Setting the Stage for Regulation of 

Heavy-Duty Vehicle Fuel Economy & 

GHG Emissions:

Issues and Opportunities

Trucks and Climate Change

AUTHORS: Dana Lowell and Thomas Balon

M.J. Bradley & Associates LLC

PREPARED BY: M.J. Bradley & Associates LLC

FOR SUBMISSION TO:

International Council on Clean Transportation

1225 Eye Street Suite 1000 Washington, DC 20005

One Hallidie Plaza Suite 503 San Francisco, CA 94102

www.theicct.org

ABOUT ICCT:

The goal of the International Council on Clean Transportation (ICCT) is to dramatically 

reduce conventional pollution and greenhouse gas emissions from personal, public, and 

goods transportation in order to improve air quality and human health, and mitigate 

climate change. The Council is made up of leading government officials and experts 

from around the world that participate as individuals based on their experience with air 

quality and transportation issues.

The ICCT promotes best practices and comprehensive solutions to improve vehicle 

emissions and efficiency, increase fuel quality and sustainability of alternative fuels, 

reduce pollution from the in-use fleet, and curtail emissions from international goods 

movement.

ACKNOWLEDGEMENTS:

The authors would like to thank Bill Van Amburg of CalStart and Mike Ogburn 

formerly of the Rocky Mountain Institute as well as the ICCT staff for reviewing and 

commenting on earlier versions of this report.

DISCLAIMER: 

This document does not necessarily represent the views of organizations or government 

agencies represented by ICCT reviewers or participants. 

February 2009

Table of Contents

Executive Summary...........................................................................................................3

1. Purpose ..........................................................................................................................5

2. The U.S. Heavy-Duty Vehicle Fleet..............................................................................6

3. Components of HDV Fuel Use................................................................................... 11

4. U.S. Efforts to Increase HDV Fuel Economy............................................................. 15

4.1 US EPA SmartWay Transport Partnership...............................................................15

4.2 DOE 21st Century Truck Partnership........................................................................16

4.3 California AB 32..............................................................................................................18

4.4 Energy Independence and Security Act of 2007 ......................................................18

4.5 Hybrid-electric Transit Buses & Trucks.....................................................................19

4.6 Hybrid Trucks Users Forum (HTUF) .........................................................................21

5. International Efforts to Increase HDV Fuel Economy.............................................. 22

5.1 Japan..................................................................................................................................22

5.2 European Union..............................................................................................................25

6. Technology Options to Increase HDV Fuel Economy ............................................. 26

6.1 Engine Technologies......................................................................................................26

6.2 Drive-train Technologies ..............................................................................................27

6.3 Vehicle Technologies .....................................................................................................28

7. Design of HDV Fuel Economy Regulations.............................................................. 29

7.1 Regulated Entity or Entities .........................................................................................29

7.2 Regulated Vehicles.........................................................................................................32

7.3 Fuel Economy/Efficiency/GHG Metric....................................................................33

7.4 Test Procedures Used for Verification......................................................................37

7.5 Form of Required Fuel Efficiency “Improvement”.................................................46

7.6 Choice of Baseline ..........................................................................................................47

7.7 Implementation Timeline & Flexibility Provisions.................................................47

7.8 Compliance/Enforcement............................................................................................49

8. Barriers to Implementation of HDV Fuel Economy Standards............................... 51

8.1 HDV Fleet Diversity ......................................................................................................51

8.2 Shared Responsibility for Components of Fuel Use ...............................................51

8.3 Vehicle Ownership Patterns.........................................................................................52

8.4 Financing & Access to Capital.....................................................................................52

8.5 Lack of HDV Fuel Economy Test Protocol ...............................................................52

8.6 Lack of Baseline Data.....................................................................................................53

8.7 Changes in Ownership Over a Vehicle’s Life...........................................................53

9. Related Issues .............................................................................................................. 55

9.1 Complementary In-use Standard................................................................................55

9.2 The Role of Non-standard Fuels .................................................................................55

9.3 Incentives for Modal Shift/System Efficiency .........................................................55

9.4 HDV Weight and Length Restrictions .......................................................................56

9.5 Reductions in Highway Speed Limits .......................................................................57

9.6 Driver Training ...............................................................................................................57

10. Key Research Areas................................................................................................... 59

10.1 Technology Options to Increase HDV Fuel Efficiency ...........................................59

10.2 HDV Fleet & Industry Characteristics .......................................................................59
Setting the Stage for Regulation of HDV Fuel Economy

2

10.3 Test Cycle(s) & Methodology...................................................................................... 60

10.4 Choice of Fuel Efficiency Metric ................................................................................. 61

Figures

Figure 2.1 Truck Weight Classes ........................................................................................................... 6

Figure 2.2 Heavy Truck Fleet and Fuel Use....................................................................................... 7

Figure 2.3 25 Largest Private and For-Hire Fleets ........................................................................... 8

Figure 2.4 Major HDV Manufacturers (non-inclusive list)............................................................10

Figure 3.1 Components of Energy Use on a Class 8 Combination Truck..................................11

Figure 3.2 Power Used to Overcome Resistance by a Typical Combination Truck................13

Figure 4.1 SmartWayTM Logos ...........................................................................................................15

Figure 4.2 SmartWayTM Equipment Standards ..............................................................................16

Figure 4.3 21st Century Truck Partners.............................................................................................17

Figure 4.4 Likely Timeline for Development and Implementation of HDV Fuel Economy 

Standards in Accordance with EISA...............................................................................19

Figure 5.1 Fuel Use Map for a Diesel Engine....................................................................................23

Figure 5.2 Schematic of Fuel Economy Determination for Japanese Regulations....................23

Figure 7.1 Shared Responsibility for Major Elements that Effect HDV Fuel Efficiency..........30

Figure 7.2 VMT of Five-axle Combination Trucks by Operating Weight 

Range (1992 TIUS)..............................................................................................................35

Figure 7.3 Illustration of Different Fuel Efficiency Metrics as Applied to Cargo Vehicles of 

Different Sizes.......................................................................................................................36

Figure 7.4 Transit Bus Test Cycles: Manhattan Cycle and Orange County Cycle....................44

Figure 9.1 Relative Carbon Emissions Using Different Freight Strategies..................................56

Tables 

Table 4.1 21st Century Truck Partnership Technology Goals......................................................17

Table 4.2 Largest Hybrid Transit Bus Fleets ..................................................................................20

Table 7.1 Comparison of Fuel Efficiency / GHG Metrics............................................................32

Table 7.2 Comparison of HDV Fuel Efficiency Test Methods ...................................................37

Table 7.3 Comparision of HDV Fuel Efficiency Regulated Entities ..........................................42
Executive Summary

3

Executive Summary

This document discusses issues related to the regulation of fuel efficiency of heavy-duty vehicles 

in the United States. While new U.S. light-duty vehicles (cars and light trucks) are required to 

meet minimum corporate average fuel economy standards, medium and heavy-duty vehicles 

(larger trucks and buses) are not. There are currently no federal standards for the fuel economy 

of large trucks and buses, either for individual models or as a fleet average.

In December 2007 Congress passed, and the President signed, the Energy Independence and 

Security Act (EISA). This law mandates, among other things, that the Department of 

Transportation develop, for the first time, fuel economy standards for medium and heavy-duty 

vehicles. The law requires new standards for both “work trucks” with a gross vehicle weight 

rating (GVWR) of 8,500 – 10,000 pounds and “medium- and heavy-duty vehicles” with a 

GVWR over 10,000 pounds. 

At the same time, the US Environmental Protection Agency (US EPA) is developing a plan to 

reduce greenhouse gas (GHG) emissions under the authority conferred by the Clean Air Act. In 

the agency’s Advance Notice of Proposed Rulemaking several options for regulating GHGs from 

medium- and heavy-duty trucks are described.

The current U.S. heavy-duty vehicle (HDV) fleet is extremely diverse, in terms of vehicle size 

and configuration, as well as usage patterns. It encompasses everything from 18-wheel 

combination trucks used to haul freight, to school and transit buses, to numerous “vocational” 

trucks such as refuse haulers, utility service trucks, and dump trucks. The largest of these 

vehicles – combination trucks comprised of a truck-tractor pulling a trailer – typically weight 

80,000 pounds or more. In 2005 the 8.5 million heavy-trucks registered in the U.S. traveled over 

222 billion miles and emitted almost 350 million metric tons of carbon dioxide to the 

atmosphere - approximately 19% of the CO2 emissions from all transportation sources. 

The development of effective fuel efficiency and GHG regulations for HDVs will require 

attention to numerous technical and policy-related details. Decisions as to the “best” regulatory 

design must be based on a thorough understanding of existing and future characteristics of the 

HDV fleet, the structure and characteristics of the HDV manufacturing industry, and potential 

technology approaches available to reduce HDV fuel use and GHG emissions.

The technical issues that must be addressed range from the metric used to measure fuel 

economy or GHG emissions, to the format of required improvements, to the test method used to 

verify compliance. Policy-related issues that can significantly affect the implementation cost 

and the effectiveness of the regulations include: specific vehicle types to be regulated, 

companies responsible for compliance, the implementation timeline, provisions for compliance 

flexibility, and methods of enforcement. 

For each technical and policy area there are a number of options available to policymakers. 

Different approaches will have different potential benefits, costs, and implementation issues. 

The optimal regulatory design will balance these different implementation issues to achieve

cost-effective improvements.

This document is intended to set the stage for an effective and productive dialogue about the 

optimal regulatory design for HDV fuel efficiency and GHG improvements. The first six 

chapters provide background information about the composition of the U.S. HDV fleet and the 

structure of the HDV manufacturing industry; major factors that contribute to fuel use by 

HDVs; current voluntary efforts and regulatory requirements to increase HDV fuel efficiency in 

the U.S., Japan, and the European Union; and the technology options available to improve 

HDV fuel efficiency. The remainder of the document discusses specific technical and policy 
Executive Summary

4

issues that must be addressed in the design of HDV fuel efficiency and GHG regulations, 

barriers to implementing these regulations in the U.S., related policy issues, and 

recommendations for further research and analysis. To address these issues the ICCT has 

developed a research work plan. The document concludes with a description of recommended 

research priorities for ICCT to consider in the near term. 
Purpose

5

1. Purpose

There is considerable interest in the U.S. and internationally in reducing fuel use and green house 

gas (GHG) emissions from heavy-duty vehicles (HDV). This interest parallels other efforts to 

reduce fuel use and GHG emissions from the entire transportation sector. Internationally these 

efforts are primarily related to reduction of GHG emissions, while in the U.S. there is also 

significant interest in increasing “energy security” by reducing the need to import petroleum and 

other fuels.

To date most government efforts to improve HDV fuel economy have been voluntary, though 

Japan has enacted regulations that mandate improvements. 

This paper is intended to set the stage for future international regulation of HDV fuel economy 

and GHGs by providing background information on heavy duty fleets and HDV fuel use, and 

by identifying and discussing the major topics and issues relevant to design and implementation 

of fuel economy standards specifically for heavy-duty vehicles. This paper will focus 

specifically on the U.S. HDV fleet. In addition to regulatory design issues, this paper discusses 

potential barriers to the implementation of HDV fuel economy regulations in the U.S. context, 

and provides recommendations on key research required to move any U.S. regulatory effort 

forward. While the specifics of HDV fleets, and the potential barriers to regulatory 

implementation, will vary by country the major issues discussed in this paper have general 

applicability in all countries.

This paper focuses exclusively on on-road heavy-duty vehicles, and does not address non-road 

vehicles and equipment used for construction, agriculture, forestry, and mining.

This paper is intended as a resource for all parties interested in this subject, including vehicle 

and technology manufacturers, government agencies, and non-governmental organizations. It is 

hoped that this paper will begin to frame the debate in a way that will allow all interested 

parties to productively discuss the relevant issues, and to move cooperatively toward effective 

and cost-effective solutions.
U.S. Heavy Duty Vehicle Fleet

6

2. The U.S. Heavy-Duty Vehicle Fleet

The U.S. heavy-duty on-road vehicle fleet is diverse, encompassing everything from 18-wheel 

combination trucks used to haul freight, to school and transit buses, to numerous “vocational” 

trucks such as refuse haulers, utility service trucks, and dump trucks.

The U.S. Department of Transportation categorizes trucks into classes based on their gross 

vehicle weight rating (GVWR)1. See Figure 2.1, which illustrates “typical” vehicles that would 

fall into each class. As shown, Class 1 and 2 vehicles lighter than 10,000 pounds are 

considered “light trucks” – these would be pick-ups, small vans and sport utility vehicles, most 

or which are powered by gasoline engines; over 80% of these light trucks are used for personal 

transportation [2-1]. In the U.S. Class 1 and 2 light trucks up to 8,500 pounds GVWR are 

currently subject to Corporate Average Fuel Economy (CAFE) standards similar to, but less 

stringent than, those imposed on cars. These light trucks are also subject to the same emission 

standards as cars. As a result, Class 2 trucks with GVWR above 8,500 lbs. are more similar to 

Class 3 trucks than to lighter Class 2 trucks.

Light-Duty Medium Heavy-Duty Heavy-Duty

Class 1 Class 2 Class 3 Class 4 Class 5 Class 6 Class 7 Class 8

Less than 

6,000 lb

6,000 to 

10,000 lb

10,000 to 

14,000 lb

14,000 to 

16,000 lb

16,000 to 

19,500 lb

19,500 to 

26,000 lb

26,000 to 

33,000 lb

Greater than 

33,000 lb

Figure 2.1 Truck Weight Classes 

 

1

 GVWR is the maximum design weight of the vehicle, including any pay load.
U.S. Heavy Duty Vehicle Fleet

7

Vehicles in weight class 3 and above are almost exclusively commercial vehicles powered by 

diesel engines, and are considered to be “heavy-duty vehicles”. Class 3 – 6 vehicles are 

considered medium heavy-duty, and generally have only a single rear axle, while Class 7 and 8 

vehicles are heavy heavy-duty and often have two 

or more rear axles. 

The largest Class 8 trucks have a GVWR of 80,000 

pounds or more, and are exclusively combination 

trucks composed of a three-axle tractor pulling a 

trailer with two or more axles. 

Vehicles, Mileage, and Fuel Use

In 2005 there were 8.5 million heavy trucks 2

registered in the U.S. [2-2]. These trucks traveled 

over 222 billion miles that year, consumed 33.5 

billion gallons of diesel fuel, and emitted almost 

350 million metric tons of carbon dioxide3 to the 

atmosphere. This was approximately 19 percent of 

the CO2 emissions from all transportation sources 

in that year [2-3].

Between 1990 and 2005 heavy truck registrations 

increased by 37 percent and annual fleet vehicle 

miles traveled increased by 52 percent. Over that 

period registrations increased at an average annual 

rate of 2.2%, while mileage increased at an average 

annual rate of 2.9%. The number of miles traveled 

annually by Class 8 trucks is expected to continue 

to increase – by as much as 40 percent through 

2020 [2-4].

Since 1990 the average fuel economy of single unit 

trucks has increased from 6.2 to 8.8 miles per 

gallon (MPG) while the average fuel economy of 

combination trucks has only increased from 5.8 to 

5.9 MPG [2-2].

See Figure 2.2, which shows the percentage of the 

truck fleet and fuel usage by weight class in 2002.

Class 3 – 6 medium heavy-duty vehicles are 

typically used for construction, agriculture, retail 

trade or for-hire local freight delivery. Larger singleunit freight haulers, most buses, many vocational 

trucks (refuse haulers, dump trucks), and all 

combination trucks are Class 7 or 8. 

Of those vehicles with more than two axles or more 

than four tires, 75 percent are single-unit trucks 

2

 This includes trucks with more than two axles or more than four tires, generally Class 4 – 8.

3

 Burning one gallon of #2 diesel creates 22.6 pounds of CO2.

% of Fuel

13.5%

75.3%

4.0% 2.3%

1.1%

3.8%

Class 3 Class 4 Class 5

Class 6 Class 7 Class 8

% of Trucks

13.3%

32.9%

41.5%

3.5%

3.2%

5.6%

Source: DOE

Figure 2.2 Heavy Truck Fleet and

 Fuel Use, 2002 [2-5]

Source: USDOE 

Figure 2.2 Heavy Truck Fleet and

 Fuel Use, 2002 [2-5]
U.S. Heavy Duty Vehicle Fleet

8

(Class 4 – 8) and 25 percent are combination trucks (Class 8) [2-2]. 

In 2005 the average single unit truck traveled 12,400 miles while the average combination truck 

traveled 68,800 miles. 

Given their greater weight, lower average fuel economy, and higher usage, in 2005 Class 8 trucks 

used approximately 75 percent of all fuel consumed by heavy-duty trucks (class 4-8) [2-2]. 

Heavy-duty Vehicle Use

Heavy-duty vehicles are found in every sector of the economy and are used to perform a wide 

array of functions, from carrying freight, to carrying passengers, to hauling trash, to mixing and 

hauling concrete. Different vehicle types can have widely varying duty cycles, including those 

characterized by mostly high-speed highway operation with few stops, medium-speed 

suburban operation, and low-speed urban operation with a high number of stops per mile. 

The single biggest use of heavy-duty trucks in the U.S. is for hauling goods and materials; over 

thirty percent of all Class 

7 and 8 vehicles are used 

to provide for-hire 

transportation of freight 

[2-1]. Trucks are used to 

carry 66 percent, by 

weight, of all goods 

shipped [2-6].

As noted above the 

majority of fuel 

consumed by the heavyduty fleet is consumed by 

Class 8 combination 

trucks. These trucks are 

used almost exclusively 

for hauling various types 

of freight long distance. 

The trailers that they pull 

include open flat bed 

trailers, enclosed box 

trailers, dump trailers, 

car haulers, and tanker 

trailers. 

Trucks are also used to 

haul “intermodal” 

shipments. These 

shipments are carried by 

rail or ship for part of 

their journey and by truck 

the rest. Intermodal 

goods are shipped in 

standard box-like metal 

shipping containers that get transferred from rail or ship to the truck without being unpacked. 

The shipping container rests on a light weight trailer frame that is pulled behind a truck tractor 

like other combination trailers; the combination of shipping container and trailer look similar to 

an enclosed box trailer. Approximately seven percent of all goods shipped within the U.S. in 

Source: Transport Topics

Figure 2.2 25 Largest Private and For-Hire Fleets [2-7]

Source: Transport Topics

Figure 2.3 25 Largest Private and For-Hire Fleets [2-7]
U.S. Heavy Duty Vehicle Fleet

9

2006 (by weight) were shipped intermodally [2-8]. Most of this volume was likely shipped in 

standard intermodal shipping containers.

Typically a specific truck is not used to pull a specific trailer full time. One Class 8 truck will 

be used to pull multiple trailers over the course of a year. 

Most Class 8 combination trucks spend the majority of their time on the nation’s highways 

operating at high, sustained speeds. Some of these trucks are used for local or regional 

deliveries and experience a greater percentage of suburban or urban driving conditions. 

Heavy-Duty Vehicle Ownership

Heavy-duty trucks can be found in the fleets of virtually all local and state governments, and 

every agency of the federal government. The vast majority, however, are corporately owned 

and used for commercial purposes. 

The largest company-owned fleet of heavy-duty vehicles in the U.S. includes over 60,000 Class 

8 tractors. The two hundred largest private and for-hire freight hauling fleets together control 

over 600,000 Class 8 tractors, and 330,000 Class 4 – 8 single-unit trucks, approximately 11% of 

registered heavy-duty vehicles [2-7]. Of these Class 8 tractors, 86% are company-owned and 

14% are “owner-operator” trucks as shown in Figure 2.3. These fleets also control over 1.1 

million trailers.

A large percentage of HDVs are owned and operated by small companies or individuals. Less 

than two hundred U.S. companies control more than two hundred freight-hauling trucks each. 

Up to fifty percent of all heavy-duty trucks are in fleets of less than ten trucks, and up to thirty

percent of all Class 8 tractors are owned and driven by an owner-operator with only one truck 

[2-9].

In many cases the truck and trailer that make up a “combination truck” on any particular day 

will be owned by different companies. 

Heavy-Duty Vehicle Manufacturing

Of the Class 7 and 8 vehicles in-use in 2002, over sixty percent had been built by only five truck 

manufacturers: Freightliner, Kenworth, International, Mack, and Peterbuilt [2-8], and these same 

five companies accounted for approximately eighty percent of new trucks sold in 2005 [2-10].

Unlike manufacturers of cars and light trucks, not all manufacturers of heavy-duty vehicles 

produce their own engines. Of new diesel engines sold in Class 8 trucks in 2005, over ninety 

percent were manufactured by five different engine companies: Caterpillar, Cummins, Detroit 

Diesel, Mack, and Volvo; only two of these engine manufacturers (Mack and Volvo) also 

manufacture on-road trucks [2-10]. 

Many heavy-duty single unit trucks, particularly vocational trucks and school buses, are 

composed of a body manufactured by one company installed on a chassis4 produced by 

another.

The manufacturers of heavy-duty trucks typically do not produce the trailers pulled by 

combination truck-tractors. These trailers are built by a different set of manufacturers. 

See Figure 2.4 for a non all-inclusive list of major HDV manufacturers [2-11].

 

4

 The chassis usually includes a frame, suspension, engine, drive train, and wheels. It may also include 

the truck cab.
U.S. Heavy Duty Vehicle Fleet

10

STRAIGHT TRUCKS/CHASSIS COMBINATION TRUCKS

Class 6 Class 8 Tractors Trailers

Daimler Trucks NA

 Freightliner Custom 

 Chassis

 Sterling Truck

Navistar Intl.

 International Trucks

 Workhorse Custom

 Chassis

General Motors

 Chevrolet

 GMC

Ford

Isuzu

Hino Motors

Mitsubishi Fuso

Paccar

 Kenworth

UD Trucks

General Motors

 Chevrolet

Daimler Trucks NA

 Freightliner

 Sterling Truck

 Western Star

Navistar Intl.

 International Trucks

Paccar

 Kenworth

 Peterbuilt

Volvo

 Mack

Daimler Trucks NA

 Freightliner

 Sterling Truck

 Western Star

Navistar Intl.

 International Trucks

Paccar

 Kenworth

 Peterbuilt

Volvo

 Mack

Fontaine Trailer

Great Dane

Hyundai

Stoughton Trailers

Strick Corporation

Trailmobile 

Corporation

Transcraft 

Corporation

Utility Trailer 

Manufacturing

Vanguard National 

Trailer Corp.

Wabash National 

Corporation

VOCATIONAL TRUCK/BODY MANUFACTURERS1

Refuse Trucks School Buses

Amrep

Autocar

Bridgeport Truck Manuf.

Crane Carrier

Dempster Equipment Co.

Leach

Haul-all Equipment Ltd.

Heil Environmental Ltd.

Ingold’s Hico, Inc.

Kann Manufacturing Corp.

Loadmaster

Mack Trucks

McNeilus Companies, Inc.

Oshkosh

Pak-Mor Manufacturing

Scranton Manufacturing Co.

Sterling Truck

Wayne Engineering Corp.

Blue Bird Corporation

Collins Bus Corporation

 Corbeil Bus Corporation

 Mid Bus Corporation

Daimler Trucks NA

 Thomas Built Buses

Girandin Minibus

Navistar International

 IC Bus2

Companies inset in italics are subsidiaries of the company listed above them.

1

 Example only. Other types of vocational trucks are built by different manufacturers. Many of these companies 

use chassis manufactured by the Truck/Chassis manufacturers.

2

 All Navistar school buses are now sold under the IC Bus brand. Navistar previously sold buses under the 

International and AmTran brands.

Source: M.J. Bradley & Associates/R.L. Polk & Company

Figure 2.4 Major HDV Manufacturers (non-inclusive list) 

 
Components of HDV Fuel Use

11

3. Components of HDV Fuel Use

The diesel engines used in current heavy-duty vehicles have on average 33% thermal efficiency 

in-use compared to gasoline engines at approximately 25%. Still only about one third of the 

input energy in the fuel they burn is turned into useful work as measured at the engine output 

shaft. The other two thirds of fuel input energy are lost to engine friction, goes out the vehicle

tail pipe as heat, or is dissipated as heat by the engine’s cooling system.

Of the energy that is turned into useful work by the engine, some is used to power engine 

accessories (i.e. alternator, air compressor, hydraulic fans) and some is dissipated in the 

vehicle’s transmission and drive train. What is left is used to overcome inertia, gravity, 

aerodynamic drag, and rolling resistance to accelerate the vehicle and keep it moving down the 

road and up and over hills. See Figure 3.1, which shows the percentage contribution of various 

energy uses for a typical combination truck operating at highway speeds on a level road.

 

The amount of net energy that goes toward overcoming inertia, versus overcoming aerodynamic 

drag and rolling resistance, varies significantly based on duty cycle. As shown in Figure 3.1, for 

a combination truck operating at highway speeds on a level road, more than half of net energy is 

typically dissipated in aerodynamic losses By comparison, aerodynamic losses are very low for 

an urban bus in slow, stop-and-go traffic, while the energy required to repeatedly accelerate the 

vehicle from a stop in that duty cycle could consume significantly more than 50% of net energy 

delivered by the engine [3-2].

Some vocational vehicles also use some engine power to do work other than driving – for 

example powering the hydraulic packer on a refuse truck. Other vehicles use a significant 

portion of total fuel to keep the engine idling while the vehicle is stationary. This is often done 

to power some relatively small “hotel” loads to provide driver or passenger comfort – for 

example on a bus that idles the engine to keep the passenger compartment warm in the winter, 

Source: USDOE

Figure 3.1 Component of Energy Use on a Class 8 Combination Truck [3-1]
Components of HDV Fuel Use

12

or a combination truck that idles the engine all night to provide heat or air conditioning, and 

electricity, to the sleeper berth while the driver is resting. 

Each of these uses of fuel energy on a heavy-duty vehicle is discussed further below. 

Engine Losses

Lean-burn compression-ignition engines, like those that operate on diesel fuel, are the most 

efficient internal combustion engines in use today. Even so, potential improvements can be 

made in net efficiency by modifying current engine equipment and control strategies; more 

significant gains may also be possible from the use of a completely different combustion cycle.

In recent years achieving efficiency gains in heavy-duty vehicles has been challenging due to 

more stringent exhaust emission standards that have required changes in the engine itself 

and/or exhaust after-treatment. In particular, the use of exhaust gas recirculation (EGR) to 

reduce nitrogen oxide emissions, and the use of diesel particulate filters to reduce particulate 

emissions, has reduced net efficiency due to higher engine pumping losses, higher engine backpressure, and diesel fuel required to regenerate active filters. Manufacturers have to date been 

able to mitigate part or all of this efficiency loss through various engine design improvements. 

Even more stringent emission requirements that take effect in the 2010 engine model year will 

require additional changes that might further impact net efficiency.

Drive Train Losses

A heavy-duty vehicle’s drive train includes all components which transfer power from the 

engine to the wheels – it typically includes an automatic or manual transmission, a drive shaft,

differentials, and rear axle(s).

Drive train losses result from friction between rotating components and the bearings that 

support them. In addition, automatic transmissions incur losses in the torque converter used to 

transfer power between the input and output shafts of the transmission. A manual transmission 

has no torque converter, so it typically incurs fewer losses than an automatic transmission.

Virtually all Class 8 combination trucks currently use manual transmissions, while automatic 

transmissions are more common in transit and school buses, and some vocational trucks. 

Acceleration and Braking

The amount of energy required to accelerate a vehicle from a stop is proportional to the vehicle’s 

mass– the heavier the vehicle is the more energy is required. The rate of acceleration can also 

affect the net engine and drive train efficiency. Moving a vehicle up a grade at constant speed 

also requires energy proportional to its mass and to the vertical component of the grade – in 

order to overcome the effects of gravity. 

For most highway vehicles the amount of energy required to overcome inertia, to accelerate the 

vehicle and climb grades, is a small percentage of the total energy required, because rolling 

resistance and aerodynamic drag exert much higher forces on the vehicle over an entire day of 

operation. However, when a conventional vehicle stops, all of its kinetic energy is converted to 

heat in the braking system5, which is lost and can not be reused. Additional energy is then 

required to accelerate the vehicle again from the stop. The percentage of total energy used to 

accelerate the vehicle, as opposed to overcoming rolling resistance and aerodynamic drag, is 

 

5 Or is dissipated by aerodynamic loads, rolling resistance, and engine/drivetrain friction/exhaust system

pressure if the vehicle coasts to a stop
Components of HDV Fuel Use

13

therefore much higher for urban vehicles that operate in stop-and-go traffic than it is for 

highway vehicles that operate at near constant speed for most of the day.

Rolling Resistance

Rolling resistance is the friction exerted on a vehicle’s tires by the roadway surface6. To keep a 

vehicle operating at constant speed, even on level ground, engine power is required to overcome 

this friction. Rolling resistance is proportional to a vehicle’s mass, and is also affected by the 

material, configuration, and air pressure of the vehicle’s tires. In general, a tire with low air 

pressure will have greater rolling 

resistance than a tire with higher air 

pressure. 

Aerodynamic Drag

Like rolling resistance, the force exerted by 

the air on a moving vehicle also acts to 

slow it down, and engine power is 

required to overcome this force and keep 

the vehicle moving at constant speed. 

This force is referred to as aerodynamic 

drag. 

Aerodynamic drag is proportional to the 

square of the vehicle’s velocity – so the 

amount of energy required to overcome 

these forces increases faster than the 

vehicle’s speed. See Figure 3.2 which 

shows the power required to overcome 

rolling resistance and aerodynamic drag 

for a typical combination truck at various 

speeds. As shown, when going from 45 

mph to 65 mph the amount of power 

required to overcome rolling resistance 

increases from approximately 45 to 

approximately 60 hp – a 33% increase. By contrast, for the same change in speed the amount 

of power required to overcome aerodynamic drag increases from approximately 50 hp to over 

150 hp – a 300% increase. This is the reason why current highway trucks get better fuel 

economy at lower speeds.

Aerodynamic drag is also affected by a vehicle’s total frontal surface area and by its shape. A 

smaller frontal surface area will produce less drag at a given speed. Likewise, sloping shapes 

that “slice through” the wind produce less drag than flat surfaces directly perpendicular to the 

direction of travel. 

On a heavy-duty combination truck total aerodynamic drag is affected by the size and shape of 

both the truck tractor and the trailer it is pulling. Issues that can affect total aerodynamic drag 

include the area and shape of the trailer surface that sticks up above the top of the vehicle cab, 

the gap distance between the back of the truck cab and the front of the trailer, open space 

 

6 Some vehicle energy is also dissipated as heat generated within the tires as they flex while rolling over a 

road surface.

Source: USDOE

 Figure 3.1 Power Used to Overcome Resistance

 by a Typical Combination Truck [3-1] 
Components of HDV Fuel Use

14

between the bottom of the trailer and the road surface in front of the trailer’s wheels, and the 

shape of the rear trailer surface.

Vehicle Accessory & Hotel Loads

All heavy-duty vehicles include engine-driven components that support various vehicle 

functions other than propulsion. These typically include an alternator (to provide electrical 

power for lights, signals, etc), an air conditioning compressor; and air compressor (for air 

brakes); a fan that is part of the engine cooling system; and oil, coolant, fuel, and power steering 

pumps. 

These components are typically belt- or gear-driven from the engine output shaft, and they 

absorb some net engine power. The amount of energy used by vehicle accessories depends on 

the vehicle and duty cycle. For example, urban buses tend to have much higher accessory loads 

than highway trucks due to their stop and go duty cycle (more air brake use, air operated 

doors), larger passenger cabin (lights and air conditioning), and rear-mounted engine (greater 

use of engine cooling fan). 

Engine Idling

Heavy-duty vehicles are sometimes left to idle so that the diesel engine can supply a relatively 

small vehicle accessory or hotel load, often to maintain driver comfort. This is of particular 

concern for sleeper-cab equipped combination trucks, which often idle for eight hours per day or 

more while the operator is resting in the sleeper berth. An idling Class 8 truck uses 

approximately 0.8 gallons of fuel per hour [3-3], and USDOE estimates that idling heavy-duty 

trucks consume up to 840 million gallons of diesel fuel annually in the US [3-4]. This is about 

two and one half percent of all fuel used by heavy trucks annually.

While this type of long duration idling is necessary on many current combination trucks, it is 

inefficient. Total fuel use could be reduced from these vehicles if they were equipped with 

smaller and more efficient auxiliary engines, or other means of powering accessory loads from 

external electricity sources while stationary.

Vocational Loads

Some heavy-duty vehicles have significant non-propulsion engine loads that support 

“vocational” equipment mounted on the vehicle. For example, many refuse haulers use a 

hydraulic ram to periodically pack collected materials more tightly into the truck body. 

Similarly, utility service vehicles often have a hydraulic bucket lift used to provide access to 

overhead lines and structures. To power the hydraulic equipment these vehicles include a large 

hydraulic pump which is driven by the truck’s main engine via a transmission power take-off 

(PTO). 
U.S. Efforts to Increase HDV Fuel Economy

15

4. U.S. Efforts to Increase HDV Fuel Economy

To date, U.S. government efforts to increase the fuel economy of heavy-duty vehicles have been 

voluntary. These efforts include US EPA’s SmartWay Program focused on combination trucks, 

and DOE’s 21st Century Truck research and development program. 

In response to a state law that mandates reductions in GHG emissions state wide, California 

regulators have adopted regulations that will mandate improvements in the fuel efficiency of 

some of the heavy-duty trucks that operate in California. The U.S. Congress also recently 

passed a law that mandates development of fuel efficiency standards for medium- and heavyduty trucks for the first time. Finally, the US Environmental Protection Agency (US EPA) is 

developing a plan to reduce greenhouse gas (GHG) emissions under the authority conferred by 

the Clean Air Act. In the agency Advance Notice of Proposed Rulemaking several options for 

regulating GHGs from medium- and heavy-duty trucks are described.

For certain types of vehicles, notably transit buses, more efficient hybrid-electric drive trains are 

currently being installed on a significant number of new vehicles. 

4.1 US EPA SmartWay Transport Partnership

The SmartWayTMTransport Partnership program was launched by U.S. EPA in 2004 in order to 

reduce fuel use, greenhouse gas emissions, and criteria pollutant emissions from the U.S. ground 

freight system (rail and truck). SmartWayTM is a voluntary public-private partnership program 

that involves all major stakeholders in the freight industry, including both service providers 

(carriers) and users (shippers). 

SmartWay partners must agree to assess their current environmental performance using EPA’s 

Fleet Logistics Energy and Environmental Tracking (F.L.E.E.T.) performance model, and commit

to improving their performance within three years. They also must assess their progress 

annually using the F.L.E.E.T model, and report their progress to US EPA. 

Carriers can meet their SmartWay goals by improving the efficiency of their shipping operations 

through implementation of various fuel saving technologies on their trucks and trailers. 

Shippers can meet their SmartWay goals by using SmartWay transport partners for at least 50 

percent of their goods shipments, and also reducing the green house gas emissions from their 

freight facility operations.

SmartWay also has a program to “certify” combination truck tractors and trailers that meet 

certain minimum requirements for using fuel-saving technologies; equipment that meets these 

standards can use the SmartWay certified label and SmartWay carriers can use this equipment 

to help meet their SmartWay goals (see Figure 4.1). Currently six heavy-duty truck 

manufacturers, including the five who had the highest market share in 2005, produce some 

SmartWay-certified models. In addition eight trailer manufacturers produce some SmartWay-

 

Figure 4.1 SmartWayTM Logos Source: USEPA
U.S. Efforts to Increase HDV Fuel Economy

16

certified trailer models [4-1]. The use of SmartWay-certified trucks and trailers together is 

expected to reduce fuel use by 10 -20% compared to non-certified equipment [4-1].

The current SmartWay certification standards are equipment-based and include a specific list 

of required features as illustrated in Figure 4.2. US EPA intends to move toward a 

“performance-based” standard for SmartWay certification – instead of requiring a specific list 

of features, trucks and tractors would receive certification by meeting or exceeding a minimum 

standard for in-use fuel economy, based on testing using a standard test protocol. 

Source: USEPA

Figure 4.2 SmartWayTM Equipment Standards

US EPA is developing, with industry input, a draft fuel efficiency test protocol for mediumand heavy-duty trucks to be used for SmartWay certification testing. A draft has been 

published, and EPA convened a public workshop to discuss the draft in March 2008. EPA 

expects to publish a revised draft protocol in the second half of 2009.

Any size business can join SmartWay as a partner, from large truck fleets to single owneroperators, and from large chain stores to small local businesses.

Companies that can demonstrate via the F.L.E.E.T model that they have superior environmental 

performance will qualify to use the SmartWay Transport partner logo in their advertising (see 

Figure 4.1).

There are currently over 600 SmartWay partner companies, including over 400 truck carriers, 

over 60 shippers, and over 60 logistics companies [4-2]. By 2012 EPA expects that SmartWay 

will reduce fuel use from the U.S. freight shipping sector by 3.3 – 6.6 billion gallons per year [4-

3]. 

4.2 DOE 21st Century Truck Partnership

The 21st Century Truck Partnership (21CTP) is a public/private program run by the U.S. 

Department of Energy which brings together government agencies and members of the heavyduty vehicle industry to work toward making trucks and buses safer, cleaner, and more efficient. 

Announced in April 2000, the program underwent a major revision of its vision, mission, and 

goals in 2003. The program is intended to be both a coordinated research and development 

effort, and a forum for information sharing across all government and industrial sectors related 

to heavy truck research. 
U.S. Efforts to Increase HDV Fuel Economy

17

Table 4.1 The 21st Century Truck Partnership Technology Goals 

Engine Systems HD Hybrids Parasitic Losses Idle Reduction Safety

 Increase thermal 

efficiency from 42% 

to 50% by 2010

 Stretch goal of 55% 

thermal efficiency in 

prototype engines by 

2013

 10% gain in overthe-road fuel 

economy by 2013, 

compared to 2010 

goal

 By 2012 develop 

drive unit with 15 

year design life that 

costs <$50/kw

 By 2012 develop 

energy storage 

system with 15 year 

design life that costs 

<$25/ peak kw

 Achieve 60% 

increase in fuel 

economy on urban 

drive cycle

 Reduce aero drag on 

Class 8 combination 

truck by 20%

 Reduce auxiliary 

loads on Class 8 

combination truck 

by 50%

 Develop materials 

and manufacturing 

that can reduce 

Class 8 combination 

truck weight by 15- 20%

 By 2009 

demonstrate add-on 

idle reduction 

devices with <2 yr 

pay back

 By 2012 produce a 

truck with fully 

integrated idle 

reduction system

 By 2015 

demonstrate 5-30 

kw fuel cell APU

 Reduce stopping 

distance from 

operational speeds 

by 30% 

 Reduce incidences of 

HDV roll over

 Develop driver aid 

systems to provide 

360° visibility and 

that promote safe 

following distance 

and in-lane tracking

Source: DOE

See Table 4.1 for a list of the major technology goals set by the partnership in each of five 

critical areas that can reduce fuel use and emissions, while increasing safety [4-4]:

 Engine systems (fuel, engine, and after-treatment)

 Heavy-duty Hybrid drive trains

 Parasitic losses (aerodynamic drag, rolling resistance, drive train losses, and auxiliary 

loads)

 Idle reduction, and

 Safety

These specific goals are based on a 

technology research roadmap developed 

under the partnership.

Program partners include sixteen 

industrial companies and four U.S. 

government agencies; the partnership also 

calls on technical expertise from twelve 

participating national laboratories. See 

Figure 4.3 for a list of 21CTP partners. 

The partners work cooperatively to 

develop a balanced portfolio of research 

aimed at achieving their research goals, 

and coordinate their research activities as 

appropriate. 

The intent is to focus research on selected 

projects that show the greatest likelihood 

of near-term success and fleet-wide 

effectiveness.

The partnership conducts regular public demonstrations of emerging heavy-truck technologies, 

and provides public data on technologies under development in annual progress reports.

Funding for this effort has dwindled in recent years and a recent review of the program 

coordinated by the National Academy of Sciences found that “the current level is not in 

Source: DOE

 Figure 4.3 21st Century Truck Partners 
U.S. Efforts to Increase HDV Fuel Economy

18

proportion to the importance of the goal of reducing fuel consumption of heavy-duty vehicles” 

[4-5].

4.3 California AB 32

California Assembly Bill 32 (AB 32), the California Global Warming Solutions Act of 2006, 

mandates state-wide reductions in green house gas emissions to 1990 levels by December 31, 

2020. The California Air Resources Board (ARB) is charged with developing the required 

implementing rules, including any mandatory reductions by sector and any authorized market 

mechanisms. 

While ARB’s major rulemakings are not due to be completed until January 2011, AB 32 requires 

the agency to develop a list of discrete early-action measures that can be implemented by 

January 2010. 

In California, heavy-duty trucks account for 20 percent of GHG emissions from transportation 

sources, and almost eight percent of all GHG emissions [4-6]. ARB has identified mandatory 

reductions in aerodynamic drag and rolling resistance from heavy-duty trucks as a potential 

early-action measure. The proposal was approved by the agency’s board in December 2008. 

The regulation requires improvements in aerodynamics and reductions in rolling resistance for 

both combination trucks (the tractor and trailer) and single-unit trucks. The requirements are 

based on implementation of technology packages “certified” under EPA’s SmartWayTM 

program, including low rolling-resistance tires and light weight wheels, low-profile aero design 

for truck cabs, and drag-reducing gap fairings and side skirts for both trucks and trailers. 

The rule applies to all new Class 8 trucks, and trailers 53 feet long or longer, beginning with the 

2010 model year. It also requires phased retrofits to all 2005 and later in-use trucks between 

2010 and 2014 depending on fleet size. Required retrofits would include light weight wheels 

and low rolling-resistance tires for all trucks, and side skirt- and gap-fairings for all trailers.

As approved the rule applies to all trucks used in California, both those with in-state and those 

with out-of-state registration. 

The ARB also approved in December 2008 the AB 32 Scoping Plan, which outlines the multisectoral plan to attain the emission reduction targets set by the bill. The final plan includes a 

proposal to promote hybridization from medium and heavy-duty vehicles in addition to the 

early action “SmartWay” measure. An earlier version of the Scoping Plan included a proposal 

for medium and heavy-duty engine GHG standards. However the agency decided it would 

consider such standards at a later date if action at the federal level does not provide expected 

benefits [4-7]. 

4.4 Energy Independence and Security Act of 2007

In December 2007 Congress passed, and the President signed, the Energy Independence and 

Security Act (EISA), which includes a number of provisions intended to reduce U.S. dependence 

on imported petroleum fuels.

In addition to renewable fuels production mandates, and a significant increase in corporate 

average fuel economy standards for cars and light trucks (increasing to 35 MPG by 2020), the 

law also mandates that the Department of Transportation (DOT) develop, for the first time, 

fuel economy standards for medium and heavy-duty vehicles. The law requires new standards 

for both “work trucks” with a GVWR of 8,500 – 10,000 pounds and “medium- and heavy-duty 

vehicles” with a GVWR over 10,000 pounds. The law specifies a lengthy regulatory 
U.S. Efforts to Increase HDV Fuel Economy

19

development process – if DOT takes the maximum time allowed for each step the new 

standards are unlikely to take effect before the 2016 model year at the earliest.

The specified regulatory development process includes a study by the National Academy of 

Science of appropriate metrics to measure fuel economy, and available technologies and likely 

costs to increase fuel economy for the target HDVs. This study must be completed within one 

year of NAS receiving a contract from DOT. DOT will then undertake its own study of the 

same issues, to be completed within one year of receiving the NAS study results. Finally, DOT 

will develop a full regulatory program to prescribe, measure, and enforce fuel economy 

standards for HDVs, and must issue the regulations within two years of completing their own 

study. 

The statute requires four years of “lead time” for manufacturers to comply after DOT has 

issued its regulations. It also requires at least three years of “regulatory stability”, which means 

that DOT can not revise the standards more frequently than once every three years.

See Figure 4.4 for a likely time line for development and implementation of the required 

standards.

Source: M.J. Bradley & Associates

Figure 4.4 Likely Timeline for Development and Implementation of HDV Fuel Economy

 Standards in Accordance with EISA

4.5 Hybrid-electric Transit Buses & Trucks 

Hybrid-electric propulsion systems combine an internal combustion engine with one or more 

electric motors and an energy storage device (battery pack), to improve over-all vehicle 

efficiency (see Section 6.2). The first U.S. heavy-duty vehicle sector in which hybrid technology 

made significant inroads was the transit bus sector. In the last few years hybrid systems have 

also been developed for medium-duty vocational trucks.

The first commercial hybrid-electric transit buses were put into service by MTA New York City 

Transit in 1998. Today, transit agencies in over seventy North American cities operate fleets of 

hybrid buses. More than 1,900 hybrid buses are currently in-service, with an additional 2,000 

buses on order with manufacturers [4-8]. The delivered and on-order hybrid buses represent 

approximately 9% of the U.S. transit bus fleet [4-9]. See Table 4.1 for a list of the largest 

hybrid bus fleets.

Several companies have developed medium- and heavy-duty hybrid diesel-electric and dieselhydraulic systems targeted to non-bus vehicle markets as well. Nearly one thousand units of 

varying sizes are either on the road or on order.

The early market leader is the International Truck and Engine Company, owned by Navistar, 

which entered early assembly-line production of medium-duty (Class 6/7) hybrid trucks in the 

fall of 2007. International has teamed with Eaton Corporation for its hybrid-electric system 
U.S. Efforts to Increase HDV Fuel Economy

20

and now has several hundred units on the 

road, with a current production capacity of 

approximately one thousand units per year. 

PACCAR, Inc. and its Kenworth and 

Peterbuilt brands have also teamed with 

Eaton for both hybrid electric and hybrid 

hydraulic systems. [4-10]. The electric

systems are already being offered on a 

limited basis on Kenworth and Peterbuilt

medium-duty trucks targeted for pick-up 

and delivery and utility fleets. Beginning in 

2009 the system will be offered on 

Peterbuilt Class 8 tractors [4-11]. 

On Class 8 tractors the system will also 

include “idle reduction mode” - the hybrid 

system’s batteries will power the heating, 

air conditioning and vehicle electrical 

systems while the engine is off, and the 

engine will only start if the batteries need to 

be charged. Peterbuilt will also enter 

production in 2008 on a hybrid hydraulic 

refuse truck based on its Model 320 chassis 

and the Eaton HLATM (Hydraulic Launch 

Assist) hybrid system. The truck is 

expected to offer fuel savings of 20-30 

percent over conventional trucks.

Mack Truck has delivered to the U.S. Air 

Force six prototype vehicles that use a 

“mild” hybrid system which incorporates 

an electric drive motor attached to the drive line down stream of the transmission. In addition 

to military vehicles, Mack is contemplating offering the system on refuse haulers, with 

production as early as 2009 if current field trials are successful [4-10]. The IC Corporation 

offers a similar hybrid system, built by ENOVA Systems, on their school buses, and Azure 

Dynamics is entering production with a class 4/5 hybrid shuttle bus. 

Arvin Meritor, in a partnership with Wal-Mart and International Trucks, is developing a Class 8 

hybrid electric tractor to compete with the Eaton system. The system, still in the prototype 

phase, would feature a unique dual series-parallel design that would use the engine to generate 

electricity for electric drive at lower speeds, but shift to a more conventional drivetrain at higher 

speeds, with the electric motors providing an assist to the main engine.

Hybrid transit buses have been shown to get 20 – 36% better fuel economy than standard diesel 

buses operated in the same service. The largest benefits were achieved in New York City where 

buses average only 6-7 MPH in service, and stop as often as 20 times per mile [4-13]. In cities 

with fewer stops per mile, and therefore higher average speeds, the gains were less [4-14]. 

The manufacturers of the Mack, Kenworth, and Peterbuilt medium-duty and heavy-duty hybrid 

trucks claim up to 35% fuel economy improvement in stop-and-go duty cycles and 5-7% fuel 

economy improvement for long-haul applications, primarily based on reducing over-night idling 

[4-10] [4-11] [4-12]. Preliminary results from 24 medium-duty hybrid utility trucks built by 

Table 4.2 Largest Hybrid Transit Bus Fleets 

Buses City In 

Service

On 

Order

Hybrid 

Manuf

New York City, NY 800 850 BAE

Toronto, ON 150 414 BAE

Washington, DC 50 500 Allison

Philadelphia, PA 32 400 Allison

Seattle, WA 235 Allison

Ottawa, ON 200 BAE

Long Beach, CA 772 762 ISE

Houston, TX 50 100 BAE

Allison

San Francisco, CA 86 BAE

Montabello, CA 52 462 ISE

Las Vegas, NV 50 ISE

Ann Arbor, MI 20 7 Allison

Newark, NJ 1 21 BAE

Elk Grove, CA 212 ISE

Pittsburgh, PA 12 Allison

Chicago, IL 10 ISE

1 Used at Newark & NYC airports

2 Gasoline-electric hybrids

Source: M.J. Bradley & Associates, ICCT
U.S. Efforts to Increase HDV Fuel Economy

21

International/Eaton, and deployed throughout the country show, a 14-54% increase in fuel 

economy compared to standard diesel trucks in that application [4-15]

4.6 Hybrid Trucks Users Forum (HTUF)

The Hybrid Truck Users Forum (HTUF) is a program partnership of the U.S. Army’s National 

Automotive Center (NAC) and CALSTART, a non-profit advanced transportation 

organization. Launched in 2002, HTUF has a goal of commercializing medium- and heavy-duty 

hybrid vehicles, particularly trucks. The Army participates in and funds the effort due to their 

tremendous need to reduce fuel use and related supply logistics activities, and to provide 

greater vehicle capabilities to deployed forces.

HTUF activities initially focused on urban work trucks such as refuse, delivery, and utility 

service vehicles. These vocational trucks, together with transit buses, provide the best near-term 

opportunity to demonstrate a business case for hybrids in commercial trucks because of their 

stop-and-go duty cycles and generally high-idling times. These types of duty cycles can make 

the best use of a hybrid architecture for saving fuel. 

The HTUF program has been successful in helping to speed the assessment, deployment, and 

early production of Class 6 and 7 hybrid work trucks. Heavier trucks, including Class 8 line 

haul and heavy regional transport trucks, are also showing potential to benefit from 

hybridization. While hybrid technologies will likely not be the only, or even the main, strategy 

to reduce fuel use in heavy trucks, it is emerging as one of the serious options. The same pooled 

purchase demand and market signals that HTUF has provided for hybrid vehicles can also 

potentially speed the development of other fuel saving approaches. HTUF is increasingly 

focusing on overlapping technology approaches, including electrified and efficient components, 

lighter weight materials, and optimized engines that can lead to both more capable hybrids and 

more efficient conventional trucks.
International Efforts to Increase HDV Fuel Economy

22

5. International Efforts to Increase HDV Fuel Economy

To date there have been limited efforts to mandate increased fuel economy for heavy-duty 

vehicles in most of the world. This section highlights efforts in Japan and the European Union.

5.1 Japan

In November 2005 the Japanese government introduced minimum fuel economy standards for all 

new heavy-duty commercial vehicles with a GVWR greater than 3.5 metric tons (7,700 pounds), 

which will take effect beginning in the 2015 model year. Vehicle manufacturers are required to 

meet a minimum sales-weighted average fleet fuel economy for each of a number of “bins” 

aggregated by vehicle class and weight. Manufacturers must meet the target for each bin and 

there is no flexibility for cross-bin crediting [5-1].

The 2015 fuel economy targets range from 3.57 – 10.83 kilometers per liter7 of fuel (km/L) 

depending on the bin. The targets are based on a “top runner” system in that they generally

represent an improvement over the “best performer” within each bin from the baseline model 

year of 2002. Depending on the bin, the 2015 targets represent a fuel economy improvement of 

2 – 13% compared to the best 2002 model, and 10 – 13% compared to the average for all 2002 

models. There are two bins, urban buses 4,501 – 6,000 kg and 6,001-8,000 kg, for which the 

2015 standard is lower than that achieved by the best performing 2002 model.

For each vehicle the regulated fuel economy is a weighted average of the simulated fuel economy 

achieved on two different test cycles. One test cycle (JE05 Test Cycle) is intended to represent 

urban driving and includes numerous vehicle stops, and a significant amount of engine idling 

time. This test cycle has been used in Japan for emissions testing of heavy-duty vehicles since 

2005. The second test cycle (Interurban Test Cycle) was developed for this regulation, and it 

involves steady-state operation at 80 km/hr and 50% vehicle load, but includes the effect of 

changes in roadway grade. Throughout the test cycle the roadway grade continually changes 

from -5% to +5%; this profile is based on a scaled-down version of the Tomei expressway, the 

busiest highway in Japan.

Depending on the vehicle type the weighting used to determine the average fuel economy varies. 

In general, lighter trucks and buses are assumed to operate almost exclusively in urban areas so 

the JE05 Cycle fuel economy is weighted at 90 – 100%. When calculating the average for the 

purposes of meeting the regulation the Interurban Cycle fuel economy is weighted at up to 35% 

for other types of trucks

To determine the fuel economy of each vehicle on each test cycle the Japanese regulation 

mandates a combination of engine testing and vehicle simulation modeling. 

Each engine to be used in a heavy-duty vehicle is mounted on an engine dynamometer and 

actual fuel use is measured at a minimum of thirty steady-state load points (six engine speed 

points times five torque points). Based on this testing the manufacturer develops a “map” of 

fuel use versus speed and torque for the engine. See Figure 5.1 which shows a typical engine fuel 

use map. 

 

7

 8.4 – 25.4 miles per gallon.
International Efforts to Increase HDV Fuel Economy

23

Figure 5.1 Fuel Use Map for a Diesel Engine 

Source: NTSEL, Japan

Engine speed (rpm)

Torque (Nm)

Engine speed (rpm)

Torque (Nm)

Next, all technical specifications for the 

vehicle (i.e. engine, transmission, rolling 

resistance, aerodynamic drag) are entered into 

a simulation model which determines the shift 

lever positions required to drive the vehicle 

over the JE05 and Interurban test cycles. For 

each test cycle these shift lever positions are 

combined with test cycle speed to determine 

the engine speed and torque at each point in 

the cycle. For each point in the cycle engine 

speed and torque are then used to access the 

engine fuel use map, to determine simulated 

fuel consumption over the test cycle. The 

total fuel consumption is then used to 

calculate vehicle fuel economy (km/L) over 

the test cycle. See Figure 5.2 for a schematic 

of how fuel economy is determined for the 

Japanese regulations. 

This method of determining vehicle fuel 

economy allows a large number of vehicle 

models/configurations to be “tested” in a cost-effective manner, reducing the burden of 

compliance for vehicle manufacturers. This method could also allow a large number of test 

cycles to be simulated with minimal cost 

and effort.

As currently configured this test method 

also has significant limitations. Currently it 

is primarily a test of engine and drive-train 

efficiency, and does not account for 

differences in rolling resistance or 

aerodynamic drag that can significantly 

affect fuel use (see Section 3). While these 

factors are included in the vehicle 

simulation model used to determine 

required engine speed and torque, the 

Japanese regulations currently mandate the 

use of standard values for these parameters 

based on vehicle category, rather than 

vehicle-specific values. Likewise the model 

does not fully account for differences 

between different transmission types, and 

does not allow a hybrid vehicle to take 

“credit” for lower net fuel use based on 

regenerated braking energy and/or idle stop.

Conceptually, many of these limitations could be at least partially alleviated by allowing for the 

use of vehicle-specific parameters in the simulation model, based on additional component or 

vehicle testing. This would add complexity and cost for regulatory compliance, but would 

significantly increase the technical options available to manufacturers to achieve compliance.

Source: ICCT

 Figure 5.1 Schematic of Fuel Economy 

 Determination for Japanese Regulations 

 
International Efforts to Increase HDV Fuel Economy

24
International Efforts to Increase HDV Fuel Economy

25

5.2 European Union

The European Commission commissioned a study investigating the policy options available to 

reduce GHG emissions from the heavy-duty sector in Europe [5-2]. This report will in part 

inform the Commission’s strategy for heavy-duty vehicles in the coming years.

The consultant team led by Faber Maunsell reviewed mandatory and voluntary programs 

proposed and in place in Europe and elsewhere. They conducted a “reality check” with various 

industry stakeholders to assess the potential real-world costs and benefits of these measures as 

well as to identify obstacles to their implementation. The study recommends several programs 

for further consideration by the European Commission including a European Heavy-Duty 

Vehicle Operational Efficiency Programme to promote fleet best practices and a labeling 

program for engine, vehicles, tires, and trailers. The authors encouraged the review of weight 

and size limits of vehicles as well as the use of market-based instruments such as taxation, road 

user charges, and the inclusion of trucks in the Emission Trading Scheme to achieve further 

emission reductions from the heavy-duty sector. 

The recently adopted conventional pollutant emissions standards for heavy-duty vehicles (Euro 

VI) lays the regulatory groundwork for a vehicle CO2 labeling program in Europe. The final text 

of the regulation instructs the Commission to “study the feasibility and the development of a 

definition and methodology of energy consumption and CO2 emissions for whole vehicles and 

not only for engines.” [5-3]. The regulation also requires that once a methodology is established, 

fuel consumption and CO2 emission for each vehicle types be made available to the public. 
Technology Options to Increase HDV Fuel Economy

26

6. Technology Options to Increase HDV Fuel Economy 

There are several ways that fuel use can be reduced from heavy-duty vehicles:

 increase engine thermal efficiency so that more of the energy in the fuel is converted to useful 

work by the engine, and less is dissipated as waste heat in the exhaust and by the cooling 

system,

 recover some thermal energy from the engine exhaust, and put it to use to power the vehicle,

 recover some of the vehicle’s kinetic and potential energy during braking (normally 

dissipated as heat in the braking system) and put it to use to power the vehicle,

 reduce friction losses in the drive train,

 reduce engine accessory loads, or

 reduce the vehicle’s weight, frontal area, aerodynamic drag, and/or rolling resistance so that 

the engine will have to produce less net energy to accelerate and move the vehicle.

There are numerous technologies currently available, or under development, that can be used to 

achieve the above objectives. Some of the most significant are listed below. Obviously, these 

technologies are not completely independent of one another – in some cases diverse technologies 

can be combined in ways which will achieve greater savings than if implemented independently.

6.1 Engine Technologies

Engine efficiency can potentially be increased by making the following types of changes; these 

generally involve only marginal modifications to existing diesel engine designs:

 Reduce internal engine friction

 Improve the handling of intake air

 Refine fuel injection strategies

 Improve turbocharger efficiency and energy recovery

 Improve thermal management/heat transfer within the engine

More radical modifications to traditional diesel engine design that are under development, and 

which might significantly increase engine efficiency and reduce emissions, include:

 Homogeneous Charge Compression Ignition (HCCI) or Pre-mixed Charge Compression 

Ignition (PCCI)8

 Sturman digital engine9

 

8

 An HCCI engine is an Otto-cycle engine in which a pre-mixed fuel-air mixture is compressed in the 

cylinder to achieve auto-ignition. As such it combines aspects of a gasoline engine (homogenous charge 

spark ignition) and a diesel engine (stratified charge compression ignition). The potential benefits include 

diesel-like thermal efficiency combined with better fuel combustion for inherently low particulate emissions. 

A PCCI engine is a variant of the concept in which the pre-mixed fuel-air mixture may be somewhat 

stratified.
Technology Options to Increase HDV Fuel Economy 

27

 Cam-less engine

Other approaches to increasing net engine efficiency involve the use of devices which can extract 

thermal energy from the engine exhaust and put it to use for vehicle propulsion, or to power 

vehicle accessory loads. These approaches include:

 Mechanical turbo-compounding

 Electrical turbo-compounding

 Diesel bottoming cycle10

6.2 Drive-train Technologies

One approach to reducing drive-train losses is to reduce friction in existing drive train 

components by using improved low-viscosity lubricants.

Net vehicle efficiency can also be increased by optimizing gear ratios throughout a vehicle’s 

drive cycle and/or by reducing the losses from traditional automatic transmissions. Potential 

approaches include:

 Use of a continuously variable transmission (CVT), or 

 Use of an automated manual transmission (AMT) in lieu of a traditional automatic 

transmission11

For some vehicles and some duty cycles significant reductions in net fuel use can be achieved by 

using an electric-hybrid or hydraulic-hybrid drive train. In an electric hybrid system the diesel 

engine is supplemented by one or electric motor/generators and a battery pack; in a hydraulic 

hybrid system the diesel engine is supplemented by a hydraulic motor/pump and a hydraulic 

accumulator. 

In either case the main benefit of the hybrid system for most vehicles is that during braking the 

vehicle’s kinetic energy can be recovered and stored (as electrical energy in the battery pack or 

as high-pressure mechanical energy in the hydraulic accumulator). During subsequent 

accelerations this stored energy can be used by the electrical or hydraulic motor to help 

accelerate the vehicle, reducing net energy required from the diesel engine. In some instances 

additional efficiency gains can be achieved by down-sizing the vehicle’s diesel engine. 

Some vocational vehicles, for example utility trucks, can also use the stored energy to power 

vocational loads, thus reducing net engine idling. The ability to reduce engine idling using a 

hybrid system may also be important for some heavy-duty line haul and drayage trucks. These 

types of vehicles typically idle for long periods, both over night (line haul) and during 

warehousing operations (drayage), using the large main engine to power very modest “hotel” 

loads on the vehicle. By providing a different power source (battery pack) for these hotel loads 

a hybrid system can significantly reduce or eliminate engine idling. 

 

9

 A cam-less engine concept incorporating digital valves to achieve better fuel injection control and 

hydraulic valve actuation.

10 A Rankine cycle system that uses waste heat from the engine to produce super-heated vapor, which 

then drives a turbine to produce electricity. The resulting electricity can be used to support engine/vehicle 

accessory loads or propulsion. 

11 CVT and AMT are best suited for vocational trucks and buses that are typically used in stop and go 

applications
Technology Options to Increase HDV Fuel Economy 

28

In general, the benefits of a hybrid drive train will be greater for vehicles with a slow-speed, 

stop-and-go duty cycle. These typically include transit and school buses, urban pick-up and 

delivery vehicles, and some vocational trucks. The potential drive cycle benefits of a hybrid 

system are lower for combination trucks that operate primarily in a line haul application, but 

even these trucks may benefit from the ability of a hybrid system to reduce or eliminate engine 

idling. 

6.3 Vehicle Technologies 

Vehicle technologies that can be used to reduce fuel use include those that reduce vehicle weight, 

rolling resistance, aerodynamic drag, or vehicle accessory loads.

Approaches to reduce vehicle weight include:

 Use of alternative materials (i.e. aluminum, composites, light weight steel)

 Use of super-single wheels

Approaches to reduce a vehicle’s rolling resistance include:

 Use of low rolling resistance tires (new and aftermarket)

 Use of super-single wheels and tires 

 Use of automatic tire inflation systems

Approaches to reduce vehicle accessory loads include:

 Improved cab thermal insulation

 Electric accessories (air compressor, cooling fan, fuel pump, air conditioning)

With respect to reducing aerodynamic drag, significant improvements are available from 

changes to single-unit trucks and combination truck tractors, as well as from changes to 

combination truck trailers. 

Truck modifications to reduce aerodynamic drag include:

 Low-profile cab

 Integrated cab-high roof fairing

 Fuel tank side fairings

 Aerodynamic bumper and mirrors

 Tractor-mounted gap reducers (combination trucks)

Trailer modifications to reduce aerodynamic drag include:

 Low profile or “low-boy” trailers

 Side skirts

 Trailer-mounted gap reducers

 Trailer rear-end fairings or boat tail
Design of HDV Fuel Economy Regulations 

29

7. Design of HDV Fuel Economy Regulations 

There are a significant number of technical issues that must be addressed when designing fuel 

economy regulations for heavy-duty vehicles. These range from the metric used to measure fuel 

economy, to the format of required improvements, to the test method used to verify 

performance. In addition, there are a number of policy-related issues that can significantly 

affect the implementation cost and the effectiveness of the regulations. These issues include: 

which specific vehicle types will be regulated, which companies will be responsible for 

compliance, the implementation time line, provisions for compliance flexibility, and methods of 

enforcement. Each of these issues is discussed below.

For each subject area there are a number of options available to policy makers. Different 

approaches will have different potential benefits, costs, and implementation issues. The 

optimal regulatory design will balance these different implementation issues to achieve costeffective improvements.

7.1 Regulated Entity or Entities

Current fuel efficiency and emission standards for cars and light trucks are imposed on the car 

manufacturer. This is logical since for virtually all cars and light trucks both the engine and the 

rest of the vehicle are designed, manufactured, and sold by a single company. The heavy duty 

vehicle market is more complicated, since for any particular HDV the engine, chassis, and body 

might each be designed and manufactured by different companies. For Class 8 combination 

trucks it is even more complicated since a truck designed and manufactured by one company is 

paired with a trailer designed and manufactured by a different company. Furthermore, tractors 

are routinely paired with different trailers.

For an HDV the engine, chassis, body, and trailer (combination trucks) all influence fuel use. As 

such, for any particular HDV responsibility for design and operating decisions that affect fuel 

efficiency are shared by as many as five different entities: the engine manufacture, the chassis 

manufacturer, the body manufacturer, the trailer manufacturer, and the fleet owner (see Figure 

7.1 for an illustration of this shared design responsibility). 
Design of HDV Fuel Economy Regulations 

30

Source: M.J. Bradley& Associates

Figure 7.1 Shared Responsibility for Major Elements that Effect HDV Fuel Efficiency 

To be fully effective fuel efficiency regulations must apply to the entiti(es) that have control over 

the major decisions that affect fuel efficiency – which as noted in some cases may be five 

different entities for a particular HDV.

Current emissions regulations for heavy-duty diesel engines apply to the engine manufacturer 

only. HDV vehicle manufacturers have no responsibility for meeting emission standards. Since 

the engine is the only component that actually consumes fuel, one possibility would be to apply 

HDV fuel efficiency standards to the engine manufacturer as well, particularly since the same 

engines are used in multiple vehicles from different vehicle manufacturers. To do so might 

forego significant opportunities for improvements in vehicle efficiency based on different drive 

train technologies and improved vehicle aerodynamics. 

Since the drive train and cab/body shape have such a significant effect on over-all fuel use, 

another approach would be to apply HDV fuel efficiency standards to the vehicle manufacturer, 

not the engine manufacturer. While there is a trend toward greater vertical integration and 

preferred partnering in the truck industry, it is still true that for many single-unit trucks the 

chassis (including operator cab) is produced by one manufacturer and is sold to a second 

manufacturer, which adds a body and sells it to the fleet customers. In this case responsibility 

for design decisions that affect fuel efficiency are shared by two different vehicle manufacturers, 

though the major responsibility generally falls to the chassis manufacturer. The chassis 

manufacturer typically controls engine and drive train choice, major vehicle accessory loads, tire 

configuration, and cab aerodynamics. The body manufacturer generally controls body 

aerodynamics and vocational loads. In addition, essentially the same chassis design is often 

used for multiple vehicle models produced by different body manufacturers. 

As such it might be more efficient to apply fuel efficiency standards primarily to the chassis 

manufacturer. This would cover most of the major design decisions that would affect fuel use, 

while minimizing compliance costs. This could be done by requiring chassis to be tested for 

compliance with a “reference body” of a standard size and shape installed (likely a worst-case 

box shape). 
Design of HDV Fuel Economy Regulations 

31

For some vehicle types it might also be advisable to apply a second, more stringent standard to 

the final vehicle with the actual body installed. This would likely only be worthwhile for 

vehicles that operate primarily at highway speeds in a line haul cycle, where the aerodynamics 

of the actual installed body could significantly affect actual fuel use. Given that the installed 

body would primarily affect vehicle aerodynamics, compliance testing of the final vehicle might 

be able to be effectively conducted using wind tunnel tests and vehicle simulation modeling, 

rather than requiring additional chassis dynamometer or test track testing (see Section 7.4.1).

To be fully effective, fuel efficiency regulations for Class 8 combination trucks must cover both 

the truck tractor and the trailer. One standard could apply to the truck manufacturer, with 

compliance testing conducted using a “reference trailer”. A separate, more stringent, standard 

could apply to the trailer manufacturer. There are three options for trailer compliance testing: 1) 

in-use, test track, or dynamometer (coast down) testing conducted using the trailer matched 

with a compliant “reference truck” (see section 7.4.4) 2) wind tunnel (aerodynamic drag) and 

rolling resistance tests of the trailer, in conjunction with vehicle simulation modeling to calculate 

an expected combination fuel efficiency if the trailer were paired with a compliant truck, or 3) 

setting maximum values for trailer rolling resistance and aerodynamic drag, to be confirmed 

using wind tunnel and other tests, but without converting this data into an expected “fuel 

efficiency rating”. See Section 7.4.1.

Another approach would be to regulate fleet owners, rather than HDV vehicle and trailer 

manufacturers, since they can make decisions to purchase or not purchase fuel efficient 

equipment, and they may be in a position to ensure that combination trucks and tractors are 

paired in a way that minimizes fuel use. This approach was chosen by the California Air 

Resources Board, which has mandated aerodynamic and rolling resistance-related retrofits for 

part of the HDV fleet operating in the state (see Section 4.3). 

Such an approach would rely more heavily on market forces to effect change in the HDV fleet, 

but would almost certainly still require a mandatory fuel efficiency testing requirement for truck 

and trailer manufacturers. Mandatory testing using a consistent test protocol would be required 

to provide fleet owners with the necessary information to make smart purchasing decisions. 

Confirmation of fleet compliance with a fuel efficiency standard could be based on either 1) a 

weighted average fuel efficiency rating for their fleet based on manufacturer test data, or 2) 

actual in-use fuel and mileage records for the fleet. In either case there would be a significant 

reporting burden for fleet owners, with a parallel burden on government to review and analyze 

the fleet-supplied data. 

See Table 7.1 for a comparison of the different entities that HDV fuel efficiency regulations 

might apply to. 
Design of HDV Fuel Economy Regulations 

32

Table 7.1 Comparison of HDV Fuel Efficiency Regulated Entities 

Regulated 

Entity Pros Cons

Engine 

Manufacturer

 In line with current responsibility 

for compliance with exhaust 

emission standards

 One set of engine test(s) required for 

numerous vehicle models 

 Would not encompass significant 

vehicle parameters that affect fuel 

efficiency: drive train, rolling 

resistance, aerodynamics, vehicle 

accessories

Truck/Chassis 

Manufacturer

 Would encompass virtually all 

vehicle parameters that affect 

fuel use for most single-unit HDVs

 Engine manufacturers would 

contribute to improvements 

through commercial relationships 

with Truck/Chassis Manufacturers

 Would not cover trailer aerodynamics 

for combination truck trailers

 Would not cover body aerodynamics 

and vocational loads for some singleunit HDVs

 Would likely require testing of single 

unit HDVs with “reference body” 

installed

Truck/Body 

Manufacturer

(if different than 

chassis manuf)

 Would encompass all vehicle 

parameters that affect fuel use for 

single-unit HDVs

 Testing of multiple vocational 

configurations on the same chassis 

might be accomplished using a 

simulation model rather than 

additional track or dynamometer 

tests

 Increased compliance costs as 

virtually identical chassis must be 

tested in multiple vocational 

configurations

Trailer 

Manufacturer

(Combination 

Trucks)

 Would include in the regulations 

equipment that has significant 

impact on fuel efficiency of 

combination trucks, especially at 

h ighway speeds

 To minimize compliance costs 

trailer testing might be 

accomplished using wind tunnel 

and rolling resistance tests 

combined with simulation 

modeling

 No precedent for fuel efficiency or 

emissions regulation of non-powered 

equipment 

 More complicated since trailers would 

likely need to be tested with a 

“reference truck”

Fleet Owner

 Relies on market forces to meet 

compliance goals

 Potentially allows a greater range 

of operational changes to achieve 

compliance 

 Significant reporting/review burden 

on fleets and government to judge 

compliance

 Would still require mandatory fuel 

efficiency testing of HDVs to provide 

fleet owners with information 

required to make smart compliance 

decisions

7.2 Regulated Vehicles 

As discussed in Section 2, the U.S. HDV fleet is extremely diverse, with a wide range of vehicle 

sizes and configurations. As such, a fuel efficiency standard that applied to all HDVs would 
Design of HDV Fuel Economy Regulations 

33

of necessity be complex, with a wide range of test cycles and numerical standards required (see 

Sections 7.3 and 7.4).

In order to reduce regulatory complexity one could more narrowly apply fuel efficiency 

requirements to some sub-set of all HDVs, or could phase-in regulation to different types of 

HDVs over time. For prioritization the most logical way to parse the HDV fleet is by weight 

class and/or vehicle type.

As discussed in Section 2, Class 8 trucks comprise only 40% of the HDV fleet, but they 

consume 75% of the fuel used by HDVs. As such it might be logical to focus fuel efficiency 

regulations on these large vehicles first, in order to maximize fuel savings resulting from the 

regulations. The Class 8 HDV fleet itself is quite diverse, encompassing single-unit freight 

hauling trucks, buses, vocational trucks, and combination trucks. Of these sub-fleets, a typical 

Class 8 combination truck uses on average eight times as much fuel annually as the various 

types of Class 8 single-unit trucks and buses. While comprising about 25% of the heavy-duty 

fleet, combination trucks use 65% or more of the fuel consumed by all U.S. HDVs. Class 8 

combination trucks are therefore logical place to focus initial HDV fuel efficiency regulation in 

order to maximize initial benefits.

Class 8 combination trucks present a particular challenge for fuel efficiency regulation since they 

are composed of a powered truck tractor pulling an unpowered trailer, but both truck and 

trailer can significantly affect fuel use, particularly at highway speeds. Since the truck and 

trailer are typically not manufactured, sold, or used as sets, to be fully effective any fuel 

efficiency regulation for Class 8 combination trucks must regulate both the truck and the trailer 

separately.

See Section 7.4.4 for a discussion of how Class 8 combination truck tractors and trailers could 

be separately tested to measure compliance with a fuel efficiency standard. 

Another approach to prioritizing fuel efficiency regulation would be to focus not on total or 

initial benefits (fuel, CO2 savings), but rather on some other factor such as ease of 

implementation or cost-effectiveness. If this approach is taken it is possible that trucks smaller 

than Class 8 would be a better target for initial regulatory efforts.

7.3 Fuel Economy/Efficiency/GHG Metric 

For most heavy-duty onroad vehicles their main purpose is to move goods or people over a 

distance12. For the purpose of fuel economy regulation it is therefore appropriate to measure 

fuel or energy use relative to accumulated mileage – i.e. miles driven per gallon of fuel used 

(MPG), or inversely, gallons used per mile driven. 

The use of a volume measurement for fuel (gallons), however, can be mis-leading when 

comparing results from trucks operated on different fuels - not all grades of diesel fuel have the 

same energy content per gallon and some heavy-duty vehicles are gasoline fueled. This metric is 

also not appropriate when using gaseous fuels (i.e. natural gas), without making a conversion to 

“equivalent gallons” based on energy content. To overcome this limitation a regulatory program 

could require the use of a “reference fuel” with constant energy density for all testing, or 

compliance could be evaluated by adjusting measured results to what they would have been 

using a reference fuel, based on the measured difference in energy density of the actual fuel used 

versus the reference fuel. 

 

12 The exception is some vocational vehicles, for which fuel use per unit time might be a more appropriate 

metric.
Design of HDV Fuel Economy Regulations 

34

A more universal metric would be based not on the volume of fuel used per mile driven, but 

rather the energy content of the fuel used per mile driven – i.e. British thermal units (btu) per 

mile, or kilowatt-hours (Kwh) per mile. Such a metric would allow direct comparison of test 

results using different fuels, without requiring an adjustment based on measured energy density. 

An energy per mile metric will suffice if the main purpose of the regulation is to promote 

efficiency and reduce the need to import transportation fuels. However, if the purpose of the 

regulation is to reduce the amount of greenhouse gases released to the atmosphere from 

transportation sources, then a different metric might be preferred. 

The main green house gas (GHG) produced by heavy-duty vehicles is carbon dioxide (CO2). An 

appropriate metric to capture the effect of heavy-duty vehicles on global warming would 

therefore be grams CO2 emitted per mile driven. This metric relates to fuel economy by virtue of 

the fact that reducing the amount of diesel fuel used per mile will reduce the amount of CO2

released per mile. However, this metric can also capture CO2 reductions based on switching to 

lower carbon fuels assuming there is a single point of regulation, and as such is a better metric if 

GHG reductions are the primary goal of regulation. 

Another GHG-related metric that could be used is grams CO2-equivalent13 (gCO2-E) per mile 

driven. CO2-E captures the effects of all GHGs emitted by a vehicle, not just CO2. Black carbon, 

a sub-set of particulate matter, is another diesel truck emission with significant climate impact 

in the near term. SCR controlled engines may emit excess N2O if the ammonia (NH3) slip 

catalyst is not appropriately formulated. Lean-burn natural gas engines may also emit a 

significant amount of methane (CH4) unless equipped with an appropriate oxidation catalyst.

As discussed in Section 2, heavy-duty vehicles come in a wide range of sizes – with GVWR 

from 10,000 to over 80,000 pounds. In general the heavier a vehicle is the more fuel it will burn 

for every mile it drives – but the more cargo it will/can carry. Regardless of whether one uses 

fuel volume, fuel energy content, CO2 emissions, or CO2-E emissions as the basis of a fuel 

economy metric, if referenced to miles driven there will need to be a different regulatory 

standard for different sized vehicles (i.e. it would make no sense to mandate that a 10,000 

pound truck and an 80,000 pound truck both must achieve at least 10 miles/gallon – the 

smaller truck could easily achieve this target while it might be impossible for the larger one).

Specifically for heavy-duty vehicles it might therefore be appropriate to use a fuel economy 

metric based not on miles driven, but rather ton-miles. A ton-mile is defined as miles driven 

times vehicle pay-load weight expressed in tons (2000 lbs/ton). For example, a truck with a 

10,000 lb pay-load driven one mile would equal 5 ton-miles, while a truck with a 40,000 lb payload driven one mile would equal 20 ton-miles).

The use of a ton-mile based fuel-economy metric for heavy-duty vehicles would simplify fuel 

economy regulations because a single numerical standard could be applied to a wider range of 

vehicle sizes. This type of metric would also explicitly acknowledge the main purpose of most 

heavy-duty vehicles, which is to move freight. When regulating the efficiency of the freight 

system it is appropriate to mandate the maximum amount of energy (or resulting CO2 or CO2-E 

emissions) allowed per ton-mile of freight moved. 

Another approach that might be appropriate for freight vehicles would be to reference a fuel 

efficiency standard to cubic-volume miles rather than ton-miles, in recognition of the fact that 

some freight fills up the available cargo space (“cubes-out”) in an HDV before the vehicle 

reaches its maximum GVWR (“weighs-out”). A cubic volume-mile is defined as miles driven 

times vehicle cargo capacity, in cubic feet or cubic yards (i.e. a truck with a cargo box 8 ft x 8 ft 

 

13 For any GHG, CO2-E is calculated by multiplying the mass (grams) of the GHG by its global warming 

potential (GWP), as defined by the Intergovernmental Panel on Climate Change.
Design of HDV Fuel Economy Regulations 

35

x 20 ft would have 1,280 ft3 [47.4 yd3] of cargo capacity; if this truck were driven one mile it 

would equal 1,280 ft3-miles [47.4 yd3-miles]).

An analysis of operating weight data from the U.S. Census Bureau’s 1992 Truck Inventory and 

Use Survey (TIUS) indicates that as many as 70 percent of vehicle miles traveled by five-axle 

combination trucks are accumulated at operating weights significantly below this type of 

vehicle’s typical gross vehicle weight rating of 80,000 pounds [7-1]. Some of those miles are 

traveled with the trailer empty (below about 35,000 pounds operating weight) or with only a 

part load. However, a significant portion of them – perhaps the majority of all miles traveled –

are accumulated with the trailer “cubed-out” as shown in Figure 7.2. A cubic volume-mile fuel 

economy metric might provide trailer manufacturers with an incentive to increase trailer volumes 

(for example by using smaller tires to lower the trailer’s floor height while keeping the roof height 

the same). This could significantly increase the efficiency of the over-all freight system by 

allowing more freight to be loaded before cubing-out the trailer. A mile per gallon or ton-mile 

per gallon metric would not provide any incentive for increasing trailer volumes. 

0.0%

5.0%

10.0%

15.0%

20.0%

25.0%

10 20 30 40 50 60 70 80 90 100 110 120 130

Operating Weight (x000 lbs)

% of Total Estimated VMT

EMPTY

9%

Cubed-Out

61%

Weighed-Out

30%

Source: U.S. DOT, FWHA

Figure 7.2 VMT of Five-Axle Combination Trucks, by Operating Weight Range (1992 TIUS) 

See Table 7.2 for a comparison of fuel efficiency/GHG metrics, and Figure 7.3 for an illustration 

of the difference between an MPG, ton-mile, and cubic volume-mile metric as applied to vehicles 

of various sizes.
Design of HDV Fuel Economy Regulations 

36

Source: M.J. Bradley & Associates

Figure 7.3 Illustration of Different Fuel Efficiency Metrics as Applied to Cargo Vehicles of Different 

 Sizes 
Design of HDV Fuel Economy Regulations 

37

Table 7.2 Comparison of Fuel Efficiency / GHG Metrics 

Basis Metric Pros Cons

miles/gallon

 Understandable to most people 

due to common usage

 Can not capture differences in 

fuel energy or carbon content

 Different vehicle sizes need 

different numerical standards

gal/mile

 A reduction in the value of the 

metric is equivalent to reduced 

fuel use 

 Same as miles/gallon

Fuel 

Volume

gal/ton-mile

or

gal/cube-mile

 Directly related to the purpose 

of most HDVs

 Same numerical standard can be 

used for different sized HDVs

 Can not capture differences in 

fuel energy or carbon content 

BTU/mile

 Efficiency of vehicles operated 

on different fuels can be 

directly compared

 Can not capture differences in 

fuel carbon content

 Different vehicle sizes need 

different numerical standards Fuel 

Energy 

Content BTU/ton-mile

or

BTU/cube-mile

 Same as BTU/mile, plus

 Directly related to the purpose 

of most HDVs

 Same numerical standard can be 

used for different sized HDVs

 Can not capture differences in 

fuel carbon content

gCO2/mile

 Captures differences in vehicle 

fuel use as well as energy or 

carbon content of fuel

 Measures vehicle impact on 

global warming

 Unfamiliar as an “efficiency” 

or “fuel economy” metric

CO2

Emissions 

gCO2/ton-mile

or

gCO2/cubemile

 Same as gCO2/mile, plus

 Directly related to the purpose 

of most HDVs

 Same numerical standard can be 

used for different sized 

vehicles

 Unfamiliar as an “efficiency” 

or “fuel economy” metric

gCO2-E/mile

 Captures effect of non-CO2 

GHGs

 Additional emissions must be 

measured during testing

GHG 

Emissions gCO2-E/tonmile

or

gCO2-E/cubemile

 Same as gCO2-E/mile, plus

 Directly related to the purpose 

of most HDVs

 Same numerical standard can be 

used for different sized 

vehicles

 Additional emissions 

components must be measured 

during testing

7.4 Test Procedures Used for Verification

As discussed in Section 3, there are numerous factors that can affect fuel use for HDVs, 

including engine and vehicle design, but also driver behavior, vehicle condition (i.e. tire pressure) 

and duty cycle (speed, number of stops, etc). Any numerical standard for HDV fuel economy or 

fuel efficiency must therefore be supported by a specific and detailed test procedure to ensure 
Design of HDV Fuel Economy Regulations 

38

that test results are repeatable, are comparable from vehicle to vehicle, and result in a 

reasonable approximation of what most vehicle owners will experience in-use.

U.S. EPA has developed a detailed test procedure for evaluating the fuel efficiency of cars and 

light trucks [7-2]. This method is used to test every new car model sold in the U.S., and the 

results must be published by the manufacturer. This procedure uses a chassis dynamometer 

and five different drive cycles to produce three fuel economy ratings (miles per gallon – MPG): 

one for slow-speed city driving, one for high-speed highway driving, and a “combined” rating 

intended to represent a typical average duty cycle. The same test data is also used to evaluate 

compliance with EPA exhaust emission standards for these vehicles. 

U.S. EPA does not currently have a similar detailed test procedure for evaluating the fuel 

efficiency of HDVs, though there are a number of industry-developed test protocols that might 

serve as the basis of such a procedure (see below). As noted in Section 4.1 EPA is currently 

developing a draft fuel efficiency test protocol for medium and heavy-duty trucks to be used for 

SmartWay certification testing, which is based on prior industry-developed protocols. 

Fuel economy testing of HDVs is significantly more complicated than fuel economy testing of 

cars for a number of reasons:

 The much larger size of most HDVs requires much larger equipment and facilities, which 

are expensive and currently in limited supply

 The HDV fleet is much more varied (size, configuration, vocational equipment), and

 There is a much wider range of “typical” duty cycles applicable to specific HDV vehicle 

types, but not others.

In addition, EPA emission standards for HDVs apply to the engine, not the vehicle. Emissions 

certification testing for heavy-duty diesel engines is done using an engine dynamometer, and 

does not evaluate the effect on emissions and fuel efficiency of other vehicle components and 

parameters (i.e. drive train, accessory loads, vehicle weight, vehicle aerodynamics, etc.).

The major issues related to development of a test procedure to evaluate HDV fuel efficiency are 

discussed below.

7.4.1 Test Equipment/Test Method

Evaluating fuel use involves measuring the amount of fuel that a vehicle consumes while it 

operates over a specific, repeatable, test cycle intended to represent “typical” vehicle 

behavior in-use. Fuel use can be measured directly (by using a portable fuel tank that is 

weighed before and after the test run) or indirectly (by measuring cumulative carbon 

emissions from the tail pipe throughout the test and imputing fuel use based on fuel carbon 

content). 

There are well-developed procedures available for gravimetric fuel measurement (SAE 

J1321) and tail-pipe emissions measurement (40 CFR Part 86, 40 CFR Part 1065) –

determining the amount of fuel used on a particular test run is not difficult. What is more 

difficult is ensuring that each test run is conducted over the same test cycle. 

There are three basic test methods that can theoretically be used to test a vehicle:

 In-use Test: operate the vehicle on public roads over its normal route. This method is 

often used by vehicle manufacturers and truck fleets to conduct comparison tests 

between two different trucks. In a comparison test the two trucks would follow each 

other on the route and the drivers would be in constant contact. At the half way point 

the drivers would change vehicles, and for combination trucks the trailers would also be 

switched. In these tests each truck typically logs 400 miles or more for each test run. 
Design of HDV Fuel Economy Regulations 

39

The use of paired trucks allows better control of independent variables that can affect 

fuel use, and the results are typically reported as a % difference in fuel use for one truck 

compared to the other, as opposed to an absolute value for fuel use. The Society of 

Automotive Engineers and the Truck Maintenance Council have developed detailed test 

procedures for conducting these types of tests (SAE 1264, SAE 1321, SAE 1526, RP 

1109) [7-3]

 Test-track: operate the vehicle over a closed test course (typically a one mile or longer 

circular or oval track with banked corners). For each test the driver is instructed how to 

operate the vehicle for the target test cycle (i.e. acceleration rate from each stop and 

target speed between specific points on the track, braking rates and stopping points, idle 

time at each stop). The TMC and SAE test procedures for in-service and dynamometer 

tests can serve as the basis for a test track test protocol.

 Chassis Dynamometer: mount the vehicle on a dynamometer with the drive wheels 

resting on one or more large cylindrical rolls. During testing the vehicle is stationary, but 

the drive wheels spin the rolls to simulate driving at different speeds. The dynamometer 

can impart to the drive wheels a varying load to represent varying vehicle inertial load, 

rolling resistance, and aerodynamic drag throughout the drive cycle. The vehicle driver is 

instructed to follow a specific profile of speed versus time, and is usually given a 

computerized drivers aid which shows actual speed versus target speed in real time. The 

Society of Automotive Engineers has developed a recommended practice for conducting 

emissions and fuel economy tests of heavy-duty vehicles on chassis dynamometers (SAE 

J2711) and EPA has detailed procedures for conducting emissions testing (40 CFR Part 

86, 40 CFR part 1065) [7-4].

Each of these methods has pros and cons. In-use testing requires no specialized equipment 

or facilities, but it is difficult to get good test cycle repeatability from run-to-run or truckto-truck. In addition, for a regulatory program each tested truck would need to be tested 

over the same section of road, or different test routes would have to be carefully compared 

to ensure sufficient similarity of road profile, road surface, traffic conditions, etc. Because 

this method is best suited for comparing one truck to another it might also require the use of

a “reference truck”, with results reported as a percentage difference from the reference, 

rather than as an absolute number.

Testing on a test track is more repeatable than in-use testing, but the complexity of the test 

cycles are limited by what it is practical for a driver to follow. A heads-up display drivers 

aid might increase the complexity of practical test cycles, but might introduce concerns 

about driver distraction and safety. Test tracks are perhaps best suited to testing on highspeed highway test cycles with relatively few stops, and limited speed changes. They are 

less suited to more dynamic urban test cycles with frequent speed changes and a greater 

number of stops per mile.

Test tracks are also affected by ambient weather conditions such as temperature, humidity, 

precipitation, and wind, which could severely limit in the possibility of testing under 

standardized conditions in some locations. Test tracks are also generally constructed to be 

flat, and can not incorporate changes in grade as part of the test cycle. There are currently 

a limited number of test tracks that would be suitable for testing HDVs, and development 

of additional facilities would be expensive.

Chassis dynamometer testing is the most repeatable of the test methods, and is generally 

minimally affected by ambient weather conditions. Relatively few heavy-duty chassis 

dynamometers exist today, and developing new ones would be expensive, but not as 

expensive as development of new test tracks. 
Design of HDV Fuel Economy Regulations 

40

With respect to HDVs, the most significant limitation of chassis dynamometer testing is its 

method of simulating vehicle aerodynamic loads. Since the vehicle is stationary during the 

test the aerodynamic load is not imposed on the vehicle surface as it is in-use. Instead, a 

simulated aerodynamic load is imposed on the vehicle through the tires, by adjusting the 

load on the dynamometer rolls. In effect, the dynamometer uses inertial and electrically 

generated loads applied through the vehicle’s tires to simulate aerodynamic load.

The required load is determined by conducting an on-road coast-down test prior to the 

dynamometer testing. In a coast-down test the vehicle is accelerated to some speed and 

then allowed to coast to a stop without applying the brakes, while vehicle speed versus

time is recorded. By calculating the varying deceleration rate of the vehicle over time, one 

can impute the forces (rolling resistance and aerodynamic drag) that were operating on it at 

each speed. 

This information is programmed into the dynamometer – so that it will impose the 

appropriate load on the vehicle at each point in the test cycle. The vehicle is then mounted 

on the dynamometer and a dynamometer coast down test is conducted to ensure that the 

coast-down profile is the same on the dyno as it was on the road.

While this method of evaluating and simulating rolling resistance and aerodynamic drag on 

a dynamometer is theoretically sound, it is critical that the coast-down test be conducted 

correctly. The largest constraint on coast-down testing is usually finding an appropriate 

location to conduct the test (straight, level, with sufficient length). 

In addition to the above vehicle test methods, engine dynamometer testing in conjunction 

with vehicle simulation modeling could also be used for regulatory certification of HDV fuel 

efficiency. This is the approach taken in Japan (see section 5.1 for a detailed description of 

this methodology). Such an approach would be the least costly method of conducting fuel 

efficiency tests of new HDVs since one laboratory engine test could be used to model 

multiple vehicles. To a certain extent the required engine tests are already conducted in the 

context of emissions certification, and the additional testing requirements would be 

minimal. The use of a simulation model would also allow manufacturers to cost-effectively 

estimate fuel efficiency for each vehicle on a large number of different test cycles using data 

from a single engine test. 

The “accuracy” of resulting fuel efficiency ratings from such a method would be limited by 

the “accuracy” of the vehicle simulation model used. To achieve a high degree of accuracy 

the simulation model would need to be highly detailed and sophisticated, and appropriate 

vehicle-specific factors would need to be developed for all parameters that might affect 

vehicle fuel use, including rolling resistance, aerodynamic drag, drive train losses, accessory 

and vocational loads, and engine idling (see Section 3).

One existing simulation model that could be evaluated for use in a regulatory program for 

HDV fuel efficiency is the Powertrain System Analysis Toolkit (PSAT) model developed by 

Argonne National Laboratory. PSAT is a "forward-looking" model that simulates fuel 

economy and performance in a realistic manner — taking into account transient behavior 

and control system characteristics. This model is used by vehicle manufacturers during 

design development, and was chosen by DOE as the primary vehicle simulation tool to 

support 21st Century Truck Partnership activities [7-5].

To develop accurate vehicle-specific factors for simulation modeling additional laboratory 

testing of vehicles or vehicle components would likely be required. For example, windtunnel testing could be conducted to determine the aerodynamic drag created by different 

vehicle configurations.

Vehicle simulation modeling could also be used in conjunction with in-use, test-track, or 

chassis dynamometer testing to minimize the testing burden on HDV vehicle manufacturers. 
Design of HDV Fuel Economy Regulations 

41

Under such a scenario a full-vehicle test would have to be conducted on a “base model” of 

a particular truck, while a simulation model would be used to develop a fuel efficiency 

rating for vehicles with “minor” changes to the base configuration – for example a different 

transmission or rear-end gear ratio, or a different style of body attached to the same vehicle 

chassis. 

See Table 7.3 for a comparison of the different test methods. 

 
Design of HDV Fuel Economy Regulations 

42

 Table 7.3 Comparison of HDV Fuel Efficiency Test Methods 

Method Equipment Pros Cons

In-Use Test

400 – 600 mile 

test course(s) on 

public roads

 Easy to conduct

 Relatively in-expensive

 Well-developed 

procedure in place

 Familiar to HDV fleets

 High test-to-test variation

 Best for comparing one truck 

to another

 May require the use of a 

“reference truck” 

Test Track 

Test

Closed, 1-5 

mile oval or 

circular test 

track

 Easy to conduct

 Good repeatability

 Facilities are limited and 

expensive

 Complexity of test cycles 

limited 

 Best for high-speed steadystate test cycles

 Can not incorporate changes 

in grade to test cycle

 Affected by ambient 

conditions

Chassis 

Dynamometer

Test

Heavy-duty 

chassis 

dynamometer

Coast-down 

test track

 Well-developed 

procedure in place

 Computerized drivers 

aids ensure very good 

compliance with 

transient test cycles

 Very good repeatability

 Facilities are limited and 

expensive

 Accuracy depends on accurate 

coast-down test

Engine Test 

plus Vehicle 

Simulation 

Modeling

Engine 

dynamometer

Vehicle 

simulation 

model

 Well-developed test 

procedure in place

 Minimal additional 

testing burden

 Lowest total cost to 

vehicle manufacturer of 

available options

 Ability to run large 

number of test cycles off 

single engine test.

 Accuracy depends on 

complexity of simulation 

model and “accuracy” of 

model inputs

 Development of vehiclespecific modeling 

parameters likely to require 

additional 

vehicle/component testing 

(i.e. wind tunnel tests of 

aerodynamic drag) 

Simulation 

Modeling for 

Changes to 

Base Model

Vehicle 

simulation 

model

 Can minimize over-all 

testing burden to 

manufacturers

 Accuracy depends on 

complexity of simulation 

model and “accuracy” of 

model inputs

 Requires careful definition of 

“major” change that triggers 

need for additional base 

vehicle testing

7.4.2 Test Cycle(s)

Regardless of the test method used, HDV fuel efficiency testing will require development 

and use of appropriate test cycles. For any HDV an “appropriate” test cycle must 
Design of HDV Fuel Economy Regulations 

43

accurately model the “typical” in-use duty cycle seen by the vehicle. Relevant aspects of a 

vehicle’s duty cycle that can significantly affect fuel use include acceleration rates, vehicle 

speed, number and severity of engine transients (changes in speed), changes in roadway 

grade, number of stops per mile, percent engine idling time, and vocational loads.

Different HDVs have significantly different duty cycles – for example a transit bus is used 

very differently than a refuse truck or a Class 8 combination truck. Any one type of HDV 

may not have a single “typical” duty cycle either. For example, Class 8 combination trucks 

often operate for long periods at sustained high speeds on interstate highways (line haul 

cycle), but they can also operate in slow speed stop-and-go urban traffic (urban cycle). 

Even line haul vehicles may have significantly different fuel use when operating on generally 

flat terrain as opposed to hilly or rolling terrain. 

One approach to HDV fuel economy testing would be to use the same test cycle(s) to test 

all HDVs, regardless of type. This would be similar to current EPA fuel economy and 

emissions testing of light duty vehicles, which uses five different test cycles to determine 

City, Highway, and Combined fuel economy ratings for every vehicle model (see Section 

7.5). While such a test protocol is appropriate for light duty vehicles, and would be 

relatively simple to implement, it would be unlikely to produce satisfactory results for 

HDVs for two reasons. 

First, there is no way that even five test cycles could be representative of “real world” 

operating behavior for all HDVs. Testing on an unrepresentative test cycle for a particular 

type of HDV might lead vehicle manufacturers to make changes that would allow them to 

meet the regulatory efficiency standard, but which would have little actual benefit in-use. 

For example, if all testing was done on a slow-speed urban test cycle manufacturers would 

have little incentive to improve vehicle aerodynamics , but would have a large incentive to 

incorporate a hybrid drive train. If the resulting vehicle were then operated exclusively at 

high sustained speeds the expected benefits from the hybrid drive train would be largely 

unrealized and a significant opportunity to reduce real-world fuel use based on improved 

aerodynamics would be missed.

Second, vehicle users are likely to use the fuel efficiency ratings developed during 

certification testing as a guide when making purchasing decisions. If these ratings are based 

on an unrepresentative test cycle for a particular vehicle type they will have little 

correlation with the purchaser’s in-use experience, and they will quickly be discredited as a 

reliable source of information.

In order to adequately cover the complexity and variety of the HDV fleet another approach 

would be to use different test cycles for each type of HDV during fuel efficiency testing. In 

this approach each major category of HDV (transit bus, refuse truck, utility truck, singleunit freight hauler, combination freight hauler, etc) would require two to five different test 

cycles to cover the range of typical operation for that type of vehicle, and these cycles 

would be different for each vehicle type. 

A third approach would be to use a limited number of test cycles to test all HDVs, but to 

mathematically combine the fuel economy results from these cycles in different ways 

depending on the type of HDV – to use the measured results to “predict” fuel use on a 

more representative cycle or cycles for each HDV type. In this scenario all HDVs would be 

tested on the same test cycles, but the weighting of fuel economy results from each cycle 

would be different depending on the type of HDV. As a simple example, consider a case 

where testing was done on a slow speed urban cycle and a high speed line haul cycle. The 

predicted regulatory fuel economy for a transit bus and a Class 8 combination truck might 

be calculated as follows: 

Transit bus = (URBAN CYCLE FE x 80%) + (LINE HAUL CYCLE FE x 20%)
Design of HDV Fuel Economy Regulations 

44

Combination Truck = (URBAN CYCLE FE x 20%) + (LINE HAUL CYCLE FE x 80%)

This approach has preliminarily been demonstrated by West Virginia University (WVU) to 

predict exhaust emissions (including CO2) on an “unseen cycle” based on the measured 

results from some number of “standard cycles” [7-6]. In WVU’s methodology the required 

weighting factors for measured emissions from each test cycle are determined based on the 

statistical characteristics of the cycle (average speed, idle time, average change in speed, 

etc.) compared to the same metrics for the target “unseen” cycle. In order to adequately 

characterize the dynamic behavior of HDVs (including engine idle time) a minimum of three 

widely variant test cycles will probably be required. Every additional independent variable 

(i.e. geography, vehicle weight, vocational PTO load, etc) would require another test cycle. 

This approach would simplify actual fuel economy testing, but would still require prior 

knowledge of “typical real world” duty cycles for the various major types of HDV, in order 

to develop appropriate type-specific weighing factors. These type-specific weighing factors 

would be used to calculate the regulatory fuel economy value for each HDV, based on the 

measured fuel economy on the test cycles. 

For some HDVs (for example transit buses) a number of chassis dynamometer test cycles 

have already been developed that might be appropriate for fuel efficiency testing. See 

Figure 7.4 for two of many examples. Preliminary work has also been done to develop 

appropriate test cycles for highway line haul vehicles, local pick-up and delivery vehicles, 

neighborhood refuse trucks, utility service trucks, and intermodal drayage trucks [7-7]. For 

some of these vehicle types additional cycles will likely be required in order to cover the full 

range of in-use operation.

Some of these dynamometer test cycles may also be appropriate for use on a test track, 

while others may be too complex to produce consistent test track results.

Specifically for sleeper cab-equipped combination trucks it might also be desirable to 

include long duration idling as part of the certification test, with appropriate cabin hotel 

loads included. This could be handled in a separate test, in addition to the baseline drive 

cycle(s). 

 

 Manhattan Driving Cycle Orange County Driving Cycle

Source: SAE

 Figure 7.4 Transit Bus Test Cycles: Manhattan Cycle and Orange County Cycle 

7.4.3 Test Conditions

In addition to specifying the testing method and test cycles, a fully developed fuel 

efficiency test protocol must specify mandatory testing conditions. This is required in 
Design of HDV Fuel Economy Regulations 

45

order to control for all of the major variables that might affect vehicle fuel use. Some of the 

test conditions that must be specified include:

 The acceptable range of ambient weather conditions (temperature, humidity, wind 

speed) 

 Vehicle test weight/payload

 Vehicle accessory loads (i.e. air conditioning on/off)

 Vehicle vocational loads

 Tire pressure and tread depth

 Vehicle pre-conditioning

 Test fuel specification

Defining an appropriate vehicle test weight is of particular concern for many HDVs, 

especially single-unit and combination freight haulers. One approach would be to test at a 

vehicle’s maximum GVWR (worst case) while another would be to test at some percentage 

of GVWR which is representative of the “average” load carried by this type of vehicle inuse, taking into account that in the real world it is not always possible to maximize vehicle 

payload on every trip. 

Vehicle accessory loads will be relatively insignificant for some HDVs (for example 

combination trucks on a line haul cycle) but much more important for others (for example 

transit buses). Likewise, the importance of vocational loads will be dependent on vehicle 

type. 

7.4.4 Combination Truck-Trailer Testing

Specifically for Class 8 combination trucks, an important consideration will be how 

truck/trailer combinations will be tested for fuel efficiency. Especially on high speed line 

haul cycles the characteristics of both the truck and trailer will significantly affect fuel use. 

As discussed in Section 2, heavy-duty truck tractors and the trailers that they pull are 

manufactured by different companies and are generally not sold as sets. In fact the truck 

tractor and trailer that make up a specific combination truck on a specific day are often 

owned by two different companies, and the tractor may be paired with a different trailer 

the following day or week. 

In this situation it will be necessary to conduct fuel efficiency testing of combination truck 

tractors while paired with a “reference trailer” of standard size and configuration. All 

aspects of this reference trailer will need to be defined, including the exterior dimensions, 

shape, and materials as well as the specifics of the axles, wheels, and tires. The distance 

between the rear of the truck cab and the front of the trailer during testing will also need to 

be specified since it can significantly affect aerodynamics.

There are two approaches that could be taken to specification of a reference trailer. The 

first would be to specify a standard box-type trailer with relatively poor aerodynamics 

and standard tire configuration, which would result in fuel use generally representative of 

what is seen today. The second would be to specify a “best-in-class” trailer design with 

improved aerodynamics and low rolling resistance tires, which would result in lower fuel 

use for every tractor with which it was paired. 

If separate trailer testing is required (see Section 7.2) it could be accomplished by testing 

trailers while paired with a “reference truck”. The reference truck could be a specific 

vehicle, or could be any vehicle which achieves a specific fuel efficiency rating when tested 
Design of HDV Fuel Economy Regulations 

46

paired with the reference trailer. It is also worth exploring the possibility of developing a 

trailer standard and test procedure independent from the truck. 

7.5 Form of Required Fuel Efficiency “Improvement” 

Regardless of the metric used (see Section 7.3) regulation of HDV fuel efficiency will require that 

a minimum standard be set for all vehicles of a specific type. There are two options for how to 

define the minimum standard: 1) by setting an absolute value for the chosen metric, or 2) by 

mandating a percentage improvement from some baseline value. 

In order to set a meaningful but realistic goal for improved efficiency, defining an absolute value 

goal (i.e. maximum of 500 BTU/ton-mile = ~7 MPG for a fully-loaded Class 8 combination 

truck) will require good information about the fuel efficiency of existing vehicles, as well as the 

potential of various technology options to reduce fuel use. A separate absolute value goal will 

have to be set for a number of different HDV types, based on the chosen test cycles (i.e. each 

test cycle will require a separate value for the fuel efficiency standard).

Mandating a percentage improvement from a baseline does not necessarily require definitive 

information on the fuel efficiency of existing vehicles, nor does it necessarily require a separate 

goal for each type of HDV. For example, one could mandate that beginning in 2015 all HDVs 

be tested using the regulatory protocol (including using different test cycles for different vehicle 

types) to develop a baseline fuel efficiency rating for each vehicle type, and that beginning in the 

2017 model year all new vehicles must have at least 10% lower fuel use than the measured 2015 

baseline.

As discussed in Section 7.4.2, most HDVs will not have a single “typical” duty cycle that 

adequately covers the full range of in-use fuel use over the vehicle’s lifetime. As such, it is likely 

that for most vehicle types it will be advisable to test on more than one test cycle. From a 

regulatory perspective one must decide how the test results from the different test cycles will be 

used to evaluate compliance with the regulatory standard. There are two options: 1) 

mathematically combine the results from the separate test cycles to create a “combined” rating 

used for regulatory compliance, or 2) set a separate regulatory standard for each test cycle 

which must all be met.

The first option is analogous to what is currently done for cars and light trucks. These vehicles 

are tested on five different test cycles14 and the city, highway, and combined fuel economy 

ratings posted on window stickers are calculated based on different weighting of results from 

each test cycle. Compliance with corporate average fuel economy standards (CAFE) is based on 

a combined MPG rating derived from only the city and highway test cycle results15 [7-8]. 

The formula used to combine test results from different HDV test cycles could be simple or 

complex, but in general would be designed to represent over-all fleet average fuel efficiency for 

each vehicle type, based on the relative percentage of time that typical vehicles spend in each 

duty cycle. 

The second option is analogous to current emission standards for locomotive engines. Unlike 

other heavy-duty diesel engines that are tested on only one test cycle, locomotive engines are 

 

14 The test cycles are: Federal Test Procedure, FTP (stop-and-go city driving), Highway Fuel Economy 

Test, HFET (rural driving), US06 (high speeds and aggressive driving), SC03 (air conditioner operation), 

and Cold FTP (cold temperature operation)

15 While the test data used are the same, the cycle weightings used to calculate MPG for compliance with 

CAFE and for the fuel economy ratings posted on window stickers are different. For any individual 

vehicle the fuel economy ratings on the window sticker may therefore not match exactly the fuel economy 

rating used for CAFE compliance calculations. 
Design of HDV Fuel Economy Regulations 

47

tested on two different test cycles – the line haul and switcher cycles – that represent the 

extremes of typical locomotive in-use duty cycles. There is a separate numerical standard for 

emissions as tested on each cycle, and every engine must meet both standards. For example, 

since 2005 new locomotive engines have been required to emit no more than 5.5 g/bhp-hr NOx 

when tested on the line haul cycle, but they are allowed to emit up to 8.1 g/bhp-hr NOx when 

tested on the switcher cycle [7-9].

7.6 Choice of Baseline

If the regulatory standard for HDV fuel efficiency is defined as a percentage improvement from 

some baseline, the baseline against which regulatory compliance will be measured must be 

defined. The baseline will typically be defined as the measured efficiency from some sub-set of 

vehicles of each type from a specific model year, as tested using the regulatory protocol.

An appropriate choice of baseline year might be one or two model years prior to 

implementation of fuel efficiency regulations. EPA emissions standards for onroad heavy duty 

diesel engines that take effect in the 2010 model year will require an 80 percent reduction in 

NOx emissions. The changes required to meet this standard may negatively affect net engine 

efficiency. As such the baseline year for any HDV fuel efficiency standards should be the 2010 

model year or later.

Given the volatility in diesel fuel prices truck owners and fleets have increased incentive to 

voluntarily adopt technologies that will reduce fuel use. If the recent high prices ($3.50+ per 

gallon) had been sustained there would likely be significant vehicle and fleet changes over the 

next few years, and a fleet fuel efficiency baseline defined for the 2012 model year or later 

would likely be higher than a baseline defined for earlier model years. 

Which ever model year is chosen as the baseline year, there are several options for defining the 

numerical standard for baseline fuel efficiency based on available vehicles from that model year. 

These choices include: 1) the average fuel efficiency of all models sold that year (model average), 

2) the sales-weighted average fuel efficiency of all models sold that year (fleet average), 3) a 

fuel-weighted average calculated based on the sales of each vehicle, their fuel economy ratings, 

and their “expected” annual mileage (fuel-weighted average) or 4) the fuel efficiency of the best 

performer of all models sold that year (top runner).

7.7 Implementation Timeline & Flexibility Provisions

There are several options for a regulatory time line for implementation of HDV fuel efficiency 

standards. The first is to set a specific fuel efficiency standard for each HDV vehicle type, to 

take effect for vehicles sold beginning in a specific vehicle model year (i.e. beginning in model 

year 2015 HDVs must get 5% better fuel efficiency than the 2012 baseline). A second approach 

would be to set a specific standard for each HDV vehicle type, to take effect for vehicles sold 

beginning in a specific vehicle model year, and to periodically tighten the standard every few 

years (i.e. beginning in model year 2015 HDVs must get 5% better fuel efficiency than the 2012 

baseline, beginning in model year 2017 HDVs must get 10% better fuel efficiency than the 2012 

baseline, etc.). 

Under this second scenario the initial standard might be “easy” to reach using off-the-shelf 

technology, while later more stringent standards would require new technology development or 

maturation. The lag for application of more stringent standards would be designed to allow 

time for the required technology development.

Whichever of these methods is chosen, it is not a given that the standard must apply to all 

HDVs sold in the first model year to which they apply. It might be advantageous to allow 

manufacturers compliance flexibility by phasing in the requirements over several model years. 

There are several options for a phase-in, including:
Design of HDV Fuel Economy Regulations 

48

 % of Models: phase-in the requirement on a percent-of-models basis (i.e. in the first year 

25% of each manufacturer’s models must meet their target, in year two 50%, etc). 

 % of Sales: phase-in the requirement on a percent-of-sales basis (i.e. in the first year 25% 

of all vehicles sold by each manufacturer must meet their target, in year two 50%, etc). 

Another approach that would allow manufacturers flexibility would be to set a fleet average 

fuel efficiency standard, rather than requiring every HDV model to meet a specific standard. 

Under fleet averaging the sales-weighted or fuel-weighted average16 of all vehicles sold by each 

manufacturer must meet a specific fuel efficiency standard, while individual vehicle models 

would be allowed to be less efficient. Obviously, to meet the fleet average standard some 

models would also have to be more efficient, and the net effect would be the same as if every 

model exactly met the standard. A fleet average requirement could also be periodically 

tightened over some range of model years to allow for technology development required to meet 

the final, most stringent standards.

U.S. Class 8 combination trucks typically burn eight times as much fuel per year as other HDVs 

because they are heavier and typically travel many more miles. In this situation, sales-weighted 

fleet averaging across all HDV types would not be optimal. Fleet averaging would have to be 

done for each separate type of HDV sold by each manufacturer, or a fuel-weighted fleet average 

would have to be used, which takes into account the amount of fuel that each truck typically 

uses in a year in addition to the number of trucks sold.

An approach that would give manufacturers additional compliance flexibility is the use of 

averaging, banking, and trading. “Averaging” is often used to mean that manufacturers are 

given “credit” for over-compliance in one area, which they can use to off-set under-compliance 

in another area. “Trading” is often used to describe the sale of a “credit” from one company to 

another. “Banking” would allow manufacturers to over-comply in earlier years, in exchange for 

lesser reductions in following years. Averaging, banking and trading could be used to ease 

compliance across vehicle types within a single model year, or across model years. One 

advantage is the ability to potentially set tighter limits at equal or possibly even lesser cost than 

standards that must be met by each and every unit.

For example, let’s say that a fuel efficiency regulation requires a separate fleet average fuel 

efficiency rating for each type of vehicle sold by a manufacturer (i.e. combination trucks, singleunit freight trucks, buses). Cross-vehicle banking and trading would allow a manufacturer to 

get credit for over compliance by their buses and apply that to offset under compliance for the 

combination trucks they sell. Likewise, under a scenario in which the fleet average standard gets 

more stringent over time, a manufacturer could be given credit for over compliance in the early 

years through “banking”, which would allow them to take more time to meet the more stringent 

standards required in later model years. 

Averaging, banking and trading schemes can be complex, and must be carefully crafted to 

ensure that the reduction in fuel use of over-complying vehicles is at least as great as the 

increase in fuel use from non-complying vehicles that are allowed to be sold under the averaging, 

banking and trading scheme. For the U.S. HDV fleet, careful attention must be paid to the 

relative “worth” of an over- or under-complying Class 8 combination truck compared to other 

HDV types which typically burn much less fuel annually.

 

16 Due to the fact that different types of HDVs have significantly different annual usage, the salesweighted average and the fuel-weighted average will not be the same. For example, if 75% of trucks sold 

are single-unit trucks that get 8 MPG and 25% are combination trucks that get 6 MPG, the sales-weighted 

average fuel economy will be 7.5 MPG. However, if single units trucks average 12,000 miles per year 

and combination trucks average 60,000 miles per year the fuel-weighted average fuel economy will be 

6.6 MPG. 
Design of HDV Fuel Economy Regulations 

49

7.8 Compliance/Enforcement 

The most significant issue for compliance and enforcement of a U.S. HDV fuel efficiency/GHG 

regulation is the agency of the federal government that would be responsible to promulgate and 

enforce the rules. The two most likely candidates would be the Environmental Protection 

Agency (EPA) and the Department of Transportation (DOT). 

EPA has responsibility for regulation of exhaust emissions from new light-duty vehicles and 

new heavy-duty engines. DOT has responsibility for regulation of new vehicle safety 

requirements (both light duty and heavy duty), commercial vehicle operations, and for the 

current fuel economy standards for light duty cars and trucks (Corporate Average Fuel 

Economy, CAFE)17. While DOT is responsible to develop and implement the CAFE standards, 

the corporate average fuel economy for each manufacturer is calculated by EPA based on test 

data collected during emissions certification testing [7-10]. Congress has tasked DOT with the 

responsibility for HDV fuel efficiency standards, given their technical responsibility for new 

vehicle safety and their current responsibility for light duty fuel economy standards.

EPA would also be in a good position to develop and implement HDV greenhouse gas 

regulations given their technical familiarity with fuel economy and heavy-duty emissions testing, 

as well as the technical efforts currently being undertaken under their SmartWay program, 

including current efforts to develop a heavy-duty vehicle fuel efficiency test protocol. 

In April 2007 the U.S. Supreme Court ruled that the Clean Air Act gives EPA the authority to 

regulate carbon dioxide emissions from vehicles, in the context of efforts to protect human 

health by reducing global warming. Further, the Court ruled that “under the Act’s clear terms, 

EPA can avoid promulgating regulations only if it determines that greenhouse gases do not 

contribute to climate change or if it provides some reasonable explanation as to why it cannot 

or will not exercise its discretion to determine whether they do.”

The decision recognized that an EPA effort to regulate CO2 emissions from vehicles would 

overlap with DOT’s mandate to promote energy efficiency by setting mileage standards, but 

affirmed that these two goals were not in conflict. The court said that “The fact that DOT’s 

mandate to promote energy efficiency by setting mileage standards may overlap with EPA’s 

environmental responsibilities in no way licenses EPA to shirk its duty to protect the public 

health and welfare.” Protecting public health and welfare is a duty mandated by the Clean Air 

Act.

Another important compliance issue for any HDV fuel efficiency standard would be labeling 

requirements. The measured fuel efficiency of every HDV subject to regulation should be 

available to the public to help inform their equipment buying decisions. How best to 

disseminate this information might be open to debate. Some issues to consider include the 

required location for fuel efficiency “labels” to be posted (i.e. on a window sticker as with 

current cars and light trucks), the format for reporting fuel efficiency (see Section 7.1), and how 

test results from different test cycles will be reported (see Section 7.2.2). 

Non-compliance with any HDV fuel efficiency regulation will require penalties. Some issues to 

consider with respect to non-compliance penalties include the form of the penalty, the value of 

the penalty, and who will be required to pay it. 

In accordance with the Clean Air Act penalties for non-compliance with heavy duty engine 

exhaust emission standards are based on the expected average cost of compliance and the 

degree of non-compliance for the engine. They are specifically designed to erase any 

 

17 The agency of DOT responsible for CAFE is the National Highway Traffic Safety Administration 

(NHTSA)
Design of HDV Fuel Economy Regulations 

50

competitive disadvantage for manufacturers that are complying. There is also an upper bound 

on allowable emissions from non-compliant engines – those whose emissions exceed the upper 

limit can not be sold at all. 

Based on penalty formulas in the Clean Air Act and EPA’s assessment of the average cost of 

compliance, in 2001 EPA proposed non-compliance penalties of $4,680 per engine for model 

year 2004 and later heavy-duty diesel engines with a NOx emissions rate of 3.0 g/bhp-hr, 

compared to the regulatory limit of 2.5 g/bhp-hr. For engines emitting 4.5 g/bhp-hr NOx the 

proposed penalty increased to $11,342 per engine [7-11]. These penalties were for the first year 

that the non-compliant engine model was sold, and they increased in subsequent years. 

Penalties for non-compliance with the CAFE standards for cars and light trucks are a fine

levied against the vehicle manufacturer of $5.50 per tenth of a mile per gallon below the 

standard, times the manufacturer’s sales volume18.

Another approach would be to levy a “gas guzzler” tax or duty on each non-compliant vehicle, 

to be paid by the purchaser. While not levied directly against the vehicle manufacturer such a 

tax would provide an indirect incentive to the manufacturer to comply, by making their vehicles

more expensive compared to compliant vehicles, and would directly discourage the purchase of 

non-compliant vehicles. To be effective the value of the tax would need to be greater than the 

per vehicle differential cost of manufacturer compliance.

One might also impose a non-monetary penalty by refusing to allow non-compliant vehicles to 

be registered by the user. This option might not be practically available to the federal 

government, but could be implemented by the individual states.

 

18 For a corporate average fuel economy of 20 MPG compared to a CAFE standard of 20.5 MPG, and an 

annual sales volume of 500,000 vehicles, the non-compliance fine would be $13.75 million.
Barriers to Implementation of HDV Fuel Economy Standards 

51

8. Barriers to Implementation of HDV Fuel Economy Standards

There are a number of factors specific to the U.S. HDV market that make HDV fuel efficiency 

regulations more difficult and complicated to design and implement than fuel efficiency 

regulations for cars and light trucks. The most significant of these are discussed here. 

8.1 HDV Fleet Diversity

As discussed in Section 2, the U.S. HDV fleet is extremely diverse, with a wide range of vehicle 

types, sizes, and typical duty cycles. To effectively cover the entire HDV fleet any fuel 

efficiency regulation will of necessity be complex.

While the same basic test protocol can be used to measure the fuel efficiency of virtually all 

HDVs, different types of HDVs may require different test cycles to replicate typical in-use 

behavior. Even a single type of HDV will likely require several different test cycles to 

adequately cover the range of typical in-use duty cycles. For any particular HDV type this is no 

different, or more difficult, than current fuel efficiency regulation of light duty vehicles, which 

uses five different test cycles. However, the greater diversity of vehicle types in the HDV fleet 

will add complexity to the over-all regulatory scheme. 

Depending on the fuel efficiency metric used, and the form of any required improvement, 

separate numerical standards for fuel efficiency may also be required for each type/size of 

HDV. 

8.2 Shared Responsibility for Components of Fuel Use

HDV manufacturing is more complicated than manufacturing of cars and light trucks. For a 

typical HDV the engine, chassis, and body may have been produced by three different 

manufacturers. In addition, Class 8 combination trucks are composed of a truck-tractor paired 

with a trailer. The truck and trailer are typically manufactured by different companies, and are 

often owned by different companies as well for in-use vehicles. Trucks and trailers are typically 

not paired long term either – a specific truck may pull a number of different trailers over the 

course of a month or a year. 

For a typical HDV no single entity controls all design decisions that affect fuel use, making it 

difficult to determine where best to assign responsibility for complying with fuel efficiency 

regulations.

For HDVs the engine manufacturer has responsibility to comply with current EPA exhaust 

emission standards. While the engine in an HDV affects fuel efficiency, so does the drive train, 

vehicle accessories, and vehicle aerodynamics - which are determined by the vehicle 

manufacturer. As such, it might be better to assign primary responsibility for complying with 

fuel efficiency standards to the vehicle manufacturer (i.e. the vehicle would be regulated, not 

just the engine). 

That being said, many HDVs are produced by two different vehicle manufacturers – the 

producer of the chassis, and a second manufacturer that buys the chassis, adds a body, and 

ultimately sells the vehicle to the user. For most of these vehicles the chassis manufacturer likely 

has greater impact on fuel use than the body manufacturer does, and the same basic chassis will 

be used for a number of different vehicle types. As such, it might be more efficient to assign 

primary responsibility for complying with fuel efficiency regulations to the chassis manufacturer, 

but it may also make sense to apply a second set of standards to some finished vehicles, with 

the final body attached.
Barriers to Implementation of HDV Fuel Economy Standards 

52

Because they have such a significant impact on fuel use, particularly at highway speeds, to 

maximize the effectiveness of any HDV fuel efficiency regulations the trailers used with Class 8 

combination trucks should also be regulated. Since they are manufactured by different 

companies they will have to be regulated separately from the Class 8 truck tractors that pull 

them. This significantly complicates regulatory fuel efficiency testing, and will likely require the 

use of “reference trailers” for truck testing and “reference trucks” for trailer testing. 

8.3 Vehicle Ownership Patterns

A high percentage of Class 8 combination trucks and other HDVs are owned by small

businesses and independent owner/operators that own only one or a few trucks.

Many of these owners may be resistant to the imposition of HDV fuel efficiency standards due 

to concerns about the affect on truck prices, and new technology risk aversion.

8.4 Financing & Access to Capital

The imposition of fuel efficiency standards will almost certainly increase prices for new HDVs 

based on the incremental cost of compliance. Because more efficient vehicles will use less fuel to 

do the same amount of work, or to carry the same amount of cargo, there will be an off-setting 

savings in annual fuel costs for the vehicle owner. 

In some cases the pay-back period of the incremental purchase cost, based on annual fuel 

savings, may be quite short19. Even so, independent owner/operators and small businesses 

may be constrained in their ability to purchase new, more efficient, trucks due to limited access 

to low cost capital funds.

8.5 Lack of HDV Fuel Economy Test Protocol

There is currently no well-established, accepted test protocol that could be used to test the fuel 

efficiency of HDVs to judge compliance with a regulatory fuel efficiency standard. There are a 

number of industry-developed fuel efficiency and emissions test procedures that could be used 

as the basis of such a protocol, but significant work is required to develop them into a 

comprehensive procedure.

EPA has developed a draft fuel efficiency test protocol intended to be used for certification of 

medium and heavy duty vehicles under their SmartWayTM program. This protocol currently 

envisions the use of chassis dynamometer and/or track testing to evaluate the fuel efficiency of 

various types of HDVs. Many aspects of the draft protocol are well developed, but the 

following areas need significantly more work to be useful for regulatory testing:

 specification of drive cycles for various types of HDVs

 specification of test weight/payload for various types of HDVs

 specification of vehicle accessory and vocational loads for various types of HDVs

 specification of required tire condition for testing (tread depth, tire pressure)

 management of engine cooling load during dynamometer testing

 

19 An average Class 8 combination truck logs 69,000 miles per year, gets 5.9 MPG, and burns 11,600 

gallons of diesel fuel annually. A ten percent increase in fuel economy would reduce annual fuel use by 

1,000 gallons. At $3.50 per gallon the vehicle owner would save $3,500 per year, $10,500 over three 

years, and $17,500 over five years. 
Barriers to Implementation of HDV Fuel Economy Standards 

53

 accounting for fuel used to regenerate active diesel particulate filters 

 evaluating and accounting for the effect of cross-winds on aerodynamic drag

In addition, while the draft SmartWayTM protocol currently envisions allowing both chassis 

dynamometer and test track testing, there is relatively little information currently available to 

evaluate the correlation of results from these two test methods for the same vehicle, or the 

correlation of results from either method to “typical” in-use results.

Companies that own large fleets of HDVs, particularly Class 8 combination trucks, regularly 

conduct formal in-use fuel economy tests to evaluate the effect on fuel use of different truck 

models and configurations, different components and tires, and after-market devices. These 

tests are usually conducted in accordance with TMC RP1109, Type IV Fuel Economy Test 

Procedure. This procedure is a paired-truck test, and testing is usually conducted on public 

roadways over the actual in-service routes used by the fleet. Results are reported as a 

percentage change in fuel use for one truck compared to the other (control) truck. The use of a

control or reference truck allows for control of many independent variables, but this type of test 

may not be practical for testing under a regulatory program due to concerns about duty cycle 

repeatability, and the need to specify and maintain a fleet of reference trucks to maintain an 

appropriate control. 

8.6 Lack of Baseline Data 

Large HDV fleets typically keep very detailed records on the usage patterns and fuel use of 

their vehicles. These fleets also regularly conduct formal in-use paired-truck fuel economy tests 

(see Section 8.5). Many of these fleets consider this data to be proprietary, and there is 

relatively little published, peer-reviewed information about these fleets. In addition, many 

trucks are owned by small businesses and owner/operators that do not keep formal or 

comprehensive records. It is therefore impossible to create a comprehensive picture of the 

ownership and usage patterns, and fuel efficiency, of the current U.S. HDV fleet.

The best, though limited, information currently publicly available comes from the Vehicle 

Inventory and Use Survey that has been conducted by the U.S. Census Bureau every five years 

since 1963. The latest survey was completed in 2002, but this program has been discontinued 

and no more surveys will be conducted.

In order to develop effective HDV fuel efficiency regulations the following types of information 

about the current HDV fleet would be useful:

 fleet ownership and use patterns for various types of HDVs

 typical duty cycles for various types of HDVs

 truck model-specific fuel economy data

 potential fuel efficiency improvements from various technology combinations

8.7 Changes in Ownership Over a Vehicle’s Life

As with other vehicle types, HDVs typically have multiple owners throughout their life. To a 

greater extent than with cars and light trucks, however, a change in ownership of an HDV might 

also bring a significant change in duty cycle. 

Different sized fleets have different purchasing patterns for HDVs. For line haul trucks, larger 

fleets with more than fifty trucks tend to buy vehicles new, and to keep them for a relatively 

short time, while smaller fleets with less than ten trucks purchase a much higher percentage of 
Barriers to Implementation of HDV Fuel Economy Standards 

54

their trucks used, and keep them for longer periods [8-1]. Heavy vocational trucks tend to be 

held longer by their first owner – seven to eleven years – even when purchased by larger fleets.

New trucks, particularly Class 8 combination trucks, also typically see more annual use than 

older trucks. While the average Class 8 combination truck travels 68,800 miles per year, 

approximately 50 percent of trucks less than two years old travel more than 100,000 miles per 

year, and some of them can travel over 200,000 miles per year [8-2].

Over it’s life time a “typical” Class 8 combination truck might be purchased new by a large 

national fleet and used for long-distance hauling for three to five years, after which it might be 

sold to a small- or medium-sized fleet and used for local or regional hauling for another five to 

eight years. It might pass through several more owners, and ultimately end up as a drayage 

truck making short local runs in and around a port or international border crossing. 

With respect to fuel efficiency regulation, this complexity of usage patterns over the life of an 

HDV might affect the choice of test cycle(s) used for compliance testing, and/or the weighting 

of results from different test cycles, when developing a combined fuel efficiency rating (see 

Sections 7.2.2 and 7.3). 
Related Issues

55

9. Related Issues

The bulk of this document discusses issues related to regulation of fuel efficiency from new 

heavy duty vehicles. There are a number of other factors that might affect fuel use and GHG 

emissions from the entire transportation sector. Some of these are briefly discussed here.

9.1 Complementary In-use Standard 

As with current exhaust emission standards for light duty vehicles and heavy duty engines, and 

current fuel efficiency standards for light duty vehicles, any new fuel efficiency regulations for 

HDVs would presumably apply only to new vehicles. 

Opportunities exist to also improve the fuel efficiency of existing HDVs. Standardizing rolling 

resistance measurement methods and labeling aftermarket tires with their rolling resistance, for 

example, would enable vehicle owners to select low rolling resistance tires. Additional 

improvements can be achieved through the application of after-market retrofit technologies 

and/or engine upgrades. In conjunction with the imposition of fuel efficiency standards for new 

HDVs one could contemplate the imposition of complementary in-use standards. This is the 

approach that California has adopted as one early-action measure to reduce GHG emissions 

state-wide (see Section 4.3).

Other states could follow California’s lead and impose in-use retrofit requirements as a 

condition of annual vehicle registration. At a federal level, engine upgrades to reduce CO2

emissions could be mandated in conjunction with engine overhaul/rebuilding, but since current 

emission standards do not apply to the entire vehicle it is likely that the mandates on engine 

upgrades could not include retrofits to other vehicle systems.

9.2 The Role of Non-standard Fuels 

Some non-standard fuels that can be used in HDVs produce lower net CO2 and GHG emissions 

than standard diesel fuel, either directly from the tailpipe (i.e. natural gas, hydrogen) or from 

the entire wells-to-wheels fuel cycle (i.e. biodiesel). Defining the actual wells-to-wheels benefits 

from some agriculturally-derived fuels has proven problematic, but if an appropriate standard 

can be developed, “low carbon fuels” might play a role in meeting fuel efficiency/GHG 

standards for some HDVs.

The test protocols discussed in this document focus on measurement/calculation of vehicle fuel 

use and tailpipe CO2 emissions. Depending on the metric chosen for a fuel efficiency regulation 

the CO2 reduction benefits of non-standard fuels could be captured directly during testing, or 

could be easily calculated using adjustments based on measured fuel parameters. 

Any “upstream” benefits from other parts of the fuel cycle would have to be 

measured/calculated separately and subtracted from the tail pipe CO2 emissions measured 

during regulatory vehicle testing.

9.3 Incentives for Modal Shift/System Efficiency

This document focuses on regulations to improve the efficiency of individual heavy duty trucks, 

many of which are used for goods movement. Improvements in HDV fuel efficiency will reduce 

over-all fuel usage and GHG emissions from the freight sector, but larger benefits could also 

accrue from modal shift of some shipments to other transportation modes. On a ton-mile basis 

rail and water-borne freight shipments generally use less fuel than shipments by truck, though 

total transport time may be longer. See Figure 9.1 for an illustration of the reductions in CO2

emissions possible from changes in freight strategies [9-1]
Related Issues

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Source: J.B. Hunt

Figure 9.1 Relative Carbon Emissions Using Different Freight Strategies

 

In 2006, approximately 75% of goods carried domestically (by weight) were carried exclusively 

by truck, and only 9% were carried intermodally [9-2]. While approximately 58% of the weight 

of exported goods and 79% of the weight of imported goods moved by intermodal shipment, 

just over one percent of purely domestic shipments moved intermodally. 

Any national policy focused on reducing fuel use from the freight sector must address and 

encourage modal shift to more efficient freight modes, as well as improvements in efficiency of 

the individual modes themselves. 

9.4 HDV Weight and Length Restrictions 

One way to reduce per ton-mile fuel use and GHG emissions from Class 8 combination trucks 

would be to allow them to be bigger and/or heavier than they currently are. Current restrictions 

on combination truck size and weight are based on existing roadway dimensions (height, width), 

safety considerations (length, GVWR), and a desire to limit the damage that HDVs cause to 

roadway pavement, substructures and bridges (GVWR, axle weight). 

Current federal law limits vehicle width to 102 inches, and limits axle weights for trucks used 

on the interstate system to 20,000 pounds for single axles and 34,000 pounds for tandem axles. 

Total GVWR for a truck-trailer combination is also limited to 80,000 pounds. 

Most states have been allowed to adjust these federal limits for certain roadways based on 

“grandfather rights”, and only seven states have adopted them state-wide without adjustment. 

All states also issue routine permits to exceed these limits. Only New Mexico (86,400 pounds) 
Related Issues

57

and Wyoming (117,000 pounds) allow virtually all trucks on the interstate system to exceed the 

federal GVWR limit, but thirteen states allow trucks on other state roadways to exceed the 

federal limit, and virtually all states issue routine permits that allow a GVWR of 120,000 

pounds or more. Most states have adopted the federal axle weight limits, but issue routine 

permits for tandem axles weighing 48,000 pounds or more [9-3].

Federal law sets a minimum length of 48-feet for single trailers used in combination trucks and 

28-feet each for trailers used in a twin trailer combination on the interstates. Most states have 

adopted a length limit on the interstates of 53 feet for single trailers, while four states only 

allow trailers up to 45 feet, and ten states allow longer trailers (up to 60 feet). Hawaii is the 

only state that has no limit on the length of trailers that can be used on interstate highways. 

Nine states limit the length of trailers used on other state roads to less than 53 feet, while nine 

have no limit on the length of trailers that can be used on state highways [9-2].

Over half of the states allow a truck to haul a two-trailer combination, and twelve states allow 

three trailers. However, federal law limits the GVWR of two- and three-trailer combinations to 

less than 130,000 pounds in most states. 

Fuel use per ton-mile could be reduced from Class 8 combination trucks by allowing higher 

GVWR, higher axle weights, longer trailer length, or greater use of two- and three-trailer 

combinations. The benefits of such a policy change would need to be weighted against potential 

dis-benefits from reduced safety and increased damage to roadways. Such a policy might also 

provide a dis-incentive for shifting more freight volume away from trucks to more efficient 

modes such as rail and water transport. 

9.5 Reductions in Highway Speed Limits

Aerodynamic drag increases as a square of vehicle speed – the faster a vehicle goes the more 

fuel it uses to push through the air and maintain its speed. The impact of speed on fuel 

economy depends on a number of factors, but a general rule of thumb indicates that increasing 

the speed of a Class 8 combination truck by one mile per hour will decrease fuel economy by 0.1 

miles per gallon [9-4].

Reducing average highway speeds from 70 miles per hour to 60 miles per hour might increase 

fuel economy for a typical Class 8 combination truck by one mile per gallon or more, and save 

over 1,200 gallons of fuel annually20 per truck. For the 2 million combination trucks on the road 

the potential annual fuel savings could total 2 billion gallons or more, approximately six percent 

of the fuel currently used annually by heavy-duty trucks. 

A national policy to reduce maximum allowable highway speeds, implemented and enforced by 

the states, could significantly reduce fuel use from the freight sector without any changes in new 

vehicle standards. With such a policy average transit times would increase, which would affect 

driver hours, productivity, and shipper costs and revenue. Any potential fuel efficiency benefits 

would need to be weighted against these factors.

9.6 Driver Training

Driver behavior can significantly increase or decrease fuel use for a heavy-duty vehicle 

regardless of the engine or vehicle technology. A few simple changes in driving habits can 

reduce fuel use by five percent or more. A Canadian study estimates that many fleets could 

 

20 Based on 5.9 MPG baseline fuel economy, 69,000 miles per year, and 75% of mileage on the highway.
Related Issues

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achieve an average ten percent fuel economy improvement through driver training and 

monitoring [9-5].

Common habits that can increase fuel use include driving with engine RPM too high, frequent or 

improper shifting, too-rapid acceleration, too-frequent stops and starts from failing to 

anticipate traffic flow, and excessive engine idling. Proper driving habits that help to save fuel 

can be taught. A study for the European Commission estimated that an annual one-day driver 

training course will improve truck fuel efficiency by five percent [9-4].

Annual or bi-annual refresher training on fuel saving driving techniques for commercial vehicle 

operators could be enforced by the states as a condition of renewal for commercial drivers 

licenses. 

 
Key Research Areas and Recommendations

59

10. Key Research Areas 

As discussed in the previous chapters of this report, the development of effective fuel efficiency 

regulations for HDVs will require attention to numerous technical and policy-related details. 

Decisions as to the “best” regulatory design must be based on a thorough understanding of 

existing and future characteristics of the HDV fleet, the structure and characteristics of the 

HDV manufacturing industry, and potential technology approaches available to increase HDV 

fuel efficiency. While much of the required information is known, additional research and 

analysis is required to further develop and elucidate key areas of interest. The most important 

research areas are discussed briefly here. These areas will form the basis of the ICCT’s research 

work plan in the near term.

10.1 Technology Options to Increase HDV Fuel Efficiency

In order to set appropriate regulatory targets for improvements to HDV fuel efficiency, more 

must be known about both the benefits and the costs of the various technology options 

available to achieve improvements. While it is appropriate for fuel economy regulations to be 

“technology forcing”, they must also be realistic, in terms of what is achievable and in terms of 

how much regulatory compliance will cost vehicle manufacturers. 

Given the complexity of the HDV fleet – the variety of vehicle types and their duty cycles - 

modeling will likely be required to fully evaluate this issue. Different technologies will have 

significantly different effects depending on the type of vehicle, as well as how it is used. 

Different technologies can not necessarily be viewed in isolation either, as there may be complex 

interactions that increase effectiveness in one type of application but not another. Modeling of 

multiple scenarios will provide an understanding of the envelope of potential improvements, the 

sensitivity of the results to various factors, and the relative ease of achieving various levels of 

improvement for different types of HDVs.

The modeling should include a realistic assessment of the time frame and cost for development 

and implementation of the modeled technologies, taking into account purchase costs, 

incremental maintenance costs, and resultant fuel cost savings. A joint project by the Northeast 

States for Clean Air Future and the ICCT to be completed in early 2009 has been exploring these 

questions for Class 8 trucks. The modeling performed by the Southwest Research Institute and 

the cost analysis by TIAX will provide an estimate of the potential fuel use and emission 

reduction offered by a range of technology packages and their associated cost effectiveness.

10.2 HDV Fleet & Industry Characteristics

While much is known about the composition and characteristics of the existing U.S. HDV fleet 

and the HDV manufacturing industry, important gaps exist in the data which is publicly 

available. More information is required about the following issues:

 Segmentation of the existing HDV truck fleet by vehicle type and weight class, including 

better information on the number of in-use vocational trucks of different types.

 Segmentation of the existing commercial trailer fleet (combination trucks) by length and 

configuration.

 Data on manufacturer and model market share for different types of trucks.

 Data on manufacturer and model market share for different types of commercial trailers
Key Research Areas and Recommendations

60

 Ownership patterns for different types of trucks, including what percentage of each truck 

type is owned and operated by fleets of various sizes

 Typical duty cycle(s) for various types of HDV, including combination trucks and 

vocational trucks. Duty cycle information should include speed versus time, as well as 

change in grade versus time, and engine accessory load/PTO load versus time.

 In-use fuel economy for all models of current HDV in a range of duty cycles.

10.3 Test Cycle(s) & Methodology

For ease of implementation there will be a strong desire to minimize the number of test cycles 

required for any HDV fuel economy regulation. On the other hand, the over-all regulatory 

regime must be robust (and complex) enough to handle the real world complexity of the HDV 

fleet and produce meaningful results. Ideally, regulatory HDV fuel economy testing should:

 accurately predict real-world differences in fuel economy due to the application of 

different technologies to different types of HDVs

 be insensitive to “gaming” by vehicle manufacturers, and

 provide consumers (truck owners) with relevant information to guide their purchasing 

decisions for different types of HDVs

The issue of the number and complexity of required test cycles for regulatory HDV fuel economy 

testing needs to be further explored, through modeling and/or analysis of existing test data. 

The issues that need to be addressed in this analysis include: 

 The relative effect of different technologies (i.e. engine improvements, aerodynamic 

improvements, hybrid drive train, etc) on fuel use when an HDV operates on different 

duty cycles

 The relative effect of duty cycle on fuel use for different HDV types (size and vocation).

 The ability to effectively “model” multiple in-use duty cycles for a particular HDV by 

different weightings of results from a limited set of test cycles

 The ability to effectively “model” real world fuel use from different types of HDVs by 

different weightings of results from one set of test cycles used for all vehicle types.

 The most important factor(s) in the duty cycle of different HDVs in determining fuel use 

(i.e. speed vs. topography vs. vocational load, etc.)

 The potential for “gaming” by a vehicle manufacturer on any specific test cycle.

 The specific questions that should be answered by the analysis include:

 How important is it to have different test cycle(s) for different types of HDVs?

 For any one type of HDV, what is the minimum practical number of test cycles required 

for effective fuel economy testing?

 Can one set of test cycles be used to effectively test the fuel economy of all HDVs? If so, 

what are the trade-offs involved? If not, why not?

 If one set of test cycles can not be used to test the fuel economy of all HDVs, which 

characteristic(s) are most important in determining that a particular type of HDV needs 

its own test cycles (i.e size, weight, vocation)? 
Key Research Areas and Recommendations

61

 Will testing all HDVs using a single set of test cycles provide meaningful data that can be 

used by consumers making buying decisions? How should this data be presented?

In order to reduce compliance costs it is also likely that there will be strong interest in the use of 

modeling to determine regulatory fuel economy compliance for some or all HDVs, either as a 

replacement for actual vehicle testing or in combination with limited vehicle testing. 

There are a number of different vehicle simulation models used by various organizations that 

might be used in a regulatory program to simulate HDV fuel efficiency. In order to evaluate the 

efficacy of modeling in the regulatory context, as well as to determine which specific model 

would be “best” for this purpose, a neutral, third-party review of the various available models 

is required. The specific issues to be addressed in this review for each model include:

 Current users, cost, and computing requirements

 Structure of the model, and required inputs

 Ease of use

 Complexity, and ability to model all parameters that effect HDV fuel use

 Strengths and weaknesses for predicting fuel use for specific vehicles/technologies/duty 

cycles

 Additional testing required to develop appropriate vehicle-specific parameters to be used 

in the model

 Correlation among models and/or calibration of models to measured data

10.4 Choice of Fuel Efficiency Metric

As discussed in Section 7.1, it may be appropriate to regulate the “fuel efficiency” of HDVs not 

in terms of gallons of fuel per mile driven, but rather gallons of fuel per ton-mile or per cubic 

volume-mile driven. These metrics explicitly acknowledge the main function of the majority of 

HDVs (to haul freight) and potentially open up additional avenues for regulatory compliance 

that would make any HDV fuel economy regulation more effective in reducing net fuel use from 

the transportation sector. 

However, ton-mile and cubic volume-mile metrics are unfamiliar, and might be conceptually 

challenging to many people. In order to justify the use of these less familiar metrics, an analysis 

of the potential net benefit of such an approach is required. This scenario analysis would use 

known characteristics of the existing freight system (current HDV vehicle miles traveled 

segmented by average trucks weights and typical volumes) as well as realistic options available 

to increase cargo capacity per truck (weight and volume) to identify the incremental reductions 

in net fuel use that might be available if a ton-mile or cubic volume-mile metric were used 

instead of a gallons/mile metric. 
References

62

References

[2-1] Davis, S. and Diegel, S., U.S. Department of Energy, Energy Efficiency and Renewable 

Energy, Transportation Energy Data Book, Edition 26, 2007, Table 5.7

 [2-2] Davis, S. and Diegel, S., U.S. Department of Energy, Energy Efficiency and Renewable 

Energy, Transportation Energy Data Book, Edition 26, 2007, Table 5.1 and 5.2

[2-3] U.S. Environmental Protection Agency, Inventory of U.S. Greenhouse Gas Emissions and 

Sinks 1990-2006, Table 3-1, EPA430-R-08-005, April 2008. According to this inventory, 

in 2005 total U.S. CO2 emissions from the transportation sector were 1,869.8 teragrams.

[2-4] U.S. Environmental Protection Agency, Procedures for Developing Base Year and Future 

Year Mass and Modeling Initiatives for the Heavy-Duty Engine and Vehicle Standards and 

Highway Diesel Fuel (HDD) Rulemaking, October, 2000.

[2-5] U.S. Environmental Protection Agency, SmartWay Transport Partnership, Partnership 

Overview, EPA 420-F-02-052, February 2004

[2-6] Davis, S. and Diegel, S., U.S. Department of Energy, Energy Efficiency and Renewable 

Energy, Transportation Energy Data Book, Edition 26, 2007, Table 5.4

[2-7] Transport Topics Magazine, Top 100 Private Carriers 2007; Transport Topics Magazine, 

Top 100 For-Hire Fleets 2007

[2-8] U.S. Department of Transportation, Federal Highway Administration, Office of Freight 

Management and Operations, Freight Analysis Framework, Version 2.2, 2007, Table 2-1. 

Weight of Shipments by Mode: 2002, 2006, 2035 (Millions of Tons); the figure of 7% 

intermodal volume excludes shipments by pipeline, and excludes shipments by U.S. 

Postal Service and parcel and courier shippers. According to the 2002 Commodity Flow 

Survey, postal service, parcel, and courier shipments accounted for approximately 20% 

of intermodal volume in 2002 (U.S Department of Transportation, Bureau of 

Transportation Statistics and U.S. Department of Commerce, Census Bureau, 2002 

Commodity Flow Survey: United States, December 2004, table 1a

[2-9] U.S. Census Bureau, 2002 Vehicle Inventory and Use Survey, author’s analysis of 

microdata records

[2-10] Winsor, J., Heavy Trucks Sales on a Roll in ’05, Diesel Progress North American Edition, 

October 2005; based on Polk and Ward’s Automotive data

[2-11] Various sources; compiled based on internet search by the authors.

[3-1] Bynum, C., U.S. Environmental Protection Agency, EPA Heavy Duty Vehicle Emissions 

Program, presentation to ICCT/NESCCAF Workshop: Improving Fuel Economy of 

Heavy Duty Fleets II, February 20, 2008, San Diego, CA

[3-2] Based on author’s experience of emissions testing for urban transit buses

[3-3] U.S. Environmental Protection Agency, Study of Exhaust Emissions from Idling 

Heavy-Duty Diesel Trucks and Commercially Available Idle-Reducing Devices, 

EPA420-R-02-025, October, 2002

[3-4] U.S. Department of Energy, Energy Efficiency & Renewable Energy, Idle Reduction 

Technologies for Heavy Duty Trucks, Technology Introduction Plan, May 13, 2004

[4-1] U.S. Environmental Protection Agency, SmartWay Tractors and Trailers, EPA 420-F-07-

033, March 2007
References

63

[4-2] U.S. Environmental Protection Agency, SmartWay Transport Partnership website, List of 

Partners, updated March 11, 2008, http://www.epa.gov/smartway/partners.htm

[4-3] U.S. Environmental Protection Agency, SmartWay Transport Partnership, Frequently 

Asked Questions, EPA 420-F-02-051, February 2004

 [4-4] U.S. Department of Energy, Energy Efficiency and Renewable Energy, 21st Century Truck 

Partnership, Roadmap and Technical White Papers, 21CTP-0003, December 2006

[4-5] National Research Council of the National Academies. Review of the 21st Century Truck 

Partnership. Washington, D.C., 2008.

[4-6] California Air Resources Board, Public Workshop Presentation, Proposed Greenhouse Gas 

Measures, http://www.arb.ca.gov/msprog/onrdiesel/onrdiesel.htm

[4-7] California Air Resources Board. Climate Change Scoping Plan. October 2008

[4-8] Personal correspondence with F. Diaz, BAE Systems, D. Mikoryak, Allison Electric 

Drives, and M. Hennessy, ISE Corporation.

[4-9] According to the National Transit Database in 2005 there were 42,000 buses operated 

by transit agencies that receive federal funding. U.S. Department of Transportation, 

Federal Transit Administration, National Transit Database, 2005, Table 17

[4-10] Sean Killcar, Heavy-Duty Hybrid, Fleet Owner Magazine online, February 1, 2007.

[4-11] David Cullen, Heavy Hybrids Ahead, Fleet Owner Magazine online, September 14, 2007

[4-12] Paccar, Inc., News Release, Peterbilt, Eaton and Wal-Mart Partner on Hybrid Electric 

Aerodynamic Model 386 Development, March 15, 2007

[4-13] Barnitt, R. and Chandler, K., National Renewable Energy Laboratory, New York City 

Transit (NYCT) Hybrid (125 order) and CNG Transit Buses: Final Evaluation Report, 

Technical Report NREL/TP-540-40125, November 2006

[4-14] Chandler, K and Walkowitcz, K, National Renewable Energy Laboratory, King County 

Metro Transit Hybrid Articulated Buses: Final Evaluation Report, Technical Report 

NREL/TP-540-40585, December 2006

[4-15] Van Amburg, B., WestStart/CALSTART, Users Forum and Policy Innovations: New 

Approaches to Engage Fleets & Industry on Fuel Efficiency, Presentation to 

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[5-1] Advisory Committee for Natural Resources and Energy (METI) and Council for 

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Operating Weight Group (milions). The data in this table is based on operating weight 
References

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data contained in the U.S. Census Bureau, 1992 Truck Inventory and use Survey. The 

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(vehicle class CS5T and CS5S).

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Motor Vehicles: Revisions to Improve Calculation of Fuel Economy Estimates, Final Rule, 

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[7-4] SAE, SAE Surface Vehicle Recommended Practice, Recommended Practice for Measuring 

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[7-5] Argonne National Laboratory, website, Transportation Technology R&D Center, 

Software, PSAT (Powertrain System Analysis Toolkit), 

www.transportation.anl.gov/software/PSAT/index.html, accessed 4/4/08

[7-6] Clark, N., et al, Diesel emissions prediction from dissimilar cycle scaling, Proceedings of the 

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[7-7] U.S. Environmental Protection Agency, SmartWay Fuel Efficiency Test Protocol for Medium 

and Heavy Duty Vehicles, Working Draft, EPA420-P-07-003, November 2007.

[7-8] U.S. Environmental Protection Agency, EPA’s Fuel Economy and Emissions Programs, 

EPA420-F-04-053, October 2004

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Federal Register, Vol. 71, No. 248, December 27, 2006

[7-9] Code of Federal Regulations, Title 40, Part 92 – Control of Air Pollution from 

Locomotives and Locomotive Engines 

[7-10] National Highway Traffic Safety Administration, website, CAFE Overview – Frequently 

Asked Questions, www. nhtsa.dot.gov/cars/rules/cafe/overview.htm, accessed 4/4/08

[7-11] U.S. Environmental Protection Agency, Environmental Fact Sheet, Non-Conformance 

Penalties for Heavy-Duty Diesel Engines, EPA420-F-01-034, December 2001

[8-1] U.S. Census Bureau, 2002 Vehicle Inventory and Use Survey, author’s analysis of 

microdata records.

[8-2] Davis, S. and Diegel, S., U.S. Department of Energy, Energy Efficiency and Renewable 

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VIUS
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[9-1] Matthews, H., J.B. Hunt’s Sustainablility Efforts, Presentation to ICCT/NESCCAF 

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20, 2008.

[9-2] U.S. Department of Transportation, Federal Highway Administration, Office of Freight 

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shipments by pipeline; intermodal shipments include shipments by the U.S. Postal 

Service and parcel and courier shippers. 

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II Issues and Background, FHWA-PL-00-029(Volume II), August 2000

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[9-5] U.S. Environmental Protection Agency, SmartWaySM Transport Partnership, A glance at 

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