies 

that were examined in this study could likely offer very 

similar benefits as with the long-haul truck.

Because regional service trucks frequently operate on a 

more stop and go type cycle than do long-haul trucks, some 

of the most cost-effective benefits for long-haul trucks – 

such as aerodynamic and rolling resistance improvements –

will not achieve the same benefit over a regional duty 

cycle. While the tires-and-wheels benefits would carry over 

to other duty cycles, aerodynamic benefits will be reduced 

under lower speed operation. On the other hand, given the 

frequent periods of inefficient low-load operation, in-use 

idling, and frequent braking, hybrids are likely to perform 

significantly better in regional service than in long-haul 

operation. 

Approaches for addressing these challenges in the regional 

fleet could include: (1) developing regional-haul specific 

retrofit packages, such as limited aero, or a start-stop idle 

reduction mode; and (2) implementing regional haulspecific fuel consumption packages in the approximately 

20 percent of new tractor sales that enter the regional fleet 

directly. 

Conclusions

The results of the analysis suggest that existing and 

emerging automotive technologies can achieve substantial 

and cost-effective reductions in heavy-duty vehicle CO2

emissions and fuel consumption in the 2012 to 2017 timeframe. Specifically, CO2

 and fuel consumption emissions 

from heavy-duty vehicles can be reduced up to 20 percent 

with technologies such as mechanical turbocompounding 

The results of the analysis suggest that 

existing and emerging automotive 

technologies can achieve substantial and 

cost-effective reductions in heavy-duty 

vehicle CO2

 emissions and fuel 

consumption in the 2012 to 2017 

timeframe.
R e s u l t s 75

and moderate aerodynamic drag and rolling resistance improvements. CO2

 and fuel consumption can be reduced up 

to 50 percent in the 2017 timeframe using more advanced 

technologies. Policy changes to require reduced road speed 

or allow for increased weight or length vehicles were not 

evaluated as part of this study but would likely be required 

to reach the 50 percent reduction level. Assuming a three 

year vehicle ownership period and a diesel fuel price of 

$2.50 per gallon, this study found that five of the technology packages capable of achieving these reductions would 

result in net cost savings to the vehicle owner, taking into 

account both incremental technology costs and fuel savings 

over the three year period, and three others achieve cost 

savings over a four year period. The analysis shows that 

some of the technology combinations that provide the 

greatest reductions would not be adopted into the fleet 

assuming a three year payback requirement. This indicates 

that given the short payback period demanded by the 

trucking industry, most of these technologies will not be 

adopted into the U.S. fleet absent regulation or incentives. 

With a longer vehicle ownership period of 15 years, net 

savings are between $30,000 and $42,000 for owners of 

vehicles achieving CO2

 and fuel consumption reductions 

in the 40 to 50 percent range. Aggressive introduction 

of the technologies and strategies modeled in this study 

into the U.S. heavy-duty long haul fleet between now and 

2030 would lead to an estimated eight billion gallons of 

diesel fuel saved annually beginning in 2030, with lesser 

reductions being achieved as soon as 2012. The 8 billion 

gallons of fuel saved annually represents approximately 

44 percent of the total projected business as usual fuel 

consumption and CO2 emitted by the heavy-duty long haul 

fleet. Cumulative fuel savings between now and 2030 

would equal approximately 90 billion gallons of diesel fuel. 

Approximately 97 million metric tons of CO2 emissions 

could be reduced beginning in 2030. Cumulative CO2

emissions avoided between now and 2030 would equal 

1.1 billion metric tons. 

A P P E N D I X A

77

APPENDIX A

A P P E N D I X A a p p e n d i x a a p p e n d i x a

a p p e n d i x a Appendix A

R E D U C I N G

Heavy-Duty Long Haul Combination 

Truck Fuel Consumption and CO2

 Emissions

APPENDIX A: Description of Heavy-Duty Technologies and Modeling Approach

A-1

TABLE

TECHNOLOGIES AND OPERATIONAL MEASURED CONSIDERED

EFFICIENCY 

MEASURE: DESCRIPTION AND CO2

/FUEL SAVINGS METHOD INCLUDED IN 

PACKAGES

ENGINE TECHNOLOGIES

1 Improved SCR 

Conversion Efficiency

After treatment improvements that allow increased engine efficiency in 

EPA 2010-compliant engines. NO

2 Engine Friction 

Reduction

Improved engine bearings to allow lower viscosity oil, reducing energy 

lost to friction. 2, 3, 12, 13,14

3 Mechanical 

Turbocompound

An extra turbine in the exhaust harvests waste energy and delivers it to 

the crankshaft. 5

4 Electric 

Turbocompound

An extra turbine in the exhaust harvests waste energy and generates 

electricity to power accessories or propel the vehicle. 6, 13

5 Dual Stage 

Turbocharging 

Twin-turbocharging with charge-air cooling for increased efficiency. 

EGR pump required to meet emissions. NO

6 EGR Pump

Mechanical pump that moves exhaust into the intake manifold. 

Required in high-efficiency turbocharger or dual-stage turbocharger 

applications to meet emissions.

NO

7 Variable Valve 

Actuation (VVA)

Advanced control of engine valves to improve efficiency, power, 

and emissions. 5, 6, 7, 13

8 Advanced VVA Advanced control of engine valves, used to create new combustion 

cycles such as in the Sturman Digital Engine. Insufficient data available. NO

9 Alternative 

Combustion Modes

Low temperature combustion (LTC), homogeneous charge compression 

ignition (HCCI), and premixed charge compression ignition (PCCI) to 

reduce emissions at certain operating points.

NO

10 Insulated Exhaust 

Ports

To increase exhaust temperature for improved energy recovery in a 

turbocompound system or a bottoming cycle. 5, 6, 8, 12, 13, 14

11 Bottoming Cycle An additional thermal cycle, such as a steam turbine, added to harness 

waste energy from hot engine exhaust. 8, 12, 14

TRANSMISSION SYSTEM AND ELECTRIFICATION TECHNOLOGIES

12 Automated Manual 

Transmission

A manual transmission clutched and shifted by a computer for 

maximum efficiency and reduced driver variability. NO

13 Moderate Hybrid 

Systems

A heavy-duty hybrid with moderate power level and moderate energy 

storage - a stop start system. 

NO

14 Aggressive Hybrid 

Systems

A heavy-duty hybrid with significant power and energy storage 

capability, studied in both parallel and series architectures. 4, 12, 14

15 Accessory 

electrification

Powering water pumps and air compressors with electricity instead of 

using traditional belts or gears. 4, 6, 12, 13, 14

16 Component Friction 

Improvements

Use of lower viscosity lubricants in the transmission, differentials, and 

axles. 2, 3, 12, 13, 14
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R E D U C I N G Heavy-Duty Long Haul Combination Truck Fuel Consumption and CO2 Emissions

EFFICIENCY 

MEASURE: DESCRIPTION AND CO2

/FUEL SAVINGS METHOD INCLUDED IN 

PACKAGES

AERODYNAMIC DRAG AND ROLLING RESISTANCE REDUCTION TECHNOLOGIES

17 Fully aerodynamic 

mirrors Mirrors shaped and positioned to minimize drag. 2, 3, 12, 13, 14

18 Cab side extenders Designed to reduce the tractor-trailer gap. 2, 3, 12, 13, 14

19 Integrated sleeper cab 

roof fairings

Large fairings to match the roof height of a truck to the height of the 

trailer. 2, 3, 12, 13, 14

20 Aerodynamic front 

bumper For smoother airflow around the hood and wheels. 2, 3, 12, 13, 14

21 Full fuel tank fairings To smooth airflow over fuel and air tanks. 2, 3, 12, 13

22 Trailer side skirt 

fairings To deflect air away from the trailer undercarriage. 2, 3, 12, 13, 14

23 Trailer gap fairing Mounted to the trailer to reduce the tractor-trailer gap. 3, 12, 13, 14

24 Rear-mounted trailer 

fairing

Sometimes called a ‘boat tail,’ used to reduce drag at the rear of the 

trailer. 3, 12,13, 14

25 Undercarriage Flow 

Device (UFD) To further deflect air away from the trailer’s undercarriage. 3, 12, 13, 14

26 Advanced tractortrailer gap seal

A device that creates a nearly-complete closure of the tractor-trailer 

gap. 3, 12, 13, 14

27

Advanced 

rear-mounted trailer 

fairing

To significantly reduce drag at the rear of the trailer. 3, 12, 13, 14

28 Mass Reduction Lightweight materials and component elimination to increase payload 

capacity and reduce the power required to accelerate or climb hills. 1

29 Reduced Rolling 

Resistance

Lowering the rolling resistance of tires through improved design and 

inflation to reduce the power required to move the truck. 2, 3, 12, 13, 14

OPERATIONAL MEASURES 

30 Lower Road Speed Reducing speed improves vehicle fuel economy and CO2

 emissions. 10, 12, 13, 14

31 Increased Vehicle 

Size and/or Weight

Changes to weight limits, number of trailers, and truck design to 

increase cargo capacity while preserving road safety and infrastructure. 9, 13, 14

IDLE REDUCTION TECHNOLOGIES

32

Auxiliary Power 

Unit (APU) or hybrid 

system that provides 

power while the 

engine is off

Provides the driver with overnight cabin heat or cooling and with 

electricity without idling the main diesel engine 2, 3, 4, 12, 13, 14

A-1

TABLE

TECHNOLOGIES AND OPERATIONAL MEASURED CONSIDERED (continued)
A p p e n d i x A 79

A-1

FIGURE

GT-POWER MODEL OF THE VOLVO D13 ENGINE

Engine System Technologies and 

Modeling

The engine system was modeled using a commercial one 

dimensional computational fluid dynamics code called GTPOWER. This code is widely used in the engine industry 

to predict engine performance characteristics. As described 

in Chapter 2, the Volvo D13 engine was chosen for use 

in this study. Chapter 2 also describes the validation work 

that was done to calibrate the model with measured engine 

data, and to demonstrate that the model provides an 

adequate simulation of the actual 2007 model Volvo D13. 

See Figure A-1 above for a layout of the GT-POWER model 

of the baseline Volvo D13 engine.

Improved SCR Conversion Efficiency

SCR systems typically have a NOx conversion efficiency of 

75 to 90 percent, which means that 75 to 90 percent of 
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the NOx in the exhaust is successfully reduced to N2 and 

O2. There is considerable work going on in the industry to 

improve conversion efficiency and improve the durability 

of SCR systems so that conversion efficiency is maintained 

over the life of the system. For a given NOx emissions 

standard, higher conversion efficiency in the SCR system 

will allow a higher engine-out NOx level. As the permitted 

engine-out NOx level increases, better fuel economy and 

lower CO2 emissions can be achieved.

Modeling Approach:

For the 2010 version of the D13, Volvo plans to add SCR to 

the existing emissions control hardware, which consists of 

a diesel particulate filter for PM control and EGR for NOx 

control. SwRI assumed that the 2010 version of the engine 

will maintain the current engine-out NOx level, which will 

require an SCR efficiency of about 82 percent. By retaining 

the current engine-out NOx, the engine also retains its 

current fuel consumption and CO2 emission levels. It may 

prove possible to improve the performance of the SCR system, so that engine-out NOx levels can be increased. Other 

design and calibration tweaks may lead to small efficiency 

gains. Depending on how much conversion efficiency can 

be achieved from the SCR system, an improvement of up to 

3 percent could be achieved in fuel consumption and CO2

emissions. Since it is not clear what increase in SCR system 

performance will prove possible over the next few years, 

and there are no published data that provide good guidance 

on this topic, SwRI did not make projections based on 

improved SCR performance. Therefore, our model of the 

2010 engine matches the efficiency and CO2

 emissions of 

the 2007 engine exactly. 

Engine Friction Reduction

Development of engine main and rod bearings is under 

way to allow the use of lower viscosity engine oils. The 

lower viscosity oil will in turn reduce engine friction in the 

bearings and between the piston, rings, and liner. About a 

10 percent reduction in engine friction is expected if the 

current standard 15W40 engine lube oil can be replaced 

by a 5W30 grade. This change has already been made 

in Europe, where $9/gallon fuel pays for the savings in 

a single oil change interval. In order to go to the lower 

viscosity oil, synthetic is required. This roughly doubles 

the cost of an oil change. A potential issue should be noted 

here: if the increased cost of low viscosity oil does not 

pay for itself in fuel savings within the oil change interval, 

operators may go back to using higher viscosity oil. Given 

the need to maintain the production of higher viscosity oils 

for older engines, it is likely that several grades of oil will 

be available on the market for many years. 

Modeling Approach:

There is no straightforward way of modeling engine friction 

reduction. Sophisticated bearing analysis can be used to 

predict friction in bearings, and other analyses can be used 

to predict friction between pistons and liners, in the valve 

train, and in other engine components. For this study, 

we made the assumption that a 10 percent reduction 

in friction could be achieved, and then did some simple 

calculations to predict the benefit. At a typical cruise 

condition, engine friction consumes around 10 percent of 

the crankshaft output power. A 10 percent reduction in this 

friction will thus provide a 1 percent improvement in fuel 

efficiency and CO2

 emissions. This effect was judged to be 

small enough to leave out of the rest of the study.
A p p e n d i x A 81

Improved Air Handling Efficiency

Almost all heavy-duty diesel engines sold in North America 

today use high pressure loop EGR for control of engine-out 

NOx levels. Engines from Caterpillar are the sole exception, and these engines are being withdrawn from the truck 

market at the end of 2009. To get EGR to flow from the 

exhaust manifold to the intake manifold, the pressure in 

the exhaust manifold must be higher than the pressure in 

the intake manifold. When the exhaust manifold pressure 

is higher than the intake manifold pressure, this is called 

having a negative Δp, where Δp refers to the difference 

in pressure between the intake and exhaust manifolds. 

High efficiency turbos naturally produce a positive Δp over 

much of the operating range, so turbocharger efficiency is 

intentionally compromised in order to facilitate EGR flow. 

If it is possible to produce EGR flow without reducing 

turbo efficiency, the overall engine efficiency will increase. 

Some potential ways of achieving improved air handling 

efficiency are listed below. 

Modeling Approach:

Both mechanical and electrical turbocompound options 

were modeled and optimized using GT-POWER. 

Mechanical Turbocompound

A power turbine is added to the exhaust system behind 

the normal turbocharger. The backpressure created by the 

power turbine allows the use of a very efficient conventional turbo, while still providing the negative Δp required 

to support EGR flow. This improves the air handling 

efficiency. The power turbine is geared to put power back 

into the crankshaft. A fluid coupling is normally used to 

isolate the power turbine from engine crankshaft torsional 

vibration. The fluid coupling also allows for some variation 

in the ratio of crankshaft speed to power turbine speed. 

The basic effect of the power turbine is to add exhaust 

restriction, which enables EGR flow. This causes the engine 

pumping loss to increase to overcome the restriction 

imposed by the power turbine. However, unlike a simple 

exhaust restriction, the power turbine can recover energy 

from the exhaust, which more than compensates for the 

pumping loss created by the added restriction.

Modeling Approach:

A power turbine was added to the engine. It was geared to 

the engine through a fluid coupling to prevent damage to 

the gears from torsional vibration. Several scenarios were 

simulated:

• Variable geometry primary and power turbines

• Fixed geometry (higher efficiency) primary and 

 power turbines

• A range of power turbine flow capacities

• Variable valve actuation

The basic strategy used in the modeling study was to 

achieve as large as possible fuel efficiency improvement 

at part load cruise conditions. As a result, the maximum 

power from the turbocompound was somewhat less 

than that found in some production applications, where 

increased engine power is often an important goal. On 

the baseline engine, a variable geometry turbocharger is 

required to control EGR flow. With the turbocompound, 

this proved unnecessary. Fixed geometry turbines proved to 

be the most efficient approach, with the added advantage 

of lower cost and complexity. A relatively small power 

turbine flow capacity was selected, in order to improve 

performance under part-load conditions. 
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Variable valve actuation (VVA) can be used to provide more 

exhaust energy to the turbos (higher exhaust temperature) 

under part load conditions, with little penalty to base 

engine efficiency. Because this approach proved effective, 

the results reported in Chapter 3 include the use of VVA. 

Overall, the best results were obtained with fixed geometry 

primary and power turbines, a relatively small power 

turbine flow capacity, and VVA.

In the course of developing the turbocompound model, 

it was important to retain the engine-out NOx and PM 

performance of the baseline engine. Therefore, care was 

taken to maintain air/fuel ratios and EGR flow at values 

very close to the baseline engine. Many iterations of the 

model were run to achieve the desired results.

Electric Turbocompound

This is the same concept as the mechanical turbocompound, except the power is fed into an electrical machine. 

Electric turbocompound is ideal as a power source for a 

hybrid system, and will in fact require a hybrid system or 

at least an electric motor connected to the driveline, since 

the power generated will be more than the accessories can 

consume under at least some operating conditions.

Modeling Approach:

The electric turbocompound benefits from the use of an 

electrical generator connected to the power turbine. This 

eliminates the need to have the power turbine and engine 

speeds match at a fixed ratio. As a result, the electric 

turbocompound is slightly more efficient. In addition, the 

electrification of accessories was combined with electric 

turbocompound. This reduced the assumed accessory 

load from 5 kW to 3 kW, providing a significant efficiency 

benefit.

The GT-POWER engine model started with the mechanical 

turbocompound results, and then the system was reoptimized for the conversion to electrical turbocompound 

configuration. Once again, considerable care was taken 

to maintain air/fuel ratios and EGR flow, to avoid any 

increase in NOx or PM emissions.

There is one aspect where the electric turbocompound is 

less efficient than the mechanical system. Because there 

are losses in generating and in using electricity, a smaller 

portion of the shaft power from the power turbine actually 

appears at the wheels of the vehicle.

Dual Stage Turbocharging with Intercooling

Modern engines require high pressure ratios. The pressure 

ratio is the ratio between intake manifold pressure and 

ambient pressure, and values up to 4 are common in production engines. One negative effect of high pressure ratio 

is that it limits the efficiency of a turbocharger. Using two 

turbos in series with intercooling between the two turbos 

and aftercooling between the second turbo and the intake 

manifold would allow higher turbocharger efficiency. This 

approach requires an EGR pump, turbocompound system, 

or other device to facilitate EGR flow. The combination of 

two engine turbochargers with an EGR pump or turbocompound results in serious cost, complexity, and packaging 

issues. This is a lot of hardware to fit on the engine.

Modeling Approach:

This technology approach was not modeled in GT-POWER. 

Based on simple spreadsheet calculations, it appears that 

the efficiency of an engine can be improved by about 

2 percent by the use of dual stage turbocharging with 

intercooling. However some, if not all, of this improvement 

would be lost in powering an EGR pump. Packaging two 
A p p e n d i x A 83

turbocharger stages with a turbocompound power turbine 

was judged to be very difficult from a cost and packaging 

standpoint, so this approach was not evaluated. 

High Efficiency Turbocharging

This is the same concept as dual stage turbocharging, but 

within the limits of a single stage turbocharger. Because an 

efficient turbocharger produces a positive Δp, this approach 

will require an EGR pump, turbocompound system, or 

other device to facilitate EGR flow.

Modeling Approach:

This is the same concept as dual stage turbocharging, 

but within the limits of a single stage turbocharger. This 

technology approach was not modeled as a stand-alone 

technology in GT-POWER. Based on simple calculations, it 

appears that the efficiency of the engine can be improved 

by about 1 percent by the use of high efficiency single 

stage turbocharging. This benefit would be lost when 

an EGR pump is added to provide adequate EGR flow. 

However, this approach is attractive in combination with 

turbocompound, where an EGR pump is not needed. A 

high efficiency single stage turbocharger was used with 

both mechanical and electric turbocompound versions as 

described in previous sections. 

EGR Pump

An EGR pump can facilitate EGR flow and help control the 

flow rate to achieve the desired level of EGR. This device 

makes EGR flow independent of the engine’s Δp, which 

allows the use of high efficiency air handling systems. 

Unfortunately, an EGR pump consumes power, which at 

least partially cancels the efficiency gain from the improved 

air handling system. Also, an EGR pump adds cost, weight, 

and complexity to the engine package.

Modeling Approach:

An EGR pump was not modeled using GT-POWER. Based 

on simple spreadsheet calculations, the EGR pump proved 

less attractive than turbocompound as a way of providing 

the negative Δp required to drive EGR flow. 

Variable Valve Actuation

In gasoline engines, variable valve actuation can have a 

huge impact on engine performance and fuel economy. 

VVA can be used to improve engine breathing, and thus 

power, and/or to reduce the pumping losses caused by 

throttling the intake. In heavy-duty diesel engines, the 

potential benefits of VVA are much more limited. This is 

partly due to the much narrower operating speed range 

of heavy-duty diesel engines. VVA allows flexibility to 

operate the turbochargers at a more efficient point on the 

compressor map. This may allow the use of a more efficient 

turbo with a narrower map. VVA would only be used at 

appropriate speed/load conditions. When applying VVA to 

a heavy-duty diesel, the designer needs to consider how 

to maintain adequate SCR temperature at low loads to 

prevent an increase in NOx emissions. VVA can also be 

used to improve the power output of a turbocompound 

system by leaving more energy (temperature) in the 

exhaust stream.

Modeling Approach:

Variable valve actuation was extensively modeled in GTPOWER, both as a stand-alone feature and in combination 

with turbocompounding and the bottoming cycle. SwRI 

modeled VVA as a way of optimizing the standard diesel 

combustion cycle. The ability of VVA to improve diesel 

engine efficiency as a stand-alone feature is rather limited. 

This is not surprising; several engine makers have evaluated VVA with the conventional diesel cycle and found 
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R E D U C I N G Heavy-Duty Long Haul Combination Truck Fuel Consumption and CO2 Emissions

little benefit. There are examples in the literature where 

dramatic improvements are claimed from modified engine 

operating cycles that VVA can enable. The Sturman “Digital 

Engine” is one example. Unfortunately, the available 

literature does not provide enough detail to allow SwRI to 

attempt to duplicate the claimed results.

Low Temperature Combustion / HCCI / PCCI

Low temperature combustion (LTC), homogeneous 

charge compression ignition (HCCI), and premixed charge 

compression ignition (PCCI) are all “alternative” combustion modes that can be used in place of standard diesel 

combustion. All of these modes have been developed in 

an effort to reduce NOx output, and in the case of HCCI, 

PM output as well. If NOx is not an issue, these alternative 

combustion modes generally suffer from lower thermal 

efficiency than conventional diesel combustion. However, 

conventional diesel combustion suffers substantial thermal 

efficiency degradation at low engine-out NOx levels, so 

these alternative modes can become attractive. The performance of these alternative combustion modes is duty cycle 

dependent: most of the potential is at low load. Typically, 

alternative combustion modes can be used up to 30 percent or 40 percent load. Therefore, alternative combustion 

modes will have little impact on the fuel economy or CO2

emissions of an engine that operates most of the time at 

higher loads, such as in a long haul truck application. PCCI 

does not require hardware changes unlike HCCI. Hardware 

changes required for HCCI include additional injector(s). 

Control changes include careful control of injection timing 

and precise control of EGR flow and air/fuel ratio in the 

cylinder. 

Modeling Approach:

These “alternative” combustion modes are intended to 

provide reduced engine-out NOx. They can reduce the 

need for aftertreatment systems, and this is the main 

reason for considering alternative combustion modes. 

These modes do not offer a fuel consumption or CO2

benefit over standard diesel combustion combined with 

SCR, so the decision was made not to pursue these modes 

for this project. Another issue is that it is extremely difficult 

to accurately model these combustion modes, and a full 

three dimensional computational fluid dynamics model is 

required.

Engine Thermal Management Improvements

The goal of thermal management features is to retain 

energy in the gas flow through the engine rather than allow 

heat to be lost to the engine coolant, to air under the hood, 

or to other loss paths. This approach is only of value if the 

retained energy is going to be used in some way, or if it is 

necessary to reduce underhood temperatures to protect 

certain components from heat related damage.

In the 1980s, there was a lot of research in the engine 

industry on the subject of “adiabatic engines.” The 

term adiabatic refers to a thermodynamic process such 

as compression or expansion in the cylinder that takes 

place without any heat transfer between the working 

gas and the combustion chamber walls. The idea behind 

the adiabatic engine concept was that by insulating the 

combustion chamber, the engine would reject less heat and 

have a higher efficiency. Unfortunately, it turned out that 

heat rejection to the coolant was not reduced as much as 

expected, and efficiency actually fell. Heat transfer between 

the working gas in the cylinder and the ceramic coated 
A p p e n d i x A 85

cylinder walls actually increased. The energy diverted from 

the cooling system went out the exhaust. This experience 

makes it clear that attempts to implement simple 

thermodynamic concepts in an engine can have 

unintended consequences. 

Modeling Approach:

Insulated ports and a bottoming cycle were modeled as 

described below. 

Insulated Ports and Manifolds

Ceramic coatings or inserts with air gaps are used to 

increase exhaust temperature. The retained energy can 

then be used in an energy recovery device, such as a 

turbocompound system or a bottoming cycle. The energy 

potential of insulated ports and manifolds is better at high 

load, but there can also be a benefit from higher temperature into an SCR system for improved NOx conversion 

efficiency.

Modeling Approach:

Insulated ports were modeled in GT-POWER. The heat 

transfer coefficient for the port walls can be adjusted in 

the model to predict the performance of insulated ports. 

Insulated manifolds were not simulated in this project. 

The heat loss of manifolds to the air outside the engine is 

expected to be significantly lower than the heat loss of the 

ports to the cooling water jacket in the cylinder head. The 

benefits of insulated ports proved to be small.

Bottoming Cycle

A bottoming cycle is a heat engine that uses waste heat 

from the primary engine (the heavy-duty diesel) to produce 

additional work. There are many concepts available for 

use in a bottoming cycle, including steam turbines. For the 

steam turbine approach, many different working fluids can 

be considered. Potential sources of waste heat include:

• The exhaust gas flow

• EGR flow

• Charge air flow

• Engine coolant

The great advantage of a bottoming cycle is that it uses 

“free” energy – energy that is going to be thrown away by 

the primary engine. The great disadvantage of a bottoming 

cycle is that its efficiency is limited by the poor quality (low 

temperature) of most waste heat. In addition, the amount 

of waste heat available also varies greatly with the engine’s 

operating condition. Bottoming cycles have been used for 

many years in stationary power plants. So far, they have 

not found application in vehicles because of cost, weight, 

packaging, reliability, and performance issues.

Another issue that must be dealt with in using a bottoming 

cycle is finding a way to deal with the very poor transient 

response of the bottoming cycle. When there is a sudden 

increase in demand for engine power, it will take considerable time for the bottoming cycle to see the resulting 

waste heat increase and increase its own power output 

accordingly. Also, if there is a sudden decrease in engine 

power demand (the driver takes his foot off the throttle), 

the bottoming cycle will continue to make power for some 

time because of waste heat already in the system.

One way to deal with the transient response issue is to 

combine the bottoming cycle with a hybrid electric drive 

system. Electricity produced by the bottoming cycle can be 
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used directly to supplement engine power when desired. If 

the bottoming cycle cannot produce power when needed, 

stored electrical energy can be used. If the bottoming cycle 

is making power that the vehicle does not immediately 

require, this energy can be stored in the hybrid system 

battery.

Unfortunately, this combination of bottoming cycle and 

hybrid technologies means that two large, complex, and 

expensive systems must be packaged together in the 

vehicle. Making all systems fit in a truck, work together, 

and achieve reliability will be a daunting challenge for 

engineers.

Modeling Approach:

After studying the available literature, SwRI decided 

to model a steam turbine bottoming cycle using water 

as the working fluid. Water has a boiling temperature 

which makes it very attractive for extracting work from a 

relatively low temperature heat source. There are issues 

that would need to be dealt with if a water-based cycle is 

used. One of the biggest issues is the potential for freezing. 

A water-based bottoming cycle will require insulation, a 

heating system to prevent freezing during extended idle 

periods, and an emergency dump system to drain the water 

in case the heating system fails.

A sophisticated spreadsheet simulation of the bottoming 

cycle was created in order to evaluate alternative designs. 

The spreadsheet takes into account many parameters, and 

calculates temperatures, pressures, and flow rates through 

the system. Many assumptions must be made in order to 

model a bottoming cycle. The assumptions used in this 

project are listed on the following page.

• Working fluid: water

• Power turbine / expander efficiency: 70 percent at 

 all operating conditions

• Feed pump efficiency: 100 percent (since the feed 

 pump power is very low, this is not a major factor)

• Pump inlet conditions: saturated water at 40o C on 

 a standard 25o C day (a range of inlet temperatures 

 was evaluated to determine the sensitivity of the 

 system to inlet temperature and thus to condenser 

 performance)

• Maximum system pressure: 35 bar

• Pressure drop across all heat exchangers: 10 kPa 

 (3” Hg)

• Approach temperature of all heat exchangers: 

 14o C (this is an assumption about the efficiency of 

 the heat exchangers – we assumed performance 

 similar to charge air coolers used on trucks)

• Expander outlet minimum quality = 0.9 (10 percent 

 liquid water maximum, to protect the hardware from 

 erosion damage)

• Variable speed feed pump (to match the system flow 

 to the available heat)

• Variable speed/geometry expander (to match the 

 available heat)

• Low side pressure: 0.07 bar (this is a substantial

 vacuum, which is required to get the condensation 

 temperature of water down to 40o C)
A p p e n d i x A 87

• Minimum exhaust temperature after heat exchanger: 

 150o C (this was selected to avoid condensation 

 issues in the exhaust)

• Exhaust stream temperature after the DPF and SCR 

 systems is assumed to be 7o C lower than the 

 turbocharger outlet temperature (based on SwRI 

 test experience)

• 90 percent efficient electrical generator and electric 

 drive motor (81 percent of the power from the 

 bottoming cycle turbine is assumed to reach the 

 vehicle transmission)

As noted above, SwRI evaluated the following four heat 

sources for the bottoming cycle: 

1) engine coolant; 

2) charge air from the turbocharger compressor; 

3) EGR gas flow, and 4) exhaust gas flow.

The engine coolant carries a large portion of the power 

released by burning fuel, and therefore it is a significant 

potential source of heat for the bottoming cycle. Unfortunately, the quality (temperature) of the coolant heat is 

very low (about 90o C), so it is hard to extract much useful 

work from coolant heat. In other words, a bottoming cycle 

using waste heat from the engine coolant will have a large 

energy input, but very low efficiency, and therefore low 

power output.

Charge air is a more promising source because at high 

engine load, the temperature is much higher than coolant 

temperature. However, charge air temperature is very sensitive to engine speed and load. At typical cruise conditions, 

the amount of heat energy and the quality (temperature) 

of the energy is fairly low. SwRI’s evaluation showed that a 

bottoming cycle using energy from the charge air would be 

fairly effective at full load, but not very effective over the 

vehicle drive cycle.

EGR gas flow is taken from the exhaust manifold before the 

turbocharger, so it offers the highest quality (temperature). 

Only about 25 to 30 percent of the exhaust flow is devoted 

to EGR, however, so this limits the total energy available 

from the EGR stream. Because of the high quality of EGR 

energy, it offers the best bottoming cycle efficiency.

Exhaust gas flow is lower in quality than EGR flow, since it 

is taken after the turbocharger turbine and the downstream 

exhaust aftertreatment systems. However, the total amount 

of energy available is high, so this is an attractive heat 

source.

In the evaluation performed by SwRI, by far the best 

performance was obtained by heating the bottoming cycle 

fluid first with the exhaust gas stream, and then adding 

additional heat from the EGR stream. This approach 

provided much better results than using either of the two 

sources alone. It was also far superior to using charge 

air and/or engine coolant as heat sources. Even when 

using both exhaust and EGR as heat sources, the amount 

of energy available from a bottoming cycle is strongly 

dependent on engine speed and load. At high speed and 

load, the highest temperatures and exhaust flow rates are 

achieved, which allows a high bottoming cycle power. 

However, the SwRI model shows that the bottoming 

cycle can provide power that is a significant percentage of 

engine power down to relatively low engine speeds and 

loads. For example, at 1200 RPM and 20 percent load, the 

bottoming cycle provides 7.3 percent of engine crankshaft 

power, which translates into a 7.3 percent reduction in fuel 

consumption and CO2

 emissions.
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Note that there are many engineering problems that will 

need to be overcome in order to implement a bottoming 

cycle in a truck. Packaging of all the necessary hardware 

into a truck will be a challenge. The bottoming cycle 

hardware will introduce a weight penalty to the truck. 

Developing the system to operate over the range of 

ambient conditions encountered in service is also a major 

controls and design challenge. The bottoming cycle hardware and controls must also be able to function over the 

full engine speed/load operating range, as well as dealing 

with startup and shutdown transients. Another important 

issue is heat rejection. Since the proposed bottoming cycle 

takes energy from the engine exhaust, about 75 percent 

of that energy must be rejected by the bottoming cycle as 

waste heat. This increases the overall vehicle heat rejection 

requirement. Higher heat rejection can lead to a greater fan 

power requirement and higher aerodynamic drag, both of 

which would counteract the benefit of the bottoming cycle. 

As a result, some design compromise is probably required 

which would limit the maximum output (and thus heat rejection) of the bottoming cycle system. Achieving adequate 

bottoming cycle reliability and durability in a vehicle where 

high levels of vibration and wide temperature swings are a 

part of everyday service will be a very difficult task.

Bottoming cycles are widely used today in stationary power 

plants. In stationary power applications, however, many 

factors are more favorable than in a truck. These include 

the following:

• Stationary power is an essentially zero vibration 

 environment

• In power plants, the operating and ambient 

 temperature ranges are limited

• Space (packaging) is not a major concern

• Heat rejection capacity is not a major concern

• The large energy stream of a power plant can justify 

 a high cost bottoming cycle system

• Operating conditions are far closer to steady state in 

 a power plant than in a truck

• Power plant load factors tend to be higher than truck 

 load factors. A high load factor favors bottoming 

 cycle performance

Transmission System Technologies

Modeling Approach:

All transmission and vehicle simulations were made using 

RAPTOR, a commercially available vehicle simulation code 

developed by SwRI.

Automated Manual Transmission

Torque converter automatic transmissions are relatively 

rare in heavy-duty truck applications. There are several 

reasons for this, including cost. Torque converter automatics are generally used only in stop-and-go applications such 

as city buses, garbage trucks, and cement mixers. Most 

heavy-duty trucks use manual transmissions with 8 to 18 

ratios available. The most common transmission for line 

haul applications is a 10 speed manual transmission with 

an overdrive top gear ratio.

Automated manual transmissions have been available on 

the market for over 10 years now, and they have been 

increasing in market share. Automated manuals allow the 

vehicle control module, rather than the driver, to decide 

when to shift. Pneumatic or hydraulic mechanisms then 
A p p e n d i x A 89

actuate the clutch and transmission controls to execute the 

shifts. An automated manual can shift as quickly as the best 

driver, and the shift schedule can be tailored to match the 

characteristics of the engine and vehicle. This reduces the 

fuel consumption and CO2 emissions variability between 

drivers, making all drivers achieve results closer to those 

of the best drivers. Automated manual transmissions also 

reduce the level of skill required, which has become an 

advantage as the trucking industry struggles to replace 

retiring drivers.

Modeling Approach:

An Eaton 10 speed manual transmission was selected as 

the baseline transmission for the project. Inputs to the 

RAPTOR model include the gear ratios of each gear, along 

with assumptions regarding the efficiency of each gear. 

SwRI assumed 98 percent efficiency for the lower gears, 

and 99 percent efficiency for the tenth gear, which is direct 

(1:1 ratio).

A key factor in modeling a manual transmission is making 

assumptions about driver behavior. The driver can have 

an appreciable effect on truck fuel economy, and selection 

of shift points is a large part of this. If the driver keeps 

the engine operating at high RPM, the fuel economy will 

suffer. If the driver is aggressive in heavy traffic, the truck 

will experience more dramatic speed fluctuations than 

with a less aggressive driver, also affecting fuel economy. 

In the current study, the speed vs. time drive cycle was 

pre-determined. This ignores the effect of different drivers 

who will vary speed more or less, depending on temperament. Shift points are still a factor that will influence fuel 

economy on the drive cycle. SwRI chose to shift up at 

1800 RPM in situations where the drive cycle called for full 

power. Downshifts were set to occur at a point resulting in 

1700 RPM if full power is required. In situations where full 

power is not required, the shift points were selected to be 

lower to achieve good fuel economy. This is the approach a 

good driver will take. The good driver might also decide to 

sacrifice some vehicle performance in order to improve fuel 

economy and use lower shift points at full load.

The shift strategy used in the RAPTOR model also represents a typical shift strategy for a fully automated manual 

transmission. For the purpose of this study, there is no 

difference between the manual and automated manual 

transmissions, since both are modeled in the same way. In 

the field, there will be a difference between manual and 

automated transmissions. A very fuel conscious driver 

might be able to do a little better than an automated 

manual, while a more performance oriented driver is likely 

to use more fuel than an automated transmission.

Moderate Hybrid Systems

These systems are similar in concept to the mild hybrids 

used in light-duty applications using an integrated starter/

generator. Engine start/stop is included, along with limited 

duration auxiliary power unit capability, electrified accessories, launch assist, and regenerative braking to recharge 

the battery. The battery size is kept modest to control cost 

and weight.

Modeling Approach:

A moderate hybrid system was not modeled for this 

project. The Steering Committee agreed that an aggressive 

hybrid offered much more potential fuel savings for heavyduty trucks.
90 A p p e n d i x A

R E D U C I N G Heavy-Duty Long Haul Combination Truck Fuel Consumption and CO2 Emissions

Aggressive Hybrid Systems

These systems are similar in concept to the full hybrids 

used in light-duty applications. Two approaches were 

considered in this study. The first approach has a 50kW 

motor/generator on the transmission with a 4 kW-hr 

battery. This is a parallel hybrid approach. Both the engine 

and the hybrid motor are connected to the drivetrain (although the engine does have a clutch). The parallel hybrid 

system uses a high voltage battery that allows electrification 

of all accessories including the engine cooling fan. This 

system can support start/stop and APU functions to greatly 

reduce idle time. Up to 50 kW of additional power is 

available for launch or hill climb support.

The second hybrid approach modeled for this study was a 

series hybrid. In this case, the engine is only connected to 

the drive wheels at highway speeds using two transmission 

ratios. At lower speed, the engine drives a generator which 

in turn is used to drive a 200 kW electric motor. The series 

hybrid has a larger capacity battery, allowing the vehicle 

to support hotel load of heating, cooling, and electricity 

supply (APU function) all night without charging. The 

larger battery also allows low speed operation of the truck 

without starting the diesel engine.

Modeling Approach:

RAPTOR includes extensive code for hybrid system 

simulation. Care is taken to make sure that the state of 

battery charge at the beginning and end of the cycle is 

the same, for example, to ensure comparability between 

design alternatives. A parallel hybrid system was evaluated 

in several configurations. The initial configuration had the 

electric motor on the engine side of the clutch, and used 

a 10 kW-hr battery. Better performance was achieved by 

moving the electric motor to the transmission side of the 

clutch. This allowed the engine to be disengaged during 

some braking conditions, which increases the amount of 

energy that can be captured from regenerative braking. 

The final version of the parallel hybrid system reduced the 

battery capacity to 4 kW-hr, in order to limit the cost and 

weight of the battery package. The system assumed that 50 

percent of the battery capacity was available for use. This is 

done to achieve good battery life.

In the series hybrid analysis done as part of this study, we 

were unable to demonstrate significant fuel savings because 

we were not able to acquire the necessary controls strategies used by developers of series hybrids. Thus, the analysis 

for this study focused on the parallel systems.

Vehicle Technologies

Modeling Approach:

All transmission and vehicle simulations were done using 

RAPTOR, a commercially available vehicle simulation code 

developed by SwRI.

Accessory Electrification

The use of a hybrid system or electric turbocompound 

provides a source of electrical energy that can be used to 

drive accessories that are engine driven on today’s vehicles. 

Given the availability of significant electric power, the 

following accessories can be converted to electric drive:

• Electric Power Steering (EPS)

• Electric Water Pump (EWP)

• Electric A/C compressor

• Electric air compressor

• Eliminate conventional alternator
A p p e n d i x A 91

If 30 kW of electric power is available, the engine cooling 

fan can also be converted to electric drive. In line haul 

applications, the efficiency savings from an electric cooling 

fan is limited, because the fan only runs as needed, and it is 

normally not required at higher vehicle speeds.

If electric power is not available, there are still some 

technologies that can be applied to reduce the parasitic 

power consumption of accessories. The alternator and air 

compressor can use clutches to disengage them when they 

are not required. This can provide a significant parasitic 

power reduction. Air compressors that are not pumping 

absorb about half the power of a pumping compressor, and 

compressors normally only pump a small percentage of the 

time.

Modeling Approach:

Good data providing power consumption values for each 

accessory over a range of operating conditions were not 

available. A simplified assumption was made that the 

average power demand for mechanically driven accessories 

is 5 kW, and the average power demand for electrically 

driven accessories is 3 kW. This provides a 2 kW advantage 

for the electrically driven accessories over the entire drive 

cycle. Since the average engine power level over the drive 

cycle is in the 100 to 200 kW range, this represents a 1 to 

2 percent improvement in efficiency and reduction in CO2

emissions. In general, the effect of accessory power consumption in trucks is much less than in cars. The average 

load on a car engine over a drive cycle may be in the 10 to

20 kW range. At this level, a 1 kW reduction in accessory 

loads makes a significant difference (5 to 10 percent). 

Given the higher loads experienced by truck engines, 

accessory demand is a much smaller share of overall fuel 

consumption.

Accessory power demand was modeled in RAPTOR as a 

continuous, steady state power draw of 5 kW for standard 

accessories, and 3 kW for electrical accessories. There is 

room for additional research to improve upon this very 

simple modeling approach by using actual measured data to 

improve the modeling assumptions.

Friction Improvements

Engine friction reduction is described in a previous section. 

Lower viscosity lubricants, and lubricants whose viscosity is 

less temperature sensitive, can also be applied in transmissions, differentials, and axles. In many cases, components 

need to be redesigned in order to be compatible with low 

friction lubricants. The benefits of friction reduction on the 

vehicle are sensitive to ambient temperature. Larger benefits are found in cold weather. These improved lubricants 

are normally higher cost synthetics. Synthetic low friction 

lubricants are already options in today’s trucks and have 

become standard on a few models.

Modeling Approach:

The modeling of vehicle related friction improvements is 

very complex. Friction arises in the transmission, driveshaft 

joints, axles, and wheel bearings. Rather than deal with this 

complexity, friction reduction assumptions were included 

in the overall rolling resistance values that are used in 

Package 2, Package 3, and all subsequent packages, which 

use the Package 3 values. Package 2 assumes no change 

in vehicle friction, while Package 3 assumes a 10 percent 

reduction in vehicle friction.

Aerodynamic Drag Reduction

There are many technical features that are available or 

under development to reduce the coefficient of drag (Cd) 

of a heavy-duty truck. In many cases, reliable data are 
92 A p p e n d i x A

R E D U C I N G Heavy-Duty Long Haul Combination Truck Fuel Consumption and CO2 Emissions

not available on the effect of individual features, or data 

are only available from the manufacturers of the features. 

Therefore, in this study, we simply modeled the effect of 

drag coefficient on the fuel economy and CO2 emissions of 

the truck. Two packages were considered. The first package 

(Package 2) assumed a drag coefficient of 0.5, which was 

estimated to be the drag coefficient of a SmartWay tractor/

trailer combination. The second, more aggressive package 

called “Advanced SmartWay” (Package 3) looked at a 

feasible drag coefficient for 2017. After much discussion 

in the Steering Committee, a drag coefficient of 0.4 was 

selected, based on available data.

The list of aerodynamic features that were discussed 

included: reduced tractor to trailer gap, trailer side skirts 

and undercarriage skirts, a boat tail, boat tail plates, 

integrated tractor roof fairings, a trailer “eyebrow,” frontal 

area reduction (not implemented, in order to keep carrying 

capacity constant), trailer edge rounding, vortex generators, 

guide vanes, active and passive pneumatics, aerodynamic 

mirrors, replacement of mirrors with cameras, a trailer 

underbody wedge, fuel tank fairings, bumper fairings, 

“teardrop” shaped trailer, wheel fairings, and hidden 

vertical exhaust stacks.

It should be noted that Package 2 is available on the 

market today. The market share of vehicles equipped with 

the full package is very low, for a number of reasons. One 

of these issues is the fact that some tractor and trailer 

aerodynamic features are very damage prone, and that 

damage results in the loss of several years worth of fuel 

saving benefits. Another issue is that fleets are concerned 

about the down time related to the failure of a wide base 

single tire. Additional development is required to mitigate 

these issues to the point where most heavy-duty truck 

buyers find them cost effective. 

Package 3 is much farther from being ready for wide-spread 

use. Other than a couple of laboratory demonstrations, 

Package 3 remains undefined in detail. There will be 

many challenges in the development of the Package 3 drag 

coefficient, especially in minimizing the impact on vehicle 

functionality (trailer volume, vehicle maneuverability, loading dock compatibility, damage resistance, and minimizing 

weight increase). It is the consensus of experts consulted 

in industry as well as members on the Steering Committee 

that these issues could be overcome by 2017.

Modeling Approach:

Modeling of aerodynamic features to determine their 

individual impact on drag coefficient is beyond the scope 

of this project. This type of modeling would require a sophisticated three dimensional computational fluid dynamics 

program. Therefore, in this study, we simply modeled the 

effect of drag coefficient changes on the fuel economy and 

CO2

 emissions of the truck. The two packages discussed 

above (SmartWay and Advanced SmartWay) were modeled. 

Drag coefficients of 0.5 (SmartWay) and 0.4 (Advanced 

SmartWay) were simply entered into the RAPTOR model 

along with vehicle frontal area. The model then calculated 

the drag power over the vehicle drive cycle.

Mass Reduction

There are opportunities to reduce the mass of a tractor / 

trailer. Reduced mass can benefit fuel efficiency and CO2

emissions in two ways. First, if the truck is running at the 

GVW limit with high density freight, more freight can be 

carried. This increases the amount of freight that can be 
A p p e n d i x A 93

moved for a given amount of fuel. Second, if the truck is 

running with lower density freight, the total vehicle mass 

is reduced, which reduces rolling resistance and the power 

required to accelerate or climb grades.

There are two primary approaches for mass reduction. 

Material upgrades can achieve the same performance with 

lighter weight. Examples include the substitution of thinner 

high strength steels for standard steel, or the use of aluminum or composite in place of heavier materials. A second 

approach is to reduce the number of components required. 

The main example of this approach is to substitute single 

wheels and tires where dual wheels are used today. Single 

wheels and tires that can carry the same load as standard 

dual wheels are commonly known as wide base singles.

Modeling Approach:

Vehicle mass is an input to the RAPTOR model. The effect 

of vehicle mass changes was evaluated by changing the 

input value in the model. RAPTOR uses vehicle mass to 

determine the energy required to accelerate and slow the 

vehicle, as well as the vehicle rolling resistance.

Reduced Rolling Resistance

Lower rolling resistance reduces the power required to 

move the truck down the road, which directly reduces 

fuel consumption and CO2 emissions. Tire design and tire 

inflation are the primary factors contributing to rolling 

resistance. Wide base single tires offer much lower rolling 

resistance than standard double wheels. Tire manufacturers 

are working on designs to decrease the rolling resistance 

of both standard and wide base single tires. Tire pressure

monitoring and automatic tire inflation systems are 

available to ensure that tires are operated at the optimum 

pressure.

Modeling Approach:

The rolling resistance coefficient is an input to the RAPTOR 

model. The baseline number came from actual vehicle 

testing on a Kenworth T-600 truck and trailer combination. 

The lower rolling resistance values used in Packages 2 and 

3 came from publications, unpublished data, or projections 

from EPA and/or Michelin. The rolling resistance assumption for Package 3 included an assumption of a 10 percent 

reduction in vehicle friction, in addition to tire-related 

improvements.

Lower Road Speed

Since aerodynamic drag is a function of speed squared, 

the fuel economy and CO2 emissions of vehicles can be 

improved by reducing speed. Limits on this approach 

include increases in trip time and possibly increases in the 

number of trucks on the road that would be required to 

deliver a given amount of freight.

Modeling Approach:

The maximum road speed is defined by the drive cycle. 

The baseline drive cycle is defined in Chapter 2. To 

evaluate the effect of imposing lower road speed limits on 

trucks, the drive cycle was modified by limiting the maximum speed to 65, 60, and 55 MPH. RAPTOR then used 

the modified drive cycles to determine the fuel savings that 

can be achieved with lower road speeds.

Increased Vehicle Size and/or Weight

Some trucks run “cubed out.” In other words, the trailer 

is completely full with low density freight, and the vehicle 

is under the GVW limit. Other trucks run “grossed out,” 

which means that the trailer is not filled, but the truck is 

at the GVW limit. Some trucks operate less than full in 

either sense. To achieve good operating efficiency, trucking 
94 A p p e n d i x A

R E D U C I N G Heavy-Duty Long Haul Combination Truck Fuel Consumption and CO2 Emissions

companies strive to load the truck until one of the two 

limits is reached. An increase in the permitted size and 

weight of trucks can reduce fuel consumption on a tonmile basis and lead to lower CO2

 emissions for the fleet.

The advantages of increased truck size and weight are 

straightforward. Fuel consumption and CO2

 emissions are 

reduced. Traffic density is reduced, since fewer trucks are 

required to move a given amount of freight. Labor cost is 

reduced, since fewer drivers are required. 

Unfortunately, there are also disadvantages to increased 

truck size and weight that must be dealt with. The first 

disadvantage is that there are both real and publicly 

perceived safety risks for larger and heavier trucks. This 

disadvantage might be dealt with by mandating vehicle 

performance characteristics such as stability control, 

braking performance, and crash compatibility. In addition, 

driver training and driver performance requirements could 

be put in place for operators of larger, heavier trucks. 

Another disadvantage is road damage from heavy trucks 

and the issue of whether trucks pay enough in taxes and 

fees to cover the damage they cause. This issue might be 

dealt with by limits on axle load, possibly with standards 

on suspension performance, and by adjustments to the tax 

and fee structure. Another factor that must be considered is 

the structural integrity of bridges. Some routes may require 

upgrades before heavier trucks could safely operate.

One final potential disadvantage of larger, heavier trucks is 

also one of the benefits: lower cost shipping. The concern 

here is that a more efficient trucking industry would lead to 

more shipping in general, and thus cancel some of the CO2 

advantage of larger, heavier trucks – frequently referred to 

as the “rebound effect.” In this study, the potential impact 

of “rebound” has not been included in the estimation of 

fuel use or CO2 reductions in the longer/heavier truck 

cases.

Modeling Approach:

RAPTOR allows the use of any desired tractor and trailer 

combination. To explore the effect of allowing larger, 

heavier vehicles, the vehicle model was modified in 

RAPTOR. Higher empty vehicle weights were applied, the 

appropriate freight weights were applied, and the model 

was run to determine changes in fuel consumption and 

CO2 emissions. In addition, the rolling resistance and Cd 

values were modified for some vehicle combinations. The 

rolling resistance of drive axle tires is higher than that for 

trailer tires, so if the ratio between drive axles and trailer 

axles changed, the rolling resistance coefficient was modified to account for the change. Similarly, the aerodynamic 

drag of a multi-trailer combination will be higher that that 

of a single trailer, because of an additional trailer-to-trailer 

gap and additional undercarriage elements. Thus, modified 

Cd values were also applied to account for the higher drag 

expected with multiple trailer combinations.
A P P E N D I X B

95

APPENDIX B

A P P E N D I X B a p p e n d i x b a p p e n d i x b

a p p e n d i x b Appendix B

R E D U C I N G

Heavy-Duty Long Haul Combination 

Truck Fuel Consumption and CO2

 Emissions

B-1

TABLE

APPENDIX B

TECHNOLOGY 

PACKAGES

FUNCTIONAL 

DESCRIPTION AND 

NOTES

INCREMENTAL 

RETAIL 

COST 

ESTIMATE*

PARTS COST* COMMENTS

Package 1. 

2008 

baseline.

Kenworth T-600 with 10-

speed manual, 2007 Volvo 

D-13 engine - adjusted to 

meet 2010 NOx emissions 

standards. Aero assumptions: Bumper fairing, 

partially aerodynamic 

mirrors, partial fuel tank 

fairing, integrated roof 

fairing, exhaust system 

out of the air stream (aero 

drag coefficient: .6298) 

(coefficient of rolling 

friction: .0068)

Package 2. 

SmartWay 

package

SmartWay package. 

Includes: Additional aero 

streamlining sufficient 

to reduce the coefficient 

of drag from 0.63 to 

0.5 to both the cab 

and the trailer. Fully 

aerodynamic mirrors, cab 

side extenders, integrated 

sleeper cab roof fairings, 

aerodynamic bumper, full 

fuel tank fairings. Trailer 

streamlining includes 

a side skirt fairing, and 

either a trailer gap fairing 

or a rear-mounted trailer 

fairing such as a boat 

tail. RR of 0.0055. Super 

singles and aluminum 

wheels. Idle reduction, 

improved lubricants

$22,930

Cab 

Streamlining: 

$2750

Trailer 

Aero -

side 

skirts, gap 

reducer 

and rear 

flap: 

$2,400

Low 

Viscosity lubricants: 

$500

cab tires: 

replace 8 

wheels w/4 

super singles: 

(4 tires + 

wheels) x 

($1,279/

tire + $575/

wheel) - 

(8 tires + 

wheels) x 

($582/tire + 

$205/wheel) 

= $1,120

trailer tires: 

replace 

8 wheels 

with 4 

super 

singles, 

same 

calculation 

as for cab 

tires times 

three trailers ($1,120 

x 3 = 

$3,360)

APU: 

$8000

see SmartWay “Technical 

Specifications and 

Requirements 2007 

tractor and 2007 trailer”. 

SmartWay specifications, 

including: 10% - 20% improvement in FE overall 

(including idle reduction) 

idle reduction capable of 

providing 8 hours of idle 

free auxiliary power, heat 

and/or air conditioning - 

assume APUassumes one 

tractor and three trailers

Package 3. 

advanced 

aerodynamics 

- 2017.

An advanced aero & tire 

package for 2015 and 

beyond that includes: Full 

trailer aero (boat tail, full 

skirting); tractor-trailer 

gap optimization; further 

tractor streamlining and 

wheel fairings; reshaped 

aerodynamic trailer. Tires 

assume RR of 0.0045 

using advanced super 

single tires. Also includes 

APU

$44,730

Cab 

Streamlining: 

$4,750

Trailer 

Aero -

side 

skirts, gap 

reducer 

and rear 

flap: 

$4,500 

($1,500 

times 

three 

trailers)

Low 

Viscosity lubricants: 

$500

cab tires - 

replace 8 

wheels w/4 

super singles: 

(4 tires + 

wheels) x 

($1,279/

tire + $575/

wheel) - 

(8 tires + 

wheels) x 

($582/tire + 

$205/wheel) 

= $1,120

trailer tires: 

replace 

8 wheels 

with 4 

super 

singles, 

same 

calculation 

as for cab 

tires times 

three trailers ($1,120 

x 3 = 

$3,360)

APU: 

$8000

Trailer 

reshaping, 

including 

tear drop 

roof, 

rounded 

edges, 

etc

assumes CD of 0.4, tire 

RR of .0045 and one 

tractor and three trailers

APPENDIX B: Summary of Incremental Costs for Technology Packages
96 A p p e n d i x B

R E D U C I N G Heavy-Duty Long Haul Combination Truck Fuel Consumption and CO2 Emissions

TECHNOLOGY 

PACKAGES

FUNCTIONAL 

DESCRIPTION AND 

NOTES

INCREMENTAL 

RETAIL 

COST 

ESTIMATE*

PARTS COST* COMMENTS

Package 4. 

Hybrid

Accessories not electric 

in package #2 would be 

electric here. Includes: 

50 kW motor generator, 

battery storage pack - 4 

kWh of which 2 kWh is 

useable, electrification 

of accessories, modified 

transmission and clutch 

assembly, power electronics, high voltage wiring 

and balance of plant. 

Engine off at extended 

idle, regenerative braking, 

launch assist.

low 

volume: 

$35,000 

($30,000 to 

$40,000). 

Higher 

volume 

$23,000 

($20,000 to 

$25,000).

50 kW 

Motor/

generator 

$1,500 

higher 

volume 

assuming 

$30 per 

kW

4 kWh 

battery 

pack 

$3,200 

assuming 

$800 per 

kWh

Power 

Electronics 

$1,500 

assuming $30 

per kW

Wiring, 

electrification 

of accessories 

and balance 

of plant 

$2,300 based 

on 25% of all 

other

modified 

clutch 

assembly 

and 

automated 

manual 

upgrade 

$2,000

electrification of 

accessories 

$1,000

Peterbilt M386 Class 

8 hybrid presented at 

2007 HTUF conference includes 60hp 

electric motor/ integrated 

starter-generator, power 

electronics, electric A/C, 

4-kWh battery pack (2 

kWh useable) capable of 

supporting hotel loads for 

55mins after a 5 minute 

recharge cycle (anti-idle). 

Provided line haul truck 

manufacturers proceed 

to launch this HEV 

configuration as a product 

line, moderate volume 

(200-1000 per year) is 

expected in 2009-2012 

and higher volume 

(2000-10,000 per year) is 

expected in 2013-2017. 

Total cost includes 2.0 

RPE factor.

Package 5. 

Mechanical turbo 

compound

Based on the Scania 12 

liter engine, and it is also 

very similar to the new 

Detroit Diesel DD15 

engine. This would 

include port liners to 

retain thermal energy, 

variable valve actuation 

added to engine cylinders, 

high efficiency power 

turbine. Assumes a Scania 

design with a 12-liter 

engine powertrain.

$2,650

port 

liners: 

$500

VVA: 

$300

high efficiency 

power 

turbine: 

$1,850

Potential 2010 system 

design variability among 

engines due to thermal 

management of after 

treatment could cause 

prices to vary by 20% 

to 30% from what is 

projected here.

Package 6. 

Electric 

turbocompounding

Includes same components 

described above for mechanical turbo compound, 

plus an electric motor/

generator, associated 

power electronics, and 

electric accessories

$6,550

all 

components 

described 

for mechanical 

turbocompound = 

$2,650

40 kW 

motorgenerator: 

$1,200

power 

electronics: 

$1,200 

at $30 

per kW

electric 

accessories at 

$1,000

balance 

of plant at 

$500

Includes same components as mechanical 

turbocompound. 

B-1

TABLE

APPENDIX B (continued)
A p p e n d i x B 97

TECHNOLOGY 

PACKAGES

FUNCTIONAL 

DESCRIPTION AND 

NOTES

INCREMENTAL 

RETAIL 

COST 

ESTIMATE*

PARTS COST* COMMENTS

Package 7. 

VVA

conventional lost motion 

VVA $300

$50 per 

cylinder 

incremental cost 

for VVA 

implementation 

in production 

volumes

Package 8. 

Bottoming 

cycle added 

to Sturman 

VVA.

VVA, steam Rankine 

bottoming cycle system. 

30 kW rating at 1600 

rpm full load and 100 

F ambient. High speed 

turbine expander-generator, flywheel, air-cooled 

condenser, stainless steel 

EGR boiler, stack boiler, 

balance of plant, controls 

and power electronics, 

battery.

$15,100 

(assuming 

thousands 

of units per 

year),

Turbine 

generator

and 

flywheel: 

$2,160 

for a 

30 kW 

system

Air-cooled 

Condenser based 

on large 

mobile AC 

condensers; 90 

kW2 

and heat 

rejection; 

13 ft2

face area: 

$550

EGR 

boiler 

stainless 

steel: 

$400

stack boiler: 

$1,000

Packaging, 

assembly 

labor and 

balance 

of plant: 

$2,000

Controls 

and 

power 

electonics: 

$1,300 

($400 

for 

controls 

plus 

$30/

kW for 

power 

electronics) 

Energy 

storage: 

$150 

(battery 

or ultracapacitor 

sized to 

capture 

peak load 

for 10 

seconds)

Total cost includes 2.0 

RPE factor.

Package 9. 

Rocky Mountain Doubles 

with GVW 

increase

Rocky mountain doubles 

include one 28’ trailer and 

one 48’ trailer. Max GVW 

is 120,000 lbs. Includes 

increased engine size 

(increase of 3L), safety features (disc brakes, stability 

controls, vision systems), 

engine cooling and after 

treatment systems also 

increase proportionally. 

the transmission is also 

modified for higher loads.

$17,500

Increase 

engine 

size from 

13L to 

16L with 

after treatment and 

modify 

transmission: 

$7,500

Add safety 

features 

(disc 

brakes, 

antilock, 

vision 

assists, 

and 

stability 

controls): 

$4,000

Incremental 

cost of 

four 

doubles 

instead 

of three 

single 

trailers, 

including 

trailer 

aero, is 

$6,000

Package 10. 

Reduced 

maximum 

road speed to 

60 MPH applied to one 

of the above 

packages

no cost item

negligible cost 

increase

B-1

TABLE

APPENDIX B (continued)
98 A p p e n d i x B

R E D U C I N G Heavy-Duty Long Haul Combination Truck Fuel Consumption and CO2 Emissions

TECHNOLOGY 

PACKAGES

FUNCTIONAL 

DESCRIPTION AND 

NOTES

INCREMENTAL 

RETAIL 

COST 

ESTIMATE*

PARTS COST* COMMENTS

Package 11. 

Advanced 

EGR

Additional EGR cooler or 

enhanced primary EGR 

cooler, as well as additional corrosion-resistant 

plumbing to remove 

excess water, minor 

changes to the system 

control.

$750

cooler 

modifications: 

$500

balance 

of plant: 

$250

Package 12. 

Bottoming 

cycle/ 

single trailer/

advanced 

aero/hybridization/lower 

road speed

combination of packages 

3, 4, 8, 9, and 10, minus 

duplicate components

$71,630

package 

3 = 

$44,730

package 4 

= 15,000

package 

8 = 

$15,100

package 10 = 

no cost

Credit for 

motor, pwr 

electronics 

= $3,600

$3,200 in 

duplicated 

components 

subtracted 

from total 

cost

Package 13: 

electrical 

turbocompounding/

hybridization/double 

trailer/lower 

road speed

combination of packages 

3, 4, 6, 9, and 10, minus 

duplicate components

$80,380

package 

3 = 

$44,730

package 4 

= 15,000

package 

6 = 

$6,550

package 9 = 

$17,500

package 

10 = 

no cost

Credit 

for 

motor, 

pwr 

electronics 

= 

$4,200

$3,400 in 

duplicated 

component costs 

subtracted 

from total 

cost

Package 14: 

bottoming 

cycle/

hybridization/double 

trailer/lower 

road speed

combination of packages 

3, 4, 8, 9, and 10, minus 

duplicate components

$89,130

package 

3 = 

$44,730

package 4 

= 15,000

package 

8 = 

$15,100

package 9 = 

$17,500

package 

10 = 

no cost

Credit 

for 

motor, 

pwr 

electronics 

= 

$3,600

$3,200 in 

duplicated 

components 

subtracted 

from total 

cost

*unless noted, all costs were obtained as retail costs from published data. For two technologies - hybrid and bottoming cycle, ex-factory costs were first estimated 

and then a retail price equivalent (RPE) markup was applied to estimate the retail cost for these packages.

B-1

TABLE

APPENDIX B (continued)
A P P E N D I X C

99

APPENDIX C

A P P E N D I X C a p p e n d i x c a p p e n d i x c

a p p e n d i x c Appendix C

R E D U C I N G

Heavy-Duty Long Haul Combination 

Truck Fuel Consumption and CO2

 Emissions

Appendix C: Detailed Information on TIAX Cost Analysis

Cost of Package 1: Baseline Vehicle

Kenworth T-600

10 speed manual

2007 Volvo D-13

Aero assumptions:

Bumper fairing, partially aerodynamic mirrors, partial fuel 

tank fairing, integrated roof fairing, exhaust system out of 

the air stream (aero drag coefficient: 0.63) (coefficient of 

rolling resistance: .0068).

Estimated Cost: $125,000 to $135,000 on a fleet purchase 

basis 

Cost of Package 2: SmartWay 1

The “SmartWay 1” package as defined by SwRI includes 

the following upgrades over the baseline tractor-trailer:

• Additional aero streamlining sufficient to reduce the 

 coefficient of drag from 0.63 to 0.5) to both the cab 

 (fully aerodynamic mirrors, cab side extenders, 

 integrated sleeper cab roof fairings, aerodynamic 

 bumper, and full fuel tank fairings) and the trailers. 

 The trailer streamlining includes a side skirt fairing, 

 and either a trailer gap fairing or a rear-mounted 

 trailer fairing such as a boat tail. 

• Improved rolling resistance sufficient to reduce 

 the coefficient of rolling resistance to 0.0055. We 

 have assumed super single low rolling resistance (RR) 

 tires and lightweight aluminum wheels. Super single 

 tires have a steer tire RR coefficient of 0.0058, a 

 drive tire RR of 0.0073, and trailer tire RR of 0.0052.

• Idle reduction (capable of providing eight hours of 

 idle-free auxiliary power, heat and/or air 

 conditioning).

• Improved lubricant package

For this package, TIAX assumed that an Auxiliary Power 

Unit was necessary at a cost of $8,000. The incremental 

cost of improved cab streamlining was estimated to be 

$2,750 for the tractor, while low viscosity lubricants were 

estimated to have a lifetime incremental cost of $500. A 

set of four super single low rolling resistance tires and their 

associated aluminum wheels are estimated to cost $1,120. 

One set of four is required for both tractor and for each 

trailer. The trailers also include $2,400 for aerodynamic 
100 A p p e n d i x C

R E D U C I N G Heavy-Duty Long Haul Combination Truck Fuel Consumption and CO2 Emissions

retrofits, which include skirts and either a front fairing or 

a boat tail. Trailer dimensions were 13’ 5” to 13’ 7” high, 

48’ - 53’ long, and 102” wide).

Total marginal cost for this package was estimated at 

$22,930 including one modified tractor, three modified 

trailers and the APU.

Cost of Package 3: SmartWay 1 + 

SmartWay 2

This advanced SmartWay package (Package 3) includes 

additional trailer aerodynamic devices needed to achieve a 

reduction in CD from 0.5 to 0.4. This package also includes 

lower rolling resistance tires sufficient to lower the coefficient of RR to 0.0045. The lower rolling resistance tires are 

assumed to be an incremental improvement from the super 

single tire package in Package 2 and therefore incur no additional cost. Achieving this level of aerodynamic improvement requires a combination of advanced drag reduction 

approaches that have not been demonstrated commercially. 

Achieving this level of drag reduction is very challenging 

given the present operational constraints of industry. Based 

on discussions with industry experts [Salari, Marinko] and 

a review of the available literature, we estimate that a CD

of 0.4 is feasible using the following combination of design 

modifications to the tractor and the trailer:

– Smartway Tractor: Going from the baseline 

 (Package 1) “partial Smartway” tractor to a full 

 Smartway tractor reduces CD of the vehicle from 

 0.63 to 0.59. This represents a 6% reduction in CD. 

– Advanced Smartway tractor modifications:

 Additional streamlining of the tractor beyond the 

 level offered by Smartway includes underbody 

 treatments, down exhaust, a lowered ride height, as 

 well as continued optimization of the tractor body. 

 It would also require wheel skirts or hubcaps. We 

 have assumed that these further design modifications 

 could reduce CD by an additional 4 to 6%.

– Gap Treatments: Improved integration between the 

 tractor and trailer interface. This could take the 

 form of a front fairing on the trailer, or extended cab 

 side and roof fairing treatments. These types of 

 devices have demonstrated reductions in CD that 

 range from 3% to 5% [TMA].

– Trailer Roof Redesign: Redesign of the trailer body 

 to use a tear drop design that smooth airflows 

 coming off the top and side of the tractor. In addition, 

 an inset roll-up door and aerodynamic mud flaps can 

 offer additional reductions. Don-Bur, a trailer 

 manufacturer in England, currently manufactures 
A p p e n d i x C 101

 trailer designs that demonstrate the type of design 

 that could realize the proscribed benefits (Figure 

 C-1). Although literature claims fuel consumption 

 reduction on the order of 10%, these numbers are 

 likely optimistic; we have instead assumed a 6 to 

 7% fuel consumption reduction. Given that roughly 

 half of semi-trailer’s road-load goes to overcoming 

 drag at highway speed, this corresponds to a 

 reduction in CD of approximately 12 to 14%.

– Full Skirting & Boat tail: In combination, a full 

 trailer skirt with a boat tail has been shown to reduce 

 CD by 16 to 20% [Marinko, TMA, Leuschen and 

 Cooper]

To our knowledge, no such fully aerodynamic tractor/

trailer combination has been tested. In the absence of such 

real-world testing, we can estimate the total CD benefit 

of the described package by combining the individual 

design modifications multiplicatively1

. Combining the 

results in this fashion yields reductions in aerodynamic 

drag on the order of 35 to 42% from the original CD of 

0.63. This would correspond to a total vehicle CD in the 

range of 0.36 to 0.41. However, given that many of the 

design modifications help streamline similar portions of 

the vehicle, this method of estimation likely overstates the 

benefits. In reality, we would expect the benefits of the full 

advanced smartway package to lie at the lower end of this 

estimate. As such, we have decreased the multiplicative 

estimate by several percentage points (33 to 38%), which 

gives a CD ranging from 0.39 to 0.42.

C-1

FIGURE

EXAMPLE TRAILER DESIGN [DON-BUR]

1 i.e., (1 - % CDMod 1) x (1 - % CDMod 2) x (...)
102 A p p e n d i x C

R E D U C I N G Heavy-Duty Long Haul Combination Truck Fuel Consumption and CO2 Emissions

DELTA CD PER TRAILER QUANTITY TOTAL

(3 TRAILERS)

Tires + Wheels – cab – $1,120 Times 1 $1,120

Tires + Wheels - trailer – $1,120 Times 3 $3,360

Smartway cab 6% $2,750 Times 1 $2,750

Advanced Smartway cab 4 to 6% $2,000 Times 1 $2,000

Tear-drop trailer 12 to 14% $7,500 Times 3 $22,500

Skirting, boat-tail, & gap 

treatment 18 to 21% $1,500 Times 3 $4,500

APU – $8,000 Times 1 $8,000

Lubricants – $500 Times 1 $500

Total ~33 to 38% $23,990 – $44,730

C-1

TABLE

COSTS & CD BENEFITS OF THE ADVANCED SMARTWAY (CD = 0.4) PACKAGE

The costs for such a package are highly uncertain, as no 

such design has been demonstrated commercially. The 

following assumptions are used to estimate the total cost of 

the advanced smartway package:

– It is assumed that as smartway trailer designs are 

 more widely adopted, features such as boat-tails, side 

 skirts, and trailer gap fairings are likely to be 

 integrated into the design of the trailer. In 

 addition, we have not included boat-tailing in the 

 advanced smartway specification. These changes 

 would dramatically reduce the cost of these features 

 compared to the retrofit devices that were priced 

 in package 1. We have assumed that the skirts, boat 

 tail, plus gap fairing will cost on the order of $1,500 

 per trailer, down from the $2,400 assumed for the 

 original Smartway package (package 2).

– The major additional cost comes from the trailer 

 design modifications that have been proposed. No 

 actual cost estimates are currently available for such 

 a system in high-volume production; it is likely that 

 demonstrator versions would cost about double 

 a typical dry-box van trailer, which cost on the order 

 of $30,000. In high volume, the cost of these design 

 modifications would be significantly lower. We have 

 assumed that in high volume, the price of this 

 advanced tear-drop design would increase the cost of 

 the trailer by 20%, giving an incremental price of 

 $7,500 per trailer.

– Design modifications to the tractor are assumed to 

 come at a slightly lower incremental cost to those 

 anticipated for Package 2. The proposed 

 modifications include evolutionary modifications 

 to the tractor design (which may increase 

 manufacturing costs), as well as underbody 

 treatments and full skirting of the cab. In 

 combination, we estimate these design modifications 

 to cost on the order of $2,000.
A p p e n d i x C 103

The total incremental cost for this package if applied to the 

Baseline truck is estimated at $44,730 for one tractor and 

three trailers.

Cost of Package 4: Hybrid

Package 4 builds on Package 2 by converting all possible 

accessories to electric and adding a parallel hybrid electric 

system. The assumed HEV System for Class-8 Tractor 

Trailer Combination is typified by Kenworth and Peterbilt 

HEV trucks announced in 2008. The Eaton Parallel system 

and the ArvinMeritor series + parallel system were both 

modeled by SwRI as part of this study.

The HEV System includes the following major modules:

1.Motor Generator- 50 kW

2.Battery Storage Pack- 4 kWh of which 2 kWh is 

 useable

3.Electrification of Accessories

4.Modified Transmission and Clutch Assembly

5.Power Electronics

6.High-voltage wiring and balance of plant

The hybrid includes a control system capable of the 

following energy saving features:

• Engine-off at extended-idle

• Power absorption during braking (regeneration)

• Launch Assist

• Maximizes utilization of electric motor at load-speed 

 points corresponding to low efficiency engine 

 operation, when battery SOC permits (modified 

 transmission shift points and motor–assist logic).

• Electric AC and other accessories during hoteling 

 (idle reduction capable of providing idle free auxiliary 

 power, heat and/or air conditioning)
104 A p p e n d i x C

R E D U C I N G Heavy-Duty Long Haul Combination Truck Fuel Consumption and CO2 Emissions

• Electrification of Cooling Fan, Steering, Brakes, 

 Water pump 

Cost Estimate and Assumed Timing of 

Market Introduction:

Moderate volume cost was estimated to be approximately 

$35,000 (range of $30,000 to $40,000). Higher volume 

cost was estimated to be approximately $23,000 (range of 

$20,000 to $26,000). Provided line haul truck manufacturers proceed to launch this HEV configuration as a product 

line, moderate volume (200-1000 per year) is expected in 

2009-2012 and higher volume (2000-10,000 per year) is 

expected in 2013-2017. The details of these cost estimates 

are provided below.

The ex-factory cost of HEV-equipped heavy duty trucks can 

be expected to follow the common evolution from high 

premiums in the early years (as driveline suppliers attempt 

to at least partially recoup their non-recurring designdevelopment investments), followed by price reductions 

due to increased sales volume (economies of scale of 

manufacturing and assembly). The price history of HEVequipped transit buses can provide an indication of these 

early cost trends. For example in the early years when HEV 

bus sales were in the 10s per year, the price premium for 

an HEV-equipped transit bus was approximately $200,000 

per bus. Later when sales volume rose to 50-100 per year, 

the price premium decreased to approximately $100,000 

per bus. Now that BAE and Allison each have about 1000 

HEV buses deployed, the initial investment is presumably 

largely recovered and prices are in position to decrease as 

volume increases more (currently 15% to 20% of all transit 

bus sales are HEV).

The Class-8 HEV truck cost evolution is expected to follow 

similar trends, only with a somewhat lower cost starting 

point (since the first HEV line-haul truck announced in 

2008 leveraged the previous heavy-duty hybrid manufacturing infrastructure). The fleet buyer’s decision for 

heavy-duty trucks will be much more sensitive to payback 

period and demonstrable fuel-saving benefits than was the 

case for the transit industry (where the FTA absorbs a large 

share of the investment of a new vehicle). A number of 

heavy-duty HEV trucks have already been purchased by 

fleets for demonstration and evaluation purposes, and in 

the early years these too have been priced at a significant 

(non-economic) premium, justified by the value of the early 

lessons and demonstration evaluation. Government funding has been available in some instances. In 2005-2007 a 

number of heavy-duty HEV truck models were announced 

to be in limited production, such as:

• In 2007 International launched their Class 6-7 

 Durastar-based HEV in volumes of about 200 trucks 

 so far, reportedly at $53,000 premium with PTO 

 ($43,000 without PTO).

• Eaton successfully completed their trial of a fleet 

 of HEV delivery trucks (Class 4) and announced they 

 are moving into production.

• Freightliner plans to produce 1500 M2 HEV trucks 

 (Class 6-7) based on the Eaton system in the next 

 three years.

• Peterbilt introduced a Class 8 hybrid using the Eaton 

 system and an automated-manual transmission. Bill 

 Kahn of Peterbilt reported $9,600 savings per year 

 through 8% FE improvement and anti-idling; and 
A p p e n d i x C 105

 indicated a less than 3 year pay-off for the hybrid 

 system.

• Volvo announced production of heavy-duty HEV 

 trucks starting in 2009.

• Arvin Meritor agreed to supply Class 8 HEV trucks 

 for Walmart.

• Azure/StarTrans producing Class 3 HEV Ford shuttle 

 buses at approximately $35,000 premium.

As of the first quarter 2008, the aggregate number of 

heavy-duty HEV trucks in service (including delivery 

trucks) is estimated at 500 and the sales volume is 

expected to be about 200-400 per year in 2008, a figure 

which includes the Fed Ex, Purolator, UPS and Coca Cola 

HEV demonstration trucks (Reference: telecom with Bill 

Van Amburg of WestStart, March 2008). Although line 

haul HEV trucks are quite few in number, this is expected 

to change since Peterbilt, Volvo, International and other 

truck builders have recently announced Class 8 Line-Haul 

HEV demonstrator vehicles.

For the short term (2009-2011), given fuel price 

expectations, the interest in HEV trucks is relatively robust, 

and year-over-year sales are expected to be robust. If this 

scenario in fact comes true, the HEV truck sales volume 

will reach approximately 1000 (which is about 3-4% of 

sales) by the year 2010. This level of sales would not be 

expected to be enough to really drive down HEV prices 

significantly, but the HEV market would then be positioned 

to rapidly expand (see below).

The key assumption is that driveline suppliers such as 

Eaton, Allison and BAE will elect to offer a single common 

HEV architecture across all heavy duty truck models and 

body types. This will accomplish economies of scale and 

volume parts discounts in the assembly of HEV trucks. For 

example the new Peterbilt Class 8 HEV Line-Haul truck 

utilizes essentially the same Eaton-assembled HEV architecture and components as used in the Class 4 Eaton HEV 

delivery truck.

Another key assumption is that the driveline manufacturer 

does not have to reach an annual production volume of 

20,000 units in order to reduce costs significantly. It is 

estimated that a new cost plateau can be reached at about 

2500 or more annual production for any given driveline 

manufacturer (and this volume can be made up of diverse 

truck types such as HEV delivery trucks, HEV utility trucks, 

HEV line haul trucks, etc)2. One scenario is that HEV truck 

sales continue to rise after 2010 and this “trigger point” of 

2500/year might be reached at some point in the 2014-

2020 timeframe, depending on a number of factors.

The market for HEV trucks (including HEV line-haul 

trucks) will be driven by several factors:

• Diesel fuel prices sustained at well above $3.00 a 

 gallon and/or increasing.

• Greenhouse gas policy actions by California and 

 other states as well as the Federal government 

 (carbon taxes, carbon cap and trade, LCFS 

 measures, etc)

• Anti-idling and over-nighting restrictions set by state 

 and local authorities

2 Telecon with Bill Van Amburg of WestStart, March 2008
106 A p p e n d i x C

R E D U C I N G Heavy-Duty Long Haul Combination Truck Fuel Consumption and CO2 Emissions

C-2

FIGURE

HEV COSTS AS A FUNCTION OF ANNUAL VOLUME

$100,000-200,000

Late 2007

Li -Ion Battery 

Cost Reduction

2-3/Year 25/Year 250/Year 2,500/Year 25,000/Year

Note: Costs in 2008 Dollars

50,000

100,000

All HD Truck Industry 

HEV Sales

10/Year 100/Year 1000/Year 10,000/Year 10,000/Year

Individual 

Supplier Volume

2004-2006 First 

Prototypes

“Trigger Point” with

Step Change in Cost

Acceleration of 

Market

(2014-2020 Timeframe)

Robust HEV 

Market

DESCRIPTION % COMPONENT COSTS AT FACTORY

Motor/Generator 50kW 13% $1,500 assuming $30 per kW

Battery Pack 4 kWh 28% $3,200 assuming $800 per kWh

Power Electronics 13% $1,500 assuming $30 per kW

Wiring/Balance of Plant %20 $2,300 based on 25% of all other

Modified Clutch Assembly and Automated 

Manual Upgrade 16% $2,000

Electrification of Accessories 9% $1,000

Total Components Cost 100% $11,500

Initial Low Volume Pricing $35,000

Higher Volume Retail Pricing @ 2.0 RPE $23,000

C-2

TABLE

HEV SYSTEM COMPONENTS
A p p e n d i x C 107

Estimated Pricing of the HEV Option for Class-8 

Line-Haul Trucks (low volume)

It is instructive to review the rough costs of individual 

major components of a typical truck sized HEV system 

Table C-2 shows the major components of a typical HEV 

system and the cost of each component (not including such 

one-time investments as design and development testing).

Based on the above reasoning the premium pricing of the 

HEV option is presented in three timeframes as follows:

• Near term (low volume) $60,000 to $100,000 

 per truck

• Moderate volume of 200-1000 per year: $30,000 to 

 $40,000 per truck

• Higher volume of 2000-10,000 per year: $20,500 to 

 $26,000 per truck

In the year 2012-2015 the moderate volume might be 

applicable, and in the year 2015-2020 the higher volume 

might be applicable.

Fleet buyer’s decision criteria as to HEV based 

on cost and benefits

The early adopters of HEV line-haul trucks are likely to be 

large fleet owners who might use a longer payback period 

as their threshold, whereas the sole-proprietors will be 

following later in the product lifecycle after volume is up 

and costs are somewhat reduced.

Forward pricing strategies are likely to come into play in 

the heavy-duty truck HEV market. The truck builders may 

offer artificial discounts on their HEV option in anticipation 

of driving up sales volumes enough to lower their unit 

production costs (ex-factory). It has been reported that 

Toyota used similar strategies in the early years of light-duty 

hybrid car sales, offering the Prius at a premium far under 

their true incremental cost.

Cost of Package 5: Mechanical 

Turbocompounding

Package 5 builds on Package 2 by adding a mechanical 

turbo compound system. This package, based on the Volvo 

D12 engine, is very similar to the new Detroit Diesel 

DD15 engine. The costs of a mechanical turbocompound 

system include the addition of port liners to retain thermal 

energy ($500), the addition of VVA to the engine cylinders 

($300), and a high efficiency power turbine ($1,850). The 

package also incorporates a Scania design with a 12-liter 

engine power train. It is important to note the potential for 

2010 system design issues and variability among engines 

due to thermal management of aftertreatment devices. This 

variability could cause a 20-30% price impact on estimated 

package cost. Total cost for this package was estimated at 

$2,650.

Cost of Package 6: Electrical 

Turbocompounding

Because there is a great deal of overlap between the 

electrical turbocompounding system and both the mechanical turbocompound and the hybrid system, the electrical 

turbocompound costs use similar assumptions to these 

other cost estimates. The electric turbocompound includes 

the same components as a mechanical turbo-compound. 

In addition, it adds an electric motor/generator, associated 

power electronics, and electric accessories. Because it 

includes several components in common with the hybrid, 

electric turbocompounding can be synergistically combined 

with the hybrid package at lower cost than would be suggested by our estimate of the two standalone systems.
108 A p p e n d i x C

R E D U C I N G Heavy-Duty Long Haul Combination Truck Fuel Consumption and CO2 Emissions

The costs of an electrical turbocompound system include 

the mechanical turbocompound package cost of $2,650 

(see above) plus the 40 kW motor-generator ($1,200), 

associated power electronics ($1,200 at $50 per kW), 

electric accessories at $1,000 and balance of plant at $500 

for a total cost of $6,550. 

Cost of Package 7: Variable Valve 

Actuation

Package 7 adds variable valve actuation (VVA) to Package 

5 (mechanical turbocompounding). VVA is expected to 

work best when combined with a turbo compound system. 

There are two distinct designs of VVA, only one of which is 

in production:

• Full-Authority VVA, which is designed to be fully 

 adjustable during engine transients, actuated with 

 fast response devices such as camless or hydraulic-

 electric mechanisms (e.g. Sturman VVA technology)

• Conventional “lost-motion” VVA which has restricted 

 preset valve settings which are cam actuated (e.g. 

 Caterpillar VVA). 

Full-Authority VVA Costs: Potential VVA technology 

suppliers such as Sturman have yet to show that their fully 

adjustable VVA system is market-ready; test data from prototypes are not available. The fully adjustable configuration 

of VVA is likely to carry a significant cost increase to the 

manufacturer. Hydraulic valve actuation or camless actuation mechanisms would add a significant cost in excess of 

any potential cost savings for manufacturers once control 

logic software is embedded in engine control software. Software advancements were assumed to be free. Presumably a 

significant portion of the cost associated with implementing 

any full-authority VVA package would be licensing fees 

and amortized development costs. We were not able to 

accurately estimate the cost for this type of VVA.

Conventional “Lost-motion” VVA Costs: This type of VVA 

design was selected as the basis for Package 7. An estimate 

of $50 per cylinder incremental cost was assigned for VVA 

implementation in production volumes. The total marginal 

cost therefore is estimated at $300 above the Package 5 

Costs (see above).

Cost of Package 8: Bottoming Cycle

Package 8 combines VVA, SmartWay 2 (Package 3) and a 

Rankine bottoming cycle system recovering heat from both 

the EGR cooler and an exhaust stack boiler. It was assumed 

that the EGR cooler and bottoming cycle system would be 

co-designed as a package to meet both emissions and fuel 

economy targets. Bottoming cycles are a relatively mature 

technology for stationary diesel and natural gas engines in 

the 1,000 kW to 20,000 kW class, and bottoming cycle 

controls and packaging issues are relatively benign because 

of constant speed operation at relative steady load. Bottoming cycles have never been used for trucks, but early-stage 

designs currently are being explored by selected engine 

manufacturers. There are current examples from the 21st 

Century Truck program, including conceptual designs 

by Cummins and Caterpillar. For example, the Cummins 

Rankine cycle [reference to DOE advanced engine paper 

needed] uses heat from a massive EGR system. However, 

because these designs are preliminary, it was decided to 

develop a preliminary generic design for a truck bottoming 

cycle on which to base the costing. The system was designed to avoid impacting the DPF or NOx aftertreatment. 
A p p e n d i x C 109

It was not clear to the study participants whether bottoming cycles will be feasible and practical for potential 

widespread adoption by the trucking industry within the 

timeframe of the study (out to 2017). Issues include cost, 

packaging, weight, maintenance/reliability and the needed 

controls to capture fuel savings potential. Our costing 

analysis attempts to capture these issues. However, the 

schematic is totally hypothetical and only one of several 

basic architectures that could be proposed.

C-3

FIGURE

SCHEMATIC OF RANKINE BOTTOMING CYCLE FOR TRUCK ENGINE

Generic bottoming cycle for a long-haul truck 

(sized for operation at highway cruise)

SwRI provided a schematic of a generic steam bottoming 

cycle operating at the cruise point which is shown in figure 

C-3 for illustration.

As shown in figure C-3, the bottoming cycle would include 

four main components: (1) A high-speed turbine expander generator (80,000-200,000 rpm); (2) An air-cooled 

condenser; (3) An EGR heat recovery boiler, which is an 

upgrade of the baseline EGR cooler; and (4)an exhaust 
110 A p p e n d i x C

R E D U C I N G Heavy-Duty Long Haul Combination Truck Fuel Consumption and CO2 Emissions

stack heat exchanger/boiler. The SwRI bottoming cycle 

design also includes additional battery storage to provide 

for absorbing excess power during rapid decelerations, hill 

climbs and other transient events. 

System sizing for the line haul truck presents an interesting optimization problem which deserves a more detailed 

analysis than was possible under this project. The highway 

cruise point on level roadway requires only a 12-14 kW 

rated bottoming cycle, but this is seen as suboptimal considering the real life situations of accelerations and climbing 

at grades. At the other extreme, the full load operation can 

support a 57 kW rated bottoming cycle, but this is seen as 

overly costly since the truck engine only rarely operates at 

true full rated load and speed. Therefore an intermediate 

rating was selected as a basis for costing. The bottoming 

cycle system was assumed to be sized for 30 kW rating at 

1600 rpm full load and 100 F ambient. The basic premise 

is that for a long-haul truck, if the bottoming cycle is not attractive at highway cruise, it probably will not make sense 

for the complete typical drive cycle. The available EGR heat 

is assumed to be supplemented by an exhaust stack heat 

exchanger. The condenser is a finned-tube air-cooled heat 

exchanger stacked with the engine radiator and assumes a 

heat transfer coefficient of 20 BTU per hr-ft2

-F. The fin-tube 

boiler has a volume of approximately 1 cubic ft. 

Cost Estimate:

The total marginal cost estimated for the 30 kW bottoming cycle was $15,100 after production volumes become 

significant (thousands per year). This technology will not 

be available until 2015-2017 at the earliest and initial cost 

the first few years would be expected to be at least double 

($34,000 to $40,000). The basis for this cost estimate is 

provided below.

Steam vs organic working fluid for Rankine 

bottoming cycle 

The system assumed for Package 8 uses a steam Rankine 

cycle. Steam has better heat transfer characteristics 

and the potential for higher efficiency, but can present 

expansion-turbine design challenges at small scale. These 

challenges arise because high sonic velocity translates into 

high turbine RPM (~200,000 RPM) and large expansion 

ratio require multiple stages to realize efficiency potential. 

Organic working fluids have higher molecular weight, 

lower speed of sound, and lower pressure ratio, and hence 

offer better matching with small turbine expanders (and 

other types of expanders as well). Most bottoming cycle 

developers for stationary engines have selected an organic 

working fluid. These other working fluid systems could also 

be an appropriate design choice.

In order to size and cost the various components, we 

analyzed the steam cycle shown in figure C-XX above, 

assuming:

• Heat to boil and superheat (by 150oF) water is 

 supplied by the recoverable heat from the exhaust, as 

 defined above.

• Heat to preheat the water from the condensing temp 

 to the boiling temperature is supplied by an 

 economizer transferring heat from the exhaust 

 leaving the boiler to the feed water.

• Rough estimates from steam tables T-s diagram, 

 assuming 70% efficient expander.

• Condensing temperature is 200oF at 100oF 

 ambient, 150oF at 60oF ambient and 100oF at 20oF 

 ambient. There is a smaller temperature difference at 
A p p e n d i x C 111

 20oF ambient because there is no air conditioning 

 load and less overall thermal stress on the cooling 

 system.

The estimated bottoming cycle power output is 14 kW at 

the truck highway cruise point. This power output can be 

obtained at boiling temperatures of either 400oF or 500oF. 

At the higher boiling temperature (500oF), less heat can 

be recovered from the exhaust, but the Rankine cycle 

efficiency is higher; the reverse is true at the lower boiling 

temperature of 400oF.

The steam Rankine cycle requires a high speed (80,000-

200,000 RPM) turbine expander – generator. The electric 

power output of this generator in turn powers a battery, 

with power extracted as needed to contribute to the engine 

shaft power output. The condenser is a finned tube air 

cooled heat exchanger, stacked with the other air cooled 

heat exchangers behind the front grill (air conditioning 

condenser, charge air cooler, bottoming cycle condenser, 

engine radiator). The estimated size and weight are based 

on the following assumptions: (1) 20 fins/inch; (2) An air 

side “h” of 20 Btu/hr-ft2

-oF; (3) Half of the overall heat 

transfer resistance occurs on the air side; and aluminum 

comprises approximately 15% of the volume solid material. 

The boiler is a finned tube HX with fins on the exhaust 

side. Its estimated size and weight are based on the following assumptions: (1) 10 fins/inch; (2) Exhaust side “h” of 

20 Btu/hr-ft2-oF; (3) Half of the overall heat transfer 

resistance occurs on the exhaust side; and aluminum 

comprises approximately 15% of the volume solid material.

Rough estimates of the dimensions and weights of the 

major bottoming-cycle components of a 30 kW output at 

100oF ambient temperature are summarized in Table C-3. 

Figure C-3 shows the dimensions of the major components 

compared with the physical dimensions of a typical heavy 

duty truck engine.

MAJOR COMPONENT OF 12 KW SYSTEM APPROXIMATE DIMENSIONS WEIGHT (LB)

Turbo expander – generator 6 inch diameter by 16 inches long 75

Air cooled condenser 36 inch X 20 inch X 1.5 inch deep 15

Exhaust heat recovery boiler 6 inch X 8 inch X 24 inch long 50

Exhaust Stack Heat Exchanger 6 inch X 8 inch X 24 inch long 50

Misc – working fluid, tubing, feed pump ~ 0.75 ft3 50

Total ~ 3 ft3 240

C-3

TABLE

ESTIMATED DIMENSIONS AND WEIGHT OF MAJOR COMPONENTS OF BOTTOMING CYCLE 
112 A p p e n d i x C

R E D U C I N G Heavy-Duty Long Haul Combination Truck Fuel Consumption and CO2 Emissions

12 KW 30 KW 57 KW COMMENTS

Turbine Generator and Flywheel $860 $2,160 $4,100 Based on turbocharger parts of $42/kW, 

$30/kW generator

Air-cooled condenser $ 500 $ 550 $1,000 Based on large mobile AC condensers; 90 

kW3

 and heat rejection; 13 ft2 face area 

EGR boiler (stainless steel) $ 500 $ 400 $ 400

Stack boiler NA $1,000 $1,500 Both boilers sized by capacity and log mean 

temperature difference

Packaging, assembly, and balance 

of plant $1,500 $2,000 $2,500

Controls and power electronics $750 $1,300 $2,100 $400 for controls plus $30/kW for power 

electronics

Energy Storage $100 $150 $300 Battery or ultracap sized to capture peak load 

for 10 seconds

Total Cost at Factory $4,200 $7,550 $11,900

Total Retail Cost $8,400 $15,100 $23,800 Applied RPE of 2.00

C-4

TABLE

DETAILED COSTS FOR BOTTOMING CYCLE COMPONENTS

C-4

FIGURE

SIZE OF MAJOR COMPONENTS OF RANKINE BOTTOMING CYCLE COMPARED TO 

DIMENSIONS OF HEAVY DUTY TRUCK ENGINE

3 For the 30 kW system
A p p e n d i x C 113

Bottoming Cycle Component Costs:

Based on the sizes, materials, and weights of these 

components, and based on the typical costs of conventional 

HVAC manufactured items such as heat exchangers and 

compressors which are similar in function, cost for the 

bottoming cycle system were estimated. The estimated 

costs for these components are detailed in Table C-4.

Figure C-4 provides a schematic illustrating the size of the 

different bottoming cycle components relative to a heavyduty truck engine.

Cost of Package 9: Longer / Heavier 

Trucks

Package 9 builds on Package 2 with “highway doubles” 

which create a gross vehicle weight (GVR) and volume 

increase. This package is assumed to be based on the 

Scandinavian approach of 60 metric tons (about 132,000 

pounds) and 25 meters total combination length. We 

estimated the cost for this package by assuming three cost 

elements:

• Powertrain modifications for maintaining speed 

 at grade

• Safety features 

• Incremental cost of two doubles vs three singles 

 (assuming that in fleets, ten “doubles” would suffice 

 in place of fifteen single trailers).

In the power-train area, the base engine size would 

increase by approximately 3L to accommodate the added 

load. Besides the engine block itself, engine cooling and 

aftertreatment systems (as well as some other smaller 

systems) would also have to increase proportionally. The 

transmission would need to be modified for higher loads. 

We estimate the incremental cost of these power-train 

modifications to be $7,500.

Safety features such as disc brakes, stability controls, and 

vision systems were assigned a retail incremental cost 

budget of $4,000.

The incremental cost of two doubles over three single 

trailers was estimated at $6,000. This includes the added 

cost of the trailer, plus the additional aerodynamic devices 

and super single tires included in the Advanced Smartway 

package.

C-5

FIGURE

ROCKY MOUNTAIN DOUBLE 

(Source: FHA)
114 A p p e n d i x C

R E D U C I N G Heavy-Duty Long Haul Combination Truck Fuel Consumption and CO2 Emissions

The total retail incremental cost for this package was 

estimated at $17,500. It is interesting to note that Rocky 

Mountain Doubles could be a negative cost package, since 

fleet operators may find that they would need fewer cabs to 

move an equivalent amount of freight. This nuance is not 

captured in our analysis.

Cost of Package 10: Reduced Road 

Speed

This package assumes speeds would drop to 60 miles per 

hour or below. There were no hardware or technology 

costs associated with this package.

Cost of Package 11: Advanced EGR

The advanced EGR concept that was modeled requires 

additional cooling to a conventional EGR system. The 

lower temperature exhaust reduces NOx, which allows 

timing to be advanced, thereby offering incremental efficiency improvement. Such a system would likely require 

an additional EGR cooler (or an enhanced primary EGR 

cooler), as well as additional corrosion-resistant plumbing 

to remove excess water and minor changes to the system 

control. We estimate this package will cost on the order of 

$750 ($500 for the cooler modifications, plus $250 for the 

additional balance of plant).

Cost of Packages 12, 13, and 14: 

Maximum Technology Combinations

The costs of three modeled packages are described in 

this section – packages 12, 13, and 14. The costs of the 

maximum technology combination packages are calculated 

as the sum of the individual technology packages, less the 

cost of any duplicate components (e.g., both the hybrid and 

electric turbocompounding include a motor/generator):

Package 12: The maximum technology combination with 

a single trailer – is estimated to cost $71,630. This includes 

the cost of Package 3 ($44,730), Package 4 ($23,000), 

Package 8 ($15,100), and Package 10 (No cost), minus 

$3,200 in duplicated components between the hybrid 

and bottoming cycle systems (motors, energy storage, and 

power electronics). Package 12 also does not need the APU 

that is included as part of package 3, because the hybrid 

system already offers these idle reduction benefits; this 

reduces the cost by an additional $8,000.

Package 13: Is estimated to cost $80,380. As described 

in Chapters 2 and 3, this package includes a longer heavier 

trailer, advanced aerodynamics (package 3 - $44,730), 

hybrid (package 4 - $23,000), Package 6 ($6,550), Package 

9 ($17,500), and Package 10 (No cost), minus $3,400 in 

duplicated components between the hybrid and electric 

turbocompounding systems and minus $8,000 for the 

omission of the APU.

Package 14: The maximum technology combination 

with a double trailer – is estimated to cost $89,130. This 

includes the cost of Package 3 ($44,730), Package 4 

($23,000), Package 8 ($15,100), Package 9 ($17,500), and 

Package 10 (No cost), minus $3,200 in duplicated components between the hybrid and bottoming cycle, and minus 

$8,000 with the removal of the APU.

O&M Costs

Operations and Maintenance (O&M) includes any additional maintenance or repair costs that are incurred with 

the addition of new technologies. For a typical long-haul 

truck, O&M accounts for 5% of the total capital cost 

every 100,000 miles [OOIDA]. We anticipate that many 
A p p e n d i x C 115

of the technologies examined would incur incremental 

O&M costs significantly lower than this, for a number of 

reasons: they typically do not require any additional routine 

maintenance; they may require variations on existing 

designs (and hence would have a similar repair schedule), 

rather than the addition of new components; and to the 

extent that new components are included, these are often 

highly reliable and may be expected to last the life of 

the vehicle. For packages that fall into this category, we 

estimated that O&M costs would be close to those seen in 

stationary applications, which are typically closer to 1% of 

the capital cost per year [IEA]4. However, several packages 

include specific components or add complexity that would 

lead to significantly higher O&M costs. We estimated O&M 

for these systems on a case-by-case basis.

Package 2 (Smartway): ($0.004/mi) The improved 

aerodynamic cab and trailer design is not anticipated to 

add significantly to O&M costs over the baseline vehicle. 

However, the additional cost of single wide tires is incurred 

every time tires are replaced and/or retreaded. OOIDA 

estimates tire replacement costs of approximately $2,800 

per 100,000 miles. The super single tires that were 

specified cost approximately 10% more than the tires that 

they replace; hence, it is assumed that they incur a $280 

incremental cost per 100,000 miles. In addition, it is 

assumed that the advanced lubricants need to be replaced 

every 300,000 miles.

Package 3 (Advanced SmartWay): (negligible) Includes 

only additional trailer aerodynamics, which we do not 

anticipate will add to O&M costs.

Package 4 (Hybrid): ($0.006/mi) The hybrid includes 

the addition of an electric motor/generator, power 

electronics, electric accessories additional wiring, and a 

battery. The added electronics and motor tend to be highly 

reliable and should not require additional maintenance. 

Added O&M due to these components is estimated at 1% 

of capital per 100,000 miles. Real-world experience with 

batteries in trucking applications, which includes a service 

life of hundreds of thousands of miles, is limited. Batteries 

in light-duty hybrids have demonstrated service lives of 

100,000 to 200,000 miles over a 10 year life. For long-haul 

trucking, we assume that batteries will last for 6 years. The 

O&M costs amortize the future (discounted at 7%) battery 

replacement cost over six years and include this cost in the 

per-mile O&M5

. 

Package 5 & 6 (Mechanical & Electrical Turbocompounding): ($0.0003-$0.0007/mi) Both packages 

require the addition of a power turbine and VVA; electrical 

turbocompounding requires a power turbine plus an 

additional motor and power electronics. These factors are 

estimated to incur 1% for every 100,000 miles. 

Package 7 (VVA): (negligible) Requires design modification to the engine cylinders. This is not anticipated to add 

significantly to O&M costs.

Package 8 (Bottoming Cycle): ($0.003/mi) The bottoming cycle adds considerable complexity to the vehicle. For 

this system, we assume a higher O&M cost of 2% for every 

100,000 miles.

4 To equate capital costs in stationary applications (expressed in $/kWh) to mobile applications ($/mi), we assume an average vehicle speed of 60 MPH.

5 The longer service life (in terms of mileage) compared to light-duty applications reflects that: (1) there is a limited window for calendar life-based 

degradation, which can be an important limit on battery lifetime; (2) the steady-state nature of most of the long-haul duty cycle suggests that the battery 

will not see nearly as many cycle as a battery in a light-duty duty cycle. These estimates will need to be validated against real-world experience.
116 A p p e n d i x C

R E D U C I N G Heavy-Duty Long Haul Combination Truck Fuel Consumption and CO2 Emissions

Package 9 (Rocky Mountain Double): ($0.002/mi)

The Rocky Mountain Double includes a larger engine and 

exhaust system, additional safety features and brakes; these 

factors are not anticipated to add significantly to vehicle 

O&M. These are estimated to incur 1% for every 100,000 

miles. In addition, because the Rocky Mountain Double 

includes 1.33 times more trailers, there is an added super 

single tire replacement cost equal to one third the tire 

replacement cost of the Smartway package.

Package 10 (60 MPH Speed Limit): (negligible) No 

added cost.

Package 11 (Advanced EGR): (negligible) As an 

enhancement to the conventional EGR system that already 

exists on the baseline vehicle, we do not anticipate 

additional costs.

Package 12 (Technology Packages): For the combined 

technology packages, O&M costs are estimated as the sum 

of the individual technology O&M costs.

The incremental cost of each technology package was 

estimated following the methods described in Chapter 2.

Cost-Benefit Results

Using the methodology described in Chapter 2, TIAX 

evaluated the cost effectiveness of different technology 

packages. As discussed previously, two different figures of 

merit were examined – the net cost of ownership over a 

fifteen year vehicle lifetime, and the net cost of ownership 

over a three year time horizon for both the 2008 EIA 

reference and high fuel price scenarios. The results of these 

calculations are shown in Figure C-6. 

Two overarching themes emerge from these calculations. 

First, there are a number of technologies that appear very 

attractive when viewed over the fifteen time horizon (or 

over a three-year time horizon with high fuel prices). 

However, under the reference fuel price scenario (roughly 

$2.50 per gallon), only the lower priced, lower benefit 

technologies (VVA, advanced EGR, mechanical turbo-compounding), and the two packages that entail operational 

changes (speed limit reduction and longer, heavier trailers) 

have a negative cost of ownership. This finding illustrates 

the challenge of deploying new technologies in the fleet: 

while a technology may be cost effective over the vehicle’s 

service life, if fuel prices remain low, it may not be adopted 

by the market.

Cost-Benefit Results of Individual Packages

Examining the results on a technology-by-technology basis, 

these cost-of-ownership calculations may be used to loosely 

group the technology packages into several categories:

Operational Changes – Speed limit & Longer, heavier 

trailers (Packages 9 and 10): These packages are highly 

cost-effective approaches to saving fuel. They each offer 

significant savings over both a fifteen-year time horizon and 

a three-year time horizon under both high and low fuel 

price scenarios. Implementing these packages is as much of 

a political question as they are an economic question. 

Low Capital Cost Technologies – Advanced EGR, 

VVA, Mechanical turbo-compounding, electric turbocompounding (Packages 5, 6, 7, and 11): These packages are generally low-cost (ranging from a few hundred 

dollars to $7,000 for electric turbo-compounding), and 

offer benefits that range from 1 to 4.5%. With the exception of electric turbo-compounding, they each offer payback 
A p p e n d i x C 117

within three years under the reference case fuel scenario; 

electric turbo-compounding achieves payback in just under 

four years under the reference case, and has a negative 

cost of ownership over a fifteen-year time horizon in both 

fuel price scenarios. These technologies are all relatively 

low technical risk and are likely to be available in the next 

several years. They would all potentially be attractive to 

buyers who are sensitive to first cost.

High Capital Cost Technologies – Smartway, 

Advanced Smartway, Hybrid and Bottoming cycle 

(Packages 2, 3, 4, and 10): These packages all offer 

significant fuel savings, but come at much higher cost 

than the technologies discussed above. None of these 

technologies achieve payback within three years under the 

reference fuel price scenario. However, both Smartway 

packages offer very high value over a fifteen year time 

horizon, and are also very attractive over a three-year 

time horizon with high fuel prices. The greatest barrier 

to widespread adoption of the Smartway package is that, 

given current standard practice in industry, the trailer 

aerodynamic devices must be deployed on three different 

trailers. The advanced Smartway package must also overcome this barrier to adoption; in addition, its implementation would require dramatic changes to trailer design. The 

bottoming cycle is a high technical risk package that could 

offer high single-digit or low double-digit fuel savings; it 

is likely to offer favorable payback over a fifteen-year time 

horizon, or over a three-year time horizon with high fuel 

prices. The hybrid package has a positive cost of ownership 

over a three-year time horizon, and just breaks even over 

fifteen years under the reference fuel price scenario. One 

of the key factors influencing the hybrid’s payback is the 

amortized cost of battery replacement. However, there are 

synergies that may be realized when the hybrid system is 

combined with other electrification strategies. 

Technology Combinations (Package 12, 13, and 14):

The technology combination packages are highly costeffective when viewed over a fifteen year time horizon, and 

are close to a negative cost of ownership over a three year 

time horizon under a high fuel price scenario. However, 

under the reference fuel price scenario, the realized fuel 

savings over the first three years are not great enough to 

overcome the high initial cost. 

To the extent that the technology combination packages 

are cost effective, it is due primarily to the inclusion of 

the obvious winning technologies (Smartway, 60 MPH 

governor, and Rocky Mountain Double). In some respects, 

the cost-effectiveness of these individual technologies, 

reflected by their negative cost of ownership, masks the 

inclusion of other, less cost-effective approaches. At the 

same time, the technology combination packages do 

benefit from synergies between the hybrid system and 

electric turbocompounding (in the case of the “Low Cost 

Technology Combination”); and synergies between the 

hybrid system and the bottoming cycle (in the case of the 

two “Max. Technology Combinations”). Because there is 

significant overlap in the components needed to implement 

these increasingly electrified systems, the combinations are 

more cost-effective than the standalone systems.

Figures C-7 and C-8 summarize graphically the 3-year and 

15-year payback analyses. Figure C-7 shows the results of 

the analysis for the 15-year payback case. The solid colored 

bars represent the EIA low fuel price scenario and the 

hatched bars represent the EIA high price scenario. In this 

graph, negative numbers indicate a savings for the truck 

owner.
118 A p p e n d i x C

R E D U C I N G Heavy-Duty Long Haul Combination Truck Fuel Consumption and CO2 Emissions

C-6

C-7

FIGURE

FIGURE

NET COST OF OWNERSHIP CALCULATION FOR TECHNOLOGY PACKAGES – 

15 YEAR TIME HORIZON WITH TWO FUEL PRICE SCENARIOS

NET COST OF OWNERSHIP CALCULATION FOR TECHNOLOGY PACKAGES – 

3 YEAR PAYBACK WITH TWO FUEL PRICE SCENARIOS

-$100

-$80

-$60

-$40

-$20

$0

$20

$40

Smartway

Adv. Smartway

HEV (Incl. Idle reduction)

Mech. Turbo

Elec. Turbo

VVA

Bottoming Cycle

Rocky Mt Double

60 MPH

Adv. EGR

Tech. Combo 1

Tech. Combo 3

Tech. Combo 2

Net Cost of Ownership (1000 $)

EIA Low Fuel Price ($2.50/gal)

EIA High Fuel Price ($3.53/gal)

Net Cost of Ownership (1000 $)

-$25

-$15

-$5

$5

$15

$25

$35

Smartway

Adv. Smartway

HEV (Incl. Idle reduction)

Mech. Turbo

Elec. Turbo

VVA

Bottoming Cycle

Rocky Mt Double

60 MPH

Adv. EGR

Tech. Combo 1

Tech. Combo 2

Tech. Combo 3

EIA Low Fuel Price ($2.50/gal)

EIA High Fuel Price ($3.53/gal)
A p p e n d i x C 119

C-8

FIGURE

ANALYSIS OF CO2 AND FUEL USE AVOIDED IN THE U.S. LONG-HAUL FLEET ASSUMING ALL 

TECHNOLOGIES WITH A 15 YEAR PAYBACK ARE USED. 

SW1 60 MPH R.M. Double

SW2

M Turbo

E Turbo

0

2

4

6

8

10

12

14

16

18

20

2007

2008

2009

2010

2011

2012

2013

2014

2015

2016

2017

2018

2019

2020

2021

2022

2023

2024

2025

2026

2027

2028

2029

2030

Fuel Used/Avoided (B Gal)

HEV+B. Cycle

HEV+ETurbo

Bottoming Cycle

E Turbo

M Turbo

SW2

R.M. Double

60 MPH

SW1

Fuel Used

2022: 4.7B Gallons of Fuel Saved

(30% below the base case)

Figure C-7 illustrates the results of the 3-year payback 

scenario. In this Figure, solid bars also represent the EIA 

low fuel price of $2.50 per gallon of diesel in 2022 and the 

hatched bars represent the EIA high fuel price scenario of 

$3.53 per gallon in 2022.

To assess the impact of fuel saving devices on the line-haul 

tractor trailer fleet, we incorporated the results of the above 

analysis into our bottom-up tractor trailer fleet model. 

Because these technologies focus primarily on the long-haul 

(as opposed to regional) portion of the fleet, the analysis 

focuses on this fleet sub-segment. Two different technology adoption scenarios were considered, and analysis was 

conducted for both high and low fuel prices scenarios. 

Reference Fuel Price Scenario

Predicted Fuel Consumption Reduction under 

Scenario A 

The fleet model estimates that the technologies adopted in 

Scenario A (the 15-year time horizon, which uses lifetime 

NPV to select technologies) have the potential to reduce 

fuel use in the long-haul truck fleet by 30%, or 4.7B gallons, by 2022 under the reference case fuel price scenario. 

These dynamics are illustrated in Figure C-6, which shows 

the total projected fuel use to 2030, as well as the avoided 

fuel use associated with individual fuel-saving technologies 

for the long-haul section of the tractor trailer fleet. 

Note that the top 3 technologies in the legend are not used under this case.
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R E D U C I N G Heavy-Duty Long Haul Combination Truck Fuel Consumption and CO2 Emissions

As shown, fleet fuel use declines until 2022 to 2024, at 

which point it slowly begins to rise again. Initially, reductions are primarily due to phase-in of trucks with SmartWay 

1 packages and the 60-MPH speed limit. Beginning in 

2017, SmartWay 2 and Rocky Mountain doubles dominate 

the reduction wedge, although the turbo-compounding 

package also offers significant benefit. The increase in fleet 

fuel use beginning in 2022 arises due to continued growth 

in freight ton-miles, coupled with the fact that no new 

improvement options are introduced into the model after 

2017. In reality, innovation will continue past this point, 

but this nuance is not captured in the model, as it is not 

clear which technology options will be available. Initially, 

mechanical turbocompounding is adopted. Because it has 

a net-negative cost of ownership and it offers greater fuel 

savings than VVA and advanced EGR, it supersedes these 

technologies in the fleet. Similarly, as the cost of electrical turbocompounding goes down and fuel prices rise, it 

supersedes mechanical turbocompounding in the market 

beginning in the 2017 to 2020 timeframe. Due to their 

high initial and O&M costs, neither the hybrid nor bottoming cycle packages are adopted under the reference fuel 

price scenario6

. 

Fuel Price and Technology Adoption Scenario 

Comparison

Figure C-9 shows the avoided fuel use in five-year increments for both scenarios under the low and high fuel price 

scenario. As shown, Scenario A offers significantly more 

fuel savings than Scenario B, particularly in the reference fuel price scenario. As might be expected, the high 

fuel price scenario has a comparatively greater effect on 

Scenario B (market-driven adoption) than on Scenario A. 

As shown, Scenario A already implements most of the 

available technologies across the entire fleet even under the 

low fuel price scenario. The additional improvements occur 

due to adoption of the bottoming cycle beginning in the 

2020 timeframe. 

The reduced fuel use in Scenario B stems from increased 

technology penetration across the board: the combined 

penetration of the two Smartway packages increases from 

35 to 40% to over 60%, while Rocky Mountain Doubles 

become nearly fully adopted. In addition, both electric 

turbocompounding and the bottoming cycle increase their 

market share at the expense of mechanical turbocompounding, VVA, and advanced EGR.

6 Appendix E includes year-by-year market penetration of different technologies.
A p p e n d i x C 121

C-9

FIGURE

AVOIDED FUEL USE ASSUMING TWO PAYBACK PERIODS AND TWO FUEL PRICES

0

1

2

3

4

5

6

7

8

2012 2017 2022 2027

Avoided Fuel Use (B Gal)

Scenario A, Ref. Case

Scenario A, High Case

Scenario B, Ref. Case

Scenario B, High Case

A P P E N D I X D

123

APPENDIX D

A P P E N D I X D a p p e n d i x d a p p e n d i x d

a p p e n d i x d Appendix D

R E D U C I N G

Heavy-Duty Long Haul Combination 

Truck Fuel Consumption and CO2

 Emissions

Fleet Model Methodology

The fleet model uses estimates of new truck sales, scrap 

rates, VMT, and fuel economy to develop a bottom-up 

estimate of fleet-wide characteristics, such as fleet fuel use, 

fleet VMT, and truck population. This approach is similar to 

that used by Bandivadekar et al [2008] for their analysis of 

the light-duty vehicle fleet.

For trucks that are n years old in year t, the total truck 

population (poptot(n,t), mileage (VMTtot(n,t)), and fuel use 

(fueltot(n,t)) for that particular vintage are calculated as 

follows:

poptot(n,t) = sales(n,t) – scrap(n)

VMTtot (n,t) = poptot(n,t) x VMT(n)

fueltot(n,t) = VMTtot(n,t) x FE(n,t) 

Appendix D: Detailed Information on the Fleet Model Analysis

Where t is the current year; n is the truck vintage; 

sales(n,t) is the new truck sales in the year (t-n); scrap(n) is 

the estimated retirement rate for a truck that is n years old; 

VMT(n) is the estimated mileage driven by an in-use truck 

that is n years old; and FE(n,t) is the average fuel economy 

of trucks sold in the year (t-n). he total truck population, 

VMT, and fuel use across all vintages in year t is then 

calculated as the sum of these factors across all vintages:

Truck population (t) = Σpoptot(n,t)

Total VMT (t) = ΣVMTtot(n,t)

Total fuel use(t) = fueltot(n,t)

Fleet Characterization and Data 

Sources 

The key assumptions and data sources used to characterize 

the regional and long-haul fleets are summarized in Table 

D-1.

REGIONAL LONG-HAUL SOURCE

Fleet Size in 20081 830,000 570,000 TEDB 2007, MOVES 2004

Fraction of TT sales 20% 80% VIUS 2002

Tractor Trailer Sales2 87,000 Wards 2008, VIUS 2002

Fleet growth rate 1.7%/Yr EIA 2008

2008 Fuel economy 6.0 MPG TEDB 2007

Median Age 19 Yrs 7.5 Yrs TEDB 2007

VMT per year 80,000 (Age = 0)

28,000 (Age = 15)

140,000 (Age = 0)

50,000 (Age = 15) VIUS 2002

D-1

TABLE

TRACTOR TRAILER FLEET ASSUMPTIONS

1 2008 bottom-up estimate; This estimate includes only that portion of the fleet which pulls box trailers. 

2 Five-year average (2002-2007) estimate for tractors. The available data segments new truck sales according to weight class, but not according to body type 

(i.e., combination vs single-body truck). As such, our estimate of combination truck sales uses published data for Class 8 trucks [Ward’s 2007], and then 

assumes that 70% of Class 8 trucks are tractors (based on fleet segmentation data from VIUS). We further assume that 60% of these tractors are used to pull box 

trailers [VIUS 2002]. Hence, the fleet model assumes that 42% (i.e., 60% x 70%) of new Class 8 sales are tractor-box trailer combinations. 
124 A p p e n d i x D

R E D U C I N G Heavy-Duty Long Haul Combination Truck Fuel Consumption and CO2 Emissions

The data sources used to characterize the fleet include the 

Vehicle Inventory and Use Survey [VIUS 2002] from the 

U.S. Census Bureau, the DOE’s Energy Information Administration [EIA 2008], the Transportation Energy Data Book 

[TEDB 2007] published by Oak Ridge National Laboratory, 

and Ward’s Automotive handbook [Ward’s 2007],. In addition, the EPA’s MOVES [2004] emissions model was used 

to help guide our methodology.

In general, sources such as Ward’s, TEDB, and the FHA 

provide the most accurate source of absolute numbers, 

such as total vehicle miles traveled (VMT) and vehicle 

population. The VIUS data, which is a broad-based survey 

of commercial truckers, was then used to add fidelity to 

these bottom-line numbers. For example, while VIUS’s 

estimate of the total truck population is likely to be less 

accurate than the FHA’s (which is based on actual registrations), it can provide useful estimates of the breakdown 

between regional and long-haul service or average annual 

VMT for trucks function of age.

An initial survey of the tractor-trailer fleet using VIUS 

indicated that these trucks exhibit widely varying duty 

cycles and annual mileage depending on the truck’s age 

and vocation. For the first five to seven years of its life, a 

typical tractor-trailer would serve in “long haul” operation: 

this duty-cycle is characterized by high annual mileage (upwards of 100,000 miles per year); long-range trips (operates 

in a radius greater than several hundred miles); and travel 

primarily over interstate highways at highway speeds. As 

trucks age, an increasing fraction of these long-haul operators migrate to “regional” operation. These regional haulers 

generally drive much shorter distances (on the order of 

50,000 miles per year); operate within a confined region; 

and may travel a significant number of miles in urban or 

exurban areas at lower speeds with more frequent stops. 

The median age of trucks in regional operation is on the 

order of 18 to 20 years. 

To capture the effect of these different operational profiles, 

we segmented the tractor trailer fleet into “regional” and 

“long haul” operators according to the average primary trip 

length: Regional haul includes those tractor-trailers that 

operate primarily within a 200-mile radius, while long-haul 

operators have a primary radius greater than 200 miles. 

Based on a review of available data, a profile for each subsegment of the fleet was developed. This profile includes 

vehicle miles traveled as a function of age, survivorship as a 

function of age, and the fraction of new vehicles that enter 

each of the different fleets. 

For both the regional and long-haul sub-fleets, mileage is 

estimated to decline linearly with age to a minimum at 

16 years, at which point the annual mileage is constant 

throughout the remainder of the vehicle’s life. There is 

limited data regarding trucks older than 16 years; however, 

experience suggests that there is a floor to the miles that 

an operator can use a truck and maintain profitability. The 

average annual miles of a tractor trailer over a 19 year 

median life is about 74,000 miles.

The segmentation of the fleet between long-haul service, 

regional service, and retired trucks is estimated as a 

function of vehicle age, shown in Figure D-1. As discussed 

above, most new trucks (estimated at 80%) begin their 

life in long-haul service and then migrate into the lowermileage regional segment. This migration is modeled using 

a “long-haul service” survivorship curve, and is based 
A p p e n d i x D 125

D-1

FIGURE

MIGRATION AND SCRAPPAGE OF COMBINATION TRUCKS

-20%

0%

20%

40%

60%

80%

100%

0 5 10 15 20 25 30 35 40 45

Vehicle Age (Yrs)

Fleet Composition (%)

Long Haul

Regional

Scrapped

Long-Haul 

migrates to 

regional service Older trucks get 

scrapped.

on empirical data showing the distribution of long haul 

vehicles as a function of age [MOVES 2004]. In addition to 

the migration from long-haul to regional service, as vehicles 

age, an increasing fraction of trucks are retired altogether. 

The rate of retirement is estimated from scrappage statistics 

for in-use trucks [TEDB 2007]3.

Technology Adoption Methodology

Overview

To reflect the process by which technologies might reasonably be added to the fleet, each of the packages modeled 

by SwRI was ranked in terms of net cost of ownership over 

either a three year or a fifteen year time horizon, depending on the scenario. The logic employed assumes that a 

buyer would first select the most cost-effective available 

technology (Package 2), followed by the next most costeffective technology (Package 3), and so forth4

. As each 

technology is adopted into the fleet, the cost of ownership 

of the remaining technologies is recalculated to reflect that 

the baseline vehicles now use less fuel. To avoid double 

counting the fuel reduction benefits of different technologies, the technologies were grouped into four categories 

according to how they achieve their benefit. The fleet 

model only allows a single option from each category to be 

adopted onto a vehicle.

3 The scrap curves for 1980-vintage, rather than 1990-vintage, vehicles were used. As discussed in MOVES, the 1990-vintage projections show dramatically 

longer lifetimes than previous projections, and appear to be contradicted by more recent data; moreover, the later projections were based on a limited data set 

(as few trucks had yet reached their end-of-life).

4 Although package 2 actually has a lower NPV than package 3, package 3 includes package 2, so package 2 would be implemented as a precursor to package 3.
126 A p p e n d i x D

R E D U C I N G Heavy-Duty Long Haul Combination Truck Fuel Consumption and CO2 Emissions

AERODYNAMICS & 

ROLLING RESISTANCE

POWERTRAIN 

EFFICIENCY HIGHER PAYLOAD REDUCE ROAD SPEED

SmartWay

Advanced SmartWay

VVA

Adv. EGR

Mech T.C.

Elec. T.C.

Bottoming Cycle

HEV

HEV + Elec T.C.

HEV + Bot. Cycle

Rocky 

Mountain 

Double

60 MPH

D-2

TABLE

GROUPINGS OF TECHNOLOGIES FOR FLEET ANALYSIS

YEAR

AERO & ROLLING 

RES. PACKAGES POWERTRAIN EFFICIENCY HIGHER PAYLOAD

REDUCED 

SPEED

SW1 SW2 MECH. TURBO ELEC. TURBO RMD 60 MPH

2007 0% 0% 0% 0% 0% 0%

2008 0% 0% 0% 0% 0% 0%

2009 20% 0% 0% 0% 0% 0%

2010 40% 0% 14% 0% 0% 20%

2011 60% 0% 29% 0% 0% 40%

2012 80% 14% 43% 0% 0% 60%

2013 71% 29% 57% 0% 0% 80%

2014 57% 43% 71% 0% 0% 100%

2015 43% 57% 86% 0% 9% 100%

2016 29% 71% 100% 0% 17% 100%

2017 14% 86% 100% 0% 26% 100%

2018 0% 100% 100% 0% 34% 100%

2019 0% 100% 86% 14% 43% 100%

2020 0% 100% 71% 29% 51% 100%

2021 0% 100% 57% 43% 60% 100%

2022 0% 100% 43% 57% 60% 100%

2023 0% 100% 29% 71% 60% 100%

2024 0% 100% 14% 86% 60% 100%

2025 0% 100% 0% 100% 60% 100%

2026 0% 100% 0% 100% 60% 100%

2027 0% 100% 0% 100% 60% 100%

2028 0% 100% 0% 100% 60% 100%

2029 0% 100% 0% 100% 60% 100%

2030 0% 100% 0% 100% 60% 100%

D-3

TABLE

ILLUSTRATIVE FLEET ADOPTION RATES FOR TECHNOLOGIES IN SCENARIO A
A p p e n d i x D 127

The total fuel consumption benefit of technologies is then 

calculated multiplicatively as follows:

% FCtotal = (1 – % FCTech1) x (1 – % FCTech2) x ... 

x (1 – % FCTechN)

Technology Adoption Methodology for 

Scenario A

The first technology adoption scenario (“Scenario A”) 

illustrates the rate of technology adoption that could be 

catalyzed by applying aggressive regulation, such as a 

fuel-economy standard, to the long-haul fleet. Under this 

scenario, the technology from each column in Table D-2 

offers the highest fuel consumption benefit and that has a 

net- negative cost of ownership over fifteen years is fully 

adopted on new vehicles, subject to a five to seven-year 

phase-in period once the technology is market-ready5

. 

An example of the dynamics of technology adoption for 

scenario A is illustrated in Table D-3. Technologies with 0% 

adoption are omitted for the sake of space. Note that the 

penetration of technologies of a given “type” (e.g., powertrain efficiency) can sum to at most 100%, and are further 

constrained by the multi-year phase-in requirement.

Technology Adoption Methodology for 

Scenario B

The second technology adoption scenario (“Scenario B”) 

uses a rational buyer model to illustrate the rate of technology adoption that might be expected in the absence of 

regulation. This scenario segments truck purchasers into 

different categories based on the expected annual VMT of 

the truck. The rate of adoption is then calculated as a function of time to payback (which varies with annual mileage).

5 SmartWay, which is already on the market uses a 5-year phase in. The 60 MPH speed limit uses a 5-year phase-in and applies to both new and in-use trucks.

D-2

FIGURE

ADOPTION RATE AS A FUNCTION OF TIME TO PAYBACK

0%

20%

40%

60%

80%

100%

0 1 2 3 4 5 6 7

Years to Payback

Adoption Rate 
128 A p p e n d i x D

R E D U C I N G Heavy-Duty Long Haul Combination Truck Fuel Consumption and CO2 Emissions

The adoption rules use a three-year payback threshold, 

which assumes that 50% of fleet owners will adopt a 

technology if it offers discounted payback in three years 

or less; 70% adopt given payback in two years or less. The 

relationship between time to payback and adoption rate is 

shown in Figure D-2. The guideline of three-year payback 

(and 70% adoption at two years) was based on feedback 

from truck industry experts on the steering committee, 

who suggested that this was a reasonable methodology to 

adopt for our market-based model. 

Unlike the criterion for adoption used in Scenario A, which 

either fully adopts a technology (subject to phase-in) or 

does not adopt it at all, the three-year payback model 

in Scenario B allows for varying fractions of the fleet to 

adopt a technology. One outcome of this approach is that 

different mutually-exclusive technologies (such as bottoming cycle and turbo-compounding, or SmartWay 1 and 

SmartWay 2) are allowed to compete in the market place. 

In these cases, the relative rate of adoption for competing 

technologies is calculated from the ratio of the estimated 

penetration rate of one technology to another6. 

An example of the dynamics of technology adoption for 

Scenario B is illustrated in Table D-4. Technologies with 0% 

adoption are omitted for the sake of space. Note that the 

penetration of technologies of a given “type” (e.g., powertrain efficiency) can sum to at most 100%, and are further 

constrained by the multi-year phase-in requirement.

6 The actual adoption rate for two technologies (Technology 1 and Technology 2), assuming that technology 1 has the higher assumed penetration rate, is 

calculated as follows: 

 Actual adoption rate, Tech 1 = ATech 1 x ATech 1/(ATech 1 + ATech 2)

Where ATech 1 is the adoption of technology 1 in isolation and ATech 2 is the adoption of tech. 2 in isolation. For example: If SmartWay 1 has a rate of 

payback that leads to 50% adoption, and SmartWay 2 has a rate of payback that leads to 25% adoption, then 

 SW1 = 0.5 x 0.5/(0.5 + 0.25) = 33%

SW2 = 0.5 x 0.25/(0.5 + 0.25) = 17%
A p p e n d i x D 129

YEAR

AERO & ROLLING 

RES. PACKAGES POWERTRAIN EFFICIENCY HIGHER PAYLOAD

REDUCED 

SPEED

SW1 SW2 ADV. 

EGR

MECH. 

TURBO

ELEC. 

TURBO VVA ROCKY MT DOUBLE 60 MPH

2007 0% 0% 0% 0% 0% 0% 0% 0%

2008 0% 0% 0% 0% 0% 0% 0% 0%

2009 9% 0% 0% 0% 0% 14% 0% 0%

2010 16% 0% 0% 0% 0% 29% 0% 20%

2011 24% 0% 0% 0% 0% 47% 0% 40%

2012 29% 0% 4% 0% 0% 61% 0% 60%

2013 34% 0% 8% 0% 0% 76% 0% 80%

2014 34% 0% 14% 0% 0% 72% 0% 100%

2015 30% 2% 19% 4% 0% 64% 0% 100%

2016 26% 4% 24% 7% 0% 55% 0% 100%

2017 24% 6% 28% 12% 0% 47% 1% 100%

2018 23% 9% 31% 15% 0% 40% 2% 100%

2019 22% 11% 31% 20% 1% 36% 3% 100%

2020 21% 14% 29% 23% 2% 34% 5% 100%

2021 19% 16% 27% 25% 4% 32% 7% 100%

2022 18% 17% 27% 24% 6% 31% 9% 100%

2023 18% 17% 27% 24% 6% 31% 12% 100%

2024 19% 17% 27% 24% 6% 31% 13% 100%

2025 19% 17% 27% 24% 6% 31% 13% 100%

2026 19% 18% 26% 24% 7% 31% 14% 100%

2027 20% 18% 26% 24% 7% 31% 14% 100%

2028 20% 18% 26% 24% 7% 30% 14% 100%

2029 21% 19% 26% 24% 7% 30% 15% 100%

2030 21% 19% 26% 24% 8% 30% 15% 100%

D-4

TABLE

ILLUSTRATIVE FLEET ADOPTION RATES FOR TECHNOLOGIES IN SCENARIO B

A P P E N D I X E

131

APPENDIX E

A P P E N D I X E a p p e n d i x e a p p e n d i x e

a p p e n d i x e Appendix E

R E D U C I N G

Heavy-Duty Long Haul Combination 

Truck Fuel Consumption and CO2

 Emissions

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[EPA 2009] Environmental Protection Agency. “Idling Reduction Technologies”. Smartway program website.

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A p p e n d i x E 133

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Symposium on Heavy Vehicle Weights & Dimensions, Penn State University. June 2006.




F U E L C O N S U M P T I O N

CLIMATE CHANGE

e m e r g i n g t e c h n o l o g i e s

t r u c k e m i s s i o n s reducing green house gas emissions

Principal Contributors:

Coralie Cooper

Transportation Program Manager

NESCAUM/NESCCAF

89 South Street, Suite 602

Boston, MA 02111

Tel: 617-259-2022

Email: ccooper@nescaum.org 

www.nescaum.org

Fanta Kamakaté

Program Director

International Council on 

Clean Transportation

One Post Street, Suite 2700

San Francisco, CA 94104

Tel: 415-399-9019

Email: fanta@theicct.org

Tom Reinhart

Program Manager, Engine 

Design & Development

Southwest Research Institute

6220 Culebra Road, P.O. Drawer 28510

San Antonio, Texas 78238-5166

Tel: 210-522-5876

Mob: 210-382-4577

Fax: 210-522-4581

Email: treinhart@swri.org

ICCT

International Council on Clean Transportation

1225 Eye ST NW Suite 900

Washington, DC 20005

Tel: 202.534.1600

Fax: 202.534.1601

www.theicct.org

One Post Street, Suite 2700

San Francisco, CA 94104

Tel: 415.399.9019

Fax: 415.399.9172

NESCCAF

89 South Street, Suite 602

Boston, MA 02111

Tel: 617.259.2000

Fax: 617.742.9162

www.nescaum.org 

www.nesccaf.org

Matt Kromer

Senior Technologist 

TIAX, LLC 

15 Acorn Park 

Cambridge, MA 02140 

Tel: 617-498-6021

Email: Kromer.Matt@tiaxllc.com

Editor:

Paul Miller

Deputy Director

NESCAUM/NESCCAF

89 South Street, Suite 602

Boston, MA 02111

Tel: 617-259-2022

Email: pmilller@nescaum.org