United States

Environmental Protection

Agency

Air and Radiation EPA420-R-00-010

July 2000

Regulatory Impact Analysis:

Control of Emissions of Air

Pollution from Highway

Heavy-Duty Engines

 Printed on Recycled Paper
EPA420-R-00-010

July 2000

Regulatory Impact Analysis:

Control of Emissions of Air Pollution from

Highway Heavy-Duty Engines

Assessment and Standards Division

Office of Transportation and Air Quality

U.S. Environmental Protection Agency
Table of Contents

CHAPTER 1: INTRODUCTION ................................................1

I. Summary of the Regulatory Impact Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

A. Chapter 2—Health and Welfare Concerns . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

B. Chapter 3—Technological Feasibility of HD Diesel and Otto-cycle Standards

..........................................................1

C. Chapter 4—Economic Impact of HD Diesel Standards . . . . . . . . . . . . . . . . . . 1

D. Chapter 5—Economic Impact of HD Otto-cycle Standards . . . . . . . . . . . . . . 1

E. Chapter 6—Environmental Impact of HD Diesel Standard . . . . . . . . . . . . . . . 2

F. Chapter 7—Environmental Impact of HD Otto-cycle Standards . . . . . . . . . . . 2

G. Chapter 8—Cost-effectiveness for HD Diesel and Otto-cycle Requirements

..........................................................2

CHAPTER 2: HEALTH AND WELFARE CONCERNS ..............................3

I. Health and Welfare Concerns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

A. Health and Welfare Effects from NMHC and NOx . . . . . . . . . . . . . . . . . . . . . 3

B. Particulate Matter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

II. Need for Ozone Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

A. Standards for 2004 HD Diesels Are a Key Part of State Air Pollution Control

Plans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

B. New Standards for 2005 HD Gasoline Engines and Vehicles Are Important for

States in Meeting Their Air Quality Goals ........................7

C. HD Diesel and Gasoline Engines Contribute to Total NOx and VOC

Emissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

III. Particulate Matter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

A. Current and Future Compliance with the PM10 NAAQS . . . . . . . . . . . . . . . . 15

B. HD Diesel and Gasoline Engines Contribute to Secondary

Formation of Particulate Matter . . . . . . . . . . . . . . . . . . . . . . . . . . 18

IV. Air Toxics from HD Engines and Vehicles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Chapter 2 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

CHAPTER 3: TECHNOLOGICAL FEASIBILITY OF HD DIESEL AND OTTO-CYCLE

STANDARDS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

I. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

II. Diesel Engine Technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

A. HD Diesel Technology Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

B. Exhaust Gas Re-circulation (EGR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

C. Fuel Injection Rate-shaping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

D. Exhaust After-treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

E. Diesel Fuel Composition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
F. Performance of Projected Emission Control Technologies over Typical In-Use

Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

G. Summary and Conclusions regarding HD Diesel Technologies . . . . . . . . . . 45

III. HD Otto-cycle Engine & Vehicle Technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

A. Base Engine Improvements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

B. Improvements in Fuel Atomization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

C. Improvements to Exhaust Aftertreatment Systems . . . . . . . . . . . . . . . . . . . . 54

D. Improvements in Engine Calibration Techniques . . . . . . . . . . . . . . . . . . . . . 57

E. Advanced Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

F. Technologies In-use On Current Otto-cycle HD Engines . . . . . . . . . . . . . . . . 59

G. Chassis-based standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62

H. Engine-based Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

IV. On-board Diagnostics for HD Diesel and Otto-cycle Engines . . . . . . . . . . . . . . . . . 66

Chapter 3 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69

CHAPTER 4: ECONOMIC IMPACT OF HD DIESEL STANDARDS . . . . . . . . . . . . . . . . . 76

I. Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76

II. Technologies for Meeting the New Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

A. Primary Technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80

B. Operating Costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84

C. Secondary Technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85

III. Summary of Costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86

IV. Aggregate Costs to Society . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87

Chapter 4 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91

CHAPTER 5: ECONOMIC IMPACTS OF HD OTTO-CYCLE STANDARDS . . . . . . . . . . . 93

I. Methodology for Estimating Costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93

II. Technology Packages for Compliance with the Regulations . . . . . . . . . . . . . . . . . . . 93

III. Technology Costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96

A. Improved Catalysts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96

B. Exhaust Gas Recirculation (EGR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102

C. Secondary Air Injection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102

D. On-board Diagnostics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103

E. Exhaust Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104

F. Electronic Control Module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105

G. Onboard Refueling Vapor Recovery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105

IV. Fixed Costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106

A. R&D and Tooling Costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106

B. Certification Costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106

C. In-use Testing Costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106

V. Summary of Costs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106

VI. Aggregate Cost to Society . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107

Chapter 5 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
CHAPTER 6: ENVIRONMENTAL IMPACT OF

HD DIESEL STANDARDS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110

I. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110

II. Description of Calculation Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111

A. General Equation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111

B. Conversion Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112

C. Vehicle Miles Traveled . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112

III. Total Nationwide Inventories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116

A. Current Inventories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117

B. NOx Emission Projections and Impacts . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117

C. NMHC Emission Projections and Impacts . . . . . . . . . . . . . . . . . . . . . . . . . . 120

IV. Per Vehicle Emission Impacts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121

V. Environmental Impacts of Emission Reductions . . . . . . . . . . . . . . . . . . . . . . . . . . . 122

A. Ozone Impacts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122

B. Air Toxics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122

C. Other Impacts of Emission Reductions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123

VI. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123

CHAPTER 7: ENVIRONMENTAL IMPACT OF THE HD OTTO-CYCLE STANDARDS 

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127

I. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127

II. Exhaust NOx and NMHC Emission Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127

A. Baseline Emission Rates (Zero-Mile Levels and Deterioration Rates) . . . . 127

B. Conversion Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128

C. Control Emission Rates (Zero-Mile Levels and Deterioration Rates) . . . . . 128

D. Emission Rate Adjustments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129

III. Per-Vehicle Exhaust NOx and NMHC Emission Reductions . . . . . . . . . . . . . . . . 130

A. Per Vehicle Emission Rates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130

B. Mileage Accumulation and Scrappage Rates . . . . . . . . . . . . . . . . . . . . . . . . 131

C. Per-vehicle Lifetime Emissions and Emission Reductions . . . . . . . . . . . . . 133

IV. HDGV Exhaust Inventory and Reductions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134

V. ORVR Benefits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137

Chapter 7 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139

CHAPTER 8: COST-EFFECTIVENESS FOR HD DIESEL AND OTTO-CYCLE

REQUIREMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140

I. Cost-Effectiveness of the Diesel Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140

II. Cost-Effectiveness of the Otto-cycle Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 143

A. Exhaust Emission Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143

B. Refueling Emission Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145

III. Other Benefits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147

IV. Cost-Effectiveness Sensitivity Analyses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147

V. Comparison of Cost-Effectiveness with Other Mobile Source NOx Control Strategies

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149
Chapter 8 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151

APPENDIX A

ANNUALIZED COST EFFECTIVENESS ANALYSIS . . . . . . . . . . . . . . . . . . . . . . A-1
Chapter 1: Introduction

CHAPTER 1: INTRODUCTION

The Regulatory Impact Analysis (RIA) for this rule presents analysis and supporting data for

the provisions EPA is reviewing or promulgating for model year 2004 and later on-highway heavyduty diesel and otto-cycle engines and vehicles. This chapter presents a brief summary of each

chapter contained in the (RIA) that follows.

I. Summary of the Regulatory Impact Analysis

A. Chapter 2—Health and Welfare Concerns

Chapter 2 provides an overview of the health and environmental effects associated with

ozone, particulate matter, and other harmful pollution associated with emissions from heavy-duty

engines and vehicles. Chapter 2 reviews some of EPA’s key concerns at this time. The chapter also

provides national NOx and VOC emissions inventories and emissions trends, with specific emphasis

on the contribution from on-highway heavy-duty diesel and otto-cycle vehicles.

B. Chapter 3—Technological Feasibility of HD Diesel and Otto-cycle

Standards

To achieve the standards reviewed or promulgated in this rule, heavy-duty engine

manufacturers will need to consider a combination of new and existing emission control devices.

Chapter 3 presents the technologies available and discusses their ability to reach the required

emission levels. Chapter 3 is divided into two major sub-chapters, the first dealing with HD diesel

technologies, and the second with HD otto-cycle technologies. 

C. Chapter 4—Economic Impact of HD Diesel Standards

Chapter 4 presents EPA’s best assessment of the economic impacts which will result from

the HD diesel standards. The assessment includes EPA’s estimates of the technology packages

manufactures will use, as well as the costs associated with new certification and compliance

requirements. Costs are estimated on a per-vehicle basis, as well as an aggregate cost to society.

Chapter 4 also includes an analysis which indicates how sensitive the cost assessment is to some of

EPA’s best estimates.

D. Chapter 5—Economic Impact of HD Otto-cycle Standards

Chapter 5 presents EPA’s best assessment of the economic impacts which will result from

the HD otto-cycle engine and vehicle standards. The assessment includes EPA’s estimates of the

technology packages manufactures will use, as well as the costs associated with new certification

and compliance requirements. Costs are estimated on a per-vehicle basis, as well as an aggregate

cost to society. 
Regulatory Impact Analysis 

2

E. Chapter 6—Environmental Impact of HD Diesel Standards

Chapter 6 describes the expected environmental impacts of the HD diesel engine NMHC plus

NOx emissions standards described in the preamble for this rule. The modeling methodology and

assumptions used to estimate nationwide NOx and VOC emission inventories (i.e., tons of pollutant

per year) are described, and the estimated benefits are presented. In addition, estimates of

nationwide PM inventories for HD diesel vehicles are presented.

F. Chapter 7—Environmental Impact of HD Otto-cycle Standards

Chapter 7 describes the expected environmental impacts of the exhaust and ORVR standards

for heavy-duty gasoline engines and vehicles described in the previous chapters. Specifically, the

chapter includes a description of how heavy-duty gasoline vehicle emission factors were developed,

the per-vehicle exhaust emission reductions due to the standards over the life of heavy-duty gasoline

vehicles, the estimated exhaust NOx and NMHC emission inventories from heavy-duty gasoline

vehicles, and the exhaust emission benefits from the exhaust standards. The chapter also includes

a description of the emission benefits from the ORVR requirements for Class 2b heavy-duty gasoline

vehicles.

G. Chapter 8—Cost-effectiveness for HD Diesel and Otto-cycle Requirements

Chapter 8 presents EPA’s estimated cost-effectiveness of the requirements for new heavyduty engines, including the new standards and related requirements, OBD, useful life, allowable

maintenance, in-use testing, and rebuild provisions. This analysis relies in part on cost information

from Chapters 4 and 5 and emissions information from Chapters 6 and 7 to estimate the costeffectiveness of the provisions in terms of dollars per ton of total emission reductions. Separate

analyses were performed for otto-cycle engines and diesel engines. Cost-effectiveness values are

presented on a per-vehicle basis using total costs and total NOx plus NMHC emission reductions

over the typical lifetime of a heavy-duty vehicle, discounted at a rate of seven percent to the

beginning of the vehicle's life. Analyses of the fleet cost-effectiveness for 30 model years after the

new engine standards take effect are also presented.
Chapter 2: Health and Welfare Concerns

(a) Carbon monoxide also participates in the production of ozone, albeit at a much slower rate than most VOC

and NOx compounds.

3

CHAPTER 2: HEALTH AND WELFARE CONCERNS

I. Health and Welfare Concerns

A. Health and Welfare Effects from NMHC and NOx

Ground-level ozone, the main ingredient in smog, is formed by complex chemical reactions

of volatile organic compounds (VOC) and nitrogen oxides (NOx) in the presence of heat and

sunlight. Ozone forms readily in the lower atmosphere, usually during hot summer weather. VOCs

are emitted from a variety of sources, including motor vehicles, chemical plants, refineries, factories,

consumer and commercial products, and other industrial sources. VOCs also are emitted by natural

sources such as vegetation. NOx is emitted largely from motor vehicles, nonroad equipment, power

plants, and other sources of combustion. 

The science of ozone formation, transport, and accumulation is complex. Ground-level

ozone is produced and destroyed in a cyclical set of chemical reactions involving NOx, VOC, heat,

and sunlight.a

 As a result, differences in NOx and VOC emissions and weather patterns contribute

to daily, seasonal, and yearly differences in ozone concentrations and differences from city to city.

Many of the chemical reactions that are part of the ozone-forming cycle are sensitive to temperature

and sunlight. When ambient temperatures and sunlight levels remain high for several days and the

air is relatively stagnant, ozone and its precursors can build up and produce more ozone than

typically would occur on a single high temperature day. Further complicating matters, ozone also

can be transported into an area from pollution sources found hundreds of miles upwind, resulting in

elevated ozone levels even in areas with low VOC or NOx emissions.

Based on a large number of recent studies, EPA has identified several key health effects

caused when people are exposed to levels of ozone found today in many areas of the country.1, 2

Unless noted otherwise, the studies discussed in the remainder of sections I(A) and I(B) of this

Chapter are from references (1) and (2), EPA Report EPA-452/R-96-007 and EPA Report

EPA/600/P-93/004aF respectively. Short-term exposures (1-3 hours) to high ambient ozone

concentrations have been linked to increased hospital admissions and emergency room visits for

respiratory problems. For example, studies conducted in the northeastern U.S. and Canada show that

ozone air pollution is associated with 10-20 percent of all of the summertime respiratory-related

hospital admissions. Repeated exposure to ozone can make people more susceptible to respiratory

infection and lung inflammation and can aggravate preexisting respiratory diseases, such as asthma.

Exposure to ozone can cause repeated inflammation of the lung, impairment of lung defense

mechanisms, and irreversible changes in lung structure, which could lead to premature aging of the
Regulatory Impact Analysis 

4

lungs and/or chronic respiratory illnesses such as emphysema, chronic bronchitis and chronic

asthma. 

Children are most at risk from ozone exposure because they typically are active outside,

playing and exercising, during the summer when ozone levels are highest. For example, summer

camp studies in the eastern U.S. and southeastern Canada have reported significant reductions in

lung function in children who are active outdoors. Further, children are more at risk than adults from

ozone exposure because their respiratory systems are still developing. Adults who are outdoors and

moderately active during the summer months, such as construction workers and other outdoor

workers, also are among those most at risk. These individuals, as well as people with respiratory

illnesses such as asthma, especially asthmatic children, can experience reduced lung function and

increased respiratory symptoms, such as chest pain and cough, when exposed to ozone during

periods of moderate exertion. 

Evidence also exists of a possible relationship between daily increases in ozone levels and

increases in daily mortality levels. While the magnitude of this relationship is still too uncertain to

allow for direct quantification, the full body of evidence indicates a likely positive relationship

between ozone exposure and premature mortality.

In addition to the effects on human health, ozone is known to adversely affect the

environment in many ways. These effects include reduced yield for commodity crops, for fruits and

vegetables, and commercial forests; ecosystem and vegetation effects in such areas as National Parks

(Class I areas); damage to urban grass, flowers, shrubs, and trees; reduced yield in tree seedlings and

non-commercial forests; increased susceptibility of plants to pests; materials damage; and visibility.

Nitrogen oxides (NOx), a key precursor to ozone, also results in nitrogen deposition into sensitive

nitrogen-saturated coastal estuaries and ecosystems, causing increased growth of algae and other

plants.3

 NOx also is a contributor to acid deposition, which can damage trees at high elevations and

increases the acidity of lakes and streams, which can severely damage aquatic life. Finally, NOx

emissions can contribute to increased levels of particulate matter by changing into nitric acid in the

atmosphere and forming particulate nitrate.

In addition to their contribution to ozone levels, emissions of NMHC contain toxic air

pollutants that may have a significant effect on the public health, as discussed below. 

B. Particulate Matter

Particulate matter (PM) represents a broad class of chemically and physically diverse

substances that exist as discrete particles (liquid droplets or solids) over a wide range of sizes.

Human-generated sources of particles include a variety of stationary and mobile sources. Particles

may be emitted directly to the atmosphere or may be formed by transformations of gaseous emissions

such as sulfur dioxide or nitrogen oxides. The major chemical and physical properties of PM vary

greatly with time, region, meteorology, and source category, thus complicating the assessment of

health and welfare effects as related to various indicators of particulate pollution. At elevated
Chapter 2: Health and Welfare Concerns

5

concentrations, particulate matter can adversely affect human health, visibility, and materials.

Components of particulate matter (e.g., sulfuric or nitric acid) contribute to acid deposition.4

Key EPA findings can be summarized as follows:

1. Health risks posed by inhaled particles are affected both by the penetration and deposition

of particles in the various regions of the respiratory tract, and by the biological responses to

these deposited materials.

2. The risks of adverse effects associated with deposition of ambient particles in the thorax

(tracheobronchial and alveolar regions of the respiratory tract) are markedly greater than for

deposition in the extrathoracic (head) region. Maximum particle penetration to the thoracic

regions occurs during oronasal or mouth breathing.

3. The key health effects categories associated with PM include premature death; aggravation

of respiratory and cardiovascular disease, as indicated by increased hospital admissions and

emergency room visits, school absences, work loss days, and restricted activity days; changes

in lung function and increased respiratory symptoms; changes to lung tissues and structure;

and altered respiratory defense mechanisms. Most of these effects have been consistently

associated with ambient PM concentrations, which have been used as a measure of

population exposure, in a large number of community epidemiological studies. Additional

information and insights on these effects are provided by studies of animal toxicology and

controlled human exposures to various constituents of PM conducted at higher than ambient

concentrations. Although mechanisms by which particles cause effects are not well known,

there is general agreement that the cardio-respiratory system is the major target of PM

effects.

4. Based on a qualitative assessment of the epidemiological evidence of effects associated with

PM for populations that appear to be at greatest risk with respect to particular health

endpoints, the EPA has concluded the following with respect to sensitive populations:

a. Individuals with respiratory disease (e.g., chronic obstructive pulmonary disease,

acute bronchitis) and cardiovascular disease (e.g., ischemic heart disease) are at

greater risk of premature mortality and hospitalization due to exposure to ambient

PM.

b. Individuals with infectious respiratory disease (e.g., pneumonia) are at greater risk

of premature mortality and morbidity (e.g., hospitalization, aggravation of respiratory

symptoms) due to exposure to ambient PM. Also, exposure to PM may increase

individuals’ susceptibility to respiratory infections.

c. Elderly individuals are also at greater risk of premature mortality and hospitalization

for cardiopulmonary problems due to exposure to ambient PM.
Regulatory Impact Analysis 

6

d. Children are at greater risk of increased respiratory symptoms and decreased lung

function due to exposure to ambient PM.

e. Asthmatic individuals are at risk of exacerbation of symptoms associated with

asthma, and increased need for medical attention, due to exposure to PM.

5. There are fundamental physical and chemical differences between fine and coarse fraction

particles and it is reasonable to expect that differences may exist between the two subclasses

of PM10 in both the nature of potential effects and the relative concentrations required to

produce such effects. The specific components of PM that could be of concern to health

include components typically within the fine fraction (e.g., acid aerosols, sulfates, nitrates,

transition metals, diesel particles, and ultra fine particles), and other components typically

within the coarse fraction (e.g., silica and resuspended dust). While components of both

fractions can produce health effects, in general, the fine fraction appears to contain more of

the reactive substances potentially linked to the kinds of effects observed in the

epidemiological studies. The fine fraction also contains the largest number of particles and

a much larger aggregate surface area than the coarse fraction which enables the fine fraction

to have a substantially greater potential for absorption and deposition in the thoracic region,

as well as for dissolution or absorption of pollutant gases.

With respect to welfare or secondary effects, fine particles have been clearly associated with

the impairment of visibility over urban areas and large multi-state regions. Fine particles, or major

constituents thereof, also are implicated in materials damage, soiling and acid deposition. Coarse

fraction particles contribute to soiling and materials damage.

Particulate pollution is a problem affecting localities, both urban and non-urban, in all regions

of the United States. Manmade emissions that contribute to airborne particulate matter result

principally from stationary point sources (fuel combustion and industrial processes), industrial

process fugitive particulate emission sources, non-industrial fugitive sources (roadway dust from

paved and unpaved roads, wind erosion from crop land, etc.), and transportation sources. In addition

to manmade emissions, consideration must also be given to natural emissions including dust, sea

spray, volcanic emissions, biogenic emanation (e.g., pollen from plants), and emissions from wild

fires when assessing particulate pollution and devising control strategies.

II. Need for Ozone Control

A. Standards for 2004 HD Diesels Are a Key Part of State Air Pollution Control

Plans

Since we published the final rule establishing the 2004 HD diesel emission standards in 1997,

those states with State Implementation Plans (SIPs) have considered the projected emission

reductions from these engines to be an important component of their overall SIPs. The NOx and

NMHC nationwide emission reductions that will result from these standards beginning in the 2004

model year will help states to attain the ozone NAAQS. These states have incorporated the
Chapter 2: Health and Welfare Concerns

7

beneficial effects of the 2004 HD diesel standards into their air quality modeling and they continue

to count on the emission reductions from this program to meet their air quality goals. 

B. New Standards for 2005 HD Gasoline Engines and Vehicles Are Important

for States in Meeting Their Air Quality Goals

 Today, many states are finding it difficult to show how they can meet or maintain

compliance with the current National Ambient Air Quality Standard (NAAQS) for ozone by the

deadlines established in the Clean Air Act. In December, 1999, 92 million people (1990 population)

lived in 32 metropolitan areas designated nonattainment under the 1-hour ozone NAAQS.5

There is a very clear risk that there will be elevated levels of ground-level ozone above the

1-hour NAAQS during the time period when the heavy-duty gasoline vehicle standards of this

rulemaking will take effect. The reductions in oxides of nitrogen (NOx) and volatile organic

compounds (VOCs) projected from the proposed new standards will benefit public health and

welfare by reducing ozone levels. This assessment is based upon our recent and extensive ozone air

quality modeling and analysis performed for the Tier 2/Gasoline Sulfur rulemaking, which predicts

that a significant number of areas across the nation are at risk of failing to meet the 1-hour ozone

NAAQS even with Tier 2 and other controls currently in place. Because ozone concentrations

causing violations of the 1-hour ozone standard are well established to endanger public health and

welfare, we conclude that today’s new standards for 2005 and later gasoline heavy-duty vehicles are

warranted.

1. Projected Air Quality Problems Remain After Tier 2/Gasoline Sulfur

Program Is in Place

In conjunction with our Tier 2/Gasoline Sulfur rulemaking efforts, we performed ozone air

quality modeling for nearly the entire eastern U.S. covering metropolitan areas from Texas to the

Northeast, and for a western U.S. modeling domain. As a part of this modeling, we considered the

air quality of these areas after the Tier 2/Gasoline Sulfur program is implemented. This modeling

predicted that without further emission reductions, a significant number of areas now experiencing

ozone exceedances across the nation are at risk of failing to meet the 1-hour ozone NAAQS in 2004

and beyond, even with the Tier 2/Gasoline Sulfur program and other current controls in place.

The general pattern that the ozone modeling shows is a broad reduction between 1996 and

2007 in the geographic extent of ozone concentrations above the 1-hour NAAQS, and in the

frequency and severity of exceedances. In the absence of additional controls beyond those that will

be achieved by current control programs -- including the Tier 2/Gasoline Sulfur program -- we

expect there will be a slight decrease below 2007 ozone concentrations and frequencies of

exceedances in 2030. However, the general trends and modeling results show that many of the areas

we modeled may have exceedances continuously throughout the period from 2007 to 2030 without

further reductions in emissions. Others may briefly attain and then return to nonattainment by 2030

or earlier. Although for practical reasons we limited our modeling of ozone concentrations to 1996,

2007, and 2030, we expect that concentrations between 2007 and 2030 will generally track the
Regulatory Impact Analysis 

(b) Air quality modeling shows that improvements in ozone levels can be expected to occur throughout the country

because of the Tier 2/Gasoline Sulfur program. EPA found that the program significantly lowers the modelpredicted number of exceedances of the ozone standard by one tenth in 2007, and by almost one-third in 2030 (Tier

2/Gasoline Sulfur Final RIA, Docket A-97-10, Document Number V-B-1). 

8

national emissions trend, showing a period of improvement after 2007 followed by a reversal of the

trend and deterioration back towards the 2007 levels. Because individual areas’ emissions trends

differ, we expect that the air quality of individual areas will also vary from this general pattern.

We believe that there is a risk that future air quality in each of these areas would exceed the

ozone standard during the time period when this rule will take effect. This belief is based on three

factors: (1) recent exceedances in 1995-1997 or 1996-1998, (2) predicted exceedances in 2007 or

2030 after accounting for reductions from Tier 2 and other local or regional controls currently in

place or required, and (3) our assessment of the magnitude of recent exceedances, the variability of

meteorological conditions, transport from areas with later attainment dates, and other variables

involved in predicting future attainment such as the potential for some areas to experience

unexpectedly high economic growth rates, growth in vehicle miles traveled, varying population

growth from area to area, and differences in vehicle choice.

Based on the Tier 2 modeling analyses and information from recently-submitted SIPs, we

have determined that over 71 million people (1996 population) in 21 metropolitan areas are likely

to be exposed to unhealthy levels of ground level ozone at some point in time between 2004 and

2030 without significant additional controls. These 21 areas are those that currently violate the 1-

hour ozone NAAQS and are predicted by the best ozone modeling we have available to exceed the

1-hour ozone standard without significant new controls. This analysis accounts for the expected

benefits from the Tier 2 program and other control programs already in place.b

 It does not include

additional control measures that states would need to implement to meet their requirements under

the recently proposed SIP findings. Table 2.1 lists these 21 areas.
Chapter 2: Health and Welfare Concerns

9

Table 2.1

Twenty-one Metropolitan Areas Likely to Exceed the 1-Hour Ozone NAAQS in 2004 or

Thereafter Without Additional Emission Reductions

Metropolitan Area 

1996

Population

(millions)

Baltimore-Hagerstown, MD PSMA 2.6

Barnstable-Yarmouth, MA MSAa 0.2

Baton Rouge, LA MSA 0.6

Beaumont-Port Arthur, TX MSA 0.4

Birmingham, AL MSA 0.9

Boston-Worcester-Lawrence, MA-NH-ME-CT CMSAa 5.6

Charlotte-Gastonia-Rock Hill, NC-SC MSAa 1.3

Dallas-Fort Worth, TX CMSA 4.6

Houma, LA MSAa 0.2

Houston-Galveston-Brazoria, TX CMSA 4.3

Huntington-Ashland, WV-KY-OH MSAa 0.3

Indianapolis, IN MSAa 1.5

Los Angeles-Riverside-San Bernardino CA CMSA 15.5

Louisville, KY-IN MSA 1.0

Memphis, TN-AR-MS MSAa 1.1

Nashville, TN MSAa 1.1

New York-Northern New Jersey-Long Island, NY-NJ-CT-PA CMSA 19.9

Philadelphia-Wilmington-Atlantic City, PA-NJ-DE-MD CMSA 6.0

Providence-Fall River-Warwick, RI-MA MSAa 1.1

Richmond-Petersburg, VA MSAa 0.9

St. Louis, MO-IL MSA 2.5

TOTAL POPULATION 71.5

a. The 1-hour ozone NAAQS does not currently apply, but we have proposed to re-instate it.

There are 14 additional metropolitan areas, with another 35 million people in 1996, for which

the available ozone modeling and other evidence is less clear regarding the need for additional

reductions. Table 2.2 lists the areas we put in this second category. Our own ozone modeling

predicted these 14 areas to need further reductions to avoid exceedences during the period when the

standards are effective. 
Regulatory Impact Analysis 

(c) Atlanta, Benton Harbor, Chicago, Cincinnati, Grand Rapids, Greater Connecticut, Milwaukee, and Washington,

DC. (The Cincinnati-Hamilton area did not have exceedances in the 1996-1998 period).

(d) Biloxi, Cleveland, Detroit, New Orleans, Pensacola, and Tampa.

10

Table 2.2

Fourteen Metropolitan Areas With Some Risk of Exceeding the 1-Hour Ozone Standard in

2004 or Thereafter Without Additional Emission Reductions. 

Metropolitan Area 1996 Population

(millions)

Atlanta, GA MSA 3.5

Benton Harbor, MI MSAa 0.2

Biloxi-Gulfport-Pascagoula, MS MSAa 0.3

Chicago-Gary-Kenosha, IL-IN-WI CMSA 8.6

Cincinnati-Hamilton, OH-KY-IN CMSAc 1.9

Cleveland-Akron, OH CMSAa 2.9

Detroit-Ann Arbor-Flint, MI CMSAa 5.3

Grand Rapids-Muskegon-Holland, MI MSAa 1.0

Greater Connecticut, CT-RI CMSAb 2.4

Milwaukee-Racine, WI CMSA 1.6

New Orleans, LA MSAa 0.3

Pensacola, FL MSAa 0.4

Tampa, FL MSAa 2.2

Washington, DC MSA 4.6

TOTAL POPULATION 35.3

a. The 1-hour ozone NAAQS does not currently apply, but we have proposed to re-instate it.

b. For the New London-Norwich portions of this area, the 1-hour ozone NAAQS does not currently apply, but we have

proposed to re-instate it.

c. Based on more recent air quality monitoring data not considered in the Tier 2 analysis, and on ten year emissions

projections, we expect to re-designate Cincinnati-Hamilton to attainment soon.

For all of these areas, recent air quality monitoring data indicate that exceedances may occur

in 2007 or 2030. Eight areas have recent exceedances, but local ozone modeling and other evidence

indicates attainment in 2007.c

 Based on this evidence, we have kept these areas separate from the

previous set of 21 areas. However, we still consider there to be some risk of future exceedances for

these eight areas.

For the other six of the 14 areas,d the air quality monitoring data shows current attainment

but with less than a 10 percent margin below the NAAQS. This suggests that these areas may remain

without exceedances for some time, but that there is still a risk of future exceedance of the NAAQS

due, for example, to meteorological conditions that may be more severe in the future.
Chapter 2: Health and Welfare Concerns

11

 

There is significant risk that at least some of these 35 areas will violate the NAAQS in 2004

or thereafter without additional reductions. We consider the situation in these areas to support our

belief that, overall, additional reductions are needed. 

2. Today’s Program Will Help Areas Meet Their Attainment and

Maintenance Requirements

The HD gasoline vehicle standards finalized today, and the HD diesel standards reviewed

today, will help all of the areas discussed above to either meet their attainment deadlines, to maintain

attainment in the future, or both. The new program will be very important to each of the areas with

deadlines in 2005 and later that will require (or may require) additional emission reductions (2005

is the year that new gasoline HD vehicles will begin to enter the fleet). As Table 2.3 shows, there

are 10 such areas with almost 66 million people. The following table lists these areas and their

expected attainment dates:
Regulatory Impact Analysis 

12

Table 2.3

Areas with 2005, 2007, or 2010 Attainment Deadlines

Metropolitan Area Attainment

Deadline

Modeling

Predictions

Population

Baltimore 2005 VOC Shortfall 2.6

Philadelphia 2005 NOx and VOC

Shortfall

6.0

Greater Connecticut

(Hartford and other

MSAs)

2007 (requested

extension)

Contingent on New

York Attainment

2.4

New York City, NYNJ-CT2007 VOC and NOx

Shortfall

19.9

Houston, TX 2007 NOx Shortfall 4.3

Chicago, IL-IN 2007 Regional modeling to

analyze existence of

shortfall is underway 

8.6

Milwaukee, WI 2007 Regional modeling to

analyze existence of

shortfall is underway 

1.6

Dallas, TX 2007 (requested

extension)

Local modeling

shows nonattainment

in 2007

4.6

Beaumont-Port

Arthur, TX

2007 (requested

extension)

Local modeling

shows nonattainment

in 2007

0.4

Los Angeles (South

Coast Air Basin), CA

2010 Approved SIP with

commitments for

unspecified 

additional controls

15.5

65.9

All of the areas in Table 2.3 with 2005 or later attainment deadlines will be able to take credit

in their attainment demonstrations (or in revisions to their demonstrations) for the expected

reductions for the preexisting standards for HD diesel engines and for today’s new standards for HD

gasoline engines and vehicles. (EPA has not approved deadline extensions for Dallas and
Chapter 2: Health and Welfare Concerns

13

Beaumont/Port Arthur at this time; if their requested extensions (to 2007) are approved, these areas,

too, could take credit for today’s program). The ability to take credit for the new HD gasoline

vehicle standards will be especially important for the several areas with emission “shortfalls” (i.e.,

those for which we have made our proposal to approve their attainment demonstrations contingent

on their adoption of new measures for further emission reductions). 

In addition to helping 8 areas from Table 2.3 meet their attainment deadlines (plus Dallas and

Beaumont/Port Arthur if they receive a deadline extension to 2005 or later), the new program will

help these and all other areas with current or potential future ozone problems to maintain their

attainment into the future. This includes at least the 37 areas we expressed concern about earlier.

In effect, the emission reductions of this program will reduce the risk that these areas that today are

in or approaching attainment will fall back into nonattainment as they face economic development

and growth in vehicle travel.

3. The Program Will Help States Avoid More Costly Measures

In general, the task of states to reach and/or maintain attainment will be easier and the

economic impact on their industries and citizens will be lighter if, as a result of today’s new gasoline

HD vehicle standards, they are able to forego other, less cost effective programs. Following

implementation of the Regional Ozone Transport Rule, states will have already adopted emission

reduction requirements for nearly all large sources of VOC and NOx for which cost-effective control

technologies are known and for which they have authority to control. Those that remain in

nonattainment therefore will have to consider their remaining alternatives. 

Thus, the emission reductions from the standards we are finalizing today will help states that

would otherwise need to seek controls for the first time from the sources that have not yet been

controlled -- mostly smaller sources including area sources that are closely related to the activities

of individuals and small businesses. The emission reductions from today’s standards will also help

states prevent or delay deeper reductions from large and small sources that have previously

implemented emission controls.

C. HD Diesel and Gasoline Engines Contribute to Total NOx and VOC

Emissions

HD engines and vehicles are major contributors to nationwide emissions of NOx and they

are moderate contributors to nationwide emissions of VOC (estimates of a geographic area’s

emissions are called “emission inventories”). Table 2.4 summarizes EPA’s current estimates for

national NOx and VOC contributions from major mobile source categories. (See Chapter 6 for more

information about how we developed these values.)
Regulatory Impact Analysis 

14

Table 2.4

2000 National NOx and VOC Emissions, (thousand short tons per year)

Emission Source NOx NOx

%

VOC VOC %

Light-Duty Vehicles 4,420 18% 4,098 25%

Heavy-Duty Vehicles 3,759 15% 355 2%

Nonroad Engines and Vehicles 5,343 22% 2,485 15%

Other (Stationary Point and Area Sources) 10,656 44% 9,567 58%

Total Nationwide Emissions 24,178 16,505

Table 2.4 indicates that HD gasoline and diesel vehicles currently represent about 15 percent

of national NOx emissions and two percent of national VOC emissions. Moreover, the local heavyduty vehicle NOx contributions are higher than the national average in many important urban areas.

Table 2.5 shows projections of local contributions to NOx from HD vehicles in 2007 in several

metropolitan areas with ozone concerns. In each of these cases, the local contributions of NOx are

greater than the projected national contribution -- in several cases, significantly higher.

Table 2.5

2007 Heavy-Duty Vehicle Contribution to Urban NOx Inventories

Metropolitan Statistical Area Contribution to 

Total NOx

Contribution to

Mobile Source

NOx

National 12% 23%

Atlanta 18% 28%

Dallas 17% 21%

Charlotte 15% 27%

Washington 15% 29%

Los Angeles 15% 19%

New York 14% 23%

Philadelphia 13% 23%

Cleveland 13% 23%

Chapters 6 and 7 of this RIA also present updated emission inventory modeling for HD

vehicles in future years. The results show that without additional HD NOx control beyond the 1998

standards, national NOx emissions from HD vehicles would decline for the next few years but that

this trend would reverse around 2006. After that, without additional emission controls, NOx

emissions from the HD vehicle fleet would again increase as a result of future growth in the HD
Chapter 2: Health and Welfare Concerns

(e) The emission inventory modeling we performed for this rule includes the excess emissions that occurred as a

result of certain HD diesel engines manufactured between 1988 and 1998. These engines were at issue in the

“consent decrees” involving certain HD diesel engine manufacturers, as discussed in Section I.C. of the preamble

for this final rule.

15

vehicle market. A similar trend is seen for national NMHC emissions from HD vehicles -- we

project that NMHC emissions will decrease until around 2009, after which growth in numbers of

vehicles will offset emission reductions and NMHC emissions from HD vehicles will increase.e

III. Particulate Matter

A. Current and Future Compliance with the PM10 NAAQS

Compliance with the current PM10 standard continues to be a problem. This section reviews

our most recent analyses regarding PM10 air quality, discussed in detail in the Regulatory Impact

Analysis for the Tier 2/Gasoline Sulfur final rule.6 The most recent PM10 monitoring data indicates

that 15 counties designated PM10 nonattainment counties, with a population of 8.6 million in 1996,

violated the PM10 NAAQS in the period 1996-1998. The areas that are violating do so because of

exceedances of the 24-hour PM10 NAAQS. No areas had monitored violations of the annual

standard in this period. Table 2.6 lists these 15 counties. The table also indicates the classification

for each area, the status of our review of the SIPs, and population for each area in 1996. 
Regulatory Impact Analysis 

16

Table 2.6

PM10 Nonattainment Areas Violating the PM10 NAAQS in 1996-1998

Area Classification SIP Approved? 1996

Population

(millions)

Clark Co., NV Serious No 0.93

El Paso, TX Moderate Yes 0.67

Gila, AZ Moderate No 0.05

Imperial Co., CA Moderate No 0.14

Inyo Co., CA Moderate No 0.02

Kern Co., CA Serious No 0.62

Mono Co., CA Moderate No 0.01

Kings Co., CA Serious No 0.11

Maricopa Co., AZ Serious No 2.61

Power Co., ID Moderate No 0.01

Riverside Co., CA Serious No 1.41

San Bernardino Co., CA Serious No 1.59

Santa Cruz Co., AZ Moderate No 0.04

Tulare Co., CA Serious No 0.35

Walla Walla Co., WA Moderate Yes 0.05

TOTAL POPULATION 8.61

Using a PM10 modeling approach conducted for the Tier 2 rulemaking, we have concluded

that the 8 areas shown in Table 2.7 have a high risk of failing to attain and maintain the PM10

NAAQS without further emission reductions. These areas have a population of nearly 8 million.

Included in the group are the counties that are part of the Los Angeles, Phoenix, and Las Vegas

metropolitan areas, where traffic from heavy-duty vehicles is substantial. These 8 areas would

clearly benefit from the reduction in emissions which would occur from the new standards for heavyduty vehicles. 
Chapter 2: Health and Welfare Concerns

17

 

Table 2.7

Areas With High Risk of Failing To Attain and Maintain 

the PM10 NAAQS Without Further Emission Reductions

Area 1996 Population

(millions)

Clark Co., NV 0.93

Imperial Co., CA 0.14

Kern Co., CA 0.62

Kings Co., CA 0.11

Maricopa Co., AZ 2.61

Riverside Co., CA 1.41

San Bernardino Co., CA 1.59

Tulare Co., CA 0.35

TOTAL POPULATION 7.76

Table 2.7 is limited to designated PM10 nonattainment areas which both had monitored

violations of the PM10 NAAQS in 1996-1998 and are predicted to be in nonattainment in 2030 in our

PM10 air quality modeling. This gives us high confidence that these areas require further emission

reductions to attain and maintain, but does not fully consider the possibility that there are other areas

which are now meeting the PM10 NAAQS which have at least a significant probability of requiring

further reductions to continue to maintain it. 

In our Tier 2 analysis, we created a second category of areas with a risk of failing to attain

the PM10 NAAQS in the future that did not rise to the level of risk attributed to those areas listed in

Table 2.7. The Tier 2 air quality modeling predicted that even considering the emission reductions

from the Tier 2/Gasoline Sulfur program and other controls already in place, there would be

violations in 2030 of the annual average PM10 NAAQS in five additional counties. We chose these

five counties because they registered, in either 1997 or 1998, single-year annual average monitored

PM10 levels of at least 90 percent of the NAAQS, but did not exceed the formal definition of the

NAAQS over the three-year period ending in 1998. Table 2.8 shows these areas. They have a

combined population of almost 17 million, and a broad geographic spread. 
Regulatory Impact Analysis 

18

Table 2.8

Five areas with a significant risk of failing to maintain 

the PM10 NAAQS without further reductions in emissions

Area 1996 Population

(millions)

New York Co., NY 1.33

Cuyahoga Co., OH 1.39

Harris, Co., TX 3.10

San Diego Co., CA 2.67

Los Angeles Co., CA 8.11

TOTAL POPULATION 16.6

Unlike the situation for ozone, for which precursor emissions are generally declining over

the next 10 years or so before beginning to increase, we estimate that emissions of PM10 will rise

steadily unless new controls are implemented. The small margin of attainment which these areas

currently enjoy will likely erode; the PM air quality modeling suggests that it will be reversed. We

therefore consider these areas to each individually have a significant risk of failing to maintain the

NAAQS without further emission reductions. There is a substantial risk that at least some of them

would fail to maintain attainment without further emission reductions. The emission reductions

from the new standards for heavy-duty vehicles will help to keep them in attainment.

B. HD Diesel and Gasoline Engines Contribute to Secondary Formation of

Particulate Matter

Because we are not changing the particulate matter emission standards for HD vehicles in

this rule, the effect of this rule on PM results primarily from reductions in NOx emissions and in turn

reductions in the secondary formation of nitrate particles in the atmosphere. Most available

modeling of PM emissions, however, focuses only on direct (primary) emissions of PM. 

We have not attempted to quantify the contribution of HD vehicles to the secondary nitrate

particles formed from the large NOx emissions of these vehicles in this final rule. We are convinced

that this contribution is substantial, especially in regions of the country where ammonia levels in the

air are relatively high (NOx reacts with ammonia to form ammonium nitrate particles). Similarly,

we believe that the very significant NOx reductions from HD diesel and gasoline vehicles that will

result from the 2004 standards will also result in important reductions in the HD contribution to

nitrate PM.

IV. Air Toxics from HD Engines and Vehicles

 In addition to contributing to the health and welfare problems associated with exceedances

of the National Ambient Air Quality Standards for ozone and PM10, emissions from HD diesel and

gasoline vehicles include a number of air pollutants that increase the risk of cancer or have other
Chapter 2: Health and Welfare Concerns

19

negative health effects. These air pollutants include benzene, formaldehyde, acetaldehyde,

1,3-butadiene, and diesel particulate matter. For several of these pollutants, motor vehicle emissions

are believed to account for a significant proportion of total nation-wide emissions. All of these

compounds are products of combustion; benzene is also found in non-exhaust emissions from

gasoline-fueled vehicles. The reductions in hydrocarbon emissions from HD vehicles resulting from

today’s program will further reduce the potential cancer risk and other health risks from these air

toxics (other than diesel PM) because many of these pollutants are themselves VOCs. 

Diesel engine particulate matter is also a potential concern because of its possible

carcinogenic and mutagenic effects on people. However, because today’s program does not include

more stringent standards for emissions of diesel PM, this action will not make a large difference in

any health effects from direct diesel PM. 

We are addressing the issues raised by air toxics from motor vehicles and their fuels in a

separate rulemaking that we recently proposed and was signed by the Administrator on July 14, 2000

under section 202(l)(2) of the Act. That rulemaking process will address the emissions of hazardous

air pollutants from motor vehicles and fuels, and the appropriate level of control of hazardous air

pollutants from these sources.
Regulatory Impact Analysis 

20

1. U.S. EPA, 1996, Review of National Ambient Air Quality Standards for Ozone, 

Assessment of Scientific and Technical Information, OAQPS Staff Paper, EPA-452/R96-007.

2. U.S. EPA, 1996, Air Quality Criteria for Ozone and Related Photochemical Oxidants, 

EPA/600/P-93/004aF.

3. Vitousek, Pert M., John Aber, Robert W. Howarth, Gene E. Likens, et al. 1997. Human 

Alteration of the Global Nitrogen Cycle: Causes and Consequences. Issues in Ecology. 

Published by Ecological Society of America, Number 1, Spring 1997.

4. U.S. EPA, 1996, Air Quality Criteria for Particulate Matter, EPA/600/P-95/001aF.

5. Memorandum to the Docket, Drew Kodjak, EPA, January 12, 2000 (found in the docket

for this rule as well). Information on ozone nonattainment areas and population as of

December 13, 1999.

6. Regulatory Impact Analysis for the Tier 2/Gasoline Sulfur final rule, available in Docket

A-97-10 (document number V-B-1) and through the Office of Transportation and Air

Quality Tier 2 web page at www.epa.gov/otaq/tr2home.htm. 

Chapter 2 References
Chapter 3: Technological Feasibility

21

CHAPTER 3: TECHNOLOGICAL FEASIBILITY OF HD

DIESEL AND OTTO-CYCLE STANDARDS

I. Overview

This chapter provides a technical discussion on emission related control technologies for

lower emissions from HD diesel and otto-cycle engines and vehicles. The chapter is divided into

two sub-chapters, the first dedicated to diesel controls, the second to otto-cycle controls. In addition,

the final section discusses on-board diagnostics for HD, both diesel and otto-cycle.

II. Diesel Engine Technologies

A. HD Diesel Technology Overview

This sub-chapter presents an assessment of emission control strategies that EPA expects will

be available for diesel engine manufacturers to use to meet the emission standards contained in this

final rule. In addition, we present a review of the technologies examined which provided the basis

on which we reviewed the HD 2004 NMHC+NOx standards which were established in 1997. To

meet the 1998 emissions standards for heavy-duty diesel engines, manufacturers have implemented

high-pressure fuel injection systems with retarded injection strategies, waste-gated turbo-chargers,

air-to-air after-coolers, advanced combustion chamber designs, and electronic controls. EPA expects

that incremental improvements will occur with respect to these strategies, but EPA does not expect

that improvements in these strategies alone will achieve the levels required by the new standards.

To meet these levels, EPA expects that, in addition to the aforementioned strategies, manufacturers

will utilize exhaust gas re-circulation (EGR), fuel injection rate shaping, and possibly exhaust aftertreatment. It is important to note that each of these technologies should be able to achieve emission

reductions over a broad range of in-use operating conditions. Of these, EGR is expected to achieve

most of the necessary reductions. As is discussed in more detail below, EGR has been shown to

reduce NOx emissions by up to 90 percent under laboratory conditions. Because these future

emission control strategies will rely on electronic controls for adequate performance, EPA expects

that the best available on-board diagnostics will be implemented to ensure that these strategies

remain effective in-use. Furthermore, although changes in diesel fuel composition might be required

to enable certain emerging aftertreatment technologies, no change in diesel fuel composition will

be required to meet the new standards. In addition, the current status of technologies which EPA

does not believe will be necessary for the requirements contained in this final rule, but which could

provide additional emission reductions beyond the final rule requirements are discussed (these

technologies include NOx absorber catalysts, urea-based SCR systems, and PM traps).

This sub-chapter is divided into five sections: EGR, fuel injection rate shaping, exhaust aftertreatment, fuel composition, and new test cycles. Several sections also discuss strategy-enabling

technologies such as variable geometry turbo-chargers (VGT) for driving EGR, or common rail fuel

systems for performing fuel injection rate shaping. 
Regulatory Impact Analysis 

22

The RIA for the 1997 HD rulemaking contains additional information regarding the

effectiveness of several of the technologies discussed here, primarily cooled EGR systems. The

conclusions in the 1997 rulemaking regarding the effectiveness of cooled EGR for the reduction of

NOx emissions from HD diesel engines continue to be relevant, but the analysis which led EPA to

the conclusion that cooled EGR would be the principle technology for meeting the standards will not

be repeated here. The reader should refer to Chapter 4 of the 1997 RIA for additional discussion of

EGR systems beyond what is covered in this RIA. In addition, a discussion of the potential

incremental improvements from control strategies already being used to meet the 1998 standards can

be found in the RIA of the 1997 final rule. 

B. Exhaust Gas Re-circulation (EGR)

EGR is the re-circulation of exhaust gas from a point in an engine’s exhaust system to a point

in its intake system. EGR is used to decrease nitric oxide (NO) emissions, the primary species in

diesel oxides of nitrogen (NOx). EGR dilutes intake air with combustion products, namely carbon

dioxide (CO2) and water vapor. These diluents decrease the adiabatic stoichiometric flame

temperature for a given mass of fuel and oxygen burned.1 This decrease in temperature

exponentially decreases the oxidation rate of dissociated nitrogen (N) to nitric oxide (NO).2 EGR

also decreases the overall mole fraction of oxygen, which proportionally decreases the oxidation rate

of N to NO.3

 Finally, the specific heats of CO2 (above 532 K) and water vapor are greater than that

of air; therefore they absorb more heat per increase in temperature than air, thus lowering the peak

temperature for a given release of heat. This last effect on NO formation, however, is small

compared to the first two.4

EGR is very effective at decreasing NOx. Laboratory studies have shown that EGR can

reduce NOx emissions by up to 90 percent at light load and up to 60 percent at full load near rated

speed.5 These studies and others have shown similar reductions at other speeds and loads.6

However, because EGR decreases the overall rate of combustion in the cylinder, EGR tends to

increase particulate matter (PM) emissions and brake specific fuel consumption (BSFC).

Furthermore, if EGR is not cooled before it is introduced to the intake system, it will reduce the

density of the intake charge, and thus decrease the volumetric efficiency of the engine, which will

decrease maximum power and increase BSFC. Hot EGR also offsets EGR’s beneficial effect on

combustion temperature because hot EGR increases the initial temperature of the air charge. Finally,

EGR without additional boost air decreases the excess air ratio. This can result in incomplete

combustion during some modes of operation and an increase in PM emissions. Through proper EGR

system design, however, researchers have demonstrated that these undesirable effects of EGR can

be minimized so that the 2004 emission standards can be met.7

From a design perspective, there have been several challenges to EGR’s feasibility, all of

which have been addressed. First, a sufficient positive pressure difference must exist between the

point in the exhaust system where the exhaust gas is extracted and the point in the intake system

where it is introduced. Second, under most conditions, EGR should be cooled for best performance,

which raises corrosion, fouling and design issues. Third, the rate of EGR must be controlled

accurately, and the control system must respond quickly to changes in engine operation.8 
Chapter 3: Technological Feasibility

23

The positive pressure difference required to drive EGR may be achieved a number of ways.

Extracting the exhaust gas downstream of the exhaust turbine and introducing it to the inlet of the

intake compressor is called Low-Pressure-Loop (LPL) EGR. LPL EGR possesses the advantage of

having a sufficient pressure differential to drive EGR over a wide engine operating range, but LPL

EGR may cause durability problems with the intake compressor and after-cooler.9,10 However,

through confidential discussions with engine manufacturers, EPA has learned that some

manufacturers may have overcome these durability issues at least for light and medium heavy-duty

engine applications.

Another way of performing EGR is by extracting the exhaust gas from the exhaust manifold

and routing it to the intake manifold. This minimizes the durability issues associated with the LPL

method by introducing the EGR after the compressor and after-cooler. This is called High-PressureLoop (HPL) EGR. HPL EGR short-circuits the compressor and after-cooler, but the required

pressure differential is difficult to achieve at high load, and particularly in heavy-duty engine

applications.11 To improve the pressure differential to enable HPL EGR, researchers have

investigated enabling technologies such as exhaust back-pressure valves, variable geometry turbochargers (VGTs), and full-flow and bypass intake venturis. In three different studies investigators

positioned exhaust back-pressure valves downstream of the exhaust turbine to drive HPL EGR.

Researchers reported significant NOx reductions, but the turbo-chargers extracted less energy in

these configurations, and the re-circulated exhaust displaced fresh air without any increase in charge

air pressure.12 Unacceptable increases in PM and BSFC resulted due to decreased excess air

ratios.13,14,15

Two recent studies concluded that turbo-charger nozzle geometry must vary in order to drive

EGR without unacceptable decreases in excess air ratios,16, 17 and a third study investigated the

application of a by-pass venturi to draw exhaust gas into the intake system.18 A variable geometry

turbocharger (VGT) is a turbocharger that has adjustable turbine inlet nozzle vanes. Closing these

vanes decreases the nozzle area, whereby exhaust back pressure is increased to drive EGR, while

simultaneously, the turbine and compressor work are increased, as well as the compressor pressure

ratio. VGTs have been demonstrated to drive EGR without significantly decreasing excess air ratios.

In fact, under some operating conditions researchers achieved simultaneous decreases in NOx, PM

and BSFC by driving HPL EGR with a VGT.19 One study combined a VGT with a full-flow EGR

venturi that was positioned within the intake system just upstream of the intake manifold. On a 12

liter 315 kW heavy-duty diesel, the venturi increased EGR suction pressure by up to 20 kPa with an

intake pressure recovery of 60% downstream of the venturi.20 Because the venturi restricted airflow,

it caused decreased excess air ratios which resulted in increased PM and BSFC. However, the

venturi can significantly extend the range of EGR flow, and it might improve the durability of a VGT

by allowing the VGT to operate at lower back pressures and temperatures.21 Another variation of

the venturi concept that does not employ a VGT is the bypass venturi. In this system EGR is

introduced into a venturi positioned in an intake duct that flows parallel to another intake duct in

which there is a controllable butterfly valve. By closing the butterfly valve in the one duct, more

intake flow is forced through the venturi’s duct, which causes more EGR to be drawn into the intake

flow.22 Results from this configuration indicated that about 30% reductions in NOx were achievable
Regulatory Impact Analysis 

24

with no significant increase in BSFC or PM over a wide range of operating conditions. Further

decreases in NOx were achievable with some increase in PM and only a slight increase in BSFC.23

Another important enabling technology for EGR is effective and durable EGR coolers. As

mentioned previously, cooled EGR is desirable under most operating conditions to maximize

volumetric efficiency and to lower intake charge temperatures. Studies have indicated that the issues

concerning EGR coolers - namely, corrosion, fouling, and compact design - have been resolved.

Corrosion is an issue because current on-highway diesel fuel contains up to 0.04% fuel sulfur

(S) by weight, which forms corrosive sulfuric acid (H2SO4) in diesel exhaust. During combustion

S is oxidized 97-99%24 to sulfur dioxide (SO2) and trace amounts of sulfate (SO3). SO3 also forms

in the exhaust manifold as equilibrium thermodynamics begin to favor its formation below ~730 C.

Reaction kinetics limit SO3’s formation rate, however.25 In diesel exhaust SO3 immediately reacts

with water vapor to form aqueous sulfuric acid (~73% H2SO4 by wt.),26 and this acid begins to

condense from about 80 to 145 C ,27,28 depending upon engine operating conditions. Although the

acid’s concentration is strong, the acid at this point only accounts for ~0.5% of the fuel sulfur.

However, once the exhaust cools below the water vapor dew point (~30 to 80 C), SO2, which

accounts for nearly all of the fuel sulfur, will begin to react significantly with condensed water to

form H2SO4.

29 For this reason, EPA expects that EGR coolers will utilize engine coolant, which is

thermostatically controlled typically between 80-90 C. This will help to prevent EGR cooling below

the exhaust’s water vapor dew point. Because ~0.5% of the <0.04% S in the fuel may condense as

strong sulfuric acid and because additional H2SO4 may form during cold engine operating conditions

(start-up, idle, cool-down, winter conditions), stainless steels with special corrosion resistance to

sulfuric acid have been selected to resolve the corrosion issue.30,31

EGR cooler fouling can be minimized if the cross-sectional area of the exhaust channel can

be designed sufficiently large. This is generally problematic because this design leads to a large

EGR cooler. However, one heat exchanger manufacturer has implemented a heat exchanger channel

design that simultaneously minimizes fouling while increasing heat transfer, thereby reducing the

EGR cooler size. The design implements winglets that are vortex-generators arranged in pairs in the

gas channel. They are opened in a V-shaped configuration in the direction of flow.32 These winglets

increase turbulence, which increases heat transfer by reducing the thermal boundary layer in the

channel. They also decrease fouling by forcing particles and vapors back toward the center of the

tube. This stable, turbulent action counters thermophoretic deposition, condensation, and diffusion

due to a concentration gradient.33 Experimental results indicate that cooler fouling stabilized after

100 hrs, and that in the end, fouling decreased cooler efficiency by only 15%.

Controlling EGR flow rate is a crucial aspect for successful EGR system design. EPA

expects manufacturers to make full use of an engine’s electronic control system to measure

parameters that should be used to control EGR rate. Many of these parameters, such as engine

speed, fuel rate, manifold pressures, temperatures and flow rates, are already being measured. EPA

expects individual manufacturers to match their control parameters to their unique EGR systems.

Sufficient control for transient response may be achieved by a number of methods. As mentioned

above, some researchers have demonstrated the use of VGTs and bypass venturis with continuously
Chapter 3: Technological Feasibility

25

variable valves in the intake system to achieve EGR control. For transient response, however, quick

and temporary EGR shut-off seems to be the best method for maintaining adequate torque response

without a sharp increase in transient PM emissions.34 For this reason EPA expects that EGR systems

will have valves positioned in the EGR loop to achieve fast response for transient engine

operation.35,36,37 Durable EGR valves have been demonstrated by various manufacturers.38 One

valve manufacturer indicated that their EGR valve design will incorporate a fast acting (<50 ms)

electrically actuated rotary solenoid, which operates an airfoil-shaped valve plate. The manufacturer

expects to have the valve in production within the 2002 time frame. 39

Because researchers and manufacturers have demonstrated that EGR strategy can result in

significant NOx reductions without unacceptable effects on PM emissions, BSFC, or performance,

and because manufacturers have demonstrated enabling technologies such as VGTs, venturis, EGR

coolers, and control valves for complete EGR system implementation, EPA expects EGR to be a

primary strategy for achieving the emission standards in this rule.

C. Fuel Injection Rate-shaping

Another key emission control strategy that EPA expects heavy-duty diesel engine

manufacturers to use to meet the new emission standards is fuel injection rate shaping. Fuel

injection rate shaping refers to precisely controlling the rate of fuel injected into the cylinder on a

crank-angle by crank-angle resolution. Specific rate-shaping methods include pilot injection where

a pilot quantity of fuel, typically less than 2% of the total fuel charge,40 is injected at some crank

angle before the main injection event. Split fuel injection refers to splitting, more or less evenly, the

main injection into two or more separate injections. Other methods include ramping the main

injection event so that it resembles a triangular profile, rather than a square-shaped profile. Effective

injection rate-shaping systems modulate the fuel injection timing, pressure, rate, and duration

independent of engine speed and load. This characteristic of the fuel system implies that it is

mechanically de-coupled from the engine. Timing is then achieved, presumably, by electronic

control.

Injection rate shaping has been shown to simultaneously reduce NOx by 20 percent and PM

by 50 percent under some conditions.41 It has also been shown to reduce BSFC by up to 10 percent

without increasing NOx emissions.42 However, it can also lead to increases in smoke emissions and

may not be as effective on low-NOx engines equipped with EGR.

Fuel injection rate shaping is used to control the rate of combustion within the cylinder. By

controlling the combustion rate, the rate of pressure and temperature rise is controlled. Therefore,

rate shaping controls NOx formation by one of the same mechanisms as EGR; it is used to lower

peak combustion temperatures. Rate shaping can affect the time and temperature at which

combustion ends, therefore, it can also lower PM emissions by enhancing the mechanisms of

in-cylinder soot oxidation.43

Several manufacturers and fuel system suppliers have demonstrated fuel injection systems

that can achieve effective rate shaping. The three most common systems are the common rail; the
Regulatory Impact Analysis 

26

mechanically actuated electronically controlled unit injector (MEUI); and the hydraulically actuated,

electronically controlled unit injector (HEUI). The common rail system consists of a high-pressure

(~25,000 psi.) fuel pump that pressurizes a pressure-regulated fuel header, or rail, that is connected

to each fuel injector. The fuel injectors are actuated by individual electronically controlled

solenoids.44,45 A variation of the common rail system eliminates the individual solenoids by utilizing

a distributor sub-system.46,47 The MEUI system has low-pressure fuel (~ 60 psi.)48 delivered to its

injectors. The MEUI injectors pressurize the fuel when an overhead cam actuates them. By passing

the pressurized fuel via an electronically controlled spill-valve controls the injection rate.49 The

HEUI system is similar except that a high-pressure hydraulic/accumulator system is used to

pressurize the fuel. One advantage of the HEUI system over the MEUI is that it is not limited in

injection timing, pressure or rate by a cam lobe profile. However, a HEUI system tends to have

lower peak injection pressures versus a MEUI; 25,000 psi vs. 30,000 psi.50 Other rate shaping

systems may utilize spool valve acceleration and fuel-hammering in the injection line, fuel tube

geometry, or dual springs at the injector needle to perform rate shaping.51,52

Several studies have suggested rate-shaping methods to achieve emissions benefits.

Researchers have reported decreased NOx and PM emissions at intermediate speeds and loads by

optimizing reduced-rate pilot injection with a high-pressure main injection,53,54,55 and one report

suggested a fuel injection strategy at high loads. At intermediate loads, burnt pilot fuel is used as

a torch to decrease ignition delay of the main injection event. This lowers peak flame temperatures

and, thus, NOx formation. At high loads the ignition delay is not as significant, but a very early pilot

event (>20 before top-dead center) can be used to distribute low-temperature burnt gas in the

cylinder, similar to EGR. This method can be optimized to decrease NOx, PM, and BSFC

simultaneously.56 Other reports have suggested ramped main injection at high loads and high speeds

to decrease NOx, square main injection at peak torque to decrease PM, and split injection at idle to

decrease volatile PM (i.e. white smoke).57

EPA expects manufacturers to utilize fuel injection rate shaping in combination with EGR

and 1998 engine technologies to meet the new emission standards. EPA believes that the fuel

injection rate shaping strategy is technologically feasible because fuel injection rate shaping is used

to a limited extent today to meet 1998 emissions standards and has been shown in testing to be

reliable and effective.58

D. Exhaust After-treatment

As described in the introduction section, engine manufacturers have been very successful in

developing a mix of technologies to lower PM and NOx concurrently while continuing to improve

fuel economy and engine durability. Although EPA is not finalizing a reduction in the highway

heavy-duty engine PM standard beyond the level of 0.10 g/bhp-hr (0.05 g/bhp-hr for urban buses),

PM control will continue to be very important. PM will remain a primary consideration along with

fuel economy and engine durability in the development of engines with lower NOx emissions. As

discussed above, HC emissions control has not been a primary focus for diesel engines due to their

relatively low HC emissions levels. With a NOx plus NMHC standard, HC emissions levels would
Chapter 3: Technological Feasibility

27

become a greater consideration in the packaging of technologies to meet overall emission targets.

Exhaust aftertreatment technologies for PM and NOx control are discussed in this section.

An extensive description of aftertreatment technologies was presented in the 1997 rulemaking

package for the 2004 standards, including the final Regulatory Impact Analysis document. The

reader is directed to the final RIA from the 1997 rulemaking for a discussion of aftertreatment

technologies as of the 1997 time frame. The following discussion will include information which

has become available since the 1997 rulemaking, and will not repeat what was in that final RIA. 

1. Particulate Matter Control

Two aftertreatment technologies have received the most attention for particulate control, the

flow-through oxidation catalyst and the particulate trap. The oxidation catalyst provides relatively

moderate overall PM reductions by oxidizing a portion of the particulate as the exhaust passes

through it. Oxidation catalysts are relatively inexpensive and are now being used by engine

manufacturers on some engines to meet the current 0.10 g/bhp-hr PM standard (0.05 for urban

buses). 

Particulate traps capture a very high percentage of the particulate and hold it until the PM can

be removed. Removing the PM from the trap, termed trap regeneration, is accomplished by

oxidizing (i.e., burning) the PM. Because diesel exhaust almost never reaches the high temperatures

needed to ignite the PM, oxidation requires either an external heat source or a catalyst material to

lower the oxidation temperature of the PM. Particulate traps have not gained wide acceptance and

use due to several concerns that have not yet been overcome, including high cost, system complexity,

fuel economy penalty, and trap durability. Also, engine manufacturers have not needed the very high

level of PM control provided by traps to meet current standards. However, research on traps has

been on-going, and some recent iterations look promising. 

(a) Diesel Oxidation Catalysts

As mentioned above, engine manufacturers have started to use diesel oxidation catalysts

(DOC) in cases where engines have needed help meeting the particulate standards. For the 1994

model year, about 30 percent of engine families certified were equipped with oxidation catalysts

(with the exception of urban buses, all of these were either light or medium HDDE’s). Another 30

percent of the engine families were certified to PM levels above the 0.10 g/bhp-hr standard through

the averaging, banking and trading program. As these families are redesigned or retired, the

percentage of engine families equipped with oxidation catalysts may change. Recent sales data on

oxidation catalyst for HD from the Manufacturers of Emission Control Association shows a

continual decrease in the number of DOC’s being sold in the U.S. (See Figure 3-1 below).
Regulatory Impact Analysis 

28

Figure 3-1 - U.S. Sales Figures for HD Oxidation Catalysts

Flow-through oxidation catalysts oxidize both gaseous hydrocarbons and the portion of PM

known as the soluble organic fraction (SOF). The SOF consists of hydrocarbons adsorbed to the

carbonaceous solid particles and may also include hydrocarbons that have condensed into droplets

of liquid.59 The carbon portion of the PM remains essentially unaffected by the catalyst. In recent

years, SOF has been reduced through new piston ring designs for oil control and fuel injection and

combustion chamber modifications for more complete combustion of the fuel. The amount of SOF

varies widely among engines but SOF often makes up 30 to 60 percent of the total mass of PM.

Catalyst efficiency for SOF varies with exhaust temperature in the range of about 50 percent

conversion at 150(C to more than 90 percent above 350(C.60 Typically, exhaust temperatures during

the HD-FTP fluctuate between 100(C and 400(C. The reduction in total particulate mass provided

by catalysts is relatively modest both because the efficiency is low at low exhaust temperatures and

because catalysts oxidize only the SOF and not the carbon portion of the PM.

Improvements in catalyst technology have been hindered to some degree by sulfur contained

in diesel fuel. Especially at higher exhaust temperatures, catalysts oxidize sulfur dioxide to form

sulfates, which contribute to total PM emissions. Catalyst manufacturers have been successful at

developing catalyst formulations that minimize sulfate formation.61 Catalyst manufacturers have also

compromised in the placement of the catalyst such that the exhaust is warm enough to achieve the

needed SOF reduction but not so warm as to cause substantial sulfate formation.62 Manufacturers

have noted that fuel with sulfur concentrations lower than 0.05 weight percent would permit the use

of more active, higher efficiency oxidation catalysts. Recent published reports show that for modern

HD diesel engines, palladium based oxidation catalysts can achieve an approximate 30% reduction
Chapter 3: Technological Feasibility

29

in PM under steady-state (European 13-mode) operation using current U.S. diesel fuel, and these

formulations show good durability.63 

A recent test program sponsored by the Manufacturers of Emission Controls (MECA),

included the testing of several oxidation catalysts on a modern HD diesel engine certified to the 1998

U.S. HD standards. The results of this report showed up to a 29% reduction in PM over the transient

FTP, and PM reductions ranging between 0 and 67% on a series of 13 steady-state modes, with one

high load mode showing a slight (15%) increase in PM due to sulfate formation, these results were

all using a typical D2 diesel fuel used in the U.S. today (sulfur content approx. 350ppm)64. This

project also reported an additional 13 percent reduction in PM from the use of low sulfur diesel fuel

(54ppm).

 Oxidation catalyst development and use is likely to continue. Future improvements in

oxidation catalysts will likely provide marginal improvements in overall PM reductions and such

refinements may prove to be valuable to engine manufacturers.

(b) Particulate Trap

The promise of particulate reductions of greater than 90 percent and the 1994 and later PM

standard of 0.10 g/bhp-hr prompted the development of particulate trap technology in the late 1980s.

Particulate trap filters that capture a high percentage of the PM in the exhaust stream were

developed. These initial particulate trap filters needed to be regenerated (cleaned) after a period of

time because the filters eventually began to fill up, creating unacceptable back pressure on the

engine. Engine manufacturers have been able to meet the 1994 particulate standards with engine

modifications and using oxidation catalysts where necessary and no trap-equipped engines were

certified for the 1994 model year.

Several companies and universities are developing a new generation of trap technologies

which have the potential to be simpler, more reliable, and less expensive than previous systems. The

majority of research and development is focused on devising new methods for trap regeneration. A

number of active and passive trap regeneration methods are in various stages of development and

testing. The 1997 RIA discusses both active and passive trap regeneration, however, the most

promising areas of improvement since that time have been in the area of passive systems, and only

those systems will be discussed here. 

Many regeneration techniques being researched involve using catalyst materials that lower

the PM oxidation temperature to the range normally experienced in diesel exhaust. The addition of

a catalyst often provides HC reductions as well. Such systems are often called passive regeneration

systems because they do not require some action to take place for regeneration at regular intervals,

such as heating the PM or blowing the PM out of the trap. Instead, regeneration occurs somewhat

continuously depending on the exhaust gas temperature. Catalysts both in the form of coatings and

fuel additives are being developed. Johnson-Matthey has developed a system that places a catalyst

at the inlet facing of the trap filter such that the exhaust flows though the catalyst before entering the

filter. The catalyst will oxidize sulfur and Johnson-Matthey is requiring the use of fuel with a sulfur
Regulatory Impact Analysis 

30

level much lower than EPA specifications. One recent study utilizing this type of trap reported large

reductions in both mass based PM and HC on a modern, direct injection, turbo-charged, intercooled,

6.8 liter HD engine, but the system requires ultra-low sulfur fuel, less than 10ppm.65

As discussed in the 1997 RIA, several companies have explored the use of fuel additives

which assist in the regeneration process by lowering the PM ignition temperature. For example, fuel

additives including a cerium-oxide additive has been developed by Rhodia Chimie (formerly RhonePoulenc) and a copper-oxide additive has been developed by Lubrizol Corporation.

A recent test program sponsored by the Manufacturers of Emission Controls Association

(MECA), included the testing of two PM filter technologies tested in a laboratory on a modern HD

diesel engine certified to the 1998 U.S. HD standards.66 One filter employed a catalytic coating

applied directly to the filter element (system A), the second filter technology utilizes a catalyst

element placed directly upstream of the filter element (system B). System A was tested on D-2

diesel fuel with current sulfur levels (368ppm), while System B requires low sulfur fuel, and was

tested with a low sulfur (54ppm) diesel fuel. System A was tested over the transient U.S. FTP,

System B was tested on both the U.S. FTP, as well as a series of 13 steady-state modes. Table 3-1

contains a summary of the FTP results.

Table 3-1

PM trap testing results from MECA test program, U.S. HD FTP test cycle

Engine Baseline (g/bhp-hr)

Results w/ trap system

installed (g/bhp-hr)

System A - tested w/ fuel

sulfur level = 368ppm 0.073 0.022

System B - tested w/ fuel

sulfur level = 54ppm ~ 0.06 0.008

Emission results on the 13-steady-state test cycle from the low sulfur fuel with System B

showed reductions ranging between approximately 20 and 70 percent, with the exception of one high

power mode, where PM increased approximately 30 percent. These emission results indicate that

PM traps applied to a 1998 technology HD diesel engine can provide large reductions in PM with

current fuel sulfur levels, and even lower PM levels may be achievable with the use of low sulfur

fuel. Durability information was not collected in this test program.

 Catalyst materials bring down the temperatures needed for PM oxidation, but still may be

challenged to reach the very low exhaust temperatures of diesel engines, which have been further

reduced by the use of air-to-air aftercooling. For systems using catalysts, it will be necessary to

optimize the system for the specific engine application under real world operating conditions. If the

temperature remains lower than the PM ignition temperature for long periods of time, say during idle

and low load conditions, the PM will continue to accumulate in the trap. When ignition temperature
Chapter 3: Technological Feasibility

31

is reached, there may be too much PM in the trap, causing overheating and trap filter damage. It may

be necessary to have a back-up active regeneration system in some cases, but these back-up systems

would likely be expensive.

Filter development is also focused on reducing the amount of exhaust back pressure and

associated fuel economy loss caused by the trap. Additionally, there are problems with ash in the

exhaust stream, which the trap captures along with the particulate matter. The ash does not oxidize

during trap regeneration and over time builds up within the trap; eventually, the filter must be

cleaned or replaced. If traps begin to play a larger role as an emission control technology,

improvements to engine oil (e.g. use of ashless oils) may increase the amount of time a trap can

perform before ash build-up becomes a maintenance issue.

In the long term, traps may be among the mix of technologies considered by engine

manufacturers in meeting future standards, if a durable system with consistent regeneration and a

reasonable cost becomes available. Issues such as regeneration, ash accumulation, and sulfur

tolerance have yet to be resolved by the 2004 time frame.

2. Oxides of Nitrogen Control

The 1997 RIA contains a description of the major developments in NOx control

aftertreatment devices which have been investigated in recent years, including lean-NOx high

temperature and low temperature catalysts, NOx absorber catalysts, and urea-based SCR systems.

Additional development work has occurred in all of these areas since the finalization of the 1997

rulemaking. The discussion below will not repeat what was contained in the final RIA for the 1997

rule, however, much of that information continues to be relevant and the reader should refer to the

final RIA for the 1997 rule for additional information.

In general, the issues associated with lean NOx catalysts, NOx absorber catalysts, and ureabased SCR systems are similar today as they were in 1997. These three systems continue to be the

focus of intensive research because of the benefits they may someday offer. The technical

difficulties discussed in 1997 continue to exist, though some progress has been made.

Lean NOx catalysts continue to offer limited NOx reduction capability when considered

across the entire temperature operating range encountered by HD diesel engines, while peak

reduction capabilities may approach 60 percent under limited operating range, overall reductions on

the U.S. HD FTP continue to be modest, between 20 and 30 percent. Lean NOx absorber catalysts

have shown a potential for much higher levels of NOx reduction, perhaps as high as 80 or 90 percent.

However, at today’s on-highway diesel fuel sulfur levels, catalysts activity can be severely impacted

in a matter of hours. Urea-based SCR systems have shown the potential for high levels of NOx

reduction from diesel engines, however, the technical issues such as urea refueling, tampering, and

ammonium slip remain to be solved. Finally, if the above issues can be solved for these

aftertreatment technologies, issues such as in-use durability, fuel economy impact, cost, and and

cost-effectiveness will also need to be examined.
Regulatory Impact Analysis 

(f) In the absence of an oxidation catalyst, total oxides of nitrogen (NOx) in diesel exhaust is primarily NO

(typically >80%) with lesser amounts of NO2. 

32

The discussion below on each of these technologies discusses in more detail some of the

promise offered by NOx aftertreatment.

(a) NOx Storage Catalysts

NOx storage catalysts (also referred to as NOx absorber catalysts) are probably the best

example of a diesel emissions control capable of large reductions (>25%) reductions in NOx

emissions, but only if diesel fuel sulfur levels are considerably reduced. A generalized schematic

of their operation is included in Figure 3-2. This catalyst system employs a high-platinum (Pt)

content catalyst for oxidation of nitric oxide (NO) to nitrogen dioxide (NO2)

f

. The NO2 is then

stored, using one of a number of barium compounds, as barium nitrate. For approximately twosecond durations every two minutes, diesel fuel is either sprayed into the exhaust, or fuel is injected

into the cylinder after combustion to provide the necessary hydrocarbons to remove the NOx from

the storage components. The NOx is then reduced over a standard three-way catalytic converter. 

The average NOx reduction potential for this technology over the light-duty Federal Test Procedure

(FTP) is 50 to 75%, with a fuel consumption penalty of approximately 3 to 5%.67 Figure 3-3

compares the NOx reducing capabilities of a NOx storage catalyst system to two other lean-NOx

catalyst systems (one of which is sulfur tolerant).

Unfortunately, the chemistry for sulfate storage in such systems is similar to the desired

nitrate storage. Sulfur dioxide from combustion of fuel sulfur compounds is oxidized to SO3 by the

platinum catalyst, and stored as barium sulfate. Purging sulfate from the storage components

requires significantly longer periods of fuel-rich conditions and significantly higher temperatures

(600 to 700 (C). The extended periods of high exhaust temperatures necessary for sulfate purging

from the storage components of the catalyst would be difficult to achieve, even for many heavy duty

diesel applications. Extended high temperature operation would also have a detrimental impact on

the useful life of the NOx storage components of the system. Creation of the necessary fuel-rich

environment would pose a significant fuel consumption penalty, and would increase PM and

hydrocarbon emissions levels. 
Chapter 3: Technological Feasibility

33

Figure 3-3

NOx-storage catalyst operation under oxidizing and reducing conditions.

Without sulfate purging, fuel sulfur levels of 350 ppm result in near complete deactivation

of NOx storage within 20 hours of operation. NOx storage catalysts are clearly not a viable NOx

exhaust aftertreatment control at current diesel fuel sulfur levels. Diesel engines employing NOx

storage catalyst systems will probably be limited to the use of diesel fuels with less than 30 to 50

ppm sulfur68. Even at such fairly low sulfur levels, additional development of catalyst components

that reduce sulfur poisoning of the NOx storage components and less frequent, lower temperature

sulfate purging cycles may still be needed. 

(b) Lean-NOx Catalysts

Various types of active (requiring a post-combustion fuel injection event) and passive (no

post-injection) lean-NOx catalysts are in production or are under investigation for reduction of NOx

emissions in lean exhaust environments such as those present in diesel exhaust. Lean-NOx catalysts

typically reduce NOx efficiently over a fairly narrow range of catalyst temperatures. There are both

“high” and “low” temperature varieties of lean-NOx catalysts. Low temperature, platinum-based

lean-NOx catalysts using zeolites for support, catalyst promotion, and adsorption of NOx and HC,

would be typical of a lean-NOx catalyst technology for light-duty diesel vehicles with catalyst

temperatures primarily in the 200 to 300 (C range. High-temperature lean-NOx catalyst

formulations are under investigation primarily for highly-loaded, heavy-duty diesel engine

applications. High-temperature lean-NOx catalysts are primarily base metal catalysts that are only

effective at exhaust temperatures exceeding 300 (C. 
Regulatory Impact Analysis 

(g) Direct PM emissions from diesel engines primarily consist of 3 constituents: elemental carbon (soot), organics,

and sulfates. 

34

A number of new common rail fuel injection systems are capable of injecting fuel after

combustion to provide additional hydrocarbons for use as a NOx reductant with active lean-NOx

catalysts. One example is the introduction of an active lean-NOx catalyst system for a European

light-duty diesel application69. Although active Pt-zeolite catalyst systems have higher NOx removal

efficiencies than similar passive catalyst systems, NOx removal efficiencies are still only in the range

of 15 to 35 % on average, and significantly below that of NOx storage catalyst systems (Figure 3-3).

It is more likely that low-temperature systems like the Pt-zeolite lean-NOx catalyst systems will be

used for incremental NOx reduction for light-duty applications in combination with other

technologies, such as cooled EGR. 

An approximately 25% reduction in catalyst NOx efficiency due to adsorption of sulfur

compounds has been reported after 40,000 miles of roadway aging in a light-duty application at a

nominal 500 ppm fuel sulfur limit70. Sulfate PM emissions (primarily sulfuric acid), rather than

sulfur poisoning, will probably be a more pressing issue with respect to fuel sulfur contentg

.

Conversion efficiencies for fuel sulfur to sulfuric acid of up to 20% are possible with Pt-zeolite leanNOx catalysts71. 

High-temperature base metal catalysts reduce NOx emissions by up to 30 % over the heavyduty FTP cycle. One such catalyst is the Cu ZSM5 catalyst72. Similar to low temperature systems,

they may be used for incremental NOx reduction in combination with cooled EGR for heavy-duty

diesel engine applications, however, in-use durability issues remain. It is not clear whether or not

long term exposure to SO2 poses a significant problem for this technology. 
Chapter 3: Technological Feasibility

35

Figure 3-3: A comparison of the NOx reduction efficiency over a range of temperature conditions

for the sulfur-intolerant NOx storage catalyst system (system for lean Gasoline Direct Injection

engine application shown73), the more sulfur-tolerant, active Pt-zeolite catalyst system and a hightemperature base-metal (Cu-ZSM5) catalyst system.74 Although peak NOx reductions efficiencies

for various types of non-storage lean-NOx catalysts (similar to the Pt-Zeolite catalyst shown here)

approach 50-60%, average reductions are 15 to 30% over various light- and heavy-duty vehicle and

engine certification cycles.

100%

80%

60%

40%

20%

0

200 300 400 500

Pt/Rh/Ba

NOx-Storage

Catalyst

Active 

Pt-Zeolite

Lean NOx 

Catalyst

% NOx Reduction

Catalyst Inlet Temperature (°C)

Hi-Temp.

Base-Metal

Lean-NOx

Catalyst
Regulatory Impact Analysis 

36

(c) Selective Catalytic Reduction

Selective catalytic reduction (SCR) for NOx control is currently available for stationary diesel

engines, and prototype systems have been developed for mobile light- and heavy-diesel applications.

SCR uses ammonia as a reducing agent for NOx over a catalyst composed of precious metals, base

metals, and zeolites. The ammonia is supplied by introducing a urea/water mixture into the exhaust

upstream of the catalyst. The urea/water mixture is typically stored in a separate tank that must be

periodically replenished. NOx reductions of 70% to 90% are possible using such systems.75 These

systems appear to be tolerant of current U.S. on-highway diesel fuel sulfur levels. 

Control of the quantity of urea injection into the exhaust, particularly during transient

operation, is an important issue with SCR systems. Injection of too large of a quantity of urea leads

to a condition of “ammonia slip”, whereby excess ammonia formation can lead to both direct

ammonia emissions and oxidation of ammonia to produce (rather than reduce) NOx. There are also

a number of potential hurdles to overcome with respect to a major emission control system that

requires frequent replenishing in order to function. This raises issues related to supply, quality

control, tampering, and the possibility of running the urea tank dry. There is currently no widespread distribution system in the U.S. for supplying the necessary water/urea mixtures for diesel

vehicles and trucks. 

E. Diesel Fuel Composition

1. Introduction

The purpose of this section is to assess the current understanding of the role diesel fuel

quality plays in the ability of diesel engines to meet the emission standards in this rule. The effects

of fuel formulation on exhaust emission formation as well as engine durability are examined.

 It has long been realized that diesel engine technology alone is not the only mechanism to

lower emissions, diesel fuel quality also plays an important role in emission formation as well as

engine performance. In addition, diesel fuel quality can play a role in the effectiveness of certain

emission control technologies, and in some cases can be considered a technology enabler, i.e., some

emission control devices may not function because of certain diesel fuel properties, such as sulfur

content.

In EPA’s 1997 final rulemaking for the 2004 standards, we stated that we believed the 2004

standards were technologically feasible thru diesel engine technology modifications alone, without

changes to diesel fuel quality (see 62 Federal Register, 54700, Oct. 21, 1997). However, we also

stated that this issue would be revisited in the 1999 technology review rulemaking, “EPA will

evaluate in light of any new information whether diesel fuel improvements are needed for the

standards to be appropriate for 2004" (see 62 Federal Register, 54700, Oct. 21, 1997). In section

2 below we review the new information which has become available since the 1997 rulemaking thru

a study performed by the Heavy-duty Engine Working Group and durability information supplied
Chapter 3: Technological Feasibility

37

by manufacturers. Section 3 below addresses issues regarding the effect of diesel fuel sulfur levels

on emission control system and engine durability for the technology neccessary for HD diesel

engines to comply with the standards in this rule.

2. Heavy-duty Engine Working Group

(a) Background

In anticipation of the need for new information regarding the influence of diesel fuel quality

on future emission technologies and achievable levels, in December of 1995 a new Working Group

called the Heavy-duty Engine Working Group (HDEWG) was formed under the Mobile Source

Technical Advisory Subcommittee of the Clean Air Act Advisory Committee. The HDEWG

consists of approximately 30 members, including representatives from EPA, heavy-duty engine

OEMs, the oil industry, state air quality agencies, private consultants and members of academic

institutions. The HDEWG formed a steering committee which consisted of representatives from

EPA, Cummins, Caterpillar, Navistar, Ford, British Petroleum, Equilon, Mobil Oil, Phillips, the

Engine Manufacturers Association, the American Petroleum Institute, and the National Petroleum

Refinery Association. The HDEWG set as their research objective to contribute to EPA’s 1999

technology review of emission standards for model year 2004 heavy-duty diesel engines by assessing

relative merits of achieving 2.5 g/bhp-hr HC+NOx level either through engine system modifications

alone, or a combination of engine system and fuel modifications.

The HDEWG established a three phase process in order to meet their objective. In Phase 1,

the goal was to determine whether the combined effects of diesel fuel properties on exhaust

emissions of “black box”, advanced prototype engines being developed by engine manufacturers

were large enough to warrant a Phase 2. “Black box” engines are advanced engines being designed

by engine manufacturers to meet the 2004 standards, but the details of each black box engine would

not be shared with the HDEWG. In addition, the HDEWG agreed to use one “transparent” engine

at an independent test facility, Southwest Research Institute (SwRI). During Phase 1, testing was

to be performed on the transparent engine at SwRI, as well as the black box engines at

manufacturers own testing facilities, to determine if the transparent engine was representative of the

black box engines with respect to diesel fuel effects on NOx emissions.

Phase 2 of the program, which would occur upon successful completion of Phase 1, would

be used to test a range of relevant fuel properties on the transparent engine at SwRI, in order to

determine the effects of those fuel properties on emissions. Finally, Phase 3 of the test program

would determine whether or not the results seen during Phase 2 on the transparent engine was in fact

representative of black box engines, i.e., advanced prototype engines being developed by engine

manufacturers to meet the 2004 standards. Phase 3 would be performed at engine manufacturer’s

laboratories using a subset of the fuel matrix from Phase 2.

(b) Phase 1 of the HDEWG Test Program
Regulatory Impact Analysis 

38

The Phase 1 test program consisted of two test phases; first, testing on three fuels by engine

manufacturers at their facilities of “black box” engines, i.e., advanced prototype engines being

designed to meet the 2004 HC+NOx standard, and second, testing on the same three fuels at SwRI

of the transparent engine. The purpose of Phase 1 was to determine first, whether or not changes in

relevant fuel properties had an important effect on NOx emissions for the black box engines which

would justify continuing to Phase 2, and second, whether or not the transparent engine behaved

similarly to the black box engines, and, thus, could be used for Phase 2 testing. Two reports are

available in the docket for this rulemaking which contain detailed information on the Phase 1 portion

of the program, the following discussion will summarize the results of Phase 1, the reader should see

the detailed reports for more in depth information.76,77 Table 3-2 describes the three fuel

formulations used for Phase 1 testing.

Table 3-2:

Diesel Fuel Formulations used for Phase 1 Testing by the Heavy-duty Engine Working Group

Fuel Property Baseline Fuel

Baseline Fuel w/

Cetane Enhancer

Naturally High Cetane,

Low Aromatic Fuel

Density kg/m3 856 856 823

Cetane Number 45.9 52.4 56.9

Monoaromatics % 26.6 26.2 15.5

Polyaromatics % 9.1 8.9 4.5

Total Aromatics % 35.7 35.1 20

It should be noted that the HDEWG’s primary focus was on the effects of diesel fuel

properties on HC and NOx emissions, not on PM emissions, and therefore fuel sulfur level was not

investigated. A significant amount of data exists on the effects of diesel fuel sulfur on engine

emissions, and in fact this data was summarized recently in an SAE paper published by members of

the HDEWG which will be summarized below. Based on the existing data on recent model year HD

engines, diesel fuel sulfur level does have a statistically significant effect on PM emissions, but no

statistically significant effect on HC, CO, or NOx emissions (on engines with no aftertreatment).

For this reason, and because of the focus on HC and NOx emissions, as well as the limitations of the

SwRI transparent engine discussed below, the HDEWG did not include fuel sulfur level as a variable

in Phase 1, 2 or 3 of their test program, nor were PM emissions measured in Phase 1 or 2.

Engine manufacturers tested the three fuels shown in Table 3-2 on a total of six black box

engines. In addition, SwRI tested the transparent engine on the same three fuels. The test cycle used

by SwRI was the so-called AVL 8-mode test. This steady-state test cycle, with associated weighting

factors, has been shown in the past to correlate very well with NOx emissions measured over the

U.S. FTP. The transparent engine is representative of a modern, heavy-heavy duty diesel engine

which could be certified to 1998 U.S. emission standards in it’s baseline condition. SwRI calibrated
Chapter 3: Technological Feasibility

39

the transparent engine on the baseline test fuel to a 2.7g/hp-hr HC+NOx level utilizing a prototype

low-pressure loop cooled EGR system, this was followed by testing on the two non-baseline fuels.

The cooled EGR system developed by SwRI was not capable of transient operation, and while the

AVL 8-mode does adequately predict transient U.S. FTP NOx, it does not accurately predict PM

emissions, therefore, PM emissions were not measured. Table 3-3 below summarizes the results of

the Phase 1 testing program.

Table 3-3:

Summary of HDEWG Phase 1 Test Results

% Change in NOx Emissions

Test Engines

Naturally High Cetane, Low

Aromatic Fuel vs. Baseline Fuel

Baseline Fuel w/ Cetane

Enhancer vs. Baseline Fuel

Six Black Box

Engines 7.6 percent decrease 2.4 percent increase

SwRI Transparent

Engine 7.0 percent decrease 3.4 percent increase

The HDEWG concluded the following from the Phase 1 test results; the transparent engine

at SwRI responds to fuel property changes similarly to the black box engines and therefore the

transparent engine is appropriate for the Phase 2 test program, and the magnitude of the fuel effects

on NOx emissions for the transparent engine and the black box engines was significant enough to

warrant the continuation of the program into the Phase 2 testing.

In addition to the test program portion of Phase 1, several members of the HDEWG

performed an extensive literature review of existing data on the effects of diesel fuel formulation on

emissions. The result of this work was recently published by Society of Automotive Engineers,

paper number 982649, “Fuel Quality Impact On Heavy-Duty Diesel Emissions:- A Literature

Review.” This paper reviewed publically available data which looked at the following fuel

properties; sulfur, cetane number, total aromatics, polyaromatics, density, volatility (back-end

volatility as determined by T90/T95) and oxygenates. This paper reviewed published results which

include test data measured from both the U.S. HD transient FTP, as well as the European steady-state

13-mode ECE R49 test cycle. The literature search included engines of various levels of emission

control technology, in general the engines were designed to meet U.S. 1991 through 1998 standards,

or European 1993 through 1996 emission limits. The authors divided the available engines into two

groups; “low emission emitting engines” and “high emission emitting engines.” Low emission

engines were those engines with NOx emissions between approximately 3.5 and 5 g/hp-hr, and PM

emissions approximately between .05 and .2 g/hp-hr. High emission engines were those engines

with NOx emissions between approximately 5.5 and 8 g/hp-hr, and PM emissions approximately

between .4 and .5 g/hp-hr. The paper offers an excellent overview of available information, and the
Regulatory Impact Analysis 

40

details of the paper will not be restated here. A summary of the effects which were found on the

“low emission emitting engines” is summarized in Table 3-4 below. 

Table 3-4:

Summary of Diesel Fuel Properties on Recent Model Year Heavy-duty Diesel Emissions from

“low emission emitting engines” from SAE paper 982649

Fuel

Modification HC CO NOx PM

Reduced Sulfur no effect no effect no effect

large effect for

moving from

.3% to .05%,

minimal effect

for reducing S

from 0.05%

Increase

Cetane no effect no effect

small decrease

in NOx no effect

Reduce Total

Aromatics no effect no effect

small decrease

in NOx no effect

Reduce Density

large increase in

HC

small increase in

CO

small decrease

in NOx no effect

Reduce

Polyaromatics

small decrease

in HC no effect

small decrease

in NOx no effect

Reduce

T90/T95

very small

increase in HC

very small

increase in CO

very small

decrease in NOx no effect

The authors noted that there was very little information available on the effect of increasing

oxygenates, and any conclusions would be very tentative, therefore, the summary of oxygenates is

not included here. It should be noted that the term “low emission emitting engines” employed by

the authors is well above the 2.5g/hp-hr HC+NOx level.

Based on the results of the Phase 1 results for “black box” engines, the “transparent” engine,

and the literature review of available data, the HDEWG agreed to proceed to Phase 2.

(c) Phase 2 of the HDEWG Test Program

The purpose of the Phase 2 component of the test program was to test a range of relevant fuel

properties on the transparent engine at SwRI in order to determine the effects of various fuel

properties on emissions. All testing during Phase 2 of the test program was done at SwRI on the

transparent engine. The parameters investigated and the results of the Phase 2 testing are
Chapter 3: Technological Feasibility

(h) Boosted cetane is achieved by the addition of a fuel additive, in this case ethylhexyl nitrate 

41

summarized in this section. A document containing detailed information on the Phase 2 test program

is available in the docket for this rulemaking, the following discussion will summarize the relevant

results of Phase 2, the reader should see the detailed report for more in depth information.78 

Based on the results of the Phase 1 testing, as well as the literature review performed under

Phase 1, the HDEWG selected four fuel properties for investigation under Phase 2: density, cetane

(natural and “boosted”h), monoaromatic content and polyaromatic content. As mentioned previously,

fuel sulfur level was not investigated. A test matrix was designed to decouple these fuel properties

from each other, in addition, fuel blends were added to the matrix to evaluate density effects as a

function of engine injection timing and a direct comparison of natural and boosted cetane number.

The design matrix included two levels of density, monoaromatic hydrocarbons, polyaromatic

hydrocarbons, and three levels of cetane. The final matrix included eighteen test fuels, with density

varying from 830 to 860 kg/m3

, cetane numbers from 42 to 48 to 53, monoaromatic content from 10

to 25 percent, and polyaromatic content from 2.5 to 10 percent. For all emission testing, the AVL

8-mode test was utilized, and all emission tests were performed at least in duplicate. In addition to

the fuel property effects, the effects of injection timing and EGR were evaluated. The SwRI

prototype, low-pressure loop, cooled EGR system was manually controlled to set EGR rates in order

to approach an AVL 8-mode composite NOx level of 2.5g/hp-hr.

The large quantity of test data generated by the test program was evaluated using statistical

techniques in order to develop exhaust emission and fuel consumption prediction models based on

the four fuel properties. All properties were evaluated using a significance level of 5 percent. The

HDEWG examined the dependence of emissions and fuel consumption on the four parameters

(density, cetane, monoaromatic content and polyaromatic content). 

The following tables summarize the most important results of the Phase 2 test program.

Table 3-5 summarizes the effects of individual fuel properties on predicted NOx, HC, and HC+NOx

emissions. Table 3-6 summarizes the combined effects of fuel properties on predicted NOx, HC,

and HC+NOx emissions. Table 3-6 contains a summary of percent changes in predicted results for

two fuels, a blend representative of current U.S. diesel fuel (based on national fuel surveys for 1994

and 1995, except for polyaromatic content, which was estimated by the HDEWG), and a “clean”

diesel fuel, i.e., a fuel low in density, high in cetane, and low in both monoaromatics and

polyaromatics.
Regulatory Impact Analysis 

42

Table 3-5:

Effects of Individual Fuel Properties on Predicted Emissions from Phase 2 Testing of the Heavyduty Engine Working Group Project (Reference values for NOx, HC, and HC+NOx of 2.57 g/hphr, 0.13 g/bhp-hr, and 2.7 g/bhp-hr respectively were used. Negative percentages represent a

decrease in emissions with the corresponding decrease in fuel property) 

Pollutant

Density

860 â 830

kg/m3

Cetane Number

52 â 42

Monoaromatics

25 â 10 %

Polyaromatics

10 â2.5 %

% NOx Change

@ 2.57 g/bhp-hr -4.8 -1.3 -3.8 -2.2

% HC Change

@ 0.13 g/bhp-hr Not Significant 14.3 -7.8 -9.2

% HC+NOx

Change @ 2.70

g/bhp-hr -4.3 Not Significant -4.3 -2.3

Table 3-6:

Combined Effects Fuel Properties on Predicted Emissions from Phase 2 Testing of the Heavyduty Engine Working Group Project (Reference values for NOx, HC, and HC+NOx of 2.57 g/hphr, 0.13 g/bhp-hr, and 2.7 g/bhp-hr respectively were used. Negative percentages represent a

decrease in emissions)

 Fuel Property Predicted Emission Change

Density

kg/m3

Cetane

Number

Monoaromatics

%

Polyaromatic

s %

% Change

in NOx

vs.

“Light” at

2.57g/bh

p-hr level

% Change

in HC vs.

“Light” at

0.13

g/bhp-hr

level

% Change

in

HC+NOx

vs.

“Light” at

2.70g/bh

p-hr level

Average U.S.

Diesel Fuel 845 45 25 9

“Light”, High

Cetane, Low

Aromatic Fuel 830 52 10 2.5 -7.2 -25.8 -8.4

The test data was also analyzed to look at the effect of the prototype low pressure loop,

cooled EGR system on measured emissions and on measured fuel consumption (not predicted).
Chapter 3: Technological Feasibility

43

Duplicate emission tests performed on each of seven test fuels with the EGR system on and off were

examined. The results indicated EGR had a strong, statistically significant effect on NOx emissions,

no effect on HC emissions, and a strong effect on HC+NOx emissions. The EGR system used

reduced NOx emissions between 35.9 and 37.2 percent, and HC+NOx emissions by 34.2 to

35.3percent. The EGR system had no statistically significant impact on brake-specific fuel

consumption.

(d) Phase 3 of the HDEWG Test Program

Phase 3 of the test program has not been completed. The purpose of the Phase 3 program

will be to determine whether or not the Phase 2 results seen on the transparent engine are

representative of “black box” engines, i.e., advanced, prototype HD diesels being developed by

manufacturers to meet the 2004 standards. The Phase 3 testing will occur at individual engine

manufacturers facilities, and will utilize full U.S. FTP transient emission testing, and will include

PM measurement. The Phase 3 program is scheduled to be competed in mid-1999.

(e) EPA Assessment of HDEWG Data

The most significant data for this rulemaking activity generated up to this point in time by

the HDEWG is presented in Tables 3-5 and 3-6. The data in Table 3-5 indicates that for engines

utilizing advanced fuel injection and a cooled EGR system operating at emissions levels near the

2004 standards, the effects of relatively large changes in individual fuel properties is statistically

significant but rather small, and for cetane number not statistically significant. A large decrease in

fuel density (from 860 to 830 kg/m3 ) or in monoaromatic content (from 25 to 10 percent) is

predicted to result in a 4.3 percent decrease in HC+NOx emissions, and a large decrease in

polyaromatics content (from 10 to 2.5 percent) is predicted to result in a 2.3 percent decrease in

HC+NOx emissions.

The data in Table 3-6 indicates the potential impacts on HC+NOx emissions from the

combined effects of significantly changing diesel fuel formulation from today’s currently available

U.S. on-highway diesel fuel. The results predict that a combined, relatively large decrease in density,

large increase in cetane, and large decrease in both monoaromatic content and polyaromatic content

would result in a 8.4 percent decrease in HC+NOx emissions. 

3. Fuel Sulfur Impact on Engine Durability

(a) Condensate Issues

Cooled EGR poses several design issues, one of those being corrosion from EGR condensate.

This condensate is composed of two major components, water and sulfuric acid. The water is a

normal byproduct of combustion and the sulfuric acid (H2SO4) is formed primarily from sulfur in

the fuel. The rate of acid condensation is proportional to the concentration of sulfur in the fuel.

Current on-highway requirements limit diesel fuel sulfur to 500 ppm or less. Manufacturers have

proposed at least 30 ppm maximum sulfur fuel to minimize sulfur induced corrosion.
Regulatory Impact Analysis 

44

The EGR cooler, intake plumbing, intake manifold, cylinder kit (piston rings and cylinder

liner), and engine oil will be exposed to this condensate. The EGR cooler will be the most critical

component from a corrosion standpoint. It will be cooling raw exhaust, which is more likely to

condense than the diluted exhaust found in the engine intake system. Corrosion of the EGR system

and intake charge plumbing can lead to contamination of the intake charge. Particles from the walls

of the intake plumbing can be released by the corrosion process and carried by the intake charge into

the cylinders. Once there, the particles act to abrasively wear the cylinder kit causing loss of oil

control. Corrosion induced pitting on the cylinder liner from the sulfuric acid entrained in the EGR

could also be an issue.

The engine oil will also be impacted by the fuel sulfur and EGR. The sulfuric acid can get

into the engine oil via the blow-by or via deposition on the cylinder liner. The result will be

accelerated depletion of the oil PH control package.

(b) Corrosion Resistance

Most of the EGR induced corrosion issues will be dealt with through careful material and

bonding process selection. Stainless steels with higher nickel or cobalt content may be necessary

to provide the required EGR cooler life.79 Bonding methods used in the construction of these coolers

are also available to reduce corrosion. Along with corrosion resistant materials, the EGR can also

be controlled to minimize condensation under adverse conditions, such as cold start. This attention

to material selection and the level of EGR cooling will minimize the condensation impact on engine

durability.

Engine oil reformulation studies have already begun to set a new standard for engines with

cooled EGR. Improved TBN control additive packages will be part of this standard along with

increased oil soot tolerance capability. These improvements should allow the oil to perform at least

as well as current (non-EGR) oils.

F. Performance of Projected Emission Control Technologies over Typical InUse Conditions

The technologies discussed in this chapter, cooled EGR, advanced fuel injection systems with

rate shaping, and variable-nozzle turbochargers, combined with electronic control systems, are all

applicable for in-use operation, under both steady-state and transient operation. The Agency expects

that this technology package can achieve the emission reductions necessary to comply with the 2004

standards under a large variety of operating conditions, not simply the test cycle contained in the

Federal transient FTP. Many of the published reports in the past several years have looked at the

application of these technologies not only under transient operation, but also under steady-state test

cycle conditions. Some of these reports included data for the steady-state cycles used in Japan and

Europe, which are similar to the EPA cycle for the steady-state MAEL requirements. As indicated

in Table 3-7, NOx and PM performance in these steady-state conditions are at or near the standards

in this rulemaking. In addition, the test results included in the 1997 RIA indicate NOx and PM

performance at or near the standards using both transient and steady-state tests. The Agency sees
Chapter 3: Technological Feasibility

45

no reason why the technologies discussed previously would not function sufficiently well under a

wide range of operating conditions, and thus we expect them to be designed to provide comparable

levels of emission control under a wide range of operating conditions in the timeframe require by

this rule. As discussed previously, cooled EGR alone has been demonstrated under laboratory

conditions to provide NOx reductions up to 90 percent at light load conditions and up to 60 percent

near rated speed. These conclusions are fully consistent with the expectation in the 1997

rulemaking.

Following the October 29, 1999 Federal Register publication of the proposal for this final

rule the Agency met with a number of HD diesel engine manufacturers to discuss the supplemental

test procedure requirements. During this time we received a substantial amount of confidential

business information from a number of HD diesel manufacturers who are designing engines to

comply with the NTE requirements under the 1998 HD diesel consent decrees. We have

summarized this information into a memorandum which is available for review in the public docket

for this rule.80 This memorandum shows that a number of manufacturers have made significant

progress towards meeting the 2007 supplemental requirements. The principle issue which

manufacturers are now in the process of addressing is the ability to drive and control cooled EGR

under high load conditions for highly rated versions of their engines. Manufacturers have

encountered a number of technical issues, depending on the engine design path they have chosen.

Some manufacturers are encountering the physical limitations of current turbocharger designs, while

others are addressing complex control strategies which in some cases push the limits of currently

available sensors and actuators. Engine manufacturers are at different stages of product development

for achieving NTE limits. Based on the information provided to the Agency, those manufacturers

who have progressed the furthest have narrowed the remaining technical issues substantially. These

manufacturers have narrowed the focus of their efforts to the ability to drive and control EGR for

the highly rated versions of their engines while maintaining engine performance, under the high load

regions of the NTE, and only under ambient conditions of high temperature and/or high altitude.

The Agency also spoke with a major turbocharger manufacturer regarding the performance

capabilities of turbocharger in the 2004 time frame and beyond.81 Based on the emission capabilities

of the emission control technologies previously discussed in this RIA (cooled EGR, advanced

turbomachinery, and advanced fuel injection systems), the information the Agency has received from

manufacturers, and the summary of the confidential information provided by a number of engine

manufacturers, the Agency concludes the supplemental test procedure requirements (NTE and SSS)

are technically feasible by 2007.

For these reasons, EPA believes the primary technologies discussed in this chapter will

provide the necessary NMHC+NOx and PM control on the existing transient FTP by 2004, as well

as the supplemental test cycles, procedures and associated standards contained in this rule for 2007.

Thus, we do not expect these requirements to impose new hardware burdens. Manufacturers are

expected to only need to conduct additional emission testing and perform recabilbration of their

engines to comply with these requirements.

G. Summary and Conclusions regarding HD Diesel Technologies
Regulatory Impact Analysis 

46

The Regulatory Impact Analysis document for the 1997 HD diesel FRM documents EPA’s

analysis which lead to the conclusion that the Agency believed the 2004 HD NOx+NMHC standards

were technologically feasible. This RIA contains EPA’s reassessment of the technological feasibility

of these standards, including a discussion of the role diesel fuel quality plays in the appropriateness

of the standards. Table 3-7 summarizes the emission performance results of several studies that were

recently conducted on heavy-duty diesel engines, and which have been discussed earlier in this

chapter. In the technological feasibility chapter of the 1997 RIA for this rule, a similar table is

presented for results up to 1997.

Table 3-7:

Summary of recently published data on 2004 capable control strategies

Technology Test

Cycle

NOx PM BSFC

VGT turbocharged, aftercooled, 4-

valve/cyl, high-pressure fuel

injection, HPL cooled EGR, with

full-flow venturi mixer82

ECE R49

13-mode

2.24 g/hp-hr 0.08 g/hp-hr No

significant

change

VGT turbocharged, aftercooled,

high-pressure electronic fuel

injection, HPL cooled EGR, with

full-flow venturi mixer83

ECE R49

13-mode

1.80 g/hp-hr 0.08 g/hp-hr 2.3% inc.

from no

EGR

VGT turbocharged, aftercooled,

HPL cooled EGR84

Japanese

13-mode

22% dec.

from no

EGR & VGT

No

significant

change

1.5% dec.

from no

EGR & VGT

waste-gate turbocharged, air-air

aftercooled, 4 valve/cyl, MEUI fuel

injection, HPL cooled EGR with

partial flow venturi mixer85

Euro-3

ESC

3.24 g/hp-hr 0.06 g/hp-hr No

significant

change

same as above, including reference Euro-3

ESC

2.33 g/hp-hr 0.08 g/hp-hr 0.9% inc.

from no

EGR

same as above, including reference Euro-3

ESC

1.83 g/hp-hr 0.15 g/hp-hr 2.4% inc.

from no

EGR

These results and the results indicated in the 1997 RIA show the types of emission values

which can be achieved from the combination of cooled EGR, advanced electronic controls, advanced

turbo-chargers, and high-pressure fuel injection systems with rate shaping capabilities. The results

above indicate that current technology can achieve NOx and PM results at or near the 2004
Chapter 3: Technological Feasibility

47

standards. Results referenced in the 1997 RIA include a study showing HC + NOx levels of 2.54

g/bhp-hr on the current transient cycle FTP. Based on the tests that have been conducted in the past

few years, EPA projects that manufacturers will continue to optimize fuel injection and EGR

strategies in the lead time available to them , and will be able to meet the NMHC+NOx emission

standards in this rule, while continuing to meet the PM standard, with little or no brake specific fuel

consumption penalty. Also, as discussed previously, the Agency has placed information into this

rulemaking record summaries of information and discussion with engine manufacturers and

component suppliers regarding the feasibility of the 2007 supplemental requirements. This

information shows manufacturers have made substantial progress towards meeting the supplemental

requirements (NTE and supplemental steady-state requirements). Considering the remaining

technical issues, the potential solution to these issues, and the significant lead time (more than six

years), the Agency concludes the supplemental requirements contained in this final rule will be

feasible by model year 2007.

III. HD Otto-cycle Engine & Vehicle Technologies

The purpose of this sub-chapter is to further expand upon the technical discussion that was

presented in the preamble. HD otto-cycle vehicle and engine exhaust emissions can be reduced by

a number of technologies, but the most potential for improvement exists in reductions to base

engine-out emissions, improvement in air-fuel ratio control, better fuel delivery and atomization, and

continued advances in exhaust aftertreatment.

The following descriptions provide an overview of the latest technologies capable of reducing

exhaust emissions. The descriptions will also discuss the state of development and current

production usage of the various technologies. It is important to point out that the use of all of the

following technologies is not required to further reduce emissions. The choices and combinations

of technologies will depend on several factors, such as current engine-out emission levels,

effectiveness of existing emission control systems, and individual manufacturer preferences. With

the exception of a few technologies, many of these technologies are used in some heavy-duty and

light-duty vehicles already in production. 

EPA used a number of references for the following discussion. EPA consulted an Energy

and Environmental Analysis, Inc. (EEA), study evaluating emission control technologies for lightduty vehicles and light-duty trucks.86 EPA used as references, the State of California Air Resources

Board (CARB) staff reports on “Low-Emission Vehicle and Zero-Emission Vehicle Program

Review,” and “LEVII” published in November 1996 and September 1998 respectively.87,88 EPA also

used as a reference information from the Manufacturers of Emission Controls Association (MECA)

and vehicle manufacturers.

While the EEA report focused on light-duty vehicles, the emissions controls for heavy-duty

vehicles would be very similar. Often technologies are first introduced on light-duty vehicles and

then later applied to heavier vehicles as needed. For example, most heavy-duty vehicles and engines

are now equipped with sequential fuel injection, three way catalyst systems with closed loop control,

and EGR. The CARB medium-duty vehicle program applies to vehicles up to 14,000 pounds
Regulatory Impact Analysis 

48

GVWR and includes LEV and ULEV standards. For heavy-duty vehicles and engine specifically,

EPA contracted Arcadis Geraghty and Miller to review technologies and perform cost analyses for

the standards that were proposed in the NPRM for this rulemaking.89

A. Base Engine Improvements

There are several design techniques that can be used for reducing engine-out emissions,

especially for HC and NOx. The main causes of excessive engine-out emissions are unburned HCs

and high combustion temperaturesfor NOx. Methods for reducing engine-out HC emissions include

the reduction of crevice volumes in the combustion chamber, reducing the combustion of lubricating

oil in the combustion chamber and developing leak-free exhaust systems. Leak-free exhaust systems

are listed under base engine improvements because any modifications or changes made to the

exhaust manifold can directly affect the design of the base engine. Base engine control strategies

for reducing NOx include the use of “fast burn” combustion chamber designs, multiple valves with

variable-valve timing, and exhaust gas recirculation.

1. Combustion Chamber Design

 Unburned fuel can be trapped momentarily in crevice volumes (i.e., the space between the

piston and cylinder wall) before being subsequently released. Since trapped and re-released fuel can

increase engine-out HC, the reduction of crevice volumes is beneficial to emission performance.

One way to reduce crevice volumes is to design pistons with reduced top “land heights” (distance

between the top of the piston and the first piston ring). The reduction of crevice volume is especially

preferable for vehicles with larger displacement engines, since they typically produce greater levels

of engine-out HC than smaller displacement engines.

Another cause of excess engine-out HC emissions is the combustion of lubricating oil that

leaks into the combustion chamber, since heavier hydrocarbons in oil do not oxidize as readily as

those in gasoline. Oil in the combustion chamber can also trap gaseous HC from the fuel and release

it later unburned. In addition, some components in lubricating oil can poison the catalyst and reduce

its effectiveness. To reduce oil consumption, vehicle manufacturers will tighten tolerances and

improve surface finishes for cylinders and pistons, improve piston ring design and material, and

improve exhaust valve stem seals to prevent excessive leakage of lubricating oil into the combustion

chamber. 

As discussed above, engine-out NOx emissions result from high combustion temperatures.

Therefore, the main control strategies for reducing engine-out NOx are designed to lower

combustion temperature. The most promising techniques for reducing combustion temperatures,

and thus engine-out NOx emissions, are the combination of increasing the rate of combustion,

reducing spark advance, and adding a diluent to the air-fuel mixture, typically via exhaust gas

recirculation (EGR). The rate of combustion can be increased by using “fast burn” combustion

chamber designs. A fast burn combustion rate provides improved thermal efficiency and a greater

tolerance for dilution from EGR resulting in better fuel economy and lower NOx emissions. There

are numerous ways to design a fast burn combustion chamber. However, the most common
Chapter 3: Technological Feasibility

(i) Some manufacturers have stated that EGR impacts the ability to control net air-fuel ratios tightly due to

dynamic changes in exhaust back pressure and temperature, and that the advantages of increasing EGR flow rates

are lost partly in losses in air-fuel ratio control even with electronic control of EGR. Higher EGR flow rates can be

tolerated by modern engines with more advanced combustion chambers, but EGR cooling may be necessary to

achieve higher EGR flow rates within acceptable detonation limits without significant loss of air-fuel control.

49

approach is to induce turbulence into the combustion chamber which increases the surface area of

the flame front and thereby increases the rate of combustion, and to locate the spark plug in the

center of the combustion chamber. Locating the spark plug in the center of the combustion chamber

promotes more thorough combustion and allows the ignition timing to be retarded, decreasing the

dwell time of hot gases in the combustion chamber and reducing NOx formation. Many engine

designs induce turbulence into the combustion chamber by increasing the velocity of the incoming

air-fuel mixture and having it enter the chamber in a swirling motion (known as “swirl”).

2. Improved EGR Design

One of the most effective means of reducing engine-out NOx emissions is exhaust gas

recirculation. By recirculating spent exhaust gases into the combustion chamber, the overall air-fuel

mixture is diluted, lowering peak combustion temperatures and reducing NOx. As discussed above,

the use of high swirl, high turbulence combustion chambers can allow the amount of EGR to be

increased from current levels of 15 to 17 percent to levels possibly as high as 20 to 25i

 percent,

resulting in a 15 to 20 percent reduction in engine-out NOx emissions. 

Many EGR systems in today’s vehicles utilize a control valve that requires vacuum from the

intake manifold to regulate EGR flow. Under part-throttle operation where EGR is needed, engine

vacuum is sufficient to open the valve. However, during throttle applications near or at wide-open

throttle, engine vacuum is too low to open the EGR valve. While EGR operation only during partthrottle driving conditions has been sufficient to control NOx emissions for most vehicles in the past,

more stringent NOx standards and emphasis on controlling off-cycle emission levels may require

more precise EGR control and additional EGR during heavy throttle operation to reduce NOx

emissions. Many manufacturers now use electronic EGR in place of mechanical back-pressure

designs. By using electronic solenoids to open and close the EGR valve, the flow of EGR can be

more precisely controlled.

 While most manufacturers agree that electronic EGR gives more precise control of

EGR flow rate, not all manufacturers are using it. Numerous LEV vehicles certified for the 1998

model year still use mechanical EGR systems, and in some cases, no EGR at all. Nonetheless, the

use of EGR remains a very important tool in reducing engine-out NOx emissions, whether

mechanical or electronic.

3. Multiple Valves and Variable-Valve Timing

Conventional engines have two valves per cylinder, one for intake of the air-fuel mixture and

the other for exhaust of the combusted mixture. The duration and lift (distance the valve head is
Regulatory Impact Analysis 

50

pushed away from its seat) of valve openings is constant regardless of engine speed. As engine

speed increases, the aerodynamic resistance to pumping air in and out of the cylinder for intake and

exhaust also increases. By doubling the number of intake and exhaust valves, pumping losses are

reduced, improving the volumetric efficiency and useful power output. 

In addition to gains in breathing, the multiple-valve (typically 4-valve) design allows the

spark plug to be positioned closer to the center of the combustion chamber (as discussed above)

which decreases the distance the flame must travel inside the chamber. In addition, the two streams

of incoming gas can be used to achieve greater mixing of air and fuel, further increasing combustion

efficiency which lowers engine-out HC emissions. 

Even greater improvements to combustion efficiency can be realized by using valve timing

and lift control to take advantage of the 4-valve configuration. Conventional engines utilize fixedvalve timing and lift across all engine speeds. Typically the valve timing is set at a level that is a

compromise between low speed torque and high engine speed horsepower. At light engine loads it

would be desirable to close the intake valve earlier to reduce pumping losses. Variable valve timing

can enhance both low speed torque and high speed horsepower with no necessary compromise

between the two. Variable valve timing can allow for increased swirl and intake charge velocity,

especially during low load operating conditions where sufficient swirl and turbulence tend to be

lacking. By providing a strong swirl formation in the combustion chamber, the air-fuel mixture can

mix sufficiently, resulting in a faster, more complete combustion, even under lean air-fuel

conditions, thereby reducing emissions. Variable valve technology by itself may have somewhat

limited effect on reducing emissions. Several vehicle manufacturers estimate emission reductions

of 3%-10% for both, NMHC and NOx, but reductions could be increased when variable valve timing

is combined with optimized spark plug location and additional EGR. 

Multi-valve engines already exist in numerous federal and California certified vehicles and

are projected by CARB to become even more common. CARB also projects that in order to meet

LEV and ULEV standards, more vehicles will have to make improvements to the induction system,

including the use of variable valve timing. 

4. Leak-Free Exhaust System

Leaks in the exhaust system can result in increased emissions, but not necessarily from

emissions escaping from the exhaust leak to the atmosphere. With an exhaust system leak, ambient

air is typically sucked into the exhaust system by the pressure difference created by the flowing

exhaust gases inside the exhaust pipe. The air that is sucked into the exhaust system is unmetered

and, therefore, unaccounted for in the fuel system’s closed-loop feedback control, resulting in erratic

and/or overly rich fuel control. This results in increased emission levels and potentially poor drive

ability. In addition, an air leak can cause an oxidation environment to exist in a three-way catalyst

at low speeds that would hamper reduction of NOx and lead to increased NOx emissions.

Some vehicles currently use leak-free exhaust systems today. These systems consist of an

improved exhaust manifold/exhaust pipe interface plus a corrosion-free flexible coupling inserted
Chapter 3: Technological Feasibility

51

between the exhaust manifold flange and the catalyst to reduce stress and the tendency for leakage

to occur at the joint. In addition, improvements to the welding process for catalytic converter

canning could ensure less air leakage into the converter and provide reduced emissions. CARB and

MECA project that vehicle manufacturers will continue to incorporate leak-free exhaust systems as

emission standards become more stringent.

5. Improvements in Air-Fuel Ratio Control

Modern three-way catalysts require the air-fuel ratio (A/F) to be as close to stoichiometric

operation (the amount of air and fuel just sufficient for nearly complete combustion) as possible.

This is because three-way catalysts simultaneously oxidize HC and CO, and reduce NOx. Since HC

and CO are oxidized during A/F operation slightly lean of stoichiometry, while NOx is reduced

during operation slightly rich of stoichiometry, there exists a very small A/F window of operation

around stoichiometry where catalyst conversion efficiency is maximized for all three pollutants (i.e.,

less than 1% deviation in A/F or roughly ± 0.15). Contemporary vehicles have been able to maintain

stoichiometric, or very close to it, operation by using closed-loop feedback fuel control systems. At

the heart of these systems has been a single heated exhaust gas oxygen (HEGO) sensor. The HEGO

sensor continuously switches between rich and lean readings. By maintaining an equal number of

rich readings with lean readings over a given period, the fuel control system is able to maintain

stoichiometry. While this fuel control system is capable of maintaining the A/F with the required

accuracy under steady-state operating conditions, the system accuracy is challenged during transient

operation where rapidly changing throttle conditions occur. Also, as the sensor ages, its accuracy

decreases. 

(a) Dual Oxygen Sensors

Many vehicle manufacturers have placed a second HEGO sensor(s) downstream of one or

more catalysts in the exhaust system as a method for monitoring the catalyst effectiveness of the

federally and California mandated on-board diagnostic (OBD II) system. In addition to monitoring

the effectiveness of the catalyst, the downstream sensors can also be used to monitor the primary

control sensor and adjust for deterioration, thereby maintaining precise A/F control at higher

mileages. Should the front primary HEGO sensor, which operates in a higher temperature

environment, begin to exhibit slow response or drift from its calibration point, the secondary

downstream sensor can be relied upon for modifying the fuel system controls to compensate for the

aging effects. By placing the second sensor further downstream from the hot engine exhaust, where

it is also less susceptible to poisoning, the rear sensor is less susceptible to aging over the life of the

vehicle. As a result, the use of a dual oxygen sensor fuel control system can ensure more robust and

precise fuel control, resulting in lower emissions.

Currently, all vehicle manufacturers use a dual oxygen sensor system for monitoring the

catalyst as part of the OBD II system. As discussed above, most manufacturers also utilize the

secondary HEGO sensor for trim (i.e., adjustments to) of the fuel control system. It is anticipated

that all manufacturers will soon use the secondary sensor for fuel trim.
Regulatory Impact Analysis 

52

(b) Universal Oxygen Sensors

The universal exhaust gas oxygen (UEGO) sensor, also called a "linear oxygen sensor”, could

replace conventional HEGO sensors. Conventional HEGO sensors only determine if an engine's A/F

is richer or leaner than stoichiometric, providing no indication of what the magnitude of the A/F

actually is. In contrast, UEGO's are capable of recognizing both the direction and magnitude of A/F

transients since the voltage output of the UEGO is "proportional" with changing A/F (i.e., each

voltage value corresponds to a certain A/F). Therefore, proportional A/F control is possible with the

use of UEGO sensors, facilitating faster response of the fuel feedback control system and tighter

control of A/F. 

Although some manufacturers are currently using UEGO sensors, discussions with various

manufacturers suggest that some manufacturers are of mixed opinion as to the future applicability

of UEGO sensors. Because of their high cost, manufacturers claim that it may be cheaper to improve

HEGO technology rather than utilize UEGO sensors. An example of this is the use of a “planar”

design for HEGO sensors. Planar HEGO sensors (also known as “fast light-off” HEGO sensors)

have a thimble design that is considerably lighter than conventional designs. The main benefits are

shorter heat-up time and faster sensor response. 

(c) Individual Cylinder A/F Control

Another method for tightening fuel control is to control the A/F in each individual cylinder.

Current fuel control systems control the A/F for the entire engine or a bank of cylinders. By

controlling A/F for the entire engine or a bank of cylinders, any necessary adjustments made to fuel

delivery for the engine are applied to all cylinders simultaneously, regardless of whether all cylinders

need the that amount of fuel delivered. For example, there is usually some deviation in A/F between

cylinders. If a particular cylinder is rich, but the "bulk" A/F indication for the engine is lean, the fuel

control system will simultaneously increase the amount of fuel delivered to all of the cylinders,

including the rich cylinder. Thus, the rich cylinder becomes even richer having a potentially negative

effect on the net A/F.

Individual cylinder A/F control helps diminish variation among individual cylinders. This

is accomplished by modeling the behavior of the exhaust gases in the exhaust manifold and using

sophisticated software algorithms to predict individual cylinder A/F. Individual cylinder A/F control

requires use of an UEGO sensor in lieu of the traditional HEGO sensor, and requires a more

powerful engine control computer.

(d) Adaptive Fuel Control Systems

The fuel control systems of virtually all current vehicles incorporate a feature known as

"adaptive memory" or "adaptive block learn." Adaptive fuel control systems automatically adjust

the amount of fuel delivered to compensate for component tolerances, component wear, varying

environmental conditions, varying fuel compositions, etc., to more closely maintain proper fuel

control under various operating conditions. 
Chapter 3: Technological Feasibility

53

For most fuel control systems in use today, the adaption process affects only steady-state

operation conditions (i.e., constant or slowly changing throttle conditions). Because transient

operating conditions have always provided a challenge to maintaining precise fuel control, the use

of adaptive fuel control for transient operation would be extremely valuable. Accurate fuel control

during transient driving conditions has traditionally been difficult because of inaccuracies in

predicting the air and fuel flow under rapidly changing throttle conditions. Air and fuel dynamics

within the intake manifold (fuel evaporation and air flow behavior), and the time delay between

measurement of air flow and the injection of the calculated fuel mass, result in temporarily lean A/F

during transient operation. Variation in fuel properties, particularly distillation characteristics, also

increases the difficulty in predicting A/F during transients. These can all lead to poor drive ability

and an increase in NOx emissions.

6. Electronic Throttle Control Systems

As mentioned above, the time delay between the air mass measurement and the calculated

fuel delivery presents one of the primary difficulties in maintaining accurate fuel control and good

drive ability during transient driving conditions. With the conventional mechanical throttle system

(a metal linkage connected from the accelerator pedal to the throttle blade in the throttle body), quick

throttle openings can result in a lean A/F spike in the combustion chamber. Although algorithms

can be developed to model air and fuel flow dynamics to compensate for these time delay effects,

the use of an electronic throttle control system, known as “drive-by-wire” or “throttle-by-wire,” may

better synchronize the air and fuel flow to achieve proper fueling during transients (e.g., the driver

moves the throttle, but the fuel delivery is momentarily delayed to match the inertial lag of the

increased airflow).

While this technology is currently used in several vehicle models, it is considered expensive

and those vehicles equipped with the feature are expensive higher end vehicles. Because of its high

cost, it is not anticipated that drive-by-wire technology will become commonplace in the near future.

B. Improvements in Fuel Atomization

In addition to maintaining a stoichiometric A/F ratio, it is also important that a homogeneous

air-fuel mixture be delivered at the proper time and that the mixture is finely atomized to provide

the best combustion characteristics and lowest emissions. Poorly prepared air-fuel mixtures,

especially after a cold start and during the warm-up phase of the engine, result in significantly higher

emissions of unburned HC since combustion of the mixture is less complete. By providing better

fuel atomization, more efficient combustion can be attained, which should aid in improving fuel

economy and reducing emissions. Sequential multi-point fuel injection and air-assisted fuel injectors

are examples of the most promising technologies available for improving fuel atomization.

1. Sequential Multi-Point 

Typically, conventional multi-point fuel injection systems inject fuel into the intake manifold

by injector pairs. This means that rather than injecting fuel into each individual cylinder, a pair of
Regulatory Impact Analysis 

54

injectors (or even a whole bank of injectors) fires simultaneously into several cylinders. Since only

one of the cylinders is actually ready for fuel at the moment of injection, the other cylinder(s) gets

too much or too little fuel. With this less than optimum fuel injection timing, fuel puddling and

intake manifold wall wetting can occur, both of which can hinder complete combustion. Sequential

injection, on the other hand, delivers a more precise amount of fuel that is required by each cylinder

to each cylinder at the appropriate time. Because of the emission reductions and other performance

benefits “timed” fuel injection offers, sequential fuel injection systems are very common on today’s

vehicles and are expected to be incorporated in all vehicles soon.

2. Air-Assisted Fuel Injectors

Another method to further homogenize the air-fuel mixture is through the use of air-assisted

fuel injection. By injecting high pressure air into the fuel injector, and subsequently, the fuel spray,

greater atomization of the fuel droplets can occur. Since achieving good fuel atomization is difficult

when the air flow into the engine is low, air-assisted fuel injection can be particularly beneficial in

reducing emissions at low engine speeds. In addition, industry studies have shown that the short

burst of additional fuel needed for responsive, smooth transient maneuvers can be reduced

significantly with air-assisted fuel injection due to a decrease in wall wetting in the intake manifold.

C. Improvements to Exhaust Aftertreatment Systems

Over the last five years or so, there have been tremendous advancements in exhaust

aftertreatment systems. Catalyst manufacturers are progressively moving to palladium (Pd) as the

main precious metal in automotive catalyst applications. Improvements to catalyst thermal stability

and washcoat technologies, the design of higher cell densities, and the use of two-layer washcoat

applications are just some of the advancements made to catalyst technology. There has also been

much development in HC and NOx absorber technology. The advancements to exhaust

aftertreatment systems are probably the single most important area of emission control development.

1. Catalysts

As previously mentioned, significant changes in catalyst formulation, size and design have

been made in recent years and additional advances in these areas are still possible. Palladium (Pd)

is likely to continue as the precious metal of choice for close-coupled applications and will start to

see more use in underfloor applications. Palladium catalysts, however, are less resistant to poisoning

by oil-and fuel-based additives than conventional platinum/rhodium (Pt/Rh) catalysts. Based on

current certification trends and information from vehicle manufacturers and catalyst suppliers, it is

expected that Pd-only and Pd/Rh catalysts will be used in the close-coupled locations while

conventional or tri-metal (Pd/Pt/Rh) catalysts will continue to be used in underfloor applications.

Some manufacturers have suggested that they will use Pd/Rh in lieu of tri-metal or conventional

Pt/Rh catalysts for underfloor applications. As palladium technology continues to improve, it may

be possible for a single close-coupled catalyst to replace both catalysts. If fact, at least one vehicle

manufacturer currently uses a single Pd-only catalyst for one of their models. According to MECA,

new Pd-based catalysts are now capable of withstanding exposure to temperatures as high as 1100(C
Chapter 3: Technological Feasibility

55

0

2

4

6

8

10

12

14

16

THC NOx

% breakthrough in European 

driving cycle

Single layer Pd/Rh

Two layer - Pd top

Two layer - Pd bottom

SAE 960802: 1.8 liter 4 cyl; 100 h aged; Pd/Rh=5/1 @ 50 g/cu. ft.

and, as a result, can be moved very close to the exhaust manifold to enhance catalyst light-off

performance.

 In addition to reliance on Pd and tri-metal applications, catalyst manufacturers have

developed “multi-layered” washcoat technologies. Automotive catalysts consist of a cylindrical or

oval shaped substrate, typically made of ceramic or metal. The substrate is made up of hundreds of

very small, but long cells configured in a shape similar to a honey-comb. The substrate is coated

with a substance containing precious metals, rare earth metals, and base-metal oxides, that is known

as the catalyst washcoat. Typical washcoat formulations consist of precious metals which either

oxidize or reduce pollutants, base-metal oxides, such as alumina, which provide the surface area

support for the precious metals to adhere to, and base components (rare earth metals) such as

lanthanum, ceria, and zirconia, which act as promoters, stabilizers, and encourage storage and

reduction of oxygen. Conventional catalysts have had a single layer of washcoat and precious

metals applied to the catalyst substrate. Multi-layered washcoats use a combination of washcoat and

precious metals on different layers. The washcoat can be applied to the substrate such that one layer

can be applied on top of another. The use of multi-layered washcoat technology allows precious

metals that have adverse reactions together to be separated such that catalyst durability and emission

reduction performance are significantly enhanced. For example, Pd and Rh can have adverse

reactions when combined together in a single washcoat formulation. A multi-layer washcoat

architecture that uses Pd and Rh could have the Pd on the bottom layer and the Rh on the top layer

or vice versa. Figure 3-4 illustrates the impact coating architecture (multi-layered washcoat

technology) can have on emission performance.

Figure 3-4. Impact of Coating Architecture on HC and NOx Emissions

Manufacturers have also been developing catalysts with substrates which utilize thinner walls

in order to design higher cell density, low thermal mass catalysts for close-coupled applications
Regulatory Impact Analysis 

56

(improves mass transfer at high engine loads and increase catalyst surface area). The greater the

number of cells there are the more surface area that exists for washcoat components and precious

metals to adhere to, resulting in more precious metal sites available for oxidizing and reducing

pollutants. Cell densities of 600 cells per square inch (cpsi) have already been commercialized, and

research on 900 cpsi catalysts has been progressing. Typical cell densities for conventional catalysts

are 400 cpsi. 

The largest source for HC continues to be from cold start operation where the combination

of rich A/F operation and the ineffectiveness of a still relatively cool catalyst result in excess HC

emissions. One of the most effective strategies for controlling cold start HC emissions is to reduce

the time it takes to increase the operating temperature of the catalyst immediately following engine

start-up. The effectiveness or efficiency of the catalyst increases as the catalyst temperature

increases. One common strategy is to move the catalyst closer to the exhaust manifold where the

exhaust temperature is greater (e.g., a close-coupled catalyst). In addition to locating the catalyst

closer to the engine, retarding the spark timing, which causes combustion to occur late in the power

stroke allowing more heat to escape into the exhaust manifold during the exhaust stroke, increased

idle speed. Increased idle speed leads to a greater amount of combustion per unit time and thus to

a greater quantity of heat for heating the exhaust manifold, headpipe, and catalyst. Another strategy

is to use an electrically-heated catalyst (EHC). The EHC consists of a small electrically heated

catalyst placed directly in front of a conventional catalyst. Both substrates are located in a single can

or container. The EHC is powered by the alternator, or solely from the vehicle’s battery, or from a

combination of the alternator and battery. The EHC is capable of heating up almost immediately,

assisting the catalyst that directly follows it to also heat up and obtain light-off temperature (e.g., the

catalyst temperature where catalyst efficiency is 50 percent) quickly. Manufacturers have indicated

that EHC’s will probably only be necessary for a limited number of LEV/ULEV engine families,

mostly larger displacement V-8's where cold start emissions are difficult to control. 

2. Adsorbers/Traps

Other potential exhaust aftertreatment systems that are used in conjunction with a catalyst

or catalysts, are the HC and NOx adsorbers/traps. Hydrocarbon adsorbers are designed to trap HC

while the catalyst is cold and unable to sufficiently convert the HC. They accomplish this by

utilizing an adsorbing material which holds onto the HC. Once the catalyst is warmed up, the

trapped HC are released from the adsorption material and directed to the fully functioning

downstream three-way catalyst. There are three principal methods for incorporating the adsorber

into the exhaust system. The first is to coat the adsorber directly on the catalyst substrate. The

advantage is that there are no changes to the exhaust system required, but the desorption process

cannot be easily controlled and usually occurs before the catalyst has reached light-off temperature.

The second method locates the adsorber in another exhaust pipe parallel with the main exhaust pipe,

but in front of the catalyst and includes a series of valves that route the exhaust through the adsorber

in the first few seconds after cold start, switching exhaust flow through the catalyst thereafter. Under

this system, mechanisms to purge the trap are also required. The third method places the trap at the

end of the exhaust system, in another exhaust pipe parallel to the muffler, because of the low thermal
Chapter 3: Technological Feasibility

57

tolerance of adsorber material. Again a purging mechanism is required to purge the adsorbed HC

back into the catalyst, but adsorber overheating is avoided. 

NOx adsorbers have been researched, but according to MECA, are generally recognized as

a control for NOx resulting from reduced EGR. They are typically used for lean-burn applications

and are not applicable to engines that attempt to maintain stoichiometry all the time.

3. Secondary Air Injection

Secondary injection of air into exhaust ports after cold start (e.g., the first 40-60 seconds)

when the engine is operating rich, coupled with spark retard, can promote combustion of unburned

HC and CO in the exhaust manifold and increase the warm-up rate of the catalyst. By means of an

electrical pump, secondary air is injected into the exhaust system, preferably in close proximity of

the exhaust valve. Together with the oxygen of the secondary air and the hot exhaust components

of HC and CO, an advanced reaction ahead of the catalyst can bring about an efficient increase in

the exhaust temperature which helps the catalyst to heat up quicker. The exothermic reaction that

occurs is dependent on several parameters (secondary air mass, location of secondary air injection,

engine A/F ratio, engine air mass, ignition timing, manifold and headpipe construction, etc.), and

ensuring reproducibility of functions demands detailed individual application for each vehicle or

engine design. 

4. Insulated or Dual Wall Exhaust System

Insulating the exhaust system is another method of furnishing heat to the catalyst to decrease

light-off time. Similar to close-coupled catalysts, the principle behind insulating the exhaust system

is to conserve heat generated in the engine for aiding the catalyst warm-up. Through the use of

laminated thin-wall exhaust pipes, less heat will be lost in the exhaust system, enabling quicker

catalyst light-off.

D. Improvements in Engine Calibration Techniques

Of all the technologies discussed above, one of the most important emission control strategies

is not hardware-related. Rather, it’s the software and, more specifically, the algorithms and

calibrations contained within the software that are used in the power-train control module (PCM)

which control how the various engine and emission control components and systems operate.

Advancements in software along with refinements to existing algorithms and calibrations can have

a major impact in reducing emissions. Confidential discussions between manufacturers and EPA

suggest that manufacturers believe emissions can be further reduced by improving and updating their

calibration techniques. As computer technology and software continues to advance, so does the

ability of the automotive engineer to use these advancements in ways to better optimize the emission

control systems. For example, as processors become faster, it is possible to perform calculations

quicker, thus allowing for faster response times for things such as fuel and spark control. As the

PCM becomes more powerful with greater memory capability, algorithms can become more

sophisticated. Manufacturers have found that as computer processors, engine control sensors and
Regulatory Impact Analysis 

58

actuators, and computer software become more advanced, and, in conjunction with their growing

experience with developing calibrations, as time passes, their calibration skills will continue to

become more refined and robust, resulting in even lower emissions.

 Manufacturers have suggested to EPA that perhaps the single most effective method for

controlling NOx emissions will be tighter A/F control which could be accomplished with

advancements in calibration techniques without necessarily having to use advanced technologies,

such as UEGO sensors. Manufacturers have found ways to improve calibration strategies such that

meeting federal cold CO requirements, as well as, complying with LEV standards, have not required

the use of advanced hardware, such as EHCs or adsorbers.

Since emission control calibrations are typically confidential, it is difficult to predict what

advancements will occur in the future, but it is clear that improved calibration techniques and

strategies are a very important and viable method for further reducing emissions.

E. Advanced Technology

Thus far, the technology assessment has focused on conventional emission control

technology for vehicles with gasoline-powered spark ignition engines. There are a number of

advanced technologies in the near horizon that may be capable even further reductions in emissions.

Examples of such technologies are fuel cells, electric vehicles, and hybrid vehicles.

Fuel cell technology converts such fuels as methanol, natural gas, and gasoline into electrical

energy without generating the pollutants associated with internal-combustion engines. A fuel cell

is made of a thin plastic film sandwiched between two plates. Hydrogen fuel and oxygen from the

air are electrically combined in the fuel cell to produce electricity. Typically, the only by-products

are heat and water vapor. A fuel cell coupled with an electrically powered drive-train is essentially

a quite, zero-emissions vehicle. 

Electric vehicles use electric motors to power the wheels. The electric motors are powered

by packs of batteries stored underneath the vehicle. These vehicles use many newer technologies,

such as advanced charging and regenerating systems as well as vehicle structural design. Battery

technology, which has been the major technical limitation to date, has been and will be the focus of

much developmental work. Improved nickel-metal hydride and lithium ion batteries are two of the

battery types being analyzed for use in electric vehicles produced in the near future.

Hybrid vehicles are typically powered by a combination of two powertrain systems. There

is usually a low or zero emitting main powertrain system (e.g., battery-powered electric motors) that

powers the vehicle during steady-state operation, when power demands are low. When more power

is required to accelerate or drive up a hill, an axillary powertrain, usually a small displacement

internal combustion engine is used. The engine may be diesel-powered, or some derivative thereof,

or an alternative-fuel powered spark ignition engine that is low emitting. Because the engine used

is small and low polluting, and the majority of operation uses the non-engine powertrain, hybrid

vehicles have the potential to be very low emitting vehicles. 
Chapter 3: Technological Feasibility

59

F. Technologies In-use On Current Otto-cycle HD Engines

Otto-cycle engine manufacturers are producing heavy-duty engines equipped with substantial

emission controls. Table 3-8 provides a list of some key technologies currently being used for HD

engine emissions control. Manufacturers have introduced improved systems as they have introduced

new or revised engine models. These systems can provide very good emissions control and many

engines are being certified to levels of less than half the current standards. Many of the technologies

have been carried over from light-duty applications.

Table 3-8:

Key Technologies for Current Engines

Sequential Fuel Injection/electronic control

3 way catalyst

pre and post catalyst heated exhaust gas oxygen sensors

Electronic EGR 

Secondary air injection 

Improved electronic control modules 

Improving fuel injection has been proven to be an effective and durable strategy for

controlling emissions and reducing fuel consumption from gasoline engines. Improved fuel injection

will result in better fuel atomization and a more homogeneous charge with less cylinder-to-cylinder

and cycle-to-cycle variation of the air-fuel ratio. These engine performance benefits will increase

as technology advances allow fuel to be injected with better atomization. Increased atomization of

fuel promotes more rapid evaporation by increasing the surface area to mass ratio of the injected fuel.

This results in a more homogeneous charge to the combustion chamber and more complete

combustion. Currently, sequential multi-port fuel injection (SFI) is used in most, if not all,

applications because of its proven effectiveness.

One of the most effective means of reducing engine-out NOx emissions is exhaust gas

recirculation (EGR). By recirculating spent exhaust gases into the combustion chamber, the overall

air-fuel mixture is diluted, lowering peak combustion temperatures and reducing NOx. Exhaust gas

recirculation is currently used on heavy-duty gasoline engines as a NOx control strategy. Many

manufacturers now use electronic EGR in place of mechanical back-pressure designs. By using

electronic solenoids to open and close the EGR valve, the flow of EGR can be more precisely

controlled.

EPA believes that the most promising overall emission control strategy for heavy-duty

gasoline engines is the combination of a three-way catalyst and closed loop electronic control of the

air-fuel ratio. Control of the air-fuel ratio is important because the three-way catalyst is only
Regulatory Impact Analysis 

60

effective if the air-fuel ratio is at a narrow band near stoichiometry. For example, for an 80 percent

conversion efficiency of HC, CO, and NOx with a typical three-way catalyst, the air-fuel ratio must

be maintained within a fraction of one percent of stoichiometry. During transient operation, this

minimal variation cannot be maintained with open-loop control. For closed-loop control, the air-fuel

ratio in the exhaust is measured by an oxygen sensor and used in a feedback loop. The throttle

position, fuel injection, and spark timing can then be adjusted for given operating conditions to result

in the proper air-fuel ratio in the exhaust. Most if not all engines have been equipped with close loop

controls. Some engines have been equipped catalysts that are achieving catalyst efficiencies in

excess of 90 percent. This is one key reason engine and vehicle certification levels are very low.

In addition, electronic control can be used to adjust the air-fuel ratio and spark timing to adapt to

lower engine temperatures, therefore controlling HC emissions during cold start operation.

All HD engines are equipped with three-way catalysts. Engine may be equipped with a

variety of different catalyst sizes and configurations. Manufacturers choose catalysts to fit their

needs for particular vehicles. Typically, federal vehicle catalyst systems are a single converter or

two converters in series or in parallel. A converter is constructed of a substrate, washcoat, and

catalytic material. The substrate may be metallic or ceramic with a flow-through design similar to

a honeycomb. A high surface area coating, or washcoat, is used to provide a suitable surface for the

catalytic material. Under high temperatures, the catalytic material will increase the rate of chemical

reaction of the exhaust gas constituents. Catalyst systems on HD vehicles tend to be large with fairly

low precious metal loading. Catalyst volumes are typically 80 to 90 percent of engine volumes.

Precious metal loadings are in the range of 1 to 4 grams per liter (g/l).

Significant changes in catalyst formulation have been made in recent years and additional

advances in these areas are still possible. Platinum, Palladium and Rhodium (Pt, Pd, and Rh) are the

precious metals typically used in catalysts. Historically, platinum has been widely used. Today,

palladium is being used much more widely due to its ability to withstand very high exhaust

temperatures. In fact, some HD vehicles currently are equipped with palladium-only catalysts. Other

catalysts contain all three metals or contain both palladium and rhodium. Some manufacturers have

suggested that they will use Pd/Rh in lieu of tri-metal or conventional Pt/Rh catalysts for underfloor

applications. Improvements in substrate and washcoat materials and technology have also

significantly improved catalyst performance. 

Tables 3-9 and 3-10 provide certification results from either the 1998 or 1999 model year for

various engines and vehicles. The engine data is from EPA certification data and the vehicle data

comes from California Medium-duty Vehicle certification data. California vehicles were certified

to the Tier 1 standards. The table provide and indication of the emissions levels that have been

achieved through the application of these technologies.
Chapter 3: Technological Feasibility

61

Table 3-9:

1998 or 1999 Model Year Certification Data (g/mile)

Manufacturer Model Engine

size

GVWR NOx

(120k)

HC 

(120k)

Chrysler Ram 3500 Cab Chassis 8.0 11,000 0.6

0.9

0.23

0.24

Ram 3500 Cab Chassis 8.0 11,000 0.7

0.9

0.24

Ram 3500 Cab Chassis 8.0 11,000 0.9 0.24

Ram 2500 Pickup 8.0 8,800 0.5 0.19

 0.21

Ram 3500 Pickup 8.0 10,500 0.5 0.19

 0.21

Ford F250/F350 5.4 8,800-

9,700

0.209

 0.212

0.301

0.314

F250/F350 Dual rear wheel 6.8 8,800-

11,000

0.273 0.263

E250 Econoline 5.4 8,550 0.289,

0.446

0.295

0.300

E350 5.4 9,100 0.278

0.654

0.263

0.283

E250 Strip Chassis 4.2 8,550 0.161 0.111

E350 6.8 9,400 0.299 0.270

E350 6.8 9,300 0.308 0.296

E350 6.8 9,300 0.364 0.276

F250/F350 5.4 8,800-

9,700

0.209

0.212

0.301

0.314

F250/F350 Dual rear wheel 6.8 8,800-

11,000

0.273 0.263

GM K2500 Suburban 5.7 8,600 0.6 0.22

K2500 Pickup 5.7 8,600 0.6 0.2

K3500 Pickup 5.7 10,000 0.6 0.27

K3500 Pickup 7.4 10,000 0.5 0.16

C/K2500 4WD Pickup 6.0 8,600 0.4

0.5

0.14

0.12

C/K2500 2WD Pickup 6.0 8,600 0.3 0.13

C/K2500, 3500, Suburban, 6.0 8,600- 0.5 0.15
Regulatory Impact Analysis 

62

Table 3-10:

1998/1999 Model Year Engine Certification Data (g/bhp-hr)

Manufacturer Engine size NOx HC 

Chrysler 5.9 3.8 0.4

8.0 1.2 0.2

Ford 5.4 0.4 0.1

6.8 0.1 0.1

6.8 0.4 0.1

GM 4.3 1.1 0.3

5.7 1.2 0.1

5.7 1.7 0.2

6.0 0.4 0.1

7.4 2.3 0.3

7.4 0.7 0.4

G. Chassis-based standards

EPA is extending the California LEV standards nationwide. California began requiring some

vehicles to meet LEV standards in 1998 and the phase-in will be complete in 2001. We have based

our technological feasibility assessment and technology projections primarily on the mix of

technologies being used to achieve California LEV emissions levels. Cold start emissions contribute

to a larger portion of the emissions measured over the chassis-based test procedure compared to the

engine-based test procedure. This will likely influence some of the technology choices

manufacturers make in response to the chassis-based standards. 

Of the anticipated changes, enhancements to the catalyst systems are expected to be most

critical. Catalyst configurations are likely to continue to vary widely among the manufacturers

because manufacturers must design the catalyst configurations to fit the vehicles. One potential

change is that manufacturers may move the catalyst closer to the engine (close-coupled) or may place

a small catalyst close to the engine followed by a larger underfloor catalyst. These designs provide

lower cold start emissions because the catalyst is closer to the engine and warms up more quickly.

Typically, the catalyst systems used in HD applications have a large total volume but with

lower precious metal content per liter compared to light-duty catalyst systems. For 2004, we are

projecting an increase in overall precious metal loading of about 50 percent for a catalyst loading of

between 4 to 5 g/l. We are not expecting significant increases in total catalyst volume. The trend
Chapter 3: Technological Feasibility

63

toward increased use of Pd and Rh is also expected to continue. Close-coupled catalysts would

likely be Pd only.

Calibration changes will also be important. The engine and catalyst systems must be

calibrated to optimize the performance of the systems as a whole. Post catalyst oxygen sensors will

allow further air fuel control. Manufacturers are moving to more powerful computer systems and

EPA expects this trend to continue. Other technologies such as insulated exhaust systems may also

be used in some cases to reduce cold start emissions. 

As shown in Table 3-9, HD vehicles in California have typically been certified with full life

emissions levels in the 0.3 - 0.5 g/mile range for NOx and the 0.1 - 0.3 g/mile range for NMOG.

These levels are well within the LEV standards and provide manufacturers with head room or

compliance cushion. We expect manufacturers would equip vehicles with very similar technologies

to meet our new standards. 

H. Engine-based Standards

As shown in Table 3-10, a few engine families are currently certified with NOx emissions

levels close to the current standards. Many others are certified with emissions levels of less than half

the standard. Manufacturers have begun to apply advanced system designs to their heavy-duty

applications. Some newer engine families have been certified with emissions levels of 0.5 g/bhp-hr

combined NOx plus NMHC. These engines and systems feature precise air/fuel control and catalyst

designs comparable to the catalyst systems being used in LEV applications. Based on industry input,

we believe that manufacturers will continue the process of replacing their old engine families with

advanced engines over the next several years. New and more advanced engines are being introduced,

and we anticipate that they will be capable of achieving our new standards.

Catalyst systems with increased precious metal loading will be the critical hardware change

for meeting the standards being finalized in this rule. Catalyst system volumes and precious metal

loading are likely to be similar to the systems discussed above for the chassis-based standards.

Engines used in vehicles above 14,000 pounds may have more rigorous duty cycles which may lead

to some catalyst enhancements. A small increase in precious metal loading over that used in chassisbased systems may be needed to ensure the thermal durability of the system. Palladium and

palladium/rhodium catalyst formulations are expected. There is likely to be less use of close coupled

systems compared with chassis-based certifications because of durability concerns. Also, there is

less emphasis on cold start emissions with the engine test than with the chassis test. Advanced

washcoats including layering may also be used to enhance durability.

Optimizing and calibrating the catalyst and engine systems as a whole will also be important

in achieving the levels required by the standards. Precise air/fuel control is critical to meeting these

standards. Increased use of air injection to control cold start emissions may occur, especially to

reduce NMHC emissions during cold start operation. Also, improved EGR systems and retarded

spark timing may be needed to reduce engine out NOx emissions levels. 
Regulatory Impact Analysis 

(j) 12.0 g engine out x.091 for catalyst efficiency + 0.65 for compliance cushion = 1.74 g NOx. The difference

between 2.0g and 1.74 g is reserved for NMHC emissions.)

64

Manufacturers have noted on several occasions that they target emissions certification levels

of about half the standard. Manufacturers noted that they maintain this cushion between the standard

and their certification level in part due to the potential for in-use deterioration of catalysts and

oxygen sensors beyond that captured during the certification process. Catalysts experience wide

variations in exhaust temperature due to the wide and varied usage of vehicles in the field. Some

vehicles may experience more severe in-use operation than is represented by the durability testing

conducted for engine certification. Manufacturers have argued that EPA should not set new standards

based on certification data because certification levels do not account for severe in-use deterioration.

Taking manufacturer practices into account, EPA would expect that engines certified in the 0.5

g/bhp-hr NOx plus NMHC range would meet a 1.0 g/bhp-hr standard.

Catalyst system durability is a key issue in the feasibility of the standards. Historically,

catalysts have deteriorated when exposed to very high temperatures and this has long been a concern

for heavy-duty work vehicles. Manufacturers have often taken steps to protect catalysts by ensuring

exhaust temperatures remain in an acceptable range. Catalyst technologies in use currently are much

improved over the catalysts used only a few years ago. The improvements have come with the use

of palladium, which has superior thermal stability, and through much improved washcoat

technology. The use of rhodium with palladium will also enhance performance of the catalyst. The

catalysts have been shown to withstand temperatures typically experienced in HD applications.

Manufacturers also continue to limit exhaust temperature extremes not only to protect catalyst

systems but also to protect the engine. EPA requirements allow manufacturers to take necessary

steps to protect engine and emission control systems from high temperatures.

In addition to general comments noted above regarding the need for compliance cushion,

manufacturers presented EPA with an analysis of the otto-cycle engine emissions standards for 2004.

The analysis assumed: 

• NOx catalyst efficiency of 90.9 percent at the end of the engine’s useful life; 

• An engine-out NOx level of 12 g/bhp-hr;

• A cushion of .3 g/bhp-hr for engine variability and a safety margin of 20 percent of the

standard;

• Tailpipe NMHC levels of 15 percent of the NOx level (.26 g/bhp-hr).

Based on these assumptions, manufacturers recommended a 2.0 g/bhp-hr NMHC plus NOx

standard.j

 Manufacturers noted that a catalyst efficiency of about 97 percent would be needed to

meet a 1.0 g/bhp-hr standard and that their assessments of post-2000 catalysts indicate worst case

performance well below this level. The manufacturers’ recommended 2.0 g/bhp-hr standard seems

to indicate that compliance cushions greater than half the standard are needed.
Chapter 3: Technological Feasibility

(k) The details of this analysis are considered Confidential Business Information.

65

Manufacturers state that their catalyst assumptions represented catalyst deterioration based

on worst case vehicle operation (highly loaded operation, high exhaust temperatures). Details of the

catalyst were not available except that manufacturers stated that the catalyst represented post-2000

catalyst technology. Due to the lack of detail, it is difficult to evaluate the assumption. However,

EPA believes that this assumption is somewhat conservative given the recent developments in

catalyst technology, the lead time available, and methods available to protect catalysts under worst

case vehicle operation.

Engine-out NOx levels are also critical to the analysis. In their analysis, manufacturers

assumed engine-out NOx levels of 12 g/bhp-hr, based on manufacturer development data for one

engine. EPA does not believe that the engine-out NOx level of 12 g/bhp-hr is a reasonable or

representative assumption. Other available data indicates that several engines have engine-out NOx

emissions well below this level in the 6 to 10 g/bhp-hr range. Also, a previous assessment of engine

standards presented to EPA by one manufacturer assumed much lower engine-out NOx levels.k EPA

does not believe that the current standards have encouraged manufacturers to place a high priority

on engine-out emissions levels. For recent engines, catalysts have provided the majority of needed

emissions control.

EPA also further considered the engine variability factor of 0.3 g/bhp-hr built into the

manufacturers analysis. The analysis as presented assumes a 12 g/bhp-hr engine-out NOx level.

Manufacturer data for the developmental engine suggests that 12 g/bhp-hr is the worst case engineout level anticipated (the actual highest test point recorded was 12.65). It appears to EPA that

manufacturers double counted engine variability by using the worst case engine data and an engine

variability factor. Using engine-out NOx levels of 12 g in the analysis but without the engine

variability factor yields a NOx + NMHC level of 1.6 g/bhp-hr. Without including a safety margin,

which may be appropriate considering the analysis is already based on worst case engine and catalyst

assumptions, the level would be 1.3 g/bhp-hr. To reach the 1.0 g/bhp-hr level with this engine and

a 20 percent safety margin, a catalyst efficiency of 94 percent would be needed. The catalyst

efficiency would need to be 93 percent if the 20 percent safety margin were not included in the

analysis. 

EPA believes that the standards will require manufacturers to focus some effort on engine-out

emissions control and that engine-out NOx levels in the 6 to 8 g/bhp-hr are reasonably achievable.

Some engines are already in this range. For other engines, some recalibration of engine systems

including the EGR system and perhaps some modest hardware changes to those systems would be

necessary. EGR plays a key role in reducing engine-out NOx and system redesign may allow more

effective use of this technology. 

When coupled with a catalyst with worst case efficiencies in the 91 to 93 percent range, these

engines could achieve the standards. Of course with higher catalyst efficiencies, manufacturers
Regulatory Impact Analysis 

66

would not have to achieve lower NOx engine-out levels. Catalyst efficiencies of about 93 percent

would allow manufacturers to maintain compliance margins in the range of 25 and 45 percent of the

standard. EPA believes these margins are sufficient considering the analysis is also based on worst

case catalyst efficiencies. 

To help address phase in concerns that could arise for manufacturers, EPA is finalizing a

modified ABT program for engines. The averaging, banking, and trading (ABT) program can be an

important tool for manufacturers in implementing a new standard. The program allows

manufacturers to comply with the more stringent standards by introducing emissions controls over

a longer period of time, as opposed to during a single model year. Manufacturers plan their product

introductions well in advance. With ABT, manufacturers can better manage their product lines so

that the new standards don’t interrupt their product introduction plans. Also, the program also

allows manufacturers to focus on higher sales volume vehicles first and use credits for low sales

volume vehicles. EPA believes manufacturers have significant opportunity to earn credits in the pre2004 time frame.

Considering all of these factors, EPA believes that the 1.0 g/bhp-hr NOx plus NMHC

standard is the appropriate standard for HD otto-cycle engines in the 2004 time frame. Certification

levels of 0.5 g/bhp-hr NOx plus NMHC have been achieved on recently introduced engines of

various sizes. EPA believes that the standard provides sufficient opportunity for manufacturers to

maintain a compliance margin. As manufacturers continue with normal product plans between now

and 2004, improved engines will continue to replace older models. The ABT program is available

for manufacturers who have not completely changed over to new engine models by 2004. ABT

provides manufacturers with the opportunity to earn credits prior to 2004 and use the credits to

continue to offer older engine models that have not yet been redesigned or retired by 2004.

IV. On-board Diagnostics for HD Diesel and Otto-cycle Engines

To meet customer demands, manufacturers of heavy-duty engines currently use on-board

diagnostics (OBD) to electronically monitor engine parameters to ensure proper engine performance

and to assist in malfunction diagnostics and repair90. Because EPA expects manufacturers to

implement electronically controlled emission control strategies such as EGR and fuel injection rate

shaping, EPA is promulgating OBD requirements for heavy-duty engines used in vehicles up to

14,000 pounds, gross vehicle weight (GVW) to ensure that emission-control components meet

certain performance standards. These requirements are intended to ensure that emission-control

components remain effective in-use. The California Air Resources Board (CARB) has already

implemented similar requirements.

EPA believes that the new requirements are already technologically feasible. All classes of

HD vehicles currently employee some form of on-board diagnostics for performance purposes, and

many of these systems are highly sophisticated. In addition, HD vehicles up to 14,000 pounds

already have to meet regulatory OBD requirements in California. Finally, federal and California

emission driven OBD regulatory requirements have been in place for Otto-cycle and diesel light-duty

vehicles for a number of years. The technology necessary to perform OBD of HD vehicles is
Chapter 3: Technological Feasibility

67

available today. The new emission control technologies employed in 2004 will also lend themselves

easily to OBD. For example, LD vehicle manufacturers have been monitoring EGR systems for

OBD for a number of years.

As discussed previously, EPA does not expect diesel engine manufacturers to utilize

aftertreatment devices in order to achieve the 2004 HD standards, or the 2007 supplemental

requirements. However, in the past engine manufacturers have used diesel oxidation to provide

typically a 20 to 30 % reduction in PM on some light- and medium-heavy duty engine families. For

these diesel oxidation catalysts, a complete failure of the catalysts would not result in an exceedance

of the 1.5 times the standard threshold, therefore monitoring of catalyst performance would not be

a requirement. For PM traps and lean NOx catalysts, neither technology is anticipated for the 2004

model year. However, in the event a manufacturer did employee either of these types of

aftertreatment devices, EPA believes a back-pressure sensor would be feasible to monitor a PM trap

for a complete failure of the trap, and either a chemical sensor (such as the oxygen sensors used for

gasoline 3-way catalysts) or potentially a temperature sensor could be used to monitor the

performance of a lean NOx catalyst. 

The final rule requires that PM traps whose failure would result in an exceedance of 1.5 times

the PM standard must be monitored. However, the rule does not require that the monitor detect an

exceedance of 1.5 times the standard threshold. Rather, the requirement is to detect a complete

failure of the device. We define complete failure as a sudden drop in exhaust back-pressure below

that of a clean or unloaded trap under monitoring conditions specified by the manufacturer. Current

pressure monitoring sensors are clearly capable of performing this detection.

Direct emission measurement has been identified as an important technology to achieve

diesel engine closed-loop feedback control and to achieve after-treatment OBD. Researchers already

have achieved promising results on a compact NOx sensor that is capable of measuring real-time

NOx within 10% accuracy of laboratory-grade instruments under a wide range of operating

conditions, including the temperature, pressure, and oxygen concentration typical of diesel engine

exhaust. This breakthrough technology could be used for closed-loop control, and, because it can

accurately measure NOx in the 100 ppm range, it would enable monitoring of NOx aftertreatment

technologies.91,92 The most recent of these papers (Kato et. al., 1999) provides an in depth

discussion the accuracy, repeatability, and durability of an on-board NOx sensor, as well strategies

for using the sensor for closed loop control and OBD monitoring of an active lean NOx absorber.

The federal requirements for OBD, as they exist today, require manufacturers to monitor

emission related powertrain components, OBD does not monitor actual regulated pollutant

emissions. It is possible that in the future the on-board measurement of actual emission performance

may become feasible. EPA is following the development of a number of emerging on-board

emission measurement technologies which may lend themselves to regulatory requirements in the

future. These technologies include in-cylinder measurement devices, on-board PM measurement

devices, and predictive emission measurement systems such as neural networks. Crank-angle

resolved pressure and/or temperature measurements would allow for NOx emission prediction, based

on the current understanding of NOx formation.93 Piezo-electric and infrared pressure sensing
Regulatory Impact Analysis 

68

technologies are currently used to measure crank-angle resolved in-cylinder pressure. Based on

recent advances in sensor durability,94,95 EPA expects that future advances could allow their use onboard. Lastly, neural networks have recently demonstrated a technique for accurately predicting

emissions based solely on currently measured engine parameters. One study has shown excellent

correlation between predicted NOx and PM measurement with respect to actual emissions

measurements.96
Chapter 3: Technological Feasibility

69

1.Heywood J.B.: Internal Combustion Engine Fundamentals, McGraw-Hill, Inc, New York, p.

590, 1988.

2.Dodge L.G., D.M. Leone, D.W. Naegeli, D.W. Dickey, K.R. Swenson: “A PC-Based Model

for Predicting NOx Reductions in Diesel Engines,” SAE paper 962060, p.149, 1996.

3.Ibid.

4.Ibid.

5. Dickey D.W., T.W. Ryan III, A.C. Matheaus: “NOx Control in Heavy-Duty Engines-What is

the Limit?”, SAE paper 980174, 1998. Dickey; and, Zelenka P., H. Aufinger, W. Reczek, W.

Cartellieri: “Cooled EGR-A Key Technology for Future Efficient HD Diesels,” SAE paper

980190, 1998.

6. Kohketsu S., K. Mori, K. Sakai, T. Hakozaki: EGR Technologies for a Turbocharged and

Intercooled Heavy-Duty Diesel Engine,” SAE paper 970340, 1997; Baert R., D.E. Beckman,

A.W.M.J. Veen: “EGR Technology for Lowest Emissions,” SAE paper 964112, 1996; and, 

Heavy-duty Engine Working Group, Mobile Source Technical Advisory Subcommittee of the

Clean Air Act Advisory Committee, “Phase 2 of the EPA HDEWG Program - Summary

Document”, available in EPA Air Docket A-98-32.

7.Dickey D.W., T.W. Ryan III, A.C. Matheaus: “NOx Control in Heavy-Duty Engines-What is

the Limit?”, SAE paper 980174, p. 9, 1998.

8.Zelenka P., H. Aufinger, W. Reczek, W. Cartellieri: “Cooled EGR-A Key Technology for

Future Efficient HD Diesels,” SAE paper 980190, p. 47, 1998.

9.Kohketsu S., K. Mori, K. Sakai, T. Hakozaki: EGR Technologies for a Turbocharged and

Intercooled Heavy-Duty Diesel Engine,” SAE paper 970340, p. 97, 1997.

10.Zelenka P., p. 46.

11.Kohketsu S., p. 97.

12.Baert R., D.E. Beckman, A.W.M.J. Veen: “EGR Technology for Lowest Emissions,” SAE

paper 964112, p. 183, 1996.

13.Ibid.

14.Kohketsu S., p. 100.

15.Zelenka P., p. 49.

Chapter 3 References
Regulatory Impact Analysis 

70

16.Baert R., p. 184.

17.Kohketsu S., p. 100.

18.Zelenka P., p. 47.

19.Kohketsu S., p. 102.

20.Baert R., pp. 181,182.

21.Ibid.

22.Zelenka P. pp. 48,50.

23.Ibid.

24.Kreso A.M., J.H. Johnson, L.D. Gratz, S.T. Bagley, D.G. Leddy: “A Study of the Vapor- and

Particle-Phase Sulfur Species in the Heavy-Duty Diesel Engine EGR Cooler,” SAE paper

981423, pp. 1-2, 7, 1998.

25.Ibid.

26.McKinley T.L: “Modeling Sulfuric Acid Condensation in Diesel Engine EGR Coolers,” SAE

paper 970636, p. 211, 1997.

27.Ibid.

28.Kreso A.M., p. 7.

29.Ibid.

30.Banzhaf M., R. Lutz: “Heat Exchanger for Cooled Exhaust Gas Recirculation,” SAE paper

971822, pp. 4,6, 1997.

31.Zelenka P., p. 50.

32.Banahaf M., p. 3,4.

33.Ibid. 

34.Dekker H.J., W.L. Sturm: “Simulation and Control of a HD Diesel Engine Equipped with

New EGR Technology,” SAE paper 960871, p. 214, 1996.

35.Zelenka P., p. 48.

36.Kohketsu S. p.98.
Chapter 3: Technological Feasibility

71

37.Baert R., p. 179.

38. Anon., “Electronic Throttle Valve From Pierburg,”, Diesel Progress, August, 1998. Copy

Available in EPA Air Docket A-98-32, Docket Item #II-D-10.

39.Fielden, G., Lucas Inc., Vandalia, OH: Phone conversation with Matt Spears,

EPCD/OMS/EPA, January 7,1999. Summary of phone call available in EPA Air Docket A-98-

32, Docket Item # II-E-01.

40.Boehner W., K. Hummel: “Common Rail Injection System for Commercial Diesel Vehicles”,

SAE paper 970345, p. 140, 1997.

41. Dickey, SAE 981074

42. Boehner, 970345; and Uchida N, K. Shimokawa, Y. Kudo, M. Shimoda: “Combustion

Optimization by Means of Common Rail Injection System for Heavy-Duty Diesel Engines”, SAE

paper 982679, 1998.

43. Heywood, J.B., Internal Combustion Engine Fundamentals, McGraw-Hill, Inc., New York,

p. 643-644, 1988.

44.Guerrassi N., P. Dupraz: “A Common Rail Injection System for High Speed Direct Injection

Diesel Engines”, SAE paper 980803, p. 19, 1998.

45.Boehner W., p. 134.

46.Youngblood, J.R.: “Cummins New Midrange Fuel System”, SAE TOPTEC presentation,

“Diesel Technology for the New Millennium”, April 21-22, 1998. Available in EPA Air Docket

A-98-32, Docket Item II-D-01.

47.Stover, T.R., D.H. Reichenbach, E.K. Lifferth: “The Cummins Signature 600 Heavy-Duty

Diesel Engine”, SAE paper 981035, p. 8, 1998.

48.Osenga M.: “Cat Gears Up Next Generation Fuel Systems”, Diesel Progress, North American

Ed., P. 82, August 1998. Available in EPA Air Docket A-98-32, Docket Item #II-D-03.

49.Ibid., pp. 88-89.

50.Ibid., pp. 82-87.

51.Youngblood, J.R.

52.Ikegami, M., K. Nakatani, S. Tanaka, K. Yamane: “Fuel Injection Rate Shaping and Its Effect

on Exhaust Emissions in a Direct-Injection Diesel Engine Using a Spool Acceleration Type

Injection System”, SAE paper 970347, p. 163, 1997.
Regulatory Impact Analysis 

72

53.Ibid, p. 174.

54.Uchida N, K. Shimokawa, Y. Kudo, M. Shimoda: “Combustion Optimization by Means of

Common Rail Injection System for Heavy-Duty Diesel Engines”, SAE paper 982679, p. 3, 1998.

55.Dickey D.W., p. 13.

56.Uchida N., p. 4.

57.Coldren D.R.: “Advanced Technology Fuel System for Heavy Duty Diesel Engines”, SAE

paper 973182, p. 10, 1997.

58.Dickey D.W., p. 9.

59. Johnson, J., Bagley, S., Gratz, L., Leddy, D., "A Review of Diesel Particulate Control

Technology and Emissions Effects - 1992 Horning Memorial Award Lecture", SAE Paper

940233, 1994.

60. Meeting between EPA and the Manufacturers of Emission Controls Association, April

1995.

61. Voss, K., Bulent, Y., Hirt, C, and Farrauto, R., "Performance Characteristics of a Novel

Diesel Oxidation Catalyst", SAE Paper 940239, 1994.

62. Johnson, J., Bagley, S., Gratz, L., Leddy, D., "A Review of Diesel Particulate Control

Technology and Emissions Effects - 1992 Horning Memorial Award Lecture", SAE Paper

940233, 1994.

63. Kawanami, M., Horichi, M., Klein, H., Jenkins, M., “Development of Oxidation and deNOx Catalysts for High Temperature Exhaust Diesel Trucks, SAE Paper 981196.

64. “Demonstration of Advanced Emission Control Technologies Enabling Diesel-Powered

Heavy-Duty Engines to Achieve Low Emission Levels: Interim Report Number 1: Oxidation

Catalyst Technology” prepared for the Manufacturers of Emission Control Associations,

December 1998, copies available in EPA Air Docket A-98-32, Docket Item II-D-07.

65. Hawker, P., et. al., “Effect of a Continuously Regenerating Diesel Particulate Filter on

Non-Regulated Emissions and Particulate Size Distribution”, SAE paper 980189, February 1998.

66. “Demonstration of Advanced Emission Control Technologies Enabling Diesel-Powered

Heavy-Duty Engines to Achieve Low Emission Levels: Interim Report Number 2: Diesel

Particulate Filter Technology” prepared for the Manufacturers of Emission Control Associations,

December 1998, copies available in EPA Air Docket A-98-32, Docket Item II-D-08.

67. Wall, J.C., Cummins Engine Co., Diesel Fuel Composition for Future emissions

Regulations. Panel discussion, SAE International Fall Fuels and Lubricants Meeting and
Chapter 3: Technological Feasibility

73

Exposition, October 21, 1998.

68. Wall, J.C., Cummins Engine Co., Diesel Fuel Composition for Future emissions

Regulations. Panel discussion, SAE International Fall Fuels and Lubricants Meeting and

Exposition, October 21, 1998.

69. Peters, A., et al., Catalytic NOx Reduction on a Passenger Car Diesel Common Rail Engine.

SAE Technical Paper Series, No. 980191, 1998.

70. Peters, A., et al., Catalytic NOx Reduction on a Passenger Car Diesel Common Rail Engine.

SAE Technical Paper Series, No. 980191, 1998.

71. Wall, J.C., Cummins Engine Co., Diesel Fuel Composition for Future emissions

Regulations. Panel discussion, SAE International Fall Fuels and Lubricants Meeting and

Exposition, October 21, 1998.

72. Engler, B.H., et al., Catalytic Reduction of NOx with Hydrocarbons Under Lean Diesel

Exhaust as Conditions. SAE Technical Paper Series, No. 930735, 1993.

73. Mitsubishi Motors, 4G93 GDI Engine Technical Information: Reduced Exhaust Emissions

1997.

74. Engler, B.H., et al., Catalytic Reduction of NOx with Hydrocarbons Under Lean Diesel

Exhaust as Conditions. SAE Technical Paper Series, No. 930735, 1993.

75. Brown, K.F., Diesel Aftertreatment Technologies. Presentation at the SAE Topical

Technical Seminar Diesel Technology for the New Millennium, Schaumburg, IL, April 22, 1998.

76. Heavy-duty Engine Working Group, Mobile Source Technical Advisory Subcommittee of

the Clean Air Act Advisory Committee, “Phase I Final Report”, April, 1997, available in EPA

Air Docket A-98-32, Docket Item # II-A-02.

77. Lee, D., Ryan, T., “Fuel Property Effects on NOx Emissions in Year 2004 Emissions

Class Diesel Engines - Final Report”, December 5, 1996, Southwest Research Institute, available

in EPA Air Docket A-98-32, Docket Item # II-A-03

78. Heavy-duty Engine Working Group, Mobile Source Technical Advisory Subcommittee of

the Clean Air Act Advisory Committee, “Phase 2 of the EPA HDEWG Program - Summary

Document”, available in EPA Air Docket A-98-32.

79.Banzhaf M., p. 4.

80. See “Summary of CBI information regarding proposed HD Supplemental Test

Requirements”, available in EPA Air Docket A-98-32.
Regulatory Impact Analysis 

74

81. See ““Summary of Conference Call between US EPA and Honeywell Turbocharging

Systems on December 22, 1999 regarding 2004 On-highway Heavy-duty Diesel Proposal”,

available in EPA Air Docket A-98-32.

82.Baert R., p. 175.

83.Dekker H.J., pp. 209, 212.

84.Kohketsu S., pp. 97, 104.

85.Zelenka P., pp. 45, 56.

86. Energy and Environmental Analysis, “Benefits and Cost of Potential Tier 2 Emission

Reduction Technologies”, Final Report, November 1997.

87. California Air Resources Board, “Low Emission Vehicle and Zero Emission Vehicle

Program Review, Staff Report”, November 1996.

88. California Air resources Board, “Proposed Amendments to California Exhaust and

Evaporative Emissions Standards and Test Procedures for Passenger Cars, Light-duty Trucks,

and Medium-duty Vehicles, LEVII”, Staff Report, September 18, 1998.

89. Arcadis Geraghty and Miller, “Cost Estimates for Heavy-duty Gasoline Vehicles” Final

Report, September 30, 1998.

90. EPA Technical Memorandum “Documentation of Sophisticated On-board Diagnostic

Systems on Current Heavy-duty Diesel Engines”, Todd Sherwood, Available in EPA Air Docket

A-98-32.

91.Kato N., H. Kurachi, Y. Hamada: “Thick Film ZrO2 NOx Sensor for the Measurement of

Low NOx Concentration”, SAE paper 980170, pp. 76-77, 1998.

92. Kato N., N. Kokune, B. Lemire, T. Walde: “Long term stable NOx sensor with integrated inconnector control electronics”, SAE paper 1999-01-0202, also see memorandum from Mr. Todd

Sherwood to EPA Air Docket A-98-32 summarizing this paper

93.Dodge L.G., pp. 148-149.

94.Atkins R.A, C.E. Lee, H.F. Taylor: “Fiber-Optic In-cylinder Pressure Sensor Developed”,

Diesel & Gas Trubine Worldwide, p. 16b, April 1995.

95.Poorman T.J., L. Xia, M.T. Wlodarczyk: “Ignition system-embedded fiber-optic combustion

pressure sensor for engine control and monitoring”, SAE paper 970845, p.1, 1997.

96.Atkinson C. : “Emissions Prediction for On-Board Diagnostics and Engine Control”, SAE

TOPTEC presentation, “Diesel Technology for the New Millennnium”, April 21-22, 1998, Air
Chapter 3: Technological Feasibility

75

Docket A-98-32, item no. II-D-02.
Regulatory Impact Analysis 

76

CHAPTER 4: ECONOMIC IMPACT OF HD DIESEL

STANDARDS

I. Methodology

EPA previously analyzed the costs of the 2004 FTP heavy-duty diesel standards for the 1997

FRM. That economic analysis was based on a study conducted by ICF Incorporated and Acurex

Environmental Corporation, which analyzed the potential costs of a wide variety of technologies.1

This current analysis is generally a re-analysis of those previous analyses (unless noted otherwise),

but also addresses new requirements such as the NTE requirements. The reader should refer to the

previous analyses for additional information and background. In the previous analyses, all costs

were described in terms of 1995 dollars. Where these costs were used in this analysis, they were

adjusted upward by 9.3 percent to be equivalent to 1999 dollars. This adjustment was based on the

Consumer Price Index. (Note: This adjustment was not made in the Draft RIA.) As was done in the

proposal, EPA is projecting costs assuming that testing will be completed in time for the 2004 model

year, even though the supplemental requirements are being finalized for the 2007 model year. We

believe that many manufacturers will choose (as a convenience) to incorporate the minor calibration

changes necessary to comply with these requirements during the 2004 model year, rather than to

modify their 2004 designs for the 2007 model year. Since this assumption means that manufacturers

would incur the testing costs three years earlier than required, it results in a slight increase in the net

present value of the costs.

While the following analysis is based on a relatively uniform emission control strategy for

designing the different categories of engines, this is not intended to suggest that a single combination

of technologies will actually be used by all manufacturers. In fact, depending on basic engine

emission characteristics, EPA expects that control technology packages will gradually be fine-tuned

to each application. Furthermore, EPA expects manufacturers to use averaging, banking, and trading

programs as a means to deploy varying degrees of emission control technologies on different

engines. EPA nevertheless believes that the projections presented here provide a cost estimate

representative of the different approaches manufacturers may ultimately take.

Costs of control include variable costs (for incremental hardware costs, assembly costs, and

associated markups) and fixed costs (for tooling, R&D, and certification). Variable costs are

marked up at a rate of 29 percent to account for manufacturers' overhead and profit.2

 For

technologies sold by a supplier to the engine manufacturers, an additional 29 percent markup is

included for the supplier's overhead and profit. Estimated variable costs for new technologies (i.e.,

EGR and VGT) include a ten percent markup to account for increased warranty costs. Fixed costs

for R&D are assumed to be incurred over the seven-year period from 1996 through 2002, tooling and

certification costs are assumed to be incurred one year ahead of initial production. Fixed costs are

increased by seven percent for every year before the start of production to reflect the time value of

money. This total preproduction cost is then amortized at the same rate over a five-year period

during which the manufacturer would be able to recoup the fixed costs. The analysis also includes
Chapter 4: Economic Impact of HDDE Standards

77

consideration of lifetime operating costs where applicable. Projected costs were derived for three

service classes of heavy-duty diesel vehicles, as depicted in Table 4-1.

In some cases, EPA expects that there may be significant overlap between technologies

needed to reduce NOx emissions for compliance with 2004 model year standards and those

technologies that offer other benefits for improved fuel economy and engine performance or for

better control of HC or particulate emissions. In the absence of future standards, manufacturers

would have continued research on and eventually deploy many technological upgrades to improve

engine performance or more cost-effectively control emissions. Specifically, this is most appropriate

for the application of VGT and improved fuel injection technologies, as is discussed in Sections

A(3) and A(4) of this chapter. For those cases, EPA is assuming that only a fraction of the fixed and

variable costs are attributable to emission control.

Table 4-1:

Service Classes of Heavy-Duty Vehicles

Service Class Vehicle Class GVWR (lbs.)

Light 2B - 5 8,500 - 19,500

Medium 6 - 7 19,501 - 33,000

Heavy 8 33,001 +

II. Technologies for Meeting the New Standards

The following discussion provides a description and estimated costs for those technologies

EPA projects will be needed to comply with the new emission standards. EPA believes that a small

set of technologies represent the primary changes manufacturers must make to meet the standards

in this rule. Other technologies applied to heavy-duty engines, before or after implementation of new

emission standards, will make smaller secondary contributions to controlling NOx or HC emissions

and are therefore considered secondary improvements for this analysis. In this category are design

changes such as improved oil control, optimized catalyst designs, and variable-valve timing. Lean

NOx catalysts are also considered secondary technologies in this analysis, not because NOx control

is an incidental benefit, but because it appears unlikely that they will be part of 2004 model year

technology packages. Modifications to fuel injection systems will also continue independently of

new standards, though some further development with a focus on reducing NOx or HC emissions

would be evaluated. While a few engines must reduce HC emission levels, EPA expects the

combination of technologies selected for meeting NOx and particulate emission standards to be

sufficient for adequate control of HC emissions.
Regulatory Impact Analysis 

78

The technology analysis includes an analysis of the baseline technology being used by

manufacturers to meet the 1998 emission standards and future technologies that will be used to

improve engine designs through model year 2003. Specification of the future technologies is based

on an observation of current trends in heavy-duty engine technology. The baseline control

technologies being assumed for engines meeting 1998 emission standards in 2003 include

technologies that contribute directly to lower NOx emissions and a variety of engine improvements

with only secondary benefits for NOx control. The assumed baseline scenario includes full

utilization of electronic controls and unit injectors. Except for urban bus engines, one-third to onehalf of diesel engines are expected to include unit injectors designed to operate independently of

engine speed; one example of such an injector is the Hydraulically-activated, Electronicallycontrolled Unit Injector (HEUI), which is currently manufactured for several Caterpillar and Navistar

engine models. Another example is the newer, more advanced, Next Generation Electronic Unit

Injector (NGEUI) developed by Caterpillar. Also, these engine models are assumed to have some

basic manipulation of the fuel injection profile (for "rate shaping"). Variable-geometry turbochargers

are expected for several engine lines as manufacturers aim for better performance and fuel economy,

and potentially for additional braking capacity. Light and medium heavy-duty engines may be

modified to further reduce the contribution of lubricating oil to particulate emissions. Manufacturers

may also pursue variable-valve timing or upgrade to four valves per cylinder for improved engine

performance. While EPA is not assuming EGR to be included among the baseline technologies,

EPA recognizes that some manufacturers may actually incorporate EGR into future engines to offset

fuel consumption increases associated with the 1998 NOx standard (due to injection timing retard).

For example, DDC recently announced the introduction of their new Series 50 heavy-duty bus and

truck engine, which is being equipped with EGR and VGT in the 2000 model year.3

 DDC

specifically noted, in its announcement, that this was being done as an alternative to retarded

injection timing in order to minimize fuel consumption. Thus, this assumption, that 100 percent of

the cost of adding EGR is attributable to compliance with the standards in this rule, is conservative

and actual compliance costs for the these standards may be significantly lower than is estimated here.

Compliance costs for 2004 and later model year engines are based on an assumed

combination of primary technology upgrades. Modifications to basic engine design features can

improve intake air characteristics and distribution during combustion. Manufacturers are also

expected to use upgraded electronics and advanced fuel-injection techniques and hardware to modify

various fuel injection parameters for higher pressure, further rate shaping, and some split injection.

EPA also expects that all engines will incorporate cooled exhaust gas recirculation and many will

incorporate variable geometry turbochargers. The costs of these individual technologies are

considered in the following paragraphs and summarized in Table 4-2. The costs of secondary

improvements are not included in this analysis since they are not expected to be needed for

compliance with these emission standards. The reader is referred to the RIA for the June 2, 2000

NPRM that proposed new standards for the 2007 model year (Docket A-99-06) for more information

regarding the potential costs of these secondary technologies. In that NPRM, EPA projected that

many of these technologies would be available for the 2007 model year.
Chapter 4: Economic Impact of HDDE Standards

79

Table 4-2

2004 Model Year Cost Estimates

Light Heavy-Duty Diesel Vehicles (Dollars per Engine)

Item

Fixed

 Cost

Variable Cost Operating Cost Fraction of Cost

For Emissions*

Cooled EGR (high-flow) 42 215 8 100%

Combustion optimization 22 0 0 100%

Improved fuel injection 9 135 0 50%

Variable geometry turbochargers 15 188 0 50%

Onboard diagnostics 1 0 0 100%

Emission map testing 2 0 0 100%

Certification 2 0 0 100%

* Costs listed in the table are the full costs for adding each of the technologies. However, because

both fuel injection improvements and variable geometry turbochargers provide performance benefits

not related to emissions control, and because these technologies may be in use prior to 2004, only

fractions of the full costs are used for the cost-effectiveness analysis.

Medium Heavy-Duty Diesel Vehicles (Dollars per Engine)

Item

Fixed

 Cost

Variable Cost Operating Cost Fraction of Cost

For Emissions*

Cooled EGR (high-flow) 103 242 49 100%

Combustion optimization 55 0 0 100%

Improved fuel injection 20 127 0 50%

Variable geometry turbochargers 35 248 0 50%

Onboard diagnostics 0 0 0 100%

Emission map testing 5 0 0 100%

Certification 2 0 0 100%

* Costs listed in the table are the full costs for adding each of the technologies. However, because

both fuel injection improvements and variable geometry turbochargers provide performance benefits

not related to emissions control, and because these technologies may be in use prior to 2004, only

fractions of the full costs are used for the cost-effectiveness analysis.
Regulatory Impact Analysis 

80

Heavy Heavy-Duty Diesel Vehicles (Dollars per Engine)

Item

Fixed

 Cost

Variable Cost Operating Cost Fraction of Cost

For Emissions*

Cooled EGR (high-flow) 103 336 104 100%

Combustion optimization 55 0 0 100%

Improved fuel injection 20 140 0 50%

Variable geometry turbochargers 35 338 0 50%

Onboard diagnostics 0 0 0 100%

Emission map testing 5 0 0 100%

Certification 9 0 0 100%

* Costs listed in the table are the full costs for adding each of the technologies. However, because

both fuel injection improvements and variable geometry turbochargers provide performance benefits

not related to emissions control, and because these technologies may be in use prior to 2004, only

fractions of the full costs are used for the cost-effectiveness analysis.

A. Primary Technologies

The following discussion presents the projected costs of the primary technological

improvements expected for complying with the new emission standards, first for fixed costs, then

for hardware and operating costs of the individual technologies. 

The cost analysis anticipates an extensive ongoing research program to develop these

technologies. While most of this R&D will be needed to develop new technologies for reducing

emissions, some will be needed to verify emission performance for compliance with the

supplemental standards and OBD requirements. R&D costs account for over 90 percent of the total

fixed costs per engine detailed in Table 4-2. Retooling is another fixed cost factored into the

analysis. Retooling costs will be incurred about one year before initial production and are discounted

accordingly. 

Manufacturers will also incur costs for certifying the range of engine families to the emission

standards. EPA previously developed a detailed methodology for calculating certification costs.4

Adjusting those figures to convert them to 1999 dollars (using the Consumer Price Index) results in

an estimated certification cost of $250,000 per engine family. This estimate, which is used here, is

the same estimate that was used in the 1997 analysis (after being adjusted to 1999 dollars). This is

because EPA believes that the new supplemental steady-state certification requirement will not

significantly affect certification costs. Certification costs will be incurred on average one year before

the beginning of production, so the calculated cost is increased by seven percent. Distributing those

costs across the different engine categories, amortizing the costs over five years, and dividing by the

number of projected 2004 model year sales for each category results in per-engine costs between $2

and $9 for each category of heavy-duty diesel vehicles.
Chapter 4: Economic Impact of HDDE Standards

81

1. Exhaust Gas Recirculation

Exhaust gas recirculation (EGR) is projected to be the most important area of technology

development that will enable manufacturers to achieve the targeted NOx emission levels. Unlike

most other technological developments, which are largely further optimization of the baseline

technologies discussed in Chapter 3.II.A, introduction of EGR would be a step change in the design

of heavy-duty diesel engines. The technological challenges facing the manufacturers in developing

EGR for diesel engines are described in Chapter 3.II.B. While some research remains to optimize

EGR systems for maximum NOx-control effectiveness with minimum negative impacts on

performance and durability, current developments show great promise for substantial emissioncontrol improvements with EGR systems.

According to the Acurex cost report, the typical cost to manufacturers of adding the hardware

for a high-flow cooled EGR system is estimated to range from $140 to $220 (in 1995 dollars) per

engine depending on the service class. Factoring in the fixed costs, the appropriate markups, and

inflation results in an increased purchase price of $257, $345, and $439 for light, medium, and heavy

heavy-duty diesel vehicles, respectively. 

2. Combustion Optimization

Manufacturers can make a variety of changes to the basic engine design that do not require

additional components. Programming the engine's electronic controls, optimizing intake air

characteristics and distribution, and making changes to piston bowl shape, the compression ratio, and

the injection timing strategy add little or no variable cost, but require significant expenses for R&D

and retooling. According to the Acurex cost report, total costs for these improvements would be

$5 million per engine line. For the different classes of vehicles, this translates to an incremental cost

between $22 and $55 per engine.

3. Improved Fuel Injection

Manufacturers are expected to improve their fuel injection systems by increasing fuel

injection pressure, improving spray patterns, and adding rate shaping and split injection capability;

however, much of this improvement is expected to occur independently of the new emission

standards.5,6,7,8,9,10 For cam-driven electronic unit injection systems, the expected fuel system

improvements will require stronger and better performing fuel injectors and solenoids. Advanced

systems such as HEUI or NGEUI technology require various reinforcements and better high-pressure

oil pumps and solenoid valves. Common rail injection systems are similar enough to HEUI designs

that the cost estimate would mirror that for HEUI systems. 

Incremental costs for this set of fuel injector improvements are roughly proportional to the

number of cylinders in an engine. EPA calculated typical costs for these improvements using the
Regulatory Impact Analysis 

82

information contained in the Acurex report. Light heavy-duty vehicles, typically equipped with

eight-cylinder engines, have an estimated total cost of $144 per engine, which is an average for the

different hardware configurations. Medium and heavy heavy-duty vehicles, with six-cylinder

engines, would have a cost between $147 and $160 per engine. These cost estimates are based on

the cost estimates in the Acurex cost report, assuming that half of light and medium heavy-duty

engines, and that two-thirds of heavy heavy-duty engines will have cam-driven unit injectors (and

that the remainder will have common rail, HEUI, or similar systems), and by adjusting to 1999

dollars. For this analysis EPA is assuming that 50 percent of the costs for these improvements are

attributable to emission control. This is because EPA believes that manufacturers would make these

improvements for many of their engines, even in the absence of these emission standards, to reduce

fuel consumption and improve engine performance.11 

4. Variable Geometry Turbochargers

For several years research has focused on improving turbocharger designs to reduce response

time and increase compressor efficiency. One such design, the variable-geometry turbocharger, is

more complex than existing turbochargers, but offers two primary operating enhancements: boost

pressure is maintained over a wider range of engine operation and response time is reduced. These

improvements contribute to lower exhaust emissions and provide control of airflow needed for

engines with EGR. Variable-geometry turbochargers require more parts and more assembly time,

resulting in a variable cost to manufacturers as high as $200 to $300 per engine according to the

Acurex cost report. However, EPA has become aware of new simpler designs for VGT systems that

are expected to be less expensive than the systems considered by Acurex. Thus EPA has revised the

Acurex estimate by reducing assembly costs by 70 percent, and eliminating the actuator costs.12 The

revised estimates of the variable cost increase to manufacturers for VGT (relative to current

technology turbochargers) range from $90 to $150. Fixed costs for R&D and retooling were

estimated at about $3.5 million per engine line. Combining the costs with the appropriate markups,

and adjusting for inflation results in costs of $203, $283, and $373 for light, medium and heavy

heavy-duty engines, respectively. For this analysis, however, 50 percent of these costs are assumed

to be attributable to emission control. As with the expected fuel injection improvements, EPA

believes that manufacturers would make these improvements for many of their engines, even in the

absence of these emission standards, to reduce fuel consumption and improve engine performance.3

An EPA technical memo to the docket for this rulemaking contains additional discussion of the

Agency’s 50 percent cost estimate for both improved electronic fuel injection, including a cost

sensitivity analysis detailing what impact this estimate has on the standards cost-effectiveness.11

This cost sensitivity is also summarized in Table 8-13 of Chapter 8, Section IV of this RIA.

5. Onboard Diagnostics

Manufacturers are not expected to make significant hardware modifications in response to

the OBD requirements for vehicles at or under 14,000 pounds. This is because, even without the

OBD regulations, manufacturers would monitor emission control components to ensure proper

engine performance. In fact, manufacturers already use onboard monitors for fuel injectors for

current engines. However, manufacturers are expected to incur additional costs for emission testing
Chapter 4: Economic Impact of HDDE Standards

83

of representative engine configurations in various malfunction modes. Based on EPA’s engineering

judgement, we estimate this testing will add $1 to the fixed costs for light heavy-duty engines, but

will not affect variable or operating costs. Even though only those light heavy-duty engines for

vehicles at or under 14,000 pounds would be subject to the OBD requirements, EPA is applying this

cost to all light heavy-duty engines for this analysis. (Note: the Draft RIA analysis estimated this

cost to be $3 using an incorrect amortization calculation.)

6. Engine Map Testing

While manufacturers are not expected to make significant hardware modifications in

response to the new supplemental standards, they are expected to conduct extensive steady-state and

transient cycle emission testing (i.e., testing at speeds and loads represented by the new supplemental

test cycles) as part of their R&D efforts. This will add $2, $5, and $5 to the fixed costs for light,

medium, and heavy heavy-duty engines, respectively, but will not affect variable or operating costs.

(Note: the Draft RIA analysis estimated this cost to be $9, $23, and $23 using an incorrect

amortization calculation.)

7. Total Technology Package Costs

The estimated incremental costs of these primary technologies depend on several judgements

about which technologies will be used. For example, predicting precisely how much these

technologies will impact engine-out PM emissions is difficult. If engine-out PM emissions are

increased, then manufacturers may need to increase the use of aftertreatment. This increases

hardware costs and there would be a greater potential for increased operating expenses. 

EPA believes it is not appropriate to assign the full cost of fuel system upgrades or the

addition of VGT to the new emission standards. As is discussed in Sections A.3 and A.4 of this

chapter, much of the anticipated improvements will come independently of the new standards and

any remaining system improvements for 2004 and later model year vehicles will provide benefits

beyond lower NOx emissions. The resulting calculation of total incremental cost for the set of

primary technologies, summarized in Table 4-2, shows the expected increase in purchase price due

to the new emission standards. Projected cost increases are $485, $657 and $803 for light, medium,

and heavy and heavy-duty vehicles, respectively for the 2004 model year. 

B. Operating Costs

EPA has assessed the potential for increased operating costs, as described below, first for

EGR-related maintenance, then for fuel economy. EGR has the potential, if not developed and

implemented properly, to increase operating costs, either by increasing fuel consumption or requiring

additional maintenance to avoid accelerated engine or component wear. While it is possible to

develop scenarios and estimate the impact on operating costs of current diesel EGR concepts, this
Regulatory Impact Analysis 

84

is of minimal value due to the expected continuing development of these technologies. One major

focus of the R&D conducted over the next several years will be to resolve potential operating cost

impacts related to the use of EGR; thus the current state of the technology is not representative of

what is expected for 2004. 

While engine-out particulate emissions are dramatically lower than only a few years ago,

recirculating even a small amount of particulate matter through an engine introduces a concern for

engine durability. To prevent wear, manufacturers might specify more frequent oil change intervals

or a greater oil sump volume to accommodate any effects of acidity or particulate agglomeration in

the oil. However, EPA expects manufacturers to make a great effort to minimize any potential new

maintenance burden for the end user. Alternatively, changing fuel or oil formulations may be the

most cost-effective way to reduce the potential for particulate-related wear. EPA originally

proposed in the 1996 NPRM that manufacturers would be able to keep engine costs lowest by

investing $10 million to $15 million industry-wide in research to address these concerns (about $25

per engine when amortized over the fleet). This estimate was based on EPA’s engineering

judgement and prior experience. Although manufacturers have had two opportunities to provide

information in their public comments, they have not provided any information that allow the Agency

to improve this estimate. Therefore, we continue to believe that it is the best available estimate of

the cost of addressing this issue. To include the affect of improved materials resulting from the

R&D effort, the analysis incorporates a 2 percent increase in the cost of engine oil. The increased

expense of oil changes over the lifetime of vehicles ranges from $8 to $33 per engine (net present

value at the point of sale).

In addition, EPA has included a cost for preventive maintenance, at the time of rebuild, to

ensure that EGR systems will not malfunction. EPA data show that nearly all engines from heavy

heavy-duty vehicles and 65 percent of those from medium heavy-duty vehicles are rebuilt.13

Rebuilding engines from light heavy-duty vehicles is rare. EPA estimates that engine rebuild occurs

at 240,000 miles for medium heavy-duty vehicles, at 500,000 miles for heavy heavy-duty vehicles,

and at 300,000 miles for urban buses. These mileage figures represent an approximate average

across the various applications within each service class, which experience widely differing mileage

accumulation rates. For example, garbage trucks have much different operating characteristics than

line-haul trucks. According to the MOBILE model, these mileage figures translate into a rebuild in

the eleventh year for both truck categories. As mentioned in the Acurex report, rebuild procedures

for EGR systems will likely include solvent cleaning of the EGR tubing and replacement of the

electronic control valve. Removal, cleaning, and replacement of the tubing are estimated to take 30

minutes at a $71 per hour labor rate. Replacing the control valve on an aftermarket basis is expected

to cost three times the manufacturers' long-term direct cost, or $73 and $105 for medium and heavy

heavy-duty vehicles, respectively. Calculated in terms of net present value at the point of sale, the

net effect of EGR servicing comes to about $55 for medium heavy-duty vehicles and $71 for heavy

heavy-duty vehicles and urban buses.

While EPA believes that sufficient R&D and the use of cooled EGR will address other

operating cost concerns, the Acurex report includes a cost estimate for increasing oil sump volumes

by 10 percent to address maintenance concerns with EGR. Oil sump volumes currently range from
Chapter 4: Economic Impact of HDDE Standards

85

4 gallons for light heavy-duty diesel vehicles to 11 gallons for heavy heavy-duty vehicles, so the cost

impact varies greatly by vehicle category. By calculating a cost at each oil change as vehicles

accumulate mileage and discounting the life-cycle costs to the point of sale, Acurex estimated that

the cost of increasing oil sump volumes by 10 percent would cost $25, $55, and $145 for light,

medium, and heavy heavy-duty vehicles, respectively (in 1995 dollars). These cost are presented

here only for informational purposes, and are not included in the cost-effectiveness analysis.

As is discussed in Chapter 3, while EGR has the potential to incur a fuel economy penalty,

it will probably be more than offset by improvements in fuel injection and the use of VGT. In fact,

EPA believes that the combined effect of these three technologies may decrease fuel consumption

by as much as 1.5 percent. EPA estimated the cost savings for each one percent decrease in fuel

consumption, based on a diesel fuel cost of $1.00 per gallon. Calculated as a net present value at the

point of sale, these estimates are $102, $178, and $891 for light, medium, and heavy heavy-duty

vehicles, respectively. This sensitivity with respect to changes in fuel consumption varies so much

by vehicle category because of the widely differing mileage accumulation rates for different vehicle

categories. As discussed in section IV of Chapter 8, we have also performed a sensitivity analysis

to estimate the impact on costs if this rulemaking resulted in an increase in fuel consumption for HD

diesel engines. Table 8-11 estimates the impact on the per-vehicle cost increase for a one percent

increase in fuel consumption, and Table 8-12 estimates the increase in per-vehicle cost-effectiveness

for a one percent increase in fuel consumption.

C. Secondary Technologies

In the 1997 FRM, EPA analyzed the potential costs of secondary technologies (i.e., those

technologies that may potentially be available, but that EPA was projecting would not be used by

manufacturers to comply with the 2004 standards). EPA is not revising this analysis of secondary

technologies for this technology review rulemaking. The reader is referred to the RIA for the 1997

FRM for more information regarding this analysis. However, new cost information has been

recently presented to the Agency which will be presented here. 

As discussed in Chapter 3, the Manufacturers of Emission Control Associations (MECA) has

recently undertaken a test program at Southwest Research Institute to evaluate the emission benefit

potential of several aftertreatment devices. Specifically, MECA members provided to SwRI a

number of diesel oxidation catalysts (DOC), particulate traps, and urea-based selective catalytic

reduction systems (SCR). As discussed in Chapter 4, DOC’s have been used in the past for some

light- and medium-heavy duty engine families in order to comply with the 0.1 g/bhp-hr PM standard

which began in 1994, and for urban buses to comply with the 0.05 g/bhp-hr PM standard. It is likely

some number of engine families would continue to rely on DOC’s for modest PM reductions. As

discussed in Chapter 3, technical issues remain to be solved before PM traps or SCR systems could

be considered feasible for wide spread us in the U.S. HD diesel market, and we believe it is unlikely
Regulatory Impact Analysis 

86

manufacturers will use either of these technologies in 2004. However, it appears that these

technologies could be available for the 2007 model year. 

III. Summary of Costs

The per-vehicle cost figures presented above are used in Chapter 9 to calculate the costeffectiveness of the program by comparing to emission reductions over the lifetime of each vehicle

category for those engines covered by the new standards. Included in that calculation are the

following modifications for later model year production.

First, manufacturers recover their initial fixed costs for tooling, R&D, and certification over

a five-year period. Fixed costs are therefore applied only to the first five model years of production.

The second modification is related to the effects of the manufacturing learning curve. This

is a well documented and accepted phenomenon dating back to the 1930s. The general concept is

that unit costs decrease as cumulative production increases. Learning curves are often characterized

in terms of a progress ratio, where each doubling in cumulative production leads to a reduction in

unit cost to a percentage "p" of its former value (referred to as a "p cycle"). The organizational

learning which brings about a reduction in total cost is caused by improvements in several areas.

Areas involving direct labor and material are usually the source of the greatest savings. These

include, but are not limited to, a reduction in the number or complexity of component parts,

improved component production, improved assembly speed and processes, reduced error rates, and

improved manufacturing process. These all result in higher overall production, less scrappage of

materials and products, and better overall quality.

Companies and industry sectors learn differently. In a 1984 publication, Dutton and Thomas

reviewed the progress ratios for 108 manufactured items from 22 separate field studies representing

a variety of products and services.14,15 The average progress ratio for the whole data was slightly

higher than 80 percent, which supports the commonly used p value of 80 percent, i.e., each doubling

of cumulative production reduces the former cost level by 20 percent. As each successive p cycle

takes longer to complete, production proficiency generally reaches a relatively stable plateau, beyond

which increased production does not necessarily lead to markedly decreased costs. In their article,

Dutton and Thomas emphasize the importance of understanding the dynamics underlying learning

processes. 

EPA applied a p value of 20 percent beginning in 2004 in this analysis. That is, the variable

costs were reduced by 20 percent for each doubling of cumulative production. However, to avoid

overly optimistic projections, EPA included several additional constraints. Using one year as the

base unit of production, the first doubling would occur at the start of the 2006 model year and the

second doubling at the start of the 2008 model year. To be conservative, EPA incorporated the

second doubling at the start of the 2009 model year. Recognizing that the learning curve effect may

not continue indefinitely with ongoing production, EPA used only two p cycles. 
Chapter 4: Economic Impact of HDDE Standards

87

EPA believes the use of the learning curve is appropriate to consider in assessing the cost

impact of heavy-duty engine emission controls. The learning curve applies to new technology, new

manufacturing operations, new parts, and new assembly operations. Heavy-duty diesel engines

currently do not use EGR of any type today (hot, cooled, or cooled and filtered). This is therefore

a new technology for heavy-duty diesel engines and will involve new manufacturing operations, new

parts, and new assembly operations. Since this will be a new and unique product, EPA believes this

is an optimal situation for the learning curve concept to apply. Opportunities to reduce unit labor

and material costs and increase productivity (as discussed above) will be great. EPA believes a

similar opportunity exists for fuel systems on heavy-duty diesel engines. While all diesel engines

have high-pressure fuel injection systems, the changes envisioned for common rail and unit injection

systems require fundamental redesign of system hardware. These new parts and new assemblies will

involve new manufacturing operations. As manufacturers gain experience with these new systems,

comparable learning is expected to occur with respect to unit labor and material costs. These

changes require manufacturers to start new production procedures, which, over time, will be

improved with experience. 

Table 4-4 lists the projected schedule of costs over time for each category of heavy-duty

diesel vehicles. The estimated long-term cost savings would reduce the impact on the total cost of

heavy-duty vehicles by about half. 

Characterizing these estimated costs in the context of their fraction of the total purchase price

and life-cycle operating costs is helpful in gauging the economic impact of the standards. Table 4-5

presents the baseline costs for each vehicle category, as developed by ICF.

IV. Aggregate Costs to Society

The above analysis develops per-vehicle cost estimates for each vehicle class. With current

data for the size and characteristics of the heavy-duty vehicle fleet and projections for the future,

these costs can be translated into a total cost to the nation for the emission standards in any year. 

The sales for the different categories of heavy-duty diesel engines that would be covered by the rule

based on the 1995 model year were determined using production information provided by

manufacturers to EPA and were assumed to grow at a linear rate of two percent from the 1995 levels.

The result of this analysis is a projected total cost starting at $479 million in 2004. Per-vehicle cost

savings over time reduce projected costs to a minimum value of $248 million in 2009, after which

the growth in truck population leads to an increase to $325 million in 2020. Total costs for these

years are presented by vehicle class in Table 4-6. 

The incremental cost associated with oil changes is incorporated on an annual basis for each

vehicle category. Incremental costs related to rebuild are not include in 2004 or 2009, since the first

rebuilds would be expected after 2009. In 2020, incremental rebuild costs are applied to the vehicles
Regulatory Impact Analysis 

88

that would be rebuilt in that year. Maintenance costs are projected to be over $44 million per year

by 2020.

Table 4-4

Projected Long-Term Diesel Engine/Vehicle Costs

(net present value at point of sale in 1999 dollars)

Vehicle Class Model

Year Change

Purchase

Price

Life-cycle

Operating

Cost (NPV)

Light heavy-duty

2004 — 485 8

2006 20 percent learning curve applied to

variable costs

410 8

2009 Fixed costs expire; 20 percent learning

curve applied to variable costs

241 8

Medium heavy-duty

2004 — 657 49

2006 20 percent learning curve applied to

variable costs

571 49

2009 Fixed costs expire; 20 percent learning

curve applied to variable costs

275 49

Heavy heavy-duty

2004 — 803 104

2006 20 percent learning curve applied to

variable costs

688 104

2009 Fixed costs expire; 20 percent learning

curve applied to variable costs

368 104

Table 4-5

Baseline Costs for Heavy-Duty Engines and Vehicles (1995 dollars)

Vehicle Class Engine Cost Vehicle Cost Operating Costs

Light heavy-duty $7,800 $22,504 $12,450

Medium heavy-duty $12,400 $46,132 $31,242

Heavy heavy-duty $21,700 $96,490 $108,027

Urban Bus $22,000 $224,000 $437,153
Chapter 4: Economic Impact of HDDE Standards

89

Table 4-6

Estimated Annual Costs for Improved Heavy-Duty Vehicles

Year Category

Cost Elements (millions of 1999 dollars)

Fixed Variable Operation Total 

2004

Light heavy-duty 36 125 0.3 161

Medium heavy-duty 38 71 0.3 109

Heavy heavy-duty 59 149 1.2 210

 Total Annual Cost 133 344 1.7 479

2009

Light heavy-duty 0 86 1.6 88

Medium heavy-duty 0 49 1.3 50

Heavy heavy-duty 0 104 6.0 110

Total Annual Cost 0 239 8.9 248

2020

Light heavy-duty 0 101 3.4 105

Medium heavy-duty 0 58 9.3 67

Heavy heavy-duty 0 121 32 153

 Total Annual Cost 0 280 45 325
Regulatory Impact Analysis 

90

1. Estimated Economic Impact of New Emission Standards for Heavy-duty On-Higway

Engines", Accurex Environmental Corporation, March 31, 1997.

2."Update of EPA's Motor Vehicle Emission Control Equipment Retail Price Equivalent (RPE)

Calculation Formula," Jack Faucett Associates, Report No. JACKFAU-85-322-3, September

1985.

3. "Detroit Diesel Unveils Year 2000 Series 50 Bus and Coach Engine", DDC Press Release,

March 17, 2000. Available in EPA Air Docket A-98-32, Docket Item #IV-G-07.

4. Draft Regulatory Impact Analysis and Oxides of Nitrogen Pollutant Specific Study, p. 3-29

ff., October 1984.

5. SAE paper 973182, “Advanced Technology Fuel System for Heavy-duty Diesel Engines”

6. Diesel Progress, August 1998, “CAT Gears Up Next Generation Fuel Systems”, available in

EPA Air Docket A-98-32, Docket Item #II-D-03.

7. Diesel Progress, August 1998, “Next Generation MEUI-B to Debut in 2001", available in

EPA Air Docket A-98-32, Docket Item #II-D-03.

8. Diesel Progress, October 1998, “No Mistaking New Cummins ISL Engine”, available in EPA

Air Docket A-98-32, Docket Item #II-D-04

9. “Cummins New Midrange Fuel System”, presented by John Youngblood, Cummins Engine

Company, at the SAE Diesel Technology TOPTEC, April 22, 1998, available in EPA Air Docket

A-98-32, Docket Item #II-D-01.

10. "GM Full-Size Trucks Make 'Power Play’ with Gasoline and Duramax Diesel Teamed with

New Automatics and Six-Speed Manual", R. Wilson, Diesel Progress, January 2000. Available

in EPA Air Docket A-98-32, Docket Item #IV-G-06.

11. "Costs and Benefits of VGT and Improved Fuel Injection with Sensitivity Analysis for Onhighway Heavy-duty Diesel 2004 Emission Standards", C. Moulis, Docket Item #A-98-32-IV-B3.

12. "Summary of Phone Conversation Between Matthew Spears, US EPA and Dr. S.M. Shahed,

Allied Signal Corporation, on January 5, 1999 Regarding Advances in Variable Nozzle

Turbocharger (VNT) Design and Manufacturing", Docket #A-98-32-IV-B-4.

13."Heavy Duty Engine Rebuilding Practices," Draft EPA Report by Karl Simon and Tom

Stricker, March 21, 1995.

Chapter 4 References
Chapter 4: Economic Impact of HDDE Standards

91

14. J.M Dutton and A. Thomas, Academy of Management Review, Rev. 9, 235, 1984. Copy

Available in EPA Air Docket A-98-32.

15. “Learning Curves in Manufacturing,” L. Argote and D. Epple, Science, February 1990, Vol.

247, page 920. Copy Available in EPA Air Docket A-98-32.
Regulatory Impact Analysis 

92

CHAPTER 5: ECONOMIC IMPACTS OF HD OTTOCYCLE STANDARDS

This chapter contains an analysis of the economic impacts of the new emission standards for

heavy-duty Otto-cycle vehicles and engines. First, a brief outline of the methodology used to

estimate the economic impacts is presented, followed by a summary of the technology packages that

are expected to be used to meet the standards. Next, the projected costs of the individual

technologies is presented, along with a discussion of fixed costs such as research and development

(R&D), tooling and certification costs. Following the discussion of the individual costs components

is a summary of the projected per-vehicle cost of the new regulations. Finally, an analysis of the

aggregate cost to society of the regulations is presented. The costs presented here are in 1999

dollars.

I. Methodology for Estimating Costs

Using the information on emission reduction technology presented in Chapter 4, we

identified packages of technologies that would be likely to be used by the manufacturers to comply

with the emission standards. These technology packages are those which are being implemented to

meet California’s low emission vehicle (LEV) standards. To identify the required technologies and

to quantify the costs of most of these technologies, we relied on the contracted study of heavy-duty

gasoline vehicle technology conducted by Arcadis Geraghty & Miller (hereafter referred to as the

Arcadis report).1 Information in the Arcadis report regarding technology costs and current

nationwide vehicle and California LEV technologies (including such things as catalyst sizes and

loadings, as well as estimates of the percentages of vehicles that will require certain technologies)

were obtained though a series of confidential discussions with vehicle and engine manufacturers,

catalyst and equipment suppliers, and other relevant entities. Costs for onboard refueling vapor

recovery (ORVR) equipment were taken from the final Regulatory Impact Analysis for ORVR

controls and updated for purposes of this analysis, and are not from the Arcadis report.2

The costs of meeting the emission standards include both variable costs (incremental

hardware costs, assembly costs, and associated markups) and fixed costs (tooling, R&D, and

certification costs). Variable costs are marked up at a rate of 29 percent to account for

manufacturers’ overhead and profit.3

 For a technology which is sold by a supplier to the vehicle or

engine manufacturer an additional 29 percent markup is included to cover the suppliers’ overhead

and profit. The exception to this is for precious metals. Vehicle manufacturers typically provide

catalyst suppliers with precious metals for use in the catalysts the suppliers manufacture. Thus, the

additional 29 percent supplier markup is not applied to the cost of precious metals. Fixed costs were

increased by seven percent for every year before the start of production to reflect the time value of

money, and are then recovered with a five year amortization at the same rate.

II. Technology Packages for Compliance with the Regulations
Chapter 5: Economic Impacts of HD Otto-cycle Standards

93

The various technologies that could be used to comply with the regulations were discussed

in the previous chapter on technological feasibility. We expect that the technology mixes being used

to meet the California LEV standards fairly accurately represent those that will be used to comply

with the federal standards beginning with the 2005 model year. Thus, in developing costs for the

associated technologies we looked at the current technology used on HDVs and compared that to the

technologies being used to meet the LEV standards in California. Table 5-1 shows both the current

baseline and expected technologies for complete vehicles. Table 5-2 shows the current baseline and

expected technologies for the engine-based standards. The information contained in these tables

comes form the Arcadis report and is derived from conversations with the vehicle manufacturers

concerning their estimated configurations to be used to meet the new standards. These tables only

show the technologies which are expected to change in some way from their current design or be

applied to different percentages of the fleet than they are currently. Technologies which are currently

being widely used on these vehicles such as sequential multi-port fuel injection and EGR, while

important to meeting the standards, are not expected to be fundamentally changed in their design,

or be utilized in different percentages of the fleet than they currently are. Thus, while such

technologies will continue to be used on these vehicles, they are not included in these tables.

However, in some cases the cost of optimizing such technologies is included in the cost estimates

and are discussed in the following section.
Regulatory Impact Analysis 

94

Table 5-1

Current and Expected Technology Packages for Complete Vehicle Standards

Technology Baseline Federal Estimated 2005

Catalysts1 60% single underfloor

40% dual underfloor

13% single underfloor

50% dual underfloor

37% dual close-coupled and 

 dual underfloor

Oxygen sensors 70% dual heated

10% triple heated

20% four heated

13% dual heated

87% four heated

ECM 50% 32 bit computers

50% 16 bit computers

100% 32 bit computers

Adaptive learning 0% 80%

Individual cylinder A/F

control

0% 10%

Leak free exhaust 90% 100%

Insulated exhaust 0% 40%

Secondary air injection 20% 30%

ORVR 0% 100%2

1. In addition to the change in catalyst configurations shown, we expect that catalyst washcoat and

precious metal compositions and loadings will change.

2. ORVR only applies to complete vehicles 10,000 lbs GVWR and under, and is phased in, with

100% application to those vehicles in 2006.
Chapter 5: Economic Impacts of HD Otto-cycle Standards

95

Table 5-2

Current and Expected Technology Packages for Engine-based Standards

Technology Baseline Federal Estimated 2005

Catalysts1 60% single underfloor

40% dual underfloor

13% single underfloor

87% dual underfloor

Oxygen sensors2 70% dual heated

10% triple heated

20% four heated

13% triple heated

87% four heated

ECM 50% 32 bit computers

50% 16 bit computers

100% 32 bit computers

Improved fuel control 50% 100%

Secondary air injection 20% 50%

1. In addition to the change in catalyst configurations shown, we expect that catalyst washcoat and

precious metal compositions and loadings will change.

2. OBD only applies to HDGEs under 14,000 lbs GVWR (approximately 60 percent of HDGEs).

III. Technology Costs

The following sections outline in detail the costs of new technologies and the costs of

improvements to existing technologies we expect will be used to comply with the standards.

A. Improved Catalysts

Improvements in catalyst systems fall into two broad categories: changes in catalyst system

configuration and changes in the catalyst precious metal and washcoat compositions and loadings.

In addition estimating costs for these improvements, we estimated the costs of substrates and

packaging (cans) for the improved catalysts.

1. Changes in Catalyst Configurations

Currently, all non-California Otto-cycle HDVs either have single or dual underfloor catalyst

configurations. Under the single underfloor catalyst system the exhaust from both banks of engine

cylinders “Y” into a single catalyst. With the dual underfloor catalyst system each bank of engine

cylinders exhaust into their own catalyst. Currently 60 percent of vehicles utilize the single catalyst

approach with the remaining 40 percent utilizing the dual catalyst approach. We expect that the

usage of the single floor catalyst system will drop to 13 percent as a result of the new standards, and

usage of the dual catalyst system will drop to 50 percent. We expect that the remaining 37 percent

of vehicles will utilize dual underfloor catalysts in conjunction with dual close-coupled catalysts. 

The costs of the single underfloor catalyst and the dual underfloor catalysts were analyzed for both

the baseline (i.e., current) scenario and for enhanced versions used in compliance with the standards.
Regulatory Impact Analysis 

96

The cost dual underfloor/dual close-coupled catalyst system was only analyzed in an enhanced

configuration for use in compliance with the standards since there are currently no close-coupled

systems in wide use outside of California. Since the required catalyst size tend to be a function of

engine size, we analyzed catalysts for two engine sizes, standard and large. For purposes of

developing an average per-vehicle cost we weighted the costs of the two catalyst systems assuming

that 75 percent of HDVs would be representative of the standard engine size and that the remaining

25 percent would be representative of the large engine size.

2. Changes in Precious Metals

The catalyst enhancements referred to in the previous paragraph consist of changes in the

catalyst precious metal and washcoat compositions and loadings. Vehicle catalysts have typically

used some combination of platinum (Pt), palladium (Pd) and rhodium (Rh). These precious metals

account for a significant portion of the catalyst cost. Historically, a Pt/Rh combination has been

used, although Pd has been used in much greater quantities (up to 100 percent). Pd is more thermally

stable than Pt and Rh and is therefore a good choice for applications which see a high degree of

thermal loading, such as close-coupled catalysts. Currently, federally-certified HDVs typically have

a precious metal mix of 6.7 grams (g) Pd for each g of Rh, with no Pt. This is generally applied at

loading of 2 grams per liter (g/L) of total catalyst substrate volume. However, Pd usage is going up.

We used a 10/1 ratio of Pd to Rh as it baseline assumption. Currently, enhanced underfloor

catalysts being used in California are loaded at 3 to 6 g/L of substrate volume at a Pd/Rh ratio of 10

to 1. Close-coupled catalysts are typically 100 percent Pd loaded at 5 to 8 g/L of substrate volume.

Current federally-certified HDVs tend to have rather large catalysts with fairly low precious metal

loadings. Thus, we expect that no increase in catalyst volume will be required to comply with the

standards. Rather, the improvements will center on the precious metals and washcoats, as well as

the movement toward increased use of close-coupled catalysts. In cases where close-coupled

catalysts will be utilized, we are assuming that total catalyst volume will remain unchanged, and that

the size of the underfloor catalysts will be reduced from the baseline size by the volume of the closecoupled catalysts. We are assuming that, on average, the new standards will be met using a Pd/Rh

combination in a 10 to 1 ratio and at a loading of 4 g/L for underfloor catalysts. For close-coupled

catalysts we assumed that 100 percent Pd will be used at a loading of 6.25 g/L.

Precious metal prices have shown some volatility in recent years. In order to smooth out this

volatility, as well as insure an uninterrupted supply of precious metals, vehicle manufacturers

typically buy precious metals in bulk and supply them to the catalyst manufacturers. It is for this

reason that the 29 percent supplier markup that we are applying to products supplied to the

manufacturers by component suppliers is not being applied to the cost of precious metals. We chose

to use the same precious metal spot prices (i.e., short-term, or daily, prices) for the purposes of this

analysis that we recently used in support of the Tier 2 emission standards for light-duty vehicles,

light-duty trucks, and medium-duty passenger vehicles. These are $868 per troy ounce for Rh and

$390 per troy ounce for Pd. We believe that the spot prices used in the Tier 2 rulemaking are

appropriate here for two reasons. First, the manufacturers affected by today’s regulations also
Chapter 5: Economic Impacts of HD Otto-cycle Standards

97

produce vehicles which must comply with the Tier 2 regulations. Second, today’s regulations and

the Tier 2 regulations take effect in the same time frame.

3. Changes in Washcoat

In addition to the changes to precious metals just discussed, we expect that the new standards

will also result in changes to the catalyst washcoat compositions and loadings. Current washcoats

are typically a combination of a cerium oxide blend (ceria) and aluminum oxide (alumina). Current

ratios of these tow components range from 75 percent ceria/25 percent alumina to 100 percent

alumina. We assumed a 70/30 ceria to alumina ratio to represent the current baseline configuration.

Of the two common washcoat components, ceria is more thermally stable and, thus, is expected in

higher concentrations in close-coupled catalysts. The We assumed that a slightly higher ceria

concentration (75/25 ratio of ceria to alumina) will be used in compliance with the vehicle-based

standards and that an even higher ceria concentration (80/20 ratio of ceria to alumina) will be used

in compliance with the engine-based standards.

Current washcoat loadings range from 160 to 220 g/L of catalyst substrate volume. For

simplicity we assumed an average loading of 190 g/L for the baseline configuration, and that this

loading would remain unchanged for compliance with the vehicle-based standards. For compliance

with the engine-based standards, we assumed that the washcoat loading will increase to 220 g/L. In

addition, we expect that a new technique of layering the washcoat and precious metals will be

employed for compliance with the engine-based standards. Currently, the precious metals and

washcoat are applied to the catalyst substrate in a single slurry. Under the layering approach there

is a separate slurry for each precious metal, with the second slurry being applied after the first dries.

This process allows for more reaction surface area, resulting in a more efficient catalyst. Table 5-3

provides a summary of the precious metal and washcoat compositions and loadings for the current

baseline vehicle, as well as those expected to be used in compliance with the vehicle-based and

engine-based standards.

Table 5-3

Current and Projected Catalyst Precious Metal and Washcoat Compositions and Loadings

Baseline Vehicle-based Engine-based

Precious Metals Pd/Rh = 10/1

Loading = 2.1 g/L

Pd/Rh = 10/1

Loading = 4.0 g/L1

Pd/Rh = 10/1

Loading = 4.5 g/L

Washcoat 30%Alumina/

70% Ceria

Loading = 190 g/L

25% Alumina/

75% Ceria

Loading = 190 g/L

20% Alumina/

80% Ceria

Loading = 220 g/L

1. For close-coupled catalysts we assumed 100 Percent Pd at a loading of 6.25 g/L.

4. Substrates
Regulatory Impact Analysis 

98

The substrate that the precious metals and washcoat are affixed to are typically ceramic

substrates of 400 cells per inch. Increasing efforts are going into developing metallic substrates,

which offer better temperature and vibration stability, as well as requiring less precious metal loading

to achieve the same emission benefits. However, information from catalyst suppliers suggested that

the increased costs of the metal substrates will tend to cancel out any savings in precious metal costs,

as discussed in the Arcadis report.. Thus, we assumed that the current ceramic substrate would

continue to be used in compliance with the standards. Based on cost data obtained from catalyst

substrate suppliers, the following linear relationship

C = $4.67V + $1.50

where:

C = cost to the vehicle manufacturer from the substrate supplier

V = substrate volume in liters

was developed in the Arcadis report and is accurate for ceramic substrates sized from 0.5 L to 4 L.

Generally, catalyst substrates for HDVs are manufactured in bricks no larger than 2.5 L, with a

catalyst of greater than 2.5 L being comprised of more than one brick.

5. Packaging

The final cost component of the catalyst system is the can. The catalyst substrate is typically

packaged in a can made of 409 stainless steel and around 0.12 centimeters thick (18 gauge). The

cost of the can is a very small portion of the overall catalyst cost.

The following tables (Tables 5-4, 5-5 and 5-6) show our estimates of the total catalyst system

cost for each of the three configurations previously discussed, and for the current, baseline

formulation as well as the formulations projected to be used to comply with the vehicle-based and

engine-based requirements. No baseline costs are shown in Table 5-6 (dual underfloor plus dual

close-couple catalyst system) because these systems are not currently in wide use on federallycertified vehicles. These tables show the estimated costs rounded to the nearest dollar.
Chapter 5: Economic Impacts of HD Otto-cycle Standards

99

Table 5-4

Estimated Catalyst Costs of Single Underfloor Catalyst System

Baseline Projected Vehicle-based

Standards

Projected Engine-based

Standards

Engine Size Standard Large Standard Large Standard Large

Catalyst

Volume (L)

4.8 5.8 4.8 5.8 4.8 5.8

Substrate $26 $31 $26 $31 $26 $31

Washcoat $19 $22 $19 $22 $23 $27

Precious

Metals

$141 $170 $268 $324 $302 $365

Can $5 $5 $5 $5 $5 $5

Total Material

Cost

$191 $228 $318 $382 $356 $428

Labor $4 $4 $4 $4 $6 $6

Labor

Overhead

@40%

$1 $1 $1 $2 $2 $2

Supplier

Markup

@29%1

$16 $18 $16 $19 $18 $21

Manufacturer

Cost

$212 $251 $339 $407 $382 $457

1

 The supplier markup is not applied to the cost of the precious metals because the precious metals

are supplied by the vehicle manufacturer.
Regulatory Impact Analysis 

100

Table 5-5

Estimated Catalyst Costs of Dual Underfloor Catalyst System

Baseline Projected Vehicle-based

Standards

Projected Engine-based

Standards

Engine Size Standard Large Standard Large Standard Large

Catalyst

Volume (L)

4.8 5.8 4.8 5.8 4.8 5.8

Substrate $26 $31 $26 $31 $26 $31

Washcoat $19 $22 $19 $22 $23 $27

Precious

Metals

$141 $170 $268 $324 $302 $365

Can $5 $6 $5 $6 $5 $6

Total Material

Cost

$191 $229 $318 $383 $356 $429

Labor $5 $6 $7 $8 $11 $12

Labor

Overhead

@40%

$2 $2 $3 $3 $4 $5

Supplier

Markup

@29%1

$17 $19 $17 $20 $20 $23

Manufacturer

Cost

$215 $256 $345 $414 $391 $469

1

 The supplier markup is not applied to the cost of the precious metals because the precious metals

are supplied by the vehicle manufacturer.
Chapter 5: Economic Impacts of HD Otto-cycle Standards

101

Table 5-6

Estimated Catalyst Costs of Dual Underfloor Plus Dual Close-coupled Catalyst System

Projected Vehicle-based Standards

Engine Size Standard Large

Catalyst Volume (L) 4.8 5.8

Substrate $29 $34

Washcoat $20 $24

Precious Metals $314 $370

Can $6 $7

Total Material Cost $369 $435

Labor $15 $16

Labor Overhead @40% $6 $6

Supplier Markup

@29%1

$22 $25

Manufacturer Cost $412 $482

1

 The supplier markup is not applied to the cost of the precious metals because the precious metals

are supplied by the vehicle manufacturer.

B. Exhaust Gas Recirculation (EGR)

Electronically controlled EGR is currently used on about 85 percent of non-California Ottocycle HDVs. Those manufacturers that do not currently employ EGR on their federally certified

vehicles are not expected to utilize it to comply with the standards. Thus, the percentage of the fleet

with EGR is not expected to change as a result of the standards. However, some improvements to

flow control are expected to be made to those EGR systems that are currently being used, primarily

to comply with the new OBD requirements. In addition to minor changes in control algorithms, we

expect minor changes to the EGR valve and gasket, as well as the EGR flow sensor. These changes

are expected to cost from $5 to $12 per vehicle. For simplicity we assumed that the EGR

improvements will cost $7 per EGR-equipped vehicle for the purposes of this analysis.

C. Secondary Air Injection

The hardware cost for vehicles which utilize secondary air injection to reduce HC and CO

is expected to be about $67 per vehicle. We expect that the usage rate of secondary air injection will

rise from its current use on about 20 percent of Otto-cycle HDVs to about 30 percent as a result of

the standards.
Regulatory Impact Analysis 

102

D. On-board Diagnostics

On-board diagnostics systems are currently required in California (OBD II). Although not

required federally, many non-California HDVs do have some form of OBD system. This is primarily

for ease of manufacturing. On lines where vehicles are being assembled for both the California and

non-California markets it is often easier to simply install the California hardware on all vehicles

rather than install different parts on vehicles depending on their destination. This is especially true

of parts such as electronic control modules, some form of which needs to be installed regardless of

the vehicle’s destination. It is less true of hardware needed specifically for the California market that

is not required outside of California, such as additional oxygen sensors for catalyst monitoring.

Thus, the changes required to implement OBD nationwide are not extensive. The main cost

components associated with adopting OBD nationwide are as follows:

• Oxygen sensors/catalyst efficiency monitoring

• Evaporative emissions purge and leak

• Electronic control module improvements

• Manifold vapor pressure sensor improvements

Each of these OBD cost components is discussed in the following sections. A National OBD

program is only being applied to HDGVs weighing 14,000 lbs GVWR or less. Thus, only 60 percent

of HDGVs certified according to the engine-based program would be required to comply with the

OBD requirements. This is reflected in the cost summary table later in this chapter.

1. Oxygen Sensors/Catalyst Efficiency Monitoring

The OBD requirements, as well as the expected changes in catalyst configuration, will result

in changes in the number and placement of oxygen sensors in the exhaust system. Oxygen sensors

in non-California are typically only placed before the catalyst and used for closed loop air/fuel ratio

control. Compliance with the OBD requirements will require the use of oxygen sensors both before

and after the catalysts, to be used to monitor catalyst efficiency in addition to controlling air/fuel

ratio.

Heated oxygen sensors are used for both California and non-California vehicles. We also

expect them to be used in compliance with the standards. Heated oxygen sensors have an average

manufacturer’s cost of $10 to $15. Thus, for simplicity we used a manufacturer’s cost of $13 for

each sensor for this analysis.

Oxygen sensors are currently required downstream of the catalyst only on California vehicles.

However, many non-California vehicles are equipped with downstream sensors as a way of reducing

part complexity when they are manufactured on the same production line as vehicles destined for

California. Of non-California vehicles, one-sixth of single underfloor catalyst vehicles and half of

dual underfloor catalyst vehicles have downstream oxygen sensors. However, the OBD requirements

(as well as the expected changes in catalyst configurations) will result in 80 percent of HDGEs

subject to the OBD requirements needing an average of two additional oxygen sensors.
Chapter 5: Economic Impacts of HD Otto-cycle Standards

103

2. Evaporative Emissions Purge and Leak

The OBD provisions include a requirement for evaporative emissions control system purge

and leak detection. The most common method of performing these functions is to close off the vent

solenoid, use manifold vacuum to purge vapors from the evaporative control system, close the vapor

management valve and monitor the system vacuum using a fuel tank pressure transducer. Any

change in the vacuum over time indicates a leak with the rate of vacuum loss related to the size of

the leak.

The additional costs associated with this system include those for the canister vent solenoid,

the fuel tank pressure transducer, tubing and wiring, and programming of the electronic control

module. The manufacturer costs are $11 for the canister vent solenoid and $16 for the fuel tank

pressure transducer. Wiring and labor bring the average unit cost of this system to around $31.

3. Electronic Control Module Improvements

Although almost all vehicles use 16 bit electronic control modules (ECMs), there is a gradual

change toward 32 bit processors on California vehicles. We expect that many non-California

vehicles will have 32 bit processors as well in order to reduce parts complexity. Thus, we assumed

that, as a baseline, 50 percent of non-California vehicles will be equipped with 32 bit processors

prior to 2005. We expect that all vehicles will be equipped with 32 bit processors in order to comply

with the standards. We expect that this move to 32 bit processors will result in a $21 increase over

the baseline vehicle. However, the need for 32 bit processors is only partly driven by the OBD

requirements. The lower emission limits will also result in a move to more powerful ECMs. Thus,

we are assigning half of the incremental cost of the improved ECM to the OBD requirements and

the other half to the exhaust emission standard requirements for all covered vehicles. For engines

we are assigning half of the ECM cost to OBD for engines under 14,000 lb GVWR (about 60 percent

of Otto-cycle HDEs) and none of the ECM cost to OBD for those over 14,000 lb GVWR.

4. Manifold Vapor Pressure Sensor Improvements

We expect that the OBD requirements will result in improved exhaust gas recirculation

(EGR) flow control. This will require improvements to the manifold vapor pressure sensor at a cost

of $6 per EGR-equipped vehicle.

E. Exhaust Systems

We expect that insulated exhaust systems will be used in close-coupled catalyst-equipped

vehicles in order to improve catalyst light-off time. We estimate that such systems will cost $42 per

vehicle. Since we project that 40 percent of chassis-based vehicles will use close-coupled catalysts,

the cost per vehicle on average will be $17.

F. Electronic Control Module
Regulatory Impact Analysis 

104

The projected improvements to electronic control modules (ECMs) were discussed in the

earlier section on OBD systems. As was discussed there, half of the cost of the ECM improvements

will be a result of the OBD requirements and half will be a result of the lower exhaust emission

standards for vehicles and those engines subject to the OBD requirements.1 Thus, we project that

ECM improvements due to the increased stringency of the exhaust emission standards will result in

a $11 per vehicle increase for vehicles, and engine subject to the OBD requirements. For those

engines over 14,000 lb GVWR (which are not subject to the OBD requirements) we are assigning

the entire $21 cost of the ECM improvements to the emission standards.

G. Onboard Refueling Vapor Recovery

We estimated the costs for onboard refueling vapor recovery (ORVR) equipment by updating

the estimates of ORVR technology cost that were developed in the Regulatory Impact Analysis for

the original ORVR regulations, as referenced at the beginning of this chapter. While we did not

ultimately adopt ORVR requirements for any heavy-duty vehicles in the original rulemaking, we did

estimate the cost of such controls separately for both light heavy-duty vehicles (8,501 through 14,000

lbs. GVWR) and heavy heavy-duty vehicles (14,001 lbs. GVWR and greater). For this analysis we

assumed that the technology required to meet the standards has not changed since the original ORVR

analysis was done, and that the nature of the light heavy-duty fleet (in terms of percentage of vehicles

with one versus two fuel tanks, etc.) also has not changed. Despite specific requests for comment

on these assumptions in the proposal, we received no comments disputing them. Thus, we simply

took the cost estimates for light heavy-duty vehicles from the original analysis and adjusted them to

account for inflation. EPA believes this is reasonable because the vehicles we are applying ORVR

requirements to in this action (complete vehicles from 8,501 through 10,000 lbs. GVWR) are a

subset of the light heavy-duty vehicle class analyzed for the original rulemaking. The original pervehicle cost estimates (in 1992 dollars) were $6.29 for variable cost and $2.60 for fixed cost. Using

the Consumer Price Index to account for inflation, these costs were adjusted (to 1999 dollars) to

$7.50 for variable cost and $3.00 for fixed cost.

In addition to variable and fixed costs, ORVR also has an associated operating cost benefit,

which takes into account both a the fuel economy penalty of the added weight of the hardware and

the much larger fuel economy benefit that comes from recovering refueling vapors and using them

in the engine. In the analysis for the original ORVR regulations this operating cost was estimated

to be a $5.50 per-vehicle lifetime credit for light heavy-duty vehicles. The credit was conservatively

calculated assuming that Stage II refueling vapor recovery controls would not be discontinued. Since

the value of this credit is entirely dependent on the price of gasoline, it was not updated to account

for inflation because the price of gasoline has not generally risen with inflation. Although gasoline

prices have risen significantly in recent months, it is too early to tell whether this is a long term trend.

Thus, a lifetime operating credit of $5.50 per vehicle is used in this analysis. Using the recent higher

gasoline prices would have resulted in a higher per vehicle credit.

IV. Fixed Costs
Chapter 5: Economic Impacts of HD Otto-cycle Standards

105

The fixed costs are broken into four main components: research and development, tooling,

certification, and in-use testing. Of these four, only certification and in-use testing costs apply to

vehicle-based certifications. In-use testing costs do not apply to engine-based certifications. These

costs are discussed individually in the following sections.

A. R&D and Tooling Costs

The vehicle-based standards will essentially require the application of California LEV

technology to HDVs nationally. Since this technology has already been developed and is being

implemented and the tooling is in place to make California vehicles on the same assembly lines as

non-California vehicles, there are no R&D or tooling costs associated with the vehicle-based

requirements. However, in the case of the engine-based standards, we expect that some R&D and

new tooling will be required. We believe that, on average, R&D costs for a single engine family will

be about $3 million, and that tooling costs will be about $75 thousand per engine family. Assuming

that annual sales per engine family average 25 thousand units and that these costs are recovered over

a five year period, we estimate that the R&D and tooling costs will be $34 per engine for the first

five years of the program.

B. Certification Costs

We relied on a previous analysis for estimating certification costs.4

 Updating those costs for

inflation using the Consumer Price Index results in an estimated certification cost of $252,750 per

engine family. Certification costs will be incurred on average one year before the start of production.

Thus, this cost is increased by seven percent. Summing the costs separately for engine families

certified to the chassis-based and engine-based and amortizing them over five years results in

projected per-vehicle certification costs of $1 for chassis-based configurations and $6 for enginebased configurations.

C. In-use Testing Costs

Using cost information developed in support of our CAP 2000 regulations, we project that

the in-use testing requirement will cost $1 per vehicle. We used the cost from the CAP 2000

rulemaking of $4,600 per test. We used the Consumer Price Index to inflate this cost from 1998 to

1999 dollars Assuming seven engine families and ten tests per engine family, total in-use testing

costs would be $334,000. Using assumed complete heavy-duty vehicle sales of just under 300,000

in 2005 yields a per vehicle in-use testing cost of just over $1. This cost will be incurred indefinitely

for each year of production, rather than being recovered over five years as with the other fixed costs.

In other words, while other fixed costs such as tooling and R&D are incurred only once and then

recovered over a five year period, the in-use testing costs are incurred every year.

V. Summary of Costs

Table 5-7 contains a summary of per-vehicle costs associated with the new standards for

Otto-cycle heavy-duty vehicles and engines. The various hardware cost components include the
Regulatory Impact Analysis 

106

manufacturers’ 29 percent markup. These costs are presented as incremental cost increases from the

cost of current vehicle emission control systems.

Table 5-7

Summary of Incremental Costs to Meet the Otto-cycle Vehicle Emission Standards

Chassis-based Standards Engine-based Standards

Catalyst $163 $187

On-board Diagnostics $68 $41

ORVR $8 --

Other Emissions Hardware $41 $28

Total Hardware $280 $256

Fixed Costs $5 $40

Operating Costs (ORVR) -$6 --

Total Incremental Cost $279 $296

VI. Aggregate Cost to Society

In addition to the per vehicle costs just described, we also calculated the aggregate cost to

society. This was done by combining the per vehicle costs with assumed future sales of HDVs. The

sales for the different categories of heavy-duty Otto-cycle vehicles and engines that would be

covered by the rule based on the 1995 model year were determined using production information

provided by manufacturers to EPA and were assumed to grow at a linear rate of two percent from

the 1995 levels. The results of this analysis are summarized in Table 5-8. The recovery of fixed

costs results in slightly reduced costs beginning in 2010, after which costs begin to rise in accordance

with projected increased sales. The aggregate costs represent a combined estimate of the fixed costs

as they are allocated over the first five years of sales (with the exception of fixed costs for in-use

testing, which continue indefinitely), variable costs assessed at the point of sale, and operating costs

(primarily in the form of fuel cost savings) for ORVR-equipped vehicles (calculated to net present

value and applied at the point of sale).
Chapter 5: Economic Impacts of HD Otto-cycle Standards

107

Table 5-8

Aggregate Cost to Society of the Heavy-duty Otto-cycle Requirements

Year Cost ($million)

2005 $110

2006 $117

2007 $124

2008 $126

2009 $129

2010 $124

2011 $126

2012 $128

2013 $131

2014 $133

2015 $135

2016 $137

2017 $139

2018 $141

2019 $144

2020 $146

2021 $148

2022 $150

2023 $152

2024 $154
Regulatory Impact Analysis 

108

1.“Cost Estimates for Heavy-duty Gasoline Vehicles,” Arcadis Geraghty & Miller, Final Report,

September 30, 1998.

2. “Final Regulatory Impact Analysis: Refueling Emission Regulations for Light Duty Vehicles

and Trucks and Heavy Duty Vehicles,” U.S. EPA, January, 1994.

3. “Update of EPA’s Motor Vehicle Emission Control Retail Price Equivalent (RPE) Calculation

Formula,” Jack Faucett Associates, Report No. JACKFAU-85-322-3, September 1985.

4. “Draft Regulatory Impact Analysis and Oxides of Nitrogen Pollutant Specific Study,” p. 3-29

ff., October 1984.

Chapter 5 References
Chapter 6: Environmental Impact of HD Diesel Standards

(l) Three terms are used in this chapter to describe organic emissions: “total hydrocarbons” (THC or HC), volatile

organic compounds”(VOC), and “nonmethane hydrocarbons” (NMHC). THC refers to the organic emissions from

an engine as measured by the test procedures of 40 CFR 86. VOC refers to organic emissions excluding

compounds that have negligible photochemical reactivity, primarily methane and ethane (see 40 CFR 51.100). 

NMHC refers to the difference obtained by subtracting methane from total hydrocarbons. Since the ethane content

of emissions is very small from diesel engines, organic emissions measured as NMHC are approximately the same

as when measured as VOC.

109

CHAPTER 6: ENVIRONMENTAL IMPACT OF

HD DIESEL STANDARDS

I. Introduction

This chapter describes the expected environmental impacts of the new heavy-duty diesel

engine NMHC plus NOx emissions standards described in the preamble. Specifically, this chapter

includes an estimated nationwide NOx, VOC, and PM10 inventory for 2000, heavy-duty diesel engine

NOx, NMHC, and PM inventory projections for future years (with and without additional control),

estimates of the impacts of the standards on typical vehicles over their lifetime, and a discussion of

the environmental effects of the emissions reductions.l

While the new standards are combined NMHC plus NOx levels, we consider the NMHC and

NOx emissions impacts separately. Given the technologies we expect manufacturers to use on

heavy-duty diesel engines to comply with the new standards, we model the fleet-average impact of

the combined standard as being equivalent to a 2.3 g/bhp-hr NOx standard and a 0.2 g/bhp-hr

NMHC standard. We base these emission factors on the judgement that manufacturers will find it

easier to design for low NMHC to give them more flexibility for their NOx calibrations. This is

consistent with statements made in informal discussions with engine manufacturers.

We emphasize, however, that this is only an analytical approach; we expect that

manufacturers will optimize each family uniquely with respect to the combined standards, balancing

the sometimes competing effects on NMHC and NOx control technologies. Thus individual engine

families may have emission levels different from the fleet-average emissions we use in this analysis.

It is also important to note that we are modeling the environmental impacts of the supplemental

testing requirements beginning in calendar year 2004, because we believe that manufacturers will

design most, if not all, of their engine models to comply with these requirements in model year 2004.

This assumption, which is consistent with the assumptions made for the economic analysis in

Chapter 4, should not significantly affect the results of the cost-effectiveness analysis in Chapter 8.

The inventory analysis described below builds on the inventory analysis in the Regulatory

Impact Analysis associated with the 1997 Final Rulemaking for heavy-duty diesel engines (HDDE).1

However, we use recent studies to improve our understanding of the emissions impact of mobile

sources. We discuss these studies and their effects on the calculated HDDE emissions inventories

in this chapter.
Regulatory Impact Analysis 

110

II. Description of Calculation Method

In modeling emissions from heavy-duty diesel engines, our intent is to be consistent with the

upcoming MOBILE6 model. MOBILE6 is the upcoming version of the MOBILE model that we

historically use to develop calendar year specific emission factors for on-highway vehicles.

However, it does not have the capability to analyze all of the scenarios needed to support the

rulemaking. Consequently, we developed a spreadsheet model which provides consistent results

with the MOBILE model, and has the needed capability.

A. General Equation

We divide HDDEs into four distinctive classes for the purpose of inventory calculations.

Table 6-1 presents these classes which have different characteristics due to the difference in their

size and use. Later in this chapter, we discuss some of these differences as they apply to emission

modeling. Our standards apply throughout an engine’s regulatory useful life. Therefore, emissions

may be cleaner earlier in an engine’s life and dirtier later in its life due to deterioration. We use

regulatory useful life in our modeling as the point in the engine’s life at which the engine just meets

the emissions standards with an assumed compliance margin.

Table 6-1

HDDE Classes and Regulatory Useful Life

Class Description* Regulatory Useful Life**

Light HDDE 8,501-19,500 lbs. GVWR 110,000 mi /10 yrs

Medium HDDE 19,501-33,000 lbs. GVWR 185,000 mi /10 yrs

Heavy HDDE > 33,000 lbs. GVWR 435,000 mi /10 yrs / 22,000 hrs

Urban Bus characterized by application 435,000 mi /10 yrs / 22,000 hrs

 * GVWR refers to gross vehicle weight rating; “urban bus” does not generally include school buses or inter-city buses. ** Whichever occurs first; for the purposes of these calculations, we use 290,000 miles for urban buses.

For our calculations, emissions from HDDEs are primarily a function of per-engine emission

factors, in-use deterioration, and vehicle miles traveled. Equation 1 presents the basic calculation

we use to determine emissions from HDDEs in short tons per year. Following this section, we

supply more detail on the components of this equation.

TonsCY = (454 x 2000) -1 x Mclass{VMT x CF x MMY/age [(ZMLMY + DETMY/ age)x TFage]} (1)

where:
Chapter 6: Environmental Impact of HD Diesel Standards

111

TonsCY - emissions for a given calendar year expressed in short tons

class - LHDDE, MHDDE, HHDDE, and urban bus

VMT- total vehicle miles traveled in a given calendar year by class

CF - conversion factor from g/bhp-hr to g/mi by class

MY/age - distribution of vehicles in a calendar year by vehicle age

ZMLMY - zero-mile emission level in g/bhp-hr for a given model year engine

DETMY/age - emissions deterioration as a function of model year and vehicle age

TFage - travel fraction of vehicles from each model year in a given calendar year

(454 x 2000) -1 - conversion from grams to short tons

B. Conversion Factors

Our engine standards are in terms of grams of pollutant per work performed. We use these

units because we believe they best characterize emissions for an engine-based emission standard.

However, we use vehicle miles traveled (VMT) to characterize heavy-duty engine operation in our

emission inventory calculations. We believe that we can more accurately determine VMT for

HDDVs than we can determine the work performed by HDDEs.

To apply VMT to our emissions calculations, we need emission factors in terms of grams per

mile. Therefore, in our calculations, we convert the g/bhp-hr figures to g/mi. Because large engines

typically perform more work in a mile of travel than small engines, we use separate conversion

factors (CF) for each class of HDDEs. These numbers are reported in units of bhp-hr/mi and are

based on work performed for MOBILE62. The conversion factor is a function of fuel density, brake

specific fuel consumption and fuel economy. Table 6-2 presents the CFs we use for 1996 and later

model year engines. For older engines, the CFs may vary, some higher and others lower than the

values in Table 6-2.

Table 6-2

Conversion Factors for HDDEs (bhp-hr/mi)

LHDDE MHDDE HHDDE Urban Bus

1.23 2.25 2.97 4.68

C. Vehicle Miles Traveled

To determine the tons of emissions in a given calendar year we need to know the total VMT

for that calendar year and the travel fraction of each model year of engines. The travel fraction is

important because engines produced before and after a new standard goes into effect will have

different emission levels.

Total Miles
Regulatory Impact Analysis 

112

To determine the tons of emissions in a given calendar year we need to know the total VMT

for that calendar year and the travel fraction of each model year of engines. The travel fraction is

important because engines produced before and after a new standard goes into effect will have

different emission levels.

To calculate nationwide emissions from HDDEs, we multiply the total VMT by the emission

factors for HDDEs. For this analysis, we base the nationwide annual VMT on Federal Highway

Administration estimates of annual VMT by highway category and vehicle type. We extrapolate the

VMT estimates out to 2030 using linear growth at approximately 3 percent for all classes of heavy

duty diesel vehicles.

We also split this VMT by MOBILE class and fuel type. To split the VMT by class and fuel

type, we use information on engine registrations by class and per-vehicle operation in miles per year

collected for use in MOBILE6.3 We use the products of the vehicle registrations and per-vehicle

operation to determine the VMT fractions. Table 6-3 presents the resulting breakdown of VMT by

class.

Table 6-3

Total VMT by Class for Heavy Duty Diesel Vehicles [million miles]

Calendar Year LHDDV MHDDV HHDDV Urban Bus

2000 41,158 37,013 143,974 2,753

2005 48,475 43,593 169,355 3,242

2010 55,713 50,102 194,643 3,726

2015 63,550 57,149 222,022 4,250

2020 71,386 64,197 249,401 4,774

2030 87,060 78,292 304,160 5,823

These HDDE VMT estimates are higher than those used in our proposal for 2004 heavy-duty

engine standards due to the use of new and updated MOBILE6 estimates of the fraction of total VMT

that is heavy-duty and the fraction of heavy-duty VMT that is diesel (see Chapter 6 of the draft RIA

for a discussion of the VMT estimates used in the proposal, available in EPA Air Docket A-98-32,

docket item III-B-01). The predominant changes were to increase VMT estimates of light heavyduty vehicles and the diesel fraction of heavy-duty vehicles, both of which are consistent with recent

trends. The net result is that if the MOBILE values 4

 are used to calculate diesel fuel consumption,

they agree very well with Federal Highway Administration estimates.5,6 This gives us added

confidence that these new estimates are accurate.

Travel Fraction
Chapter 6: Environmental Impact of HD Diesel Standards

113

Travel fraction refers to the percentage of total miles driven in a given calendar year coming

from each surviving model year of vehicles. In determining the travel fraction of vehicles by age,

we considered both the survival rates of HDDVs and the average annual mileage accumulation rates

by age. The survival rates give us the distribution of the number of vehicles of each model year in

a given calendar year. HDDEs are operated less as they age; therefore, we consider the miles

traveled by age when determining our travel fraction. We use the age distributions and VMT by age

rates developed for MOBILE6.7 Table 6-4 presents survival distribution and mileage accumulation

rates by age.
Regulatory Impact Analysis 

114

Table 6-4

Survival Distribution of HDDEs by Age

Vehicle

Age

Survival Distributions Mileage Accumulation Rates

Light Medium Heavy Bus Light Medium Heavy Bus

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

0.740

1.000

0.932

0.870

0.811

0.756

0.705

0.657

0.613

0.572

0.533

0.497

0.464

0.432

0.403

0.376

0.351

0.327

0.305

0.284

0.265

0.247

0.231

0.215

0.207

0.194

0.177

0.167

0.153

0.119

0.535

1.000

0.935

0.875

0.818

0.765

0.715

0.669

0.626

0.585

0.547

0.512

0.478

0.447

0.418

0.391

0.366

0.342

0.320

0.299

0.280

0.262

0.245

0.229

0.218

0.204

0.191

0.179

0.165

0.151

0.535

1.000

0.935

0.875

0.818

0.765

0.715

0.669

0.626

0.585

0.547

0.512

0.478

0.447

0.418

0.391

0.366

0.342

0.320

0.299

0.280

0.262

0.245

0.229

0.218

0.204

0.191

0.179

0.165

0.151

0.500

1.000

1.000

1.000

1.000

1.000

1.000

1.000

1.000

0.999

0.996

0.989

0.970

0.925

0.832

0.662

0.413

0.197

0.161

0.132

0.108

0.089

0.072

0.059

0.065

0.033

0.033

0.033

0.016

0.016

28,951

26,479

24,226

22,173

20,301

18,593

17,035

15,613

14,314

13,128

12,043

11,052

10,146

9,317

8,558

7,864

7,227

6,645

6,111

5,622

5,173

4,762

4,384

4,038

3,720

3,427

3,159

2,913

2,686

2,477

36,493

33,203

30,221

27,519

25,069

22,849

20,836

19,012

17,359

15,861

14,502

13,271

12,155

11,145

10,228

9,397

8,644

7,962

7,342

6,782

6,274

5,814

5,396

5,017

4,674

4,363

4,082

3,826

3,595

3,385

113,208

102,211

92,288

83,332

75,250

67,954

61,369

55,424

50,059

45,214

40,840

36,892

33,327

30,107

27,200

24,575

22,204

20,063

18,129

16,382

14,804

13,379

12,091

10,928

9,877

8,928

8,069

7,294

6,595

5,962

45,171

43,731

42,337

40,987

39,681

38,416

37,191

36,005

34,857

33,746

32,670

31,629

30,620

29,644

28,699

27,784

26,898

26,041

25,211

24,407

23,629

22,875

22,146

21,440

20,757

20,095

19,454

18,834

18,234

17,652

To calculate the annual VMT by age for an average HDDV, we multiply the vehicle survival

distribution by the vehicle mileage accumulation by age. To get the travel fraction, we divide the

annual VMT by the total average lifetime miles. Table 6-5 presents the annual VMT by age for an

average HDDV and the total average lifetime miles.
Chapter 6: Environmental Impact of HD Diesel Standards

115

Table 6-5

Average Annual VMT by Age for HDDVs

Vehicle Age LHDDE MHDDE HHDDE Urban Bus

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

21,426

26,479

22,591

19,281

16,461

14,059

12,011

10,265

8,776

7,505

6,421

5,495

4,704

4,028

3,450

2,957

2,534

2,173

1,863

1,598

1,372

1,177

1,011

868

771

664

559

485

411

294

19,511

33,203

28,263

24,067

20,503

17,476

14,904

12,718

10,859

9,279

7,934

6,790

5,816

4,987

4,280

3,678

3,164

2,725

2,350

2,030

1,756

1,522

1,321

1,149

1,020

892

730

684

593

512

60,517

102,211

86,321

72,905

61,577

52,011

43,934

37,113

31,353

26,487

22,378

18,908

15,976

13,499

11,407

9,640

8,147

6,885

5,819

4,918

4,157

3,514

2,971

2,511

2,177

1,845

1,445

1,306

1,090

903

22,579

43,731

42,337

40,987

39,681

38,416

37,191

35,995

34,847

33,707

32,547

31,273

29,692

27,427

23,876

18,381

11,115

5,136

4,070

3,228

2,559

2,028

1,605

1,275

1,353

655

634

614

297

288

Total 201,689 244,716 713,926 567,521

III. Total Nationwide Inventories

This section looks at 2000 emission inventories of NOx, NMHC and PM from HDDEs as

well as projected inventories for NOx and NMHC. We present our projected baseline and controlled

emissions inventories in addition to our anticipated benefits.
Regulatory Impact Analysis 

116

A. Current Inventories

The 1997 Trends Report estimates total nationwide emissions of NOx, VOC, and PM. The

purpose of including these inventories here is to show the relative importance of heavy-duty sources.

The highway emissions were estimated using EPA’s emissions factor models MOBILE5a (NOx and

NMHC) and PART5 (PM) and information from the Federal Highway Administration’s Highway

Administration’s Highway Performance Monitoring System and the 1980 U.S. census. More

information about the methodologies used to estimate the mobile source emissions, as well as the

other emissions, can be found in the Trends Report.

Due to recent information, we adjust the HDV NOx and VOC estimates to reflect the changes

described above and those described in the next chapter. In addition, we modify the nonroad

inventories to be consistent with recently finalized rules for land-based nonroad diesel engines8

 and

for marine diesel engines.9 Light duty vehicle estimates reflect emission inventory estimates

projected in the recent Tier 2 rule10 with a small adjustment in light-duty VMT due to the updated

total VMT splits by class (see section II.C).

The national NOx, VOC, and PM10 inventories for HDVs are summarized in Table 6-6.

These data indicate that emissions from “current” heavy-duty diesel vehicles account for about 17

percent of total NOx emissions and 1.7 percent of total VOC emissions. The PM numbers presented

in this table represent total vehicle emissions, which includes brake wear, and exhaust. Excluding

fugitive dust and wind erosion, HDDVs account for about 1.0 percent of total PM emissions. The

PM data presented in Table 6-6 is for informational purposes, this rule does not establish new PM

standards for HD vehicles.

Table 6-6

2000 National NOx, VOC, and PM Emissions

(thousand short tons per year)

Emission Source NOx VOC PM10

Light-Duty Vehicles 4,005 3,965 96

Heavy-Duty Diesel Vehicles 4,181 282 131

Heavy-Duty Gasoline Vehicles 298 241 8

Nonroad 5,343 2,485 642

Other 10,656 9,567 8,206

Total Nationwide Emissions 24,485 16,540 9,044

B. NOx Emission Projections and Impacts
Chapter 6: Environmental Impact of HD Diesel Standards

117

We calculate NOx emissions using the same methodology as was used for the 1997 RIA.

However, this analysis uses new conversion factors, scrappage rates, and vehicle miles traveled as

described above. Baseline EFs and DFs for 1988 to 2003 model year engines are based on a report

which considered certification data from 1988 to the present.11 These emission factors were

developed for use with MOBILE6. For earlier years, we continue to use the EFs and DFs in

MOBILE5b. As discussed in the introduction to this chapter, we modified the controlled emission

factor for NOx.

For both the baseline and controlled EFs, we assume a compliance margin of 8%. We base

this compliance margin on historical certification data showing past practices. In other words, we

assume that the manufacturers will conservatively design their engines to be 8% below the standards.

Therefore, for a NOx standard of 2.3 g/bhp-hr, we use a level of 2.12 g/bhp-hr for the deteriorated

emission level at the regulatory useful life of the engine. Table 6-7 presents baseline and controlled

EFs and DFs for HDDEs. For the purposes of the HDDE inventory calculations, EF refers to the

emission factor at the end of the regulatory useful life.

Table 6-7

NOx Emission Factors and Deterioration Rates for

2004 and Later Heavy-Duty Diesel Engines

Zero-Mile Level [g/bhp-hr]

LHDDE MHDDE HHDDE Urban

Bus

DR [g/bhp-hr per 10,000 miles]

LHDDE MHDDE HHDDE Urban

Bus

Baseline 3.26 3.69 3.68 3.90 0.001 0.001 0.003 0.000 

Controlled 2.10 2.10 1.99 2.21 0.001 0.001 0.003 0.000 

In our current analysis of HDDE emissions, we may underestimate emissions due to engine

deterioration in-use. We believe, that current modeling only represents properly maintained engines

but may not be representative of in-use malmaintenance or tampering. One study12 shows much

larger deterioration rates for HDDEs. However, in the time frame of this rule, we have not been able

to fully consider this study or assess other relevant information. In our future modeling efforts, we

intend to strengthen this part of our analysis.

The EFs and DFs in Table 6-7 above do not account for excess emissions from engines,

produced in the past, that operate with higher NOx in-use than on the certification test cycle which

were at issue in the 1998 consent decree between EPA and a number of HDDE manufacturers.

Although it does not affect the emissions benefits from this rule, we add excess emissions to our

annual NOx projections for some HDDE engines built in the 1988 through 1998 model years to

accurately represent the entire HDDE inventory over time. We use the excess emissions inventory

developed by the EPA’s Office of Enforcement and Compliance Assurance.13
Regulatory Impact Analysis 

118

0

1,000,000

2,000,000

3,000,000

4,000,000

5,000,000

6,000,000

2000 2005 2010 2015 2020

NOx [short tons/year]

Baseline

Controlled

Figure 6-1: Projected National Exhaust NOx Emissions from HDDEs

Figure 6-1 shows our national projections of total NOx emissions with and without the new

engine controls. The new standards should result in about a 43% reduction in NOx from new

engines. Table 6-8 presents these projections with the estimated NOx benefits for selected years.

Table 6-8

Estimated National NOx Emissions and Benefits from HDDEs

(thousand short tons per year)

Calendar Year Baseline Controlled Benefit

2005 3,410 3,150 266

2010 3,470 2,570 900

2015 3,830 2,490 1,340

2020 4,250 2,600 1,650

2030 5,130 3,000 2,130
Chapter 6: Environmental Impact of HD Diesel Standards

119

C. NMHC Emission Projections and Impacts

Estimates of the impact of the new standards on NMHC emissions are described below. 

Heavy-duty engines do not currently have applicable NMHC standards, so the discussion in this

section focuses on total hydrocarbons. For this analysis, we assume that the effect of the combined

standards is equivalent to 0.2 g/bhp-hr NMHC-only standards. Emissions are modeled using the

same methodology as in the 1997 RIA with the updates described earlier.

It should be noted that the analysis of the NMHC emission impacts is limited to a large extent

by the difficulty in projecting what the NMHC emissions from heavy-duty engines will be in the

future in the absence of new standards. This difficulty arises because NMHC emission levels from

heavy-duty diesel engines are largely the incidental result of a variety of other engine design

constraints, and thus are highly variable. As is described below, the fact that total HC emissions

from current engines are so far below the applicable HC standards, and that they vary among

different engine families by more than an order of magnitude, is evidence of the incidental nature

of HC emission reductions. Although the current HC standard is much higher than the baseline HC

emission factors in our calculations, the actual certification levels for HDDEs have shown

historically low HC emissions compared to the standards.

Baseline EFs and DFs for 1988 to 2003 model year engines are based on a report which

considered certification data from 1988 to the present.14 These emission factors were developed for

use in MOBILE6. For earlier model years, we rely on the EFs and DFs in MOBILE5b. Table 6-9

presents the baseline and controlled emission factors and deterioration rates. As with NOx, we

assume a compliance margin of 8 percent.

Table 6-9

NMHC Emission Factors and Deterioration Rates for

2004 and Later Heavy-Duty Diesel Engines

Zero-Mile Level [g/bhp-hr]

LHDDE MHDDE HHDDE Urban

Bus

DR [g/bhp-hr per 10,000 miles]

HDDE Urban Bus

Baseline 0.26 0.31 0.22 0.08 0.001 0.000 

Controlled 0.17 0.17 0.14 0.08 0.001 0.000 

Figure 6-2 shows our national projections of total NMHC emissions with and without the

new engine controls. The new standards should result in about a 32% reduction in NMHC from new

engines. Table 6-10 presents these projections with the estimated NMHC benefits for selected years.
Regulatory Impact Analysis 

120

0

50,000

100,000

150,000

200,000

250,000

300,000

350,000

400,000

450,000

2000 2005 2010 2015 2020

NMHC [short tons/year]

Baseline

Controlled

Figure 6-2: Projected National Exhaust NMHC Emissions from HDDEs

Table 6-10

Estimated National NMHC Emissions and New Benefits from HDDEs

(thousand short tons per year)

Calendar Year Baseline Controlled Benefit

2005 253 238 14

2010 251 202 49

2015 296 223 73

2020 339 249 90

2030 409 292 117

IV. Per Vehicle Emission Impacts

Using the emissions factors and lifetime vehicle miles traveled described above, lifetime

emissions can be calculated for individual heavy-duty diesel vehicles. Table 6-11 presents the

lifetime benefits associated with this new control program on a per-vehicle basis. Because emissions
Chapter 6: Environmental Impact of HD Diesel Standards

121

reductions are considered to be more valuable in the present than in the future, we present these

benefits both with and without a seven percent discount on the value of emissions reductions.

Table 6-11

Per-Vehicle Average Lifetime Emission Reductions

Due to the New Standards for Heavy-Duty Diesel Engines

Vehicle

Category

Undiscounted Reductions (lbs.) Discounted Reductions (lbs.)

NOx NMHC NOx NMHC

LHDDV 634 49 423 33

MHDDV 1,930 170 1,270 112

HHDDV 7,890 374 5,308 251

Urban Bus 9,887 — 5,848 — 

V. Environmental Impacts of Emission Reductions

A. Ozone Impacts

We expect the effect of the reduced NOx on ozone concentrations to vary geographically.

In general, when fully phased-in, the effect of this action in most nonattainment areas should be a

reduction in ozone concentrations on the order of a few percent. It should be noted, however, that

the potential exists for a few localized areas to actually experience slight increases in ozone

concentrations as a result of NOx emission reductions. The effect of the NMHC reductions on ozone

concentrations will be positive, though relatively small.

B. Air Toxics

The term “hydrocarbons” includes many different molecules. Speciation of the hydrocarbons

would show that many of the molecules are those which are considered to be air toxics including

benzene, formaldehyde, acetaldehyde, and 1,3-butadiene. Speciated hydrocarbon data was collected

for heavy-duty diesel engines.15,16,17,18 According to this data, hydrocarbons from a HDDV include

approximately 1.1 percent benzene, 7.8 percent formaldehyde, 2.9 percent acetaldehyde, and 0.6

percent 1,3-butadiene. Table 6-12 shows the estimated air toxics reductions associated with the

hydrocarbon reductions in this rule.
Regulatory Impact Analysis 

122

Table 6-12

Estimated Annual Air Toxics Reductions [short tons]

Year Benzene Formaldehyde Acetaldehyde 1,3-Butadiene

2005 159 1,130 419 87

2010 541 3,840 1,430 295

2015 799 5,670 2,110 436

2020 990 7,020 2,610 540

C. Other Impacts of Emission Reductions

The discussion in this section was contained in the RIA from the 1997 rulemaking for HD

diesel standards which established the 2004 HDDE NMHC+NOx standard, and the estimates

contained here were not re-analyzed for the affirmation of these standards contained in this

rulemaking activity. The expected reductions in NOx emissions should also positively affect

visibility, acid deposition, and estuary eutrophication. Both NO2 and nitrate particulates are optically

active, and in some urban areas, NO2 and nitrate particulates can be responsible for 20 to 40 percent

of the visible light extinction. The effect of this action on visibility should be small, given that it is

expected to reduce overall NOx emissions by several percent. For example, we expect the new

engine controls to result in about five percent less total NOx in the year 2020, and therefore would

be expected to decrease haze by about one percent where NO2 and nitrate particulates cause 20

percent of the haze.

We also expect the new standards to provide benefits with respect to acid deposition. The

1.7 million ton per year reduction expected in 2020 as a result of this action is greater than the

400,000 ton per year reduction expected from Phase I of the Agency’s acid rain NOx control rule (59

FR 13538, March 22, 1995), which was considered to be a significant step toward controlling the

ecological damage caused by acid deposition. It is not clear, however, that reducing emissions of

NOx from ground-level sources such as heavy-duty vehicles is truly equivalent to reducing NOx

emissions from elevated smokestacks, since NOx emitted higher into the atmosphere is likely to

travel further downwind, undergoing additional reactions before deposition. In any case, it is clear

that there will be some significant reduction in the adverse effects of acid deposition as a result of

this rule.

This action should also lead to a reduction in the nitrogen loading of estuaries. This is

significant since high nitrogen loadings can lead to eutrophication of the estuary, which causes

disruption in the ecological balance. The effect should be most significant in areas heavily affected

by atmospheric NOx emissions. One such estuary is Chesapeake Bay, where as much as 40 percent

of the nitrogen loading may be caused by atmospheric deposition.

VI. Summary
Chapter 6: Environmental Impact of HD Diesel Standards

123

0

250,000

500,000

750,000

1,000,000

1,250,000

1,500,000

1,750,000

2,000,000

2,250,000

2000 2005 2010 2015 2020 2025 2030

NOx [short tons]

0

25,000

50,000

75,000

100,000

125,000

150,000

175,000

200,000

NMHC [short tons]

NOx

NMHC

Figure 6-4: Projected Benefits of Control for NOx and NMHC

The projected total NOx and NMHC emission reductions as a result of this action are shown

in Figure 6-4. NOx reductions are projected to be about 1.7 million tons per year in 2020. NMHC

reductions are projected to be much smaller, about 90,000 tons per year in 2020, which would be

much less than one percent of the national NMHC (or VOC) inventory. These emission reductions

are expected to contribute very significantly towards reducing and controlling ambient ozone levels

in the future, counteracting the expected effects of new sources and growth in the vehicle miles

traveled. The new controls would also result in benefits with respect to visibility, acid deposition,

and estuary eutrophication.
Regulatory Impact Analysis 

124

1. “Control of Emissions of Air Pollution from Highway Heavy-Duty Engines; Final Rule,” 

Federal Register, pp.54694-54730, October 21, 1997.

2. “Update Heavy-Duty Engine Emission Conversion Factors for MOBILE6: Analysis of Fuel

Economy, Non-Engine Fuel Economy Improvements, and Fuel Densities,” U.S. Environmental

Protection Agency, EPA420-P-98-014, May 1998.

3. “Update of Fleet Characterization Data for Use in MOBILE6 - Final Report,” U.S.

Environmental Protection Agency, EPA420-P-98-016, June 1998.

4.“Update Heavy-Duty Engine Emission Conversion Factors for MOBILE6: Analysis of Fuel

Economy, Non-Engine Fuel Economy Improvements, and Fuel Densities,” U.S. Environmental

Protection Agency, EPA-420-P-98-014, May 1998.

5. Petroleum Supply Annual, 1998, Volume #1, Energy Information Administration (EIA),

Department of Energy (DOE), DOE/EIA-0340(98)/1.

6. Draft MOBILE6 fuel economy estimates.

7. “Fleet Characterization Data for MOBILE6: Development and Use of Age Distributions,

Average Annual Mileage Accumulation Rates and projected Vehicle Counts for Use in

MOBILE6,” U.S. Environmental Protection Agency, EPA420-P-99-011, April 1999.

8. “Control of Emissions of Air Pollution from Nonroad Diesel Engines; Final Rule,” Federal

Register, pp. 56967-57023, October 23, 1998.

9. “Control of Emissions of Air Pollution from New CI Marine Engines at or Above 37 kW;

Final Rule,”Federal Register, p. 73300, December 29, 1999.

10. “Control of Air Pollution from New Motor Vehicles: Tier 2 Motor Vehicle Emissions

Standards and Gasoline Sulfur Control Requirements,” Regulatory Impact Analysis, EPA420-R99-023, U.S. Environmental Protection Agency, December 1999.

11. “Update of Heavy-Duty Emission Levels (Model Years 1988-2004+) for Use in MOBILE6,”

U.S. Environmental Agency, EPA420-R-99-010, April 1999.

12. “Modeling Deterioration in Heavy-Duty Diesel Particulate Emissions,” Engine, Fuel, and

Emissions Engineering, Incorporated, prepared for the U.S. Environmental Protection Agency,

September 30, 1998.

13. Memo from Mike Samulski to Docket A-99-06, “OECA Estimates of Defeat Device NOx

Emissions,” November 10, 1999.

Chapter 6 References
Chapter 6: Environmental Impact of HD Diesel Standards

125

14. “Update of Heavy-Duty Emission Levels (Model Years 1988-2004+) for Use in MOBILE6,”

U.S. Environmental Agency, EPA420-R-99-010, April 1999.

15. Springer, K., “Investigation of Diesel-Powered Vehicle Emissions VII,” U.S. EPA, EPA460/3-76-034, 1977.

16. Springer, K., “Characterization of Sulfates, Odor, Smoke, POM and Particulates from Light

and Heavy-Duty Engines – Part IX,” U.S. EPA, EPA-460/3-79-007, 1979.

17. Bass, E., and Newkirk, M., “Reactivity Comparison of Exhaust Emissions from Heavy-Duty

Engines Operating on Gasoline, Diesel, and Alternative Fuels,” Southwest Research Institute,

SwRI 9856, 1995.

18. College of Engineering - Center for Environmental Research and Technology, “Evaluation

of Factors that Affect Diesel Exhaust Toxicity,” submitted to California Air Resources Board,

Contract No. 94-312, 1998.
Regulatory Impact Analysis 

(m) “Update of Heavy-Duty Emission Levels (Model Years 1988-2004+) for Use in MOBILE6", EPA document

EPA-420-R-99-010.

126

CHAPTER 7: ENVIRONMENTAL IMPACT OF THE HD

OTTO-CYCLE STANDARDS 

I. Introduction

This chapter describes the expected environmental impacts of the new exhaust and ORVR

standards for heavy-duty gasoline engines and vehicles described in the previous chapters.

Specifically, this chapter includes a description of how heavy-duty gasoline vehicle emission factors

were developed, the per-vehicle exhaust emission reductions due to the new standards over the life

of heavy-duty gasoline vehicles, the estimated exhaust NOx and NMHC emission inventories from

heavy-duty gasoline vehicles, and the exhaust emission benefits from the new exhaust standards.

Last of all, the chapter concludes with a description of the emission benefits from the new ORVR

requirements for Class 2b heavy-duty gasoline vehicles.

In evaluating the environmental impact of today’s heavy-duty gasoline engine and vehicle

standards for 2005 and later, we developed estimates of exhaust NOx and NMHC emissions from

HDGVs (excluding California) both with and without the effect of the standards. The analysis

performed to estimate the emission reductions from HD gasoline vehicles and engines in this final

rule is identical to the analysis performed for the Agency’s recently announced proposal to reduce

emissions from HD gasoline engines in the 2007 time frame (published on June 2, 2000 (65 FR

35430)). This analysis is different than the analysis we performed for the proposed rulemaking. In

the proposal we used the EPA MOBILE5 emission model, with in-use adjustment factors developed

specifically for the proposal. As discussed in the RIA, the draft MOBILE6 emission rates for HD

gasoline engines and vehicles have been completed, so we use those emission rates in this final rule.

Because MOBILE6 is not complete, we used the updated emission rates from MOBILE6 in

MOBILE5 for our analysis. The EPA report in which these emission rates are reported has gone

through an external stakeholder review.m For this final rule we use zero-mile and deterioration rates

for 1988 and later model year HD gasoline exhaust emissions developed for the draft MOBILE6

emission model. The impact of this change on this final rule, as compared to the proposal, was to

decrease the estimated in-use emission rates, for both the baseline and controlled scenarios, for 1998

and later model year HD gasoline engines. Full details of the environmental impact analysis can be

found in Chapter 7 of the RIA. The following paragraphs summarize the key results.

II. Exhaust NOx and NMHC Emission Factors

A. Baseline Emission Rates (Zero-Mile Levels and Deterioration Rates)

To determine the impact of the standards, we first estimate the emission levels of vehicles

currently in the fleet and then estimate the emission levels of vehicles that will meet the new
Chapter 7: Environmental Impact HD Otto-cycle Standards

127

standards. For the emission rates of engines currently in the fleet, we use the recently updated zeromile level and deterioration rates for 1988 and later model years that were developed for the

upcoming MOBILE6 model.1

 (For pre-1988 model year heavy-duty gasoline vehicles, we use the

standard MOBILE5 emission rates.) Because MOBILE6 is not yet complete, we perform our

emissions calculations by running MOBILE5 with the updated emission rates. Table 7-1 presents

the zero-mile level in grams per brake horsepower-hour (g/bhp-hr) and the deterioration rate in

g/bhp-hr per 10,000 miles for 1988 and later model year heavy-duty gasoline engines.

Table 7-1

Baseline Exhaust Emission Rates for 1988 and later Model Year

Heavy-Duty Gasoline Engines

Model Year

Zero-Mile Level

g/bhp-hr

Deterioration Rate

g/bhp-hr per 10,000 miles

NOx NMHC NOx NMHC

1988-1989 4.96 0.62 0.044 0.023

1991 3.61 0.35 0.026 0.023

1991-1997 3.24 0.33 0.038 0.021

1998-2004 2.59 0.33 0.038 0.021

B. Conversion Factors

Up until this rulemaking, we expressed the emission standards for heavy-duty gasoline

engines in units of g/bhp-hr. To convert the emissions of engines certified to g/bhp-hr standards to

g/mi levels, we multiply the g/bhp-hr levels by a conversion factor that is expressed in units of bhphr/mi. The conversion factor is a function of fuel density, brake specific fuel consumption and fuel

economy. We recently updated the conversion factors for heavy-duty engines.2

 Table 7-2 contains

the conversion factors assumed in this analysis for heavy-duty gasoline engines.

Table 7-2

Conversion Factors for Heavy-Duty Gasoline Engines (bhp-hr/mi)

Class 2b Class 3 Class 4 Class 5 Class 6 Class 7 Class 8a

1.096 1.150 1.134 1.324 1.311 1.446 1.540

C. Control Emission Rates (Zero-Mile Levels and Deterioration Rates)

Using the 120,000 mile useful life for heavy-duty gasoline engines, we estimate that a typical

1998 and later model year heavy-duty gasoline engine would emit NOx at roughly 3.0 g/bhp-hr, or
Regulatory Impact Analysis 

128

75 percent of the level of the standard of 4.0 g/bhp-hr. This is based on current and historical

certification data for heavy-duty Otto-cycle engines, which shows manufacturers have relied on a

large compliance margin when certifying, as well as statements from the engine manufacturers

indicating they attempt to target certification levels as low as one-half the emission standard (see the

discussion in Chapter 3(III)(H) for additional discussion of the manufacturers statements on

certification levels). Assuming manufacturers maintain the same amount of cushion below the

standard, we estimate the end of useful life level emissions levels associated with the new standards.

From these reduced levels, we determine the corresponding zero-mile levels and deterioration rates

assuming the ratio of the zero-mile level emissions to the deterioration rate (for 1998 engines) stays

the same as shown in Table 7-1. Table 7-3 presents the resulting controlled zero-mile levels and

deterioration rates for the three classes of heavy-duty gasoline engines and vehicles used in this

analysis (i.e., Class 2b complete vehicles, Class 3 complete vehicles, and incomplete HDGVs).

Table 7-3

Estimated Controlled Exhaust Emission Rates for 2005 and later Model Year

Heavy-Duty Gasoline Engines and Vehicles

Vehicle Category Zero-Mile Level

grams per mile (g/mi)

Deterioration Rate

g/mi per 10,000 miles

NOx NMHC NOx NMHC

Class 2b Completes 0.574 0.119 0.008 0.008

Class 3 Completes 0.638 0.140 0.009 0.009

Incomplete HDGVs 0.674 0.117 0.009 0.007

D. Emission Rate Adjustments

In the Draft RIA for the NPRM, we adjusted the emission rates in an attempt to quantify

increases in in-use emissions due to fuel that differs from the test fuel, to driving that differs from

the test cycle, fuel that differs from the test fuel, and to account for “high emitters” in the fleet

(engines that have much higher emissions than certification due to emission control failure).

However, we remove these adjustments from the final analysis.

MOBILE5 includes adjustment factors for HDGVs to account for in-use fuel with different

properties than certification test fuel. However, this adjustment is primarily driven by higher sulfur

levels seen in-use. Due to the recent Tier 2 standards for light-duty vehicles which included low

sulfur fuel requirements, this adjustment is no longer needed once the low sulfur fuel goes into effect

in 2004. Therefore we t urn off this fuel adjustment for 2004 and later calendar years. As a result,

the projected emission reductions from HDGVs, which begin in 2005, are not affected by this

adjustment.
Chapter 7: Environmental Impact HD Otto-cycle Standards

129

MOBILE5 includes speed correction factors which adjust the emission rates relative to the

average speeds above and below the average speed of the federal test procedure. These adjustments

consider the type of operation that is typically seen at these various average speeds such as stop-andgo driving at low average speeds. However, these correction factors are not specifically designed

to account for off-cycle effects such as control strategies that are designed to the test procedure that

may not work as well off the test procedure. We plan to work with stakeholders to explore

augmenting our existing test procedures to address off-cycle concerns. If appropriate we will

develop a regulatory proposal to address this issue. For this reason we do not include a further

adjustment for in-use operation in our final analysis.

MOBILE5 does not include high-emitter adjustments for HDGVs. In addition, no highemitter adjustments have been developed for the upcoming MOBILE6 model. Our NPRM analysis

used high-emitter adjustments that were based on information collected on light-duty vehicles and

may not represent heavy-duty vehicle emissions. For the final analysis we believe it is appropriate

to be consistent with the upcoming MOBILE6 model. In the future, we intend to look into this issue

further.

III. Per-Vehicle Exhaust NOx and NMHC Emission Reductions

To determine the cost-effectiveness of the new standards, we estimate the per-vehicle

emissions and emission reduction over the lifetime of typical heavy-duty gasoline vehicles. The

following sections presents the per-vehicle emission reduction analysis for three sub-categories of

heavy-duty gasoline vehicles (Class 2b completes, Class 3 completes, and incomplete HDGVs).

A. Per Vehicle Emission Rates

To estimate the per-vehicle lifetime emission reduction from the new standards, we first

estimated the emission rates of pre-control engines (i.e., model year 1998-2003 model years) and

controlled engines (i.e., model year 2004 and later). Table 7-4 presents the zero-mile levels and

deterioration rates that we use in our analysis. This is the same as Tables 7-1 and 7-3, except that

the baseline rates are broken out by class and expressed in units of g/mi using the conversion factors

in Table 7-2.
Regulatory Impact Analysis 

130

Table 7-4

Final Exhaust Emission Rates for Pre-control and Controlled

Heavy-Duty Gasoline Engines and Vehicles

Vehicle

Category

Model Year

Grouping

Zero-Mile Level,

grams per mile (g/mi)

Deterioration Rate

g/mi per 10,000 miles

NOx NMHC NOx NMHC

Class 2b

Completes

1998-2004 2.839 0.362 0.042 0.023

2005+ 0.574 0.119 0.008 0.008

Class 3

Completes

1998-2004 2.979 0.380 0.044 0.024

2005+ 0.638 0.140 0.009 0.009

Incomplete

HDGVs

1998-2004 3.435 0.438 0.050 0.028

2005+ 0.674 0.117 0.009 0.007

B. Mileage Accumulation and Scrappage Rates

Table 7-5 presents the HDGV mileage accumulation rates and scrappage rates used in this

analysis. The mileage accumulation rates come from our recently updated rates for heavy-duty

gasoline vehicles developed for the MOBILE6 emissions model.3

 We took the scrappage rates from

a National Highway Traffic Safety Administration (NHTSA) study. These scrappage rates are based

on light-duty truck (LDT) scrappage rates.4 (The scrappage rate represents the fraction of engines

still in the fleet at a given age.) The NHTSA study did not include information on HDGVs. We

believe the LDT scrappage rates would be similar to those for most HDGVs since three-quarters of

all HDGV sales are in the Class 2b truck category, which is the weight category just above the LDT

cutoff of Class 2a trucks.
Chapter 7: Environmental Impact HD Otto-cycle Standards

131

Table 7-5

Annual Mileage Accumulation, Scrappage, and Composite Mileage Accumulation Rates

for Heavy-duty Gasoline Vehicles

Age Class 2b/3

Annual Mileage

Class 4+

Annual Mileage

Scrappage Rate

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25+

19,977

18,779

17,654

16,596

15,601

14,666

13,787

12,961

12,184

11,454

10,768

10,122

9,516

8,946

8,409

7,905

7,432

6,986

6,568

6,174

5,804

5,456

5,129

4,822

4,533

21,394

19,692

18,125

16,683

15,356

14,134

13,010

11,975

11,022

10,145

9,338

8,595

7,911

7,282

6,703

6,169

5,679

5,227

4,811

4,428

4,076

3,752

3,453

3,178

2,926

0.998

0.995

0.989

0.980

0.967

0.949

0.924

0894

0.857

0.816

0.795

0.734

0.669

0.604

0.539

0.476

0.418

0.364

0.315

0.271

0.232

0.198

0.169

0.143

0.648

Table 7-6 contains the annual mileage accumulation rates for typical Class 2b/3 vehicles and

typical incomplete vehicles factoring the effect of scrappage. (For the incomplete vehicles, We

sales-weight the mileage accumulation rates for Class 2b/3 and Class 4+ vehicles in Table 7-8 based

on sales data on incomplete vehicles submitted by manufacturers to EPA.)
Regulatory Impact Analysis 

132

Table 7-6

Annual Mileage Accumulation Rates (Factoring in Scrappage)

for Typical Heavy-duty Gasoline Vehicles

Age

Class 2b/3 Complete

Vehicle Annual Mileage

Incomplete

Vehicle Annual Mileage

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25+

19,937

18,685

17,460

16,264

15,086

13,918

12,739

11,587

10,442

9,346

8,561

7,430

6,366

5,403

4,532

3,763

3,107

2,543

2,069

1,673

1,347

1,080

867

690

2,937

20,524

19,062

17,653

16,299

14,988

13,709

12,441

11,221

10,028

8,903

8,089

6,964

5,921

4,986

4,151

3,420

2,802

2,277

1,839

1,477

1,180

940

749

592

2,505

Lifetime Mileage 197,832 192,722

C. Per-vehicle Lifetime Emissions and Emission Reductions

Table 7-7 presents the NOx and NMHC emissions from typical heavy-duty gasoline vehicles

over the life of the vehicle. We determine these levels by combining the emission rate information

contained in Table 7-7 with the mileage accumulation rate information contained in Table 7-9.
Chapter 7: Environmental Impact HD Otto-cycle Standards

133

Table 7-7

Lifetime NOx and NMHC Emissions from Heavy-duty Gasoline Vehicles

Vehicle

Category

Model Year

Grouping

Undiscounted, Lifetime

Emissions, tons

NOx NMHC

Class 2b

Completes

1998-2004 0.71 0.13

2005+ 0.14 0.04

Class 3

Completes

1998-2004 0.74 0.13

2005+ 0.15 0.04

Incomplete

HDGVs

1998-2004 0.83 0.83

2005+ 0.16 0.16

Table 7-8 presents the expected per vehicle NOx and NMHC emission benefits for heavyduty gasoline vehicles from the new exhaust emission standards, both undiscounted and discounted

(at a rate of seven percent). In addition to the three subclasses of heavy-duty gasoline vehicles, Table

7-8 also contains the reductions for all HDGVs calculated on a sales-weighted basis from the three

individual categories.

Table 7-8

Per Vehicle Exhaust Emission Reductions

from the Heavy-duty Gasoline Engine and Vehicle Standards

Vehicle Category

Undiscounted Lifetime

Emission Reductions, tons

Discounted Lifetime

Emission Reductions, tons

NOx NMHC NOx NMHC

Class 2b Completes 0.57 0.09 0.38 0.05

Class 3 Completes 0.60 0.10 0.40 0.06

Incomplete HDGVs 0.67 0.11 0.45 0.07

All HDGVs 0.60 0.09 0.40 0.06

IV. HDGV Exhaust Inventory and Reductions

To estimate the exhaust NOx and NMHC inventories from heavy-duty gasoline vehicles, we

calculate the average emissions of all heavy-duty gasoline vehicles in the fleet for a variety of years.
Regulatory Impact Analysis 

134

To estimate the fleet average emissions for heavy-duty gasoline vehicles, we ran the MOBILE5b

emissions model with the updated information on emission levels and vehicle usage characteristics

as described in Sections II and III of this chapter. We multiply these resulting fleet average emission

levels by the estimated fleetwide vehicle miles traveled (VMT) for heavy-duty gasoline vehicles for

the corresponding year to yield the exhaust emission inventories.

We use the same methodology as described in Chapter 6 for HDDEs to determine the annual

VMT. We use Federal Highway Administration estimates of total VMT then use information

collected for MOBILE6 to split by class and fuel type. We exclude miles traveled by medium-duty

passenger vehicles because they are covered by the Tier 2 FRM for light-duty vehicles.

Table 7-9 presents the exhaust NOx and NMHC fleet average emissions, VMT, and

inventories from heavy-duty gasoline vehicles both without the new standards and with the new

standards taking effect in the 2004 model year. The inventories presented in Table 7-9 represent

nationwide inventories excluding California. California is excluded to simplify this analysis since

they are claiming reductions from their own emission program for these engines. A more detailed

description of the inventory development has been placed in the docket for this rulemaking.5

Table 7-9

Fleetwide Exhaust NOx and NMHC Emission Factors, Vehicle Miles Traveled, and Inventories

from Heavy-duty Gasoline Vehicles (49-state analysis)

Pollutant Calendar

Year

49-state

VMT

(1010 miles)

Heavy-duty Gasoline Vehicle Fleet Emission Levels

without new standards with the new standards

g/mi 103 short tons g/mi 103 short tons

NOx 2000

2005

2010

2015

2020

2030

6.68

7.83

9.03

10.27

11.52

14.01

4.05

3.65

3.47

3.34

3.31

3.29

298

315

345

378

420

507

4.05

3.50

2.18

1.46

1.12

0.83

298

302

217

165

142

127

NMHC 2000

2005

2010

2015

2020

2030

6.68

7.83

9.03

10.27

11.52

14.01

1.70

1.06

0.74

0.66

0.66

0.66

125

91

73

75

84

102

1.70

1.04

0.59

0.43

0.38

0.34

125

90

59

49

48

52

Table 7-10 contains the estimated exhaust NOx and NMHC emission reductions due to the

new standards for heavy-duty gasoline vehicles. As noted above, the reductions are for the entire
Chapter 7: Environmental Impact HD Otto-cycle Standards

135

0

100,000

200,000

300,000

400,000

500,000

600,000

2000 2005 2010 2015 2020 2025 2030

NOx [short tons/year]

Baseline

Controlled

Figure 7-1: Projected 49-State Exhaust NOx Emissions from HDGVs

United States excluding California. Figures 7-1 and 7-2 present the heavy-duty gasoline vehicle

exhaust NOx and NMHC inventories, respectively.

Table 7-10

49-State Exhaust Emission Reductions due to the Standards

for Heavy-duty Gasoline Engines and Vehicles

Calendar Year

Emission Benefits (thousand short tons)

NOx NMHC

2005 13 1

2010 128 14

2015 213 26

2020 278 35

2030 380 50
Regulatory Impact Analysis 

(n) Stage II vapor recovery systems on fuel pumps use hoods over the refueling nozzle to collect vapor from

vehicles during refueling.

136

0

20,000

40,000

60,000

80,000

100,000

120,000

140,000

2000 2005 2010 2015 2020 2025 2030

NMHC [short tons/year]

Baseline

Controlled

Figure 7-2: Projected 49-State Exhaust NMHC Emissions from HDGVs

V. ORVR Benefits

Along with the new exhaust standards, we are requiring ORVR regulations for Class 2b

heavy-duty gasoline vehicles. Back in the early 1990s, we proposed, but never finalized, ORVR

requirements for heavy-duty gasoline vehicles.6 For this analysis, we rely on the earlier analysis to

estimate the HC benefits of ORVR requirements.

Because many areas of the country have Stage II vapor recoveryn on fuel pumps at the gas

station, we developed an estimate of the HC benefits that were attributable to the ORVR equipment.

For this analysis, we assume that Stage II will remain in place in the areas that currently have Stage

II controls even after the ORVR requirements for light-duty vehicles and trucks have finished taking

effect. This assumption lowers the benefits attributable to the ORVR requirements and likely results

in a conservative estimate of benefits and cost-effectiveness as well.

Table 7-11 presents the assumptions we use in estimating the per-vehicle HC emission

benefits attributable to the new ORVR requirements for Class 2b heavy-duty gasoline vehicles and

the estimated benefits. The gram per gallon (g/gal) refueling HC emission benefit is taken from
Chapter 7: Environmental Impact HD Otto-cycle Standards

137

Table 4.10 of the above mentioned rulemaking. The gallon/mile (gal/mi) Class 2b fuel consumption

value is taken from the MOBILE6 Conversion Factor report referenced earlier. We determined the

benefits over the lifetime mileage accumulation of a typical Class 2b heavy-duty gasoline vehicle

as specified in Table 7-6 of this chapter on both an undiscounted basis and a discounted basis (at a

rate of seven percent).

Table 7-11

Determination of Per-Vehicle Hydrocarbon Benefits from the ORVR Requirements

for Class 2b Heavy-duty Gasoline Vehicles

Refueling Hydrocarbon Emission Benefit Rate 2.42 g/gal

Class 2b Heavy-duty Gasoline Vehicle Fuel Consumption 0.0987 gal/mi

Lifetime Undiscounted Emission Benefit 0.052 tons

Lifetime Discounted Emission Benefit 0.033 tons
Regulatory Impact Analysis 

138

1. “Update of Heavy-Duty Emission Levels (Model Years 1988- 2004+) for Use in MOBILE6,”

EPA Report No. EPA420-R-99-010, Christian Lindhjem and Tracie Jackson, U.S EPA, OMS,

AMD, April 1999.

2. “Update Heavy-Duty Engine Emission Conversion Factors for MOBILE6,” prepared by

Arcadis for EPA, May 1998.

3. “Update of Fleet Characterization Data for Use in MOBILE6,” prepared by Arcadis for EPA,

May 1998.

4. “Updated Vehicle Survivability and Travel Mileage Schedules,” U.S. Department of

Transportation, National Highway Traffic Safety Administration, November 1995.

5. “Development of Heavy-Duty Gasoline Emissions Inventories for the Tier 2/Sulfur NPRM,”

EPA memo from John W. Koupal to Docket A-97-10, March 26, 1999.

6. “Final Regulatory Impact Analysis: Refueling Emission Regulations for Light Duty Vehicles

and Trucks and Heavy Duty Vehicles,” U.S EPA, OAR, OMS, RDSD, SRPB, January 1994.

Chapter 7 References 
Chapter 8: Cost-Effectiveness

139

CHAPTER 8: COST-EFFECTIVENESS FOR HD

DIESEL AND OTTO-CYCLE REQUIREMENTS

This chapter assesses the cost-effectiveness of the requirements for new heavy-duty engines,

including the new standards, OBD, useful life, allowable maintenance, in-use testing, and rebuild

provisions. This analysis relies in part on cost information from Chapters 4 and 5 and emissions

information from Chapters 6 and 7 to estimate the cost-effectiveness of the provisions in terms of

dollars per ton of total emission reductions.

Separate analyses were performed for otto-cycle engines and diesel engines. The analysis

presented in this chapter for heavy-duty diesel vehicles is an updated version of the analysis

performed for the 1997 FRM. Both the otto-cycle and diesel analyses were performed on a pervehicle basis using total costs and total NOx plus NMHC emission reductions over the typical

lifetime of heavy-duty vehicle, discounted at a rate of seven percent to the beginning of the vehicle's

life. Analyses of the fleet cost-effectiveness for 30 model years after the new engine standards take

effect are also presented.

The following section describes the cost-effectiveness of the new engine NOx and NMHC

standards for the various categories of heavy-duty diesel vehicles noted above. As discussed in

Chapters 5 and 6, the estimated cost of complying with the provisions varies depending on the model

year under consideration. Therefore, the following section presents the per-vehicle costeffectiveness results for the different model years during which the costs are expected to change.

Just as the emission standard combines NOx and NMHC emissions, the cost-effectiveness of

adopting the new standard is calculated by dividing the combined NOx and NMHC emission

reductions into the cost of compliance.

Also presented is the fleet cost-effectiveness over the first 30 model years after the new

engine standards take effect (i.e., model years 2004 through 2033). These cost-effectiveness

numbers are calculated by weighting the various model year per-vehicle cost-effectiveness results

by the fraction of the total 30 model year sales they represent. The sales for the different categories

of heavy-duty diesel engines that would be covered by the rule based on the 1995 model year were

determined using production information provided by manufacturers to EPA and were assumed to

grow at a linear rate of two percent from the 1995 levels. It is important to note that 30-year

estimates are discounted so that they emphasize the higher costs which occur during the first several

years of these programs.

I. Cost-Effectiveness of the Diesel Requirements

Tables 8-1, 8-2, and 8-3 contain the total net present value costs based on the information

presented in Chapter 4, the lifetime emission reductions as presented in Chapter 6, and the resulting

cost-effectiveness values for light-, medium-, and heavy-heavy duty diesel vehicles, respectively.

Tables 8-1, 8-2, and 8-3 also contain the fleet cost-effectiveness covering the first 30 model years
Regulatory Impact Analysis 

140

after the new engine standards take effect (i.e., model years 2004 through 2033). As was noted in

Chapters 4 and 6, we are modeling both the costs and benefits of the supplemental testing

requirements as if they begin in model year 2004. We are doing this because we expect that

manufacturers will design most, if not all, of their engine models to comply with these requirements

in 2004.

Table 8-1

Cost-Effectiveness for Light Heavy-Duty Diesel Vehicles

Model Year

Grouping

Total NPV

Costs per

Vehicle

Discounted

Lifetime Reduction (tons)

Discounted

Per-Vehicle

CostEffectiveness

($/ton of

NOx+NMHC)

NOx NMHC

2004-05 $493

0.232 0.018

$1,969

2006-08 $417 $1,668

2009+ $249 $995

30 Year Fleet — — — $1,230

Table 8-2

Cost-Effectiveness for Medium Heavy-Duty Diesel Vehicles

Model Year

Grouping

Total NPV

Costs per

Vehicle

Discounted

Lifetime Reduction (tons)

Discounted

Per-Vehicle

CostEffectiveness

($/ton of

NOx+NMHC)

NOx NMHC

2004-05 $706

0.764 0.067

$849

2006-08 $620 $746

2009+ $323 $389

30 Year Fleet — — — $506
Chapter 8: Cost-Effectiveness

141

Table 8-3

Cost-Effectiveness for Heavy Heavy-Duty Diesel Vehicles

Model Year

Grouping

Total NPV

Costs per

Vehicle

Discounted

Lifetime Reduction (tons)

Discounted

Per-Vehicle

CostEffectiveness

($/ton of

NOx+NMHC)

NOx NMHC

2004-05 $907

3.189 0.151

$272

2006-08 $792 $237

2009+ $472 $141

30 Year Fleet — — — $174

Table 8-4 contains the total net present value costs, the lifetime emission reductions, and the

resulting cost-effectiveness values for all heavy-duty diesel vehicles. In determining the costeffectiveness for all heavy-duty diesel vehicles, the cost and emission reductions for all heavy-duty

diesel vehicles were determined by weighting the corresponding light, medium, and heavy heavyduty diesel vehicle results by the respective sales estimates for each year.

Table 8-4

Cost-Effectiveness for All Heavy-Duty Diesel Vehiclesa

Model Year

Grouping

Total NPV

Costs per

Vehicle

Discounted

Lifetime Reduction (tons)

Discounted

Per-Vehicle

CostEffectiveness

($/ton of

NOx+NMHC)

NOx NMHC

2004-05 $682

1.365 0.074

$474

2006-08 $591 $410

2009+ $342 $238

30 Year Fleet — — — $296

a

 combined cost-effectivness weighted by distribution of vehicles by class
Regulatory Impact Analysis 

142

II. Cost-Effectiveness of the Otto-cycle Requirements

A. Exhaust Emission Standards

We analyzed the cost-effectiveness of the new exhaust emission standards for three different

categories of heavy-duty Otto-cycle vehicles. The three categories analyzed were incomplete

vehicles, Class 2b complete vehicles, and Class 3 complete vehicles. Tables 8-5 through 8-7 contain

the discounted lifetime per-vehicle cost based on the information in Chapter 5, the discounted

lifetime emission reductions as presented in Chapter 7, and the resulting cost-effectiveness values

for the three categories of heavy-duty Otto-cycle vehicles. Each of the tables also contains the fleet

cost-effectiveness covering the first 30 model years after the new standards take effect (i.e., model

years 2005 through 2034). Table 8-8 contains the cost-effectiveness of the new standards for all

categories of heavy-duty Otto-cycle vehicles combined. A copy of the spreadsheet prepared for the

heavy-duty Otto-cycle vehicle cost-effectiveness analysis has been placed in the public docket for

the notice of new rulemaking.1 The reader is directed to the spreadsheet for a complete version of

the cost-effectiveness calculations.

Table 8-5

Cost-Effectiveness for Incomplete Heavy-Duty Otto-cycle Vehicles

Model

Year

Grouping

Total

NPV

Cost per

Vehicle

Discounted Lifetime

Reduction (tons)

Discounted

Per-Vehicle 

Cost-Effectiveness

 ($/ton of

NOx+NMHC)

NOx NMHC

2005-09 $296

0.45 0.07

$565

2010+ $256 $489

30 Year

Fleet

— — — $511
Chapter 8: Cost-Effectiveness

143

Table 8-6

Cost-Effectiveness for Class 2b Complete Heavy-Duty Otto-cycle Vehicles

Model

Year

Grouping

Total

NPV

Cost per

Vehicle

Discounted Lifetime

Reduction (tons)

Discounted

Per-Vehicle 

Cost-Effectiveness

 ($/ton of

NOx+NMHC)

NOx NMHC

2005-09 $274

0.38 0.05

$635

2010+ $273 $633

30 Year

Fleet

— — — $634

Table 8-7

Cost-Effectiveness for Class 3 Complete Heavy-Duty Otto-cycle Vehicles

Model

Year

Grouping

Total

NPV

Cost per

Vehicle

Discounted Lifetime

Reduction (tons)

Discounted

Per-Vehicle 

Cost-Effectiveness

 ($/ton of

NOx+NMHC)

NOx NMHC

2005-09 $274

0.40 0.06

$596

2010+ $273 $594

30 Year

Fleet

— — — $595
Regulatory Impact Analysis 

144

Table 8-8

Cost-Effectiveness for All Heavy-Duty Otto-cycle Vehicles

Model

Year

Grouping

Total

NPV

Cost per

Vehicle

Discounted Lifetime

Reduction (tons)

Discounted

Per-Vehicle 

Cost-Effectiveness

 ($/ton of

NOx+NMHC)

NOx NMHC

2005-09 $281

0.40 0.06

$612

2010+ $268 $586

30 Year

Fleet

— — — $598

B. Refueling Emission Standards

We also separately analyzed the cost-effectiveness of the new onboard vapor recovery

requirements for complete Class 2b heavy-duty Otto-cycle vehicles. Table 8-9 contains the

discounted lifetime per-vehicle cost based on the information in Chapter 5, the discounted lifetime

emission reductions as presented in Chapter 7, and the resulting cost-effectiveness values for the new

ORVR requirements for complete Class 2b heavy-duty otto-cycle vehicles.

Table 8-9

Discounted, Lifetime Cost-effectiveness of the New ORVR Requirements

for Complete Class 2b Heavy-duty Otto-cycle Vehicles

Model Year

Grouping

Discounted

Lifetime Cost

Discounted Lifetime NMHC

+ NOx Emission Reductions

Discounted Lifetime Costeffectiveness

2005-2009 $5 0.035 tons $141/ton of NMHC

2010+ $2 0.035 tons $56/ton NMHC
Chapter 8: Cost-Effectiveness

145

III. Other Benefits

In addition to the primary benefit of reducing ozone within and transported into urban ozone

nonattainment areas, the NOx reductions from the new engine standards are expected to have other

benefits as well. These other benefits, which are discussed in Chapter 2, include impacts with

respect to agricultural yields, visibility, soiling (due to secondary particulate), and ecosystems (e.g.,

through the reduced effects of acid deposition and eutrophication). These benefits are real, and they

have monetary value. For the 1997 FRM for on-highway HD diesels, an EPA contractor report from

1996 was used to estimate the monetary value of a number of these other benefits.2

 However, EPA

has been reevaluating the techniques used to estimate the value of these benefits since 1996.

Therefore, it is not presented here. 

IV. Cost-Effectiveness Sensitivity Analyses

The following section presents an analysis of the sensitivity of the cost-effectiveness results

for heavy-duty diesel vehicles to different assumptions regarding the impact of the new standards

on fuel economy or other costs. As noted in Chapter 4, EPA is projecting a small increase in

operating costs associated with oil changes and EGR maintenance. However, based on the analysis

discussed in Chapter 3 and 4, as well as the substantial lead time available for R&D, EPA is not

projecting other significant maintenance costs, or losses in fuel economy or engine durability. Even

if such impacts were to occur for a few engines, EPA believes that they could be eliminated with

additional R&D, and would thus be short-term in nature. Nevertheless, as a sensitivity analysis, EPA

estimated the discounted per-vehicle lifetime cost associated with a 1.0 percent fuel economy penalty

calculated over the typical lifetime of each class of heavy-duty diesel vehicles. These costs are

shown in Table 8-11. To calculate the effect on cost-effectiveness of the new standards with the fuel

economy penalty, the fuel economy penalty costs in Table 8-11 were divided by the emission

reductions (as presented in Table 8-4). Table 8-12 contains the resulting discounted per-vehicle costeffectiveness numbers.

Table 8-11

Increase in Discounted Per-Vehicle Lifetime Operating Costs

Associated with a One Percent Fuel Economy Penalty

For Diesel Fuel Cost of One Dollar per Gallon

Light HD Medium HD Heavy HD

$102 $178 $891
Regulatory Impact Analysis 

146

Table 8-12

Effect on Cost-Effectiveness for All Heavy-Duty Diesel Vehicles

For a One Percent Fuel Economy Change

Fuel Price

($/Gal)

Average

NPV Fuel

Cost

Discounted

Lifetime Reduction

from New

Standards (tons)

Increase in Per-Vehicle

Cost-Effectiveness

($/ton) for Each

One Percent Increase in

Fuel Consumption

NOx NMHC

$1.00 $390 1.365 0.074 $271

$1.50 $585 1.365 0.074 $407

EPA performed a similar sensitivity analysis to show the effect of assuming that only 50

percent of the costs for VGT and improved fuel injection are attributable to emission control. In this

sensitivity analysis, EPA included the full costs for VGT and improved fuel injection in the estimates

of per vehicle costs, and recalculated the total cost effectiveness of the program. The results are

shown in Table 8-13. The effect of this assumption can be seen by comparing this table with Table

8-4.

Table 8-13

Cost-Effectiveness for All Heavy-Duty Diesel Vehicles

Assuming Full Costs for VGT and Improved Fuel Injection

Model Year

Grouping

Total

NPV

Costs per

Vehicle

Discounted

Lifetime Reduction

(tons)

Discounted 

Per-Vehicle

CostEffectiveness

With Full Costs

($/ton)

Discounted 

Per-Vehicle

CostEffectiveness

With Partial

Costs

NOx NMHC (From Table 8-4)

2004-05 $896

1.365 0.074

$623 $474

2006-08 $766 $532 $410

2009+ $466 $324 $238

30 Year

 Fleet

— — — $396 $296
Chapter 8: Cost-Effectiveness

147

V. Comparison of Cost-Effectiveness with Other Mobile Source NOx Control

Strategies

In an effort to evaluate the cost-effectiveness of the new standards, EPA has summarized the

cost-effectiveness results for other recent EPA mobile source rulemakings that required reductions

in NOx emissions, the primary focus of the new standards. Both EPA and states have previously

adopted numerous NOx emission control measures, and remaining measures may be more expensive

than those previously employed. As additional control measures are applied, more expensive ones

may be necessary over time. Table 8-14 summarizes the cost-effectiveness results from the Clean

Fuel Fleet Vehicle Program, Phase II of the Reformulated Gasoline Program, Tier 2 and Tier 3

Standards for Nonroad Diesel Engines, and Standards for Locomotives.

The projected long-term cost-effectiveness of the diesel vehicles is $296 per ton of NMHC

and NOx. The projected long-term cost-effectiveness of the Otto-cycle vehicles is $598. The costeffectiveness of these standards in this rule falls within the range of these other programs. The costeffectiveness of these standards compare favorably with the other programs listed in Table 8-14.

Table 8-14

Summary of Cost-Effectiveness Results for Recent EPA Mobile Source Programs

EPA Final Rule

Pollutants Considered

in Calculations

Cost-Effectiveness

($/ton)

Clean Fuel Fleet Vehicle Program

(Heavy-duty)

NOx $1,300-1,500

(1994 dollars)

Reformulated Gasoline—Phase II NOx $5,000

(1990 dollars)

Nonroad Diesel Engines—Tiers 2

and 3

NMHC+NOx $410-600

(1995 dollars)

Locomotives NOx $160

(1997 dollars)
Regulatory Impact Analysis 

148

1. “Cost Effectiveness Analyses of Proposed Heavy-Duty Gasoline Engine and Vehicle

Standards,” EPA memo from Phil Carlson to Docket A-98-32.

2. See Chapter 7, Section 1 of “Final Regulatory Impact Analysis: Control of Emissions of Air

Pollution from Highway Heavy-Duty Engines”, September, 1997. Available in EPA Air Docket

A-95-27, Docket Item # V-B-01.

Chapter 8 References
A-1

APPENDIX A

ANNUALIZED COST EFFECTIVENESS ANALYSIS

This appendix contains tables that show EPA's estimates of 20-year annualized costs and emission

reductions. These data come from the analyses contained in Chapters 4 through 8. The analyses

assume a 7 percent discount rate.
Regulatory Impact Analysis 

A-2

Annual Diesel NOx and NMHC Benefits (Tons) and Costs

With Annualized 20-Year Cost-Effectiveness

(All numbers were rounded after calculation)

NOx NMHC Total Discounted Benefits Total Costs Discounted

Year (tons) (tons) (tons) (tons) (Undiscounted) Costs

2004 97,000 5,000 103,000 103,000 $479,000,000 $479,000,000

2005 266,000 14,000 280,000 262,000 $489,000,000 $457,000,000

2006 417,000 23,000 440,000 384,000 $427,000,000 $373,000,000

2007 555,000 30,000 586,000 478,000 $436,000,000 $355,000,000

2008 681,000 37,000 718,000 548,000 $444,000,000 $338,000,000

2009 795,000 43,000 838,000 597,000 $248,000,000 $177,000,000

2010 900,000 49,000 949,000 632,000 $253,000,000 $169,000,000

2011 999,000 55,000 1,054,000 656,000 $258,000,000 $161,000,000

2012 1,093,000 60,000 1,152,000 670,000 $262,000,000 $153,000,000

2013 1,180,000 64,000 1,244,000 677,000 $267,000,000 $145,000,000

2014 1,260,000 69,000 1,329,000 676,000 $296,000,000 $151,000,000

2015 1,336,000 73,000 1,409,000 669,000 $301,000,000 $143,000,000

2016 1,407,000 76,000 1,483,000 658,000 $306,000,000 $136,000,000

2017 1,474,000 80,000 1,554,000 645,000 $311,000,000 $129,000,000

2018 1,537,000 84,000 1,621,000 629,000 $316,000,000 $122,000,000

2019 1,597,000 87,000 1,684,000 610,000 $320,000,000 $116,000,000

2020 1,654,000 90,000 1,744,000 591,000 $325,000,000 $110,000,000

2021 1,709,000 93,000 1,802,000 570,000 $330,000,000 $104,000,000

2022 1,762,000 96,000 1,858,000 550,000 $335,000,000 $99,000,000

2023 1,813,000 99,000 1,912,000 529,000 $339,000,000 $94,000,000

20-Year Total = 23,760,000 11,134,000 $6,741,000,000 $4,011,000,000

20-Year Annualized NPV = 1,051,000 tons $379,000,000

 20-Year Cost-Effectiveness

Discounted 20-Year $/ton (NOx+NMHC) = $360

Undiscounted 20-Year $/ton (NOx+NMHC) = $283
A-3

Annual Otto-Cycle NOx and NMHC Benefits (Tons) and Costs

With Annualized 20-Year Cost-Effectiveness

(All numbers were rounded after calculation)

NOx NMHC Total Discounted Benefits Total Costs Discounted

Year (tons) (tons) (tons) (tons) (Undiscounted) Costs

2005 13,000 3,000 16,000 16,000 $110,000,000 $110,000,000

2006 39,000 7,000 46,000 43,000 $117,000,000 $109,000,000

2007 63,000 11,000 74,000 65,000 $124,000,000 $109,000,000

2008 86,000 15,000 101,000 82,000 $126,000,000 $103,000,000

2009 107,000 19,000 126,000 96,000 $129,000,000 $98,000,000

2010 128,000 23,000 151,000 108,000 $124,000,000 $89,000,000

2011 146,000 26,000 172,000 115,000 $126,000,000 $84,000,000

2012 165,000 30,000 195,000 121,000 $128,000,000 $80,000,000

2013 181,000 33,000 214,000 125,000 $131,000,000 $76,000,000

2014 197,000 36,000 233,000 127,000 $133,000,000 $72,000,000

2015 213,000 39,000 252,000 128,000 $135,000,000 $69,000,000

2016 224,000 42,000 266,000 126,000 $137,000,000 $65,000,000

2017 235,000 44,000 279,000 124,000 $139,000,000 $62,000,000

2018 248,000 47,000 295,000 122,000 $141,000,000 $59,000,000

2019 263,000 50,000 313,000 121,000 $144,000,000 $56,000,000

2020 278,000 52,000 330,000 120,000 $146,000,000 $53,000,000

2021 288,000 54,000 342,000 116,000 $148,000,000 $50,000,000

2022 298,000 56,000 354,000 112,000 $150,000,000 $47,000,000

2023 308,000 58,000 366,000 108,000 $152,000,000 $45,000,000

2024 318,000 60,000 378,000 105,000 $154,000,000 $43,000,000

20-Year Total = 4,503,000 2,080,000 $2,694,000,000 $1,478,000,000

20-Year Annualized NPV = 196,000 tons $139,000,000

 20-Year Cost-Effectiveness

Discounted 20-Year $/ton (NOx+NMHC) = $710

Undiscounted 20-Year $/ton (NOx+NMHC) = $598