Assessment of Fuel 

Economy Technologies 

for Medium- and HeavyDuty Vehicles 

Final Report 

Report to 

National Academy of Sciences 

500 Fifth Street NW 

Washington, DC 20001 

November 19, 2009 

Contract Number: DEPS-P290355 

Prepared by 

Matthew A. Kromer 

Wendy W. Bockholt 

Michael D. Jackson 

TIAX LLC 

20813 Stevens Creek Blvd. 

Suite 250 

Cupertino, California 95014-2192 

Tel 408-517-1550 

Fax 408-517-1551

TIAX Case D0506 

iii

Table of Contents 

Abbreviations................................................................................................................................. xi 

Acknowledgement ....................................................................................................................... xiii 

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

1. Introduction...................................................................................................................... 1-1 

2. Vehicle and Duty Cycle Descriptions.............................................................................. 2-1 

2.1 Class 8 Tractor Trailer ......................................................................................... 2-2 

2.2 Class 8 Refuse Hauler.......................................................................................... 2-4 

2.3 Class 3-6 Box and Bucket Trucks........................................................................ 2-4 

2.4 Urban Transit Bus................................................................................................ 2-5 

2.5 Motor Coach ........................................................................................................ 2-6 

2.6 Class 2b Pickups and Vans .................................................................................. 2-7 

3. Technology Matrix Description....................................................................................... 3-1 

4. Fuel Saving Technologies................................................................................................ 4-1 

4.1 Engine and Emissions Technologies ................................................................... 4-1 

4.1.1 Overview.............................................................................................................. 4-1

4.1.2 Diesel Engine Technologies ................................................................................ 4-2 

4.1.3 Diesel Engine Technology Descriptions.............................................................. 4-8 

4.1.4 Diesel Engine Technology Packages................................................................. 4-20 

4.1.5 Gasoline Engine Technologies .......................................................................... 4-30 

4.1.6 Class 2b Engine Packages.................................................................................. 4-33 

4.2 Aerodynamics .................................................................................................... 4-34 

4.2.1 Overview............................................................................................................ 4-34 

4.2.2 Class 8 Tractor Trailers...................................................................................... 4-37 

4.2.3 Straight Box Truck Aero.................................................................................... 4-51 

4.2.4 Motor Coach ...................................................................................................... 4-52 

4.2.5 Class 2b Pickups and Vans ................................................................................ 4-53 

4.3 Tires and Wheels................................................................................................ 4-54 

4.3.1 Overview............................................................................................................ 4-54 

4.3.2 Technologies for Reducing Rolling Resistance................................................. 4-55 

4.3.3 Application of Tire and Wheel Technology to Different Vehicle Classes ........ 4-58 

4.4 Weight Reduction .............................................................................................. 4-61 

4.4.1 Overview............................................................................................................ 4-61 
iv

4.4.2 Class 8 Tractor Trailer ....................................................................................... 4-62 

4.4.3 Transit Bus......................................................................................................... 4-64 

4.4.4 Motor Coach ...................................................................................................... 4-65 

4.4.5 Class 3-6 Straight Box and Bucket Trucks........................................................ 4-66 

4.4.6 Refuse Hauler..................................................................................................... 4-66 

4.4.7 Class 2b Pickups and Vans ................................................................................ 4-67 

4.4.8 Weight Increases................................................................................................ 4-67 

4.5 Transmission and Driveline ............................................................................... 4-68 

4.5.1 Tractor Trailer (On-highway, manual transmission) ......................................... 4-68 

4.5.2 Class 3-6 box and bucket, refuse haulers, and urban transit buses.................... 4-70 

4.5.3 Motor Coach (On-Highway, automatic transmission)....................................... 4-72 

4.5.4 Class 2b Pickups and Vans ................................................................................ 4-73 

4.6 Hybrid Technologies.......................................................................................... 4-74 

4.6.1 Overview............................................................................................................ 4-74 

4.6.2 Overview of Hybrid System Architectures........................................................ 4-76 

4.6.3 Cross-Cutting Issues and Future Outlook.......................................................... 4-79 

4.6.4 Summary — Hybrid Applications ..................................................................... 4-81 

4.7 Idle Reduction.................................................................................................... 4-89 

4.7.1 Automatic Shut-Down/Start-Up Systems.......................................................... 4-90 

4.7.2 Battery-Powered ................................................................................................ 4-90 

4.7.3 Fuel-Operated Heaters ....................................................................................... 4-92 

4.7.4 Auxiliary Power Units ....................................................................................... 4-92 

4.7.5 Truck Stop Electrification.................................................................................. 4-94 

4.7.6 Idle Reduction System Comparison................................................................... 4-94 

4.8 Driver Management and Coaching .................................................................... 4-96 

4.8.1 Overview............................................................................................................ 4-96 

4.8.2 Description of Management and Coaching Strategies....................................... 4-97 

4.8.3 Summary............................................................................................................ 4-99 

5. Packages........................................................................................................................... 5-1 

5.1 Capital Costs, Benefits, and Capital Cost Per Percent Reduction (CCPPR) ....... 5-1 

5.2 Payback Analysis............................................................................................... 5-11 

Appendix A. References ............................................................................................................ A-1 
v

List of Tables 

Table ES-1. Approaches for Reducing Fuel Consumed in Medium and Heavy-Duty 

Trucking Applications.................................................................................... ES-2 

Table ES-2. 2008 Vehicle Technology and Duty Cycle Baseline ......................................ES-3 

Table ES-3. Fuel consumption reduction, capital cost, and CCPPR - 2015 to 2020 

vehicle technology ..........................................................................................ES-6

Table ES-4. Simple Payback Analysis for Tractor Trailer, Transit Bus, Refuse 

Hauler, and Class 3-6 Box Trucks ..................................................................ES-8 

Table 1-1. NAS Committee on Medium- and Heavy-Duty Fuel Economy Members .......1-2 

Table 1-2. Site Visits Performed by Committee Members, NAS, and TIAX staff ............1-4 

Table 2-1. DOT and EPA truck weight classifications.......................................................2-1 

Table 2-2. Fuel consumption by vehicle weight class and type [VIUS 2004] ................... 2-2 

Table 2-3. Energy balance for a fully loaded Class 8 vehicle operating on a level 

road at 65 miles per hour for 1 hour ..................................................................2-3 

Table 3-1. Technology matrix table descriptions ...............................................................3-1 

Table 3-2. 11 to 15L engine technology matrix..................................................................3-5 

Table 3-3. 6 to 9L engine technology matrix......................................................................3-7 

Table 3-4. 5 to 8L gasoline engine technology matrix .......................................................3-9 

Table 3-5. Tractor trailer technology matrix.....................................................................3-11 

Table 3-6. Refuse hauler technology matrix.....................................................................3-17 

Table 3-7. Transit bus technology matrix.........................................................................3-19 

Table 3-8. Class 3-6 box and bucket truck technology matrix .........................................3-21 

Table 3-9. Class 2b pickup and van technology matrix....................................................3-23 

Table 3-10. Motor coach technology matrix.......................................................................3-25 

Table 4-1. Medium- and heavy-duty vehicle technology matrix assumptions...................4-1 

Table 4-2. Baseline characteristics for 2007 medium- and big-bore diesel engines ..........4-5 

Table 4-3. 2008 and 2010 11 to 15L sample heavy-duty diesel engine specifications ......4-6 

Table 4-4. 2008 and 2010 6-9L heavy-duty diesel engine specifications........................... 4-7 

Table 4-5. Baseline engine efficiency assumptions [Site Visits, DOE 2000, NHTSA 

2009].................................................................................................................. 4-8 

Table 4-6. Emissions strategies...........................................................................................4-9 

Table 4-7. Strategies to reduce heat transfer and exhaust losses ......................................4-11 

Table 4-8. Strategies to reduce gas exchange loss............................................................4-13 
vi

Table 4-9. Friction reduction strategies ............................................................................4-15 

Table 4-10. Parasitic load reduction strategies ...................................................................4-16 

Table 4-11. Waste heat recovery strategies ........................................................................ 4-16 

Table 4-12. Technology Road Map for 11-15 L Diesel Engines........................................4-21 

Table 4-13. Engine Technology road map for 6-9L diesel engines....................................4-22 

Table 4-14. Engine technology package capital cost.......................................................... 4-23 

Table 4-15. Overview of engine technology packages....................................................... 4-24 

Table 4-16. 2010 engine technologies ................................................................................ 4-25 

Table 4-17. 2013 engine technologies ................................................................................ 4-27 

Table 4-18. 2015 engine technologies ................................................................................ 4-28 

Table 4-19. 2016 to 2020 engine technologies ...................................................................4-29 

Table 4-20. Gasoline engine technology capital costs and benefits ...................................4-31 

Table 4-21. Class 2b engine technology packages .............................................................4-33 

Table 4-22. Impact of Highway Speed on Aerodynamic Improvement Potential..............4-35 

Table 4-23. Comparison of aerodynamic evaluation methodologies .................................4-36 

Table 4-24. Class 8 tractor trailer aerodynamic technologies.............................................4-37 

Table 4-25. Summary of Aerodynamic Retrofit Devices Literature Review ..................... 4-44 

Table 4-26. Tractor trailer aerodynamic packages .............................................................4-50 

Table 4-27. Straight box truck aerodynamic technologies .................................................4-51 

Table 4-28. Motor coach aerodynamic technologies..........................................................4-53 

Table 4-29. Class 2b pickup and van aerodynamic technologies .......................................4-53 

Table 4-30. Assumed tire characteristics for class 8 tractor trailers ...................................4-57 

Table 4-31. Tire pressure monitoring and inflation systems ..............................................4-58 

Table 4-32. Rolling resistance scaling parameters .............................................................4-58 

Table 4-33. Class 8 tractor trailer tire and wheel technologies...........................................4-59 

Table 4-34. Motor coach tire and wheel technologies........................................................4-59 

Table 4-35. Class 3-6 box and bucket truck tire and wheel technologies...........................4-60 

Table 4-36. Transit bus tire and wheel technologies .......................................................... 4-60 

Table 4-37. Refuse hauler tire and wheel technologies ......................................................4-61 

Table 4-38. Class 2b tire and wheel technologies...............................................................4-61 

Table 4-39. Weight reduction capital cost and benefit for volume-constrained class 8 

tractor trailers...................................................................................................4-64 

Table 4-40. Weight reduction capital cost and benefit for transit buses.............................4-65 

Table 4-41. Weight reduction capital cost and benefit for motor coaches .........................4-66 
vii

Table 4-42. Weight reduction capital cost and benefit for class 3-6 box and bucket 

trucks ...............................................................................................................4-66 

Table 4-43. Weight reduction capital cost and benefit for refuse haulers .........................4-67 

Table 4-44. Weight reduction capital cost and benefits for class 2b pickups and vans......4-67 

Table 4-45. Weight penalty for fuel savings and emissions control...................................4-68 

Table 4-46. Driveline and transmission options for class 8 tractor trailers .......................4-70 

Table 4-47. Estimated capital cost of going from 6 to 8 speed automatic transmission.....4-72 

Table 4-48. Driveline and transmission strategies for refuse hauler, class 3-6 box and 

bucket trucks, and transit buses ....................................................................... 4-72 

Table 4-49. Driveline and transmission strategies for motor coach ...................................4-73 

Table 4-50. Driveline and transmission strategies for class 2b pickups and vans..............4-73 

Table 4-51. Hybrid architectures ........................................................................................4-76 

Table 4-52. Production-intent medium duty and heavy duty HEV systems, no ePTO ......4-81 

Table 4-53. Hybrid technology capital costs and FC benefits for class 3-6 box trucks .....4-82 

Table 4-54. Hybrid technology capital cost and FC benefits for class 3-6 bucket 

trucks ...............................................................................................................4-83 

Table 4-55. Hybrid technology capital cost and FC benefits for refuse haulers.................4-84 

Table 4-56. Hybrid technology capital cost and benefits for class 8 tractor trailer 

hybridsa

............................................................................................................ 4-85 

Table 4-57. Hybrid technology capital cost and benefits for transit buses.........................4-87 

Table 4-58. Hybrid technology capital cost and benefits for motor coaches......................4-88 

Table 4-59. Hybrid technology capital cost and benefits for class 2b pickups and 

vans.................................................................................................................. 4-89 

Table 4-60. Automatic shut-down/start-up systems comparison........................................4-90 

Table 4-61. Battery-powered idle reduction systems comparison...................................... 4-91 

Table 4-62. Fuel-operated heater comparison ....................................................................4-92 

Table 4-63. Available auxiliary power unit comparison ....................................................4-93 

Table 4-64. Truck stop electrification comparison.............................................................4-94 

Table 4-65. Idle reduction systems comparison .................................................................4-95 

Table 4-66. Driver management and coaching strategies –capital costs and benefits......4-100 

Table 4-67. Driver management and coaching strategies – approach ..............................4-100 

Table 5-1. Tractor Trailer 2015-2020 Technology Package............................................... 5-2 

Table 5-2. Class 3-6 Box 2015-2020 Technology Package................................................5-3 

Table 5-3. Class 3-6 Bucket 2015-2020 Technology Package ...........................................5-3 

Table 5-4. Class 8 Refuse Hauler 2015-2020 Technology Package................................... 5-4 
viii

Table 5-5. Transit Buses 2015-2020 Technology Package ................................................ 5-5 

Table 5-6. Motor Coaches 2015-2020 Technology Package.............................................. 5-5 

Table 5-7. Class 2b Pickups and Vans 2015-2020 Technology Package ........................... 5-6 

Table 5-8. Fuel consumption reduction, capital cost, and CCPPR - 2013 to 2015 

vehicle technology.............................................................................................5-7 

Table 5-9. Fuel consumption reduction, capital cost, and CCPPR - 2015 to 2020 

vehicle technology.............................................................................................5-8 

Table 5-10. Operational characteristics for payback evaluation......................................... 5-12 
ix

List of Figures 

Figure ES-1. Examples of Vehicle Applications Considered................................................ES-2 

Figure ES-2. Comparison of 2015-2020 Fuel Savings Technology for Tractor Trailer 

(TT), Class 3-6 Box (Box), Class 3-6 Bucket (Bucket), Class 8 Refuse 

(Refuse), Transit Bus (Bus), Motor Coach (Coach), and Class 2b Pickups 

and Vans (2b) ...................................................................................................ES-4 

Figure ES-3 Cost curves for 2015-2020 technology packages. The transit bus extends to 

$250,000 at a benefit of 50 percent....................................................................ES-7 

Figure 2-1. Class 8 tractor trailer .........................................................................................2-3

Figure 2-2. Class 8 refuse hauler.......................................................................................... 2-4 

Figure 2-3. Class 3-6 box or van truck (left) and bucket truck (right)................................. 2-5 

Figure 2-4. Transit Buses ..................................................................................................... 2-6 

Figure 2-5. Typical over-the-road motor coach ...................................................................2-7 

Figure 2-6. Examples of class 2b vans and pickup trucks ........................................................... 2-7 

Figure 4-1. 2007 diesel engine energy audit [Duggal 2009]................................................4-3 

Figure 4-2. Past and possible future brake thermal efficiency improvements for large 

bore engines [Site Visits, Duggal 2009, Cummins 2009a] ...............................4-4 

Figure 4-3. Detroit Diesel Mechanical turbo-compound system [Detroit Diesel 

2009a].............................................................................................................. 4-17 

Figure 4-4. Electric turbo-compound design schematic [Kruiswyk 2005] ........................4-19 

Figure 4-5. Influence of aerodynamic drag on vehicle power demand as a function of 

speed................................................................................................................4-34 

Figure 4-6. Standard sleeper tractor aero technologies [Kenworth 2008] .........................4-39 

Figure 4-7. Prostar and LoneStar Tractors [Navistar.com]................................................4-40 

Figure 4-8. Examples of trailer side skirts [Laydon 2009, Freight Wing 2009] ................4-42 

Figure 4-9. Examples of trailer base treatments (boat tail on the left, structural base 

flaps on the right) [Aerovolution 2009, AT Dynamics 2009] .........................4-42 

Figure 4-10. Examples of trailer gap treatments – front fairing (left), and splitter plate 

(right) [NoseCone 2009].................................................................................. 4-42 

Figure 4-11. Survey of Trailer Aerodynamics (see Table 4-25 for detailed sourcing)........4-43 

Figure 4-12. Example of a trim top roof fairing [Leuschen 2006]....................................... 4-45 

Figure 4-13. Influence of rolling resistance and aerodynamic drag on vehicle power 

demand as a function of speed.........................................................................4-54 

Figure 4-14. Range of CRR for currently available tires [Bradley 2009]............................. 4-55 
x

Figure 4-15. Tractor trailer weight reduction opportunities [Alcoa 2009] ..........................4-63 

Figure 4-16. ALCOA estimates of weight-saving opportunities for tractor trailers 

[Scheps 2008] .................................................................................................. 4-63 

Figure 4-17. Weight savings realized for lightweight demonstration bus in China 

[Scheps 2008] .................................................................................................. 4-65 

Figure 4-18. Parallel hybrid architecture [Coryell 2008].....................................................4-77 

Figure 4-19. Parallel Hydraulic Hybrid (“Launch Assist”) Architecture [Gotting 2007]....4-78 

Figure 4-20. Lithium-ion vs. NiMH cost curves [Miller 2006] ...........................................4-79 

Figure 4-21. Fuel economy benefits of 40-foot hybrid transit buses compared to 40-

foot diesel transit buses ...................................................................................4-86 

Figure 4-22. Variance in driver performance [Cummins 2007]........................................... 4-96 

Figure 5-1. Comparison of Fuel Savings Technology for Tractor Trailer (TT), Class 

3-6 Box (Box), Class 3-6 Bucket (Bucket), Class 8 Refuse (Refuse), 

Transit Bus (Bus), Motor Coach (Coach), and Class 2b Pickups and 

Vans (2b) ......................................................................................................... 5-10 

Figure 5-2. Cost curves for 2013-2015 packages. The transit bus extends to $215,000 

at a benefit of 40 percent .................................................................................5-10 

Figure 5-3. Cost curves for 2015-2020 packages. The transit bus extends to $250,000 

at a benefit of 50 percent .................................................................................5-11 
xi

Abbreviations 

ABA American Bus Association 

APTA American Public Transportation Administration 

BSFC Brake specific fuel consumption 

CCPPR Capital cost per percent reduction 

CD Coefficient of aerodynamic drag 

CRR Coefficient of tire rolling resistance 

DD Detroit Diesel 

DOE United States Department of Energy 

DOHC Dual overhead cam 

DPF Diesel Particulate Filter 

EGR Exhaust Gas Recirculation 

EPA United States Environmental Protection Agency 

FC Fuel consumption 

FE Fuel economy 

FI Fuel injection 

Gal Gallon 

GDI Gasoline direct injection 

HCCI Homogeneous charge compression ignition 

HD Heavy Duty 

HP Horse Power 

HPh Horse Power Hour 

ICCT International Center for Clean Transportation 

Kg Kilogram 

kW Kilowatt 

kWh Kilowatt hour 

Lb Pound 

LB GDI Lean-burn gasoline direct inject 

MD Medium duty 

MPG Miles per gallon 

MPH Miles per hour 
xii

NAS National Academy of Sciences 

NESCCAF Northeast States Center for a Clean Air Future 

NHTSA National Highway Traffic Safety Administration 

NOx Oxides of nitrogen 

O&M Operations and maintenance 

OBD Onboard diagnostics 

OHV Overhead valve 

PM Particulate matter 

RPE Retail price equivalent 

SwRI Southwest Research Institute 

SCR Selective catalytic reduction 

sGDI Stoichiometric gasoline direct injection 

SOHC Single overhead cam 

TT Tractor trailer 

VG Variable geometry 

VVA Variable valve actuation 

VVL Variable valve lift 

VVT Variable valve timing 

Wt Weight 
xiii

Acknowledgement 

This report was prepared for the National Academy of Sciences (NAS) as part of their prime 

contract with the National Highway Traffic Safety Administration (NHTSA) to assess fuel 

economy technologies for medium and heavy duty vehicles. The National Research Council 

(NRC) Division on Engineering and Physical Sciences was responsible for this work and 

assigned the effort to the Board on Energy and Environmental Systems. The project identifier is 

BEES-J-08-A. The NAS project director was Mr. Duncan Brown and the TIAX principal 

investigator was Michael D. Jackson. Dr. Andrew Brown, Jr. chaired the NAS committee, 

initiated the project, and provided valuable guidance to help direct and focus TIAX’s research. 

Mr. David Merrion was the NAS committee’s group leader on fuel economy technologies and 

assisted TIAX in developing site visits and reviewing and commenting on the results. 

We would also like to thank all the companies that participate in the site visits. These companies 

took time out of their schedules to meet with TIAX staff, NAS staff, and committee members. 

Their willingness to host the site visits and to actively participate by providing their perspective 

on truck fuel economy technologies and future standards is greatly appreciated. 

ES-1

Executive Summary

The Energy Independence and Security Act of 2007 (EISA) requires that the National Highway 

Transportation and Safety Administration (NHTSA) conduct rulemaking to implement a 

commercial medium-duty (MD) and heavy-duty (HD) on-highway vehicle and work truck fuel 

efficiency improvement program. To support this rulemaking activity, NHTSA engaged the 

National Academies of Sciences (NAS) to develop a report that evaluates MD and HD vehicle 

fuel economy. One of the NAS committee’s tasks requires the assessment of technologies and 

capital costs for improving MD and HD fuel economy. 

TIAX was contracted to support the committee’s evaluation of MD and HD technologies. The 

goal of this effort was to develop a matrix of fuel-saving technologies, their fuel consumption 

benefits, and their capital costs that could be implemented in medium- and heavy duty vehicles 

within a ten-year timeframe. To complete this work, TIAX, together with committee members, 

gathered data from a number of sources, including site visits with industry and research 

laboratories; data presented to the committee during open sessions; publicly available literature; 

prior TIAX technology and cost modeling; and discussions with experts from industry. In all, 

TIAX participated in 15 different site visits to truck OEMs, end-users, suppliers, research 

laboratories, and engine manufacturers. 

The TIAX effort emphasized engine and vehicle technologies that save fuel. Our effort did not 

address productivity improvements or operations and logistics improvements. Both productivity 

and operations/logistics improvements can significantly reduce fuel consumed in many trucking 

applications. Table ES-1 summarizes what is included in the TIAX analysis. 

TIAX focused on identifying fuel reduction technologies and strategies for seven different 

vehicle classifications: Class 8 Tractor Trailers, Class 3-6 Straight Box Trucks, Class 3-6 Utility 

(“Bucket”) Trucks, Class 8 Refuse Haulers, Urban Transit Buses, Motor Coaches, and Class 2b 

Pickups Trucks and Vans. Figure ES-1 shows examples of the types of vehicles considered in 

this study. 

Collectively, these vehicles, or other vehicles with similar mission profiles and characteristics, 

account for approximately 80 to 90 percent of the fuel used in the medium- and heavy-duty, 

onroad truck sector. For each vehicle class, TIAX defined baseline vehicle characteristics that 

reflect industry-standard characteristics for a 2008 to 2009 model year vehicle compliant with 

2007 emissions regulations. TIAX also qualitatively characterized duty cycles for each vehicle 

class. Characteristics for each vehicle class are summarized in Table ES-2. 
ES-2

Table ES-1 Approaches for Reducing Fuel Consumed in Medium and Heavy-Duty 

Trucking Applications

Approach TIAX analysis includes...

TIAX analysis does not 

include...

Technology

Deploy fuel efficient 

technologies into the vehicle 

fleet 

• Identification of 

Technologies 

• Estimate of fuel 

consumption benefit 

• Cost estimates, retail price 

equivalent (RPE) 

• Breakdown of RPE 

• Analysis of manufacturing 

processes 

• Operations & Maintenance 

(O&M) Costs/Life Cycle 

Costing 

Productivity 

Increase the use of longer & 

heavier vehicles 

• Estimates of fuel 

consumption benefit 

• Identification of enabling 

technologies 

• Cost analysis 

• Infrastructure analysis 

• Policy landscape 

Operations & Logistics 

Optimize fleet management 

• On-vehicle optimization 

tools (e.g., driver training, 

telematic navigation, etc) 

• Off-vehicle fleet optimization 

tools 

• Optimization of goods 

movement 

2 

Figure ES-1. Examples of Vehicle Applications Considered

Tractor Trailer

Refuse Hauler

Class 3-6 Box

Class 2b

40 ft Transit

Motor Coach

Class 3-6 Bucket
ES-3

Table ES-2. 2008 Vehicle Technology and Duty Cycle Baseline 

Truck Technology Duty Cycle 

Class 8 

Tractor 

Trailer 

• 11 to 15L diesel engine 

• Smartway Tractor, 53’ Dry box van trailer; CD = 

0.6 

• Standard steel-rim dual tires 

• 10 speed manual transmission w/overdrive 

• 34,500 lbs unloaded 

• 65,000 lb average; 80,000 lb max 

• No idle reduction technology 

Line-Haul duty cycle: 

• 55 to 60 MPH avg speed 

• 120,000 miles per year 

• 1,500 to 2,400 hrs/yr overnight 

idle 

Class 3-6 

Box Truck 

• 6 to 9L diesel engine 

• No aerodynamic treatments 

• 6 speed automatic transmission, PTO 

• Standard steel-rim dual tires 

• 16,500 lbs unloaded 

Regional or Pickup & Delivery duty 

cycle 

• ~150 miles per day 

• Average speed ~ 30 MPH 

Class 3-6 

Bucket Truck 

• 6 to 9L diesel engine 

• No aerodynamic treatments 

• 6 speed automatic transmission 

• Standard steel-rim dual tires 

• 16,500 lbs unloaded 

Utility Vehicle Duty Cycle: 

• 6 hours idle per day 

• ~30 to 40 miles per day 

Refuse 

Hauler 

• 11 to 15L diesel engine 

• 6 speed automatic transmission 

• Standard steel-rim dual tires 

• 35,000 lbs unloaded 

• 80,000 lb GVW 

Refuse duty cycle: 

• 150 ft between stops 

• 500 to 800 stops per day 

• Average speed ~ 12 MPH 

• 50 to 60 miles per day 

40-ft Transit 

Bus 

• 6 to 9L diesel 

• l engine 

• 6 speed automatic transmission 

• Standard steel-rim dual tires 

• 28,500 lbs unloaded 

Urban duty cycle: 

• Average speed ~ 12 MPH 

• Stops & starts 

• 30 to 40 kW accessory load 

Motor Coach • 11 to 15L diesel engine 

• 6 speed automatic transmission 

• Standard steel-rim dual tires 

• 36,000 lbs unloaded 

High speed duty cycle: 

• Average speed 45 to 50 MPH 

• 56,000 miles per year 

Class 2b 

pickups & 

vans 

• 5 to 8L Gasoline engine 

• 4 speed automatic transmission 

• Standard truck tires 

• 10,000 lbs unloaded 

High speed duty cycle: 

• Mixed duty cycle 

• Average speed ~ 30 MPH 

• 15,000 miles per year 

For each vehicle classification, fuel savings strategies were categorized into one of several 

categories: engine efficiency improvement, aerodynamic drag reduction, tires and wheels, 

hybridization, transmission and driveline, weight reduction, driver management and coaching, 

and idle reduction1. In cases where capital cost data were not available for a specific technology, 

TIAX used bottom-up cost methodologies to estimate costs. In cases where fuel efficiency or 

capital cost data were not available for a particular vehicle class, TIAX applied data from other 

 

1

 In this context, idle reduction refers specifically to overnight hotel loads. 
ES-4

classes using appropriate scaling metrics such as vehicle weight, duty cycle characteristics, or 

engine torque. The results of this analysis of individual technologies were compiled into a matrix 

of costs and benefits for each vehicle class. 

From these estimates of individual technologies, packages were developed for each vehicle 

segments and for two time periods: 2013-2015 and 2015-2020. These technology packages are 

representative of what is possible in these time frames. Estimates of fuel consumption savings, 

capital costs, and capital cost per percent fuel consumption reduction (CCPPR) were then made 

for each vehicle application based on the results of our site visits and existing literature. In 

general, these estimates are specific to the applications considered and as such should be a 

reasonable first cut of the overall fuel savings. Detailed drive cycle modeling will be necessary 

to refine and confirm these estimates. 

Figure ES-2 shows the overall results of possible fuel consumption (FC) benefits for each 

trucking application in the 2015-2020 time frame. These results indicate for most applications it 

is possible to reduce fuel consumption by 50 percent. The exceptions were the refuse hauler and 

motor coach applications. The major enabling technologies necessary to achieve these 

reductions were hybridization, advanced diesel engines, and aerodynamics. Hybridization is 

0%

10%

20%

30%

40%

50%

60%

TT Box Bucket Refuse Bus Coach 2b

FC Benefit

Aero Engine

Weight Tires & Wheels

Transmission Hybrid

Mgmt & Coaching

Figure ES-2. Comparison of 2015-2020 Fuel Savings Technology for Tractor Trailer (TT), 

Class 3-6 Box (Box), Class 3-6 Bucket (Bucket), Class 8 Refuse (Refuse), 

Transit Bus (Bus), Motor Coach (Coach), and Class 2b Pickups and Vans 

(2b) 
ES-5

particularly important in those applications with stop and go duty cycles characteristic of the 

Class 3-6 box and bucket, refuse, transit buses, and Class 2b applications. Hybrid drivetrains 

could include a variety of architectures from series to parallel and from electric to hydraulic 

systems. Diesel and gasoline engine advancements are also needed for all applications and will 

have to include continuing improvements to fuel injection systems, emission control, and air 

handling systems, in addition to commercialization of waste heat recovery systems and 

electrification of engine accessories. The third major technology improvement is improved total 

vehicle aerodynamics, especially in over-the-road applications like tractor trailers and motor 

coaches. Other technologies that will play a role in reducing fuel consumption in all vehicle 

segments are low rolling resistance tires, improved transmissions, idle reduction technologies, 

weight reduction, and driver management and coaching 

Table ES-3 summarizes package results for 2015-2020 technologies for the various vehicle 

segments. This table shows technology benefits, capital costs, and CCPPR (defined as the cost 

to reduce fuel consumption by 1 percent, or $/percent fuel consumption benefit) for technologies 

that will be market-viable2

 between 2015 and 2020. The technologies that are included vary by 

market segment, but broadly speaking, they include a hybrid system for urban vehicles and 

aerodynamic improvements coupled with first generation waste heat recovery on highway 

vehicles. All of the technologies include significant engine efficiency improvements as shown. 

The capital costs of the 2015-2020 technology packages range from $14,000 (Class 2b) to 

$250,000 (transit bus). However, the most of the applications lie in a narrow band from $40,000 

to $85,000. Many of the technologies benefit from anticipated reductions in the cost of hybrid 

vehicles during this timeframe. CCPPR estimates range from $250 to $5,000 per percent 

improvement, depending on vehicle class. For five of the seven vehicle classes, the benefits lie in 

a range from $500 to $1,700 per percent fuel consumption reduction. 

Although the cumulative reductions and capital costs for vehicles classes are relatively similar, 

the likely pathway to achieve these benefits varies considerably. For line-haul vehicles, wasteheat recovery and aerodynamics represent the largest opportunities, but high single-digit gains 

are possible in nearly every category. For urban vehicles (box & bucket, buses, and refuse), 

hybridization provides the bulk of the benefit. In addition, engine optimization provides 

significant benefits to all vehicle classes. To characterize these differences in the technology 

effectiveness of different strategies across vehicle segments, each strategy was ranked in order of 

CCPPR for each vehicle class. These data were then used to generate cost-curves as shown in 

Figure ES-3. 

 

2

 “Market-viable” means that the technology will have matured to the point at which it could be widely deployed; it does not imply 

that a particular technology offers attributes (such as rapid payback) that will lead to market adoption. 
ES-6

Table ES-3. Fuel consumption reduction, capital cost, and CCPPR - 2015 to 2020 

vehicle technology 

TT Box Bucket d Refuse Bus Coach 2b 

Fuel Consumption Reduction 

Aero 11.5% 6% — — — 8% 3% 

Engine 20% 14% 11.2% 14% 14% 20% 23% 

Weight 1.25% 4% 3.2% 1% 6.25% 1.05% 0.75% 

Tire 11% 3% 2.4% 2.5% 1.5% 3% 2% 

Transmission 7% 4% 3.2% 4% 4% 4.5% 7.5% 

Hybrid 10% 30% 40% 25% 35% — 18% 

Mgmt 6% — — — — — —

Idle Reductiona — — — — — — —

Subtotalb 51.0% 49.4% 51.3% 40.2% 50.4% 32.5% 44.9% 

Added Wt (lb)c 2,030 1,100 1,050 1,500 2,000 1,100 300 

Adj. FC Total 50.5% 47.1% 49.6% 38.4% 47.8% 32.0% 44.5% 

Capital Cost 

Aero $ 12,000 $ 3,250 $ - $ - $ - $ 4,500 $ 100 

Engine $ 23,000 $ 13,000 $ 13,000 $ 14,800 $ 13,000 $ 23,000 $ 4,000 

Weight $ 13,500 $ 4,770 $ 4,770 $ 3,000 $ 15,300 $ 6,000 $ 600 

Tire $ 3,600 $ 300 $ 300 $ 300 $ 300 $ 450 $ 10 

Transmission $ 5,800 $ 1,800 $ 1,800 $ 2,700 $ 1,800 $ 2,400 $ 1,000 

Hybrid $ 25,000 $ 20,000 $ 30,000 $ 30,000 $ 220,000 $ — $ 9,000 

Mgmt $ 1,700 $ — $ — $ — $ — $ — $ —

Idle Reduction a $ — $ — $ — $ — $ — $ — $ —

Total $ 84,600 $ 43,120 $ 49,870 $ 50,800 $ 250,400 $ 36,350 $ 14,710 

CCPPR ($/Percent Fuel Consumption Benefit) 

Aero $ 1,043 $ 542 $ - $ - $ - $ 563 $ 33 

Engine $ 1,150 $ 929 $ 929 $ 1,057 $ 929 $ 1,150 $ 174 

Weight $ 10,800 $ 1,193 $ 1,193 $ 3,000 $ 2,448 $ 5,714 $ 800 

Tire $ 327 $ 100 $ 100 $ 120 $ 200 $ 150 $ 5 

Transmission $ 829 $ 450 $ 450 $ 675 $ 450 $ 533 $ 133 

Hybrid $ 2,500 $ 667 $ 750 $ 1,200 $ 6,286 $ — $ 500 

Mgmt $ 283 $ — $ — $ — $ — $ — $ — 

Idle Reductiona $ — $ — $ — $ — $ — $ — $ —

All Packages $ 1,674 $ 915 $ 1006 $ 1,323 $ 5,232 $ 1,135 $ 331 

a Overnight idle reduction is assumed to be implemented as part of the hybrid package b Does not include fuel consumption penalty associated with added weight of fuel savings technologies c Added weight of fuel savings technologies d Assumes that 80% of fuel is used on road, and 20% is used at idle 
ES-7

$-

$10,000

$20,000

$30,000

$40,000

$50,000

$60,000

$70,000

$80,000

$90,000

$100,000

0% 10% 20% 30% 40% 50% 60%

% Benefit

Package Cost

Tractor-Trailer

Straight Box

Bucket

Refuse

Bus

Coach

Class 2b

Figure ES-3. Cost curves for 2015-2020 technology packages. The transit 

bus extends to $250,000 at a benefit of 50 percent 

A simple payback analysis was performed to estimate how viable the 2015-2020 packages are 

for each application. Table ES-4 shows operating characteristics for a typical tractor trailer, 

transit bus, refuse hauler, and Class 3-6 box truck fleets. Key to this analysis was the assumed 

annual mileage and vehicle fuel economy. Fuel consumption for each application was 

determined with the results shown in Table ES-4. Then using the fuel savings potential shown in 

Table ES-1 for these four applications, fuel saved per year was estimated as was cost savings 

assuming diesel at $4 per gallon. As shown, except for transit buses the simple payback period 

is in the 2 to 4 year range. The transit bus numbers are reduced to 2.3 years if Federal transit 

subsidies are included. 

A more sophisticated life cycle costing will be required to adequately address the economic 

viability of the various fuel saving packages of each specific application. However, preliminary 

results are favorable. 
ES-8

Table ES-4. Simple Payback Analysis for Tractor Trailer, Transit Bus, Refuse Hauler, 

and Class 3-6 Box Trucks 

Characteristic Tractor 

Trailer Transit Bus Refuse Hauler 

Class 3-6 

Box 

Annual Mileage (miles per year) 120,000 40,000 25,000 60,000 

Average speed (miles per hour) 46.2 12 12 28.8 

Driver work week (days per week) 6 5 5 5 

Driver time (hours per week) 50 64a 40 40 

Fuel economy (miles per gallon) 6.5 3.5 3.3 8 

Fuel consumption (gallons per year) 18,500 11,400 7,600 7,500 

1% Fuel consumption savings 

(gal per yr) 

185 114 76 75 

Fuel cost savings for 1% reduction 

(@$4 per gallon diesel) 

$738 $457 $303 $300 

Fuel cost savings for 1% reduction 

 (at $3 per gallon diesel) 

$554 $343 $227 $225 

Fuel use reduction (gal/year) 9,350 5,456 2,918 3,534 

Fuel cost savings ($/year)@ $4/gal 

diesel $37,402 $21,825 $11,672 $14,136 

Total added technology costs $84,600 $250,400 $50,800 $43,120

Payback Period (years) 2.3 11.5a 4.4 3.1

Payback Period (months) 27.1 137.7a 52.2 36.6

 a With Federal subsidies technology costs are $52,400 and payback is 2.4 years or 28.8 months 

TIAX’s analysis shows that there is potential to achieve fuel consumption benefits of 40 to 50 

percent across a broad subset of the medium- and heavy-duty vehicle fleet between 2015 and 

2020, at costs that range from $40,000 to $90,000. The technologies used to achieve these 

benefits vary by segment: on urban vehicles, benefits are largely driven by hybridization, while 

on-highway vehicles achieve benefits through waste-heat recovery and aerodynamics. We 

speculate that some, but not all, of these fuel consumption benefits will be achieved without 

regulation. A commonly cited rule of thumb is that line-haul tractor trailer fleets will pay $900 

for 1 percent of efficiency improvement. Our analysis shows that 30 percent efficiency 

improvement can be achieved at a CCPPR of $640 per percent, while 50 percent efficiency 

improvement is achieved at a CCPPR of $1,700 per percent. In other vehicle segments, which 

have lower mileage, fuel efficiency is commonly valued at $250 per percent. In these segments, 

adoption is likely to be much lower. We project that in several segments, 50 percent fuel 

efficiency can be achieved at a CCPPR of $500 to $900 per percent. 

It needs to be emphasized that our package results are very dependent on the vehicle’s duty cycle 

and as such should be viewed as averages for each truck segment. Further, although the data for 

this analysis were obtained for the specific truck segments and, in general, for typical duty cycles 

for these segments, detailed vehicle stimulation modeling was not done to establish the fuel 
ES-9

consumption benefit of combined fuel savings technologies for each duty cycle. Follow up work 

is needed to confirm not only the individual estimated benefits but also the packaged benefits. 

Finally, the results of our data collection effort indicate two additional observations: 

1. Technology is being developed today that could eliminate all idling from heavy-duty 

applications. This will require hybrid technologies and energy storage systems. These 

systems are anticipated to be commercialized in the next 10 years. 

2. A national maximum speed limit could be set, and all new trucks could have this speed 

governed. This would unify at least one of the many truck specifications and would 

significantly reduce fuel use. 

1-1

1. Introduction 

Congress requested the Department of Transportation to execute an agreement with the National 

Academy of Sciences (NAS) to develop a report evaluating medium-duty and heavy-duty truck 

fuel economy standards.3 In response to this request, the National Academy of Sciences 

convened a committee with expertise in a broad spectrum of areas including: compression 

ignition engine technology, fuels, emission control technologies, vehicle systems engineering, 

R&D management, truck operations and management, design and manufacturing, 

commercialization of new technology, safety, fuel economy standards and policy, testing 

procedures, and transportation policy. 

This committee is addressing a series of tasks with an ultimate goal of preparing a report with 

conclusions and recommendations for fuel economy standards of medium- and heavy-duty 

vehicles. The committee is tasked to: 

• Consider appropriate approaches to measure fuel economy for medium- and heavy-duty 

vehicles that would be required for setting standards; 

• Assess current and potential technologies and estimate improvements in fuel economy for 

medium-duty and heavy-duty trucks that might be achieved; 

• Address how the technologies identified may be used practically to improve mediumduty and heavy-duty truck fuel economy; 

• Address how such technologies may be practically integrated into the medium-duty and 

heavy-duty truck manufacturing process; 

• Assess how such technologies may be used to meet fuel economy standards to be 

prescribed under section 32902(k) of title 49, United States Code, as amended by Energy 

Independence and Security Act of 2007; 

• Discuss the pros and cons of approaches to improve the fuel efficiency of moving goods 

as opposed to setting vehicle fuel economy standards; and, 

• Identify the potential capital costs and other impacts on the operation of medium-duty 

and heavy-duty trucks. 

Members of the medium- and heavy-duty committee are shown in Table 1-1 and include current 

and prior industry leaders, academics, and members of national labs. This committee, as part of 

its approach to identify current and potential fuel economy technologies, decided to reach out to 

the trucking industry to gather information on these technologies, their benefits, and their costs. 

Site visits to truck manufacturers, engine manufacturers, and hybrid suppliers were planned to 

gather information on current as well as future technologies. 

 

3

 Energy Independence and Security Act of 2007 (H.R. 6), Section 108 
1-2

Table 1-1. NAS Committee on Medium- and Heavy-Duty Fuel Economy Members 

Chair

Dr. Andrew Brown, Jr. (NAE)a

 

Exec. Director & Chief Technologist 

Delphi Corporation 

Members

Dr. Dennis Assanis (NAE)a

Jon R. & Berverly Holt Professor of Engineering

University of Michigan 

Dr. Roger Bezdek 

President 

Management Information Services, Inc. 

Oakton, Virginia 

Dr. Nigel Clark 

Prof. & Director Center for Alternative Fuels, Engines & 

Emissions 

West Virginia University

Mr. Thomas Corsi 

Director, Supply Chain Mgmt Center, Logistics, Business 

& Public Policy 

University of Maryland 

Mr. Duke Drinkard 

VP, Maintenance (Retired) 

Southeastern Freight Lines 

Lexington, SC 29073 

Dr. David Foster 

Professor of Mechanical Engineering 

University of Wisconsin 

Dr. Roger Fruechte 

Director, Electrical & Controls Integration Lab (Retired) 

General Motors R&D 

Dr. Ronald Graves 

Director, Fuels, Engines & Emissions Research Center 

Oak Ridge National Laboratory 

Mr. Garrick Hu 

Consultant 

West Bloomfield, MI 

Dr. John H. Johnson 

Presidential Professor 

Michigan Tech University 

Houghton, Michigan

Mr. Drew Kodjak 

Executive Director 

International Council on Clean Transportation 

Washington, DC 

Mr. David Merrion 

Exec. VP, Detroit Diesel (Retired) 

Brighton, Michigan 

Mr. Tom Reinhart 

Program Manager, Engine Design & Development 

Southwest Research Institute 

Mr. Aymeric Rousseau 

Program Manager 

Argonne National Laboratory 

Dr. Charles Salter 

Exec. Director, Engine Development (Retired) 

Mack Trucks / Volvo Powertrain 

Chambersburg, Pennsylvania 

Dr. James Winebrake 

Chair, Dept. of Science, Technology & Public Policy 

Rochester Institute of Technology 

Mr. John Woodrooffe 

Head, Transportation Safety Analysis 

University of Michigan Transportation Institute 

Dr. Martin Zimmerman 

Clinical Professor of Business Administration 

University of Michigan 

a Member National Academy of Engineers 

TIAX LLC was asked to assist the committee in arranging and attending site visits and to 

develop a report summarizing current and future fuel economy technologies for Class 2b through 

Class 8 trucks. Our scope was to identify, for each truck class and application, technologies that 

could improve fuel economy, their fuel consumption benefits, and their costs. TIAX was also 

asked to gather public information on technologies to improve truck fuel economy that could be 

used by the committee in its report. Finally, we were tasked to document our results in a report 

to the committee and NAS. 
1-3

Table 1-2 shows the site visits that were planned by TIAX and includes the committee members 

who attended these visits, as well as NAS staff (Jim Zucchetto, Jason Ortego, Joe Morris, 

Duncan Brown), NTHSA staff (Mary Versailles, Ryan Harrington) and TIAX staff (Michael 

Jackson, Matt Kromer, Steven Lasher, Ray Schubert). 

For each site visit, a presentation was developed that outlined Congress’ request, members of the 

committee, and technical information on fuel economy technologies. Most of the data on fuel 

economy technologies were initially obtained from the literature but were refined as further 

information was obtained from the site visits. A total of 15 site visits were performed as shown 

in. In addition, TIAX attended the following committee meetings: April 6-7, 2009 in Detroit, 

MI; June 18-19, 2009 in Ann Arbor, MI; August 6-7, 2009 in San Antonio, TX. A number of 

companies presented at these meetings, and information provided in their presentations was also 

included in our data gathering effort. 

TIAX also attended the UMTRI International Conference on Efficient, Safe, and Sustainable 

Truck Transportation held at the University of Michigan on June 16 and 17, 2009, and TIAX 

staff participated in site visits to the US EPA and UMTRI facilities in Ann Arbor on June 19, 

2009. Again, data collected during these meetings and visits were included in our data collection 

effort. 

This report documents the work performed to date on identifying fuel economy technologies, and 

their FC benefit and capital costs by truck class and use. Estimates are based on a survey of 

publicly available studies and reports, presentations to the committee, and discussions during site 

visits with medium- and heavy-duty truck manufacturers, suppliers, and end-users. Due to the 

sensitive nature of information shared during the site visits with industry representatives, data 

gathered is cited as “site visits”. 

Section 2 provides an overview and description of the classes of trucks investigated in this effort. 

This overview is followed in Section 3 by summary matrices of fuel economy technologies for 

each vehicle class. Section 4 provides additional description of the technologies and our 

assumptions regarding interpretation of the various inputs collected and received. Finally, 

Section 5 presents possible technology packages for each vehicle class and application and 

estimates aggregate fuel consumption benefits and capital costs. This section also includes a 

simple payback analysis. 
1-4

Table 1-2. Site Visits Performed by Committee Members, NAS, and TIAX staff

Date Company Visited Location Products Committee Members 

April 8, 2009 Ford Motor 

Company 

Dearborn, MI Truck OE 

Class 2b-7 

Dave Merrion, Chuck Salter, Drew Kodjak, Tom 

Reinhart, Jamie Winebrake, Marty Zimmerman, Jim 

Zucchetto, Jason Ortego, Michael Jackson 

April 8, 2009 Daimler Trucks 

North America, 

Detroit Diesel 

Detroit, MI Truck OE 

Class 4-8 

Dave Merrion, Chuck Salter, Drew Kodjak, Tom 

Reinhart, Jamie Winebrake, Marty Zimmerman, Jim 

Zucchetto, Jason Ortego, Michael Jackson 

April 8, 2009 Azure Dynamics Oak Park, MI Tier 1 Hybrid 

System 

Supplier 

John Johnson, Roger Fruechte, Dennis Assanis, 

Nigel Clark, Duke Drinkard, Joe Morris, Ryan 

Harrington, Stephen Lasher 

April 8, 2009 Eaton Southfield, MI Tier 1 Hybrid 

System 

Supplier 

Andy Brown, Garrick Hu, Aymeric Rousseau, 

Dennis Assanis, John Woodrooffe, David Foster, 

Ron Graves, Duncan Brown, Mary Versailles, Matt 

Kromer 

April 8, 2009 Arvin Meritor Troy, MI Tier 1 Heavy 

Duty 

Component 

and Hybrid 

Supplier 

Andy Brown, Garrick Hu, Aymeric Rousseau, 

Dennis Assanis, John Woodrooffe, David Foster, 

Ron Graves, Duncan Brown, Mary Versailles, Matt 

Kromer 

April 8, 2009 TARDEC Warren, MI End-user and 

Army Vehicle 

R&D 

John Johnson, Roger Fruechte, Dennis Assanis, 

Nigel Clark, Duke Drinkard, Joe Morris, Ryan 

Harrington, Stephen Lasher 

April 9, 2009 Navistar Fort Wayne, 

IN 

Truck OE 

Class 3-8 

Andy Brown, Tom Reinhart, Chuck Salter, Ryan 

Harrington, Mike Jackson, Matt Kromer 

May 4, 2009 PACCAR Mount 

Vernon, WA 

Truck OE 

Class 3-8 

Duncan Brown, Andrew Brown, David Merrion, 

Michael Jackson, Raymond Schubert 

May 7, 2009 ISE Corporation Poway, CA Tier 1 Hybrid 

and Fuel Cell 

Drive System 

Supplier 

Michael Jackson, Raymond Schubert Andrew 

Brown, Jr. (by phone), Dave Merrion (by phone) 

May 13, 2009 Volvo Trucks NA Greensboro, 

NC 

Truck OE 

Class 6-8 

Chuck Salter, Ron Graves, Duke Drinkard, Roger 

Fruechte, Duncan Brown, Michael Jackson, Matt 

Kromer 

May 14, 2009 Allison 

Transmissions 

Indianapolis, 

IN 

Tier 1 

Transmission 

and Hybrid 

Supplier 

Duncan Brown, Michael Jackson, Matt Kromer, 

Dave Merrion, Tom Reinhart 

May 15, 2009 Cummins Engine 

Company 

Columbus, IN Medium, 

Heavy Duty 

Engine 

Supplier 

Andy Brown, Jr, Dave Merrion, Chuck Salter, Tom 

Reinhardt, Ron Graves, Duncan Brown, Michael 

Jackson, Matt Kromer 

July 22, 2009 Peterbilt Trucks, 

Great Dane Trailers, 

Wal-Mart 

Denton, TX Truck OE, 

Trailer OE, 

Regional 

Truck Hauler 

Andy Brown, Jr, Dave Merrion, Chuck Salter, 

Roger Fruechte, Ron Graves, Duncan Brown, 

Michael Jackson, Matt Kromer 

August 11, 

2009 

Auto Research 

Center 

Indianapolis, 

IN 

Aerodynamic 

Testing of 

Scaled Truck 

Models 

Tom Reinhart, Duke Drinkard, Ron Graves, Chuck 

Salter, Drew Kodjak, Duncan Brown, Steve Lasher 

August 12, 

2009 

Transportation 

Research Center 

East Liberty, 

OH 

Road Testing 

of Heavy Duty 

Vehicles 

Tom Reinhart, Duke Drinkard, Ron Graves, Steve 

Lasher 
2-1

2. Vehicle and Duty Cycle Descriptions 

The analysis focuses on fuel efficiency technologies for seven different types of medium- and 

heavy-duty vehicles. These vehicle types represent a large fraction of total fuel use in the 

medium- and heavy-duty category, operate over a range of duty cycles, and can benefit from an 

assortment of the most likely fuel efficiency improvement technologies considered in this study. 

Although these categories do not capture all of the fuel consumed in the medium- and heavyduty onroad vehicle sector, the selection of vehicles represents a significant portion of it. The 

general vehicle categories selected are: 

• Class 8 Tractor Trailer 

• Class 8 Refuse Hauler 

• Class 3-6 

– Straight Box Truck 

– Bucket Truck 

• Urban Transit Bus 

• Motor Coach 

• Class 2b Pick-up Trucks and Vans 

For the purpose of this evaluation, we are using the truck weight classifications as defined by the 

Department of Transportation as shown in Table 2-1. We have also included EPA weight 

categories and the associated engine durability requirements [NRC 2008]. 

Table 2-1. DOT and EPA truck weight classifications 

DOT Weight 

Class 

Minimum 

GVWR (lbs) 

Maximum 

GVWR (lbs) EPA Category EPA Engine Durability Reqs 

Class 1 6,000 Light-Duty N/A 

Class 2a 6,001 8,500 

Class 2b 8,501 10,000 

Class 3 10,001 14,000 

Class 4 14,001 16,000 

Class 5 16,001 19,500 

Light HeavyDuty 110,000 Miles, 8 Years 

Class 6 19,501 26,000 

Class 7 26,001 33,000 

Medium HeavyDuty 185,000 Mi, 8 Years 

Class 8 33,001 80,000 Heavy HeavyDuty 

435,00 Miles, 10 Years, 

23,000 Hrs 
2-2

Table 2-2 compares the relative fuel use and weight class of a variety of truck types as identified 

in the 2002 Vehicle Inventory and Use Study [VIUS 2004]. As shown, tractor trailers consume 

61 percent of the total fuel in the medium- and heavy-duty category, followed by pickup and 

vans at 13 percent. The rest of the truck types each consume less than 5 percent of the total fuel. 

Table 2-2. Fuel consumption by vehicle weight class and type [VIUS 2004] 

Weight Class Truck Type 

2b 3 4 5 6 7 8 

% of MD/HD Fuel 

Consumed 

Straight Trucks 

 Pickup/Van/SUV z z } } 13 

 Service/Utility z z } } } } 3 

 Tow/Wrecker z z z 1 

 Step Van z z z } } 3 

 Basic Van z z z z z z 4 

 Flatbed z z } } z z 4 

 Refrigerated Van z z 1 

 Beverage } } <1 

 Tank Truck z z z 2 

 Dump Truck } } } } z 5 

 Refuse Hauler z 2 

 Concrete z 1 

Tractor Trailer z 61 

z Primary 

} Secondary 

The following sections provide a brief overview of each of the vehicles evaluated, including, 

when available, vehicle population, descriptions of the primary duty cycles, energy audits, and 

fuel consumption. 

2.1 Class 8 Tractor Trailer 

With more than 60 percent of the fuel use in the medium- and heavy-duty market and nearly 

98 percent of the Class 8 vehicles in-use, tractor trailers represent the largest segment of heavyduty vehicles in-use today. Line-haul operation – characterized primarily by highway driving on 

routes that are separated by several hundred miles –accounts for 60 to 70 percent of the fuel use 

in this class. The other 30 to 40 percent of the fuel use occurs in other short- and medium-haul 

regional applications. TIAX’s analysis focuses specifically on the Class 8 tractor trailer’s use as 

a line-haul truck. The analysis of vehicle tractor trailer aerodynamics further focuses on the subsegment of the tractor trailer fleet that pulls 53-foot dry box van trailers, which account for 60 to 

70 percent of heavy-duty Class 8 on-road mileage [VIUS 2004]. Dry box vans can take 

advantage of a number of aerodynamic improvement devices available, represent a relatively 

homogeneous body type, and can therefore maximize potential fuel efficiency improvements. 

Other duty cycles (e.g., regional haul or drayage) and other types of trailers will not achieve the 
2-3

same benefits from the fuel efficiency technologies we have identified. Figure 2-1 shows a Class 

8 tractor trailer similar to those considered in this evaluation. 

Figure 2-1. Class 8 tractor trailer 

The 21st Century Truck Partnership Roadmap presents an energy audit of a typical Class 8 tractor 

trailer as shown in Table 2-3 [DOE 2000]. Efficiency improvements can focus on each of the 

energy sources and fall into the following categories: tractor aerodynamics, tires and wheels, 

weight reduction, engine, transmission and driveline improvements, driver education, idle 

reduction, and hybridization. 

Table 2-3. Energy balance for a fully loaded Class 8 vehicle 

operating on a level road at 65 miles per hour for 1 houra

Energy Sources 

Baseline 

(kWh) Baseline (HPh) 

Engine losses per hour 240 321.8 

Auxiliary loads 15 20.1 

Drivetrain energy 9 12.1 

Aerodynamic energy 85 114 

Rolling resistance energy 51 68.4 

Total energy used per hour 400 536.4 

a

 from 21st Century Truck Technology Roadmap [DOE 2000]

A typical line-haul duty cycle is characterized by high mileage (upwards of 100,000 miles per 

year) at highway speeds. The unloaded vehicle weight of a tractor trailer is 35,000 to 40,000 lbs. 

Truck loads may be volume constrained (“cubed out”), weight constrained (“grossed out” at 80K 
2-4

lbs), or less than truckload (LTL). On average, tractor trailers are loaded at 55,000 to 60,000 lbs 

and are volume limited; however, all three categories of truck loads are significant. In addition 

to over the road fuel use, many line-haul vehicles need to provide “hotel loads” for drivers who 

sleep on the road – typically 1,600 to 2,400 hours per year. Fuel to meet these hotel loads can 

consume up to 10% of a tractor trailer’s total fuel. A typical cruise point for a line-haul tractor 

trailer range from 60 to 70 MPH, while the average speed (including transient operation) ranges 

from 55 to 60 MPH; however, these details will vary widely by fleet. Newer tractor trailers have 

fuel economy that range from 6.5 to 7 MPG, although the fleet average is closer to 6 MPG 

[VIUS 2002, Sodolsky 2002, Smartway 2009a, Smartway 2009b, Davis 2008]. 

2.2 Class 8 Refuse Hauler 

The analysis also examines potential fuel efficiency improvements for Class 8 refuse haulers as 

shown in Figure 2-2. Refuse haulers operate over an urban cycle that is characterized by lowspeed operation with frequent stops. A typical refuse hauler travels 100 to 150 feet between 

stops and makes on the order of 500 to 800 stops per day, followed by travel – potentially at 

highway speeds – to an unloading site [Site Visits]. However, these parameters will vary widely 

depending on the density of pick-up locations in the service area. Daily mileage is roughly 

50 miles; however, significant additional energy is used in refuse compaction, which accounts 

for roughly two thirds of a refuse hauler’s fuel budget. 

Figure 2-2. Class 8 refuse hauler 

2.3 Class 3-6 Box and Bucket Trucks 

The Class 3-6 vehicle category includes both straight box trucks and bucket trucks, as shown in 

Figure 2-3. The box trucks are assumed to operate over a “regional haul” duty cycle consisting of 

both urban and highway driving, with average speeds of 25 to 30 MPH, and total daily mileage 

on the order of 150 to 200 miles. Table 2-4 shows an energy audit for a Class 3-6 box or van 

truck operating at 40 MPH for 1 hour. It should be noted that a typical box truck duty cycle 

involves significantly more transient operation than that reflected in Table 2-4. 
2-5

 

Figure 2-3. Class 3-6 box or van truck (left) and bucket truck (right) 

Table 2-4. Energy balance for a fully loaded Class 6 Medium 

duty truck vehicle operating on a level road at 40 

miles per hour for 1 houra

Energy Sources 

Baseline 

(kWh) 

Baseline 

(HPh) 

Engine losses per hour 73.1 98.0 

Auxiliary loads 1.5 2.0 

Drivetrain energy 3.3 4.4 

Aerodynamic energy 18.9 25.3 

Rolling resistance energy 23.0 30.8 

Total energy used per hour 119.8 160.6 

a

 correspondence with Karbowski [2009]

The bucket truck runs over a significantly different duty cycle—an urban work duty cycle which 

consists of low mileage (tens of miles per day), urban driving, and extended periods of idling (on 

the order of 6 hours per day). Based on feedback received during site visits, we have assumed 

that bucket trucks consume roughly 20% of their fuel at idle and 80% on road [Site Visits]. 

2.4 Urban Transit Bus 

According to the American Public Transportation Association (APTA), there are more than 

65,000 transit buses in operation throughout the United States [APTA 2009]. These vehicles, 

shown in Figure 2-4, accrue more than 2.3 billion miles and use more than 670 million gallons of 

fossil fuels4

 (more than 490 million gallons of diesel) each year. This market segment has long 

been a target for alternative fuel technologies, and significant documentation is available for 

transit buses on their typical duty cycles for emissions, fuel use, and lifecycle costs. Transit buses 

 

4

 Fossil fuels here are defined as diesel, gasoline, LNG, CNG, Biodiesel and other. 
2-6

 

a. 40-Foot Transit Bus b. 60-Foot Articulated Bus 

Figure 2-4. Transit Buses 

have helped to pave the way for lower emission technologies and can be leaders in fuel 

efficiency improvements as well. 

For this evaluation, a typical transit bus is assumed to operate over a high-mileage (150-250 

miles per day) and low-speed (12 MPH average) urban duty cycle with high accessory loads 

(primarily air-conditioning). Table 2-5 shows an energy audit for a transit bus operating over the 

Central Business District (CBD) cycle for 1 hour. 

Table 2-5. Energy balance for half seated load with air 

conditioning on 40 ft transit bus (32,000 lbs) 

operating over the CBD cycle for 1 houra

Energy Sources 

Baseline 

(kWh) 

Baseline 

(HPh) 

Engine losses per hour 86.8 116.4 

Auxiliary loads 36.4 48.8 

Drivetrain energy 13.4 18.0 

Aerodynamic energy 1.3 1.7 

Rolling resistance energy 7.2 9.7 

Total energy used per hour 145.1 194.6 

a

 from 21st Century Truck Technology Roadmap [DOE 2000]

2.5 Motor Coach 

According to the American Bus Association (ABA), there are more than 33,000 motor coaches 

operating in the United States [ABA 2009]. With an average fuel economy of 5.7 miles per 

gallon and an annual average of 56,000 miles per vehicle [Nathan 2008], motor coaches in the 

United States consume nearly 330 million gallons of fuel each year. 
2-7

Motor coaches, shown in Figure 2-5, typically operate over the highway in high-mileage, highspeed duty cycles. Occasionally, they also operate in urban cycles. 

Figure 2-5. Typical over-the-road motor coach 

2.6 Class 2b Pickups and Vans 

Class 2b pickups and vans operate over a variety of duty cycles, but often in urban driving cycles 

of relatively low mileage (tens of miles per day). Currently, class 2b vehicle sales are split about 

evenly between gasoline and diesel engines. Historically, diesels engines tended to hold 

approximately 70 percent market share for GMC, Ford, and Dodge Ram trucks. However, due in 

large part to the high cost of emissions systems and the higher cost of diesel fuel relative to 

gasoline, the market share of diesel ensures dropped to about 50 percent in 2008. This share 

could decline further with the new 2010 emissions requirements [Visnic 2009]. Figure 2-6 

shows typical van and pickup truck applications in the class 2b category. 

Figure 2-6. Examples of class 2b vans and pickup trucks 

3-1

3. Technology Matrix Description 

The technology matrix consists of individual tables for the three different engine classes (11 to 

15L diesel, 6 to 9L diesel, and 5 to 8L gasoline) and the seven different vehicle categories 

(tractor trailers; refuse haulers; transit buses; Class 3-6 box and bucket trucks; Class 2b pickups 

and vans; and motor coaches). Each table incorporates benefits of a variety of emission control 

strategies (SCR and EGR in-cylinder technologies). The matrix tables are included in this section 

as shown in Table 3-1. 

Table 3-1. Technology matrix table descriptions 

Table No. Engine or Vehicle Class/Application 

Table 3-2 11—15L Engines 

Table 3-3 6—9L Engines 

Table 3-4 5—8L Engines 

Table 3-5 Tractor Trailers 

Table 3-6 Refuse Haulers 

Table 3-7 Transit Buses 

Table 3-8 Class 3 –6: Box and Bucket Trucks 

Table 3-9 Class 2b Pickups and Vans 

Table 3-10 Motor Coaches 

Baseline assumptions 

In order to clearly define a reference benchmark against which fuel consumption benefits are 

measured, the matrix for each engine and vehicle application includes a number of “2008 

baseline” assumptions. These assumptions allow for reasonable comparison among technologies. 

11-15 L engines are assumed to have a peak brake thermal efficiency of between 41 and 42 

percent; depending on the truck’s duty cycle, the actual average brake thermal efficiency over a 

drive cycle will typically be several percentage points lower than this peak value. The 11-15L 

engines are also assumed to operate using high pressure, direct injection, common rail (1,800 to 

2,000 bar) or unit fuel injection (~30,000 psi) systems, turbocharging, cooled exhaust gas 

recirculation (EGR) plus diesel particulate filters (DPF), and 190 to 200 bar cylinder pressure. 

6-9L engines are assumed to have a peak brake thermal efficiency of between 40 and 41 percent. 

The 6-9L engines are also assumed to operate using direct injection, common rail fuel systems 

(1,600 to 2,000 bar), turbocharging, cooled EGR plus DPF, and 170 to 180 bar cylinder pressure. 
3-2

For the 5-8L gasoline engines, the 2008 baseline assumptions include port-fuel injection, fixed 

valve, and no turbocharging. 

Each of the vehicle application matrix tables incorporates variations of three sets of assumptions: 

aero and tire; engine; and driveline and idle/accessory. 

The Tractor Trailer baseline is assumed to have a CD of 0.59 to 0.6, a Crr of 0.0068, full roof 

fairings, a sloped hood, aero bumpers, and no undertreatment [Salari 2009, Marinko 2009, 

NESCCAF 2009]. The trailer is assumed to be a 53-foot standard box trailer with standard dual 

tires and steel wheels. The tractor is powered by an 11-15L engine with the associated 

assumptions described above. The trucks are assumed to operate using a 10-speed manual 

transmission with over-drive, low-speed idle but no anti-idle technologies, mechanical 

accessories, limited “driver-management” tools, and governors at 75 MPH. 

The 2008 baseline Refuse Haulers are assumed to have no aero-shaping, standard dual tires with 

steel wheels, 6-speed automatic transmission, and a hydraulic power take-off (PTO). 

The 2008 baseline 40-ft Transit Buses operate using a 6-9L engine as described above. 

Additionally, they are assumed to be equipped with standard dual tires, steel wheels, no aeroshaping, 6-speed automatic transmission, low-speed idle and no anti-idling technologies, 

mechanical accessories, and limited “driver-management” tools. 

The Class 3-6 Box and Bucket Trucks are assumed to run on 6-9L engines as described above 

and have standard dual tires and steel wheels. The baseline vehicles are assumed to have no aero 

add-on devices but some cab streamlining. Like the transit buses, it is assumed that the box and 

bucket trucks are equipped with 6-speed automatic transmission, low-speed idle but no antiidling technologies, mechanical accessories, and limited “driver management” tools. 

The baseline Class 2b Pickup and Truck assumptions 6-8L gasoline engines with natural 

aspiration, port fuel injection, and 4-speed automatic transmission. 

Motor Coaches are assumed to use an 11-15L engine. As with the transit buses and box and 

bucket trucks, the motor coaches evaluated here are equipped with standard dual tires, steel 

wheels, 6-speed automatic transmission, low-speed idle and no anti-idling technologies, 

mechanical accessories, and limited “driver-management” tools. 

How to interpret the tables 

Definitions of each column in the matrix tables are as follows: 

Category: Indicates the broad class of fuel reduction strategies to which the specified 

technology applies. Examples include “Aerodynamics”, “Transmission & Driveline”, etc. 

Technology: An individual fuel consumption reduction strategy that could be deployed into 

medium- and heavy-duty vehicles within the next ten years. 
3-3

Fuel consumption (FC) benefit: The reduction in fuel consumption associated with adopting a 

given technology. The fuel consumption benefit of “A” is defined as follows: 

A

baseline

baseline

A

benefit MPG

MPG

FC

FC FC = 1− = 1− Equation 1 

The relationship between the percent fuel consumption (FC) benefit and the fuel economy (FE) 

benefit of a technology is as follows: 

benefit

benefit FE

FC

1 %

1 % 1

+ = − Equation 2 

The fuel consumption benefit reflects the reduction in fuel consumption that an owner would 

expect to see on a typical duty cycle for the given application. A short description of the typical 

duty cycle for each vehicle type is included in Chapter 2. A range in the fuel consumption benefit 

reflects both variations in the technology configuration (for example, a larger waste heat 

recovery system would recapture more energy); and/or variations due to duty cycle conditions. 

The source for fuel consumption benefit estimates are described in Section 4 on a technology-bytechnology basis. 

Capital cost: For technologies that are currently on the market, our estimates indicate the actual 

price that consumers typically pay. For future technologies, our estimates are expressed in terms 

of a “retail price equivalent” (RPE). All costs are estimated in 2009 dollars. The RPE reflects 

the marginal cost that a truck buyer would expect to pay to purchase a given technology5

, and 

includes the following factors: 

• Amortized ex-factory cost 

• Factory overhead and mark-up, including warranty, research and development (R&D), 

marketing and sales, engineering, depreciation, legal, corporate overhead, retirement and 

health benefits, accounting, shipping and distribution, corporate taxes and dealer support 

• Dealer discount or mark-up 

• Profit 

The cost estimates do not include additional operating and maintenance (O&M) costs. In some 

cases, for currently available technology, the “list price” of a technology was provided by 

manufacturers or dealerships. Industry feedback suggested that the selling price is typically about 

60 percent of the list price, so these list prices were multiplied by a factor 0.6. For technologies 

that are not currently on the market, or are on the market in low numbers, both low volume and 

high volume costs were included. 

 

5

 Prices include installation costs, except for trailer aerodynamic devices, which are currently sold as after-market “add-ons”. If 

these devices become widely adopted, they will become standard options on new trailers, which will greatly reduce the 

installation cost. 
3-4

It should also be noted that transit bus hybrid systems appear to be priced significantly higher 

than their actual component costs would indicate. We speculate that this is due in part to the 

90% government subsidy of hybrid bus technology, which allows the market to bear significantly 

higher costs than an unsupported market; it may also be due to low production volumes. Hence, 

for the specific case of transit hybrid technologies, we have included information as to both the 

subsidized and unsubsidized costs of transit buses. 

A range in capital cost for a given technology can reflect any of several different factors. These 

include: 

• Variations between different configurations of a given technology (For example, trailer side 

skirt designs range from simple “belly boxes” to automatically retractable, flexible skirts.) 

• Uncertainty in the cost of the technology – this applies to technologies that are not yet in 

production (For example, advanced engine technologies such as next-generation fuel systems 

or onboard diagnostics.) 

• A combination of both uncertainty and design variation (For example, bottoming cycle 

systems are still under development; moreover, they can be sized to recover varying levels of 

waste heat, and can be implemented as either an electric or a mechanical system.) 

The meaning of ranges in technology cost will be described in the text on a technology-bytechnology basis. 

Cd/Crr/Wt Change: Identifies the effect, if any, that a given technology has on the vehicle’s 

aerodynamic drag, coefficient of rolling resistance, or weight. 

Intro Year: This column reflects the year in which the technology is expected to be introduced. 

These are based on data from technology roadmaps from suppliers when available and on 

estimates for cases in which technologies are too distant to be included in actual production 

plans. Some technologies included in the table, such as improved combustion chamber design 

that allows increased cylinder pressure or streamlining of the tractor aerodynamics, do not reflect 

a discrete introduction of new technology but rather evolutionary changes to existing designs. In 

these cases, technology is incrementally improved with each successive technology generation. 

For these types of continually improving technologies, the year of introduction is said to be 

“continuous” in the table. 

Market penetration: Where available, the market penetration identifies the adoption rate of a 

technology in 2008. Technologies that are on the market in limited, pre-production quantities 

(ranging from single vehicle to a few hundred) are identified as “demos”. 

Baseline: This column lists the technology or vehicle configuration against which the fuel 

consumption and incremental cost are measured. 

Reference: Identifies the section of the report in which the given technology is discussed. 
Table 3-2. 11 to 15L engine technology matrix 

 Description FC Improvement Capital cost (RPE) Intro Year 

A Reduce Heat Transfer and Exhaust Losses 

A.1 High pressure fuel injection (up to 4,000 bar), multiple injections per cycle, rate shaping, etc 1 to 4% $0 to $1,000 Continuous A.2 Increase cylinder pressure 1 to 3% $500 to $1,500 Continuous A.3 OBD w/Engine controls and sensors — closed loop control, run engine @ NOx limits across the map 1 to 3% $60 to $150 2013 A.4 Emissions Control 

A.4.1 Add SCR (optimizes engine for efficiency, not NOx) – includes 2% DEF penalty 2 to 3% $9,000 to $10,000 2010 A.4.2 Improved NOx conversion efficiency 1 to 3% $0 Continuous, post 201A.4.3 Passive DPF regen and reduced back pressure 1 to 1.5% $0 2010 A.4.4 High-Rate EGR -1 to -2% $8,000 2010 A.4.5 Mixed-mode advanced combustion — (e.g., PCCI @ low/med load) 1 to 2% $10,000 2012 to 2015 

Subtotal NOx/Fuel efficiency/Particulate Trade-off Technologies Up to 6% $9,000 to $10,000 Continuous 

Total Heat Transfer and Exhaust Loss Reduction Technologies up to 10% $9,000 to $12,650 Continuous 

B Reduce Gas Exchange Loss Reduction 

B.1 VVA 1% $300 2012 B.2 Advanced low-temperature EGR, lower pressure drop 1 to 1.5% $500 to $750 2010 to 2013 B.3 Turbocharger efficiency or advanced configurations (e-turbo, multi-stage, etc) 1 to 2% $0 to $1,000 Continuous 

Total Gas Exchange Loss Reduction Technologies up to 3% $0 to $2,050 Continuous 

C Reduce friction - lubricants, bearings, etc 

Total Friction Reduction Technologies 0.5 to 2% 0 to $500 Continuous 

D Reduce Parasitic and Accessory Loads 

D.1 Incremental improvements to existing baseline 0 to 0.5% $0 to $200 Continuous D.2 Variable displacement pumps, incremental improvements 1 to 2% $200 to $500 2012 D.3 Accessory Electrification — Electric Auxiliaries (alternator, air compressor, power steering pump, air cond, fan, fuel pump, water pump); in combination with hybrid or other vehicle electrification. 1 to 3% $1,000 to $2,000 2012 

Total Parasitic and Accessory Loads Reduction Technologies 0 to 3% $0 to $2,000 Continuous 

E Recover Waste Heat 

E.1 Turbo-Compound – Mechanical 2.5 to 3% $2,000 to $3,000 2010 E.2 Electric Turbo-Compound, including accessory electrification 4 to 5% 

$6,000 to $7,000 

($3,000 to $4,000 inc. 

to Hybrid) 

2013 

E.3 Thermo-electric or thermo-acoustic 2 to 3% ? 2015 E.4 Bottoming Cycle, Steam Cycle or ORC – 15 to 60 kW 6 to 10% $7,200 to $15,100 2015 

Total Waste Heat Recovery Technologies 2.5 to 10% $2,000 to $16,000 2010 

Table 3-3. 6 to 9L engine technology matrix 

Item Description FC Improvement Capital cost (RPE) Introduction 

A Reduce Heat Transfer and Exhaust Losses 

A.1 High pressure fuel injection (up to 4,000 bar), multiple injections per cycle, rate shaping, etc 1 to 4% $0 to $1,000 Continuous A.2 Increase cylinder pressure 1 to 4% $500 to $1,500 Continuous A.3 OBD w/Engine controls and sensors — closed loop control, run engine @ NOx limits across the map 1 to 4% $60 to $150 2013 A.4 Emissions Control 

A.4.1 Add SCR (optimizes engine for efficiency, not NOx) – includes 2% DEF penalty 2 to 3% $7,000 to $8,000 2010 A.4.2 Improved NOx conversion efficiency 1 to 3% $0 Continuous, post 20A.4.3 Passive DPF regen and reduced back pressure 1 to 1.5% $0 2010 A.4.4 High-Rate EGR -1 to -2% $6,000 2010 A.4.5 Mixed-mode advanced combustion — (e.g., PCCI @ low/med load) 1 to 2% $8,000 2012 to 2015 

Subtotal NOx/Fuel efficiency/Particulate Trade-off Technologies (assumes SCR) Up to 6% $7,000 to $8,000 Continuous 

Total Heat Transfer and Exhaust Loss Reduction Technologies up to 12% $7,000 to $9,650 Continuous 

B Reduce Gas Exchange Losses 

B.1 VVA 1% $300 2012 B.2 Advanced low-temp EGR, lower pressure drop 0 to 1.5% $500 to $750 2010 to 2013 B.3 Turbocharger efficiency and performance enhancements; e-turbo, super-charging, etc 1 to 3% $0 to $1,000 Continuous 

Total Gas Exchange Losses Reduction Technologies up to 4% $0 to $2,050 Continuous 

C Reduce Friction - lubricants, bearings, etc 

Total Friction Reduction Technologies 0.5 to 2% 0 to $500 Continuous 

D Reduce Parasitic and Accessory Loads 

D.1 Incremental improvements to existing baseline 0 to 0.5% $0 to $200 Continuous D.2 Variable displacement pumps, incremental improvements 0.5 to 2% $200 to $500 2012 D.3 Accessory Electrification -- Electric Auxiliaries (air compressor, power steering pump, air cond, fan, alternator, water pump); in combination with hybrid or other vehicle electrification. 1 to 3% $1K to $2K (Low) $500 to $1,000 (High) 2012 

Total Parasitic and Accessory Loads Reduction Technologies 0 to 3% $0 to $2,000 Continuous 

Table 3-4. 5 to 8L gasoline engine technology matrix 

 Description FC Improvement Capital cost (RPE) Introduction 

A/B Reduce Gas Exchange, Exhaust Heat, and Heat Transfer Losses 

A/B.1 VVT 1 to 3% $122 2008 A/B.2 VVL (Discrete or Continuous) 1 to 3.5% $400 to $750 2008 A/B.3 Stoichiometric GDI 2 to 3% $512 to $930 2008 A/B.4 Lean burn GDI 10 to 14% $750 2012 + low sulfur fuA/B.5 Turbo-charged, down-sized engine 2.1 to 2.2% $1,229 2008 A/B.6 Cylinder deactivation 2.5 to 3% $75 2008 A/B.7 Gasoline HCCI 10 to 12% $685 ? 

Total Gas Exchange, Exhaust Heat, and Heat Xfer Loss Reduction Technologies Up to 15% $0 to $4,200 Continuous 

C Reduce Friction - lubricants, bearings, etc 

Total Friction Reduction Technologies 0.5 to 2.5% $110 to $500 Continuous 

D Reduce Parasitic and Accessory loads 

D.1 Variable displacement pumps, incremental improvements 0.5 to 2% $200 to $500 2012 D.2 Accessory Electrification — Electric Auxiliaries (air comp, ps pump, air cond, fan, alt, water pump); in combination with upgrade to 42V electrical system or hybrid. 1 to 3% $1,000 to $2,000 (current) $500 (high volume) 2012 

Total Parasitic and Accessory Load Reduction Technologies 0 to 3% $0 to $2,000 Continuous 

Table 3-5. Tractor trailer technology matrix 

Category Technology FC Benefit Cd/Crr/Wt Change Capital cost (RPE) 

Load Reduction 

Roof top fairing, sleeper cab 7 to 10% 15 to 20% (Standard) $500 to $1,000 Roof top deflector, day cab 4 to 7% 13% $1,000 to $1,300 Cab Side extension (aka, "side fairing") 2 to 3% 4 to 5% $300 to $500; (Standard on some vehicles) Chassis Skirts (aka, "chassis fairing", "fuel tank fairing") -— full length 3 to 4% 4 to 7% $1,500 to $2,000 Chassis Skirts (aka, "chassis fairing", "fuel tank fairing") — partial length 2 to 3% 4 to 6% $500 to $1,200 Baseline Package - Smartway Aero Cab: Aero mirrors, cab side extenders, integrated sleeper cab roof fairing, aero bumper, full fuel tank fairings; 4 to 6% 22 to 25% $2,750 to $3,500 

Tractor Aero 

"Next generation" Smartway aero cab: Current Smartway cab, PLUS aero bumper w/underbody treatment; improved streamlining; wheel skirts 

3 to 4% beyond 

Smartway 6 to 8% $2,750 

Partial Skirts (4 to 6 m) 2 to 3% 2 to 6% $1,500 to $2,000 Full Skirts (7 to 9 m) 4 to 5% 5 to 11% $2,000 to $4,000 Partial Gap Fairing 1 to 2% 2 to 4% $800 to $1,000 Full Gap fairing 2 to 3% 4 to 6% $1,000 to $1,500 Boat tail — structural or inflatable 4 to 6% 6.5 to 9% $1,500 to $2,000 Bogie Fairing – fairing for the trailer rear wheel assembly 1% ~2% $500 Hub caps 0 to 0.5% ~1% ? Pneumatic Aero Drag Reduction - Unproven 3.5 to 4.0% ? $2,500 - $5,250 Smartway trailer – partial skirts + partial gap fairing or boat tail 5 to 6% 10 to 12% $3,000 per trailer 

Trailer Aero 

Full next-generation trailer aero – full skirts, boat tail, and full gap fairing 8 to 9% 17 to 19% $4,000 per trailer No aero -10 to -12% -22 to -25% - Smartway Tractor - CD ~ 0.59 - Smartway Tractor + Smartway Trailer 5 to 6% 10 to 12% $3,000 per trailer Improved Smartway Tractor + Smartway Trailer 7 to 9% 15 to 17% $2,750 + $3,000 per trailer 

Tractor + Trailer Aero Pkgs Full Aero Tractor & Trailer 11 to 12% 22 to 24% $2,750 + $4,000 per trailer 

Table 3-5. Tractor trailer technology matrix (continued) 

Category Technology FC Benefit Cd/Crr/Wt Benefit Capital cost (RPE) Intro Year 

Flat-nose Trailer 3 to 4% 7% - - Double trailer -10% - - 

Aero Fender-mounted mirrors, bug deflector, etc. -1.5 to -3% - - 

Penalties 

Cattle hauler, car hauler, flatbed -5 to -13% -10 to -30% - - Low Rolling Resistance Smartway Duals, tractor and trailer 2 to 3% 9% $30 per tire 2008 Low rolling resistance WBS Tires w/aluminum wheels, Tractor only 3 to 6% 19% $225 per wheel + tire 2008 Low rolling resistance WBS Tires w/aluminum wheels, Tractor + Trailer 6 to 9% 19% $225 per wheel + tire 2008 Next-generation dual 4 to 5% 15% $30 per tire 2013 to 2015 Next-generation WBS (Tractor Only) – Crr 0.0045 8 to 11% 33% $225 per wheel + tire 2013 to 2015 Next-generation WBS (Tractor+trailer) – Crr 0.0045 11 to 14% 33% $225 per wheel + tire 2013 to 2015 Tractor tire monitor 0.6% $100 2008 Tractor ATI 0.6% $4,000 to $5,000 2008 

Tires and Wheels 

Trailer ATI 0.6% $300 to $400 2008 WBS + aluminum wheels — benefit is included in WBS line item under tires 0 to 0.3% 100 lbs per tire $225 per wheel + tire 2008 Volume-constrained  0 to 1,000 lbs  1,000 to 2,000 lbs  2,000 to 3,000 lbs 

0.4 to 0.6% Per 1,000 lbs $2 to $4/lb $4 to $8/lb 

$8 to $10/lb 

Continuous 

Weight Reduction Weight-constrained 0 to 1,000 lbs 1,000 to 2,000 lbs 

 2,000 to 3,000 lbs 

2.2% Per 1,000 lbs $2 to $4/lb $4 to $8/lb 

$8 to $10/lb 

Continuous 

Powertrain 

2010 engine – 43.2 to 44.2% 4 to 5% +400 to 500 lbs $9.6 to $10.6K 2010 2013 engine – 45.5 to 47.5% 9 to 12% +50 lbs $13.2 to $15.2K 2013 2015 engine – 47.9 to 51.4% 13 to 18% +450 to 550 lbs $14.7 to $18.2K 2015 

Engine (13 to 

16L) 

2020 engine – 47 to 51% 18 to 22% +600 to 800 lbs $21.4 to $25.9K 2020 

Table 3-5. Tractor trailer technology matrix (continued) 

Category Technology FC Benefit Cd/Crr/Wt Benefit Capital cost (RPE) Intro Year Sale

Pen

Appropriate spec-ing of truck: match the axles, transmission gears, etc for the intended route, road speeds, and vocation* 1 to 3% — Pre-2008 60-9Direct Drive 1 to 1.5% — — Pre-2008 ? Friction Reduction 1 to 1.5% — $0 to $500 Continuous — Single drive axle 1% — $200 to $300 2012-2013 — Automatic transmission 0 to 5% +200 lbs $15,000 2008 <5% 

Transmission and Driveline 

AMT/Optimized Shift Strategy 4 to 8% +70 lbs $4,000 to $5,700 2008 10% Route Management – telematics for congestion & weather avoidance 0 to 1% — $400 to $800 2010 — Engine & Driveline Management (load-based speed control, multi-torque) 1 to 2% — — 2009 ? Adaptive cruise control — Slows according to traffic 0 to 1% — $2,000 to $3,000 pre-2008 10% Predictive cruise control — adjusts vehicle according to topology, conditions 1 to 2% — $100 2012 — Speed Governor - 60 MPH 0.4 to 0.5% per MPH — — pre-2008 25 to 5

Driver Management and Coaching Training & Feedback — driving training, sweet-spot indicator, rewards, etc 1 to 4% — $0 to $1,600 Continuous 25 to 5

Automatic Engine Idle Management - 0.5 gal/hr, 1,500 to 2,400 hrs/yr 3% — $1,000 to $4,000 2008 ? Direct fire heater - saves 0.2 to 0.3 gal/hr 500 to 800 hrs/yr 1.3 to 2.3% — $1,000 - $3,000 2008 ? Battery System – 0 gal/hr, ~10 hours of life; requires off-board charging 5 to 9% 400 to 500 lbs $3,000 to $8,000 2008 ? 

Idle Reduction 

Packages 

APU – 0.2 to 0.3 gal/hr, 1,500 to 2,400 hrs/yr 4 to 7% 400 to 500 lbs $6,000 to $8,000 2009 ? "Moderate Hybrid": Dual mode, all electric capability; Includes electrified accessories, overnight hotel loads, and engine-off at idle 6 to 9% ~750 lbs $45 to $5K (Low) $25 to $30K (High) 2013 Dem"Mild Hybrid": 40 to 50 kW motor; Parallel, single motor and clutch; integrated hybrid assembly (motor, clutch, transmission) and power electronics (battery, inverters, controls); Includes electrified accessories, hotel loads, and engine-off at idle 

5 to 7% ~ 500 lbs $35 to $45K (Low) 

$20 to $25K (High); 2013 Dem

Hybrid Packages Gen II hybrid: Integration w/engine and after-treatment — optimize engine 

operation; implemented on either hybrid package. Requires reg. change. 2 to 3% — — 2014-2015 — 

Table 3-6. Refuse hauler technology matrix 

Category Technology FC Benefit Cd/Crr/Wt Change Capital cost (RPE) Intro Year S

P

2010 engine – Peak efficiency of 43.2 to 44.2% 4 to 5% +400 to 500 lbs $9.6 to $10.6K 2010 2013 engine – Peak efficiency of 45 to 46.5% 8 to 10% +400 to 500 lbs $11.2 to $12.2K 2013 2015 engine – Peak efficiency of 47.2 to 49.2% 12 to 15% +400 to 500 lbs $12.7 to $14.2K 2015 

Engine (11L to 13L) 

2020 engine – Peak efficiency of 47.6 to 50.3% 13 to 16% +400 to 500 lbs $13.4 to K14.9K 2017 to 2020 Appropriate spec-ing: match the axles, transmission gears to the application 1 to 3% — — Pre-2008 6

1

Increased Transmission Gears – 6 spd to 8 spd AT 2 to 3% — $2,100 to $2,600 2010 Reduced AT parasitics and friction 1% — 0 to $500 Continuous 

Transmission and 

Driveline 

Aggressive Shift Logic and Early Lockup 0.5 to 1% — $100 2010 Parallel HEV 20% 450 lbs $35-$40K (Low) 2009 Parallel HEV, Future 25 to 30% 350 lbs $18-$20K (High) 2014 Parallel HEV, ePTO 25% 650 lbs $52K 2010 Parallel HEV, Future 30 to 35% 500 lbs $25 to $30K 2014 Parallel HHV 20 to 25% 1,000 lbs $40K (Low) 

$30K (High) 

2009 

Series HHV 40 to 50% ~1,500 lbs $50K (Low) 

$40K (High) 

2013 

Hybrids 

Integration of emissions control w/hybrid system 2 to 3% — — 2014-2015 Low Rolling Resistance Smartway Dual Tires 1.2 to 1.8% 9% $30 per tire 2008 Next generation low rolling resistance duals 2.4 to 3% 15% $30 per tire 2013 

Tires and 

Wheels 

Tire Inflation Monitor 0.36% — $100 2010 

Weight 

Reduction 

 0 to 1,000 lbs  1,000 to 2,000 lbs 1.4 to 2.3% Per 1,000 lbs

$4 to $8/lb 

$8 to $10/lb Continuous 

Table 3-7. Transit bus technology matrix 

Category Technology FC Benefit Cd/Crr/Wt Change Capital cost (RPE) Intro Year S

P

2010 engine – Peak thermal efficiency of 41.7 to 43.2% 4 to 5% +300 lbs $7.6 to $8.6K 2010 — 2013 engine – Peak thermal efficiency of 43.4 to 45.4% 8 to 10% +300 lbs $9.8 to $10.8K 2013 2015 engine – Peak thermal efficiency of 45.4 to 48.1% 12 to 15% +300 lbs $11.5 to $13K 2015 

Engine (8 to 9L) 

2020 engine – Peak thermal efficiency of 45.9 to 49.1% 13 to 16.4% +300 lbs $12.2 to 13.7K 2020 Appropriate spec-ing: match the axles, transmission gears to the application 1 to 3% — — Pre-2008 6

10

Increased Transmission Gears – 6 spd to 8 spd AT 2 to 3% — $1,100 to $1,650 2010 Reduced AT parasitics and friction 1% — 0 to $500 Continuous 

Transmission and 

Driveline 

Aggressive Shift Logic and Early Lockup 0.5 to 1% — $100 2010 Gasoline Series: 270 kW engine, 200 kW generator, 170 kW motor, 200 kW NiMH battery or ultracap 25 to 35% 2,000 lbs 

$200,000 

($20K w/90% 

subsidy) 

 Pre-2008 15

the 

Diesel Series: 270 kW engine, 200 kW generator, 170 kW motor, 200 kW NiMH battery or ultracap 30 to 40% 2,600 lbs $220,000 ($22K w/subsidy) Pre-2008 75 

r

Diesel Parallel 22 to 35% 940 to 2,840 $200,000 ($20K w/subsidy) Pre-2008 2

3

Hybrid 

Integration of emissions control w/hybrid system 2 to 3% — — 2014 Low Rolling Resistance Smartway Dual Tires 0.8 to 1.2% 9% $30 per tire 2008 Next generation low rolling resistance duals 1.6 to 2% 15% $30 per tire 2013 

Tires and 

Wheels 

Tire Inflation Monitor 0.25% ? $100 2010 

Weight 

Reduction 

 0 to 800 lbs  800 to 1,600 lbs  1,600 to 2,800 lbs 

2 to 3% Per 1,000 lbs 

$2 to $4/lb $4 to $8/lb 

$8 to $10/lb 

Continuous 

Table 3-8. Class 3-6 box and bucket truck technology matrix 

Category Technology FC Benefit Cd/Crr/Wt Change Capital cost (RPE) Intro Year 

2010 engine – Peak thermal efficiency of 41.7 to 43.2% 4 to 5% +300 lbs $7.6 to $8.6K 2010 2013 engine – Peak thermal efficiency of 43.4 to 45.4% 8 to 10% +300 lbs $9.8 to $10.8K 2013 2015 engine – Peak thermal efficiency of 45.4 to 48.1% 12 to 15% +300 lbs $11.5 to $13K 2015 

Engine (6 to 9L) 

2020 engine – Peak thermal efficiency of 45.9 to 49.1% 13 to 16.4% +300 lbs $12.2 to 13.7K 2020 

Roof Deflector 2 to 3% 7 to 7.5% $500 to $800 2008 Fuel Tank/Chassis fairings 0.5 to 1% 2.5 to 3% $400 to $500 2010-2012 Box Skirts 2 to 3% 4.5 to 5% $500 to $1,000 2010-2012 Cab side extension or Cab/Box Gap fairing (e.g., Nosecone) 0.5 to 1% 2.4 to 2.7% $500 to $650 2010-2012 Aft Box Taper 1.5 to 3% 7.6 to 8% $1,000 2014-2015 Cab streamlining: aero mirrors, aero bumper, streamlined shape 1 to 2% 5 to 6% $750 2010-2012 

Aero 

Straight Truck aero combination package 5 to 8% 20% $3,000 to $3,500 2015 Low Rolling Resistance Smartway Dual Tires 1.4 to 2.1% 9% $30 per tire 2008 Next generation low rolling resistance duals 2.8 to 3.5% 15% $30 per tire 2013 Tire Inflation Monitor 0.42% ? $100 2010 

Tires and Wheels 

Low rolling resistance wide base single (WBS) w/aluminum wheels 2.1 to 4.2% 12% $225 per tire + wheel 2008 

Appropriate spec-ing: match the axles, transmission gears to the application 1 to 3% — — Pre-2008 Increased Transmission Gears – 6 spd to 8 spd AT 2 to 3% — $1,000 to $1,650 2010 Reduced AT parasitics and friction 1% — 0 to $500 Continuous 

Transmission and 

Driveline 

Aggressive Shift Logic and Early Lockup 0.5 to 1% — $100 2010 WBS + aluminum wheels -- benefit is included in WBS line item under tires 

0.1% for 4 

wheels 

~100 lbs per 

tire+wheel 

See WBS under 

tires 2008 

Weight Reduction 0 to 470 lbs 

 470 to 940 lbs  940 to 1,650 lbs 

3 to 5% Per 1,000 lbs

$2 to $4/lb $4 to $8/lb 

$8 to $10/lb 

Continuous 

Parallel HEV 20 to 25% 450 lbs $35-$40K (Low) 2007 Parallel HEV, Future (Engine-off at idle, electric accessories, optimized controls, lighter components, high volume production) 25 to 35% 350 lbs $18-$20K (High) 2014 Parallel HHV 20 to 25% 1,000 lbs $40K (Low) $30K (High) 2011 Series HHV 40 to 50% ~1,500 lbs $50K (Low) $40K (High) 2013 Parallel HEV w/ePTO 30 to 40% 650 lbs $49 to $52K (Low) 2007 

Hybrid 

Parallel HEV w/ePTO, Future ((Engine-off at idle, electric accessories, optimized controls, lighter components, high volume production) 35 to 45% 500 lbs $25 to $30K (High) 2014 

Table 3-9. Class 2b pickup and van technology matrix 

Category Technology FC Benefit Cd/Crr/Wt Change Capital cost (RPE) Intro Year S

P

Improved controls - Aggressive Shift logic, early lock-up 1.5 to 2.5% - $60 2010 6-speed to 8-speed AT 2.7 to 4.1% - $500 to $1,650 2011 AMT 5.5 to 9.5% - $700 to $1,400 2011 Friction Reduction 0 to 1% - 0 to $500 Continuous 

Transmissions 

Lower Final Drive 2 to 3% - $- 2009 

10% Reduction in aero drag 2 to 3% 10% $60 to $120 Continuous Weight reduction via materials substitution, up to 2% 0.6 to 0.9% per 3% saved 1 to 2% $1 to $2/lb 2012 Materials substitution - Weight Reduction - 5% 0.6 to 0.9% per 3% saved 2 to 5% $2 to $4/lb 2014 

Load Reduction 

Low rolling resistance tires 1 to 2% - $6 to $9 2008 

Elec. Acc. 2 to 4% - $500 to $2,000 2014 • Package 1: VVT and VVL - gasoline 2.5 to 9% - $632 to $1,372 2010 • Package 2: SGDI, VVL and VVT - gasoline 7 to 14% - $1,200 to $2,400 2012 • Package 3: Turbo-charged gasoline, down-sized engine; Includes SGDI, VVLT 11 to 17% - $2,500 to $3,600 2012 • Package 4: Diesel, turbo charged, HPCR (1,800 bar), NOx Adsorber or SCR 19 to 24% +500 lbs $7,900 to $9,400 2010 5• Package 6: Improved Diesel - adopts higher FI, increased cylinder pressure, improved controls and turbo; similar to 2010-2012 HD tech 4 to 5% - $1,000 to $2,000 2012 Lean burn GDI 20 to29% - $3,250 to $4,350 2014 

Engine 

Gasoline homogeneous charge compression ignition (HCCI) 20 to 27% - $3,185 to $4,285 2014 

Parallel hybrid 15 to 20% 200 lbs 

$16.4 to $20.6K 

(High) 

$8.2 to $10.3K 

(Low) 

2012-2014 

Hybrid 

Dual-mode or power-split hybrid 20 to 30% 250 lbs $12 to $17K (High) $24 to $34K (Low) 2012-2014 

Table 3-10. Motor coach technology matrix 

Category Technology FC Benefit Cd/Crr/Wt Change Capital cost (RPE) Intro Year S

P

2010 engine – 43.2 to 44.2% 4 to 5% +400 to 500 lbs $9.6 to $10.6K 2010 2013 engine – 45.5 to 47.5% 9 to 12% +50 lbs $13.2 to $15.2K 2013 2015 engine – 47.9 to 51.4% 13 to 18% +450 to 550 lbs $14.7 to $18.2K 2015 

Engine (11 to 13L) 

2020 engine – 47 to 51% 18 to 22% +600 to 800 lbs $21.4 to $25.9K 2020 Boat Tail 4 to 6% 6.5 to 9% $1,500 to $2,000 2012-2014 Streamlining - no cost estimate 3 to 4% 6 to 8% $2,750 2012-2014 

Bus 

Aero 

Motor Coach Aero Combination (boat tail + streamlining 7 to 10% 13 to 15% $4,250 to $4,750 2014-2015 Low Rolling Resistance Smartway Duals, tractor and trailer 1.4 to 2.1% 9% $30 per tire 2008 Low rolling resistance WBS Tires w/aluminum wheels + LRR duals 2.1 to 4.2% 19% $225 per wheel + tire 2008 ~Next-generation dual 2.8 to 3.5% 15% $30 per tire 2013 to 2015 Next-generation WBS + LRR duals – Crr 0.0045 5.6 to 7.7% 33% $225 per wheel + tire 2013 to 2015 

Tires and Wheels Tire monitor 0.42% $100 2008 

ATI 0.42% $300 to $400 2008 Automatic Manual Transmission 4 to 8% +70 lbs -$10,000 2008 Appropriate spec-ing: match the axles, transmission gears to the application 1 to 3% — — Pre-2008 6

1

Increased Transmission Gears – 6 spd to 8 spd AT 1.5 to 2% — $1,870 to $2,200 2010 Reduced AT parasitics and friction 1 to 1.5% — 0 to $500 Continuous 

Transmission and 

Driveline 

Aggressive Shift Logic and Early Lockup 1 to 2% — $100 2010 

Weight 

Reduction 

 0 to 1,000 lbs  1,000 to 2,000 lbs  2,000 to 3,500 lbs 

0.7% Per 1,000 lbs

$2 to $4/lb $4 to $8/lb 

$8 to $10/lb

Continuous 

Parallel HEV Line-haul “Mild Hybrid": 40 to 50 kW motor; Parallel, single motor and clutch 7 to 10% 500 lbs $30 to $40K 2015 Parallel Diesel HEV Transit Bus 10 to 15% 1,000 to 2,000 lbs 

$180,000 to $220,000 

($36 to $44K w/80% 

subsidy) 

Available now ~

Hybrid Packages Gen II hybrid: Integration w/engine and after-treatment -- optimize 

engine operation; implemented on either hybrid package 2 to 3% - ? - should be nominal controls upgrade 2014-2015 

4-1

4. Fuel Saving Technologies 

This section provides detailed descriptions of fuel saving technologies that are either available 

currently or will be in the near future (five to ten years). The fuel saving technologies are divided 

into one of several categories: engines and emissions, aerodynamics, tires and wheels, weight 

reduction, transmission and driveline, hybrid technologies, idle reduction, and driver management 

and coaching. For each category, we describe the technologies, how they improve fuel efficiency, 

and the extent to which they apply to different vehicle classes and applications. Throughout this 

discussion, several different terms are used to reflect different types of energy efficiency or fuel 

savings. These terms are defined as follows: 

Fuel consumption (FC) benefit: The fuel saved, in terms of percentage by a given vehicle 

operating over a typical drive cycle (see Chapter 2 for discussion of vehicle and drive cycle 

assumptions). 

Peak Brake Thermal Efficiency: The thermodynamic efficiency of an engine operating at its most 

efficient point. The engine’s thermodynamic efficiency is defined as the energy out divided by the 

energy content of the fuel used. 

Drive Cycle Efficiency: The average brake thermal efficiency of an engine operating over a typical 

drive cycle for a given application. 

4.1 Engine and Emissions Technologies 

4.1.1 Overview 

Present-day medium- and heavy-duty trucks use both gasoline and diesel engines6. Diesel engines 

range in size from about 6 liters up to 16 liters. Gasoline engines lie primarily in the 5 to 8 liter 

range. This evaluation of medium-duty and heavy-duty engine technologies segments the engine 

market into three classes: “big bore” diesel engines (11 to 15L range); “medium bore” diesels (6 to 

9L range); and gasoline engines (5 to 8L). This segmentation is summarized in Table 4-1. 

Table 4-1. Medium- and heavy-duty vehicle technology matrix assumptions 

Engine In-Use Application 

11 to 15L diesel engine Class 8 tractor trailer 

Refuse hauler 

Motor coach 

6 to 9L diesel engine Class 3-6 box and bucket trucks 

Transit buses 

Class 2B pickups and vans 

5 to 8L gasoline engines Class 2B pickups and vans 

 

6

 Some alternatively fueled engines are also used, including propane in medium-duty trucks and natural gas in port trucks/pickup 

and delivery applications and transit buses. Electricity and hydrogen are also used in transit buses 
4-2

4.1.2 Diesel Engine Technologies 

4.1.2.1 Approach 

A key takeaway from discussions with engine manufacturers was that engines are complex 

systems that must be optimized as a whole. As such, it is difficult to assign discrete efficiency 

benefits to individual technologies: some approaches directly increase fuel efficiency (e.g., 

reducing friction), while others are enablers for improving efficiency (e.g., improved engine 

controls allow combustion to occur closer to NOx limits). In addition, many strategies address 

similar problems in different ways: for example, energy from waste heat may be recovered either 

through a turbo-compounding system or from a bottoming cycle. Due to these complexities, 

evaluating engine technologies as a series of discrete options runs the risk of double counting. 

To address this challenge, this evaluation of diesel engine technologies employs a top-down 

approach that identifies thermodynamic loss mechanisms and other engine losses. Individual 

technology strategies are then categorized according to the following loss or waste heat recovery 

mechanisms: 

• Heat transfer and exhaust 

• Gas exchange 

• Engine friction 

• Parasitic engine loads and vehicle accessories 

• Waste heat recovery7

Characteristics of individual engine technologies were sourced from published specifications for 

current (2007 emissions-compliant) and 2010 engines, results of DOE-funded research by 

industry, publicly available reports, and data gathered during site visits. 

Individual technologies were then collected into plausible packages, each associated with a 

specific market segment and timeframe. A package is defined as a collection of discrete 

technologies, which are associated with an estimated peak thermal efficiency and a “drive cycle” 

thermal efficiency (defined below). For example, an energy audit of a present-day diesel engine 

as shown in Figure 4-1, based on data furnished by engine manufacturers, was used to estimate 

the peak engine thermal efficiency for a baseline 2007 emissions-compliant big-bore engine. A 

list of technologies that defines this 2007 engine was then compiled from the literature. 

 

7

 Waste heat recovery actually reduces exhaust gas losses, but because it functions separately from the engine itself, we have 

included it as a separate category. 
4-3

Indicated Closed

Cycle Efficiency

50%

Heat Transfer

26%

Exhaust

24%

Fuel Energy

100%

Gas Exchange

4%

Friction

1.5%

Accessories

2.5%

Brake Power

42%

Indicated Closed

Cycle Efficiency

50%

Heat Transfer

26%

Exhaust

24%

Fuel Energy

100%

Gas Exchange

4%

Friction

1.5%

Accessories

2.5%

Brake Power

42%

Figure 4-1. 2007 diesel engine energy audit [Duggal 2009]

The estimated peak thermal efficiency of each package relies primarily on details from engine 

manufacturer technology roadmaps that were shared during site visits. Although diesel engine 

manufacturers differed in terms of precisely how they would meet various targets, they are in 

general agreement that improvements on the order of 20 percent are feasible in the next ten to 

fifteen years, with the potential to achieve peak thermal efficiencies on the order of 51 to 

53 percent for an advanced engine and up to 55 percent with waste heat recovery. 

To construct engine packages associated with a specific time frame, TIAX extrapolated from the 

current engine status to the long-term target of 51 to 53 percent peak thermal efficiency; and then 

assigned technologies to these packages based on estimates of when specific technologies might 

come into the market. This technology roadmap draws largely on information furnished by 

Cummins during the committee’s site visit [Cummins 2009a], which was supported by 

information offered to the committee during site visits. Figure 4-2 shows the current history of 

peak thermal efficiency for large bore engines and possible future improvements. Also shown on 

this figure is the history of the NOx and PM standards. 

Incremental future engine efficiency improvements are not corrected for the truck’s duty cycle. 

For example, improving the engine peak thermal efficiency by 1 percent using a next-generation 

fuel injection system would improve the cycle thermal efficiency by 1 percent. For discrete 

technology packages – such as waste heat recovery systems – the data reflect estimates for fuel 

consumption reduction over a representative duty cycle. 
4-4

30%

35%

40%

45%

50%

55%

60%

65%

1985 1990 1995 2000 2005 2010 2015 2020 2025

Brake Thermal Efficiency (%)

BTE

NOx Std

PM Std

0.6

0.1

NOx PM 

Emission Std g/bhp-hr

6

4

2

0.3

0.2

0.4

0.5

NOx PM

10

8

Electronic

Controls

Turbo

Eff

Increasing 

Inj P; Cyl P

EGR, VG

Turbo

DPF SCR

OBD, Controls

Waste Heat

Recovery

Adv Engine Concepts,

Vehicle Electrification

Figure 4-2. Past and possible future brake thermal efficiency improvements for 

large bore engines [Site Visits, Duggal 2009, Cummins 2009a] 

To the extent possible, costs are estimated from direct references in the literature or data 

furnished on site visits. Because many of the engine technology strategies entail continuous 

minor modifications and are implemented as a collective package when a new engine platform is 

introduced, in many cases, capital cost estimates are informed by past engine cost increases 

(from one generation engine to the next) and by soft estimates offered during site visits. 

Published sources that are several years old often identify technologies and costs that are already 

widely deployed. In cases where these estimates correspond to continuous improvement 

opportunities, capital costs from one generation engine to the next are considered to plausibly 

carry over. 

Most of the literature and site visit discussions focused on the benefits, capital costs, and 

technical potential of the heavy-duty 11 to 15L diesel engines. As such, a number of assumptions 

were made to extend the results of the analysis to the 6 to 9L category. In general, it is assumed 

that a similar slate of engine efficiency technologies can be applied to the smaller engines. 

However, the medium-duty diesel technologies and technology packages are differentiated from 

each other and their heavy-duty counterparts in the following ways: 

 Because the medium-duty applications tend to be lower mileage, there is less market pull 

for fuel efficiency. Therefore, in some cases, it is assumed that continuously improving 

strategies (such as fuel system or cylinder pressure) are one generation behind the heavyduty vehicles. Based on a review of engine manufacturer data for 2007 and 2010, this 

appears to be a reasonable assumption. 

Year 
4-5

 Technology costs are scaled down to medium-duty on a case-by-case basis. Some fuel 

reduction strategies, such as friction reduction or engine controls, were judged to incur 

similar costs regardless of the system size; others, such as aftertreatment, are expected to 

scale with engine size. 

 Waste heat recovery systems are assumed to be a viable strategy only for vehicles that 

operate over high-speed, steady-state duty cycles. In practical terms, this means that 

waste heat recovery was only considered for line-haul and motor coach applications. It is 

also conceivable that electric turbo-compounding could be used in a series hybrid bus, for 

which the engine duty cycle could be near steady state. 

4.1.2.2 Baseline Diesel Engine Description 

Characteristics of the baseline medium- and big-bore diesel engines are based on a review of the 

technologies that are available in 2007 emissions-compliant engines for the two different engine 

classes. These characteristics are summarized in Table 4-2. A detailed table summarizing all of 

the engines that were reviewed is included in Table 4-3 and Table 4-4. 

Table 4-2. Baseline characteristics for 2007 medium- and big-bore diesel engines 

Engine 

Technologies 11 to 15L 6 to 9L 

Cylinder pressure 190-200 Bar 170-180 Bar 

Fuel Injection 1800 to 2200 bar common rail -or33K psi unit injector 

Multiple injections per cycle 

1600 to 1800 bar common rail 

NOx Control Cooled medium rate EGR, DPF Cooled medium rate EGR, DPF 

Particulate Control DPF w/active regen DPF w/active regen 

Aspiration Variable geometry turbo charger Variable geometry turbo charger 

Engine Controls Open-loop Open-loop 

Low-speed idle Yes Yes 

Waste-heat recovery None None 

Accessories8 Belt-driven mechanical 

1 to 5 kW 

Belt-driven mechanical 

1 to 5 kW, except bus – 30 to 40 kW 

Weight 2,200 to 3,100 lbs 1,100 to 1,700 lbs 

 

8

 Accessory load estimates from 21st Century Truck [DOE 2000] 
4-6

Table 4-3. 2008 and 2010 11 to 15L sample heavy-duty diesel engine specifications

Size (L) Engine HP Torque (ft-lb) Wt (lb) CR Turbo Machinery Fuel Injection Emis

ns 

2007-Compliant 11 to 15L Engines 

14L DD Series 60 445-515 1450-1650 2557 17:1 Elec. VG Turbo 

Dual solenoid electronic unit 

injectors ~2000 Bar, multi 

injections 

Med E

DP

11-15L 

Cummins ISX 

Cummins ISM 

385-600 280-425 

145-1850 

1150-1550 

3,021 2,268 

? Electronically actuated VG Turbo Unit Injection Med E

DP

11-13L 

MaxxForce 13 MaxxForce 11 

410-475 330-390 

1450-1700 1250-1400 

2,244 2,244 

17:1 17:1 

Twin series turbochargers; 

Air/Liquid Intercooler 

Common rail, 1800 Bar, multinjections/cycle Med E

DP

11-16L 

Volvo D16 Volvo D11 

450-600 325-405 

1650-2050 1250-1450 

3,091 2,246 

16:1 Sliding nozzle VG Electronically Actuated turbo 35,000 PSI Dual Solenoid Unit Injector Med E

DP

12.8L DD MBE4000 350-450 1250-1650 2270 18:1 Wastegated turbo 

2000 Bar Unit injector 

(SMART Fuel System), multi 

injection, rate shaping 

Med E

DP

2010-Compliant 11 to 15L Engines 

11-16L 

Volvo D16 Volvo D11 

450-600 325-405 

1650-2050 1250-1450 

3,091 2,246 

16:1 Sliding nozzle VG Electronically Actuated turbo 35,000 PSI (2400 Bar) Dual Solenoid Unit Injector SCR, 

EGR, 

11L-15L Cummins ISX 

400-600 310-425 

1450-2050 1150-1650 

3,186 2,812 

? Sliding nozzle VG Electronically Actuated turbo 2,200 Bar common rail XPI Fuel System – multiple injections per cycle SCR, 

EGR, 

11/13L 

MaxxForce 13 MaxxForce 11 

410-475 330-390 

1450-1700 1250-1450 

2,400 2,400 

17:1 

16.5:1 

Dual stage turbocharger, 

Intercooler & Aftercooler 

2,200 bar common rail, multinjections/cycle Mass

EGR, 

15L DD15 455-560 1550-1850 2880 18.4:1 Mechanical Turbo Compound & Non-VG Turbo 

2,100 Bar; Amplified 

Common Rail Fuel System 

(ACRS), variable rate 

shapes, multi injections/cycle 

SCR, 

EGR, 

a Cummins 2009b, Cummins 2009c, Detroit Diesel 2009a, Detroit Diesel 2009c, Detroit Diesel 2009d, Volvo 2009a, Volvo 2009b, MaxxForce 2009, Sturg
4-7

Table 4-4. 2008 and 2010 6-9L heavy-duty diesel engine specifications

Size (L) HP Torque (ft-lb) Wt (lb) CR Turbo Machinery Fuel Injection 

2007-Compliant 6 to 9L Diesel Engines

6.7-9 

Cummins ISL 

Cummins ISB 

345-365 200-325 

1150-1250 

520-750 

1,685 1,190 

? 

Sliding nozzle VG 

Electronically 

Actuated turbo 

1800 Bar High pressure 

common rail, multiinjection/cycle Me

9.3 MaxxForce 10 310-350 1050-1150 1,560 ? Turbocharged Electro-hydraulic fuel system - 1600 Bar Me6.4 MaxxForce 7 200-230 560-620 1,160 17.5:1 Elec. Turbocharger w/charge air cooler Electro-hydraulic fuel system - 1600 Bar Me

7.2L DD MBE900 190-250 520-660 1,392 18:1 Wastegated turbo 

~1,800 Bar Unit injector 

(SMART Fuel System), 

multi injection, rate 

shaping 

Me

2010-Compliant 6 to 9L Diesel Engines

9 Cummins ISL 345-380 1150-1300 1,850 ? 

Sliding nozzle VG 

Electronically 

Actuated turbo 

2,200 Bar common rail 

XPI Fuel System – 

multiple injections per 

cycle 

6.7 Cummins ISB 200-325 520-750 1,340 ? 

Sliding nozzle VG 

Electronically 

Actuated turbo 

1800 Bar common rail fuel 

System – multiple 

injections per cycle 

9.3 MaxxForce 10 310-350 1050-1150 1,425 17.2:1 

Dual stage 

turbocharger, 

Intercooler & 

Aftercooler 

1900 Bar Electrohydraulic high pressure M

6.4 MaxxForce 7 220-300 560-660 1,225 16.7:1 

Regulated dualstage turbocharger 

w/intercooling 

1900 Bar Electrohydraulic high pressure M
4-8

The baseline engine efficiency assumptions are based on two parameters: 

1.) What is the engine size? Big bore engines are assumed to have adopted the most advanced 

technology and therefore have higher peak thermal efficiency. 

2.) Is the duty cycle dominated by urban (stop-and-go) or highway driving? Engines spend more 

time operating outside the optimum efficiency regime during stop-and-go (and hence have a 

greater spread between peak thermal efficiency and cycle thermal efficiency). 

Table 4-5 shows the assumptions used for the applications under consideration. 

Table 4-5. Baseline engine efficiency assumptions [Site Visits, DOE 2000, NHTSA 

2009] 

Application Engine Size Duty Cycle 

ηPeak

(2007compliant)

ηCycle 

(2007 compliant)

Tractor Trailer 11 to 15L Highway 41 to 42% 38 to 39% 

Refuse 11 to 15L Urban 41 to 42% 34 to 37% 

Box truck 6 to 9L Urban 40 to 41% 31 to 35% 

Bucket truck 6 to 9L Urban 40 to 41% 31 to 35% 

Transit bus 6 to 9L Urban 40 to 41% 34 to 37% 

Motor coach 11 to 15L Highway 41 to 42% 36 to 38% 

Pickup and Van (Diesel) 6-9L Mix 40 to 41% 30 to 35% 

Pickup and Van (Gas) 5-8L Mix 33 to 36% 20 to 25% 

4.1.3 Diesel Engine Technology Descriptions 

A brief description of individual strategies for improving the efficiency of diesel engines beyond 

the 2007-compliant baseline is included below. 

4.1.3.1 Emissions Systems 

Table 4-6 shows our assumptions regarding future technologies to meet the upcoming 2010 

emission standards. Included are estimates of fuel consumptions effect, capital costs, and year of 

introduction. 

Improving the efficiency of heavy-duty diesel engines entails a complex tradeoff between 

minimizing particulate and NOx emissions and maximizing fuel efficiency. While higher engine 

efficiency leads to lower fuel use and reduces particulates, it leads to higher NOx levels. 

Optimizing these tradeoffs requires tightly coupled integration between the engine, the 

aftertreatment, and controls. This process includes adjusting a number of different engine subsystems in parallel. Although technically not a “fuel efficiency” strategy, modern emissions 

systems are tightly integrated with the engine, and much of the engine design challenge revolves 

around managing the tradeoffs between NOx and fuel efficiency. 
4-9

Table 4-6. Emissions strategies 

Technology % FC Benefit Capital cost Intro 

SCR w/Low-rate EGR 3 to 6 (incl. DEF 

penalty) 

$9,000 to $10,000 (11 to 15L) 

$7,000 to $8,000 (6 to 9L) 

2010 

High-rate EGR -1 to -2 $8,000 (11 to 15L) 

$6,000 (6 to 9L) 2010 

High-rate EGR w/Mixed 

Mode Combustion 

1 to 2 $10,000 (11 to 15L) 

$8,000 (6 to 9L) 

2012 

Two different emissions pathways are summarized in the technology matrix: an in-cylinder only 

pathway, and an in-cylinder system coupled with SCR aftertreatment pathway. Lean NOx

adsorbers offer yet another option in place of SCR, but these were not included9

. Although both 

an SCR and in-cylinder only emissions pathways were characterized, the engine technology 

packages assume that the in-cylinder SCR pathway is adopted, as this appears to be the industry 

trend. 

Selective Catalytic NOx Reduction 

Selective catalytic reduction (SCR) combined with EGR will be introduced on most 2010 

engines to meet the new EPA NOx standards. Because SCR is a highly effective aftertreatment 

approach, its introduction will enable engines to be optimized to maximize fuel efficiency, rather 

than minimize engine-out NOx. Based on information gathered during site visits and company 

literature, 2010 SCR systems are estimated to improve engine efficiency by approximately 4-

5 percent compared to a 2007 in-cylinder EGR-based emissions system [Site Visits, 

factsaboutscr.com] and by an even greater percentage compared to 2010 in-cylinder approaches 

[Stanton 2008]. This 4-5 percent increase in engine efficiency is offset by the use of diesel 

emission fluid (DEF) in the SCR system. The volume of DEF use is about 2 percent that of 

diesel fuel used. Assuming DEF is priced the same as diesel, this 2 percent should then be 

subtracted from the engine benefit of 4-5 percent giving a net efficiency improvement of 

2-3 percent for the 2010 SCR engines. As more effective low-temperature catalysts are 

developed, the NOx conversion efficiency of the SCR system will increase. Next-generation SCR 

systems could then enable still further efficiency improvements; alternatively, these advances 

could be used to maintain efficiency while down-sizing the after-treatment. It was suggested that 

continued optimization of the catalyst could offer 1 to 2 percent additional reduction in fuel use 

[Site Visits]. 

The chief drawbacks of an SCR emissions system are its higher capital cost and the added cost 

and inconvenience of maintaining diesel emissions fluid (DEF) levels, which is integral to the 

NOx reduction process. Volvo has announced that their SCR system will incur a surcharge of 

$9,600 on their large bore (11 to 16L) engines [McNamara 2009], and this cost will include the 

 

9

 Although NOx adsorbers are being considered for light-duty diesels and were used in some MD 2007 engines, they are being 

phased out of the medium- and heavy-duty segments. This is due to a combination of high cost, sensitivity to sulfur poisoning, 

and adverse fuel efficiency impacts. 
4-10

SCR catalyst, DEF storage and injection system, and controls. Daimler has announced that their 

system will range from $7,000 (for their smaller, 6 to 9L engines) to $9,000 (for their larger 11 

to 15L offerings) [LMT 2009]. We have assumed an SCR cost of $7,000 to $8,000 for 6 to 9L 

engines and $9,000 to $10,000 for 11 to 15L engines. 

DEF consumption is expected to be about 2 percent of diesel consumption and cost on the order 

of $2.75 per gallon [truthaboutscr.com]. For a line-haul truck, this would incur an additional 

annual operating cost of approximately $1,100 per year (assuming 120,000 miles and 6 MPG). 

Note we have included this cost in our estimates of efficiency improvements assuming that DEF 

costs are the same as diesel. If DEF costs are lower, as might be expected in large volume 

dispensing, then the SCR efficiencies would be slightly higher. 

Diesel Particulate Filters 

Diesel particulate filters (DPFs) are standard on all 2007 emissions-compliant diesel engines. 

The 2007 DPF systems degrade fuel efficiency due to higher back-pressure on the engine, which 

increases pumping losses, and since they require occasional “active” regeneration, in which a 

small amount of fuel is burned to assist in particulate filter regeneration. Beginning with the 

introduction of 2010 SCR-equipped engines, which will have lower engine-out particulates 

(enabled by less EGR), information furnished during site visits suggests that the need for active 

regeneration will be much lower, and back-pressure will be reduced. With these changes, DPFs 

are likely to decrease from a 1.5 to 2 percent fuel consumption penalty to significantly less than 

0.5 percent [Site Visits, truthaboutscr.com, Volvo 2009a, Duleep 2008].10

In-Cylinder Approach 

An in-cylinder emissions approach is primarily a low-cost emissions enabler – not a fuel 

efficiency enabler. The proposed in-cylinder emissions pathway to meet 2010 NOx standards 

uses high-rate cooled EGR and makes use of advanced low-temperature combustion concepts 

such as homogeneous or premixed charge compression ignition (PCCI or HCCI) not only in the 

low load-speed operating conditions but also in the high load-speed operating conditions. This 

approach offers lower initial costs than SCR and does not require any additional operating cost 

(SCR users must periodically replenish DEF levels for proper operation) but does not allow for 

higher engine out NOx and lower fuel consumption. Navistar is currently the only manufacturer 

that has committed to this approach for their 2010 engines.11 Navistar has announced that the 

incremental cost of their high-rate EGR system is $6,000 for smaller (6 to 9L) engines and 

$8,000 for their larger (11 to 13L) engines [Transport Topics 2009]. 

While 2010 SCR-based systems will reduce fuel consumption by approximately 3 percent 

compared to 2007 engines, it is likely that the higher rate EGR needed to approach the 2010 NOx

limits will degrade system efficiency still further (perhaps 1 to 2 percent). A few strategies exist 

to reduce these EGR-related losses, such as using an EGR cooler or an EGR pump; these are 

 

10 Note that this improvement pre-supposes an SCR-based after-treatment system, which is being pursued by all of the OEMs 

except for Navistar. 

11 Navistar will be using NOx emission credits to offset their higher NOx emissions of 0.5 g/bhp-hr in order to meet the standard of 

0.2 g/bhp-hr. 
4-11

described in the section on gas-exchange losses. However, they do not come close to the fuel 

savings offered by SCR. 

Achieving 2010 NOx levels using high rate EGR will likely require an advanced combustion 

technology such as HCCI. Implementation entails additional technologies such as variable valve 

actuation (VVA), a start of combustion sensors, and a dual-staged turbocharger to achieve 2010 

emissions levels. These advanced combustion concepts are expected to offer a minor fuel 

efficiency benefit compared to high rate EGR – 1 to 2 percent – at an incremental cost on the 

order of $2,000. 

4.1.3.2 Heat Transfer and Exhaust Losses 

Table 4-7 summarizes our estimates of fuel consumption benefits and capital costs for fuel 

injection, controls, and combustion systems. 

Table 4-7. Strategies to reduce heat transfer and exhaust losses 

Technology % FC Benefit Capital cost Intro 

Fuel Injection Systems 1 to 4 0 to $500 Continuous 

Controls 1 to 4 $60 to $150 Continuous 

Combustion 1 to 3 $500 to $1,500 Continuous 

Fuel injection Systems 

Finely controlled, high pressure fuel injection is a key enabler for more efficient combustion and 

a cleaner, more consistent fuel burn. Current state-of-the-art systems that are planned for 

deployment in 2010 engines include high pressure (2000 to 2,400 bar) common rail injection 

systems with advanced nozzle designs that are capable of finely shaped and controlled spray with 

multiple injection events per cycle [Cummins 2009b, MaxxForce 2009, Detroit Diesel 2009a]; 

they also include high pressure unit injectors [Volvo 2009a]. 

Potential future improvements will continue to improve spray control, allow more accurate 

timing of injection with combustion events, and increase fuel injection pressure. Improved 

material properties and controls could enable pressures of up to 3,000 bar in the 2015 timeframe 

and perhaps 4,000 bar by 2020. Future systems will also utilize increasingly sophisticated 

injection techniques such as variable spray nozzles, piezo-electric injectors, or super-critical fuel 

injection12. These advances are possible in the 2013 to 2015 timeframe [Site Visits, Cummins 

2009a]. Fuel injection systems were estimated on site visits to offer between 1 and 4 percent 

improvement in fuel efficiency. These estimates are lower than other information found in the 

literature; for example, Vyas [2002] estimates fuel injection systems have the potential to 

improve efficiency by 6 percent, and this estimate has been widely propagated (e.g., Frey [2007] 

and EIA [2009]). However, it is not clear what the baseline system to which this efficiency 

 

12 Refers to fuel changing instantaneously from liquid state to super critical gaseous state at injection. 
4-12

increment refers; as these studies are several years old, it is likely that the envisioned changes 

have already been adopted. As such, we have used the more conservative estimate. 

Because fuel injection systems are tightly integrated with the design of the overall engine 

platform, and because they are undergoing continuous incremental modification, it is difficult to 

identify an exact cost. Vyas [2002] projects that an improved fuel injection system costs on the 

order of $500. Discussions during site visits supported this estimate: historically, advanced fuel 

injection approaches have come at a minor incremental cost and may even be cost neutral once 

economies of scale are fully realized. As such, we estimate fuel injection system costs to range 

from $0 to $500. 

Engine Controls 

Advanced engine controls will be enabled in part by the onboard diagnostic systems that will be 

mandated for medium- and heavy-duty trucks, beginning in 2010 and becoming fully phased in 

by 2013. Increasingly sophisticated engine controls – particularly a transition to closed-loop 

controls approaches – enable engine efficiency improvements. Closed loop controls will feed 

information about the engine’s operating regime and emissions back to the system controls. This 

improved feedback will allow manufacturers to optimize emissions and fuel savings across a 

variety of operating conditions. During site visits, the benefits of improved engine controls were 

estimated to range from 1 to 4 percent. Similar results are reported by Zhang [2008] as part of 

DOE-funded research by Detroit Diesel. However, this number should be regarded with caution 

as improved engine controls really acts as an enabler for other improvements. 

In addition to the required software changes, onboard diagnostic systems (OBDs) and closedloop controls will require NOx sensors. In the EPA final notice of rulemaking on onboard 

diagnostics, the total cost of the hardware is estimated at $43 (2010 to 2012) to $57 to $60 (post2012). When non-recurring engineering costs are included, the cost of an OBD system is 

estimated at between $100 and $155; these higher costs are only incurred during years when 

development is most active (i.e., 2010 to 2012, and when new engine platforms are introduced in 

later years). The EPA estimates include only upgrades to the vehicle computer and the required 

algorithm development; they assume that NOx sensors are already implemented as part of other 

emissions control [EPA 2008a]. Based on the EPA’s analysis, the cost of advanced engine 

controls is estimated to range in cost from $60 to $150. It should be noted these costs could be 

significantly higher if NOx sensors are not already incorporated into existing emissions control. 

Combustion Chamber Design/Increase Cylinder Pressure 

Improved combustion chamber design allows for improved air management and mixing and 

improved materials that enable higher cylinder pressures. These enhancements allow a more 

complete burn of fuel and higher combustion temperatures, both of which improve engine 

thermal efficiency. Combustion chamber design enhancements will require more advanced 

materials and a more complex machining process. In addition, because higher cylinder pressures 

lead to higher temperature combustion – which fosters NOx formation – these higher pressures 

must be accompanied by concomitant reductions in NOx via other approaches, such as improved 

NOx conversion efficiency by the system aftertreatment, advanced fuel injection techniques, and 
4-13

improved engine controls. The fuel consumption benefit of these improvements is estimated at 1 

to 3 percent. 

Vyas [2002] estimates that increased cylinder pressure incur an incremental cost of $500. 

However, during discussions on site visits, it was suggested that this estimate might understate 

the cost; other information in the literature estimates $2,200 for these types of improvements 

plus advanced fuel injection [Global Insight 2004]. Combustion chamber improvements will 

entail new, potentially more expensive materials, and, as designs become more complex or 

materials harder to work with, are likely to be accompanied by increasing machining costs. 

Based on this feedback, we have estimated a range of costs from $500 up to $1,500. 

4.1.3.3 Reduce Gas Exchange Losses and Improve Air Handling 

For EGR flow to occur from the engine exhaust to the engine intake, the exhaust pressure needs 

to be higher than intake pressure. This condition, known as negative delta p (-∆p), degrades the 

efficiency of the turbocharger, which prefers a high pressure intake [NESCCAF 2009]. A 

number of approaches exist that can help reduce these “gas exchange” losses (also called “air 

handling” losses). These techniques offer benefits on high-rate EGR emissions system, as well as 

SCR-based systems. Table 4-8 summarizes systems that could reduce gas exchange loses. 

Table 4-8. Strategies to reduce gas exchange loss 

Technology % FC Benefit Capital cost Intro 

Advanced EGR 1 to 1.5 $750 2010 

Turbocharging (improved efficiency, dualstage, e-turbo) 1 to 2 $0 to $1,000 Continuous 

VVA 1 $300 2012 

Advanced EGR Approaches 

An improved EGR system can reduce the efficiency penalty due to EGR in several ways. One 

approach uses an EGR pump to drive exhaust gas from the exhaust to the intake, rather than the 

passive flow mechanism that is currently used. Such a system allows the engine intake to remain 

at higher pressure (overcoming the pressure drop condition described above), which allows for 

more effective and efficient turbocharging. This improved efficiency needs to be balanced 

against the increased parasitic load of the pump, as well as the added cost. 

Another approach to reduce the fuel efficiency penalty of EGR systems entails cooling EGR 

gases (beyond the cooling level offered by present-day cooled EGR systems). Lowering the 

temperature of the charge in the engine reduces NOx formation, which then allows an advance in 

engine timing, thereby increasing the engine’s average thermal efficiency. Such a system would 

require an additional EGR cooler. The capital cost and efficiency of this system were estimated 

as part of the NESCCAF/ICCT study at $750 and 1.2 percent, respectively [NESCCAF 2009]. 
4-14

Turbocharger Improvements 

All of the diesel engines currently sold in the medium- and heavy-duty market are turbocharged; 

of these, most use a variable geometry design. Turbochargers can enhance engine thermal 

efficiency beyond the level offered by current designs by improving the efficiency of the 

turbocharger itself; by boosting the engine intake pressure; or by reducing the turbocharger 

system response time, which allows the engine to operate in higher efficiency regimes at low 

loads. Improved response time is particularly beneficial for stop-and-go duty cycles, in which the 

engine spends more time operating in a part-load condition. 

Turbocharger efficiency is a function of compressor and turbine design, both of which are likely 

to benefit from continuous minor enhancements. Strategies for improving response time include 

dual-stage turbochargers, or using electronically actuated single-stage turbos. Approaches for 

boosting intake pressure include electrically or hydraulically assisted turbocharging. 

Enhanced turbocharger improvements are estimated to come at an incremental cost that ranges 

from cost-neutral to $1,000 and could offer up to 2 percent reduction in fuel consumption. The 

estimates of fuel savings are based primarily on feedback from site visits. As another data point, 

Walsh cites improvements ranging from 2.5 to 4.5 percent, but it is unclear what the baseline for 

this estimate is; Kruiswyk [2008] reports that similar benefits (3.7%) were demonstrated by 

Caterpillar as part of DOE-funded research. These benefits arise from improved turbocharger 

efficiency. Capital costs are based on TIAX estimates that were subsequently reviewed during 

the site visits. The nominal logic is that the cost of the above proposed enhancements are 

bracketed on the low-end by turbocharger efficiency improvement and at the high-end by the 

dual-stage turbocharging system, which would replace one larger turbocharger with two smaller 

units. Frey [2007] estimates the cost of a turbocharger for medium and heavy-duty trucks at $700 

to $1,000; Global Insights/TIAX [2004] estimates $1,700 for a large turbo-compound unit. 

Because this technology requires a smaller unit, we have used the lower cost estimate. 

Variable Valve Actuation (VVA) 

As a standalone system, variable valve actuation (VVA) can offer efficiency improvements on 

the order of 1 percent [NESCCAF 2009] by allowing the turbocharger to operate at its most 

efficient point. However, it also acts as an enabler for other technology strategies. These include 

mixed mode combustion or HCCI, for which it helps precisely control combustion events and 

waste-heat recovery, for which it can be used to maximize the energy remaining in the exhaust 

[Gutterman 2008]. The incremental cost of VVA was estimated at $300, based on estimates from 

NESCCAF [2009]; this estimate is in close agreement to that estimated for the cost of variable 

valve lift and timing in gasoline engines from the NHTSA light-duty study ($400 to $600) 

[NHTSA 2009]. 

4.1.3.4 Friction Reduction 

There are a number of low-cost opportunities to reduce engine friction. These include using 

advanced lubricants (synthetics, perhaps vapor-phase long term), improved bearings, and other 

minor modifications in moving parts within the engine (piston/cylinder, etc). Based on 

information gathered during site visits, total thermodynamic losses due to friction were estimated 
4-15

to reduce engine thermal efficiency from 1.5 to 2.5 percent.13 Using a combination of strategies, 

manufacturers were in general agreement that reducing engine friction could reduce fuel 

consumption by at least 1 percent and potentially up to 2 percent. The cost for these 

improvements ranges from minimal cost (~$0) for changes such as synthetic lubricants to $500 

for a full combination of design changes. In the light-duty rulemaking, some of the more costly 

approaches identified for reducing friction include improved material coatings, materials 

substitution, and thermal management [NHTSA 2009]. Frey [2007] estimates the cost of friction 

reduction at $500; NHTSA uses a range of $5 to $392 for large trucks. The NHTSA estimates 

scale according to the number of cylinders; they include estimates for gasoline engines that have 

up to 8 cylinders. We have used a range of $0 to $500 as shown in Table 4-9. 

Table 4-9. Friction reduction strategies 

Technology % FC Benefit Capital cost Intro 

Friction Reduction 

(lubricants, bearings, 

materials, coatings, etc) 

1 to 2 $0 to $500 Continuous 

4.1.3.5 Parasitic Engine Loads and Accessories 

Parasitic loads include accessories needed to run the engine or provide power to vehicle systems, 

such as cooling fans, the alternator, actuators, power steering pumps, air brake compressors, 

water pumps, and fuel pumps and creature-comfort loads such as the air conditioning 

compressor, ventilation, and heating system. In current vehicles, parasitic loads are primarily 

mechanically driven off the engine. 

Parasitic loads may be reduced by either improving the efficiency of mechanical systems – such 

as by using variable displacement pumps – or by switching to electric accessories. Electric 

accessories are advantageous because they can be operated on an as-needed basis – independent 

of the engine operation – and can be inherently more efficient than their mechanical counterparts 

over a wider range of operating conditions. They also allow the engine to be shut down during 

idling. 

Currently, accessory electrification is primarily considered as a component of a broader 

electrification strategy, such as hybridization or electric waste-heat recovery.14 This is because 

electric accessories require higher voltage electric systems and may require additional energy 

storage beyond that which is currently deployed on mechanical systems. In addition, due to low 

production volumes, unit prices remain high. When implemented as part of a broader 

electrification package, accessory electrification is both lower cost and more beneficial than as a 

standalone approach. Hybrid systems and electric waste heat recovery already include the 

tertiary system upgrades identified above (higher voltages and increased energy storage). 

 

13 One company lumped friction and parasitic losses together at 5 percent. We have interpreted these results to suggest that 

parasitic losses contribute 2.5 percent and friction losses contribute 2.5 percent. 

14 This includes electric turbo-compounding, a Rankine cycle coupled to a generator, and thermo-electric waste heat recovery. 
4-16

Moreover, electrified accessories offer a ready demand for electric power that is generated by 

waste heat recovery or regenerative braking. Direct utilization of this recovered electric energy 

(as distinguished from conversion to mechanical power) will be more efficient. These systems 

can also enable full, mild, or start-stop hybrids to shut the engine-off at idle. This would offer 

minor benefit on long-haul routes but significant fuel savings in the city. If hybrid production 

volumes increase, thereby reducing the cost of electric accessories, accessory electrification may 

become a more viable fuel consumption reduction strategy on its own. 

Frey estimates an incremental cost of $500. However, we received feedback from reviewers that 

these costs were far too low for today’s low volume production. Based on this feedback, in the 

near-term, electrifying accessories is estimated to add $1,000 to $2,000 incremental cost. As 

production volumes increase, this incremental cost could reduce to $500 to $1,000 – near the 

levels seen in the light-duty sector [NHTSA 2009]. The fuel consumption benefit of electrified 

accessories has been estimated to range anywhere from 1 to 5 percent [Lane 2009, Site Visits, 

NESCCAF 2009, Greszler 2006]. Most sources tend to fall in the range from 1 to 3%, so we 

have used the lower end of these estimates. 

Based on feedback received during site visits, we estimate that mechanical systems with variable 

displacement pumps can reduce fuel consumption by 1 to 2 percent, at an incremental cost of 

$200 to $500. 

Table 4-10 summarizes the Parasitic Engine Loads and Accessories benefits and capital costs. 

Table 4-10. Parasitic load reduction strategies 

Technology % FC Benefit Capital cost Intro 

Variable Displacement 

Pumps 

1 to 2 $200 to $500 2010 

Accessory Electrification 1 to 3 $1,000 to $2000 (low volume) 

$500 to $1,000 (High volume) 

2012 

4.1.3.6 Waste Heat Recovery 

Table 4-11 shows several technologies to recover engine waste heat. 

Table 4-11. Waste heat recovery strategies 

Technology % FC Benefit Capital cost Intro 

Mechanical Turbo-compound 2.5 to 3 $2,000 to $3,000 2010 

Electrical Turbo-compound 4 to 5 $6,000 to $7,000 

($3,000 to $4,000 w/Hybrid) 

2013 

Bottoming Cycle 6 to 10 $7,200 to $15,100 2015 
4-17

Waste heat recovery systems offer the opportunity to reduce the fuel consumption of highway 

vehicles by up to 10 percent. Because they rely on recovering energy from the exhaust, waste 

heat recovery has the most promise for line-haul duty cycles or other applications that entail 

extended periods operating the engine at high load. For the purposes of this study, we have 

considered waste heat recovery for line-haul and motor coach applications. A number of 

different approaches to waste heat recovery are being considered. These include mechanical and 

electrical turbo-compound systems, thermo-electric or thermo-acoustic devices, and bottoming 

cycles. 

Mechanical Turbo-Compound 

A mechanical turbo-compound system uses hot exhaust gas to drive a small gas turbine. The 

turbine is coupled to the engine shaft, thereby supplementing the engine’s power output. 

Mechanical turbo-compound systems are just coming to market: a mechanical turbo-compound 

system is implemented on Detroit Diesel’s 2008 DD15 engine; other manufacturers have not yet 

implemented this strategy on their engines. At peak load, the system offers 50 additional 

horsepower as indicated in Figure 4-3 [Heil 2009]. 

Figure 4-3. Detroit Diesel Mechanical turbo-compound system 

[Detroit Diesel 2009a] 

A similar mechanical turbo-compounding system was modeled as part of the NESCCAF/ICCT 

[2009] study and found to reduce fuel consumption by 2.5 to 3 percent; Duleep [2008] and 

information furnished on site visits also suggest benefits on the order of 3 percent. Other sources 

estimate the benefit of turbo-compounding as high as 4 to 5 percent [Kruiswyk 2008, Kruiswyk 

2006]. We have chosen to use the lower range estimates (2.5 to 3 percent), as these estimates are 

based on verifiable, real-world results (drive-cycle modeling, as in the case of NESCCAF/ICCT 

and on-road testing, as in the case of Detroit Diesel). 
4-18

NESCCAF/ICCT estimates the capital costs of a mechanical turbo-compounding at $2,650 but 

with some uncertainty due to variations as to how different manufacturers would implement such 

a system and as to which design modifications are already included in current designs. These 

estimates are based on bottom-up estimates of the design modifications needed to implement the 

system, which include port-liners to help retain thermal energy in the exhaust, VVA, and a power 

turbine. Including the cost uncertainty gives a range from $1,900 to $3,500; Duleep [2008] 

estimates costs as high as $5,000. 

Although Detroit Diesel has not published data as to the cost of their system, the up-charge from 

a Series 60 engine to their new DD15 engine is $2,500 [Merrill 2009]. The bulk of this price 

increase is likely due to the addition of a mechanical turbo-compounding system, although the 

new engine does include additional design enhancements (notably, an advanced fuel injection 

system). This data point would suggest that the addition of the mechanical turbo-compounding 

system adds between $2,000 and $2,300 to the engine price. This estimate should also be treated 

with caution, as manufacturer pricing strategies may not reflect the actual incremental cost of the 

technology – particularly during initial product introduction when economies of scale have not 

been fully realized. 

Based on NESCCAF report and information on the DD15 engine, we have estimated the capital 

cost of a mechanical turbo-compounding system to range from $2,000 to $3,000, and offer a 2.5 

to 3 percent fuel consumption reduction over a highway duty cycle. Given that the benefits of a 

turbo-compounding system depend on high-load, steady state operating conditions, we have not 

included it in the medium bore technology pathway. 

Electric Turbo-Compound 

A mechanical turbo-compounding system can be enhanced by coupling the turbine to an electric 

generator – thereby converting engine waste heat into electric power. This surplus power can be 

used to charge batteries (for later use), power electric accessories, or instantaneously supplement 

engine power. Its primary advantage compared to a mechanical system is that it decouples the 

waste heat recovery apparatus from the engine, allowing supplemental power to be used when it 

is most advantageous. 

In addition to the components required to implement a mechanical turbo-compounding system, 

an electric turbo-compounding system requires: an energy storage system; a generator that 

couples to the energy recovery turbine; an additional motor/generator that couples to the engine 

crankshaft; electric accessories; and a power electronics/control system. A schematic of a typical 

system is shown in Figure 4-4. 

SwRI modeled a 40 kW electric turbo-compound as part of the NESCCAF/ICCT work [2009] 

and estimated benefits at 4.2 percent, including electrification of accessories. Caterpillar, as part 

of DOE-funded work, modeled a system (Figure 4-4) that showed 3 to 5 percent improvement 

[Kruiswyk 2005], while John Deere investigated a system (off-highway) that offered 10 percent 

improvement [Vuk 2006]; it is unclear if this estimate represents a single point (peak) benefit or 

was meant to reflect operation under real-world conditions. None of these systems has been 

demonstrated commercially. Due to the greater certainty surrounding the Caterpillar and 
4-19

Figure 4-4. Electric turbo-compound design schematic 

[Kruiswyk 2005] 

NESCCAF estimates, we have used a range of 4 to 5 percent for our estimate. This includes the 

benefits of electric accessories. 

The costs of the electric turbo-compounding system have not been well-characterized in the 

literature. TIAX, as part of the NESCCAF/ICCT [2009] study estimated costs at $6,550, which 

includes the elements of a mechanical turbo-compounding system, plus the addition of electrical 

motors, controllers, and accessories. The John Deere work estimated $50/kW at mature 

production volumes, but it is not clear what this system includes, nor is it clear if this refers to 

capital cost or a retail price equivalent (RPE). As such, we have used the TIAX cost estimate, 

adjusted to reflect the uncertainty in the cost of a mechanical turbo-compounding system – 

$6,000 to $7,000. 

An electric turbo-compound is most attractive when implemented as part an overall vehicle 

electrification strategy. This is because a number of system components overlap with those that 

go into a hybrid. In a hybrid vehicle, an electric turbo-compounding system could be 

implemented with the marginal addition of a mechanical turbo-compound plus a small electric 

generator. The costs of such an electric turbo-compounding system incremental to a hybrid 

vehicle would then range from $3,000 to $4,000. 

Bottoming Cycle 

A number of approaches have been proposed to implement a Rankine bottoming cycle. These 

vary depending on the working fluid that is used (steam vs. organic), the output (electrical vs. 

mechanical), and the size of the system. In general, the system costs and benefits vary depending 

on system size, as well as if output is electrical or mechanical. Discussions with manufacturers 

suggested that they envision the bottoming cycle as a promising technology that could come into 

the market in the 2015 timeframe. However, it is still in the early stages of development, and 

there are significant capital cost and packaging issues to be resolved. They view the bottoming 
4-20

cycle as a bolt-on engine option, as distinguished from a package that is tightly integrated with 

the engine. 

NESCCAF/ICCT [2009] modeled a full-sized electric steam bottoming cycle. The modeled 

system was sized to capture waste heat at peak load (57 kW). However, later analysis suggested 

that most of the benefits could be realized using a smaller, lower cost system. As such, two 

smaller size systems were costed, and the fuel consumption benefit of these smaller systems was 

estimated using spreadsheet analysis. System costs were estimated from bottom-up analysis of 

the components that would be used to build such a system. The final results of the 

NESCCAF/ICCT study estimated the following capital costs and benefits for three different 

bottoming cycle systems: 

• 57 kW – 10 percent reduction in fuel use, $23,800 

• 32 kW system – 8 percent reduction in fuel use, $15,100 

• 12 kW system – 6 percent reduction in fuel use, $8,400 

System weight, again based on the components used to build the system, was estimated at 

240 lbs. 

Information gathered from the literature and during site visits shows a similar range of fuel 

consumption benefits to those estimated above15. As such, the fuel consumption benefits of 

bottoming cycle systems were estimated to range from 6 to 10 percent. The range in fuel 

consumption benefits reflects variations due to system sizing and whether the output is electrical 

(higher efficiency, more expensive) or mechanical (lower efficiency, less expensive). The 

optimal working fluid is still an open question; both steam and organic Rankine bottoming cycles 

have been considered. 

Manufacturers could not provide firm costing information on these systems, as they are still in 

the developmental stage. However, it was suggested that they expect to be able to offer payback 

in 18 to 24 months if development proceeds projected. For a line-haul truck, this would suggest a 

low-end system cost of $7,200 to $8,400 for a system that gives 6 percent efficiency16. These 

capital costs are highly uncertain, and actual system costs may be much higher. We bracket the 

high-end cost of a bottoming cycle at $15,100; this is based on the NESCCAF/ICCT estimate, 

which corresponds to a large system (32 kW) and generates electric power, which adds to the 

balance of plant. 

4.1.4 Diesel Engine Technology Packages 

We estimated for the two diesel engine sizes how the various engine technologies would be 

implemented over the next 10 years. Table 4-12 shows our projections for the large bore engines 

(11 to 15 L), and Table 4-13 shows our projections for the small bore diesel engines. Our 

projections are mostly based on information obtained during site visits. Both these tables show 

 

15 DOE 2008, pp 208-211 

16 120,000 miles per year, $4.00 gallon fuel, 6 MPG 
4-21

Table 4-12. Technology Road Map for 11-15 L Diesel Engines 

Engine 

Technology 2007 Baseline 2010 Engine 2013 Engine 2015 Engine 2015 to 

Cylinder 

Pressure 190-210 Bar Increasing Cylinder pressure 

Fuel system

1,800 to 2,200 Bar

Common rail or 33K 

psi Unit Injector 

Common rail, multiple injections per cycle, Higher injection pre

Emissions 

Control

Med-rate cooled 

EGR, DPF w/active 

regen 

SCR, low-rate 

cooled EGR, DPF 

w/passive regen

Improved cat conversion efficiency, advanced 

Aspiration VG Turbocharger Improved VG Turbocharger E-Turbo 

Engine Controls Open-loop Closed-loop Improved Closed-loop 

Waste-heat 

recovery

None Mech. Turbo- compound Mech or Electric turbo- compound Botto

Accessories Belt-driven mech. Var disp pumps -or- electric accessories Electric 

Weight 2,200 to 3,100 lbs +400 lbs +450 lbs Similar to 2013 +7

Peak Efficiency 41 to 42 % 43.2 to 44.2% 45.5 to 47.5% 47.9 to 51.4% 50.6 

Package Cost — $10K $14K $16.5K $
4-22

Table 4-13. Engine Technology road map for 6-9L diesel engines

Engine 

Technology 2007 Baseline 2010 Engine 2013 Engine 2015 Engine 2015 to 

Cylinder 

Pressure 170-280 Bar Increasing Cylinder pressure 

Fuel system

1,600 to 1,800 Bar

Common rail or Unit 

Injector 

Common rail, multiple injections per cycle, Higher injection 

Emissions 

Control

Med-rate cooled EGR, 

DPF w/active regen 

SCR, low-rate 

cooled EGR, DPF 

w/passive regen

Improved cat conversion efficiency, adva

Aspiration VG Turbocharger Improved VG Dual Stage Turbocharger E-Turbo, Dual Stage 

Engine Controls Open-loop Closed-loop Improved Closed-loop 

Accessories Belt-driven mech. Var disp pumps -or- electric accessories Electric 

Weight 1,100 to 1,700 lbs +300 lbs Similar to 2010 Similar to 2013 Simil

Peak Efficiency 40 to 41 % 42 to 43% 43 to 45% 45 to 48% 46 

Package Cost — $8.1K $10.3K $12.2K 
4-23

the category of engine improvement (e.g. fuel system), the 2007 baseline, and our estimates of 

technologies for 2010, 2013, 2015, 2015 to 2020. 

From these technology roadmaps, engine packages were estimated for 2010, 2013-2015, and 

2020 11 to 15 L engines with waste heat recovery, 11 to 15 L engines without waste heat 

recovery, and for 6 to 9 L engines. Table 4-14 shows the estimated capital costs for each 

package as well as a breakdown of the capital costs for each package component. 

These results were then use to estimate the engine efficiencies, percent improvement (relative to 

2007 baseline), capital costs, and weight for tractor trailer, motor coach, refuse hauler, and Class 

3-6 applications and transit buses. These results are summarized in Table 4-15. 

The following sections provide details as to the technologies and assumptions that were used to 

specify these engine technology packages. 

Table 4-14. Engine technology package capital cost 

Package Capital cost Components (Thousands of Dollars)17

Pkg 

Total Capital 

cost 

 Emissions  Fuel System  Combustion  Controls  Turbo  Adv EGR  VVA  Friction  Parasitics  Waste Heat 

11 to 15L Engines, with Waste Heat Recovery 

2010 $9.6 to $10.6K 9.5 0.125 0.375 — — — — 0.125 — —

2013 $13.2 to $15.2K 9.5 0.25 0.75 0.1 0.1 0.75 — 0.25 — 2.5

2015 $14.7 to $18.2K 9.5 0.375 1.125 0.1 0.5 0.75 — 0.375 0.75 3

2020 $21.4 to $25.9K 9.5 0.5 1.5 0.1 0.5 0.75 — 0.5 0.75 9.5

11 to 15L Engines, without Waste Heat Recovery 

2010 $9.6 to $10.6K 9.5 0.125 0.375 — — — — 0.125 — —

2013 $11.8 to $12.8K 9.5 0.25 0.75 0.1 0.1 0.75 — 0.25 — —

2015 $13.2 to $14.7K 9.5 0.375 1.125 0.1 0.5 0.75 — 0.375 0.75 —

2020 $13.9 to $15.4K 9.5 0.5 1.5 0.1 0.5 0.75 — 0.5 0.75 —

6 to 9L Engines 

2010 $7.6 to $8.6K 7.5 0.125 0.375 — — — — 0.125 — —

2013 $9.8 to $10.8K 7.5 0.25 0.75 0.1 0.7 0.75 — 0.25 — —

2015 $11.5 to $13K 7.5 0.375 1.125 0.1 1 0.75 0.3 0.375 0.75 —

2020 $12.2 to $13.7K 7.5 0.5 1.5 0.1 1 0.75 0.3 0.5 0.75 —

 

17 For technologies that include a cost range, the mid-point of the assumed cost is shown in the component breakdown. 
4-24

Table 4-15. Overview of engine technology packages 

% FC Imp relative to... 

Pkg 

Engine Peak 

Thermal Eff. ’07 Baseline Prev. pkg Capital cost Wt 

Tractor Trailer 

2007 41 to 42% — — — — 

2010 43 to 44% 4 to 5% — $9.6 to $10.6K +400 

2013 45 to 48% 8.8 to 11.7% 5 to 7% $13.2 to $15.2K +450 

2015 48 to 52% 13.4 to 18.3% 5 to 7.5% $14.7 to $18.2K +450 

2020 51 to 53% 18 to 21.5% 2 to 4% $21.4 to $25.9K +700 

Motor Coach 

2007 41 to 42% — — — — 

2010 43 to 44% 4 to 5% — $9.6 to $10.6K +400 

2013 45 to 48% 8.8 to 11.7% 5 to 7% $13.2 to $15.2K +450 

2015 48 to 51% 13.4 to 18.3% 5 to 7.5% $14.7 to $18.2K +450 

2020 51 to 53% 18 to 21.5% 2 to 4% $21.4 to $25.9K +700 

Refuse Hauler 

2007 41 to 42% — — — — 

2010 43 to 44% 4 to 5% — $9.6 to $10.6K +400 

2013 45 to 47% 7.8 to 9.8% 4 to 5% $11.2 to $12.2K +400 

2015 47 to 49% 12 to 14.7% 4.5 to 5.5% $12.7 to $14.2K +400 

2020 48 to 50% 12.9 to 16.4% 1 to 2% $13.4 to $14.9K +400 

Class 3-6 Box and Bucket and Transit Bus 

2007 40 to 41% — — — — 

2010 42 to 43% 4 to 5% — $7.6 to $8.6K +300 

2013 43 to 45% 7.8 to 9.8% 4 to 5% $9.8 to $10.8K +300 

2015 45 to 48% 12 to 14.7% 4.5 to 5.5% $11.5 to $13K +300 

2020 46 to 49% 12.9 to 16.4% 1 to 2% $12.2 to $13.7K +300 

4.1.4.1 2010 Engine 

Although they are not yet sold, detailed specifications of 2010 engines are currently available 

through company literature. Our 2010 engine package represents a loose consensus among the 

engine manufacturers of the technologies that they are offering in 2010-compliant engines. It is 

not meant to represent any single manufacturer’s technology strategy. This generic 2010 package 

omits two particular technology strategies that are being used on some 2010 engines: 
4-25

• High-rate EGR emissions control system: Navistar is using an EGR only-based NOx

strategy in their MaxxForce engines. Our 2010 engine package assumes that an SCR 

emissions control system is used. This reflects the fact that the other engine 

manufacturers are pursuing this approach. 

• Mechanical turbo-compounding: Detroit Diesel has included a mechanical turbocompounding system in their 2008 DD15 and DD16 engines. They are the only US 

manufacturer to do so. The inclusion of the turbo-compounding system is likely driven in 

part by Daimler/Detroit Diesel’s strong presence in Europe, in which high fuel prices are 

more likely to lead to adopting such a technology. We consider turbo-compounding to 

become a technology strategy that will be more prevalent in the 2013 to 2015 time frame. 

The technologies included in the 2010 engine package are summarized in Table 4-16. 

Table 4-16. 2010 engine technologies 

Engine Technology 11 to 15L 6 to 9L 

Cylinder Pressure 210 to 220 bar 190 to 200 bar 

Fuel injection Common rail 

2,200 to 2,400 Bar fuel injection, 

Rate shaping, multiple injections 

per cycle 

Common rail 

2,000 Bar fuel injection, 

Multiple injections per cycle 

NOx Control SCR, low-rate cooled EGR SCR, low-rate cooled EGR 

Particulate Control DPF w/passive regen DPF w/passive regen 

Aspiration Elec. Actuated VG Turbocharger Elec. Actuated VG Turbocharger 

Engine Emission Controls Open-loop Open-loop 

Waste-heat recovery None None 

Accessories Belt-driven mechanical Belt-driven mechanical 

Weight +400 lbs (SCR system and DEF ) +300 lbs(SCR system and DEF) 

Peak Thermal Efficiency 43 to 44% 42 to 43% 

Package Cost $9.6 to $10.6K $7.6 to $8.6K 

As a package, both the 2010 big-bore and medium-bore engines are estimated to offer a 4 to 5 

percent reduction in fuel consumption compared to 2007 engines. This is based on published 

estimates from several manufacturers18 and from feedback offered during site visits. Nominally, 

this fuel consumption benefit includes: 

• SCR after-treatment allows for lower EGR flow, higher temperature combustion, and 

allows for passive regeneration of the DPF — 3 percent 

 

18 Manufacturer brochures: Cummins ISX 2010 [Cummins 2009]; Detroit Diesel DD15 [Detroit Diesel 2009], and Volvo SCR 

information [Volvo 2009] 
4-26

• Fuel injection system improvements — 1 percent 

• Miscellaneous (friction, improved turbocharging) — 1 percent 

In reality, this type of breakdown masks some of the differences among technology strategies 

that have been pursued by different companies. 

The major additional capital cost for the 2010 engine is the SCR system. We have also assumed 

additional costs of $500 for more advanced fuel injection systems and design changes needed to 

enable higher cylinder pressures and $125 for friction improvement. In sum, the 2010 package is 

estimated to cost $9,600 to $10,600 for big bore engines, and $7,600 to $8,600 for medium bore 

engines. 

4.1.4.2 2013 Engine 

The 2013 engine package includes several enhancements to the 2010 engine. With static 

emissions requirements for the first time in a decade, manufacturers will be able to focus on 

improving the fuel efficiency of their engine offerings. Some of the design changes that could be 

expected in this timeframe are: 

• Closed-loop engine controls will be enabled by the onboard diagnostic systems mandated 

by the EPA. This change, coupled with continuing improvement of NOx -reduction 

catalysts will enable engines to be operated at higher thermal efficiency across their 

operating map. (1 to 2 percent fuel consumption benefit) 

• Turbocharger efficiency improvements plus advanced EGR approaches to improve air 

handling. Medium-duty vehicles and refuse haulers might use dual-stage or series 

turbochargers due to their favorable response characteristics. (1 to 2 percent fuel 

consumption benefit) 

• Incremental Friction improvements (0.5 percent fuel consumption benefit) 

• Mechanical turbo-compounding, including VVA (only in heavy-duty, on highway 

vehicles) (2 to 2.5 percent fuel consumption benefit) 

In combination, these technologies would increase brake thermal efficiency in 11 to 15L engines 

by 5 to 7 percent compared to the 2010 engine package or 9 to 12 percent compared to the 2007 

baseline. Turbo-compounding is not included for refuse vehicles, which lowers the efficiency 

improvement to 4 to 5 percent. The medium-bore engines would not include mechanical turbocompounding but could benefit more from closed loop controls given that these engines operate 

over a wider portion of their map. These engines are projected to improve by 4 to 5 percent 

compared to the 2010 medium bore package or 8 to 10 percent compared to the 2007 baseline. 

Table 4-17 summarizes 2013 engine technologies. 

Additional capital costs for the 2013 system (beyond those projected for 2010) include 

continuing enhancement to the fuel system and combustion chamber (~$500 total), friction 

reduction, advanced cooled EGR (~$750), and advanced controls, sensors, and actuators for 

closed-loop controls (~$100) for both the big-bore and medium-bore offerings. 
4-27

Table 4-17. 2013 engine technologies 

11 to 15L 6 to 9L 

Cylinder Pressure 220 to 230 bar 210 to 220 bar 

Fuel injection 2600 bar, piezo-electric system 2400 bar 

Emissions system 2010, w/improved catalyst 

conversion efficiency 

2010, w/improved catalyst 

conversion efficiency and 

advanced EGR or VVA 

Aspiration Improved VG Turborcharger, 

advanced EGR Dual-stage VG Turborcharger 

Engine Controls Closed-loop Closed-loop 

Waste-heat recovery Gen 1 Mech. Turbo-compounding 

(Optional) 

Cooled EGR 

Accessories Belt-driven mechanical Belt-driven mechanical 

Weight +50 lbs (Turbo-compounding) Same as ‘10 

Peak Thermal Efficiency 45 to 48% (w/WHR) 

45 to 47% (w/out WHR) 43 to 45% 

Package Cost $13.2 to $15.2K (w/WHR) 

$11.8 to $12.8K (w/out WHR) $9.8 to $10.8K 

The big-bore engines, with the exception of the refuse hauler, also include mechanical turbocompounding ($2,000 to $3,000) and an improved turbocharger ($100). The medium-bore 

engines and the refuse hauler both include a dual-stage turbocharger ($700, incremental to a 

single-stage). 

4.1.4.3 2015 Engines 

The technology packages that might be marketable in the 2015 timeframe are far less certain 

than the 2010 packages (which are soon to begin initial roll-out), and the 2013 engines, which 

are already being developed as part of the standard product development cycle. 

During this timeframe, it is possible, perhaps likely, that hybrid-electric vehicles will come into 

the medium-duty segment, and perhaps in line-haul applications, in large numbers. If hybrids do 

capture a large portion of market, this would likely lead to a technology strategy that includes 

electric accessories, e-turbo, and electric waste heat recovery (electric turbo-compounding, 

thermoelectric devices, or electric bottoming cycle) – all of which can interact synergistically 

with a hybrid vehicle. In this scenario, even non-hybrid vehicles could transition to some of these 

technologies if high production volumes from hybrids bring the costs down. 

In the absence of electrification, manufacturers would focus instead on reducing parasitic loads 

using technologies such as variable displacement pumps and would continue to pursue 

mechanical waste heat recovery opportunities, such as mechanical turbo-compounding (perhaps 

enhanced from the 2013 incarnation) and mechanical bottoming cycle systems. 
4-28

In parallel, engine manufacturers are likely to roll out new engine designs during this timeframe. 

These could include next-generation fuel systems that could push fuel injection pressures past 

3,000 bar using piezo-electric or super critical fuel injection and new combustion chamber 

designs capable of still higher efficiency combustion, as well as reduced friction. VVA could 

come into the medium-duty segment during this timeframe. Table 4-18 summarizes the 2015 

engine technologies. 

Table 4-18. 2015 engine technologies 

Engine Technology 11 to 15L 6 to 9L 

Cylinder pressure 230 to 240 bar 220 to 230 bar 

Fuel injection 3,000 bar super critical system 2600 bar, piezo-electric 

system 

Emissions system Same as 2013 Same as 2013 

Aspiration Electrically boosted VG 

Turbocharger 

Electrically boosted Dualstage VG Turbocharger plus 

VVA 

Engine Controls Improved Closed-loop Improved Closed-loop 

Waste-heat recovery Mech. turbo-compounding, 

Electric turbo-compounding, or 

None 

None 

Accessories Variable displacement pumps -orelectric accessories Variable displacement pumps 

-or- electric accessories 

Weight Similar to 2013 Similar to 2013 

Peak Thermal Efficiency 48 to 51% (w/WHR) 

47 to 50% (w/out WHR) 

45 to 48% 

Package Cost $14.7 to $18.2K (w/WHR) 

$12.7 to $14.2K (w/out WHR) 

$11.5 to $13.0K 

In combination, the 2015 big-bore package is projected to reduce fuel consumption by 5 to 

7.5 percent compared to the 2013 engine, or 13.5 to 18 percent total. For the smaller 6 to 9L 

engines, the fuel consumption reduction is estimated to range from 4.5 to 5.5 percent compared 

to the 2013 engine package or 12 to 15 percent compared to the 2007 baseline. The range in 

percent improvement reflects the differences between mechanical and electric technology 

strategies. These improvements include: 

• Improved fuel injection, combustion chamber design – 2 percent fuel consumption benefit 

• Controls, e-turbo – 1 percent fuel consumption benefit 

• Friction – 0.5 percent fuel consumption benefit 

• Accessories – 1 percent (variable displacement pumps) to 2 percent (electric accessories) fuel 

consumption benefit 
4-29

• Waste-heat – 0.5 percent to 2 percent fuel consumption benefit (11 to 15L Tractor trailer 

only) 

Additional capital costs for this system include parasitic load reduction strategies ($500 to 

$1,000), friction reduction ($125), electric turbocharging, and evolutionary engine improvements 

($500). The marginal cost of adding an electric turbo-compound system to a big bore engine that 

is hybridized and includes a mechanical turbo-compound is estimated at $1,000. 

4.1.4.4 2016 to 2020 Engine + Bottoming Cycle 

Beyond 2015, engine improvements are highly uncertain. The major addition to the 2020 engine 

package is a bottoming cycle, although we speculate that engines will continue to benefit from 

conventional incremental improvement opportunities, such as higher cylinder pressure, improved 

fuel systems, and better controls. During this timeframe, we also speculate that electrification 

technologies will have come into the market and fully realize savings from high volume. 

Table 4-19. 2016 to 2020 engine technologies 

Engine Technologies 11 to 15L 6 to 9L 

Cylinder pressure 240 bar 220 to 230 Bar 

Fuel injection 4,000 bar super critical 

atomization 

3,000 bar 

Emissions system Same as 2015 Same as 2015 

Aspiration Electrically boosted VG 

Turbocharger 

Electrically boosted Dualstage VG Turbocharger 

Engine Controls Improved Closed-loop Improved Closed-loop 

Waste-heat recovery Bottoming cycle (optional) None 

Accessories Electric accessories Electric accessories 

Weight +200 to 300 lbs 

(bottoming cycle) 

Same as 2015 

Peak Thermal Efficiency 51 to 53% (w/WHR) 

47 to 50% (w/out WHR) 

46 to 49% 

Package Cost $21.4 to $25.9K (w/WHR) 

$13.9 to $15.4K (w/out WHR) 

$12.2 to $13.7K 

The big bore engine with waste heat recovery (WHR) offers an incremental savings of 2 to 

4 percent compared to the high-end 2015 engine, giving a total fuel consumption reduction of 18 

to 22 percent compared to the 2007 baseline. This is based on the assumption that the electric 

turbo-compound system (~4 to 5 percent efficiency improvement) in the 2015 engine is replaced 

with a bottoming cycle that offers 6 to 8 percent efficiency improvement. 

Depending on if the 2015 engine is assumed to include a mechanical or electric turbocompounding system, the incremental cost of the bottoming cycle is $4,000 to $9,000. We have 
4-30

assumed that bottoming cycle costs range from $8,000 to $11,000, which lies towards the low 

end of the range specified. 

The medium bore engine does not include significant changes compared to the 2015 engine. We 

have included continued development of fuel systems, combustion, and friction reduction, which 

are estimated to offer fuel consumption reductions on the order of 1 to 2 percent. 

4.1.5 Gasoline Engine Technologies 

Information on gasoline engine technologies was gathered primarily from the NHTSA light-duty 

study [2009], with additional supplemental information provided by the EPA [2008b] and by 

manufacturer websites. We received very little specific information regarding class 2b vehicles 

during our site visits. 

This section will first define the baseline engine, then briefly discuss individual technologies that 

can be integrated into 5 to 8L gasoline engines, and finally combine these technologies into 

engine packages. Because both gasoline and diesel engines are present in this market segment, 

we have treated a transition to diesel engine technology as one potential “gasoline” engine 

package. 

4.1.5.1 Baseline Gasoline Engine 

Currently, both V8 and V10 gasoline engines, ranging in size from 5.4L to 8.1L, are sold for use 

in medium- and heavy-duty applications. We have assumed that the baseline gasoline engine is a 

port fuel injected, naturally aspirated, fixed valve engine with 8 to 10 cylinders. This is based on 

survey of Class 2b gasoline engines that are currently sold.19

4.1.5.2 Fuel Efficiency Strategies for Gasoline Engines 

The NHTSA light-duty vehicle rulemaking uses a decision tree to package engine technologies 

together. This approach involves incrementally adding technologies in a way that reflects an 

anticipated manufacturer technology roadmap. Given that their analysis extends up to V8 

engines for use in trucks that weigh up to 8,500 lbs, we felt it reasonable to extend their analysis 

to the V8 and V10 engines that are currently used in the Class 2b vehicles. As appropriate, we 

have scaled the NHTSA cost estimates for engine size using similar methodology to that applied 

in their rulemaking. 

One of the intricacies of the decision-tree approach employed by NHTSA is that changes in 

engine configuration can dictate a different technology path. For example, according to their 

analysis, engines that use an overhead valve (OHV) configuration would adopt technologies in a 

different order than those with a single (SOHC) or dual (DOHC) overhead cam. A review of 

currently available large gasoline engines showed that they primarily use an SOHC 

configuration. As such, we have followed the technology pathway that is defined for SOHC and 

DOHC engines. A summary of these NHTSA-derived estimates is shown in Table 4-20. In this 

 

19 This is based on survey of Class 2b gasoline engines that are currently sold [Ford 2009a, Ford 2009b, GMC 2009, Dodge 2009] 
4-31

Table 4-20. Gasoline engine technology capital costs and benefits 

Incremental Capital Cost and Benefit Technology Incremental 

to... % FC Benefit Cost 

Friction reduction — 0.5 to 2.5% $110 to $500a

Variable Valve Timing (VVT) Friction 1 to 3% $122 

Variable Valve Lift (VVL)b VVT 1 to 3.5% $400 to $750 

Cylinder Deactivationc VVL 2.5 to 3% $75 

Stoichiometric GDId Cyl. 

Deactivation 2 to 3% $512 to $930 

Turbo charging and 

Downsizing S-GDI 2.1 to 2.2% $1,229 

Diesel — 19 to 24% $7,900 to $9,400 

Lean-burn GDI S-GDI 10 to 14% $750 

Gasoline HCCI S-GDI 10 to 12% $685 

Accessory Electrification Applicable to 

any package 2 to 4% 

$1,000 to $2,000 

(current) 

$500 (high volume) 

a

$13 to $49 per cylinder + $5 for lubricants 

b

$51 per cylinder for discrete VVL; $70 to $75 per cylinder for continuous VVL 

c

 Offers marginal benefit on DOHC engines; these benefits reflect SOHC 

d

$64 to $93 per cylinder

table, the capital costs and benefits of each technology are expressed in terms of their 

incremental benefit to the technology specified in the second column. 

The following is a description of each of the technologies included in the table: 

Friction reduction: Includes advanced lubricants, low tension piston rings, roller cam followers, 

improved crankshaft design and bearings, material coatings, material substitution, and piston and 

cylinder surface treatments. 

Variable Valve Timing (VVT): Reduces gas exchange loss by altering the timing of the intake 

and exhaust valves. Several implementations were considered, including intake cam phasing, 

coupled cam phasing, and dual cam phasing. 

Variable Valve Lift (VVL): Reduces gas exchange loss by altering the cam profile; this reduces 

the amount of throttling required. This can be implemented as a series of discrete cam profiles, 

or, for slightly improved efficiency, a continuously varying profile. 

Cylinder Deactivation: Reduces gas exchange loss by deactivating half of the cylinders when 

the engine is operating at low load. 
4-32

Stoichiometric Gasoline Direct Injection (S-GDI): Injects gasoline directly into the cylinder, 

which cools the air-fuel mixture as gasoline evaporates. This allows for higher compression 

ratio, which in turn, reduces exhaust gas losses. 

Turbocharging and Downsizing: Boosting an engine (increasing the intake pressure using a 

turbocharger) can be used to increase the power density of an engine. This enables engine 

downsizing – which reduces engine friction. Turbocharging also reduces gas exchange losses by 

increasing engine load and reducing throttling. 

Diesel: Shifting from gasoline to diesel engines offers significant fuel efficiency benefits. This is 

primarily due to higher compression ratios and reduced gas exchange losses. However, it should 

be noted that, due to emissions regulations (which have degraded the efficiency of diesels) and 

advances in spark-ignition technology (e.g., HCCI, turbocharging), the difference between 

gasoline and diesel thermal efficiency has narrowed considerably. NHTSA estimates the 

incremental cost of a diesel engine with 2010 emissions treatment at $7,000; this estimate may 

be too low. A review of current (2007-compliant) diesel engine up charges on Dodge [2009], 

GMC [2009], and Ford [2009a] trucks shows that incremental costs range from $6,100 to $8,600. 

Feedback offered on site visits suggested that the 2010 emissions package for these vehicles will 

add an additional $1,800. Adding this estimate to the range of current engine prices, we have 

assumed an incremental cost for diesel of $7,900 to $9,400. The NHTSA rulemaking does not 

assume a fuel consumption benefit for using an SCR system; we have used their estimate but 

note that it may underestimate the efficiency gain in going from a gasoline to diesel engine. 

Lean-Burn Gasoline Direct Injection (LB-GDI): Uses a lean, carefully controlled fuel 

injection to improve efficiency beyond that offered by stoichiometric GDI by reducing gas 

exchange losses. This technology requires the addition of a lean NOx trap and ultra-low sulfur 

gasoline. Because it requires low-sulfur gasoline, NHTSA did not include it in their rulemaking. 

We have included it here as a separate package; its capital costs and benefits use estimates from 

EPA and are expressed relative to stoichiometric GDI. 

Gasoline HCCI: Gasoline homogeneous charge compression ignition (HCCI) uses pre-mixing 

of fuel and tightly controlled combustion conditions to achieve higher compression ratios than 

can be achieved by conventional gasoline engines. This allows the gasoline engine to approach 

diesel-like efficiencies. These systems are still in development and hence are unlikely to come to 

market in the near-term. NHTSA did not include them for this reason; we have included them as 

a possible market entrant in 2014. The cost of gasoline HCCI is estimated from EPA [2008b] at 

$685, incremental to the cost of stoichiometric GDI. 

Accessory Electrification: The NHTSA rulemaking does not include improved accessories as 

an option for large trucks. This is because they are not currently offered at high volume and will 

likely require higher voltage (42V) systems. We have included accessory electrification here on 

the logic that our analysis has a longer time horizon than does the NHTSA rulemaking. For the 

vehicle classes to which electric accessories do apply, NHTSA estimates an incremental cost of 

$275 to $330 for technologies such as electric power steering, an improved alternator, electric air 

conditioning, and electric coolant pumps. We have extended these estimates to include additional 

hardware to go to a 42V system (estimated at $200). This give a high-volume cost of $475 to 

$530. At current low volumes, costs are much higher – we have estimated $1,000 to $2,000, 
4-33

based on feedback received during site visits. Electric accessories are estimated to offer a 2 to 4 

percent fuel consumption benefit. 

4.1.6 Class 2b Engine Packages 

We have largely followed NHTSA’s lead in packaging gasoline engine technologies for Class 2b 

vehicles but have included additional packages for HCCI and lean-burn GDI, with the caveat that 

these are still in the development stage and, in the case of lean-burn GDI, require low-sulfur fuel. 

The capital costs, benefits, and description of technologies for each of the Class 2b engine 

packages are included in Table 4-21. We have not included electric accessories in any of the 

engine packages; rather, they may be considered as an add-on to any of the future packages. To 

clarify, our approach for these engine packages differs from that used in packaging diesel 

engines in several ways: 

 Both diesel and gasoline engines are considered. It should be noted that, if the diesel 

pathway is followed, then the technology roadmap described for small (6 to 9L) diesels 

may be followed. The logic behind this approach is that both gasoline and diesel engines 

compete in this market segment. 

 Most of the technologies identified are available and being deployed in some vehicle 

segments now. As such, packages are defined in terms of how far down the NHTSA 

decision tree they rest, as distinguished from their year of introduction. For example, the 

“Turbo GDI” package builds on the GDI package (by turbocharging and downsizing the 

engine). 

Table 4-21. Class 2b engine technology packages 

Package Capital Cost FC Benefit 

Intro 

Year 

Friction VVL VVT Cyl. Deactivation S-GDI Turbo Gasoline HCCI LB-GDI Diesel 

VVL and Turbo $632 to $1,372 2.5 to 9% 2010 X X X 

GDI $1,200 to $2,400 7 to 14% 2012 X X X X X 

Turbo GDI $2,500 to $3,600 11 to 17% 2012 X X X X X X 

’10 Diesel $7,900 to $9,400 19 to 24% 2010 X X

L.B. GDI $3,250 to $4,350 20 to 29% 2014 X X X X X X X 

Gas HCCI $3,185 to $4,285 20 to 27% 2014 X X X X X X X 

Elec. Acc. $500 to $2,000 2 to 4% 2014 
4-34

4.2 Aerodynamics 

4.2.1 Overview 

The power (P) required to overcome aerodynamic drag on a vehicle is a function of the vehicle’s 

frontal area (A), the vehicle velocity (V), air density (ρ), and the vehicle’s shape (expressed in 

terms of the coefficient of drag, or CD): 

P = 0.5 ρ V3 A CD Equation 3 

Of these factors, vehicle velocity has the greatest influence at high vehicle speeds. This is 

because aerodynamic drag increases with the cube of speed. The relative impact of reducing 

aerodynamic drag is illustrated in Figure 4-5 for an 80,000 lb vehicle with a frontal area of 116 

ft2

. As shown in this figure reducing aerodynamic drag by a third from 0.6 to 0.4 has a large 

effect at higher speeds. The power to overcome drag dominates the power to overcome rolling 

resistance after about 50 to 65 MPH. 

Figure 4-5. Influence of aerodynamic drag on vehicle power demand as a 

function of speed 

A widely cited rule of thumb in industry is that, for a vehicle traveling 60 MPH, a 2 percent 

reduction in aerodynamic drag reduces fuel consumption by 1 percent. The practical outcome of 

this observation is that reducing aerodynamic drag offers the greatest benefit on duty cycles that 

travel at highway speeds for a good portion of their trips. Table 4-22 shows the approximate 

benefit, based on assumed highway speeds, of reducing aerodynamic drag for the various truck 
4-35

classifications that form the focus of this study. As shown, the tractor trailer and the motor coach 

both gain the most benefit from improving the vehicle’s aerodynamic drag. In addition, both 

straight box trucks and Class 2b pickups and vans could benefit from these types of 

improvements – particularly for trucks within these classes that spend significant time on the 

highway. The bucket truck, refuse vehicle, and urban transit bus – which spend the majority of 

their time traveling at low speeds – gain minimal benefit from drag reduction. 

Table 4-22. Impact of Highway Speed on Aerodynamic Improvement Potential 

Truck Application 

Highway Average 

Speed 

(MPH) 

Approximate % FC 

Benefit for 1 Percent 

Reduction in CD

20

Efficacy of 

Aerodynamic 

Improvements 

Tractor trailer 55 to 65 ~0.5% High 

Motor Coach 50 to 60 ~0.4% High 

Straight Box Truck 25 to 35 ~0.25% Medium 

2b Pickups and Van 25 to 35 ~0.25% Medium 

Bucket Truck 15 to 20 ~ 0.1% Low 

Refuse 10 to 15 < 0.1% Low 

Urban Transit 10 to 15 < 0.1% Low 

It should also be noted that in addition to lowering the drag coefficient (CD), aerodynamic force 

could also be reduced by either reducing the average speed of the vehicle (lowering the V3

 term 

in Equation 2), or reducing the vehicle’s frontal area (lowering the A term in Equation 2). The 

efficacy of limiting road speed is discussed in Section 4.8. Reducing vehicle frontal area is a 

challenging prospect for most of the vehicle classes under consideration given their operational 

characteristics. For example, reducing the height of the trailer in a combination vehicle would 

reduce the total frontal area of the vehicle but at the expense of either ground clearance or cargo 

capacity. The exception to this is the Class 2b pickups and vans, which have less rigidly defined 

operational parameters. 

Estimates of the fuel savings potential of aerodynamic devices are based on a literature review of 

and discussions with sources that include truck manufacturers, trailer aerodynamic device 

manufacturers, and labs that have conducted wind tunnel test or computational modeling of 

different fuel savings technologies. The results reported by these sources tend to be reported 

either as percent changes to the coefficient of drag (CD) or fuel consumption benefit, typically at 

a constant speed of 55 to 65 MPH. For cases in which benefits are reported in terms of a 

coefficient of drag, the fuel consumption benefit is assumed to be one half that of the CD at 65 

MPH (i.e., 2 percent change in CD gives 1 percent change in FC) and one quarter that of the CD

at 30 MPH (i.e., 4 percent change in CD gives percent change in FC). 

 

20 Note that the data shown in this column reflects estimates based purely on average vehicle speed – it does not take into account 

the non-linear impacts of deviations from this average speed. Actual simulation over a well-defined drive cycle would be needed

to estimate the actual elasticity of CD on fuel consumption 
4-36

Data from this literature review may be based on the results of computational fluid dynamics 

(CFD) modeling, wind tunnel tests simulating travel at constant speed (typically 65 MPH) for 

both full-sized or scale-model vehicles, controlled tests on a track (typically at a constant speed 

of 65 MPH)21, or actual in-use results from fleet testing. None of these measurement techniques 

is perfect. For example, wind tunnel tests offer robust measurements of the change in CD under 

controlled conditions but do not offer actual estimates of fuel consumption benefit in real-world 

operation. A summary of these strengths and weakness is provided in Table 4-23. To the extent 

possible, the data reflects the fuel consumption benefits or drag benefits of wind-averaged data 

(i.e., collected over a sweep of wind headings). Wind-averaged measurements are standard 

practice in wind tunnel tests; similarly, real-world fleet tests should reflect wind-averaged 

results. It is less clear that this is the case for results conducted on track tests at constant speed. 

Table 4-23. Comparison of aerodynamic evaluation methodologies 

Strengths Weaknesses 

Computational 

Fluid Dynamics 

(CFD) Modeling 

• Simple, low cost 

• Useful for initial screening and 

down-selecting designs 

• Does not accurately capture 

complexity of vehicle dynamics 

Wind tunnel 

testing 

• Fully controlled environment 

• Robustly estimates CD

• May miss some nuances of actual 

in-use vehicle dynamics 

• Does not directly measure fuel 

consumption 

Test track 

• Actual data on fuel 

consumption 

• Controlled conditions 

• Does not necessarily represent a 

realistic duty cycle 

• High variance between individual 

test runs 

• May not test wind-averaged drag 

In-use fleet test 

• Realistic duty cycle 

• Actual data on fuel 

consumption 

• Results may not be broadly 

applicable 

The results presented in the technology matrix presented in Section 3 represent a synthesis of the 

results from a number of sources. For devices for which there is wide variance in the reported 

benefits, we have attempted to explain possible reasons for the discrepancy and make reasoned 

judgments about which results seem most credible. We have attempted to group similar 

aerodynamic devices together. As such, a range in device costs and benefits reflects both 

variations between implementing a given device and variations due to duty cycle. 

The next sections discuss our research on the capital cost and benefits for aerodynamic devices 

for heavy duty applications of Class 8 tractors and trailers, straight trucks, and motor coaches 

and for light duty applications of Class 2b pickups and vans. No estimates were made for bucket 

trucks, refuse haulers, or transit buses. These applications spend a large fraction of their duty 

 

21 These tests typically follow the SAE Type II test procedure. This is a well-defined procedure for measuring fuel use across 

multiple trials under controlled test conditions. However, the SAE Type II test does not define an actual drive cycle. 
4-37

cycle performing low speed stop-and-go driving and therefore will not benefit as much as other 

applications. 

4.2.2 Class 8 Tractor Trailers 

Strategies for reducing the aerodynamic drag of combination tractor trailers can be broadly 

categorized according to whether they focus on the tractor, the trailer, or optimization of the 

tractor/trailer interface. Our estimates for the potential fuel consumption reduction for these 

different categories are summarized in Table 4-24. Of these categories, present-day trucks have 

already adopted many of the improvements that reduce drag on the tractor, and fleets have 

Table 4-24. Class 8 tractor trailer aerodynamic technologies 

Technology FC Benefit CD Improvement Capital Cost Status 

Tractor Aero 

Roof Fairing 7 to 10% 15 to 20% $500 to $1,000 Standard 

Deflector, Day cab 4 to 7% 13% $1,000 to $1,300 Most 

Chassis Skirt 3 to 4% 4 to 7% $1,500 to $2,000 50 to 60% 

Side Extender 2 to 3% 4 to 5% $300 to $500 80 to 90% 

Next Generation Aero 3 to 4% 6 to 8% $2,750 2012 Intro 

Trailer Aero 

Partial Skirt 2 to 3% 2 to 6% $1,500 to $2,000 Demos 

Full Skirt 4 to 5% 5 to 11% $2,000 to $4,000 Demos 

Partial Gap 1 to 2% 2 to 4% $800 to $1,000 Demos 

Full Gap Fairing 2 to 3% 4 to 6% $1,000 to $1,450 Demos 

Boat Tail 4 to 6% 6.5 to 9% $1,500 to $2,000 Demos 

Aero Packages 

No aero -10 to -12% -22 to -25% — — 

Smartway Tractor — — — Baseline 

Smartway Tractor + 

Smartway Trailer 

5 to 6% 10 to 12% $3,000 per trailer 2010 to 2012 

Improved Smartway 

Tractor + Smartway 

Trailer 

7 to 9% 15 to 17% $2,750 + $3,000 

per trailer 

2012 to 2013 

Full Aero Tractor & 

Trailer 

11 to 12% 22 to 24%22 $2,750 + $4,000 

per trailer 

2013 to 2014 

 

22 Assumes CD benefit of full trailer package is 17 to 19 percent 
4-38

adopted many strategies that aim to optimize the tractor/trailer interface. However, trailer 

aerodynamic design improvements have not yet been adopted into the fleet in significant 

numbers. We assume that the baseline vehicle has a CD of 0.58 to 0.6 based on data from a 

number of sources [Marinko 2009, Salari 2009, Storms 2004, Ang-Olson 2002].23 This is 

consistent with an aerodynamic tractor pulling a standard 53’ box trailer without any 

aerodynamic improvements. The aerodynamic tractor includes an integrated roof fairing, cab 

side extenders, chassis fairings, and an aerodynamic chassis. These features are described in 

greater detail below. 

Given the prevalence of aerodynamic tractors already on the market, the best opportunities for 

further reducing aerodynamic drag of combination trucks stem from deployment of trailer 

aerodynamic devices and from improved design integration between the tractor and the trailer. 

Coupled with continued incremental improvements to the tractor, these improvements to vehicle 

aerodynamics have the potential to reduce drag by 25 to 30 percent and reduce fuel consumption 

by 10 to 15 percent. 

There may be an additional opportunity to reduce vehicle drag by incentivizing independent 

owner operators and less-than-truckload fleets to more fully adopt drag reduction devices that are 

already available and prevalent in the large commercial fleets. 

4.2.2.1 Tractor Aero 

Modern tractors have already introduced a number of design features that optimize body 

contours to streamline airflows. These include aerodynamic bumpers and mirrors, sloped hoods 

and windshields, and rounded corners. In addition, OEMs offer several aerodynamic options for 

Class 8 tractors. These include “roof fairings” (also called “air fairings” or “roof deflectors”), cab 

side extenders, and chassis fairings (also known as “chassis skirts”, “fuel tank skirts”, or “fuel 

tank fairings”). Examples of these different devices are shown in Figure 4-6 for a typical sleeper 

tractor. Roof fairings match the height of the tractor to the height of the trailer and streamline the 

air flows coming off the top of the vehicle. Cab side extenders reduce the gap between the tractor 

and the trailer, thereby reducing airflow through the gap. Chassis fairings streamline flows along 

the side of the tractor. A partial chassis fairing extends the length of the cab (typically just 

covering the fuel tank), while a full fairing extends all the way to the first drive axle. 

 

23 The NESCCAF/ICCT study assumes an average drag coefficient of 0.63. However, this is based on data from an older Kenworth 

T600 Truck, which is not a full Smartway cab; it is meant to reflect an average of the line-haul trucks that are currently on the 

road. In separate conversations with Kambiz, Salari, and Fritz Marinko, it was suggested that a slightly lower baseline CD would 

be appropriate. 
4-39

Figure 4-6. Standard sleeper tractor aero technologies [Kenworth 2008] 

These devices are also available for day cabs although the options tend not to be as integrated in 

design and function. 

In tandem with deployment of these aerodynamic designs, it is standard practice to optimize the 

interface between the tractor and the trailer for the specific load that is being hauled. This entails 

adjusting the height and profile of the roof fairing to match the trailer, adjusting the position of 

the wheels, and adjusting the length of the cab side extender. For example, a tractor that typically 

pulls a box trailer would use a higher roof fairing than one that typically transports equipment on 

a flatbed. 

In combination, a fully aerodynamic tractor that is properly matched to its load has been shown 

to reduce aerodynamic drag by 17 to 25 percent compared to a baseline vehicle that does not 

implement any of the devices described above [Cummins 2007, Kenworth 2008, Leuschen 

2006]. This fully aerodynamic tractor would reduce fuel consumption by approximately 10 to 

12 percent. Most of this benefit comes from the roof fairing, but other features offer significant 

additional benefit. 

Additional opportunities for reducing drag on the tractor were identified during site visits and 

discussions with experts. These include minor modifications to airflows along the chassis (for 

example, reshaping the hood, windshield, and front bumper), reducing the aerodynamic profile 

of mirrors; improving airflows along the underbody, and adding skirts or fairings to the wheel 

wells. Successfully implementing these future adjustments could require changes to existing 

regulations and operational considerations related to mirror size and tractor width. They must 

also be balanced against other considerations such as providing adequate air flow for cooling the 

engine system, which is a frequently sited concern for design changes to the underbody or the 

front grill. One manufacturer suggested that the packaging flexibility offered by electrified 

accessories – which need not be coupled directly to the engine – might yield significant benefits 

as an enabler for improved aerodynamics. 
4-40

Another factor that can increase aerodynamic drag is truck selection and specification. While the 

most aerodynamic vehicles have adopted many, if not all, of the features described above, there 

continues to be some market pull for tractors that have a more traditional flat-nose design and 

that do not include all of the fairings described above. This tendency is particularly prevalent 

among independent-owner operators, who are more sensitive to first cost and more likely to 

consider vehicle styling in their purchase. For example, according to company literature from 

Navistar, their ProStar tractor – which is marketed to large fleets – has 7 percent lower drag than 

their LoneStar offering, which is marketed to independent owner/operators; during site visits, 

other manufacturers suggested similar differentiation between their aerodynamic models and 

their flat-nosed, less aerodynamic options. Figure 4-7 compares the vehicle styling of the two. 

 

Prostar LoneStar 

Figure 4-7. Prostar and LoneStar Tractors [Navistar.com] 

It should also be noted that several features that are commonly purchased by truck buyers have a 

negative effect on aerodynamic drag. These include large mirrors (2 percent reduction in drag, 

compared to aerodynamic mirrors), fender mounted spot mirrors (1 to 2 percent per mirror), bug 

deflector (~2 percent), and splash guards (~0.6 percent) [Leuschen 2006, Site Visits]. 

Feedback during site visits with manufacturers suggested that these types of improvements to the 

tractor’s aerodynamics could yield an additional 3 to 4 percent fuel consumption benefit beyond 
4-41

that seen in today’s Smartway-certified tractors. The combined cost of these “next generation” 

improvements is estimated to be $2,750. This estimate is arrived at as follows: 

• $750 for additional cab streamlining. This is based on estimates from Vyas [2002] which 

estimates the incremental cost of cab streamlining for a previous generation of 

aerodynamic improvement. 

• $500 for an underbody treatment. This is similar to the cost of a partial chassis fairing or 

a standard cab side extension. 

• $1,500 for wheel skirts. This is similar to the cost of a chassis fairing. 

4.2.2.2 Trailer and Tractor/Trailer Interface Aerodynamics 

Salari [2008] estimates that the trailer contributes 34 percent of the total vehicle drag, and 66 

percent is contributed by the tractor. However, as discussed above, the tractor aerodynamic 

profile has already been largely optimized. Going forward, there are a number of opportunities 

available to reduce trailer drag and, by potentially optimizing the tractor and trailer as a single 

unit, to better integrate the design between the two. It is further estimated that of the 34 percent 

drag contribution on the trailer, 16 percent comes from the trailer body and 18 percent from the 

trailer axle and wheels (i.e., the underbody). In addition, a portion of the drag off of the tractor 

may be reduced by optimizing the tractor/trailer interface. 

Current trailers do not typically include any aerodynamic features. A number of devices have 

been tested in limited fleet deployments and are commercially available as retrofit options from a 

number of small independent companies. None of the major trailer manufacturers or truck OEMs 

has currently integrated trailer aerodynamics into their product offerings, and users have not yet 

widely adopted them as retrofit options. 

Options for reducing the aerodynamic drag of the trailer underbody include side skirts of varying 

lengths and configurations, belly boxes, or axle bogey fairings (Figure 4-8). 

The drag profile of the trailer body may be reduced by aerodynamic boat tails (also called “base 

flaps”, “base treatment”, etc.), which include both structural and inflatable devices that extend 

off the rear of the trailer (Figure 4-9). Drag from the tractor/trailer interface can be addressed by 

design modifications to either the tractor or the trailer; examples of trailer modifications are 

shown in Figure 4-10. 

There is wide range of estimates in the literature as to the efficacy of trailer aerodynamic 

devices, particularly in comparison to the relatively narrow range of estimates we found for 

tractor drag reduction. This is due to a number of factors: there are many different configurations 

and no clear consensus as to the single best approach, and there have been limited numbers of 

real world fleet tests, meaning that data sources are drawn largely from track tests by device 

makers or wind tunnel laboratory tests. It is also possible that the current approach of using 

retrofit devices that are installed post-manufacture leads to sub-optimal implementation. An 

additional confounding factor is that the benefits of these devices are not necessarily additive. 
4-42

Figure 4-8. Examples of trailer side skirts [Laydon 2009, Freight Wing 2009] 

Figure 4-9. Examples of trailer base treatments (boat tail on the left, structural 

base flaps on the right) [Aerovolution 2009, AT Dynamics 2009] 

Figure 4-10. Examples of trailer gap treatments – front fairing (left), and splitter plate 

(right) [NoseCone 2009] 

To help address these issues, we compiled a comprehensive list of estimated benefits for trailer 

and tractor/trailer interface aerodynamic options. Because there is so much variation in how 

devices can be configured, it was instructive to characterize devices into one of several 

categories: 
4-43

• Base flaps, which include both structural and inflatable boat tails 

• Full skirts: Refers to a skirt that runs the length of the trailer and extends most of the 

way to the ground. It may include a combined skirt and belly box. 

• Partial skirts: Refer to a skirt that covers only a portion of the trailer underbody and 

does not extend all the way to the ground; this also includes belly boxes. 

• Partial gap fairings: Narrows the gap beyond current standard practice, which is 

typically around to 40”, to 20 to 30”. 

• Full gap fairings: Fully closes the gap between the tractor and the trailer 

• Partial Trailer Aero Package: Includes two out of the three basic aerodynamic drag 

reduction approaches (rear base, underbody, and gap), but it may not use the most 

aggressive implementation of these devices. For example, a partial skirt and boat tail 

would constitute a “partial package.” 

• Full Trailer Aero Package: Includes all three of the basic aerodynamic drag reduction 

approaches (rear base, underbody, and gap). For example, a full or partial skirt, base 

treatment, and a partial gap treatment would constitute a “full package”. 

Figure 4-11 shows the range of fuel consumption benefits that were found based on this survey 

of the available literature. This data includes the results of CFD modeling, laboratory wind 

1.3%

2.2%

3.5%

5.2%

4.3%

5.8%

9.3%

0%

2%

4%

6%

8%

10%

12%

14%

012345678

Fleet Tests

Track

Wind Tunnel or CFD

Average

Partial Gap

Not included in average

Full Gap Partial Skirts Full Skirts Base Flaps Partial Pkg Full Pkg

Figure 4-11. Survey of Trailer Aerodynamics (see Table 4-25 for detailed sourcing) 

Fuel Consumption Benefit 

Aerodynamic Devices 
4-44

Table 4-25. Summary of Aerodynamic Retrofit Devices Literature Review 
4-45

tunnel tests, and on-road demonstrations by device manufacturers, fleets, and OEMs. All of the 

data is sourced from publicly available literature. To facilitate comparison between different 

sources, drag reduction benefits were converted to a fuel consumption benefit by dividing CD

by 2. The data shown in Figure 4-11 provides a high-level summary of the efficacy of trailer drag 

reduction options; individual approaches and results are discussed in further detail in the 

following sections. 

We estimate that implementation of a partial aerodynamic package gives fuel consumption 

benefits on the order of 5 to 7 percent, and a full aerodynamic package offers benefits on the 

order of 9 to 10 percent. 

4.2.2.3 Design Integration of the Tractor/Trailer Interface 

The gap between the tractor and the trailer is a major source of aerodynamic drag, particularly at 

non-zero wind yaw angles (i.e., in a cross-wind condition). For example, wind tunnel tests have 

shown that a non-optimized gap (i.e., no roof fairing, 60” gap) can increase aerodynamic drag on 

the order of 35 percent in cross-wind conditions. With no wind, this effect on drag drops to 

nearly zero [Storms 2004]. 

Continually narrowing this gap and streamlining airflows from the tractor to the trailer offer 

continuous benefits. It is suggested in the literature that reducing the gap by 10” reduces drag by 

0.5 to 1 percent, with benefits continuing all the way to a fully sealed gap [Storms 2004, 

Kenworth 2008, Cummins 2007]. Although maximally beneficial from the perspective of fuel 

efficiency, a sealed gap presents a major operational challenge due to the restrictions on vehicle 

turning radius and maneuverability. Figure 4-12 shows one concept for reducing the tractor 

trailer gap. 

Figure 4-12. Example of a trim top roof fairing [Leuschen 2006] 
4-46

A number of options for addressing the trailer/trailer gap have been considered experimentally, 

some of which are mounted on the trailer, and some of which are mounted from the tractor: 

Tractor: 

• As discussed above, it is standard practice to employ cab side extensions and move the 

tractor fifth wheel forward to the extent allowed by load and route characteristics24. 

Collectively, these might narrow the interface from 60” to about 40” [Marinko 2009, Salari 

2009]. These adjustments, coupled with the roof fairing, greatly mitigate the drag 

contribution from the tractor/trailer interface to the total vehicle drag. 

• Extended cab side extenders may be used to further narrow the gap beyond that of standard 

extensions; this approach would also include a roof fairing extension to match the length of 

the cab extensions. Such a system may deploy to fill part of the gap or the entire gap. One 

approach to addressing operational issues with a fully sealed gap deploys the extensions at 

speeds over 35 MPH. Wind tunnel tests by International and Mack [TMA 2006] and by 

CNRC [Leuschen 2006] measured the benefit of gap sealing devices to range from 2 to 4% 

reduction in total drag. 

• A “trim top” roof fairing extension fits horizontally along the top of the roof fairing, closing 

the gap over the top. This device has demonstrated fuel efficiency improvements on the order 

of 1 percent [TMA 2006, Leuschen 2006]. 

Trailer: 

• Trailer front fairing (“nose cone”), attached to the front of the trailer, extending across the 

top and possibly down the sides of the trailer 

• A gap splitter plate, also called a “vortex generator”, which extends towards the tractor along 

the vertical axis of the trailer. 

It is not clear that there is any distinct fuel efficiency advantage to optimizing the gap from the 

trailer front versus the cab rear. Rather, factors that discriminate between trailer front fairings vs. 

cab extensions include: (1) trailer front devices require one treatment per trailer, so may be more 

costly, and (2) it may be problematic to add extensions to cabs that pull many different types of 

loads. As such, trailer front fairings are most attractive for users that pull varied loads, while 

extended tractor extensions may be most attractive for large fleets that pull relatively 

homogeneous loads. 

Results from a variety of tests showed drag benefits on the order of 2 to 4 percent for a partial 

treatment with up to a 6 percent drag reduction for a fully sealed gap. These results correspond to 

a 1 to 2 percent fuel consumption benefit for a partial treatment, and a 2 to 3 percent benefit for a 

 

24 The relative axle position is constrained by bridge formula load limits, which vary depending on a vehicle’s load and which bridges 

it needs to cross. 
4-47

full treatment25. In practical terms, a fully sealed gap presents major challenges given turning 

radius requirements. Some manufacturers have explored addressing this issue by using a gap 

treatment that fully deploys only at high speeds. However, this may add considerable cost and 

complexity for a relatively marginal additional benefit. 

Costs on trailer front fairings are published for two different manufacturers and range from $800 

to $1,450 [FreightWing 2009, Nosecone 2009]. 

4.2.2.4 Trailer Underbody Treatments 

The majority of trailer underbody treatments consist of side skirts that extend the length of the 

trailer, thereby lessening the gap between the bottom of the trailer and the roadway. There are a 

number of different skirt configurations that have been proposed or a currently available. These 

vary in terms of: 

• Length: Some skirts extend only a few meters along the trailer underside in front of the 

wheels; others extend the full length of the trailer to the rear wheels and include a short 

section that extends to the rear of the wheels. 

• Material: Both aluminum and composite skirts have been considered. Aluminum skirts are 

lower cost but weigh more. 

• Height: The lower the ground clearance of a skirt, the greater the fuel consumption benefits. 

However, this must be balanced against the practical constraints imposed by obstacles that 

could damage the device. 

• Durability: To address ground clearance issues, some manufacturers sell a flexible skirt; 

others offer skirts that retract at low speeds and deploy at high speed. 

Other underbody treatments include “belly boxes”, which are simple boxes that attach to the 

trailer underside, or trailer bogey fairing, which smoothes airflows around the rear axle. Benefits 

of a belly box are generally reported to be similar to those of a partial skirt and are treated as a 

variation on a partial skirt in this analysis26. Bogey fairings have been demonstrated to offer 

fairly minor drag reduction benefits – on the order of 2 percent. Several studies tested the 

benefits of using a belly box in combination with skirts and found that the combination reduced 

drag by an additional 3 percent [TMA 2006, Storms 2004]. To our knowledge, neither of these 

devices is available commercially – likely due to a combination of implementation issues and 

lower benefits. 

Data from skirt manufacturers estimate the fuel consumption benefit of full skirts range from 4 to 

7 percent [Laydon 2009, AT Dynamics 2009, Freight Wing 2009, Windyne 2009, AdamWorks 

2009]. One skirt manufacturer also cites data on a partial skirt, for which a 4 percent benefit is 

 

25 One source cited much higher fuel consumption benefits as high as 14 percent; however, it appears that this is relative to a 

baseline tractor that does not include any aerodynamic treatments. It is also not clear what test methodology was used 

[NoseCone]. 

26 Both International and Mack evaluated belly boxes as part of the TMA [2006] study, as did Storms [2004]. 
4-48

claimed [Freight Wing 2009]. Independent tests show fuel consumption benefits that are 

considerably lower than these. There is a fair amount of variation in the data, but in the 

aggregate, full skirts are estimated to offer fuel consumption benefits of 4 to 5 percent, while 

partial skirts offer benefits of 2 to 3 percent. Measured drag reductions range from 5 to 11 

percent for full skirts, and 2 to 6 percent for partial skirts [TMA 2006, Leuschen 2006, Leuschen 

2005, Storms 2004, Salari 2008, Site Visits]. The benefits reported by independent tests seem 

more credible than those reported by device manufacturers. This is the case both insofar as that 

they are more consistent with feedback obtained on site visits, and they are more consistent with 

our subsequent review of trailer aerodynamic packages. 

Price on skirts that are currently available varies from approximately $1,500 for relatively basic 

designs (i.e., rigid design, unretractable) to up to $4,000 for a fully retractable design [Site Visits, 

Freight Wing 2009, Windyne 2009]. 

4.2.2.5 Boat Tails 

Boat tails attach to the rear of the trailer, reducing aerodynamic drag due to the trailer’s wake. 

Two basic designs have been considered: rigid base plates that fan out around the rear of the 

trailer door (and may collapse flat to facilitate loading/unloading), and bladders that attach to the 

rear of the trailer and inflate once the vehicle is at cruising speed. A number of variations on 

these designs have been considered. For example, a number of tests have been conducted on the 

optimum angle for base plate designs [TMA 2006, Storms 2004, Salari 2006]. 

There is relatively strong agreement in the literature as to the benefit of boat tail designs. Fuel 

consumption benefits are generally estimated to range from 4 to 6 percent, and CD benefits range 

from 6.5 to 9 percent. (One study did show CD benefits ranging from 14 to 19 percent, but this 

was based on a scale model wind tunnel test and appears to be an outlier [Storms 2004]). 

Boat tail costs were estimated from several different sources, with prices ranging from $1,500 to 

$2,000 [Site Visits, AT Dyanmics, Schubert 2008]. 

4.2.2.6 Other Aerodynamic Drag Reduction Approaches 

A number of additional approaches to reducing vehicle drag have been proposed. These 

approaches include: 

• Active flow conditioning, which uses pneumatic blowing to equalize pressure along the 

vehicle surfaces [Englar 2004]. 

• Fully skirted wheels 

• Extreme reshaping of the tractor or trailer 

• Replace side mirrors with monitors 

While these may be promising, it does not appear that they are viable strategies over the time 

horizon of our analysis. This is due either to technical complexity, or regulatory or operational 

barriers. 
4-49

4.2.2.7 Challenges to Deployment of Trailer Aerodynamics 

There are number of challenges to widespread deployment of trailer aerodynamic devices. 

• On average, fleets operate three trailers for every one tractor and have optimized their 

operations to take advantage of multiple trailers per tractor. Without a change to the 

operations side of freight movement, operators would need to outfit three trailers for each 

tractor, effectively multiplying the capital cost by three. 

• “For hire” motor carriers (as distinguished from private fleets) do not necessarily own the 

trailers that they transport, which are often owned by the shipper. Because the motor carrier 

captures the windfall fuel savings that accrue from improved aerodynamics, the shipper has 

little incentive to invest in fuel efficiency. 

• Tractor trailers must conform to federal size and weight restrictions to travel on interstate 

highways. These restrictions are not necessarily relaxed for trailer aerodynamic devices 

(although some waivers have been granted on a limited basis). Add-on devices may add to 

trailer length (as in the case of a boat tail), width (as in the case of wheel fairings, which are 

not currently offered on the market), and weight. The weight issue is exacerbated if snow and 

ice collect under the side skirts, which has been an issue in some fleet trials [Site Visits]. 

• Durability: There is some concern as to whether devices can withstand the rigors of a linehaul operational service life. For example, side skirts can be damaged by obstacles on the 

ground, and a boat tail may be damaged if deployed when a truck backs into a loading area. 

• Trailer aerodynamic devices are not currently standard equipment. Using them in a fleet 

requires seeking out and purchasing them from a third party vendor and installing them as a 

retrofit. Device manufacturers claim that typical installation time is approximately 6 manhours.27

• Trailer aerodynamic devices are not universally deployable on all types of trailers. The 

devices discussed above are intended primarily for box trailers, although side skirts could 

likely be implemented on many different trailer configurations. 

4.2.2.8 Combined Tractor trailer Aerodynamic Packages 

As discussed previously, the benefits of aerodynamic drag improvements are not additive. As 

such, it is important to directly test specific packages of devices to accurately estimate the 

combined aerodynamic drag reduction. To facilitate comparisons between different studies, 

trailer aerodynamic packages were categorized as either “partial aero packages”, or “full aero 

packages”. 

Partial aero packages would generally include some side skirting and either a gap treatment or a 

boat tail. 

 

27 Aero device manufacturer websites [Laydon, AT Dynamics] 
4-50

Such a partial package is estimated by Smartway [2009a] to offer a 5 percent fuel consumption 

benefit. In the NESCCAF/ICCT report [2009], SwRI modeled a similar package and calculated 

approximately a 6 percent benefit28. Other tests of similar packages show fuel consumption 

benefits ranging from 4 to 6 percent [Freight Wing 2009, TMA 2006, Yatsko 2006, Site Visits]. 

These results would suggest reductions in CD on the order of 10 to 12 percent, although the one 

test that measured drag directly for a partial package estimated a 17 percent drag reduction. This 

result is closer to the results seen for a full package and hence is considered an outlier. 

A full aero package includes a full side skirt that rides low to the ground, a boat tail, and a gap 

treatment. Packages similar to this have been tested in a number of different contexts. The drag 

reduction benefit of a full aero package is estimated to range from 17 percent up to 23 percent. 

There is greater variation in the measured fuel consumption benefit of these packages, which 

range from 6 to 11.5 percent [TMA 2006, Leuschen 2006, FreightWing, Marinko 2009, Salari 

2009]. Strikingly, results from testing of an aerodynamic trailer by International Trucks in 

partnership with Wal-Mart showed wide variation between Wal-Mart’s initial evaluation of the 

vehicle and International’s final testing after making minor modifications to the vehicle (11.5 

percent) [TMA 2006]. All of the referenced sources appeared to use a robust methodology and 

offer credible results. Given the number of CD tests that all show drag benefits on the order of 17 

to 23 percent, the fuel consumption benefit of the full package is estimated to range from 8 to 10 

percent. 

Synthesizing the results from our analysis of the tractor and of the trailer gives results as shown 

in Table 4-26. It appears feasible to reduce total vehicle drag on the order of 22 to 24 percent 

using approaches and design modifications that are on the market or are expected to be offered in 

the next several years. It seems likely that achieving benefits that go significantly beyond these 

levels would likely require implementing some of the approaches detailed in Section 4.2.2.6. 

Table 4-26. Tractor trailer aerodynamic packages 

Tractor Trailer Estimated CD % Improvement 

No aero Standard trailer 0.79 to 0.829 -22 to -25% 

Baseline (Smartway) Standard trailer 0.59 to 0.6 — 

Baseline (Smartway) Partial aero package 

(Smartway) 0.52 to 0.53 10 to 12% 

Improved Baseline Partial aero package 

(Smartway) 0.49 to 0.51 15 to 17% (6% add’l benefit)

Improved Baseline Full aero package 0.45 to 0.47 22 to 24%30

(8% add’l benefit) 

 

28 The results presented for “Package 2” in the NESCCAF/ICCT study include a full Smartway tractor + Smartway trailer, which is 

assumed to reduce CD to 0.5. The SwRI modeling showed that this package gives an 8 percent fuel consumption benefit. 

However, the baseline tractor is a partial Smartway configuration. The 6 percent benefit referenced above assumes that ~25 to 

30 percent of the drag reduction is applied to the tractor (to reduce CD to 0.59-0.60), and the rest is applied to the trailer. 

29 Leuschen 2005 

30 Assumes CD benefit of full trailer package is 17 to 19 percent 
4-51

4.2.3 Straight Box Truck Aero 

Straight box trucks can leverage many of the same design features as combination tractor trailers 

to improve aerodynamics. A summary of potential options is included in Table 4-27. However, 

adoption of these design features is fairly uncommon. This low adoption rate is due to a 

combination of the lower average speeds, which decrease the fuel savings benefit of 

aerodynamic devices, and lower annual mileage, which increases the time to payback. 

Table 4-27. Straight box truck aerodynamic technologies 

Technology % FC Benefit CD Improvement Capital Cost Status 

Aero Devices 

Roof Deflector 2 to 3% 7 to 7.5% $500 to $800 Available 

Chassis Fairings 0.5 to 1% 2.5 to 3% $400 to $500 Not Available 

Box Skirts 2 to 3% 4.5 to 5% $500 to $1,000 Demos 

Box Fairing 0.5 to 1% 2.4 to 2.7% $500 to $650 Available 

Cab Streamlining 1 to 2% 5 to 6% $750 Available 

Aft Box Taper 1.5 to 3% 7.6 to 8% $1,000 Not Available 

Aero Packages 

Combination of 

Straight Truck Aero 5 to 8% 20% $3,000 to $3,500 Not Available 

Options for improving the aerodynamics of these vehicles include the following: 

• Roof deflectors: Simpler versions of the roof fairings which are common in combination 

vehicles. These devices are offered by OEMs but have a relatively low adoption rate. In 

addition, because they are not part of a standard package, there can be an additional 

installation cost. Capital costs are based on data provided during site visits. 

• Fuel tank fairings: Similar to those available for tractor trailers. The fuel consumption 

benefits are based on information furnished during site visits; the capital costs are 

estimated to be similar to the low-end of cost estimates for the tractor trailers. To our 

knowledge, these devices are not currently offered. 

• Box skirts: Similar to the side skirts that are offered for combination trucks. At least one 

company offers a modular skirt design that can be used on straight trucks [Laydon 2009]. 

The benefits of box skirts are based on information gathered on site visits and 

information from the Laydon composites web site. Capital costs for this device are 

estimated to be half that of similar devices that are intended for tractor trailers. 

• Aft box taper: This is a similar concept to that of a boat tail in a combination truck. It 

could entail actually molding the trailer box to provide better exit flows or an add-on 

device. To our knowledge, no one is actively pursuing this approach. Estimated benefits 
4-52

are based on discussions during site visits; costs are assumed to be similar to that of the 

low-end tractor trailer estimate. 

• Nose cone or box front fairing: Similar to the trailer gap fairings that attach to the trailer 

front that were discussed in reference to combination trucks. These devices may offer 

significant drag reduction benefits on straight trucks, as the roof top deflectors do not 

fully integrate air flow with the rest of the truck. Capital costs are based on information 

from the Nose Cone [2009] website and from discussions with a truck dealer [Merrill 

2009]; benefits are based on information furnished during site visits. 

• Cab streamlining: In addition to the above strategies, many of the same tractor body 

streamlining approaches that have already been adopted into the tractor trailer fleet may 

be implemented in box trucks. These approaches include sloped hoods and windshield, 

aerodynamic mirrors, and aerodynamic bumpers. Capital costs and benefits of these 

design modifications are estimated based on information from Vyas [2002], which 

includes a similar list of modifications, but applies them to a tractor trailer. 

We are not aware of any studies that have looked at combinations of devices for straight box 

trucks. However, multiplying the results suggests a maximum technical potential on the order of 

25 to 30 percent reduction in CD.

31 Given that the drag reduction benefit of these technologies is 

not additive, the likely CD benefit of all of the above approaches taken in combination is on the 

order of 20 percent, at a cost of approximately $3,000 to $3,500. Assuming that the fuel 

consumption benefit is about 25 percent that of the CD for a vehicle with average speed of 

30 MPH, the total fuel consumption benefit of the total package is on the order of 5 percent. A 

vehicle that operates more frequently at higher speeds (average speed of 45 MPH) would see fuel 

consumption benefits between 7 and 8 percent. 

4.2.4 Motor Coach 

Because of their frequent high speed operation, motor coaches may benefit significantly from 

aerodynamic drag reduction. However, there is limited information available in the literature and 

little additional data provided during site visits that speak directly to motor coach aerodynamics. 

As such, our estimates of motor coach aerodynamic drag reduction potential are based on 

extending results of the line-haul analysis to the motor coach segment. 

 

31 This is the result that is obtained if (1 – FC benefit) of each line item in the technology is multiplied together. 
4-53

Table 4-28 summarizes our estimates of motor coach aerodynamic improvements. 

Table 4-28. Motor coach aerodynamic technologies 

Technology FC Benefit CD Improvement Capital Cost Status 

Boat Tail 4 o 6% 6.5 to 9% $1,500 to 

$2,000 Not Available 

Vehicle Streamline 3 to 4% 6 to 8% $2,750 Not Available 

Aero Packages 

Combination of 

Motor Coach Aero 7 to 10% 13 to 15% $4,250 to $4,750 Not Available 

The following approaches were considered for optimizing the aerodynamics of the tractor trailer: 

cab streamlining, boat tailing, underbody treatments, gap treatments, wheel fairings, removing 

the mirrors, and active flow control. Of these, gap treatments are clearly not applicable. Given 

the already-low ride height, skirts and underbody treatments likely do not offer a significant 

benefit. Active flow control has not yet been demonstrated; moreover, it is most beneficial on 

streamlined, as distinguished from bluff, bodies [Salari 2009]. 

Of the remaining options, cab streamlining and boat tailing would appear to offer the best 

prospects for reducing aerodynamic drag. Boat tailing on a tractor trailer is assumed to reduce 

drag by 6.5 to 9 percent and offer fuel consumption benefits of 4 to 6 percent. Additional cab 

streamlining in the line-haul segment is estimated to reduce drag by 6 to 8 percent and reduce 

fuel consumption by 3 to 4 percent. In combination, these approaches would reduce drag by 13 

to 15 percent and could offer a 7 to 10 percent reduction in fuel consumption. It is assumed that 

these benefits come at similar cost to those assumed for the line-haul segment: $2,750 for 

streamlining and $1,500 to $2,000 for boat tailing. 

4.2.5 Class 2b Pickups and Vans 

The potential for aerodynamic drag reduction in the Class 2b segment is estimated based on 

analysis conducted during the NHTSA rulemaking for the light-duty CAFE standard published in 

2009. Although the NHTSA analysis extends only to Class 2a vehicles (<8500 GVW), it is 

assumed that similar aerodynamic improvements can be implemented in Class 2b. In general, 

Class 2b vehicles have a similar form factor to their lighter counterparts that were considered in 

the NHTSA rulemaking, which suggests that this is a reasonable approximation. 

Table 4-29 summarizes our estimates of aerodynamic improvements in Class 2b vehicles. 

Table 4-29. Class 2b pickup and van aerodynamic technologies 

Technology FC Benefit CD Improvement Capital Cost 

Aero streamlining 3% 10% $60 to $116 
4-54

The NHTSA rulemaking considers a similar list of approaches to those discussed previously 

relative to tractor streamlining in line-haul vehicles [Pg 327–330]. These include underbody 

treatments; streamlined hood, windshield, fenders, and grill; reduced ride height (analogous to 

trailer side skirts); low drag side mirrors; optimized air flow pathways; and wheels or wheel 

wells. In combination, the NHTSA rulemaking assumes that a 10 percent reduction in CD is 

feasible. For heavier trucks, this level of drag reduction is assumed to offer a 3 percent fuel 

consumption benefit. 

These benefits are estimated to range from $60 to $116 in added cost. These cost estimates were 

applied independent of vehicle class, so no adjustment was applied to translate these to Class 2b 

vehicles. 

4.3 Tires and Wheels 

4.3.1 Overview 

According to the 21st Century Truck vehicle energy audit discussed in Chapter 2, rolling 

resistance accounts for 13 percent of energy used in a Class 8 tractor trailer at 65 MPH; 9 percent 

in a medium-duty vehicle at 40 MPH; and 5 percent in a transit bus traveling on the CBD duty 

cycle [DOE 2000]. Losses due to rolling resistance are higher for heavier vehicles and for 

vehicles traveling at higher speeds. The influence of vehicle speed on rolling resistance is 

illustrated in Figure 4-13. These losses may be mitigated by using lower rolling resistance tires 

and by adequately maintaining tire pressure while the vehicle is in use. This chapter will describe 

technologies that are available or forthcoming which reduce losses due to vehicle rolling 

resistance. Following this overview of technologies, we will discuss how these technologies 

apply to different vehicle classes. 

Figure 4-13. Influence of rolling resistance and aerodynamic drag on vehicle 

power demand as a function of speed 
4-55

4.3.2 Technologies for Reducing Rolling Resistance 

4.3.2.1 Low Rolling Resistance Tires 

Tire manufacturers are continually refining tire characteristics to reduce rolling resistance while 

maintaining tread life and safety. Low rolling resistance tires include conventional duals with a 

lower CRR, and wide base singles (WBS) or “super single” tires. Wide base singles reduce weight 

(about 50 lbs per tire) and can offer lower rolling resistance than duals. They are often deployed 

in combination with aluminum wheels, which save an additional 40 lbs per wheel [Merrill 2009]. 

As part of data gathered for the NESCCAF/ICCT study [2009], it was estimated that a typical set 

of standard duals has an average CRR of 0.0068, while a set of low rolling resistance wide base 

singles on tractor and trailer has an average CRR of 0.0055, an improvement of 19 percent. 

Michelin provided data to the committee that showed the variation in rolling resistance for 

different types of tires (Figure 4-14) [Bradley 2009]. Based on this information, our baseline 

Class 8 tractor trailer is assumed to use steel-rimmed duals with a CRR of 0.0068. The 

methodology for extending these results to other vehicle classes is discussed in Section 4.3.3. 

Figure 4-14. Range of CRR for currently available tires [Bradley 2009] 

Estimates of the capital costs and fuel efficiency benefits of low rolling resistance (wide-base 

single and dual) tires vary widely. Some of the reasons for this variance are as follows: 

• It is unclear what the baseline for estimates is. Sources judge the improvement from low 

rolling resistance tires relative to a previous generation tire – which is itself a moving 

target given continuing improvement. 

• Wide-base single tires are not necessarily low rolling resistance tires. 

• Benefits vary widely depending on duty cycle and vehicle weight: grossed out vehicles 

will see a greater benefit than cubed out vehicles. 

Example Range of Rolling Resistance Coefficients 

for Heavy Truck Tires

0

2

4

6

8

10

12

Rolling Resistance Coefficient, kg/T

Steer Drive Trailer Wide-base

Single

(NGWBST)

EPA

SmartWay

tire 

thresholds
4-56

The fuel efficiency benefits of low rolling resistance dual tires were estimated to range from 

2 percent to 7 percent [Smartway 2004a, Frey 2007, Site Visits, Michelin 2009]. It is possible 

that the high end of this range corresponds to a relatively high rolling resistance tire used for the 

baseline, as well as differences in duty cycle. As such, we have estimated the benefits relative to 

an average tire at 2 to 3 percent. Estimates for the cost of low rolling resistance duals range from 

cost-neutral to $550 [Site Visits, Frey 2007] to replace all 18 tires. This equates to $30 per tire. 

We have used this higher estimate in the technology matrix. These tires are widely adopted and 

provide rapid payback. However, some users have been reluctant to use low rolling resistance 

tires on cold weather routes due to safety concerns about less traction. 

Estimates for the fuel efficiency benefit of wide-base singles range from 2 percent to upwards of 

10 percent. One reason for the wide range is that some estimates assume that WBS tires are 

installed only on the tractor, while others assume that they are installed on the tractor and the 

trailer; other reasons include differences in duty cycle and different dual tires used as a basis for 

comparison. Data gathered by Oak Ridge National Labs sheds some light on this issue: they 

performed a year-long study of fuel use across a cross-section of tractor trailers using dual tires 

and WBS tires in different configurations (i.e., tractor only, trailer only, tractor+trailer, and no 

WBS tires). They found fuel savings of 6.5 percent for WBS on the tractor only, and 9.2 percent 

on the tractor + trailer [Davis 2008, Table 5.10]. Based on a loose consensus of these different 

estimates, we estimate that the fuel efficiency of wide-base singles ranges from 3 to 6 percent on 

the tractor only, and from 6 to 9 percent on the tractor + trailer. We received cost estimates for 

WBS tires that ranged from cost-neutral to $1,800 for a set of four tires and wheels [Site Visits, 

Merrill 2009, Smartway 2004a, Schubert 2008]. Our final estimate is based on information 

received from an actual dealer [Merrill 2009], who quoted $900 for four tires plus four aluminum 

wheels (tractor only). 

There are a number of issues that preclude full adoption of WBS tires. These include reports of 

increased tread wear and susceptibility to damage on urban routes; inability to “limp” home on a 

flat, as one can do with duals; and lack of availability in the event of a flat. It was suggested 

during the course of the site visits that tire makers are continuously refining their treads, and endusers are willing to continue testing to see if the durability issues are addressed. It was also 

suggested that some systems – such as WBS spare tire systems and auto-inflate devices – enable 

further deployment of WBS. 

As part of the NESCCAF/ICCT study [2009], the steering committee concluded that a “next 

generation” WBS tire could achieve a rolling resistance of 0.0045. Modeling by SwRI showed 

that this level of CRR offers an additional 5 percent benefit relative to the current low rolling 

resistance WBS (CRR = 0.0055). This would suggest that these future WBS tires would reduce 

fuel use by 11 to 14 percent relative to the baseline duals. In a similar vein, we estimated that 

future conventional duals will also improve offering an additional 2 percent fuel savings relative 

to today’s low rolling resistance dual tires. 

Our estimates for Class 8 tractor trailer tires are summarized in Table 4-30. 
4-57

Table 4-30. Assumed tire characteristics for class 8 tractor trailers 

Tire Options Avg CRR CRR Imp. FC Benefit 

Standard Duals Package 0.0068 

Low rolling resistance duals 0.0061 to 0.0062 

(Est) 10% 2 to 4% 

Wide base singles (WBS) 

(Tractor Only) 0.0055 19% 3 to 6% 

Wide base singles (WBS) 

(Tractor + Trailer) 0.0055 19% 6 to 9% 

Next generation WBS 0.0045 34% 11 to 14% 

4.3.2.2 Pressure Monitors and Auto-Inflation Systems: 

It is estimated that underinflated tires decrease fuel consumption by 0.5 to 1 percent for every 10 

psi of under inflation, with higher penalties corresponding to more heavily loaded vehicles 

[Cummins 2007, Smartway 2004b]. Feedback offered from a number of sources on site visits 

suggested that on average, vehicles run 10 to 20 psi under-inflated. Arvin Meritor presented 

information from a study that found that over half of tires on combination trucks were at least 

5 psi under inflated, and 22% of trucks have at least one tire underinflated by over 20 psi [Hicks 

2009]. These data suggest an average penalty of 0.5 to 2 percent due to under-inflated tires. Frey 

[2007] estimates a 0.6 percent benefit; reviewers generally felt this was a credible estimate, 

although published information from Wal-Mart estimates benefits for their fleet at 1 to 3 percent 

[Yatsko 2007], and Arvin Meritor estimates a 1% benefit [Hicks 2009]. 

Both tire pressure monitors and full auto-inflate systems are currently available for both trucks 

and trailers. Tire pressure monitor systems simply alert drivers if tire pressures are low; 

automatic tire inflation (ATI) systems actually maintain recommended tire pressure. 

We received wildly divergent estimates as to the cost of these systems. Smartway estimates that 

an ATI system for a truck’s drive axles and trailer costs $900 [Smartway 2004b], while feedback 

from one site visit suggested a cost of $13,000. It was suggested that the Smartway estimate 

might be reasonable for an inflation monitor but was far too low for an ATI on a tractor. As a 

third data point, Arvin Meritor presented data to the committee describing a trailer ATI system 

that sells for $300 to $400 [Hicks 2009]. Subsequent discussions suggested that the cost of a 

trailer inflation system is far lower than a tractor tire inflation system but that $4,000 to $5,000 

might be a more a reasonable estimate. Based on this feedback, we have estimated capital costs 

and benefits for three different systems: a tractor based ATI, a tractor based monitoring system, 

and a trailer-based ATI (Table 4-31). 

Nitrogen-filled tires were also mentioned as a potential strategy for managing pressure. Using 

nitrogen reduces the amount of moisture in the tire, which can keep the tire from heating up and 

over-inflating. We did not have enough information to characterize this strategy. 
4-58

Table 4-31. Tire pressure monitoring and inflation systems 

System Capital Cost Benefit 

Tractor tire monitor $900 [Smartway 2004b] 0.6% 

Tractor ATI $4,000 to $5,000 [Site Visits] 0.6% 

Trailer ATI $300 to $400 [Hicks 2009] 0.6% 

4.3.3 Application of Tire and Wheel Technology to Different Vehicle Classes 

As discussed previously, the effect of rolling resistance on vehicle fuel use varies depending on 

vehicle application. Because low rolling resistance offers the most benefit at high speeds and 

vehicle weight, most of the information that was available and discussed above applies to Class 8 

tractor trailers. To extend these results to other vehicle classes, we have scaled results according 

to the 21st Century Truck energy audit discussed in Chapter 2 [DOE 2000]. As discussed 

previously, according to this audit, rolling resistance accounts for: 

• 13 percent of energy used in a class 8 tractor trailer at 65 MPH; 

• 9 percent in a medium duty vehicle at 40 MPH; and 

• 5 percent in a transit bus traveling on the CBD duty cycle. 

Based on these estimates, we have scaled the benefit estimated for a Class 8 tractor trailer data 

for different applications as shown in Table 4-32, with appropriate adjustments made for vehicle 

weight. It should be stressed that an accurate estimate of these parameters will require actual 

drive cycle modeling for different vehicle applications and duty cycles. 

Table 4-32. Rolling resistance scaling parameters 

Vehicle Class Estimated contribution of Rolling 

Resistance to energy losses 

Rel. Efficacy of Rolling 

Resistance 

Tractor trailer (65K lbs) 13% 1.0 

Motor Coach 9% 0.7 

Box and Bucket 9% 0.7 

Transit Bus 5% 0.4 

Refuse 8% 0.8 

4.3.3.1 Tractor Trailers 

Currently, 5 to 10 percent of users use wide-base single tires, and an additional 60 percent 

specify a low-rolling resistance tire. Market penetration of WBS tires is challenging due to 

concerns over flat tires and tread-wear as discussed above. A summary of our assumed benefits 

for tractor trailer tire and wheel technologies is included in Table 4-33. 
4-59

Table 4-33. Class 8 tractor trailer tire and wheel technologies 

System Capital Cost FC Benefit 

Low rolling resistance dual $30 per tire 2 to 3% 

Wide base single (WBS) with aluminum wheels – 

Tractor only 

$900 

($225 per tire + wheel) 3 to 6% 

Wide base single (WBS) with aluminum wheels – 

Tractor + 1 Trailera $1,800 6 to 9% 

Next-generation dual $30 per tire 4 to 5% 

Next-generation WBS (Tractor Only) $900 8 to 11% 

Next-generation WBS (Tractor+trailer) $1,800 11 to 14% 

Tractor tire monitor $900 0.6% 

Tractor ATI $4,000 to $5,000 0.6% 

Trailer ATI $300 to $400 0.6% 

a

For 3 trailers, this cost goes to $3,600 

4.3.3.2 Motor Coaches 

Motor coaches can benefit from low rolling resistance tires, wide base singles, or automatic 

inflation systems. Wide-base singles are available for motor coaches, but we do not believe that 

they are widely deployed. There is only a single axle on a motor coach that uses dual tires (and 

hence can take advantage of a WBS). Benefits are estimated from the Class 8 tractor trailer and 

are scaled using a factor of 0.9 to account for differences in duty cycle and weight. A summary 

of motor coach tire and wheel fuel consumption technologies and benefits is included in Table 

4-34. 

Table 4-34. Motor coach tire and wheel technologies 

System Capital Cost FC Benefit 

Low rolling resistance dual $30 per tire 1.4 to 2.1% 

Wide base single (WBS) $450 ($225 per tire + wheel) 2.1 to 4.2% 

Next-generation dual $30 per tire 2.8 to 3.5% 

Next-generation WBS $450 5.6 to 7.7% 

Tire monitor $900 0.42% 

ATI $4,000 to $5,000 0.42% 

4.3.3.3 Class 3-6 Box and Bucket Trucks 

Class 3-6 Box trucks gain some benefit from low rolling resistance duals and potentially from 

wide-base singles. WBS tires face a steep challenge in this application, due in large part to 

concerns over tread life and tire wear (e.g., side wall damage) [Site Visits]; that said, WBS tires 
4-60

are available for this application and could gain market share on regional routes – particularly if 

future version improve tread life. Inflation monitors could possibly come into this segment; full 

ATI systems are unlikely due to high cost. Benefits are estimated from the Class 8 tractor trailer 

and are scaled using a factor of 0.7 to account for differences in duty cycle and weight. A 

summary of box and bucket truck tire and wheel fuel consumption technologies and benefits is 

included in Table 4-35. 

Table 4-35. Class 3-6 box and bucket truck tire and wheel technologies 

System Capital Cost FC Benefit 

Low rolling resistance dual $30 per tire 1.4 to 2.1% 

Wide base single (WBS) $900 ($225 per tire + wheel) 2.1 to 4.2% 

Next generation dual $30 per tire 2.8 to 3.5% 

Tire monitor $900 0.42% 

4.3.3.4 Urban Transit Buses 

Transit buses gain only minor benefit from low rolling resistance tires, and they are unlikely to 

adopt wide base singles. We have also included inflation monitors as a potential technology for 

this application. Benefits are estimated from the Class 8 tractor trailer and are scaled using a 

factor of 0.4 to account for differences in vehicle duty cycle. A summary of box and bucket 

truck tire and wheel fuel consumption technologies and benefits is included in Table 4-36. 

Table 4-36. Transit bus tire and wheel technologies 

System Capital Cost FC Benefit 

Low rolling resistance dual $30 per tire 0.8 to 1.2% 

Next generation dual $30 per tire 1.6 to 2% 

Tire monitor $900 0.25% 

4.3.3.5 Refuse Haulers 

Refuse haulers, like transit buses, gain only minor benefit from low rolling resistance tires and 

are unlikely to adopt wide base singles. Benefits are estimated from the Class 8 tractor trailer and 

are scaled using a factor of 0.6 to account for differences in vehicle duty cycle. This scale factor 

reflects the low speed duty cycle (which reduces the impact of rolling resistance), and high 

weight (which increases the impact). A summary of refuse hauler tire and wheel fuel 

consumption technologies and benefits is included in Table 4-37. 
4-61

Table 4-37. Refuse hauler tire and wheel technologies 

System Capital Cost FC Benefit 

Low rolling resistance dual $30 per tire 1.2 to 1.8% 

Next generation dual $30 per tire 2.4 to 3% 

Tire monitor $900 0.36% 

4.3.3.6 Class 2b Pickups and Vans 

Rolling resistance opportunities for Class 2b vehicles are estimated from the NHTSA study. 

NHTSA does not include low rolling resistance tires as an option for its large truck segment. 

Although they are technically feasible, the rulemaking deems that there are issues with adoption 

due to traction and handling requirements at payload and towing limits. We have included the 

NHTSA estimates for light-duty applications with the caveat that these issues may preclude the 

adoption of low rolling resistance tires in this segment. The NHTSA rule estimates a 10 percent 

reduction in tire rolling resistance; for this application, it is estimated that a 10 percent reduction 

in CRR reduces fuel use by 1 to 2 percent. Class 2b tire and wheel technologies are summarized 

in Table 4-38. 

Table 4-38. Class 2b tire and wheel technologies 

System Capital Cost FC Benefit 

Low rolling resistance tires $6 to $9 1 to 2% 

4.4 Weight Reduction 

4.4.1 Overview 

The size of medium- and heavy-duty vehicles is dictated by the vehicle’s mission. Unlike the 

light-duty sector, where larger vehicles are often a luxury, reducing weight by downsizing 

vehicles is not a viable option for the medium- and heavy-duty sector. 

Weight can be reduced in medium and heavy-duty vehicles by substituting new, lighter weight 

materials. Potential material substitutes include high-strength steel, aluminum, or composites. 

Weight reduction is of benefit to truck operators for several reasons: 

• In grossed-out vehicles, it offers a productivity benefit, which can save fuel by allowing 

shippers to increase the amount of cargo per truckload. 

• In smaller heavy-duty vehicles, keeping weight under 33,000 lbs avoid a $12,000 federal 

excise tax. 

• In all vehicles, reducing weight reduces the vehicle’s road load, thereby saving fuel. 
4-62

The fuel efficiency benefit of material substitution varies by duty cycle and by application. In 

general, weight reduction is most effective over urban drive cycles that feature a lot of braking 

and low road speeds. Data from Helms [2003] shows that on a city duty cycle, 89 percent of the 

vehicle’s road load is weight dependent, compared to 38 percent on a steady-state 55 MPH duty 

cycle, and 25 percent on a steady state 75 MPH duty cycle. 

Estimates of capital costs and benefits rely primarily on a study conducted by the Institute for 

Energy and Environmental Research (IFEU) [Helms 2003] and on information presented to the 

committee by the Aluminum Association [Alcoa 2009]. This information is supplemented with 

information gathered on site visits and additional sources from the literature. 

This section presents estimates for the capital costs and fuel efficiency benefits of varying levels 

of weight reduction for each of the different vehicle classes. The benefits of weight reduction are 

presented in terms of “% fuel saved per 1,000 lbs of weight reduction”, except for Class 2b 

vehicles, which present savings in terms of “% fuel saved per 3 percent weight reduction”. 

Capital costs are expressed in dollars per lb, with increasing costs as the amount of weight 

removed rises. Following discussion of capital costs and benefits for each vehicle class, we 

discuss historic trends and the effect of fuel efficiency and emissions control technologies on 

vehicle weight. 

4.4.2 Class 8 Tractor Trailer 

The benefits of weight reduction for Class 8 tractor trailers vary depending on whether the 

application is weight-constrained (“grossed out”) or volume-constrained (“cubed out”). For 

weight-constrained vehicles, any weight that is removed from the truck can be replaced with 

additional cargo, leading to fewer truck-miles. We have assumed that this offers a fuel 

consumption benefit that is equal to the extra cargo. For a 35,000 lbs truck that carries 45,000 lbs 

of cargo, reducing weight by 1,000 lbs increases capacity, and hence reduces fuel consumption, 

by 2.2 percent32. 

For cubed-out vehicles, the benefits of weight reduction relate directly to fuel savings. A number 

of sources in the literature provide estimates as to the efficacy of weight reduction in Class 8 

tractor trailers. These estimates range from a low of 0.17 percent savings per 1,000 lbs of weight 

reduction to a high of 1.25 percent savings per 1,000 lbs of weight reduction. One reason for this 

variance is differences in the duty cycle – typically higher numbers correspond to regional or 

urban routes. A number of studies congregate in a middle range that varies from 0.4 to 0.6 

percent fuel savings per 1,000 lbs [Alcoa 2009, Helms 2003, Cummins 2007, NESCCAF 2009, 

Smartway 2004d]. The feedback from reviewers on site visits generally suggested that this was a 

reasonable estimate of the weight savings benefit. 

The Aluminum Association [Alcoa 2009] presented data to the committee that indicates that 

3,500 lbs of weight reduction is a viable target for Class 8 tractor trailers using approaches as 

 

32 In their presentation to the committee, the Aluminum Association [Scheps 2009] sited data that suggests 0.55 percent fuel saving 

for 1 percent weight reduction, or 0.69 percent savings per 1,000 lbs in an 80,000 lb vehicle. It is not clear why this number is so 

low for a weight-constrained application. 
4-63

illustrated in Figure 4-15. Alcoa has published data showing a roadmap to achieve 3,500 to 

4,500 lbs of weight reduction, as shown in Figure 4-16. Other weight savings features that are 

Figure 4-15. Tractor trailer weight reduction opportunities [Alcoa 2009] 

Figure 4-16. ALCOA estimates of weight-saving opportunities for tractor trailers 

[Scheps 2008] 
4-64

not included in these figures, but were pointed out during site visits include disc brakes, 

lightweight brake drums, and wide base single tires. 

Capital costs were estimated based on feedback from the Aluminum Association presented to the 

committee. During this discussion, it was suggested that there are a series of weight reduction 

opportunities that cost $2 to $4 per lb which are or have been adopted into vehicles. This 

includes lightweight cab structure, fuel tanks, HVAC components, bell housing, and aluminum 

wheels. Data from Smartway references lightweight tractors and trailers that are currently 

available that saves 1,000 to 2,000 lbs at a cost of $1 to $2 per lb. Given that many of these 

lightweight technologies have already been adopted, we opted to use the higher range cost 

estimate for the “low cost” weight reduction opportunities. This is followed by a tier of weight 

reduction that costs $4 to $8 per lb for which adoption rates are on the order of 10 percent, such 

as a lightweight 5th wheel and landing gear. Finally, the highest cost options considered tend to 

cost $8 to $10 per lb.33 We used this information to establish three cost tiers to achieve a 3,500 lb 

weight reduction. Results are summarized in Table 4-39. 

Table 4-39. Weight reduction capital cost and benefit for volume-constrained class 8 

tractor trailers 

Weight Reduction Cost Fuel Savings (per 1,000 lb) 

0 to 1,000 lbs $2 to $4 per lb 0.4 to 0.6% 

1,000 to 2,000 lbs $4 to $8 per lb 0.4 to 0.6% 

2,000 to 3,500 lbs $8 to $10 per lb 0.4 to 0.6% 

4.4.3 Transit Bus 

Given their low speed, stop-and-go duty cycle, transit buses can benefit greatly from weight 

reduction. Data on the benefits of weight reduction in this segment are sourced from the 

Aluminum Association’s presentation to the committee and the IFEU report. Estimates from the 

IFEU report range from 3.75 to 7.5 percent fuel savings for a 10 percent weight reduction. These 

estimates apply to a 15 metric ton bus traveling on an urban, congested drive cycle. Data 

presented by the Aluminum Association estimated fuel savings ranging from 5 to 8 percent per 

10 percent weight savings from three different studies. Based on this data, we have used an 

estimate of 5 to 7.5 percent fuel savings per 10 percent weight reduction. For a 25,000 lbs bus, 

this equates to 2 to 3 percent fuel savings per 1,000 lbs of weight. 

Data presented by Alcoa estimates that there is potential to save 3,000 to 3,500 lbs from an urban 

transit bus. Figure 4-17 shows an illustration of how to achieve this degree of weight savings. To 

estimate cost for this package, we applied the same costs as those estimated for the tractor trailer, 

but scaled the weight ranges to which these costs apply based on the ratio of the tractor trailer 

weight to the bus weight. This approximation attempts to account for the fact that the tractor 

 

33 We initially used estimates from Frey [2007] of $2,000 to achieve fuel savings ranging from 1 to 3 percent, but received feedback 

that this was too low of a cost. Using an elasticity of 0.5 percent per 1,000 lbs, this equates to $0.3 to $1 per lb. 
4-65

Figure 4-17. Weight savings realized for lightweight demonstration bus in China 

[Scheps 2008] 

trailer is a heavier vehicle, and as such should be easier to shed weight. Given that the unloaded 

weight of our baseline tractor trailer is approximately 35,000 lbs and the weight of the transit bus 

is 28,000 lbs, we use a scale factor of 0.8 to yield the estimates shown in Table 4-40. 

Table 4-40. Weight reduction capital cost and benefit for transit buses 

Weight Reduction Capital Cost Fuel Savings (per 1,000 lb) 

0 to 800 lbs $2 to $4 per lb 2 to 3% 

800 to 1,600 lbs $4 to $8 per lb 2 to 3% 

1,600 to 2,800 lbs $8 to $10 per lb 2 to 3% 

4.4.4 Motor Coach 

Estimates for the benefit of weight reduction in motor coaches are drawn from the IFEU report, 

which estimates 2.4 percent fuel savings per 10 percent weight reduction. Data was estimated for 

an 18 metric ton vehicle traveling on a primarily highway duty cycle. For a 36,000 lb coach, this 

fuel savings estimate equates to 0.7 percent per 1,000 lbs saved. Capital costs are estimated using 
4-66

the same logic as that described for the transit bus. We have assumed a 36,000 lb coach, which 

weighs approximately the same as a tractor trailer, so no scaling is needed. Table 4-41 shows our 

results for motor coaches. 

Table 4-41. Weight reduction capital cost and benefit for motor coaches 

Weight Reduction Capital Cost Fuel Savings (per 1,000 lb) 

0 to 1,000 lbs $2 to $4 per lb 0.7% 

1,000 to 2,000 lbs $4 to $8 per lb 0.7% 

2,000 to 3,500 lbs $8 to $10 per lb 0.7% 

4.4.5 Class 3-6 Straight Box and Bucket Trucks 

Fuel savings for Class 3-6 Box and Bucket trucks are estimated based on data from the IFEU 

report and data presented by the Aluminum Association. The Aluminum Association presented 

data that estimates 6.3 percent fuel savings per 10 percent weight reduction for a 16,340 lb truck 

on the HTUF duty cycle. Because this is a similar estimate to that of the transit bus from the 

same study, we have assumed the same 5 to 8 percent savings per 10 percent weight reduction 

that we use for the transit bus (for which there are more data). For a 16,000 lbs vehicle, this 

equates to 3 to 5 percent savings per 1,000 lbs of weight reduction. Capital costs are estimated 

using the methodology described in the transit bus section, and use a scale factor of 0.41. The 

results are shown in Table 4-42. 

Table 4-42. Weight reduction capital cost and benefit for class 3-6 box and bucket trucks 

Weight Reduction Capital Cost Fuel Savings (per 1,000 lb) 

0 to 470 lbs $2 to $4 per lb 3 to 5% 

470 to 940 lbs $4 to $8 per lb 3 to 5% 

940 to 1,650 lbs $8 to $10 per lb 3 to 5% 

4.4.6 Refuse Hauler 

We are not aware of any data that estimates the benefits of weight reduction for refuse vehicles. 

As such, we have extended the estimates from the transit bus to the refuse vehicle. The logic for 

doing so is that they both travel on highly urban routes that feature a number of stops. Applying 

our estimate of 5 to 8 percent fuel savings per 10 percent weight reduction to a refuse hauler 

(assumed weight of 35,000 lbs) equates to a fuel savings of 1.4 to 2.3 percent per 1,000 lbs. 

Given that these vehicles require many high-strength elements, it is unclear to what extent lowcost weight reduction is viable. As such, we have assumed that only 2,000 lbs of weight 

reduction are feasible, and that these come at higher cost than those estimated for the tractor 

trailer, as shown in Table 4-43. 
4-67

Table 4-43. Weight reduction capital cost and benefit for refuse haulers 

Weight Reduction Capital Cost Fuel Savings (per 1,000 lb) 

0 to 2,000 lbs $4 to $8 per lb 1.4 to 2.3% 

4.4.7 Class 2b Pickups and Vans 

Weight reduction of Class 2b vehicles is estimated based on data included in the NHTSA lightduty rulemaking. NHTSA considers up to 5 percent weight reduction a viable target for large 

(5,000 lb GVW) light trucks. They estimate that a 3 percent reduction in weight gives a 0.6 to 

0.9 percent reduction in fuel use. This weight reduction is estimated to cost $1 to $2 per lb for 

0 to 2 percent weight reduction, and $2 to $4 per lb for 2 to 5 percent weight reduction. We have 

assumed that these estimates carry over to the heavier Class 2b vehicles as shown in Table 4-44. 

Table 4-44. Weight reduction capital cost and benefits for class 2b pickups and vans 

Weight Reduction Capital Cost Fuel Savings (per 3%) 

0 to 2% $1 to $2 per lb 0.6 to 0.9% 

2 to 5% $2 to $4 per lb 0.6 to 0.9% 

4.4.8 Weight Increases 

While this section has focused on weight reduction, a more pressing issue for industry is 

increased weight due to emissions technologies. 

Emissions control systems, starting with low-rate EGR, moving to medium rates, and finally on 

to SCR systems, have added approximately 500 lbs to vehicle weight. In addition, many of the 

fuel savings technologies that are being considered add significantly to vehicle weight. These 

include waste-heat recovery systems (200 to 300 lbs); hybrid-electric technology (400 to 1,000 

lbs); hydraulic hybrids (~1,000 lbs); and aerodynamic treatment devices for trailers (750 lbs) and 

tractors (unknown, but perhaps 200 to 300 lbs). In combination, these technologies could add 

upwards of 2,000 lbs to vehicle weight, in addition to emissions control systems. As a group, fuel 

savings plus emissions technology could add 2,000 to 3,000 lbs to vehicle weight, as 

summarized in Table 4-45. 
4-68

Table 4-45. Weight penalty for fuel savings and emissions control 

Vehicle Class Added weight (lb) Fuel Consumption Penalty 

Class 8 Tractor Trailer 2,000 to 3,000 1 to 1.5% 

Transit Bus 2,500 5 to 7.5% 

Motor Coach 2,000 to 3,000 1.4 to 2.1% 

Class 3-6 Box and Bucket 1,000 3 to 5% 

Refuse Hauler 1,500 2.1 to 3.5% 

Class 2b 500 to 1,000 2 to 3% 

4.5 Transmission and Driveline 

“Transmission and driveline” refers to, collectively, the system that connects the propulsion 

system to the wheels. It includes the transmission, the final drive, and the axle. Options for 

realizing fuel efficiency benefits by optimizing the transmission and driveline generally fall into 

one of two categories: 

• Improved driveline efficiency: Strategies that increase the efficiency of power transfer 

from the propulsion system to the wheels.

• Improved systems integration: Strategies that enable the engine to operate at higher 

average drive cycle efficiency. These approaches may have significant overlap with 

driver management and coaching strategies and hybrid technologies.

Broadly speaking, a different set of strategies applies to vehicles for which automatic 

transmissions are prevalent than those for which manual transmissions dominate; to a lesser 

extent, the same is true for vehicles traveling on stop and go duty cycles than those operating 

primarily over the highway. We have identified three different technology roadmaps, depending 

on the vehicle duty cycle and baseline transmission technology: 

• On-highway, manual transmission: Includes tractor trailers

• Urban, automatic transmission: Class 3-6 Box and Bucket, refuse haulers, and urban 

transit buses

• On-highway, automatic transmission: Includes motor coach

• Mixed duty cycle, mixed technology: Class 2b

4.5.1 Tractor Trailer (On-highway, manual transmission) 

The baseline tractor trailer is assumed to come equipped with a 10-speed manual transmission 

with overdrive. Fuel savings approaches include reducing mechanical losses in the driveline 

itself, or improving powertrain integration to improve the average engine thermal efficiency. 
4-69

Reducing mechanical losses in the driveline offers potential for 1.5 to 2.5 percent reduction in 

fuel consumption. Approaches identified during site visits include reducing driveline friction; 

using direct drive in top gear instead of overdrive; and switching to one drive axle instead of two. 

Driveline friction may be reduced by using improved lubricants and materials, or by improving 

lubrication management. One approach that was discussed uses an active lube level control 

system to vary the amount of lubrication depending on vehicle speed. At high speed, system 

inertia is great enough to overcome friction without lubrication. Under these conditions, 

lubrication actively contributes to driveline losses, so reducing lube levels provides an efficiency 

benefits. In total, driveline friction reduction is estimated to improve fuel efficiency by 1 to 1.5 

percent. These friction reduction opportunities are estimated to range from cost-neutral (as in the 

case of incremental friction reduction) to $500 [Frey 2007]. 

Using a direct drive top gear instead of overdrive, or switching to a single larger drive axle 

(instead of two smaller ones) can each improve driveline efficiency by reducing the number of 

mechanical connections. Benefits of direct drive were estimated to range from 1.5 to 2 percent at 

zero-cost. Using a single drive axle was estimated to improve driveline efficiency by about 1 

percent at high speed. This approach also allows a vehicle to use lower rolling resistance tires, on 

the new non-drive axle, which may enable an additional 1 to 2 percent benefit. We did not 

receive any information as to the cost of this system; its implementation requires additional 

vehicle controls and modification of the vehicles suspension system [Site Visits]. We estimate 

that the cost of these upgrades range from $200 to $300. 

Improved integration of the driveline with the powertrain in a tractor trailer can raise the average 

efficiency of the engine over an actual real-world drive cycle. The lowest hanging fruit entails 

appropriately matching system gearing to the specific application. This process entails selecting 

a top gear and rear axle ratio that matches typical cruise speed (ensuring that the engine is in its 

peak efficiency window). These specifications vary from fleet to fleet; to the extent that a vehicle 

purchaser knows the specific roads on which a truck will travel, systems can be highly optimized 

to match their application. Conversely, some purchasers simply use standard specs, or spec 

vehicles based on what they purchased in the past. As such, all of the major OEMs make a 

concerted effort to work with purchasing agents to properly manage the vehicle spec process. 

Beyond appropriately spec-ing the vehicle, there are several options for actively optimizing gear 

selection while in use. These include increasing the number of transmission gears, or selecting an 

automatic manual (AMT) or automatic (AT) transmission. Increasing the number of transmission 

gears offers only minor benefits for most line-haul applications. However, on some routes (such 

as through the mountains), increased transmission gearing can offer benefits of up to 5 percent 

[Site Visits]; however, this does not appear to be a major opportunity in this market segment. 

Adding additional transmission gears is estimated to add $1,000 [Global Insight 2004]. 

Both automatic and automatic-manual transmissions have some presence in this market segment. 

Based on information provided during site visits, we estimate penetration of these systems to be 

5 percent and 10 percent, respectively. AMTs and ATs both allow the vehicle to optimize gear 

selection to maximize engine efficiency. Although ATs optimize gear selection, they introduce 

an additional parasitic load to the driveline, which decreases or negates the efficiency benefit. 

AMTs, which are simply manual transmissions with an automated mechanical shift schedule, 

achieve the shift optimization benefits of an AT without the accompanying parasitic loads. 
4-70

Estimates of the fuel consumption benefits of AMT and AT technology vary widely – as low as 

2 percent, and as high as 19 percent [Detroit Diesel 2009b, Site visits]. This is due in large part to 

variations between drivers and duty cycles. However, feedback offered on site visits suggested 

that, on average, AMTs offer medium single-digit FC benefits. As such, we have estimated the 

benefit of an AMT to range from 4 to 8 percent for an average driver at a cost range from $4,000 

to $5,70034. However, it should be noted that the best, most well-trained driver with appropriate 

driving aids can approach the fuel efficiency benefits of an AMT, and some fleets have adopted 

this approach. Automatic transmissions are estimated to range from 0 to 5 percent benefit. This 

range reflects variation due to both duty cycle and the level of driver training. An AT is 

estimated to cost $15,000. Capital cost estimates are based on information provided during site 

visits and discussions with a dealer [Merrill 2009]. 

Table 4-46 summarizes the fuel consumption benefit, weight, and capital costs for tractor trailer 

driveline and transmission options. 

Table 4-46. Driveline and transmission options for class 8 tractor trailers 

Strategy % FC Benefit Weight Capital Cost 

Appropriate spec-ing 1 to 3% — — 

Friction reduction 1 to 1.5% — $0 to $500 

Direct drive 1.5 to 2% — — 

Single drive axle 1% — $200 to $300 

AMT 4 to 8% 80 lbs $4,500 to $5,700 

AT 0 to 5% 200 lbs $15,000 

4.5.2 Class 3-6 box and bucket, refuse haulers, and urban transit buses (urban, 

automatic transmission) 

Class 3-6 straight box trucks, bucket trucks, refuse haulers, and urban transit buses all operate on 

a predominantly urban, stop-and-go duty cycle which requires more shifts per mile than for other 

applications. Given the nature of this duty cycle, feedback offered during site visits suggest that 

automatic transmissions are appropriately matched to this segment. The entirety of the refuse 

truck and urban bus market currently use automatic transmissions; it is estimated that about 70 

percent of Class 3-6 box and bucket trucks also use ATs [Site Visits]. We have assumed that the 

baseline vehicle for these urban duty cycles uses a 6-speed automatic transmission. 

In these market segments, automatic power shift transmissions offer uninterrupted shifts, which 

gives increased vehicle drivability (which helps with driver retention), productivity, and in some 

cases, fuel efficiency. The productivity benefit is a result of the automatic transmissions offering 

better acceleration than manual or automatic-manual transmissions (AMT). As such, they allow 

users with large numbers of stops to get their job done faster. In certain applications, this can 

 

34 These estimates assume that the actual selling price is 0.6 times the list price furnished by manufacturers. 
4-71

save fuel. In addition, the smoother shifting associated with an AT allows the engine to run in a 

high efficiency regime more of the time, which can also offer fuel efficiency benefits. 

Opportunities for improving the fuel efficiency of the assumed baseline vehicle include friction 

reduction, reducing transmission parasitic losses, using more aggressive shift logic, and 

increasing the number of transmission gears. In addition, appropriately spec-ing the driveline can 

pay similar dividends to those observed in Class 8 tractor trailers in these market segments. Frey 

estimates that driveline friction reduction and transmission parasitics can improve fuel efficiency 

by up to 1 percent at costs ranging from 0 to $500. Aggressive shift logic (ASL) and early lockup 

is estimated by NHTSA to offer 1.5 to 2.5 percent improvement in light-duty vehicles at a cost of 

$59. Because it is not clear to what extent this is already employed in the medium and heavy 

duty sector, we have estimated the benefit for ASL to range from 0.5 to 1 percent at a cost of 

$100. 

Estimated benefits of increasing the number of transmission gears range from 1 to 5 percent 

[Walsh 2006, Site visits, NHTSA 2009], although it is not always clear what the baseline 

assumptions are. The NHTSA light-duty regulation estimates the fuel efficiency benefit of 

increasing from a 4/5 speed AT to a 6/7/8 speed AT to range from 2.7 to 4.1 percent. This would 

imply that the incremental benefit in going from a 6-speed to an 8-speed transmission is 

1.4 percent for a light truck. This estimate may be low for applications such as package delivery 

vehicles, transit buses, or refuse trucks, which have a highly transient duty cycle. As such, we 

have used a mid range of the benefit estimated in literature of 2 to 3 percent. 

NHTSA estimates that increasing from a 5-speed to an 8-speed automatic transmission costs 

$638 for a 5,000 lbs GVW truck. Information available on company websites35 includes a $405 

up-charge to go from a 5-speed to 6-speed transmission in a Class 2b Pickup. Given that the 

baseline vehicle uses a 6-speed, we estimate that the incremental cost of going from 6-speeds to 

8-speeds in a large light-duty truck is $425. To extrapolate this estimate to different vehicle 

segments, we scaled this value by the engine torque for a standard baseline vehicle, as shown in 

Table 4-47. 

Table 4-48 summarizes the fuel consumption benefit and capital costs of various driveline 

options for refuse haulers, transit buses, and Class 2b applications.

 

35 Dodge Ram website 
4-72

Table 4-47. Estimated capital cost of going from 6 to 8 speed automatic transmission 

Vehicle Class Torque (ft-lb) Multiplier Capital Cost 

Class 2a truck (NHTSA estimates) 332 

(5L gasoline) 

1.0 $425 

Class 2b pickup and van 365 to 750 

(5.4L gas to 6.7L diesel) 

1.1 to 2.3 $500 to 1,650 

Class 3-6 truck 750 to 1,300 

(6.7L to 9L) 

2.3 to 3.9 $1,000 to $1,650 

Transit Bus 850 to 1,300 

(7.6L to 9L) 

2.6 to 3.9 $1,100 to $1,650 

Motor coach 1,450 to 1,700 

(11L to 13L) 

4.4 to 5.1 $1,870 to $2,200 

Refuse 1,650 to 2,050 

(13L to 15L) 

5.0 to 6.2 $2,100 to $2,600 

Table 4-48. Driveline and transmission strategies for refuse hauler, class 3-6 box and 

bucket trucks, and transit buses 

Strategy % FC Benefit Capital Cost 

Appropriate spec-ing 1 to 3% — 

Aggressive Shift Logic and Early Lockup 0.5 to 1% $100 

Reduced AT parasitics and friction reduction 1% $0 to $500 

8-speed AT 2 to 3% See Table 4-47 

4.5.3 Motor Coach (On-Highway, automatic transmission) 

Motor coaches are unique in that they all use automatic transmissions but spend much of their 

time on the highway. This is because automatic transmissions offer a smoother ride, which is 

important in a passenger-driven application. That said, European motor coaches tend to use 

manual or automatic manual transmissions. We have assumed the following to characterize 

transmission and driveline opportunities in the motor coach segment: 

• Motor coaches generally use similar technologies to those used by tractor trailers to 

improve driveline efficiency, but adopt similar technologies to the transit bus to enhance 

transmission efficacy. 

• Because the motor coach does not have two drive axles, unlike the tractor trailer, it cannot 

benefit from switching to a single drive axle. 

• Because the motor coach spends more time at high speed, the efficiency benefit of using 

an 8-speed transmission is estimated to be lower. 
4-73

Table 4-49 summarizes driveline strategies for motor coaches. 

Table 4-49. Driveline and transmission strategies for motor coach 

Strategy % FC Benefit Capital Cost 

Appropriate spec-ing 1 to 3% — 

Aggressive shift logic and early lockup 1 to 2% $100 

Reduced AT parasitics and friction 

reduction 

1 to 1.5% $0 to $500 

AMT 4 to 8% -$10,00036

8-speed AT 1.5 to 2% $1,870 to $2,200 

(See Table 4-47) 

4.5.4 Class 2b Pickups and Vans 

The baseline class 2b vehicle is assumed to use a 6-speed automatic transmission. The capital 

costs and benefits for transmission and driveline strategies in Class 2b pickups and vans were 

primarily extrapolated from the NHTSA light-duty rulemaking. Benefits were assumed to be the 

same for Class 2b vehicles as for the NHTSA “large truck” category (GVW of 5,000 lbs). 

Capital costs are scaled according to engine torque, as this is a good proxy for transmission 

sizing. The results are shown in Table 4-50. 

Table 4-50. Driveline and transmission strategies for class 2b pickups and vans 

Strategy % FC Benefit Capital Cost 

Aggressive shift logic and lock-up 1.5 to 2.5% $60 

6 speed to 8 speed AT 2.7 to 4.1% $500 to $1,650 

AMT 5.5 to 9.5% $700 to $1,400 

The following options were considered: 

• Aggressive Shift Logic (ASL) and transmission lock-up, estimated directly from the 

NHSTA report. 

• Increased transmission gears: NHTSA estimates that the fuel efficiency benefit of 

increasing from a 4/5 speed AT to a 6/7/8 speed AT ranges from 2.7 to 4.1 percent. 

Capital costs were estimated by scaling the NHTSA data to the torque of a typical Class 

2b engine, as shown in Table 4-47. 

 

36 AMTs are a net cost savings in this application, as they would be replaced an AT. 
4-74

• Automatic-Manual transmission: Capital costs were estimated by scaling the NHTSA 

data to the torque of a typical Class 2b engine, as shown in Table 4-47. 

4.6 Hybrid Technologies 

4.6.1 Overview 

Hybrid vehicles represent a major fuel savings opportunity, particularly for vehicles that travel 

on duty cycles with frequent starts and stops or that spend large amount of time idling. Hybrid 

vehicles can improve the fuel efficiency of medium and heavy-duty vehicles in a number of 

ways: 

• Regenerative braking: Hybrid vehicles can recapture vehicle kinetic energy using 

electric motors or hydraulic pumps and store this energy for later use. 

• Engine-off at idle: A hybrid can shut the engine off when the vehicle is stopped. In 

medium and heavy-duty vehicles, three different types of idle reduction are possible: 

– Shutting the engine off at short stops, such as at traffic lights or package drop-off 

points. This is primarily important on urban pickup & delivery (P&D) routes. 

– Electrification of overnight hotel loads, which is primarily beneficial on line-haul 

vehicles. 

– Electrification of power take off (ePTO) systems: service trucks such as utility 

vehicles operate 

• Increase engine efficiency: A hybrid system can be used to improve the operating 

efficiency of the engine (i.e., the “drive cycle efficiency” that was discussed in the 

Section 4.1). This can be accomplished in several ways: 

– Launch assist: The hybrid energy source (either electricity, as in a hybrid-electric 

vehicle, or hydraulic power, as in a hydraulic hybrid) can replace or supplement 

engine power when the engine is at an unfavorable point on its operating map. This is 

the logic behind “launch-assist” systems, which use only electric or hydraulic power 

during low speed, low load operation. 

– Down-sizing: The hybrid system can be used to supplement engine power at peak 

load. In theory, the engine can then be down-sized. Down-sizing saves weight and 

reduces engine pumping losses37. In practice, this approach is only viable for vehicles 

that infrequently operate at high load. Vehicles that spend a large fraction of time 

operating at high load will quickly deplete the energy storage if this energy is being 

used to supplement the engine at high load. 

 

37 Reduced pumping losses is primarily a benefit for spark-ignition engines, but of some benefit in diesels. 
4-75

– Emissions integration: In theory, a hybrid system can be used to supplement engine 

power and reduce emissions.. This would allow engine manufacturers greater 

flexibility in reducing fuel consumption and emissions. In practice, current heavy 

duty emissions standards only regulate engine-out emissions, so using an innovative 

hybrid strategy that reduces vehicle emissions does not offer any current regulatory 

benefit. 

• Accessory electrification (HEVs only): Given the availability of electric power, HEVs 

enable accessory electrification, which allows parasitic loads to be run on an as-needed 

basis. Electric accessories can also be more efficient than belt-driven systems. 

• Systems integration: Electrification can enable waste heat recovery. Waste heat recovery 

systems can generate and store electricity allowing waste heat to be used when it is most 

beneficial to system efficiency. In addition, some engine manufacturers and suppliers 

suggested that the flexibility offered by hybrids (e.g., down-sized engines, accessories 

decoupled from the engine) could offer aerodynamic benefits especially in Class 8 over 

the road trucks. 

The benefits of hybridization vary widely depending on the duty cycle. This dependence is 

apparent even within a single homogeneous fleet using similar vehicles over ostensibly similar 

duty cycles. For example, data was presented to the committee that showed, for the same fleet, 

hybrid benefits varied on P&D routes from 10 to 35 percent [Davis 2008, Site Visits]. Similarly, 

controlled testing showed that similar buses operating on the stop-and-go CBD duty cycle 

demonstrated a 50 percent fuel savings, while those operating on a commuter duty cycle offered 

a 12 percent savings. Given this variance, it is very important to carefully define the duty cycle 

when assessing the fuel consumption benefits. 

Estimates of the fuel consumption benefits of hybrids are based on a loose consensus of 

published data and information that was furnished to the committee. One important point to 

stress regarding these estimates is that companies frequently report the benefits of hybrids in 

terms of fuel economy (i.e., MPG). As discussed in the introduction, fuel efficiency benefits are 

presented in terms of fuel consumption (gallons per mile). While the difference between the 

percent fuel economy benefit and the percent fuel consumption benefit are minor for differences 

on the order of a few percent, the difference grows as a function of the percent benefit. The 

relationship between the two is as follows: 

benefit

benefit FE

FC

1 %

1 % 1

+ = − Equation 4 

In the case of hybrids, for which fuel economy benefits of 30 to 40 percent are frequently 

reported, the difference between data presented in the technology matrix and that frequently cited 

in company literature and presentations to the committee is noticeable. In this case, the fuel 

consumption benefit would range from 23 to 29 percent. 

This chapter first summarizes the various hybrid architectures that are either currently in 

production, or that industry is developing. Then, we discuss factors that will influence the 
4-76

adoption of hybrid technology. The final portion of this chapter matches architectures that are 

discussed in this section to the specific applications that form the focus of this report. 

4.6.2 Overview of Hybrid System Architectures 

A number of different system architectures are being considered for the applications of interest. 

These are summarized in Table 4-51. 

Table 4-51. Hybrid architectures 

Architecture Technology Status Primary applications 

Medium Duty/Heavy Duty Parallel 

HEV 

Available now: 

Eaton, Azure, Volvo 

Refuse, Urban Pickup & 

Delivery (P&D) 

Medium Duty/Heavy Duty Parallel 

HEV w/ePTO 

Available now: 

Eaton, Volvo 

Bucket Truck 

Parallel Gasoline or Diesel HEV 

Bus 

Available now: 

ISE, Enova, BAE 

Transit Bus 

Dual Mode Diesel HEV Bus Allison Transit Bus 

Series Gasoline or Diesel HEV 

Bus 

Available now: 

ISE 

Transit Bus 

Parallel Hydraulic Hybrid Introduced in 2009: 

Eaton, Parker Hannifin, Crane 

Carrier 

Refuse, Urban P&D 

Series Hydraulic Hybrid Demo vehicles Refuse, Urban P&D 

Parallel Class 2b No production plans Class 2b pickups & vans 

Dual Mode Class 2b No production plans Class 2b pickups & vans 

Line-haul dual-mode HEV Demo vehicles Line-haul Tractor trailer, 

Line-haul parallel HEV Demo vehicles Line-haul Tractor trailer, motor 

coach 

4.6.2.1 Parallel Hybrid-Electric Vehicles 

A parallel HEV couples a small electric motor to the engine crankshaft (in a pre-transmission 

architecture), or to the drive axle (in a post-transmission architecture). Pre-transmission 

architectures are more prevalent. In a parallel architecture, the motor and the engine are both 

directly coupled to the drive shaft; the motor can be used to supplement or replace engine power 

during engine transients (especially at low speeds—so-called “launch assist”), or to recover 

kinetic energy through regenerative braking. Current systems use both lithium-ion and nickel 

metal-hydride (NiMH) batteries, as well as ultra capacitors, although there is widespread 

consensus that eventually lithium-ion batteries will dominate. Energy flows, power conditioning, 

and battery management are controlled by power electronics and an electronic control module. 

An example of one medium-duty parallel hybrid is shown in Figure 4-18. 
4-77

Figure 4-18. Parallel hybrid architecture [Coryell 2008] 

Parallel HEV systems are currently available in transit bus, motor coach, and Class 3-6 box & 

bucket trucks, and in fleet demonstration stage for refuse haulers. There have been a few 

demonstrations of Class 8 tractor trailers using a parallel architecture. We speculate that in the 

future, they may gain market share for Class 2b pickups and vans, although no systems are 

currently under development. 

4.6.2.2 Series Hybrid-Electric Vehicles 

A series HEV couples a small engine in series to an electric generator, which connect to an 

energy storage system and an electric motor. The motor is directly coupled to the drive shaft. In a 

series architecture, the electric system provides all of the motive energy for the vehicle, while the 

engine maintains energy storage charge level within a specified tolerance. This allows the engine 

to operates in a high-efficiency regime all of the time, which can offer benefits on highly 

transient duty cycles. However, because energy from the engine is converted to electrical and 

then mechanical energy, a series architecture incurs losses in the driveline that make it 

undesirable for steady-state, high-speed duty cycles. Series hybrids are used in some transit 

buses, but not in any other applications. 

4.6.2.3 Dual-Mode Hybrid-Electric Vehicle 

A dual mode system uses a double clutch system to switch between parallel operation, in which 

the engine and motor are both coupled to the drive shaft, and series mode, in which the engine is 

decoupled from the direct drive. A dual-mode vehicle operates in series mode at low speed, and 

in parallel mode at high speed. At low speed, the engine operates only on an as-needed basis, 

turning on to charge the battery when it is at low state-of-charge. At high speed, the engine 

switches to a direct drive, with the motor recovering braking energy and supplying supplemental 

power as dictated by the vehicle controls. 
4-78

A dual-mode system has been demonstrated by Arvin Meritor in Class 8 tractor trailer in a single 

vehicle, but they do not have any firm production plans. A dual-mode system has also recently 

been deployed in large light-duty pickups (e.g., the Cadillac Escalade, Chevy Tahoe, and the 

GMC Yukon), so we speculate that this architecture could be deployed for Class 2b pickups and 

vans. 

4.6.2.4 Hydraulic Hybrids 

Hydraulic hybrid vehicles employ the same basic architecture as hybrid-electric vehicles. 

However, in a hydraulic hybrid vehicle, the battery is replaced with a hydraulic accumulator, and 

electric motor/generators are replaced with hydraulic motors/pumps. As in a hybrid-electric 

architecture, kinetic energy from braking can be recovered and stored: in a hydraulic hybrid, 

braking energy is used to drive a hydraulic motor that pumps fluid from a low pressure fluid 

reservoir, to a high pressure accumulator. This energy can then be used to supplement engine 

power by releasing the fluid in the high-pressure accumulator back to the low-pressure reservoir, 

driving the motor in process (Figure 4-19). 

Figure 4-19. Parallel Hydraulic Hybrid (“Launch Assist”) Architecture 

[Gotting 2007] 

In practical terms, the key discriminator between a hydraulic hybrid and a hybrid-electric system 

is that hydraulic systems can recover energy far more efficiently, while electric systems can store 

significantly more energy. Current hydraulic hybrids are capable of capturing on the order of 

70 percent of kinetic energy from heavy-duty vehicles – this is due to both the high rates at 

which power can be recovered and the fact the energy storage system is virtually lossless 

[Gotting 2007]. In contrast, a hybrid electric vehicle is forced to scrub a significant amount of 

braking energy using conventional friction brakes, and it must also deal with roundtrip energy 

losses from electrochemical energy storage systems. Conversely, the energy density of hydraulic 

storage is significantly lower than that of electrical energy storage. Due to these differences, 

hydraulic hybrids are targeted for power-driven applications – that is, duty cycles that have high 

regenerative braking requirements but relatively low energy requirements, such as refuse trucks 

and house-to-house delivery. 
4-79

Parallel hydraulic hybrids are currently available for refuse trucks, but suppliers also intend to 

introduce hydraulic launch assist systems for urban package delivery vehicles and shuttle buses 

in the next several years [Gotting 2007, Site Visits]. Series hydraulic hybrids are still in the 

prototype stage. They are being evaluated for pickup & delivery vehicles and for refuse haulers, 

for which they have demonstrated fuel consumption reductions on the order of 50 percent 

[Kargul 2009]. 

4.6.3 Cross-Cutting Issues and Future Outlook

During discussions with manufacturers and suppliers, a number of overarching themes emerged 

with respect to hybrid technology. These issues are summarized below: 

Capital costs: Due to low production volumes, hybrid systems are currently prohibitively 

expensive for many applications. Depending on annual mileage, payback for urban delivery or 

refuse vehicles is currently 5 to 10 years (not including brake savings). There is general 

consensus that as production volumes increase, costs will decrease significantly (see Figure 4-

20). This is particularly true for battery technology. Current systems use both NiMH and lithiumion batteries; in the bus market, ultra capacitors are also used. NiMH batteries are the lowest cost 

option (estimated on site visits at $700 to $800/kWh). Lithium-ion batteries are currently a lowvolume item in the automotive sector. However, as the light-duty hybrids switch to using 

lithium-ion, these volumes should increase and costs come down significantly. 

Figure 4-20. Lithium-ion vs. NiMH cost curves [Miller 2006] 

Reliability: In hybrid-electric systems, battery life and performance over the life of the vehicle is 

still unproven. Manufacturers currently offer warranties that range from 3 years (standard) to 

6 years (extended), and expect systems to last eight years [Ham 2008, Site Visits]. Eight years is 
4-80

a typical service life for a service or delivery vehicle and 12 years is the service life for a transit 

bus. However, system reliability over the life of the vehicle has not yet been demonstrated in any 

large fleet tests. In addition, batteries are frequently oversized as a means of reducing the depth 

of discharge and to manage power fade as the system ages. End-of-life may be particularly 

problematic in line-haul applications, which may go through several owners and last for upwards 

of 15 to 20 years. 

Similarly, hydraulic hybrids have not been tested in large numbers over a full automotive 

lifetime. Components such as hydraulic pumps/motors have in many cases been developed 

specifically for hydraulic hybrids, and will need to be thoroughly vetted. 

Electrification of accessories. These issues were discussed in greater detail in Section 4.1. It 

was mentioned during several different site visits that these parts are not currently available in 

large quantities, leading to high cost. Electrifying accessories will allow the engine to shut off at 

idle, which can offer significant (~5 percent) additional fuel savings on urban routes. Some 

systems are already fully electrifying accessories, but adoption is not yet universal. 

Brake O&M benefits: In addition to saving fuel, hybridization significantly reduces brake costs. 

Suppliers and OEMs expect that hybrids will more than double the brake life. For some 

applications, these savings can outweigh the fuel savings. 

System integration: As hybrid systems become more fully integrated into overall vehicle 

architecture, there are a number of opportunities to further optimize the system: 

• Depending on the application, hybridizing a vehicle can enable engine down-sizing. 

Currently, this is not widely done. Part of the reason is that industry is still figuring out which 

applications can use a down-sized engine without sacrificing mission performance. Another 

important factor is that smaller engines may be unavailable that meet medium/heavy-duty 

warranty requirements. One supplier suggested that they would be able to offer optimized, 

right-sized powertrains at volumes of 5,000 to 10,000 vehicles per year. 

• There is opportunity for substantial integration between hybrid systems and exhaust 

aftertreatment systems. For example, a system designer could vary engine load to manage 

exhaust gas temperature, thereby offering emissions benefits. However, current standards 

measure engine-out emissions. To get credit for any benefit, EPA would need to switch to 

measuring emissions on a vehicle basis or develop a method to credit the lower vehicle 

emissions. 

• Improved system power density, component efficiency, and design integration is expected to 

offer additional fuel savings opportunities. 

• Electrification is viewed as an enabler for more efficient waste-heat recovery systems – such 

as electric turbo-compounding or electric bottoming cycles. In a hybrid vehicle, electric 

waste heat systems can offer an additional 1 to 2 percent efficiency benefit at neutral cost 

compared to an equivalent mechanical waste-heat system. 
4-81

• By narrowing the design window, hybrid systems enable the engine to be optimized to 

deliver peak efficiency within a narrow operating band. This opportunity applies primarily to 

dual-mode or series systems. 

Taken as a whole, improved systems integration can offer an additional 5 to 10 percent 

improvement in fuel efficiency in future systems. In tandem, higher sales volume can reduce 

capital costs by a factor of two. 

4.6.4 Summary — Hybrid Applications 

This section summarizes the hybrid systems that are currently available, system costs and fuel 

consumption benefits, and future outlook for each of the vehicle classes that form the focus of 

our analysis. 

4.6.4.1 Class 3-6 Straight Box 

Straight box trucks typically travel on an urban pickup and delivery (P&D) duty cycle that 

matches very well with hybrid-electric and hydraulic hybrid architectures. Over the long-term, 

there is also potential for plug-in hybrid or all-electric vehicles to come into this market segment. 

All of the major OEMs currently offer production HEVs in this segment (see Table 4-52). 

Eaton’s system is the most common system; they have sold approximately 1,400 units since 

launching series production. These systems have demonstrated fuel consumption benefits on the 

order of 20 to 25 percent, although benefits vary considerably depending on the duty cycle. The 

production systems all use a parallel hybrid architecture and either currently use lithium-ion 

batteries, or intend to in the near future. Current costs range from $35,000 to $42,000 [Site 

Visits, Merrill 2009, Laviolette 2009]. Based on feedback offered during site visits, there is 

general agreement that increased automotive lithium-ion production volumes could decrease 

these costs by a factor of two. There are also a number of opportunities to continue to optimize 

the system. These include full electrification of accessories, which will allow engine shut-down 

at idle; integration of the hybrid system with emissions control; engine down-sizing; and 

improved integration and packaging. In combination, these enhancements could improve fuel 

consumption benefits by another 5 to 10 percent. 

Table 4-52. Production-intent medium duty and heavy duty HEV systems, no ePTOa 

System Attribute Eaton Volvo Azure 

Motor (peak) 44 kW 120 kW 100 kW 

Battery Li-Ion, 2 kWh Li-Ion NiMH 

2.4 kWh; 288 V 

% FC 20 to 25% 20% 23 to 25% 

No Idle? No Yes Yes 

Elec. Launch? Yes Yes – 12 MPH Yes 

Applications Class 3-7 Delivery; 

Refuse soon 

Refuse; 

Delivery soon 

Small Delivery, 

Shuttle 
4-82

 a Site Visits, Carpenter 2008, Ham 2008, Volvo 2009c, Volvo 2009d, Azure 2009, GCC 2008 

Hydraulic hybrid vehicles (HHVs) have not yet been commercially introduced in this segment 

but are intended as future offering for package delivery vehicles. Both parallel and series HHVs 

have potential in this segment. The fuel consumption benefit for the parallel HHV is estimated to 

range from 20 to 25 percent [Gotting 2007]; based on feedback from site visits, costs are 

estimated to range from $30,000 (high volume) to $40,000 (initial production), as shown in 

Table 4-53. The series HHV has been demonstrated to offer 40 to 50 percent fuel consumption 

benefit [Kargul 2009]; estimates provided during site visits suggest an incremental cost of 

$40,000 (high volume) to $50,000 (low volume). 

Table 4-53. Hybrid technology capital costs and FC benefits for class 3-6 box trucks 

Architecture Capital Cost %FC Benefit Intro year Weight 

Parallel HEV $35-$40K (Low) 20 to 25% 2007 450 lbs 

Parallel HEV, 

Future 

$18-$20K (High) 25 to 35% 2014 350 lbs 

Parallel HHV $40K (Low) 

$30K (High) 

20 to 25% 2011 1,000 lbs 

Series HHV $50K (Low) 

$40K (High) 

40 to 50% 2013 ~1,500 lbs 

For some applications, plug-in hybrid or fully electric vehicles could greatly reduce or eliminate 

fuel use at low cost. However, these systems were not fully evaluated for this study. 

4.6.4.2 Class 3-6 Bucket Trucks 

Bucket trucks typically spend only a few hours per day driving, and the rest of the time idling to 

operate onboard machinery. This extensive idle time presents a major opportunity for 

hybridization. Most of the HEV systems offered in the straight box truck segment are also 

offered with electronic power take-off (ePTO) systems targeted for service and utility vehicles. 

These ePTO systems use the same architecture as the conventional HEV, but include a larger 

battery pack that is capable of powering mission loads for several hours at a time. On a typical 

duty cycle, the engine is required to turn on for only short (~6 minute) periods to recharge the 

battery every one to two hours. 

HEVs with an ePTO system have demonstrated a 30 to 40 percent reduction in fuel consumption, 

and nearly 90 percent reduction in idle time. Capital costs estimates for these systems range from 

$49,000 to $52,000 [Site Visits, Merrill 2009], as shown in Table 4-54, but have the same 

potential to realize significant cost reductions due to battery scale as the straight box segment. In 

high-volume, these costs could decrease to $25,000 to $30,000. Grid-charged vehicles – either 

plug-in hybrid or electric vehicles – could eventually become important in this segment. 
4-83

Table 4-54. Hybrid technology capital cost and FC benefits for class 3-6 bucket trucks 

Architecture Capital Cost % FC Benefit Intro year Weight 

Parallel HEV 

w/ePTO 

$49 to $52K (Low) 30 to 40% 2007 ~650 lbs 

Future Parallel 

HEV w/ePTO 

$25 to $30K (High) 35 to 45% 2014 ~500 lbs 

4.6.4.3 Refuse Haulers 

Given the high number of stops and starts in a refuse duty cycle, refuse trucks are ideally suited 

to the highly efficient energy recovery capability of hydraulic hybrid architectures. HEVs are 

also being evaluated in this segment. 

Production parallel HHVs are being introduced at the end of 2009. Fleet tests have demonstrated 

fuel consumption benefits on the order of 20 percent. These systems can also be tuned to 

maximize acceleration, which increases productivity by allowing a single vehicle to visit more 

houses per day. Systems tuned to maximize productivity have been shown to increase 

productivity by 11.5 percent while decreasing fuel use by 14 percent for a total fuel savings of 

26 percent. HHVs also offer a significant O&M savings by more than doubling brake life. Based 

on information provided during site visits, initial production systems are expected to cost 

$40,000; with increased volume, costs may come down incrementally. We have estimated a 

high-volume incremental cost of $30,000. 

Parallel HEVs may also gain traction in this segment, particularly for smaller refuse vehicles that 

do not generate as much braking energy. Eaton is considering introducing their parallel HEV 

system in a refuse vehicle, and Volvo has already developed such a system. The Volvo/Mack 

system includes an optional grid-charged compactor system that they claim reduces fuel use by 

an additional 10 percent; we did not find any information that describes the size of the battery 

pack needed to achieve this benefit, but we speculate that it is much larger than would be viable 

in a production system [Volvo 2009c, 2009d, GCC 2008]. As such, we have reduced the ePTO 

benefit by one half. It is estimated that the HEV offers a 20 percent fuel consumption benefit for 

refuse vehicles at a similar incremental cost to that seen in the box truck segment. The gridcharged compactor option reduces fuel use by 25 percent, and is estimated to cost the same as the 

bucket truck ePTO system, as shown in Table 4-55. 
4-84

Table 4-55. Hybrid technology capital cost and FC benefits for refuse haulers 

Architecture Capital Cost 

% FC 

Benefit Intro year Weight 

Parallel HEV $35-$40K (Low) 20% 2010 450 lbs 

Parallel HEV (Future) $18-$20K (High) 25 to 30% 2014 ~350 lbs 

Parallel HEV, ePTO $52K 25% 2010 ~650 lbs 

Parallel HEV, ePTO (Future) $25 to $30K 30 to 35% 2014 ~500 lbs 

Parallel HHV $40K (Low) 

$30K (High) 

20 to 25% 2009 1,000 lbs 

Series HHV $50K (Low) 

$40K (High) 

40 to 50% 2013 ~1,500 lbs 

4.6.4.4 Class 8 Tractor trailer 

A line-haul duty cycle limits the amount of energy that can be recovered from regenerative 

braking. Rather, the advantages of hybridizing in this segment come from electrifying 

accessories and hotel loads, as well as limited gains from energy recovery and launch assist. 

Hybridizing a tractor trailer may also act as an enabler for waste heat recovery or aerodynamic 

drag reductions. The benefits of a hybrid on a line-haul duty cycle are expected to be much lower 

than those seen for urban vehicles; however, given the high annual mileage in line-haul 

applications, many in industry are optimistic that HEVs will become market viable in the next 

five years. 

Two different hybrid architectures are being considered for Class 8 tractor trailers: a dual-mode 

HEV (Arvin Meritor’s system) [Kramer 2008], and a parallel HEV (Eaton’s system) [Coryell 

2008, Carpenter 2007]. Over the road benefits (i.e., not including idle reduction) are estimated to 

range from 5 to 7 percent for the parallel system [NESCCAF 2009, Coryell 2008], and 6 to 9 

percent for the dual-mode38. The benefits for both architectures are unproven in real-world 

applications, and feedback offered on site visits indicated that the actual real-world benefits are 

significantly lower. However, the systems that demonstrated these lower real-world benefits 

were not optimized for line-haul operation and did not include a full slate of electric accessories. 

As such, we have used the estimates from drive cycle modeling, which more fully characterized 

the hybrid system’s capabilities. 

These on-road benefits are supplemented by overnight hotel road reduction, which reduces fuel 

use by an additional 5 to 8 percent, similar to that observed for APU idle reduction systems. 

Hotel loads are met by running the engine for a few minutes (4 minutes per hour, according to an 

Eaton/PACCAR demonstration) to recharge the battery [Carpenter 2007]. Both architectures are 

in the early development stage. 

 

38 Arvin Meritor has claimed benefits of 10 to 15 percent, but these estimates include overnight hoteling. 
4-85

Feedback offered on site visits suggest that demonstrated on-road fuel consumption benefits of 6 

to 7 percent is needed to interest fleets in this application. There is potential to further refine 

these initial prototype systems to narrow the engine’s design window (thereby increasing engine 

efficiency) and possibly allow further integration with the emissions control system. 

Hybridization of the line-haul segment can also act as an enabler for electric waste-heat recovery 

and for improved vehicle aerodynamics (by removing belt driven accessories, for example). 

Incremental costs for the parallel architecture are estimated to range from $30,000 to $40,000 for 

initial production; and come down to $20,000 to $25,000 for high volume production. The dualmode system is estimated to cost $45,000 to $55,000, which could drop to $25,000 to $30,000 in 

high volume. Costs for the parallel architecture are based on bottom-up costing from the 

NESCCAF/ICCT study; these are fairly consistent with our projection for medium-duty hybrids, 

which we believe will be of similar size. The dual-mode system requires additional energy 

storage (perhaps 10 to 20 kWh in a production system, versus ~4 kWh in a parallel architecture), 

and an additional motor/generator. The higher cost estimate attempts to account for this 

additional hardware. Table 4-56 summarizes the benefits and costs for these hybrid systems. 

Table 4-56. Hybrid technology capital cost and benefits for class 8 tractor trailer hybridsa

Architecture Capital Cost % FC Benefit Intro year Weight 

Parallel $35 to $45K (Low); 

$20 to $25K (High) 

5 to 7% 2013 ~500 lbs 

Dual-Mode $45 to $55K (Low); 

$25 to $30K (High) 

6 to 9% 2013 ~750 lbs 

a

Does not include idle reduction benefits 

4.6.4.5 Transit Bus 

Hybrid powertrains are already widely deployed in the transit bus segment, due in large part to 

large federal subsidies (90 percent of the incremental costs of hybrid systems are funded).39 They 

are estimated to comprise 25 to 30 percent of the market in 2009. Most of the systems on the 

road use a parallel diesel configuration, although diesel series hybrids and gasoline series hybrids 

are also offered. 

As transit buses are the most mature market segment, they offer insight as to the impact of duty 

cycle on the benefits of hybridization. Road testing performed on 40 ft transit buses at Altoona 

using SAE Type II fuel economy test procedures are summarized in Figure 4-21 for a variety of 

bus manufacturers [Altoona]. The Altoona tests were performed on three bus test cycles: central 

business district (CBD), Arterial, and Commuter. The arterial and commuter cycles are higher 

speed and have less stops compared the CBD cycle. The CBD cycle includes acceleration from 0 

to 20 mph, followed by a segment of 20 mph steady speed, a deceleration, and idle. This is 

 

39 For hybrid and alternative fueled buses 80% of the diesel/baseline bus is funded and 90% of the incremental costs of the hybrid or 

alternative bus is also covered by Federal subsides. 
4-86

 Road and Dyno Tests

0

2

4

6

8

10

0 10 20 30 40 50

Cycle Average Speed (mph)

Fuel Economy (mpg)

New Flyer 2007 diesel

New Flyer 2005 hybrid

New Flyer 2004 gasoline

hybrid

Orion 2003 diesel

Orion 2002 hybrid

Orion 2004 hybrid

Gillig 2004 diesel

Gillig 2004 hybrid

CBD Arterial Altoona Commuter

50% 18% 12%

Average HEB Benefit

Figure 4-21. Fuel economy benefits of 40-foot hybrid transit buses 

compared to 40-foot diesel transit buses 

repeated over 2 miles. Data on this figure also includes several dynamometer tests performed on 

buses over the CBD cycle [Clark]. The New Flyer buses were tested with the ISE series system 

(gasoline) and the Allison EV40 system. The Orion buses used the BAE hybrid system. The 

Gillig buses used the Allison EV40 hybrid system. 

These data indicated that over the CBD cycle fuel economy increases some 50 percent compared 

to the non-hybrid diesel baseline. The benefit decreases to 18 and 12 percent for the arterial and 

commuter cycles, respectively. This decrease is expected since the hybrid system’s benefit is 

increased for cycles with more stops and starts (regeneration energy from braking can be used 

during acceleration). 

The curb weight the diesel baseline buses ranged from 27,000 lbs to 28,000 lbs and the hybrid 

buses curb weight ranged from 28,000 lbs to 30,000 lbs. The weight of the hybrid systems 

ranged from a low of 940 lbs to a high of 2,800 lbs. Both New Flyer and Orion indicate that they 

will be introducing new hybrid buses that will be more streamlined and some 2,000 lbs lighter 

than those previously tested at Altoona. Their diesel buses will also be lighter--in the range of 

25,000 lbs curb weight [New Flyer, Orion] 

Based on these data, fuel consumption benefits range from 12 to 50 percent depending on the 

severity of the duty cycle. Incremental system costs are $200,000 to $220,000, depending on 
4-87

hybrid architecture and whether a gasoline or diesel engine is used. It is unclear to what extent 

these high costs are a function of low production volumes (and hence reflect that actual system 

cost), and to what extent they simply reflect what the market will bear – particularly in light of 

the heavy government subsidies. These results are summarized in Table 4-57. It should be noted 

the transit bus market is fairly small – on the order of 5,000 buses per year – and hybrids already 

have 25 percent market share, so production volumes will not increase that much beyond present 

day levels. 

Table 4-57. Hybrid technology capital cost and benefits for transit buses 

Architecture 

Incremental 

Capital 

Cost % FC Benefit Intro year 

Incremental 

Weight 

Gasoline Series $200,000 25 to 35%a Available – ~150 on road 2,000 lbs 

Diesel Series $220,000 30 to 40% Available – ~ 75 on road 2,600 lbs 

Diesel Parallel & 

Dual-Mode or dual 

mode 

$200,000 22 to 35%b

 Available – 2,000 to 3,000 on road 940 to 2,840

a Site Visits 

b FTA 2005, Altoona 

4.6.4.6 Motor Coach 

Currently, 20 to 25 percent of hybrid bus systems are sold in motor coaches [Site visits]. 

Presumably, these systems go into motor coaches that travel in primarily urban applications. 

Longer term, we would expect motor coach hybrid systems to more closely resemble the systems 

that are being considered for line-haul applications. This is because the motor coach duty cycle is 

more similar to a regional line-haul tractor trailer than to a transit bus. 

The track testing discussed in the transit bus section (see Figure 4-21) indicates that hybrid 

benefits on a commuter cycle are approximately 12 percent. The Northeast Advanced Vehicle’s 

Consortium showed on-road fuel savings for an MCI motor coach of 5 to 40 percent on a highspeed suburban duty cycle [FTA 2005]. MCI has quoted fuel savings that range from 20 to 

54 percent for their system [MCI 2008], but we speculate that these numbers correspond to a 

motor coach operating on a city or suburban drive cycle. 

It seems unlikely that hybrids will have a major impact in this sector given the high cost of 

hybrid bus systems and the relatively low benefit on a commuter motor coach duty cycle. We 

have considered two potential hybrid architectures for the motor coach segment: 

• A parallel HEV system similar to that used in transit-buses. This system would have a 

large (>20 kWh) energy storage system, and is likely oversized for this application. 

• Longer term (2015 timeframe), a parallel HEV system similar to that prototyped for Class 

8 tractor trailers. This system would likely be better matched to the motor coach duty 

cycle, but it is not clear that there will be enough inertia to develop such a system for this 
4-88

market segment. Given the low volume of vehicles in this segment, we only included the 

“low volume” cost estimate for the line-haul hybrid. 

We anticipate benefits that range from 7 to 15 percent, and costs that are similar to the analogous 

system from either the transit bus or Class 8 line-haul segment (see Table 4-58). We suspect air 

conditioning loads will be one of the major drives for considering hybrids in the application. 

Table 4-58. Hybrid technology capital cost and benefits for motor coaches 

Architecture Capital Cost % FC Benefit Intro year Weight 

Parallel HEV 

Transit Bus 

$180,000 to 

$220,000a 10 to 15% Available – a few 

hundred on the road 

1,000 to 

2,000 lbs

Parallel HEV 

Line-haul 

$30,000 to 

$40,000 7 to 10% 2015 500 lbs 

a

 MacPherson 2008 

4.6.4.7 Class 2b Pickups & Vans 

No hybrids systems are currently offered in the class 2b segment, and we are not aware of any 

specific plans to begin production. Nor does the NHTSA [2009] rulemaking for light-duty 

vehicles anticipate any new “large truck” (5,000 to 6,000 lb GVW) hybrids coming into the 

market by 2011; as such, they did not explicitly model the costs or benefits of such a system. 

We have estimated the costs and benefits for two different class 2b hybrid systems: a dual-mode 

hybrid, similar to those used in some of the larger light-duty hybrids (for example, the Cadillac 

Escalade); and a simple integrated starter/generator parallel hybrid similar to the Eaton system or 

the Azure system used in Class 3-6 vehicles. 

System costs were estimated by extrapolating NHTSA’s hybrid vehicle cost model to Class 2b 

vehicles. The NHTSA cost model includes component cost estimates (expressed in $/kW, for 

example) and sizes for a mid-size vehicle, and then scales these costs to different vehicle 

segments according to certain vehicle parameters, such as gross vehicle weight, footprint, and 

engine displacement. Applying this cost model across a range of Class 2b vehicle weights (6,000 

to 10,000 lbs) and engine displacements (5.4L to 6.8L) gives high volume cost estimates as 

shown in Table 4-59. Because the NHTSA study uses component costs consistent with high 

production volumes, we have included a low-volume cost estimate that simply multiplies the 

high volume cost by a factor of 2. 

The fuel consumption benefits for a Class 2b dual-mode hybrid is estimated to range from 20 to 

30 percent; this is based on estimates from Vyas [2002] and EPA [2008] – neither of which 

applies specifically to this market segment. No estimates are available for the benefits of a 

parallel Class 2b vehicle. Given the mixed duty cycle, we estimate benefits would range from 15 

to 20 percent for this vehicle class. The EPA study also includes a 42V start-stop hybrid; 

however, feedback provided during site visits suggested that the benefits for this configuration 

are unproven, so we did not include it. 
4-89

Table 4-59. Hybrid technology capital cost and benefits for class 2b pickups and vans 

Item Parallel Dual-Mode 

FC Benefit 15 to 20% 20 to 30% 

High-volume cost 

(NHTSA cost model) 

$8,200 - $10,300 $12,000 - $17,000 

Low-volume cost 

(NHTSA x 2) 

$16,400 - $20,600 $24,000 - $34,000 

Intro Year 2014 2014 

Weight ~200 lbs ~250 lbs 

4.7 Idle Reduction 

Idle reduction technologies transfer the work done by the main propulsion engine for powering 

auxiliary systems (such as air conditioners, heaters, and engine warmers) to other more efficient 

systems. For refuse haulers, transit buses, box and bucket trucks, and motor coaches, idle 

reduction technologies target reducing in-use idling in traffic or at work sites using electrification 

of auxiliaries and engine-off at idle. These idle reduction strategies are discussed in the section 

on engines (Section 4.1) and hybrid vehicles (4.8). This section focuses on options to reduce 

overnight hotel loads in long-haul tractor trailers. 

In 2000, it was estimated that, on average, diesel intercity tractor trailers idle more than 1,800 

hours per year when parked overnight consuming more than 838 million gallons of fuel annually 

[Stodolosky 2000]. However, idling regulations have been enacted in 25 states to address urban air 

quality concerns and may have motivated a reduction in the annual average idling hours in large 

part through the introduction of anti-idling technologies [ATRI 2009]. As such, our estimates of 

the average engine idle time, which are based on data that is now nearly ten years old, may be 

high. On the other hand, a high mileage truck may idle significantly more than this: a truck that 

idles for eight hours per day for 300 days per year spends 2,400 hours per year in a hotel mode. 

EPA estimates that fuel use during idle uses 0.8 to 0.9 gallons of fuel per hour [Smartway]. This 

equates to 1,440 to 2,160 gallons of fuel per year – or 7 to 10 percent of the total fuel used by a 

line-haul truck40. Hence, reducing these overnight hotel loads for tractor trailers can significantly 

impact fuel efficiency in this segment. High diesel prices and anti-idling regulations have led to 

the development of a variety of truck idle reduction technologies. Truck idle reduction 

technologies fall into five main categories: 

• Automatic Shut-Down/Start-Up Systems 

• Battery Powered 

• Fuel Operated Heaters 

 

40 Assume: 120,000 miles per year, 6 MPG, 1,800 to 2,400 hours of idle at 0.8 to 0.9 gal/hr 
4-90

• Auxiliary Power Units or Generator Sets 

• Truck Stop Electrification 

Each idle reduction technology targets a specific set of operational requirements. Benefits 

depend upon the amount of idling, climate, time of year, and types of auxiliary loads. There is 

not one solution that fits the northern (high heating loads) and southern (high cooling loads) 

climates. There is a great deal information on idle reduction strategies, fuel economy and capital 

costs on EPA’s Smartway website [Smartway 2009b]. 

4.7.1 Automatic Shut-Down/Start-Up Systems 

Automatic engine idle management systems monitor cabin and engine temperature and turn the 

engine on/off as needed to maintain the desired temperatures. Several engine manufacturers offer 

electronically controlled optimized idling control devices. Higher end integrated systems include 

thermal storage. More advanced systems run the engine at higher load to keep the maximize 

engine efficiency when it is on. Table 4-60 characterizes several such systems. We did not 

receive information as to the rate of fuel use for this type of system. However, Duleep [2008] 

estimates that these systems reduce fuel consumption by 3 percent. 

Table 4-60. Automatic shut-down/start-up systems comparison 

Feature/Supplier BBW 

IdleSmart 

Cummins 

ICONTM Idle 

Control 

TAS TempA-Start 

Monitors temperature inside and out 9 9 9

Auto starts engine 9 9 9

Increases engine speed for maximum efficiency 9 9

Monitors system (i.e., oil and cab temperature, battery voltage) 9 9 9

Heats and cools cab 9 9 9

Idles down 9 9

Shuts down engine 9 9 9

Transferable to successive trucks 9 9 9

Weight (lbs) 30 na 14

Retail price $3,750 $1,325 $2,500

4.7.2 Battery-Powered 

Battery-powered idle reduction systems incorporate the use of either the vehicle’s battery or a 

separate battery pack to power the heating and/or cooling of the cab and powering of on-board 

appliances. A few systems also offer shore power connections. Each of these systems provides 

between 8 and 12 hours of runtime. Because of this limited duration, they may not be ideal for 

applications that require longer term (weekend) heating or cooling. Table 4-61 compares a 
4-91

Table 4-61. Battery-powered idle reduction systems comparison 

Feature/Supplier 

Autotherm 

T-2500 Energy 

Recovery System 

Bergstrom NITE 

Dometic 

Driver Comfort 

System 

Glacier Bay 

ClimaCab 

Idle Free Systems 

Reefer Link System 

Kenworth Clean 

P

Heats cab 9 9 9 9 9 9 9 Cools cab 9 9 9 9 9 9 Powers on-board appliances 9 9 Circulates heated coolant from engine to heater coils 9Runs off of vehicle battery 9 9 Runs off separate battery pack 9 9 9 9 9 9 Shorepower connection 9 9 9Automatic start 9

at engine off 

9 9

Automatic shut down 9 9 9Monitors system (coolant temperature, battery voltage) 9 9(cab only) 9 9 Run time (hours) na 10 10-15 10 (heating) 12 (cooling) 10 (coolinThermal storage cooler 9 Direct fueled heater 9 9 Weight (lbs) 5 210 na 520 

161 

(not including 

batteries) 

200 550 

Retail price $575 to $710 $3,495 $3,500 to $7,500 $6,895 $7,995 
4-92

variety of systems currently available as identified by the U.S. EPA Smartway website [2009b]. 

As shown, each system offers various features and have a retail cost between $575 and $7,500. 

Both Kenworth and Peterbilt have introduced idle reduction systems on their products. The 

Kenworth system is called Clean Power and operators could see as high as 8 percent reduction in 

fuel consumption. The system, however, depends greatly on the application. Operators with 

substantial heating requirements could see the benefit reduced to 1 to 2 percent. Both systems 

depend on the current battery capacity. Current systems use lithium-ion batteries and 

manufacturers are looking at various chemistries for future generations. There is an expectation 

the passenger car market will drive economies of scale and lower battery costs. 

We have assumed that these systems fully displace the engine idle load but need to be recharged 

frequently from an off-board source to achieve this benefit. 

4.7.3 Fuel-Operated Heaters 

Also known as direct-fired heaters, fuel-operated heaters are available to heat either the cab or 

engine or both (Table 4-62). These heaters use significantly less fuel than the primary engine by 

supplying heat from either a combustion flame or a small heat exchanger, thereby, eliminating 

losses from engine friction or heat loss. In MY07, there was about 10 percent market penetration 

for direct-fired heater option. 

Table 4-62. Fuel-operated heater comparison 

Espar Heater 

System 

Webasto Product North 

America 

Feature/Supplier 

Automotive 

Climate 

Control Cab Engine Cab Engine 

Heats cab 9 4 models 2 models 

Manual or automatic control Yes Auto Auto Auto 

Battery-powered fuel fired heaters 9 9 9 9 9

Heats engine 2 models 3 models 

Fuel use 1 gal per 

24 hours 

1 gal per 

20 hours

1 gal per 

4-6 hours 

1 gal per 

20 hours 

0.03 to 0.24 

gal per hour 

Retail price $920 to 

$1,200 $1,000-$3,000 $1,000-$3,000 

4.7.4 Auxiliary Power Units 

Auxiliary power units (APUs) provide electricity and heat with the help of a small internal 

combustion engine equipped with a generator and heat recovery device. Cooling can be provided 

with the installation of an electric air-conditioner in the cab. Many APU devices are available. In 

addition to those APUs compared in Table 4-63, Navistar recently announced in a press 

release41: 

 

41 http://www.reuters.com/article/pressRelease/idUS213209+07-May-2008+BW20080507
4-93

Table 4-63. Available auxiliary power unit comparison 

Supplier Heats cab Cools cab Heats engine FC (gal/hour) 110V AC Auto-on S

Auxiliary Power Dynamics Yes Yes Yes 0.25 Yes Yes Black Rock Systems 26,000 btu 26000 btu 0.20 or 0.30 Carrier Transicold Yes Yes Yes 0.2 Yes Yes Comfort Master 31,000 btu 31,000 btu 0.25 Yes Yes Crawfurd Manufacturing 22,000 btu 22,000 btu Diamond Power Systems 14,500 btu 14,500 btu 0.26 Yes Yes Double Eagle Industries Yes Yes Yes 0.3 DC Flying J Yes Yes Yes Yes Yes Frigette Truck Climate System Yes Yes Yes Idlebuster Yes Yes Yes Yes Yes Kohler 10,000 btu 12,000 btu Yes Yes Kool-Gen Optional Yes Yes Mechron Power Systems 

5,000 to 

10,000 btu 

10,000 to 

14,000 btu 0.21 Yes 

Pony Pack Yes Yes Yes 0.2 DC Rig Master Power Yes Yes Yes 0.2 Yes Star Class Thermo King 13,000 btu Yes Yes 0.04 to 0.14 Yes Yes TRIDAKO Energy Systems 30,000 btu 24,000 btu Yes 0.4 Truck Gen Yes Yes 0.2 Yes 
4-94

Operating at 4.2 kW, the MaxxPower APU equates to best-in-class fuel consumption of 

0.18 gallons per hour. It features EPA Tier IV certification and is in the process of 

acquiring CARB '08 emissions compliance. Several states currently offer incentives for 

trucks with idle reduction systems. Production is slated for later this year.

Note that APUs need to be emissions compliant to operate in California, which can be 

accomplished with the installation of a $3,000 DPF [Site Visits]. 

4.7.5 Truck Stop Electrification 

There are currently 138 truck stops equipped with truck stop electrification identified in the 

Alternative Fuel Data Center (AFDC) Truck Stop Electrification (TSE) database.42 Located in 34 

states, these sites provide truckers the opportunity to “plug-in” to power heaters, air conditioners, 

lights, and other accessories. There are generally two types of electrified parking spaces: dual 

system, and single system. A dual system requires equipment on both the truck and the ground. 

A single system only requires equipment at the truck stop. Table 4-64 summarizes the various 

truck stop electrification strategies. 

Table 4-64. Truck stop electrification comparison 

Supplier Capital Cost Service Fee 

Dual Systems 

 Phillips and Temro $125 

 Shurepower $200 to $2,000 $0.50 per hour 

 Teleflex (Proheat) $2,500 

 Xantrex $1,500 inverter/charger

$1,500 electric HVAC $2,500 per space 

Single Systems 

 Cabaire 

 Craufurd Manufacturing $8,550 per space 

 IdleAire Technologies $10 adapter $2.18 per hour retail 

$1.85 per hour fleet 

4.7.6 Idle Reduction System Comparison 

Idle reduction systems differ in a number of respects. Some of the key discriminators are fuel use 

per time; functionality (heating ability, cooling ability, and electric loads); infrastructure 

requirements; and capital Cost. These features are summarized in Table 4-65 for each of the five 

idle reduction strategies we have examined. Cells that are shaded light green correspond to 

favorable attributes; cells that are shaded yellow correspond to mild drawbacks; and cells that are 

shaded dark orange correspond to major drawbacks. 

 

42 http://www.afdc.energy.gov/afdc/progs/tse_listings.php 
4-95

Table 4-65. Idle reduction systems comparison 

Heating Cooling Electric Requires Recharge Infrastructure Service Fee Emissions Control Needed? Idle time avoided per year Fuel Use (gal/hr) % FC Benefit Capital Cost 

Engine Ctrl Yes Yes Yes No No No 1,500 to 

2,400 ~0.5 3% $1,000 to $4,000 

Heater Yes No No No No No 500 to 

800 

0.2 to 

0.3 

1.3 to 

2.3% 

$1,000 to 

$3,000 

APU Yes Yes Yes No No In CA 1,500 to 

2,400 

0.2 to 

0.3 

4 to 

7% 

$6,000 to 

$8,00043

Battery Yes Yes Some Yes No No 1,500 to 

2,400 - 5 to 9% 

$3,000 to 

$8,000 

Shore Power Yes Yes Yes Yes Yes Yes 1,500 to 

2,400 - 5 to 9% ~$100 

The fuel savings benefits are estimated using the following assumptions, which rely on estimates 

from the online Smartway fuel savings calculator [Smartway 2009b], as well as work by 

Argonne National Laboratory on truck idling [Stodolsky 2000]: 

• An idling engine consumes 0.8 gallons of fuel per hour. This is based on a Smartway 

estimate for idle engine fuel consumption, and is consistent with a 4 kW accessory load with 

an engine operating at 15 percent efficiency. The 21st Century Truck Partnership estimates a 

typical accessory load of 3 to 5 kW for a line-haul truck [DOE 2000]. It is possible that 

current engines have lower idle fuel consumption rates, but we have no specific data to 

support this. 

• A line-haul truck is assumed to operate under hotel loads for between 1,500 and 2,400 hours 

per year. This range is meant to bracket the range between a medium and high-mileage 

vehicle. 

• A line-haul truck is assumed to use 20,000 gallons of fuel per year on road. 

• We have assumed that a direct-fire heater is in-use for 600 to 800 hours per year. Smartway 

estimates 800 hours per year of heater fuel use. 

 

43 May require a DPF, at an additional cost of $3,000 
4-96

4.8 Driver Management and Coaching 

4.8.1 Overview 

Many of the lowest cost, most robust approaches to improve fuel efficiency revolve around 

driver management and coaching. These strategies aim to optimize shift strategies, manage 

vehicle speed and acceleration, and use telematic systems to optimize route. Significant fuel 

efficiency benefits may be achieved either technologically, or with improved driver training. 

There is general consensus in industry that driver variability can lead to a 20 to 35 percent 

variation in fuel economy (Figure 4-22) [Ang-Olson 2002, Cummins 2007, Site Visits]. While 

none of the technological approaches do as well as the best, most well-trained drivers, 

technological aids can shift average and below-average drivers towards the top performers. 

Figure 4-22. Variance in driver performance [Cummins 2007] 

Technological approaches to driver management and coaching include telematic systems that 

help monitor vehicle route; intelligent cruise control; driver fuel efficiency feedback systems; 

engine speed and load management controls; and speed governors. These strategies may be 

employed in tandem with driver training to significantly reduce fuel consumption. Driver 

management and coaching mechanisms are directed primarily towards Class 8 line-haul tractor 

trailers. We did not consider these technological approaches to driver management as a viable 

strategy in other vehicle classes in the next five to ten years. 

At their core, many of the driver management strategies aim to insure that the engine operates in 

a high efficiency regime more of the time. This is a different way of achieving the same goal as 

many of the transmission and driveline strategies. For example, a fleet can improve a driver’s 

average cycle efficiency by purchasing an automatic-manual transmission (AMT); by training 

the driver in appropriate shift techniques; or by using technology that offers driver feedback and 
4-97

actively manages vehicle operation. Different fleets have opted to pursue different strategies. For 

example, one fleet has tested both automatic transmissions and AMTs, but found that they could 

approach these benefits through driver training, optimized shift strategies, speed governors, and 

smart cruise control. 

4.8.2 Description of Management and Coaching Strategies 

The following sections will give an overview of driver management strategies, and finish with a 

summary of the total potential for driver management strategies: 

Driver feedback/incentives and Training: Driver feedback gauges and fuel efficiency rewards 

offer a complementary approach to encourage more fuel efficient driving. These range from 

instantaneous fuel economy indicators to regulated governors that allow drivers to earn higher 

speed driving if they meet fuel efficiency targets. In addition, fleets diligently monitor the fuel 

use of their drivers, and can use this information to reward high-performing drivers or train poor 

performers. This information can help to decrease on-road fuel consumption, as well as reduce 

idle time. Southeastern Freight presented data that showed that idle time monitoring had reduced 

idle time by 45 percent in the last year [Drinkard 2009]. Some level of driver feedback monitor is 

standard on present-day tractors, but units with more features (such as engine boost indicator or 

instantaneous and trip fuel use) include an up charge [Kenworth 2008]. Data gathered by the 

FMSCA 2009 evaluates several such systems – Detroit Diesel’s ProDriver, Caterpillar’s 

Messenger, and the Cummins Road Relay 4. They estimate the cost of the Cummins system at 

$800. A fully integrated driver management system would also include GPS, which is estimated 

to range in cost from $400 to $800, plus $20 to $40 per month in service fees [FMSCA 2009, 

www.trackyourtruck.com 2009]. A combination of a low-level activity monitor and driver 

training was estimated by Duleep [2008] to cost $1,400. Although the benefit for individual 

drivers will vary considerably, an integrated driver training program is estimated in the literature 

to improve fuel efficiency by 3.8 to 4 percent [Duleep 2008, Ang-Olson 2002]. 

Based on this cost information, we have characterized several different driver feedback/training 

approaches: 

1.) Simple driver feedback monitor: standard equipment, 1 percent savings 

2.) Advanced driver feedback: $800, 1 to 2 percent fuel savings 

3.) Advanced driver feedback with GPS system: $1,200 to $1,600, 3 to 4 percent fuel 

savings 

4.) Driver feedback monitors with training programs: $1,400, 3 to 4 percent fuel savings 

In combination, we estimate fuel savings that range from 1 to 4 percent, at costs that range from 

$0 to $1,600. 

Route management: Telematic systems using GPS can be used to manage driver routes to avoid 

bad weather and congestion. These systems can be implemented at low marginal cost on vehicles 

that are already GPS-equipped. We estimate that a GPS system costs between $400 and $800, 
4-98

plus service fees that range from $20 to $40 per month [FMSCA 2009, www.trackyourtruck.com 

2009]. We estimate fuel savings potential of up to 1 percent.

Engine and Driveline Management Strategies: These strategies maximize engine efficiency by 

controlling engine speed44 and torque characteristics when at cruise speeds. Examples include 

load-based speed control (offered by Cummins), and multi-torque engines (offered by Detroit 

Diesel). Load-based speed control limits the engine speed available to the driver based on the 

actual load; this compels the driver to aggressively up-shift, thereby saving fuel. A multi-torque 

engine enables two different torque settings in high gear, and matches the torque to the load – 

thereby limiting engine speed. Cummins [2007] has published real-world data that suggests 

optimizing shift strategies offers 3 to 4 percent improvement; load-based speed control will not 

capture all of these benefits. We estimate that it could offer a 1 to 2 percent improvement, which 

is similar to estimates for the fuel efficiency benefit of multi-torque engines. These options are 

offered as part of standard packages on 2010 engines, so we consider them to be cost-neutral. 

Speed governors: Speed governors are standard on all Class 8 tractor trailers, but purchasers 

have flexibility as to what speed to use. Some fleets and many independent operators do not 

govern speeds at all. Data was presented to the committee by a number of fleets [Miller 2009, 

Site Visits] that have opted to govern their speed, and have chosen to do so more aggressively in 

recent years: 

• Con Way Freight went from 65 to 62 MPH 

• Con Way Truckload went from 70 to 65 MPH (2.8 percent MPG improvement) 

• Wal-Mart currently governs at 65 MPH, but is strongly considering going to lower speed. 

Issues with governing speed include potential productivity loss (due to slower freight 

movement), and resistance from drivers, who are paid by the mile. Based on feedback on site 

visits, none of the OEMs had a firm handle on how large the productivity loss is from reducing 

speed, but there was general consensus that an elasticity of well less than 1 is likely45. Given that 

fleets have been moving towards lower speed operation, one would speculate that the benefits 

outweigh the productivity loss. It should also be noted that to achieve these fuel efficiency 

benefits, the vehicle drivetrain needs to be matched to the appropriate speed. One option that 

guarantees vehicles will be appropriately specified and insures speed limit reductions is to 

hardwire the governed speed at the factory. 

Several sources site a rule of thumb that reducing speed increases fuel economy by 0.1 MPG 

[Kenworth 2008, Cummins 2007, Ang-Olson 2002]. This corresponds to an elasticity of 

approximately 1.4 percent fuel savings per mile per hour of speed reduction46. However, SwRI 

modeling for NESCCAF/ICCT [2009] projects an elasticity of 0.4 to 0.5 percent per MPH. Realworld data from Con Way [2009] supports this estimate; they have found that reducing speed 

 

44 Engine speed control is not to be confused with vehicle speed governors. The former keeps engine RPM below a specified target;

the latter keeps vehicle speed below a specified target. 

45 An elasticity of 1 would mean that a 1 percent decrease in speed leads to a 1 percent decrease in productivity. In general, people 

felt that a 1 percent decrease in speed might lead to a lower productivity hit – perhaps a 0.2 percent drop. 

46 Assumes that going from 70 MPH to 60 MPH increases fuel economy from 6 MPG to 7 MPG 
4-99

from 70 to 65 MPH reduces fuel use by 2.8 percent, or 0.56 percent per MPH. We have used the 

SwRI estimate of 0.4 to 0.5 percent per MPH in the technology matrix. This does not include any 

estimate of potential productivity impacts. Speed governors are included as a standard option 

with current vehicles, so this technology is considered cost-neutral. 

One factor that could influence the variation in the literature is that the fuel consumption of a 

more aerodynamic truck is less sensitive to high-speed driving. Conversely, it is important to 

recognize that, if road speeds are reduced, aerodynamic drag reduction saves less fuel than it 

would at higher speed. 

Advanced cruise control: Advanced cruise control systems include currently available 

“adaptive” systems, as well as future “predictive” systems. Adaptive cruise control improves fuel 

economy by adjusting vehicle speed according to surrounding traffic. This helps prevent sudden 

braking. Predictive cruise control will actually be able to adjust vehicle operation based on 

factors such as traffic and topology. For example, a predictive system could decrease vehicle 

speed in anticipation of a curve, adjust speed to take advantage of vehicle inertia in hilly terrain, 

or delay turning on the engine cooling fan just before the top of a hill. 

Adaptive cruise control systems are currently available on current vehicles (primarily as a safety 

feature), but are not widely adopted. We did not find any firm estimates of the fuel consumption 

reduction benefits of adaptive cruise control; we estimate that these systems reduce fuel 

consumption by less than 1 percent, depending on the driver and drive cycle. According to 

published cost information, adaptive systems are estimated to range in cost from $1,100 to 

$3,000; systems for heavy-duty vehicle vehicles tend to lie at the upper end of this cost range 

(i.e., $2,000 to $3,000) [JD Power 2009, RITA 2007, Howard 2009]. 

Predictive cruise control systems rely primarily on telematic information from GPS, as well as 

computer hardware and software upgrades to actively manage vehicle operation to reduce fuel 

use and improve safety. These systems are just coming to market. For the high-speed long-haul 

duty cycle on which our analysis focuses, discussions during site visits suggested that predictive 

cruise control can reduce fuel consumption by 1 to 2 percent [Site Visits]. However, it should be 

noted that the benefits of predictive cruise control may be much higher on regional duty cycles 

that include significant travel on congested roads with a number of stops and starts. We assume 

that GPS units will already be adopted for other driver management or fleet optimization 

strategies, and that the radar is already included in adaptive systems. As such, we estimate these 

system costs at $100 – similar to the firmware upgrades required for onboard diagnostics. 

4.8.3 Summary 

Approaches to managing and training drivers are summarized in Table 4-66. We have estimated 

the adoption rate for driver management systems that are currently available at 25 to 50 percent. 

Although some features – such as speed governors – are standard on all vehicles, not all users 

take advantage of them. Our estimate is based on data offered during site visits that suggested 

that about half of vehicle purchasers also purchased driver feedback information. Given that this 

is an entry-level type of system, we speculate that adoption rates for more advanced approaches 

are lower. 
4-100

Table 4-66. Driver management and coaching strategies –capital costs and benefits 

Strategy % FC Improvement Capital Cost Adoption/Intro Yr 

Training and Feedback 1 to 4% $0 to $1,600 25 to 50% 

Engine and Driveline Mgmt 1 to 2% - 100% 

Route Management 0 to 1% $400 to $800 2010 

Govern speed 0.4 to 0.5% per MPH - 25 to 50% 

Adaptive Cruise Control 0 to 1% - 100% 

Predictive Cruise Control 1 to 2% $100 2012 

These approaches to driver management and coaching that were characterized fall into one of 

four categories: optimizing shift strategies, limiting road speed, optimizing acceleration and 

braking, and optimizing the route (Table 4-67). Given that different approaches are used to attack 

the same problem, it is important to recognize that the benefits of these management and 

coaching strategies are not additive. As they are packaged together, they will offer diminishing 

returns. 

Table 4-67. Driver management and coaching strategies – approach 

Strategy 

Optimize 

Shift 

Strategy 

Limit road 

speed 

Optimize 

Acceleration and 

Braking 

Optimize 

Route 

Training and Feedback X X X 

Engine and Driveline Mgmt X 

Route Management X 

Speed Governor X 

Cruise Control X 

An integrated driver management and coaching strategy might include the following elements: 

• Speed governed to 60 to 62 MPH 

• Onboard GPS 

• Some type of driver sweet spot indicator 

• Driver training and/or fuel efficiency incentive program 

• Advanced predictive cruise control 

• Some sort of speed limited engine 

In combination, these strategies could reduce fuel consumption by 7 to 8 percent for an average 

driver. 
5-1

5. Packages 

There has been much discussion in the previous sections regarding the importance of not 

attempting to simply add the benefits of each of the identified fuel savings technologies, in large 

part because many of the technologies will interact and may increase or decrease the combined 

effect. Nevertheless in this section, we will look at specific applications, assume a specific set of 

vehicular and operational characteristics, and likely fuel savings technologies to identify the 

capital costs, benefits and payback required for implementation. We fully realize that vehicle 

modeling is necessary to estimate the combined effects of individual technologies. As such, the 

results presented here should be viewed as very preliminary estimates. 

5.1 Capital Costs, Benefits, and Capital Cost Per Percent Reduction (CCPPR) 

Using the results from the analysis of individual technology strategies, technologies were 

packaged together to estimate total feasible fuel savings costs and benefits for each vehicle 

segment. The following tables show the results of this analysis for 2015-2020 technologies. 

Each of these tables shows the category of fuel savings technologies, a description of the 

technology, percent fuel consumption (FC) benefit, estimated costs in 2009 dollars (retail price 

to consumer), CCPPR ($/percent FC improvement), and weight of technology. 

For each vehicle class, the fuel consumption benefit of the combined technology packages is 

calculated as follows: 

% FCPackage = 1 - (1-% FCTech 1)(1-% FCTech 2)(1-% FCTech N) Equation 5 

Where % FCTech x is the percent benefit of an individual technology. Note that this gives the 

same result as calculating the ratio of total fuel used by the package of technologies (FCPackage) to 

the fuel used with no technologies included (FCOriginal) 

% FCPackage = 1 - FCPackage/FCOriginal Equation 6 

The tractor trailer results are shown in Table 5-1. Recall this is a line-haul or over-the-road 

trucking application accumulating over 100,000 miles per year and with a duty cycle dominated 

by high speed interstate driving. Technologies include advance tractor and trailer aerodynamics, 

a diesel engine with bottoming cycle approaching 53 percent brake thermal efficiency, wide base 

single, low rolling resistance tires, an AMT with reduced driveline friction, tractor hybrid 

system47, driver management, idle reduction, and some light weighting. These technologies 

provide a 48.9 percent reduction in fuel use at an estimated cost of $84,600. Total vehicle 

weight is estimated to decline by 470 lbs. 

 

47 Hybrid system could also be added to trailer but this was not consider in this analysis. 
5-2

Table 5-1. Tractor Trailer 2015-2020 Technology Package 

Category Description 

% FC 

Benefit 

Capital 

Cost 

CCPPR 

($/%) 

Weight 

(lbs) 

Aero Improved Smartway Tractor 

+ 3 Aero Trailers 

11.5 $ 12,000 $ 1,043 750 

Engine Adv. 11-15L Diesel 

w/Bottoming Cycle 

20 $ 23,000 $ 1,150 800 

Tire Improved WBS on Tractor + 

3 Trailers 

11 $ 3,600 $ 327 -400 

Transmission & 

Driveline 

AMT, Reduced driveline 

friction 

7 $ 5,800 $ 829 80 

Hybrid Mild parallel hybrid w/idle 

reduction 

10 $ 25,000 $ 2,500 400 

Mgmt & Coaching 60 MPH Spd limit; predictive 

cruise control w/telematics; 

Driver Training 

6 $ 1,700 $ 283 — 

Idle Reduction Incl. w/Hybrid system — $ — $ — — 

Tot. Added Weight Added Components -1 $ — $ — +2,030 

Weight Reduction Mat. Substitution - 2,500 lbs 1.25 $ 13,500 $ 10,800 -2,500 

Total 2015-2020 Package 50.5% $ 84,600 $ 1,674 -470 

Two estimates were made for the Class 3-6 applications: box truck and bucket truck. This 

distinction was made to account for the differences in duty cycles. The box truck’s application is 

primarily pickup and delivery, whereas the bucket truck has extended idle and power take off 

(PTO) operation. Both of these duty cycles can benefit from hybridization. Table 5-2 shows our 

estimates for a box truck, and Table 5-3 shows our results for a bucket truck. For the box truck 

we have included aerodynamic cab and box, our 2015-2020 6-9L diesel engine package (similar 

to the larger bore engines but without bottoming cycle), low rolling resistance tires, an 8-speed 

automatic transmission couple to a parallel hybrid system, and some light weighting. This 

package results in fuel savings of 47.1 percent at a cost of $43,120 and a net weight increase of 

100 lbs. 

The bucket truck is similar to the box truck except that we have not included any aerodynamics 

since a lot of time for this application is spent at idle using the PTO. We also made some 

adjustments of the benefits of the advance diesel engine and low rolling resistance tires based on 

the differences in duty cycles. The hybrid system benefits also increase due to extended PTO 

operation. The package results in estimate fuel savings of 49.6 percent at a cost of $49,900 and a 

net weight increase of 50 lbs. 
5-3

Table 5-2. Class 3-6 Box 2015-2020 Technology Package 

Category Description 

% FC 

Benefit Capital Cost CCPPR ($/%)

Weight 

(lbs) 

Aero Aero cab, skirts, 

round corners 

6% $ 3,250 $ 542 300 

Engine Adv. 6-9L Engine 14% $ 13,000 $ 929 400 

Tire Improved LRR Duals 3% $ 300 $ 100 — 

Transmission & 

Driveline 

8-Spd AT, Reduced 

driveline friction, Agg. 

Shift Logic 

4% $ 1,800 $ 450 — 

Hybrid Parallel hybrid 30% $ 20,000 $ 667 400 

Mgmt & Coaching — — $ — $ — — 

Idle Reduction — — $ — $ — — 

Tot. Added 

Weight 

Added Components -4.4% $ — $ — +1,100 

Weight Reduction Mat. Substitution - 

1,000 lbs 

4% $ 4,770 $ 1,193 -1,000 

Total 2015-2020 Package 47.1% $ 43,120 $ 915 +100 

Table 5-3. Class 3-6 Bucket 2015-2020 Technology Package 

Category Description % Benefit Capital Cost CCPPR ($/%)

Weight 

(lbs) 

Aero — — $ — $ — — 

Engine Adv. 6-9L Engine 11.2% $ 13,000 $ 1,161 400 

Tire Improved LRR Duals 2.4% $ 300 $ 125 — 

Transmission 

& Driveline 

Reduced driveline 

friction 3.2% $ 1,800 $ 450 — 

Hybrid 

Parallel hybrid 

w/ePTO 40.0% $ 30,000 $ 667 650 

Mgmt & 

Coaching — — $ — $ — — 

Idle Reduction — — $ — $ — — 

Tot. Added 

Weight Added Components -3.4% $ — $ — +1,050 

Weight 

Reduction 

Mat. Substitution - 

1,000 lbs 3.2% $ 4,770 $ 1,193 -1,000 

Total 2015-2020 Package 49.6% $ 49,870 $ 1,005 +50 
5-4

The Class 8 refuse truck results are shown in Table 5-4. Refuse trucks’ duty cycle includes 

many 100-150 ft stops, compaction, and some high speed operation. The duty cycle is dominant 

by the many stops and subsequent accelerations. This type of operation is ideal for hybrid 

drivetrains and we assumed a hydraulic hybrid system (a hybrid electric system could also have 

been assumed). Conservatively, we have assumed 25 percent fuel consumption benefit for the 

hybrid system. We also included in this package an advanced 11-15 L diesel engine without 

bottoming cycle, improved low rolling resistance tires, reduced driveline friction, and some light 

weighting. This package results in fuel savings of 38.4 percent at a cost of $50,800 and a net 

weight increase of 1,000 lbs. 

Table 5-4. Class 8 Refuse Hauler 2015-2020 Technology Package 

Category Description % Benefit Capital Cost CCPPR ($/%)

Weight 

(lbs) 

Aero — — $ — $ — — 

Engine Adv. 11-15L Engine 14% $ 14,800 $ 1,057 500 

Tire Improved LRR Duals 2.50% $ 300 $ 120 — 

Transmission 

& Driveline 

Reduced driveline 

friction 4% $ 2,700 $ 675 — 

Hybrid Parallel hydraulic hybrid 25% $ 30,000 $ 1,200 1,000 

Mgmt & 

Coaching — — $ — $ — — 

Idle Reduction — — $ — $ — — 

Tot. Added 

Weight Added Components -3% $ — $ — +1,500 

Weight 

Reduction 

Mat. Substitution - 500 

lbs 1% $ 3,000 $ 3,000 -500 

Total 2015-2020 Package 38.4% $ 50,800 $ 1,323 +1,000 

The transit bus results are shown in Table 5-5. Due to the stop and go nature of transit buses’ 

duty cycle, we again included hybridization, as well as an advanced diesel engine, improved low 

rowing resistance tires, improved driveline friction, and fairly aggressive light weighting. This 

package results in fuel savings of 47.6 percent at a cost of $250,400 and a net weight decrease of 

500 lbs. The high costs are primarily due to the high cost of hybrid systems for transit buses. 

The cost of buses are subsidized by the Federal government and, if we include this subsidy at 90 

percent of the incremental costs, then the total package costs is reduced to $54,400, more in line 

with the costs of Class 3-6 hybrid packages. 

Motor coach results are shown in Table 5-6. Here, since these vehicles spend a good portion of 

their time on interstates we have included improve aerodynamics, an advanced 11-15 L diesel 

engine with bottoming cycle, low rolling resistance tires, 8 speed automatic transmission, and 

minor light weighting. This package results in fuel savings of 32 percent at a capital cost of 

$36,350 and a reduction in vehicle weight or 400 lbs. 
5-5

Table 5-5. Transit Buses 2015-2020 Technology Package

Category Description % Benefit Capital Cost CCPPR ($/%)

Weight 

(lbs) 

Aero — — $ — $ — — 

Engine Adv. 6-9L Engine 14% $ 13,000 $ 929 500 

Tire Improved LRR Duals 1.50% $ 300 $ 200 — 

Transmission & 

Driveline 

8-Spd AT, Reduced 

driveline friction, Agg. Shift 

Logic 

4% $ 1,800 $ 450 — 

Hybrid Diesel Series Hybrid 35% $ 22,0001 

 $ 220,000 

$ 6,286 1,500 

Mgmt & Coaching — — $ — $ — — 

Idle Reduction — — $ — $ — — 

Tot. Added 

Weight 

Added Components -5% $ — $ — +2,000 

Weight Reduction Mat. Substitution - 2,500 lbs 6.25% $ 15,300 $ 2,448 -2,500 

Total 2015-2020 Package 47.8% $ 52,4001 

$ 250,400 

$ 1,096 

$ 5,238 

-500 

Table 5-6. Motor Coaches 2015-2020 Technology Package

Category Description % Benefit Capital Cost CCPPR ($/%)

Weight 

(lbs) 

Aero — 8% $ 4,500 $ 563 300 

Engine 

Adv. 11-15L Engine 

w/Bottoming Cycle 20% $ 23,000 $ 1,150 800 

Tire 

Improved LRR Duals 

+ WBS 3% $ 450 $ 150 — 

Transmission 

& Driveline 

8-Spd AT, Reduced 

driveline friction, Agg. 

Shift Logic 

4.50% $ 2,400 $ 533 — 

Hybrid — — $ — $ — — 

Mgmt & 

Coaching — — $ — $ — — 

Idle Reduction — — $ — $ — — 

Tot. Added 

Weight Added Components -0.75% $ — $ — +1,100 

Weight 

Reduction 

Mat Substitution - 

1,500 lbs 1.05% $ 6,000 $ 5,714 -1,500 

Total 2015-2020 Package 32.0% $ 36,350 $ 1,136 -400 
5-6

The final package we evaluated was for Class 2b pickups and vans. The results of this analysis 

are shown in Table 5-7. For this package we assumed some aerodynamic improvements, low 

rolling resistance tires, 8-speed transmission coupled to a parallel hybrid system and minor light 

weighting. We assumed that the baseline engine for this segment was gasoline and our package 

includes an advanced turbocharged, downsized stoichiometric direct injected gasoline engine. 

Similar fuel consumption benefits can be achieved with an advanced diesel engine. This 

package results in fuel savings of 44.5 percent at a capital cost of $14,710 and at no increase in 

vehicle weight. 

Table 5-7. Class 2b Pickups and Vans 2015-2020 Technology Package

Category Description % Benefit Capital Cost CCPPR ($/%)

Weight 

(lbs) 

Aero — 3% $ 100 $ 33 — 

Engine 

5-8L Turbocharged 

Downsized s-GDI 

Gasoline Engine 

23% $ 4,000 $ 174 — 

Tire Improved LRR 2% $ 10 $ 5 — 

Transmission 

& Driveline 

8-Spd AT, Reduced 

driveline friction, Agg. 

Shift Logic 

7.50% $ 1,000 $ 133 — 

Hybrid Parallel Hybrid 18% $ 9,000 $ 500 300 

Mgmt & 

Coaching — — $ — $ — — 

Idle Reduction — — $ — $ — — 

Tot. Added 

Weight Added Components -0.75% $ — $ — +300 

Weight 

Reduction 3% -- approx. 300 lbs 0.75% $ 600 $ 800 -300 

Total 2015-2020 Package 44.5% $ 14,710 $ 331 0 

A similar analysis was performed for the intermediate years 2013 to 2015. These results are not 

shown in the same format as the previous analysis for 2015-2020 vehicle segments. Instead we 

have summarized the results as shown in Table 5-8 for all the applications: tractor trailer (TT), 

Class 3-6 box (box), Class 3-6 bucket (bucket), Class 8 refuse (refuse), transit buses (Bus), 

Motor Coaches (Coach), and Class 2b pickups and vans (2b) This table shows for each 

application and for each technology package the technology costs, FC benefits, and the CCPPR 

for technologies that will be market viable48 between 2013 and 2015. The technologies that are 

included vary by market segment, but broadly speaking, they include a high-cost first generation 

hybrid system for urban vehicles; and aerodynamic improvements coupled with first generation 

 

48 “Market viable” means that the technology will have matured to the point at which it could be widely deployed; it does not imply 

that a particular technology offers attributes (such as rapid payback) that will lead to market adoption. 
5-7

waste heat recovery on highway vehicles. All of the technologies include significant engine 

efficiency improvements as indicated. 

Table 5-8. Fuel consumption reduction, capital cost, and CCPPR - 2013 to 2015 vehicle 

technology 

Technology TT Box Bucket c Refuse Bus Coach 2b 

Fuel Consumption Reduction 

Aero 5.5% — — — — — 3.0% 

Engine 10.5% 9.0% 7.2% 10.5% 9.0% 10.5% 14.0% 

Weight 0.8% 2.0% 1.6% — 3.0% 0.7% 0.4% 

Tire 4.5% 1.8% 1.4% 1.5% 1.0% 1.8% 1.0% 

Transmission 5.0% 1.5% 1.2% 1.5% 1.5% 2.0% 4.5% 

Hybrid — 22.0% 35.0% 20.0% 30.0% — —

Mgmt 3.0% — — — — — —

Idle Reduction 6.0% — — — — — —

Subtotala 30.6% 32.7% 42.2% 30.5% 39.7% 14.5% 21.4% 

Added Wt (lb)b 1,530 800 1,050 1,500 2,000 800 0

Adj. FC Total 30.0% 30.5% 40.2% 28.4% 36.6% 14.0% 21.4% 

Capital Cost 

Aero $ 9,000 $ - $ - $ - $ - $ - $ 100 

Engine $ 14,200 $ 10,300 $ 10,300 $ 12,300 $ 10,300 $ 14,200 $ 3,000 

Weight $ 6,000 $ 1,590 $ 1,590 $ - $ 4,800 $ 3,000 $ 225 

Tire $ 900 $ 300 $ 300 $ 300 $ 300 $ 240 $ 10 

Transmission $ 5,200 $ 200 $ 200 $ 200 $ 200 $ 300 $ 1,100 

Hybrid $ — $ 38,000 $ 50,000 $ 40,000 $ 200,000 $ — $ — 

Mgmt $ 1,000 $ — $ — $ — $ — $ — $ — 

Idle Reduction $ 8,000 $ — $ — $ — $ — $ — $ — 

Total $ 44,300 $ 50,390 $ 62,390 $ 52,800 $ 215,600 $ 17,740 $ 4,435 

CCPPR ($/Percent Fuel Consumption Benefit) 

Aero $ 1,636 $ — $ — $ — $ — $ — $ 33 

Engine $ 1,352 $ 1,144 $ 1,144 $ 1,171 $ 1,144 $ 1,352 $ 214 

Weight $ 8,000 $ 795 $ 795 $ - $ 1,600 $ 4,286 $ 563 

Tire $ 200 $ 167 $ 167 $ 200 $ 300 $ 133 $ 10 

Transmission $ 1,040 $ 133 $ 133 $ 133 $ 133 $ 150 $ 244 

Hybrid $ — $ 1,727 $ 1,429 $ 2,000 $ 6,667 $ — $ — 

Mgmt $ 333 $ — $ — $ — $ — $ — $ — 

Idle Reduction $ 1,333 $ — $ — $ — $ — $ — $ — 

All Strategies $ 1,475 $ 1,652 $ 1,552 $ 1,859 $ 5,890 $ 1,268 $ 207 

a

 Does not include fuel consumption penalty associated with added weight of fuel savings technologies b Added weight of fuel savings technologies 

c Assumes that 80% of fuel is used on road, and 20% is used at idle. This de-rates the fuel consumption benefit of all technologies, 

except for the hybrid. 

For the near term packages, the projected fuel consumption benefits range from 14 to 42 percent, 

while costs range from $4,000 (for the Class 2b pickup and van segment) to $215,000 (for the 

transit bus, which includes a high-cost hybrid system). However, most of the vehicle classes lie 

in a relatively narrow band that shows 30 to 40 percent improvement at capital costs that range 
5-8

from $40,000 to $60,000. The CCPPR of these packages is $600 to $1,100 per percent benefit 

for four of the vehicle classes, but ranges from $56 (for Class 2b vehicles) to $3,600 per percent 

(for transit buses). 

Table 5-9. Fuel consumption reduction, capital cost, and CCPPR - 2015 to 2020 vehicle 

technology 

TT Box Bucket d Refuse Bus Coach 2b 

Fuel Consumption Reduction 

Aero 11.5% 6% — — — 8% 3% 

Engine 20% 14% 11.2% 14% 14% 20% 23% 

Weight 1.25% 4% 3.2% 1% 6.25% 1.05% 0.75% 

Tire 11% 3% 2.4% 2.5% 1.5% 3% 2% 

Transmission 7% 4% 3.2% 4% 4% 4.5% 7.5% 

Hybrid 10% 30% 40% 25% 35% — 18% 

Mgmt 6% — — — — — —

Idle Reductiona — — — — — — —

Subtotalb 51.0% 49.4% 51.3% 40.2% 50.4% 32.5% 44.9% 

Added Wt (lb)c 2,030 1,100 1,050 1,500 2,000 1,100 300 

Adj. FC Total 50.5% 47.1% 49.6% 38.4% 47.8% 32.0% 44.5% 

Capital Cost 

Aero $ 12,000 $ 3,250 $ - $ - $ - $ 4,500 $ 100 

Engine $ 23,000 $ 13,000 $ 13,000 $ 14,800 $ 13,000 $ 23,000 $ 4,000 

Weight $ 13,500 $ 4,770 $ 4,770 $ 3,000 $ 15,300 $ 6,000 $ 600 

Tire $ 3,600 $ 300 $ 300 $ 300 $ 300 $ 450 $ 10 

Transmission $ 5,800 $ 1,800 $ 1,800 $ 2,700 $ 1,800 $ 2,400 $ 1,000 

Hybrid $ 25,000 $ 20,000 $ 30,000 $ 30,000 $ 220,000 $ — $ 9,000 

Mgmt $ 1,700 $ — $ — $ — $ — $ — $ —

Idle Reduction a $ — $ — $ — $ — $ — $ — $ —

Total $ 84,600 $ 43,120 $ 49,870 $ 50,800 $ 250,400 $ 36,350 $ 14,710 

CCPPR ($/Percent Fuel Consumption Benefit) 

Aero $ 1,043 $ 542 $ - $ - $ - $ 563 $ 33 

Engine $ 1,150 $ 929 $ 929 $ 1,057 $ 929 $ 1,150 $ 174 

Weight $ 10,800 $ 1,193 $ 1,193 $ 3,000 $ 2,448 $ 5,714 $ 800 

Tire $ 327 $ 100 $ 100 $ 120 $ 200 $ 150 $ 5 

Transmission $ 829 $ 450 $ 450 $ 675 $ 450 $ 533 $ 133 

Hybrid $ 2,500 $ 667 $ 750 $ 1,200 $ 6,286 $ — $ 500 

Mgmt $ 283 $ — $ — $ — $ — $ — $ — 

Idle Reductiona $ — $ — $ — $ — $ — $ — $ —

All Packages $ 1,674 $ 915 $ 1006 $ 1,323 $ 5,232 $ 1,135 $ 331 

a Overnight idle reduction is assumed to be implemented as part of the hybrid package b Does not include fuel consumption penalty associated with added weight of fuel savings technologies c Added weight of fuel savings technologies d Assumes that 80% of fuel is used on road, and 20% is used at idle 
5-9

Table 5-9 summarizes the individual results shown in Tables 5-1 through 5-7 into a format 

similar to Table 5-8 for the 2013-2015 technologies. This table gives similar set of metrics for 

technologies that will be market viable between 2015 and 2020. The technologies in this 

timeframe include a second generation hybrid system at lower cost for urban vehicles; and 

advanced aerodynamic improvements coupled with a bottoming cycle to recover waste heat on 

highway vehicles. 

The 2015-2020 packages reduce fuel consumption by 30 to 50 percent; all of the technologies 

with the exception of the motor coach range are over 40 percent. The costs of these packages 

range from $14,000 (Class 2b) to $250,000 (transit bus). However, the other applications lie in a 

narrow band from $40,000 to $85,000. Many of the technologies benefit from anticipated 

reductions in the cost of hybrid vehicles during this timeframe. The 2015-2020 technologies have 

higher CCPPR than the 2013-2015 packages. Estimates range from $250 to $5,000 per percent 

improvement, depending on vehicle class. For five of the seven vehicle classes, the benefits lie in 

a range from $500 to $1,700 per percent fuel consumption reduction. 

It needs to be emphasized that these results are very dependent on the vehicle’s duty cycle and as 

such should be viewed as averages for each truck segment. Further, although the data for this 

analysis were obtained for the specific truck segments and, in general, for typical duty cycles for 

these segments, detailed vehicle stimulation modeling was not done to establish the fuel 

consumption benefits. Follow up work is needed to confirm not only the individual estimated 

benefits for each technology, but also the packaged benefits. We recommend, therefore, that our 

analysis be extended by modeling actual vehicle technologies identified in this analysis to 

appropriately capture the synergies of complex vehicle systems. 

Although the cumulative benefits and capital costs for vehicles classes are relatively similar, the 

likely pathway to achieve these benefits varies considerably. For line-haul vehicles, waste-heat 

recovery and aerodynamics represent the largest opportunities, but high single-digit gains are 

possible in nearly every category. For urban vehicles (box & bucket, buses, and refuse), 

hybridization provides the bulk of the benefit. In addition, engine optimization provides 

significant benefits to all vehicle classes. Figure 5-1 illustrates the importance of all 

technologies for tractor trailer applications and the importance of hybrid systems for those 

applications that are dominated by stop and go duty cycles or extended PTO operation. 

To characterize these differences in the technology effectiveness of different strategies across 

vehicle segments, each strategy was ranked in order of CCPPR for each vehicle class. These data 

were then used to generate cost-curves as shown in Figures 5-2 and 5-3. 

TIAX’s analysis shows that there is potential to achieve fuel consumption benefits of 40 to 

50 percent across a broad subset of the medium- and heavy-duty vehicle fleet between 2015 and 

2020, at costs that range from $40,000 to $90,000. The technologies used to achieve these 

benefits vary by segment: on urban vehicles, benefits are largely driven by hybridization, while 

on-highway vehicles achieve benefits through waste-heat recovery and aerodynamics. We 

speculate that some, but not all, of these fuel consumption benefits will be achieved without 

regulation. A commonly cited rule of thumb is that line-haul tractor trailer fleets will pay $900 

for 1 percent of efficiency improvement. Our analysis shows that 30 percent efficiency 

improvement can be achieved at a CCPPRof $640 per percent, while 50 percent efficiency 
5-10

0%

10%

20%

30%

40%

50%

60%

TT Box Bucket Refuse Bus Coach 2b

FC Benefit

Aero Engine

Weight Tires & Wheels

Transmission Hybrid

Mgmt & Coaching

Figure 5-1. Comparison of Fuel Savings Technology for Tractor Trailer (TT), Class 3-6 

Box (Box), Class 3-6 Bucket (Bucket), Class 8 Refuse (Refuse), Transit Bus 

(Bus), Motor Coach (Coach), and Class 2b Pickups and Vans (2b) 

$-

$20,000

$40,000

$60,000

$80,000

$100,000

0% 5% 10% 15% 20% 25% 30% 35% 40% 45%

% Benefit

Package Cost

Tractor-Trailer

Straight Box

Bucket

Refuse

Bus

Coach

Class 2b

Figure 5-2. Cost curves for 2013-2015 packages. The transit bus extends to $215,000 at a 

benefit of 40 percent 
5-11

$-

$10,000

$20,000

$30,000

$40,000

$50,000

$60,000

$70,000

$80,000

$90,000

$100,000

0% 10% 20% 30% 40% 50% 60%

% Benefit

Package Cost

Tractor-Trailer

Straight Box

Bucket

Refuse

Bus

Coach

Class 2b

Figure 5-3. Cost curves for 2015-2020 packages. The transit bus extends to $250,000 at a 

benefit of 50 percent 

improvement is achieved at a CCPPR of $1,700 per percent. In other vehicle segments, which 

have lower mileage, fuel efficiency is commonly valued at $250 per percent. In these segments, 

adoption is likely to be much lower. We project that in several segments, 50 percent fuel 

efficiency can be achieved at a cost of $500 to $900 per percent. 

5.2 Payback Analysis 

For the purposes of this evaluation, we compare paybacks for two fuel price scenarios: $4.00 and 

$3.00 per gallon (gasoline or diesel). Vehicle classifications that we compared are Class 8 linehaul tractor trailer, transit bus, refuse hauler and Class 3-6 box truck. Table 5-10 compares the 

mileage, average speed, driver characteristics, fuel economy, and fuel consumption for the four 

applications. Also shown is what a 1 percent reduction in fuel consumption would be and the 

savings that would result by reducing fuel consumption by that 1 percent. 

For each vehicle class we determined the fuel savings for the 2015-2020 technologies from the 

percent fuel consumption benefit shown in Table 5-9. Annual dollar savings were then estimated 

for $4 per gallon diesel fuel and for $3 per gallon diesel fuel. These fuel savings were compared 

to the total costs of the technology to determine the payback in years and months. The results 

are shown in Table 5-11. This payback estimate does not include any other operating and 

maintenance (O&M) costs or savings associated with the added fuel economy technologies. This 

analysis was done to provide a first cut estimate of payback. A more sophisticated discount 
5-12

Table 5-10. Operational characteristics for payback evaluation 

Fleet Characteristics Tractor 

Trailer Transit Bus Refuse Hauler 

Class 3-6 

Van 

Annual Mileage (miles per year) 120,000 40,000 25,000 60,000 

Average speed (miles per hour) 46.2 12 12 28.8 

Driver work week (days per week) 6 5 5 5 

Driver time (hours per week) 50 64a 40 40 

Fuel economy (miles per gallon) 6.5 3.5 3.3 8 

Fuel consumption (gallons per year) 18,500 11,400 7,600 7,500 

1% Fuel consumption savings (gal per yr) 185 114 76 75 

Fuel cost savings for 1% reduction 

(@$4/gal diesel) 

$738 $457 $303 $300 

Fuel cost savings for 1% reduction 

 (at $3/gal diesel) 

$554 $343 $227 $225 

a

 On average bus will be operated by more than one driver 

Table 5-11 Simple Payback Analysis for Selected Vehicle Applications 

Cost Item Tractor 

Trailer 

40 Ft Transit 

Bus 

Refuse 

Hauler 

Class 3-6 

Box 

Technology Costs ($) 84,600 250,400 50,800 43,120 

Annual Fuel used (gal) 18,500 11,400 7,600 7,500 

FC savings (%) 50.5 47.9 38.4 47.1 

Fuel saved (gal) 9,350 5,456 2,918 3,534 

$4 per gallon Diesel Price 

Annual $ saved 37,402 21,825 11,672 14,136 

Payback (yrs) 2.3 11.5 4.4 3.1 

Payback (months) 27.1 137.7 52.2 36.6 

$3 per gallon Diesel Price 

Annual $ saved 28,051 16,369 8,754 10,602 

Payback (yrs) 3.0 15.3 5.8 4.1 

Payback (months) 36.2 183.6 69.6 48.8 

analysis is needed and this analysis should include time value of money, O&M costs, other 

owner’s costs such as insurance and excise taxes, and any replacement costs.
5-13

As shown the payback periods for vehicle applications except transit buses range from 2 to 

4 years at $4 per gallon diesel price and from 3 to 6 years at $3 per gallon diesel price. Without 

Federal funding, the costs of transit buses and, in particular, the incremental cost of hybrid buses, 

the payback periods at either fuel price are quite high. With Federal funding covering the 

majority of the upfront hardware costs, the incremental technology costs reduce to $52,400 and 

the corresponding paybacks are 2.4 years for $4 diesel and 3.2 years for $3 diesel. This is more 

in line with the other vehicle applications. 

These estimated paybacks are only a first cut of the possible economics of fuel savings 

technologies. In this first cut, we included all technologies that could be available in the 2015 to 

2020 period. This represents the maximum benefit for each application but also the highest cost. 

We did not try to apply the technologies based on the best CCPPR—adding lowest CCPPR 

technologies first followed by the more expensive technologies. Finally, we also have to caution 

that the fuel consumption benefits were combined without the benefit of vehicle simulation 

modeling and estimated benefits could increase or decrease depending on the integration of these 

technologies. 

We feel these payback periods are probably marginal and would have to be lower for users to 

adopt these packages of fuel savings technologies without any other mitigating factors. Also 

there other O&M cost savings like reduced brake wear that could reduce payback periods. This 

analysis was done to get an ideal of whether the capital cost and benefits were in the ballpark of 

being acceptable. We believe this to be the case, but a more sophisticated life cycle costing is 

necessary. 

A-1

Appendix A. References 

References 

Adam Works. www.adamworksinc.com. Accessed June 2009. 

Aerovolution. http://www.aerovolution.com/information.shtml. Accessed June 2009. 

Alcoa. “Improving the Sustainability of Transport: Aluminum is Part of the Solution.” 

Altoona Bus Research and Testing Center, Online Bus Database, http://www.altoonabustest.com/ 

American Bus Association (ABA) “Motorcoach Facts 2009”. 

http://www.buses.org/files/AmericanBus2009.pdf 

American Public Transportation Association (APTA). “2009 Public Transportation Fact Book60th edition.” April 2009. 

American Transportation Research Institute (ATRI). “Compendium of Idling Regulations.” 

Update June 2009. http://www.atri-online.org/research/idling/atri_cabcard6_22_09.pdf 

Ang-Olson, J and Schroeer, W. “Energy Efficiency Strategies for Freight Trucking: Potential 

Impact on Fuel Use and Greenhouse Gas Emissions.” Transportation Research Record 1815, 

Paper No. 02-3877, 2002. 

AT Dynamics. www.atdynamics.com. Accessed June 2009. 

Azure Dynamics. “Balance Hybrid Electric Specifications and Ordering Guide.” Available at 

http://www.azuredynamics.com/products/documents/BalanceHybridElectricSpecificationsandOr

deringGuideRevC.pdf, Accessed July 2009. 

Bradley, C and Nelson, S. “Truck Tires and Rolling Resistance: Modeling and Impact on Fuel 

Consumption.” Michelin. Presentation to the NAS Committee for Assessment of Fuel Economy 

Technologies for Medium and Heavy Duty Vehicles. February 4, 2009. 

Carpenter, J. “Heavy-Duty Hybrid Overview and Medium-Duty Hybrid Update.”. 

Clark, Nigel, W. S. Wayne, F. Zhen, S. R. Khan, J. J. Schiavone, C. A. Chambers, and K. L. 

Chandler, "A Review of the Performance of Hybrid-Electric Bus Technology on Fuel Economy 

and Emissions," APTA 2006 Bus & Paratransit Conference proceedings paper, May 2006 

Clean Heavy-Duty Conference, Los Angeles, CA. February 15, 2007. 
A-2

Coryell, R. “PACCAR – Eaton Hybrid Collaboration: Taking HD Hybrid from Concept to 

Commercialization.” Eaton. Presented at Improving the Fuel Economy of Heavy-Duty Fleets II, 

San Diego, CA. February 20, 2008. 

Cummins (2009a). Presentation to the NAS Committee for Assessment of Fuel Economy 

Technologies for Medium and Heavy Duty Vehicles. May 15, 2009. 

Cummins (2009b). Cummins Every Time – Data sheets for ISX, ISM, ISL, ISC, and ISB 

Engines. Available at http://www.everytime.cummins.com/every/misc/brochures.page?. 

Accessed July, 2009. 

Cummins (2009c). “Cummins Every Time – Dodge Ram – 6.7L Turbodiesel.” Online at 

http://www.everytime.cummins.com/every/applications/dodge_ram/ram67.page, Accessed June 

2009. 

Cummins. “Cummins MPG Guide”. February, 2007. 

Davis, S. “Trouble Truck Demonstration.” Eaton Corporation. Presented at Plug-In 2008, 

August 2008. 

Davis, S, Diegel, S, and Boundy, R. “Transportation Energy Data Book: Edition 27.” Oak 

Ridge National Laboratory, ORNL-2981. Prepared for the US Department of Energy, 2008. 

Detroit Diesel (2009a). “Detroit Diesel – DD15 Diesel Engine Fuel Economy”. Accessed July 

2009. http://detroitdiesel.com/engines/dd15/economy.aspx 

Detroit Diesel (2009b). “Detroit Diesel – Automatic Truck Transmission, Smooth, FuelEfficient Performance.” Accessed July, 2009. 

http://detroitdiesel.com/drivetrains/ags.aspx 

Detroit Diesel (2009c). “Detroit Diesel –Diesel Engines”. Accessed July 2009. 

http://detroitdiesel.com/engines/ 

Detroit Diesel (2009d). “MBE 4000”. http://www.detroitdiesel.com/pdf/engines/6sa580.pdf, 

Accessed July 2009. 

Department of Energy (DOE). “Roadmap for the 21st Century Truck Program”. US Department 

of Energy, 21CT-001. December, 2000. 

Dodge. “Dodge – Build My Own – Model Selection.” 

http://www.dodge.com/hostc/bmo/models.do. Accessed July, 2009. 

Drinkard, D. “LTL Carrier’s view of past and current technologies: Southeastern Freight Lines 

as a Case Study.” Presentation to the NAS Committee for Assessment of Fuel Economy 

Technologies for Medium and Heavy Duty Vehicles. June 18, 2009. 
A-3

Duggal, V. “Diesel Engine Efficiency Technology and Integration - 21CTP Engine Team 

View.” Presentation to the Committee. April 7, 2009. 

Duleep, KG. “Heavy Duty Truck Fuel Economy Supply Curves.” Energy and Environmental 

Analysis. Presentation to the NAS Committee for Assessment of Fuel Economy Technologies 

for Medium and Heavy Duty Vehicles. December 2008. 

Duray, V. “High Power, High Value, Hydraulic Hybrids.” Eaton. February 22, 2008. 

Energy Information Administration. “Assumptions to the Annual Energy Outlook 2009”. 

Department of Energy, Energy Information Administration. Report #DOE/EIA-0554(2009). 

March, 2009. 

Englar, R. “Continued Development and Improvement of Pneumatic Heavy Vehicles.” Georgia 

Tech Research Institute. Heavy Vehicle Systems FY 2004 Annual Report, pp 27-34. February, 

2005. 

Environmental Protection Agency (EPA 2008a). “Final Technical Support Document: 

Regulations Requiring Onboard Diagnostic Systems on 2010 and Later Heavy-Duty Engines 

Used in Highway Vehicles Over 14,000 Pounds; Revisions to Onboard Diagnostic Requirements 

for Diesel Highway Vehicles Under 14,000 Pounds.” Office of Transportation and Air Quality, 

U.S. Environmental Protection Agency. EPA-420-R-08-019. December 2008. Online at 

http://www.epa.gov/otaq/regs/im/obd/regtech/420r08019.pdf 

Environmental Protection Agency (EPA 2008b). “EPA Staff Technical Report: Cost and 

Effectiveness Estimates of Technologies Used to Reduce Light-duty Vehicle Carbon Dioxide 

Emissions.” EPA420-R-08-008. March 2008. 

http://www.epa.gov/OMS/climate/420r08008.pdf, Accessed July 2009. 

Frey, C and Kuo, P. “Best Practices Guidebook for Greenhouse Gas Reductions in Freight 

Transportation.” Prepared for the US Department of Transportation. N.C. State University. 

October 4, 2007. 

factsaboutscr.com. “Facts About SCR.” Accessed July, 2009. http://www.factsaboutscr.com/ 

Federal Motor Safety Carrier Administration (FMSCA). “Appendix B – VDR Capability and 

Cost Profiles.” US Department of Transportation. Accessed July 2009. 

http://www.fmcsa.dot.gov/facts-research/research-technology/report/vehicle-data-recordersdec05/appn-b.htm 

Federal Transit Administration (FTA). “Analysis of Electric Drive Technologies for Transit 

Applications: Battery-Electric, Hybrid-Electric, and Fuel Cells.” US Department of 

Transportation, FTA-MA-26-7100-05.1. August 2005. 

http://www.navc.org/Electric_Drive_Bus_Analysis.pdf 

Ford (2009a). “Ford Build & Price.” 
A-4

http://www50.forddirect.fordvehicles.com/FordVehicles.jsp?target=config&sModel=2010superd

uty&sBrand=Ford. Accessed July 2009. 

Ford (2009b). “2010 Ford Super Duty Engine Specs.” Online at 

http://www.fordvehicles.com/trucks/superduty/specifications/engine/, accessed July 2009. 

Freight Wing. www.freightwing.com. Accessed June 2009. 

Global Insight and TIAX, LLC. “Future Heavy Duty Powertrain Technologies: The Next 

Generation”. Multi-Client Study. December 2004. 

GMC. “GMC: 2009 Sierra Truck: Full-Size Pickup Truck.” 

http://www.gmc.com/sierra/index.jsp. Accessed July, 2009. 

Gotting, G. “Hydraulic Launch Assist HLA System.” Eaton. Presented to the Houston 

Advanced Research Center, 2007. Available online at 

http://files.harc.edu/Projects/HybridTrucks/HydraulicLaunchAssistSystem.pdf, accessed July 

2009. 

Green Car Congress (GCC). “Volvo Group Plans Wide Application of Heavy-Duty Hybrid 

Drive.” September 22, 2008. http://www.greencarcongress.com/2008/09/volvo-grouppla.html#more 

Greszler, A. “US Heavy Duty Fleets – Fuel Economy.” Volvo. Presented at Improving the Fuel 

Economy of Heavy-Duty Fleets, San Diego, CA. February 22, 2006. 

Gutterman, J. “Variable Valve Actuation for Advanced Mode Diesel Combustion.” Delphi 

Corporation. Annual Progress Report 2008 Vehicle Technologies Program: Advanced 

Combustion Engine Technologies, US Department of Energy. Pp 191-194. December 2008. 

Ham, J. “Hybrid Technologies“. Navistar. Presented at the Central Indiana Clean Cities 

Alliance Heavy and Medium Duty Fleet Workshop, November 4, 2008. 

http://www.cicca.org/workshops/HDFWorkshop11-4-08/DurastarHybirdPresentation.pdf 

Heil, B, Schmid, W, Teigeler, M, Sladek, W, Öing, H, Arndt, S, and Melcher, S. “The New 

Daimler Heavy Commercial Vehicle Engine Series.” MTZ 01/2009, Volume 69. 

Helms, H, Lambrecht, U, and Hopfner, U. “Energy savings by light-weighting.” Institute for 

Energy and Environmental Research. Report to the International Aluminum Institute. January, 

2003. 

Hicks, B. and Korn, A. “ArvinMeritor’s Advanced Safety Technologies for Commercial 

Vehicles.” Arvin Meritor. Presentation to the NAS Committee for Assessment of Fuel Economy 

Technologies for Medium and Heavy Duty Vehicles. June 18, 2009. 
A-5

Howard, W. “Ford Offers Radar Based Cruise Control Starting at $1,195”. Gearlog.com. 

August 18, 2009. Available online at http://www.gearlog.com/2009/08/ford_offers_radarbased_adapti.php, Accessed October, 2009. 

International. “Pro Star Fuel Economy Brochure”. 

http://internationaltrucks.com/InternationalTrucks/V2Global/Brochures/ProStar_Fuel_Economy.

pdf. Accessed July, 2009. 

JD Power & Associates. “Adaptive Cruise Control”. Available online at 

http://www.jdpower.com/autos/articles/Adaptive-Cruise-Control. Accessed October, 2009. 

Johnson, C. “AES -Advanced Electric Systems & Aerodynamics for Efficiency Improvements 

in Heavy Duty Trucks”. Caterpillar. Presented at the 2006 U.S. Department of Energy Heavy 

Vehicle Systems Review. April 20, 2006. 

Karbowski, D. E-Mail correspondence regarding vehicle drive cycle modeling and energy 

balances. Argonne National Laboratory, October 9, 2009. 

Kargul, J. “Hydraulic Hybrid Technology.” U.S. Environmental Protection Agency. 

Presentation to the NAS Committee for Assessment of Fuel Economy Technologies for Medium 

and Heavy Duty Vehicles. April 7, 2009. 

Kenworth Truck Company. “White Paper on Fuel Economy”. August, 2008. 

Kramer, D. “Emerging Advanced Heavy-Duty Technologies and Designs.” Arvin Meritor. . 

Presented at Improving the Fuel Economy of Heavy-Duty Fleets II, San Diego, CA. February 

20, 2008. 

Kruiswyk, R. “An Engine System Approach to Exhaust Waste Heat Recovery.” Caterpillar, Inc. 

Annual Progress Report 2008 Vehicle Technologies Program: Advanced Combustion Engine 

Technologies, US Department of Energy. Pp 212-214. December 2008. 

Kruiswyk, R. “Diesel Engine Waste Heat Recovery Utilizing Electric Turbocompound 

Technology.” Caterpillar, Inc. 2005 Annual Progress Report for Advanced Combustion Engine 

Technologies, US Department of Energy. Pp 286-281. January 2006. 

Lane, W. “DOE Program on Parasitic Energy Loss Reduction for Class 7/8 Trucks”. 

Caterpillar. Presented at the 2006 U.S. Department of Energy Heavy Vehicle Systems Review. 

April 19, 2006. 

Laviolette, B. “DuraStar Hybrid medium-duty tractor truck gives six-cylinder an electric boost.” 

The Flint Journal. March 19, 2009. 

http://www.mlive.com/auto/index.ssf/2009/03/durastar_hybrid_mediumduty_tra.html, Accessed 

July 2009. 

Laydon Composites. www.laydoncomp.com. Accessed June 2009. 
A-6

Leuschen, J and Cooper, K. “NRC/NRCan Fuel Efficiency/Greenhouse Gas Program.” 

Canadian National Research Council. Presented at the DOE Heavy Vehicle Aerodynamics 

Meeting. May 12, 2005. 

Leuschen, J and Cooper, K. “Full-Scale Wind Tunnel Tests of Production and Prototype, 

Second-Generation Aerodynamic Drag-Reducing Devices for Tractor trailers.” National 

Research Council, Canada. SAE 06CV-222. 2006. 

Light and Medium Trucks (LMT) . “Daimler Sets 2010 Engine Prices”. 8/10/2009. Accessed 

8/11/2009. http://www.lmtruck.com/articles/lmtbase.aspx?storyid=542 

MacPherson, J. “High gas prices give boost to small town bus plant.” International Business 

Times. May 25, 2008. Available at http://www.ibtimes.com/articles/20080525/high-gas-pricesgive-boost-to-small-town-bus-plant_all.htm 

Marinko, F. Telephone conversation, July 17, 2009. Automotive Research Center. 

Maxxforce. Maxxforce Engine Datasheets – 5 to 13L Engines. 

http://maxxforce.com/Application/on-highway, Accessed June 2009. 

McNamara, J. “Volvo Trucks announces emissions technology surcharge for EPA’10”. Volvo 

Press Release. March 2, 2009. Accessed July, 2009. 

http://www.volvo.com/trucks/na/enus/news_and_events/news_releases/2008pressreleases/NewsItemPage.htm?ItemId=59108 

Merrill, E. Interview, May 20, 2009. D&K Trucking Company. 

Michelin. Michelin Americas Truck Tire Fuel Savings Calculator Page. 

http://www.michelintruck.com/michelintruck/toolbox/FuelSavcalculator.jsp, Accessed July 

2009. 

Miller, D. “Effective Practices and Programs for Improving Fuel Economy, Case Study: Conway Inc.” Con-Way. Presentation to the NAS Committee for Assessment of Fuel Economy 

Technologies for Medium and Heavy Duty Vehicles. June 18, 2009. 

Miller, T. “Hybrid Battery Technology and Challenges.” Ford Motor Company. Technology 

Review’s Emerging Technology Conference, 9/28/2006. 

Motor Coach Industries (MCI). “MCI Showcases Hybrid Coach, Other Popular Models to 

Combat Carbon Emissions.” Motor Coach Industries, Press Release Archive. September 30, 

2008. http://www.mcicoach.com/enTouchCMS/app/viewDocument?docID=644, Accessed July 

2009. 

Nathan Associates, Inc. “Motorcoach Census 2008”. December 18, 2008. 

http://www.buses.org/files/Motorcoach%20Census%202008%2012-18-2008.pdf 
A-7

National Highway Traffic Safety Administration (NHTSA). “Average Fuel Economy Standards 

Passenger Cars and Light Trucks Model Year 2011.” National Highway Traffic Safety 

Administration, US Department of Transportation. Docket No. NHTSA-2009-0062. March 

2009. 

National Research Council. “Review of the 21st Century Truck Partnership.” Board on Energy 

and Environmental Systems, National Research Council. 2008. 

Nelson, C. “Exhaust Energy Recovery.” Cummins, Inc. Annual Progress Report 2008 Vehicle 

Technologies Program: Advanced Combustion Engine Technologies, US Department of Energy. 

December 2008. 

New Flyer website: http://www.newflyer.com/index/cms-filesystemaction?file=7304_nfi_primo_brochure%20final.pdf 

Northeast States Center for a Clean Air Future (NESCCAF), The International Council on Clean 

Transportation (ICCT), TIAX, and Southwest Research Institute (SwRI). “Reducing HeavyDuty Long Haul Truck Fuel Consumption and CO2 Emissions.” October, 2009. 

Nose Cone. www.nosecone.com. Accessed June 2009. 

OrionWeb site: 

http://www.orionbus.com/Projects/c2c/channel/documents/845706_Orion_Hybrid_Transit_Prese

ntation_Q1_2009.pdf; and conversation with Tom Utrup, Orion Bus 

(Thomas.Utrup@dcbusna.com, 315-223-5100) 

PacLease Truck Rental and Leasing. “PacLease Guide to Fuel Efficiency”. Available online at 

http://www.paccar.com/company/environmental/FuelEfficiency_KW_final.pdf, Accessed June 

2008. 

Research and Innovative Technology Administration (RITA). “Cost Estimates to Install 

Collision Warning Systems”. January, 2007. Available online at 

http://www.itsbenefits.its.dot.gov/its/benecost.nsf/ID/D1C6E98ECAC4D5EF852573EC005231

DD?OpenDocument&Query=CApp, Accesed October 2009. 

Salari, K. Telephone conversation, July 15, 2009. Lawrence Livermore National Laboratory. 

Salari, K et al. “Heavy Vehicle Drag Reduction Devices: Computational Evaluation & Design.” 

Lawrence Livermore National Laboratory. Presented at DOE Heavy Vehicle Systems Review, 

April 18-20, 2006. 

Salari, K. “DOE’s Effort to Reduce Truck Aerodynamic Drag through Joint Experiments and 

Computations.” Lawrence Livermore National Laboratory. Presented at the DOE Annual Merit 

Review. February 28, 2008. 
A-8

Saricks, C, Vyas, A, Stodolsky, F and Maples, J. “Fuel Consumption of Heavy-Duty Trucks: 

Potential Effect of Future Technologies for Improving Energy Efficiency and Emissions.” 

Transportation Research Record 1842, Paper No. 03-3648. 

Scheps, R. “Improving the Sustainability of Transport: Aluminum is Part of the Solution.” 

Alcoa. Presented at the 2008 Clean Heavy Duty Vehicle Conference, San Diego, CA. February 

22, 2008. 

Scheps, R. “The Aluminum Advantage: Exploring Commercial Vehicle Applications.” The 

Aluminum Association. Presentation to the NAS Committee for Assessment of Fuel Economy 

Technologies for Medium and Heavy Duty Vehicles. June 18, 2009. 

Schubert, R and Kromer, M. “Heavy-Duty Truck Retrofit Technology: Assessment and 

Regulatory Approach.” TIAX, LLC. Prepared for the Union of Concerned Scientists, 

September 12, 2008. 

Site Visits: 

April 8, 2009 Ford Motor Company 

April 8, 2009 Daimler Trucks North America, Detroit Diesel 

April 8, 2009 Azure Dynamics 

April 8, 2009 Eaton 

April 8, 2009 Arvin Meritor 

April 8, 2009 TARDEC 

April 9, 2009 Navistar 

May 4, 2009 PACCAR 

May 7, 2009 ISE Corporation 

May 13, 2009 Volvo Trucks NA 

May 14, 2009 Allison Transmissions 

May 15, 2009 Cummins Engine Company 

July 22, 2009 Peterbilt Trucks, Great Dane Trailers, Wal-Mart 

August 11, 2009 Auto Research Center 

August 12, 2009 Transportation Research Center 

Smartway Transportation Partnership (2009a). “SmartWay Technology Package Savings 

Calculator – Explanation of Assumptions.” United State Environmental Protection Agency. 

http://www.epa.gov/smartway/transport/calculators/calculatorexplanation.htm. Accessed June 

2009. 

Smartway Transportation Partnership (2009b). “Idling Reduction Technologies”. United States 

Environmental Protection Agency. http://epa.gov/smartway/transport/what-smartway/idlingreduction-available-tech.htm, Accessed 7/20/2009. 
A-9

Smartway Transport Partnership (2004a). “A Glance at Clean Freight Strategies: Single WideBased Tires.” US Environmental Protection Agency, Office of Transportation and Air Quality. 

EPA 420-F-04-004. February 2004 

Smartway Transport Partnership (2004b). “A Glance at Clean Freight Strategies: Automatic Tire 

Inflation Systems.” US Environmental Protection Agency, Office of Transportation and Air 

Quality. EPA 420-F-04-010. February 2004. 

Smartway Transport Partnership (2004c). “A Glance at Clean Freight Strategies: Low-Viscosity 

Lubricants.” US Environmental Protection Agency, Office of Transportation and Air Quality. 

EPA 420-F-04-006. February 2004. 

Smartway Transport Partnership (2004d). “A Glance at Clean Freight Strategies: Low-Viscosity 

Lubricants.” US Environmental Protection Agency, Office of Transportation and Air Quality. 

EPA 420-F-04-005. February 2004. 

Stanton, D. “Advanced Diesel Engine Technology Development for High Efficiency, Clean 

Combustion.” Cummins, Inc. Annual Progress Report 2008 Vehicle Technologies Program: 

Advanced Combustion Engine Technologies, US Department of Energy. Pp 113-116. 

December 2008. 

Stodolsky, F, Gaines, L, and Vyas, A. “Analysis of Technology Options to Reduce the Fuel 

Consumption of Idling Trucks”. Argonne National Laboratory. Center for Transportation 

Research. June 2000. 

Storms, B, Satran, D, Heineck, J, and Walker, S. “A Study of Reynolds Number Effects and 

Drag-Reduction Concepts on a Generic Tractor trailer.” 34th AIAA Fluid Dynamics Conference 

and Exhibit. AIAA-2004-2251. 2004. 

Sturgess, S. "Cummins Bombshell: No Big Bore SCR for 2010.” Heavy Duty Trucking. 

October, 2007. http://www.heavydutytrucking.com/2007/10/092a0710.asp, Accessed July 2009. 

Thrift, J. “Reducing Your Transportation Carbon Footprint.” Ryder System, Inc. February 22, 

2008. 

Track Your Truck. “Vehicle Tracking Products.” Accessed July 

2009.http://www.trackyourtruck.com/products.html 

Transportation Research Center (TRC). “Freightwing Type II Class Eight Semi Trailer 

Aerodynamic Fuel Economy Comparison Test.” Project # 20030712. May 2004. 

Transport Topics (TT). “Navistar Increases Truck Prices $6,000 to $8,000 for 2010 Engines.” 

7/29/2009. Accessed 8/7/2009. 

http://www.ttnews.com/articles/basetemplate.aspx?storyid=22427 

Truck Manufacturers Association (TMA). “Test, Evaluation, and Demonstration of Practical 

Devices/Systems to Reduce Aerodynamic Drag of Tractor/Semitrailer Combination Unit 
A-10

Trucks”. Prepared for the National Energy Technology Laboratory, Contract Number DE-FC26-

04NT42117. April, 2007. 

truthaboutscr.com. “The Truth About SCR”. Accessed July, 2009. 

http://www.truthaboutscr.com/media/pdfs/SCR_Brochure_Heavy_2-26-09b.pdf 

Vehicle Inventory and Use Survey: 2002 (VIUS). U.S. Department of Commerce, U.S. Census 

Bureau. Issued December 2004. 

Visnic, B. “Buyers of Heavy-Duty Pickups Turning Their Backs on Diesel.” Edmund’s Auto 

Observer. July 9, 2008. Online at http://www.autoobserver.com/2008/07/buyers-of-heavy-duty 

pickups-turning-their-backs-on-diesel.html 

Vuk, C. “Electric Turbo Compounding...A Technology Who’s Time Has Come.” John Deere 

Technical Center. Presented at DEER 2006. August, 2006. 

Vyas, A, Saricks, C, and Stodolsky, F. “The Potential Effect of Future Energy-Efficiency and 

Emissions-Improving Technologies on Fuel Consumption of Heavy Trucks”. Argonne National 

Labs ANL/ESD/02-4. August, 2002. 

Volvo (2009a). Powertrain – Volvo. Engine Datasheets and literature. Available at 

http://www.volvo.com/trucks/na/en-us/products/engines/pt.htm, Accessed July 2009. 

Volvo (2009b). “SCR: Preferred Technology for EPA 2010 Engines.” Available at 

http://www.volvo.com/NR/rdonlyres/CB38C044-9C8E-4F42-8090-

D3349CB7DDB1/0/SCR_EGR_041609.pdf, Accessed September, 2009. 

Volvo (2009c). “Discover the New Volvo 7700 Hybrid.” 

http://www.volvo.com/NR/rdonlyres/EA6658C7-DCF4-49F0-B616-

D244B3099A51/0/Hybrid_UK.pdf, Accessed July 2009. 

Volvo (2009d). Volvo FE Hybrid Brochure & Data Sheet. Online at 

http://www.technischweekblad.nl/Uploads/Files/303441.pdf, Accessed July, 2009. 

Walsh, M. “Global Efforts to Encourage Heavy Duty Vehicle Fuel Economy Improvements.” 

Presented at Improving the Fuel Economy of Heavy-Duty Fleets. February 2006. Online at 

http://www.nescaum.org/documents/improving-the-fuel-economy-of-heavy-duty-fleets/ 

Windyne. www.windyne.com. Accessed June 2009. 

Yatsko, T. “Private Truck Fleet Environmental Sustainability Strategy.” Wal-Mart. Blue 

Skyways Meeting, February 2007. http://www.blueskyways.org/pdf/meetingpresentations/february-2007/wal-mart-transportation.pdf, Accessed July 2009. 

Zhang, H. “Advancements in Engine Combustion Systems to Enable High Efficiency Clean 

Combustion for Heavy-Duty Vehicles.” Detroit Diesel. Annual Progress Report 2008 Vehicle 
A-11

Technologies Program: Advanced Combustion Engine Technologies, US Department of Energy. 

Pp 130-133. December 2008.