Use of Data from “Development of 

Emission Rates for the MOVES Model,” 

Sierra Research, March 3, 2010 
EPA-420-R-12-022 

August 2012

Assessment and Standards Division 

Office of Transportation and Air Quality 

U.S. Environmental Protection Agency

 Use of Data from “Development of 

Emission Rates for the MOVES Model,” 

Sierra Research, March 3, 2010 

NOTICE 

This technical report does not necessarily represent final EPA decisions or 

positions. It is intended to present technical analysis of issues using data 

that are currently available. The purpose in the release of such reports is to 

facilitate the exchange of technical information and to inform the public of 

technical developments.
a-1 

Use of data from “Development of Emission Rates for the MOVES Model,” 

Sierra Research, March 3, 2010

U.S. EPA, August 2012

Overview

The report Development of Emission Rates for the MOVES Model, Sierra Research, 

March 3, 2010, was developed to document inputs provided to the EPA Motor Vehicle 

Emissions Simulator (MOVES). This cover note provides additional detail on how this data was 

incorporated into official versions of MOVES, particularly MOVES2010, MOVES2010a and 

MOVES2010b, as released in 2009, 2010 and 2012. 

The Sierra Research report covers a variety of topics, namely:

• Sulfur dioxide (SO2) and SO4 fractions for all vehicles 

• Ammonia (NH3) emission rates for all vehicles

• NO2 and NO fractions of NOx for all vehicles 

• Motorcycle emission rates for many pollutants

• Motorcycle fleet and activity inputs

• Emission factors/algorithms for a large number of mobile source air toxics. 

This note describes how each set of data was incorporated into MOVES.

Sulfur dioxide (SO2) and Sulfate (SO4) fractions 

Data from the Sierra Research work on sulfur was used to populate the 

sulfateEmissionRate table in MOVES for all vehicles and fuels. The Sierra inputs were used in 

MOVES2010, MOVES2010a and MOVES2010b. 

Ammonia (NH3) emission rates for all vehicles

Data from the Sierra Research work on ammonia was used to populate the 

emisisonRateByAge table in MOVEs. The same inputs were used in MOVES2010, 

MOVES2010a and MOVES2010b. The report does not discuss crankcase emissions. These are 

set to zero in MOVES since ammonia emissions are formed in the catalyst and thus do not exist 

in the crankcase.

NO2 and NO fractions of NOx for all vehicles

Data from the Sierra Research work on nitrogen oxide and nitrogen dioxide ratios was 

used to populate the nono2ratio table to allocate NOx emissions between these species.a

 For 

 

a

 Note, the MOVES NOx, NO and NO2 results are all reported in terms of NO2. In 

MOVES2010, the ratio table was mistakenly populated with modelyeargroupid = 0 for all 
a-2 

MOVES2010b, nitrous acid (HONO) was added to the model. This required a change in the 

NO2 and NO fractions. The HONO fraction was set to 0.008 for all records.

1

 The HONO 

fraction was subtracted from the MOVES2010a NO2 fraction to create a new NO2 fraction such 

that the fractions still sum to one across the three pollutants. 

Motorcycle emission rates for many pollutants

The Sierra Research motorcycle emission rates were used to populate the exhaust and 

evaporative emission factor tables in MOVES2010, MOVES2010a and MOVES2010b. 

The Sierra Research data was used to populate the EmissionRateByAge and the 

CrankcaseEmission Ratio tables for motorcycle exhaust emissions of total hydrocarbons (THC), 

carbon monoxide (CO), oxides of nitrogen (NOx), elemental carbon (EC) and organic carbon 

(OC). While motorcycle exhaust emissions are in the EmissionRateByAge table, they are 

constant across all ages. For evaporative emissions, the Sierra data was used to populate the 

EmissionRateByAge and the CumTVVCoeff table. The vapor venting rates do vary with age for 

some modelyear groups. 

The Sierra report did not address emissions of methane (CH4), nitrous oxide (N2O), 

tirewear, brakewear or energy consumption rates for motorcycles. These rates were populated 

in MOVES based on other data sources. 

Motorcycle fleet and activity inputs

Vehicle Population and Growth

Motorcycle default population data is stored in the MOVES sourcetypeYear table. This 

table also includes sales growth rates which are used to grow the population from the base year 

to the analysis year, and an unused field for “migration rates.” In MOVES2010, MOVES2010a 

and MOVES2010b, the base year motorcycle populations (1990 and 1999) come from FHWA 

registration data.

2

 In MOVES2010a and MOVES2010b, the MOVES default database 

incorporates the salesgrowth factors indicated in the Sierra Report, including their forecasts for 

future motorcycle sales growth rates. b 

Sierra also provided motorcycle migration rates. However, the migrationrate field in 

MOVES is not used. The Sierra-provided rate was stored in the MOVES2010 default database; 

however, for clarity, it was replaced with values of “1”in the MOVES2010a and MOVES2010b 

databases. 

 

records. This created erroneous NO and NO2 results in the MOVES2010 output. As 

documented in the MOVES2010 Errata/Information Sheet, the MOVES2010 error was corrected 

in MOVES2010a and in the intermediate 20100512 MOVES database. 

b In MOVES2010, the sales growth factors were inadvertently unchanged from Draft MOVES2009, where 

they had been set equal to passenger car data.
a-3 

Survival Rates 

In MOVES, the survival fraction is multiplied by the population of vehicles of a given 

age to calculate the population at the next age, thus it indicates the fraction of vehicles that 

remain from one year to the next. However, the motorcycle survival rate documented in the 

Sierra report and provided to EPA was the fraction of the initial population that remains at the 

end of each year. 

In MOVES2010, the Sierra survival values were input directly. This overestimated 

scrappage and led to smaller motorcycle populations than expected. For MOVES2010a (and 

2010b), we revised these rates. We calculated the revised scrappage rate in the format needed 

for MOVES using following equation: New scrappage rate (age i) = Original scrappage rate 

(age i)/Original scrappage rate (age i-1). Because the initial value was developed from a fitted 

curve, the revised value was a constant of 0.940 for all ages 2 and greater. 

Relative Mileage Accumulation Rates

In MOVES, the relative mileage accumulation rate is a normalized measure of the 

average number of miles driven by vehicles of each age. The relativeMARS for motorcycles 

provided by Sierra were used in MOVES2010, MOVES2010a and MOVES2010b. 

Age Distribution

Sierra calculated a motorcycle age distribution based on data for calendar year 2008. For 

MOVES2010, MOVES2010a and MOVES2010b, this was used as the 1999 base-year age 

distribution in the SourceTypeAgeDistribution table. 

Base Year Vehicle Miles Travelled (VMT) and VMT Growth

MOVES2010, MOVES2010a and MOVES2010b used the Sierra-calculated base year

VMT and VMT growth factors for motorcycles for years through 2008. The 2009-and-later 

VMT growth rates were based on AEO2006 projections of VMT growth for cars.

Daily Trip Patterns

MOVES2010, MOVES2010a and MOVES2010b use the Sierra-provided motorcycle 

information to populate the tables SampleVehicleDay and SampleVehicleTrip. Note the 

spreadsheet MOVES_MC_SampleVehicleDay.csv lacks seven vehicleids that are in MOVES 

and are listed in MOVES_MC_SampleVehicleTrip.csv. 

Temporal Distribution of Activity

The text of the Sierra report discusses differences between weekend and weekday activity 

for motorcycles, as well as seasonal differences. This information was used to update the daily 

trip pattern information (SampleVehicleTrip and SampleVehicleDay), but it was not used to 

update the values in MonthVMTFraction or DayVMTFraction. The MOVES VMT fractions by 

month and daytype are the same for all sourcetypes3

. 

Driving Cycles 

As recommended in the Sierra report, and in absence of better data, MOVES uses driving 

cycles for passenger cars to represent driving cycles for motorcycles.
a-4 

Emission factors and algorithms for mobile source toxics

MOVES2010 and MOVES2010a estimate emissions for a short list of mobile source air 

toxics. MOVES2010b models many more “hazardous air pollutants” (HAPs). Most of these 

emission rates were developed by EPA staff from available data. 4

 The Sierra report was used 

for the following emission rates for all vehicle types: 

1) Exhaust gaseous HAPs for pre-Tier 2 vehicles running on gasoline (E0) and gasohol 

(E10). 

2) Gas and particle phase polycyclic aromatic hydrocarbon (PAH) allocation factors (but 

not actual emission rates).

3) Toxics ratios for pre-2007 diesels for 2,2,4-trimethylpentane, hexane, 

propionaldehyde, and toluene (but not other gaseous HAPs). 

 

1 Kurtenbach, R., Becker, K. H., Gomes, J.A.G., Kleffmann, J., Lorzer, J. C., Spittler, M., Wiesen, P., 

Ackermann, R., Geyer, A., Platt, U., 2001. Investigations of emissions and heterogeneous formation of HONO in a 

road traffic tunnel. Atmospheric Environment 35, 3385–3394.

2

U.S. EPA, 2010, “MOVES2010 Highway Vehicle Population and Activity Data,” EPA-420-R-10-026, 

November 2010, http://www.epa.gov/otaq/models/moves/420r10026.pdf

3 EPA-420-R-10-026

4 U.S. EPA, 2012, “MOVES 2010b: Additional Toxics Added to MOVES,” EPA-420-B-12-029a, May 

2012, http://www.epa.gov/otaq/models/moves/documents/420b12029a.pdf
Development of Emission Rates 

for the MOVES Model

prepared for:

U.S. Environmental Protection Agency

March 3, 2010

prepared by:

Sierra Research, Inc.

1801 J Street

Sacramento, California 95811

(916) 444-6666
DEVELOPMENT OF EMISSION RATES FOR THE MOVES 

MODEL

prepared for: 

U.S. Environmental Protection Agency 

March 3, 2010 

Principal authors: 

Thomas R. Carlson 

Thomas C. Austin 

Dennis McClement 

Sierra Research, Inc. 

1801 J Street 

Sacramento, CA 95811 

(916) 444-6666 
-iDEVELOPMENT OF EMISSION RATES 

FOR THE MOVES MODEL

Table of Contents

Page

1. INTRODUCTION .......................................................................................................1

1.1 Background ..........................................................................................................1

1.2 Project Summary ..................................................................................................2

1.3 Organization of the Report...................................................................................4

2. NITROGEN- AND SULFUR-BASED EMISSION RATES ......................................5

2.1 Ammonia Emission Rates ....................................................................................5

2.2 Sulfur-Based Emission Rates .............................................................................14

2.3 Nitrogen Oxide and Nitrogen Dioxide Ratios ...................................................17

3. HIGHWAY MOTORCYCLE EMISSION RATES AND ACTIVITY FACTORS .21

3.1 Highway Motorcycle Characteristics .................................................................21

3.2 Uncontrolled Emissions Characteristics ............................................................24

3.3 Controlled Emissions .........................................................................................34

3.4 Inspection and Maintenance Effect ....................................................................47

3.5 Motorcycle Populations and Activity ................................................................49

3.6 Incorporation into MOVES Tables ....................................................................60

4. AIR TOXIC SPECIATION RATIOS ........................................................................72

4.1 MOVES Speciation Ratios ................................................................................72

4.2 Light-Duty Gasoline-Fueled Ratios ...................................................................75

4.3 Heavy-Duty Diesel-Fueled Ratios .....................................................................76

5. REFERENCES ..........................................................................................................82
-iiList of Figures

Figure Page

Figure 2-1 Ammonia Emissions (g/hr) vs. Operating Mode by Model Year Group ........9

Figure 2-2 Exhaust SO4 vs. Fuel S – 1981 and Newer ....................................................15

Figure 2-3 Exhaust SO4 vs. Fuel S – 1980 and Older ......................................................16

Figure 3-1 Exhaust Hydrocarbons vs. Odometer Pre-1978 4-Stroke Models ................26

Figure 3-2 Exhaust Carbon Monoxide vs. Odometer Pre-1978 4-Stroke Models ..........26

Figure 3-3 Exhaust Oxides of Nitrogen vs. Odometer Pre-1978 4-Stroke Models ........27

Figure 3-4 Exhaust Hydrocarbons vs. Odometer Pre-1978 2-Stroke Models ................28

Figure 3-5 Exhaust Carbon Monoxide vs. Odometer Pre-1978 2-Stroke Models ..........28

Figure 3-6 Exhaust Oxides of Nitrogen vs. Odometer Pre-1978 2-Stroke Models ........29

Figure 3-7 Exhaust Hydrocarbons vs. Odometer 1978–1985 4-Stroke Models .............36

Figure 3-8 Exhaust Carbon Monoxide vs. Odometer 1978–1985 4-Stroke Models ......37

Figure 3-9 Exhaust Oxides of Nitrogen vs. Odometer 1978–1985 4-Stroke Models .....37

Figure 3-10 Exhaust Hydrocarbons vs. Odometer 1986–1999 Models ..........................38

Figure 3-11 Exhaust Carbon Monoxide vs. Odometer 1986–1999 Models ...................39

Figure 3-12 Exhaust Oxides of Nitrogen vs. Odometer 1986–1999 Models .................39

Figure 3-13 Idle HC Versus Motorcycle Age Arizona I/M Data – July to 

September 1997 .................................................................................................................40

Figure 3-14 Idle CO Versus Motorcycle Age Arizona I/M Data – July to 

September 1997 .................................................................................................................41

Figure 3-15 Motorcycle Survival Fraction vs. Age Based on Analysis of 

Registration and Retail Sales Data .....................................................................................52

Figure 3-16 Average Annual Lifetime Mileage vs. Age .................................................53

Figure 3-17 World Motorcycle Test Driving Cycle SAFD (%) ......................................58

Figure 3-18 California Urban & Rural Weighted (CalWtd) Driving Cycle SAFD 

(%)......................................................................................................................................59
-iiiList of Tables

Table Page

Table 2-1 CE-CERT Ammonia Test Program Vehicle Counts .........................................6

Table 2-2 VSP Scaling Step 1 ............................................................................................8

Table 2-3 VSP Scaling MY 1996-2001 .............................................................................8

Table 2-4 VSP Scaling MY 1992-1995 .............................................................................8

Table 2-5 VSP Scaling MY 1981-1991 .............................................................................9

Table 2-6 Fleet Average Ammonia Emissions (mg/mi) ..................................................11

Table 2-7 Extended Fleet Average Ammonia Emissions (mg/mi) ..................................12

Table 2-8 Ammonia Emissions for Diesel and Heavy Duty Vehicles (mg/mi) ..............13

Table 2-9 Gasoline NONO2 Ratios .................................................................................18

Table 2-10 Diesel Without DPF trap NO/NO2 Ratios .....................................................19

Table 2-11 Diesel With DPF trap NONO2 Ratios ...........................................................20

Table 2-12 Diesel With DPF trap and Extended Idle NONO2 Ratios ............................20

Table 3-1 Uncontrolled Highway Motorcycle Evaporative Emissions ...........................31

Table 3-2 Uncontrolled Highway Motorcycle Emissions (g/mi) ....................................33

Table 3-3 Motorcycle Exhaust Emission Standards (grams per kilometer, g/km) ..........35

Table 3-4 Controlled Highway Motorcycle Evaporative Emissions ...............................44

Table 3-5 Controlled vs. Uncontrolled Emissions (g/mi) ................................................47

Table 3-6 On-Highway Motorcycle Population and Survival Estimated from 

Registration and Retail Sales Data .....................................................................................51

Table 3-7 Motorcycle Annual VMT vs. Age (years) .......................................................55

Table 3-8 Portion of Annual Operation by Season ..........................................................56

Table 3-9 Normalized Motorcycle Running Exhaust Emission Rates (g/hr per 

gram Hot FTP) by Operating Mode Bin ...........................................................................64

Table 3-10 MOVES Evaporative Processes by Pollutant/Process and OpMode ............67
-ivTable 4-1 List of New MOVES HAPs and Numerical Codes .........................................73

Table 4-2 Tier 1 and Earlier Light-Duty Gasoline Vehicle Speciation Ratios ................75

Table 4-3 Tier 2 Light-Duty Gasoline Vehicle Speciation Ratios ...................................76

Table 4-4 Study Data Represented in CRC-75 Speciation Database ..............................77

Table 4-5 Mult-Phase PAH Allocation Factors Used ......................................................80

Table 4-6 Heavy-Duty Diesel Speciation Ratios and Basic Statistics .............................81
-1- 

1. INTRODUCTION 

This introduction provides a review of the background behind the effort, a brief summary 

of the key issues and findings, and the organization of the remainder of the report. 

1.1 Background

The successor to MOBILE6, MOtor Vehicle Emissions Simulator (MOVES), was 

released in April 2009 in draft form without certain emission rates included. Emission 

rates that need to be added include certain nitrogen compounds and toxic air pollutants 

from cars and trucks and all pollutants and activity rates from highway motorcycles. For 

some of the missing emissions rates, EPA has data that needed to be analyzed and 

processed into a form which is appropriate for MOVES. In other areas, additional data 

needed to be identified. The purpose of this effort was to identify, analyze, and process 

available data to create estimated emission rates for the above-described pollutants 

currently missing from MOVES. 

Highest priority was assigned to the development of sulfur dioxide (SO2), ammonia 

(NH3), nitrogen dioxide (NO2), and nitrogen oxide (NO) emissions (or NOx fractions) for 

all vehicle categories. Currently, the NMIM and/or MOBILE6.2 / PART5 models 

contain estimates for NO, NO2 and SO2 pollutants and processes such as running and 

start, and in some cases, crank-case and extended idle. Unfortunately, most of these 

estimates were out of date (some date back to the 1970s), and needed to be updated or at 

least reviewed. 

Second priority was assigned to the development of motorcycle emission and fleet 

activity rates. Rather than simply carrying forward motorcycle emissions and activity 

data from MOBILE6 (that were originally developed in MOBILE5), EPA left 

―placeholders‖ in the Draft MOVES2009 model and underlying database structure until 

more up-to-date emissions and activity data could be analyzed and incorporated into 

MOVES. 

Lower priority was assigned to the development of revised emission factors for an 

expanded set of mobile source air toxics compounds. Draft MOVES2009 relied on 

algorithms carried over from MOBILE6.2 and implemented these air toxic emission 

factors as speciation ratios relative to VOC. These algorithms were derived from U. S. 

EPA’s Complex Model for Reformulated Gasoline, developed in the early 1990s for the 
-2- 

Federal Reformulated Gasoline Rule. Also, Draft MOVES2009 included emission rates 

for only the following seven air toxic pollutants: 

Benzene, 

1,3-Butadiene, 

Formaldehyde, 

Acetaldehyde, 

Acrolein, 

Naphthalene and 

Ethanol. 

This included the addition of toxic speciation ratios for vehicles running on E-85 fuel. 

None of the long list of other toxics included in EPA’s National Mobile Inventory Model 

(NMIM)—designated as Additional Hazardous Air Pollutants (HAPS)*throughout the 

remainder of this report—were inserted into Draft MOVES2009. Thus, assembly of data 

and development of toxic speciation ratios for these Additional HAPS was the focus of 

this element of the study. 

1.2 Project Summary

Under Contract No. EP-C-05-037, Work Assignments 3-03 and 4-03, Sierra Research, 

Inc. (Sierra) was contracted to assist EPA in the assembly and development of these 

emission rates and activity data that had not been included in Draft MOVES2009 but 

would be implemented in a future release of the model. 

The effort was divided into three analytical tasks as follows: 

1. Nitrogenous and Sulfur Pollutant Rates; 

2. Highway Motorcycle Emission and Activity Rates; and 

3. Additional Air Toxic Speciation Ratios. 

Data Sources EPA provided Sierra with a list of existing studies and associated 

databases that the agency had assembled to support the development of MOVES 

emission rates and air toxic speciation ratios in each of these three task areas. In addition 

to these sources, Sierra performed additional literature searches. Key additional sources 

(which are cited later in the report sections where they were used) included the following: 

Unpublished emission test data (FTP, idle and 50 mph cruise measurements) 

obtained from the California Air Resources Board (CARB) for a small sample of 

 

*

 Table A-l from the Work Assignment contains the complete list of Additional HAPS to be considered 

under this task. (The exceptions on the list that are not considered Additional HAPS for the purposes of 

this effort are HC, CO, NOx, SO2, CO2, SOA, PM10, PM2.5, NH3, acetaldehyde, acrolein, benzene, 

formaldehyde, 1,3 butadiene, and MTBE.) 
-3- 

newer model heavy-duty Diesel vehicles with selective catalyst reduction (SCR) 

and Diesel particulate filter (DPF) after-treatment systems; 

Modal (second-by-second) motorcycle exhaust emissions test data from a 2000 

testing program sponsored by CARB; 

Nationwide on-road motorcycle registrations for calendar year 2008 compiled by 

R.L. Polk and obtained through the Motorcycle Industry Council (MIC); and 

Current highway motorcycle activity and usage data obtained from a recently 

completed motorcycle owner survey. 

Key Issues/Findings – During the course of this effort, several key issues arose in 

evaluating data sources and assembling the required MOVES emission rates. These key 

issues and findings are summarized below and described in greater detail in the body of 

the report. 

Factors Affecting Ammonia Emission Rates – Prior studies and test measurements 

show a clear inverse relationship between ammonia emission rates and NOx 

emission controls. Catalytic NOx reduction implemented on vehicles beginning 

in the early 1980s led to increases in ammonia emission rates up until phase in of 

NLEV and Tier 2 emission standards. 

Highway Motorcycle Tampering Effects – In-use emission rates for highway 

motorcycles are significantly affected by the assumed or estimated level of 

tampering. Survey and test data indicate that OEM catalyst removal and use of 

aftermarket exhaust systems are most significant in affecting in-use motorcycle 

emissions. These types of tampering often occur soon after a motorcycle is sold. 

Thus, all of the tampering/deterioration effects for motorcycles were assumed to 

occur within the newest vehicle age group (0-3 years) defined in MOVES. 

Limited Motorcycle Evaporative Data – Although exhaust emission data were 

available for roughly 170 individual motorcycle tests, evaporative emission 

measurements were more limited. One-hour SHED measurements were available 

for about 35 vehicles and only a handful of real-time 24-hour evaporative tests 

were available. This necessitated conversion of the one-hour SHED data to an 

equivalent 24-hour estimate in order to translate the test results into the new 

evaporative emission processes defined and employed in MOVES. 

Processing Required for Air Toxic Speciation Data – Speciation ratios for Dieselfueled vehicles were developed from a CRC database for which a number of data 

processing and validation steps were necessary (e.g., matching emission tests for 

both the toxic compound and the ―base‖ criteria pollutant upon which its ratio was 

based). 
-4- 

Hole-Filling Required to Generate MOVES Rates – Given the highly 

disaggregated design of most of the MOVES emission rate tables, a fairly 

extensive amount of extrapolation of ―hole-filling‖ was necessary to populate the 

data tables, by model year, age group, and operating mode. The report clearly 

identifies the extent to which hole-filling was performed and the assumptions that 

were made in doing so. 

Difficulty in Quantifying Uncertainty – In the MOVES emission rate tables 

developed under this effort, Sierra provided estimates of both mean emission rates 

as well as calculated uncertainty, expressed as the coefficient of variation (COV). 

However, sample sizes were often small and variance within the available data 

large so that COVs entered into the MOVES tables were often capped at an upper 

limit of 0.5 per EPA’s direction. 

1.3 Organization of the Report

Following this introductory section, the remainder of the report is organized in a manner 

consistent with the three separate analytical tasks in the effort (Tasks 2 through 4). 

Section 2 describes the sources considered and assembly, validation, and processing of 

various emission test data to develop MOVES emission rate tables for nitrogen- and 

sulfur-based pollutants not already represented in the model. Separate sub-sections in 

Section 2 present methods for development of ammonia emission rates, sulfate and sulfur 

dioxide emission rates, and nitrogen oxide/nitrogen dioxide emission rate ratios. 

Section 3 describes the data sources and discusses the step-by-step methodologies used to 

develop MOVES exhaust and evaporative emission rates (for all criteria pollutants) and 

fleet activity data for motorcycles. It also includes a separate discussion of how these 

emission and activity data were tabulated and integrated into the specific table structures 

employed in the MOVES database. 

Section 4 discusses the data sources, data assembly, and validation methods used to 

develop speciation ratios for an additional list of mobile source air toxic compounds 

identified by EPA for subsequent implementation in MOVES. 

Section 5 contains a list of references cited in the body of the report. 

###
-5- 

2. NITROGEN- AND SULFUR-BASED EMISSION RATES 

In Draft MOVES2009, priority was placed on developing complete sets of underlying 

emissions rates for those criteria pollutants and precursors that have significant emissions 

from on-road vehicles: hydrocarbons (HC), carbon monoxide (CO), oxides of nitrogen 

(NOx) and particulate matter (PM). The first analytical task under this effort consisted of 

developing emission rates for three other nitrogenous and sulfur-based pollutants that had 

not yet been built into MOVES: 

1. Ammonia (NH3);

2. Sulfur dioxide and sulfates; and 

3. Nitric oxide (NO) and nitrogen dioxide (NO2) ratios. 

The data sources and methods used to develop these new emission rates and structure 

them into MOVES-ready database tables are presented in the following three subsections. 

2.1 Ammonia Emission Rates

Early testing revealed trace ammonia emissions from both gasoline and Diesel-powered 

Internal Combustion Engines (ICE). Studies in the 1970s and 1980s concluded that the 

levels of ammonia emissions produced by then-current mobile sources were not a cause 

for concern, or reason to trigger limiting regulations, but that levels should be monitored 

in the future. 

The early 1980s introduction of vehicles equipped with three-way catalytic converters 

quickly raised concerns regarding ammonia emissions. Many studies revealed increased 

levels of ammonia from early examples of such vehicles. Detailed studies revealed an 

inverse relationship with NOx control: catalytic reduction of NOx in the exhaust stream 

resulted in elevated NH3 levels.

As emissions standards continued to drop and vehicle emission control technology 

continued to improve, ammonia emissions fell to nearly the levels observed prior to the 

introduction of the three-way catalyst. In addition, as the early 1980s vehicles aged, NOx 

emissions rose with catalyst deterioration, and ammonia levels dropped proportionately. 
-6- 

The results of several programs were combined to calculate emission rates for the range 

of VSP bins used in MOVES. 

The most important source of continuous ammonia emissions data was a program 

performed by the Center for Environmental Research and Technology (CE-CERT) of the 

University of California, under a Cooperative Agreement with the US EPA (CX827692-

01-0). In the program, 39 modern production vehicles received standard Federal Test 

Procedure (FTP) emission tests that included second-by-second ammonia measurements. 

The test fleet was designed to represent the in-use fleet in 2001, including such factors as 

manufacturer, age, engine/emission control technology, and car/truck split. Five of the 

newest vehicles received additional tests using cycles at lower and higher speeds than the 

FTP. Results from 35 of the vehicles were retrieved from EPA’s Mobile Source 

Observation Database (MSOD) with enough information to allow transformation of the 

second-by-second ammonia emissions results into the VSP bins used in the MOVES 

emissionsRateByAge table. In MOVES, results are stratified by model year and age at 

time of test. 

Table 2-1 summarizes the distribution of the CE-CERT test fleet with respect to model 

year and age. The MOVES table schema stratifies results into seven age groups, as 

shown below. 

While it is possible to enter individual model year groups into MOVES, the results of this 

limited program were pooled into model year groups roughly corresponding to the 

stringency of the emission standards and resulting engine/emission control technology 

included in the years represented. This averaging was performed to prevent single 

vehicles from biasing the emission factors for small subgroups. The model year groups 

Table 2-1 

CE-CERT Ammonia Test Program Vehicle Counts

MY 

Group

Age Group

Num

Vehs

0-34-56-78-910-1415-19>=20

00-01 3

98-99 10 20

96-97 7

94-95 2

10 91-93 8

87-90 4

5

81-87 1

<81 0
-7- 

selected were 1981-1990, 1991-1995, and 1996-2001. There were five vehicles in the 

oldest group, 10 vehicles in the middle group, and 20 vehicles in the newest group. 

In MOVES, 23 Operating Mode Bins are defined for running emissions processes. Bins 

0 and 1 apply to braking and idle operation, 11-16 to operation at speeds between 0-25 

mph, 21-30 to speeds between 25-50 mph, and bins 33-40 to speeds above 50 mph. The 

bins are defined in terms of vehicle specific power (VSP). VSP was calculated using the 

procedures described EPA’s Draft MOVES2009 documentation.1* 

Essentially, Track Road Load Horsepower (TRLHP) for each vehicle was allocated to A, 

B, and C coefficients using default fractions of 0.35, 0.10, and 0.55, respectively. Actual 

speed and dynamometer inertia weight were then used to compute acceleration and VSP 

for each second of operation. A specific bin number, as defined in the EPA report, was 

assigned to each individual second. The grams of ammonia measured during individual 

seconds were then summed by VSP bin. The overall average ammonia emissions for 

each bin within the three model year groups was calculated by summing the observed 

emissions and dividing by the number of seconds included in the sum. Results were then 

converted from milligrams per second to the grams per hour scale used in MOVES. 

The driving schedule used for the FTP test does not include the speed and accelerations 

required to enter higher VSP bins. Additional testing was performed, however, on five of 

the vehicles in the 1996-2001 model year group. The US06 test, a component of the 

Supplemental Federal Test Procedure (SFTP), includes operation at high speeds and rates 

of acceleration. Results from these US06 tests were used to fill the missing bins (referred 

to as ―hole-filling‖ in other EPA documentation). 

The US06 results of the five vehicle fleet were scaled to conform to the average FTP 

results in the 20-vehicle fleet in two steps. First, the US06 results were scaled to match 

to the corresponding FTP results in the five vehicle subset. Table 2-2 displays the five 

vehicle FTP and US06 averages for Bins 25-40. An offset was noted between the tests. 

As only a few seconds of data were collected in bin 28 of the FTP, bin 27 was selected as 

the ―pivot point‖ to fill Bins 28, 29, and 30. The ratio between the FTP results for bin 27 

and the US06 results for Bin 27 was calculated (12.139/4.487 = 2.705). The US06 results 

for Bins 28, 29, and 30 were calculated by dividing the original US06 results by 2.705 

(12.628/2.705=4.668). Similarly, bin 35 was selected to scale the US06 results for Bins 

37, 38, 39, and 40. The results for the five-car fleet were then merged as shown, using 

the original FTP results for Bins 1-27 and 33-35 and the scaled US06 results for Bins 28-

30 and 37-40. 

Next the merged results for the five-car fleet were scaled to the averages observed in the 

twenty-car fleet. The same pivot points were selected (Bins 27 and 35), and the merged 

five-car results were scaled to the 20-car results. The initial and final transformed results 

are shown in Table 2-3. The final merged results were used as the average ammonia 

emission factors for vehicles manufactured between 1996 and 2001 at between 0 and 5 

years of age. 

 

*

 Numeric superscripts denote references provided in Section 5. 
-8- 

Table 2-2 

VSP Scaling Step 1

VSP Bin 25 27 28 29 30 33 35 37 38 39 40

FTP 2.126 4.487 2.627 1.684 2.081

US06 1.680 12.139 12.628 13.840 29.497 8.259 10.485 20.700 28.760 24.776 36.148

Scaling 2.705 4.668 5.116 10.903 5.039 4.108 5.708 4.917 7.174

Merged 2.126 4.487 4.668 5.116 10.903 1.684 2.081 4.108 5.708 4.917 7.174

Table 2-3 

VSP Scaling MY 1996-2001

VSP Bin 25 27 28 29 30 33 35 37 38 39 40

Merged 2.126 4.487 4.668 5.116 10.903 1.684 2.081 4.108 5.708 4.917 7.174

FTP 20 1.782 2.668 1.673 1.941

Scaling 1.682 2.775 3.042 6.482 1.072 3.831 5.323 4.586 6.690

20 Merge 1.782 2.668 2.775 3.042 6.482 1.673 1.941 3.831 5.323 4.586 6.690

The next group of vehicles included model years 1992 through 1995. Only FTP results 

were available for this group. Lacking any other source of data, the US06 ammonia 

results obtained with the first group were scaled to the FTP results obtained with the 

older cars using the same approach as described above. Results are shown in Table 2-4. 

The final group of vehicles in this program included model years 1981 through 1991. 

The same approach was again applied, with results displayed in Table 2-5. 

Table 2-4 

VSP Scaling MY 1992-1995

VSP Bin 25 27 28 29 30 33 35 37 38 39 40

Merged 2.126 4.487 4.668 5.116 10.903 1.684 2.081 4.108 5.708 4.917 7.174

FTP mid 2.929 3.248 2.690 3.236 3.527

Scaling 1.381 3.379 3.704 7.893 0.590 6.964 9.675 8.335 12.161

MidMerge 2.929 3.248 3.379 3.704 7.893 3.236 3.527 6.964 9.675 8.335 12.161
-9- 

Table 2-5 

VSP Scaling MY 1981-1991

VSP Bin 25 27 28 29 30 33 35 37 38 39 40

Merged 2.126 4.487 4.668 5.116 10.903 1.684 2.081 4.108 5.708 4.917 7.174

FTP old 1.338 0.823 0.309 2.028 1.524

Scaling 5.450 0.856 0.939 2.000 1.365 3.009 4.181 3.602 5.255

OldMerge 1.338 0.823 0.856 0.939 2.000 2.028 1.524 3.009 4.181 3.602 5.255

The results from this scaling are summarized in Figure 2-1. The pattern observed is 

similar to that obtained by EPA for other emissions, with factors within a speed group 

(<25 mph, 25-50 mph, and >50mph) rising exponentially in the highest VSP bins. The 

1992-1995 MY group generally had higher ammonia emissions, while the 1981-1991 

group in general had the lowest. Bin 39 for all three groups had an unusual drop, which 

may be related to the US06 cycle that was used to generate these results. 

Figure 2-1 

Ammonia Emissions (g/hr) vs. Operating Mode by 

Model Year Group 

0

5

10

15

0 10 20 30 40

VSP Bin (MOVES Operating Mode)

Ammonia (grams/hour)

96-01

92-95

81-91
-10- 

Similar EPA analyses generally included thousands of tests. The patterns observed 

between subgroups were generally much smoother; reflecting the effect of the relatively 

small sample size used for this analysis. 

Other test programs were used to estimate emission factors for earlier (1980 and older) 

and more modern (2002 and later) vehicles. 

CRC program E-602revealed significant reductions in average fleet emissions for current 

technology vehicles (LEV and better). The CRC program also tested artificially aged 

catalysts equivalent to 120,000 road miles. The deterioration rate observed in the E-60 

fleet was used to project deterioration from the rates observed at low mileage MOVE bins 

derived in the first CE-CERT program to the aged bins for the complete MOVES 

database. 

A final significant study combining the results of a number of additional studies was 

reported in SAE paper 830987.3

 This literature survey reports the average and range of 

ammonia emissions found in several previous testing programs. This 1983 paper 

includes results from light-duty vehicles without catalyst, with oxidation-only catalysts, 

and three way catalysts. Also reported are average emissions observed with heavy-duty 

gasoline trucks and light- and heavy-duty Diesel trucks. 

The E-60 and 1983 SAE paper did not, however, report the second-by-second emission 

results required to develop MOVES database tables corresponding to the vehicles tested. 

The average emission levels were, however, used to scale the MOVES bins developed in 

the CE-CERT study to earlier and later vehicles. 

The limited number of vehicles included in the primary studies could not directly 

represent all possible MOVES bins combinations. While it was possible to estimate 

future and past composite emissions, the second-by-second data required to fill all 

possible MOVES strata were not available. Simple ratios were used to scale the VSP bin 

results developed with the CE-CERT data to ―hole fill‖ the remainder of the MOVES 

emissionRateByAge table. 

The most prevalent unit found in the literature to express average emission rate is mg/mi. 

Table 2-6 displays the average rates drawn from the three programs described above. 

Scaling factors for vehicle deterioration were estimated using the E-60 results. Tests in 

this program were performed with as-received catalysts and with catalysts that had been 

artificially aged the equivalent of 120,000 miles. The average as-received emissions for 

the fleet were 14 mg/mi while the results with the aged catalysts were 21 mg/mi. A 

factor of 21/14 = 1.5X was used to estimate the effect of aging full useful life. Linear 

interpolation was used to assign an aging factor of 1.2X for half useful life deterioration. 

No additional deterioration was assumed for the 20+ year age group. 
-11- 

Table 2-6 

Fleet Average Ammonia Emissions (mg/mi)

Program: E-60 CE-CERT SAE 830987

MY 

Range: 2002+ 96-01 92-95 81-91 81-83 75-80 <1975

Age/

0-5 14 43 101 15 11

6-9 83 15 11

10-19 21 37 11

20+

These deterioration factors were applied to the CE-CERT program to arrive at emission 

factors for the 1996-2001 model year groups of 43 mg/mi, 1.2X43 for the 6-9 year age 

group, and 1.5X43 for the 10-20+ year age groups. Assuming some deterioration had 

already taken place with the 1992-1995 vehicles, an emission factor of 1.1X83 was 

assigned to the 10-19 year old vehicles and 1.2X83 to the 20+ year old vehicles. No 

additional deterioration was assigned to the 1981-1991 vehicles in the 10-19 year old age 

group, leaving the average emission factor of 37 mg/mi for the 20+ year old group. 

These average emission rates were then used to scale the VSP bins previously calculated 

from the CE-CERT results. The 0-5 year VSP averages for the 1996-2001 vehicles 

remained the same. Each bin in the 0-5 year group was multiplied by 1.2 to arrive at VSP 

bins for the 6-9 year group. Each bin in the 0-5 year group was multiplied by 1.5 to 

estimate VSP bins for the 10-19 and 20+ year groups of this model year group. The 

1992-1995 model year VSP bin results were multiplied by 1.1 to represent the 10-19 year 

old results and 1.2 to represent the 20+ year old vehicles. For the 1981-1991 vehicles, 

the 10-19 year old bins were assigned without correction to the 20+ year old age group. 

No second-by-second data were found for the newer vehicles. After reviewing results 

obtained with large samples for HC, CO, and NOx, it appeared reasonable to scale the 

newest CE-CERT VSP bin results (1996-2001) to the 2002+ model years, in proportion 

to the fleet average composite results. Thus the 2002+ model year VSP bins were 

assigned a value equal to 14/43 times the individual bin results for the 0-5 year old 

newest vehicles. The deterioration rates were applied to the 0-5 year old bins by again 

multiplying by 1.2 and 1.5. 

The least amount of data was available for the earliest model year vehicles. The literature 

review SAE paper provided averages and ranges for three groups of vehicles: 

not-catalyst-equipped; equipped with oxidation-only catalysts; and equipped with 

three-way catalysts. It was apparent that the oxidation catalyst and non-catalyst vehicles 
-12- 

presented substantially lower ammonia emission rates than the newer technology 

vehicles. Oxidation catalysts came into widespread use in 1975 following nationwide 

installations of unleaded fuel dispensers. Three-way catalysts were introduced in federal 

vehicles in 1981 to meet technology-forcing standards (requiring significant NOx 

reduction). The non-catalyst results were therefore assigned to all model years prior to 

1975, and the oxidation catalyst results were assigned to model years 1975-1980. No 

deterioration results were available for either group. Recognizing the relatively small 

remaining population of these older vehicles, a single set of VSP emission factors was 

calculated for the 1975-1980 group by applying the ratio of that group to the 1981-1991 

results (15/37 = .405) times the individual 1981-1991 VSP bins. These bins were used 

for all age groups in the 1975-1980 model year range. Similarly, a factor of 11/37=0.297 

was used to scale the 1981-1991 bins to all model years prior to 1975. 

One significant group of unfilled strata remained: those representing vehicles at a 

younger age than were available when the vehicles were tested in 2000-2001. It was not 

possible to test a MY1985 vehicle at 0-10 years of age in CY2000. This does not present 

major problems for a run performed in CY2009: all 1985 vehicles are 20+ years old. 

While it is acknowledged that certain baseline runs representing earlier calendar years are 

affected by these vehicles, again because of the lack of data, the results collected in the 

CE-CERT program were applied to the younger vehicle age strata without modification. 

Table 2-7 repeats the base results from Table 2-6 and summarizes the extrapolation and 

interpolation used to complete this group of vehicles. 

Table 2-7 

Extended Fleet Average Ammonia Emissions (mg/mi)

Program: E-60 CE-CERT SAE 830987

MY 

Range: 2002+ 96-01 92-95 81-91 81-83 75-80 <1975

Age/

0-5 14 43 83 37 101 15 11

6-9 17 52 83 37 15 11

1.2 X

10-19 21 65 91 37 11

1.5 X

20+ 21 65 91 37 0.405 X 0.297 X

1.5 X 81-91 81-91
-13- 

The MOVES EmissionRateByAge table requires identification of the fuel type and the 

regulatory class of each entry. To this point only gasoline-fueled vehicles have been 

discussed (fuel type 1). The regulatory classes of the vehicles included are 20 – Light 

Duty Vehicles and 30 – Light Duty Trucks. Continuing the practice used in other 

MOVES tables, the factors for gasoline are used when no data are available for ethanol. 

Ethanol is fuel type 5. 

The 1983 SAE paper reported tests of light- and heavy-duty Diesel trucks, and heavyduty gasoline-powered trucks. While Diesel-powered light and heavy-duty vehicles have 

been subjected to increasingly stringent emission standards, emission control technology 

for this class of vehicles has not included closed loop fuel mixture control and three-way 

catalyst converters. For this effort, the approach used for oxidation and non-catalyst 

vehicles was continued by applying the ratio of the reported average fleet emissions to 

the emission bins computed using the 1981-1991 CE-CERT fleet. 

Light-Duty Diesel Trucks (LDDT) were reported to have an average ammonia emission 

rate of 7 mg/mi, which is 7/37 = 0.189 of the 37 mg/mi reported in the CE-CERT 

program for 1981-1991 vehicles. This factor was used to develop binned VSP factors for 

all group 20 and 30 Diesel-powered vehicles. Heavy-duty Diesel trucks (HDDT) were 

reported to produce an average of 27 mg/mi, a ratio of 0.730 of the CE-CERT factor. 

These results were applied to all group 41, 42, 46, 47, and 48 Diesel-powered vehicles. 

These results are summarized below in Table 2-8. 

Table 2-8 

Ammonia Emissions for Diesel and Heavy Duty 

Vehicles (mg/mi)

Class mg/km mg/mi

1981-

1991 Ratio

LDDT 4.2 7 37 0.189

HDDT 16.8 27 37 0.730

HDGT 28 45 37 1.216

Significant emission control rule changes have been enacted for Diesel powered vehicles 

in recent years. Most manufacturers have elected to employ Selective Catalyst Reduction 

(SCR) emission control technologies including urea injection to achieve the new 

emission standards. A by-product of SCR is the release of excess ammonia (slip) from 

the SCR device. Commonly reported SCR systems for on-road vehicles include a final 

ammonia slip catalyst to minimize this release. These devices are reported to reduce 

ammonia release to ―negligible‖ levels, with one system reporting 1-3 ppm in the exhaust 

stream. That level in a large Diesel engine would represent between 1 and 2 grams/hour 

of ammonia. It would be appropriate to review in-use performance as production SCR 
-14- 

systems are placed into service to determine if the ammonia emission factors 

recommended here should be updated. 

The last type of vehicle for which ammonia emission factors were developed was 

motorcycles (regulatory class 10). No test program including measurement of ammonia 

with motorcycles was identified. The results of the CE-CERT program were therefore 

used, with consideration of differing emission standards and emission control 

technologies applied to the two different types of vehicle. As catalytic converters were 

not common on motorcycles before 1999, the non catalyst (pre-1975) light-duty vehicle 

rates were applied to this group. Catalytic converters and feedback fuel control systems 

became increasing common on motorcycles between 2000 and 2005, so the 1975-1980 

light-duty vehicle rates were applied. New standards have been phased in for 

motorcycles, and three-way catalysts with feedback systems have become the norm. The 

1981-1991 light-duty vehicle results were used for 2006 and newer motorcycles. As no 

significant number of Diesel motorcycles are expected, no ammonia emission factors 

were developed. 

The amount of second-by-second test data, and information regarding changes in 

ammonia formation with vehicle age, is extremely limited. No information regarding 

ammonia emissions with the use of ethanol blends was found. The newest technology 

(LEV) vehicles, on the other hand, were found to produce extremely low levels of 

ammonia. One remote sensing study4

attributes more than 20% of total daily ammonia 

emissions in the South Coast Air Basin to on-road vehicles. Kean reports5that heavyduty Diesel emissions are difficult to measure in a tunnel study because of interference 

from relatively higher light-duty ammonia emission production, but he does consider the 

potential impact of ammonia slip. Future studies should be monitored to determine if 

additional data collection for the purpose of updating the recommended factors is 

appropriate. 

2.2 Sulfur-Based Emission Rates

The Draft2009 MOVES model includes the sulfateEmissionRate table. The table was 

populated using early results from the Kansas City program. A draft report6

detailing the 

analytical procedure used was provided with the Work Assignment. 

The sample size used in the original analysis was limited because QC review had not 

been completed and each point required both the exhaust sulfate level and fuel sulfur 

level. Thirteen points were included in the original analysis. An updated MSOD 

database including results from Kansas City was provided with the Work Assignment. 

Forty additional tests with both exhaust sulfate and fuel sulfur were identified in the 

database. The analytical approach described in the draft report was applied to the 

combined results. 
-15- 

Figure 2-2 displays the results obtained with 1981 and later vehicles. The solid square 

points reflect the data initially used, while the ―X‖ points represent the new data. A 

regression was performed to determine the slope of the equation: 

SO4 (g/mi) = slope × fuel S (ppm) (forcing zero intercept) 

Figure 2-2 

Exhaust SO4 vs. Fuel S – 1981 and Newer 

0.0000

0.0005

0.0010

0.0015

0.0020

0.0025

0 100 200 300 400 500

Fuel S (ppm)

Exhaust SO4 (g/mi)

Original

New Data

Linear (Original)

Linear (New Data)

The newly developed combined slope was slightly more than half of that developed with 

the original limited sample: 

Original 0.000002952 

Update 0.000001597 

Only four of the more modern vehicles had SO4 emissions results above 0.0005 g/mi, 

with little response to varying sulfur level in the fuel. 

The average SO4 emission rate for this group of vehicles was 0.000344. 
-16- 

The results obtained with 1980 and older vehicles were similar and are displayed in 

Figure 2-3. The original analysis included only three vehicles. The slope was 

determined by averaging the three Exhaust SO4 measurements and dividing by the 

average fuel S for those tests. Several additional tests were found, and a slope was 

determined using linear regression. 

Original 0.00002892 

Update 0.00001907 

Figure 2-3 

Exhaust SO4 vs. Fuel S – 1980 and Older 

0.0000

0.0020

0.0040

0.0060

0.0080

0.0100

0.0120

0.0140

0 50 100 150 200

Fuel S

Exhaust SO 4 - g/mi

Original

New Data

Linear (Original)

Linear (New Data)

The slope developed with the combined data set for older vehicles is more than 10X the 

slope obtained with the 1981 and newer vehicles. 

No additional results were obtained for Diesel vehicles. The same factors were used for 

ethanol fuel, with the assumption that the sulfur level used as an input will be the level 

measured in the diluted fuel + ethanol blend used on the road, not just in the blend fuel. 

Lacking other information, the same factors were used for starting, running, and extended 

idle. 
-17- 

2.3 Nitrogen Oxide and Nitrogen Dioxide Ratios

NO and NO2 ratios are to be expressed in MOVES as a fraction of total NOx. The 

NONO2Ratio table will include the MOVES variables: 

meanBaseNONO2ratio

NO to NOx ratio for entries including polProcessID 32xx 

NO2 to NOx ratio for entries with polProcessID 33xx 

meanBaseRateCV

Coefficient of Variation (COV) standard deviation / mean 

Results were additionally classified in terms of MOVES variables sourceTypeID (types 

11-62), polProcessID (with pollutantID 32 for NO and pollutantID 33 for NO2), 

fuelTypeID (initially gasoline, Diesel, and ethanol) and modelYearGroupID (including 

vehicle model years 1960-2050). The ―Datasource‖ field for entries in the table initially 

refer to this report with an ID of 8101. A ―chained‖ calculator will retrieve total NOx 

and the coefficients in the NONO2Ratio table to compute individual NO and NO2 results. 

A wide range of NO2 to NOx ratios is reported in the literature. Because NO oxidizes to 

NO2 over time, a significant problem is defining when to measure and report results. 

Values of 1-3% are frequently reported for gasoline-powered vehicles. One study, 

utilizing nearly instantaneous real-time exhaust emission data, reports an average value of 

less than 1%.7 The study continues with the conclusion that CVS bag measurements are 

questionable because ―fast oxidation of NO to NO2 occurs when diluted exhaust is 

sampled in bags.‖ Other studies report NO2 fractions as high as 30% with certain types 

of emission control equipment and operating conditions.8,9,10

A study including continuous NO and NO2 results from a representative cross-section of 

modern gasoline powered vehicles was identified—the CE-CERT study previously used 

in the development of ammonia emissions factors.11 EPA’s MSOD database contains 

second-by-second NO and NO2 results for 20 of the vehicles, providing a representative 

cross-section of results for vehicles ranging from Tier 0 (1981-1989) through NLEV and 

ULEV (2001) light-duty cars and trucks. The data allow calculation of both average 

emission levels and variation of results within groups. No studies reporting individual 

1980 and earlier vehicle results were identified. This includes vehicles produced prior to 

the introduction of catalytic converter (generally 1960-1974), and to vehicles produced 

with oxidation catalysts (1975-1980). The ―widely accepted assumption‖ of 2.5% NO2 to 

NOx ratio was used to populate the MOVES tables for 1960 through 1974 vehicles. 

Results for the remaining groups of gasoline-powered light-duty vehicles were computed 

using the CE-CERT data, and are summarized in Table 2-9. 
-18- 

Table 2-9 

Gasoline NONO2 Ratios

Model

Years

Average

NOx Level

Running

NO2 ratio COV

Start

NO2 ratio COV

1960-1980 - 0.025 - 0.025 -

1981-1990 0.764 0.068 0.094 0.039 0.040

1991-1995 0.824 0.046 0.054 0.013 0.003

1996+ 0.107 0.164 0.099 0.049 0.020

For the 1981-1996+ groups, the second-by-second NO and NO2 readings were summed 

for each bag of each test in the respective groups, and then the ratios of NO and NO2 to 

the total (NO+NO2) were calculated. The average and standard deviation of the ratios 

within each model year group were then determined. The average NO2 ratio is reported 

in the table. (The NO ratio must be 1 minus the NO2 ratio.) The Coefficient of Variation 

(COV) is the standard deviation of the individual values divided by their average. 

The limited sample sizes yielded a slightly higher average NOx g/mi value from the 

1991-1995 than the 1981-1990 vehicle groups. This was not caused by a single outlier 

vehicle, but rather normal variation found within small samples (six tests versus seven 

tests). Of greater interest is the consistency found in the NO and NO2 ratios to the total in 

their groups—all less than 10%. The most modern cars, with very low average total 

NOx, resulted in the highest NO2 ratio (16%); the remaining tests displayed results 

ranging between 1 and 7%, consistent with the general results reported in the literature. 

The model year groups for sourceTypeID’s 21, 31, and 32 (light-duty cars and trucks) 

were assigned the coefficients displayed in Table 2-9. The model year grouping for 

sourceTypeID 11 (motorcycles) was modified to account for the differences in emission 

standards and control technologies employed, with 2010+ motorcycles receiving the 

coefficients assigned to 1991-1995 automobiles. Similarly, assignments to vehicles in 

sourceTypeIDs ranging between 41-62 (heavy-duty gasoline powered trucks) were 

aligned with emission standards and technology changes. 

No single study of NO/NOx ratios was identified for Diesel powered vehicles. Several 

SAE papers summarizing testing on individual vehicles were reviewed, and provided 

reasonably consistent results within technology groups. Earlier technologies had little 

reported impact on NO/NO2 ratios, but advanced technologies potentially can have a 

major influence. 

Lanni12 included measurement of both NO2 and NOx total emissions, citing research that 

indicated that retrofit of CRDPFs (Continuously Regenerating Diesel Particulate Filters) 

had resulted in an increase in NO2 emissions. The CRDPF in the vehicles studied uses an 
-19- 

upstream catalyst that partially oxidizes NO to NO2, as well as oxidizing HC, CO, and 

SOF. A downstream particulate filter traps soot particles. The particulate trap is 

continuously regenerated by combustion of the soot particles with the NO2 remaining in 

the exhaust stream. Lanni reports his unmodified test vehicles ―agrees well with the 8% 

average NO2/NOx volume ratio reported in the literature‖ and continues that total NOx 

emissions were not affected by the DPF, but elevated NO2 emissions resulted in elevated 

NO2/NOx ratios, approaching 50%. 

Ayala13 reported similar results on Diesel-powered buses before and after installation of a 

retrofit DPF, using parallel analysis of NO and NOx during several test cycles. 

Unpublished results provided by Dr. Ayala on a Diesel-powered Class 8 tractor was also 

considered. 

Table 2-10 displays the results used to determine average ratios without DPF controls. 

Table 2-10 

Diesel Without DPF trap NO/NO2 Ratios

Pollutant

or Ratio

SAE 2003-01-0300 SAE 2002-01-1722 Ayala II

CBD CBD CBD SS

OEM OEM NYBDC OEM OEM Baseline

NO2 2.1 1.6 4.6 0.92 2.14 1.26

NO 24.5 22.5 65.70 29.28 22.49 19.87

NOx 26.6 24.1 70.30 30.20 24.63 21.13

NO2/NOx 0.079 0.066 0.065 0.030 0.087 0.060

NO/NOx 0.921 0.934 0.935 0.970 0.913 0.940

The average NO2/NOx ratio observed was 0.065, with a standard deviation of 0.019 and a 

COV of 0.301. 

Table 2-11 displays average results obtained in three programs for Diesel vehicles with 

DPF traps installed. The average NO2/NOx ratio for this sample is 0.594, with a standard 

deviation of 0.406 and COV of 0.193. 
-20- 

Table 2-11 

Diesel With DPF trap NONO2 Ratios

Pollutant

or Ratio

SAE 2003-01-0300 SAE 2002-01-1722 Ayala II

UDDS UDDS CBD SS NYBC UDDS CRT VSCRT ZSCRT DPX CCRT

NOx 25.9 22.1 34.4 26.5 52.1 23.1 18.8 5.2 5.7 10.58 8.0 

NO 12.8 11.8 17.7 13.8 28.3 14.1 12.9 3.9 4.2 7.75 3.3 

NO2 13.1 10.3 16.7 12.7 23.8 9.0 5.8 1.3 1.5 2.83 4.7 

NO/NOx 0.494 0.534 0.515 0.521 0.543 0.610 0.688 0.747 0.731 0.733 0.412 

NO2/NOx 0.506 0.466 0.485 0.479 0.457 0.390 0.312 0.253 0.269 0.267 0.588 

Table 2-12 displays results obtained following extended idle. The average NO2/NOx 

ratio observed was 0.108, with a standard deviation of 0.070 and COV of 0.645. 

Table 2-12 

Diesel With DPF trap and Extended Idle NONO2 Ratios

Pollutant

or Ratio

Ayala II

CRT VSCRT ZSCRT DPX CCRT

NOx 90.50 77.2 43.05

NO 86.53 69.6 35.18

NO2 3.97 7.6 7.86

NO/NOx 0.956 0.901 0.817 

NO2/NOx 0.044 0.099 0.183 

###
-21- 

3. HIGHWAY MOTORCYCLE EMISSION RATES 

AND ACTIVITY FACTORS 

Task 3 of this study required the development of emission and activity factors for 

highway motorcycles. Subtasks included a review and analysis of available emissions 

data and consultation with the Motorcycle Industry Council (MIC) to obtain retail sales 

data, registration data, and the results of an owners survey. 

This section of the report identifies the data sources for the highway motorcycle emission 

rates and activity data being developed for MOVES and describes the methods used to 

process and validate these data and assemble them into MOVES-ready database tables. It 

is organized into sub-sections that provide an overview of key highway motorcycle 

characteristics, describe uncontrolled and controlled emission rates, discuss Inspection 

and Maintenance program effects on emissions, present latest estimates on motorcycle 

populations and activity levels and finally, describe how the emission rate and activity 

data were organized into specific MOVES-ready tables. 

3.1 Highway Motorcycle Characteristics

The U.S. highway motorcycle fleet encompasses an extremely wide range of vehicles. 

The variation in available models is actually greater than the variation in passenger cars 

in terms of engine size, engine power, vehicle weight, and vehicle performance. At one 

end of the spectrum are small scooters weighing less than 200 pounds and equipped with 

<50 cc single cylinder engines and CVT transmissions that have inadequate performance 

for freeway operation. Historically, many of the <50 cc scooters have used 2-stroke 

engines. At the other end of the performance spectrum are 400–500 pound sport models 

equipped with 1000–1300 cc, 4-cylinder, 4-stroke engines and 6-speed manual 

transmissions with performance capabilities exceeding those of high-performance 

passenger cars. At the other end of the size spectrum are 3-wheeled ―trike‖ configuration 

vehicles weighing close to 1,500 pounds with automotive V-8 engines exceeding 6 litres 

displacement. 

Excluding the relatively low volume of 3-wheeled vehicles classified as motorcycles, 

highway motorcycle models are commonly divided into six separate categories: 

―scooter,‖ ―standard,‖ ―dual-sport,‖ ―sport,‖ ―touring,‖ and ―cruiser.‖ Some 

manufacturers use variations on these categories. The term ―super sport‖ is sometimes 

used to distinguish ultra-high-performance models from lower-powered models of the 

same basic design. ―Sport touring‖ and ―luxury touring‖ are terms used to describe 
-22- 

subcategories of touring motorcycles. (There are also a number of ―crossover‖ models 

that do not fit neatly into any of the six categories.) 

―Scooters‖ might be considered the motorcycle equivalent of an economy car. They are 

motorcycles designed primarily for providing low-cost transportation in an easy-to-ride 

configuration with a ―step-through‖ frame, a relatively low seat, an upright riding 

position, and an automatic transmission. Most scooters use some form of automatic 

transmission, making them easier for inexperienced riders to use. They usually have a 

short wheelbase to facilitate maneuverability in congested urban areas. Almost all 

scooters have a partial fairing and windscreen to provide wind and weather protection. 

Scooters have smaller diameter wheels and tires than other motorcycles. There is an 

extremely wide range of performance within the scooter category, ranging from models 

that are too slow for freeway driving to more powerful models that have the performance 

of typical passenger cars. 

―Standard‖ models are conventional motorcycles with an upright riding position and no 

fairing. They are sometimes referred to as ―naked‖ bikes; however, small windscreens 

and partial fairings may be standard on some models and available as an option on others. 

They are seldom equipped with saddlebags, but may have bags available as optional or 

aftermarket equipment. Standard motorcycles are usually intended to be general-purpose 

vehicles for all-around riding. Standard models are available in a wide range of 

performance levels, ranging from barely adequate for freeway travel to ultra-high 

performance. Representative models include the BMW R1200R and the Suzuki Bandit 

1250S. 

―Touring‖ models are the motorcycle equivalent of luxury sedans and sports sedans. 

They have the upright riding position of a ―standard,‖ which is the most comfortable for 

long distance riding, in combination with a fairing, windscreen, and saddlebags. The 

distinction between ―luxury touring‖ and ―sport touring‖ models is primarily related to 

size and performance. Sport touring models tend to be smaller, more nimble, and higher 

performance. Representative models include the Yamaha FJR1300 and the Kawasaki 

Concours 14. Pure touring models are larger and designed to provide more room and 

wind protection for a rider and a passenger. Representative models include the Honda 

Gold Wing and the BMW K1200LT. The minimum level of performance from touring 

motorcycles is adequate performance for freeway travel. At the other end of the 

spectrum, some sport touring models have a level of performance comparable to a typical 

―sport‖ bike. 

―Sport‖ motorcycles are designed primarily for exceptional handling and performance. 

They are the motorcycle equivalent of a ―sports car.‖ They generally have a relatively 

short wheelbase, and narrow, forward-located handlebars that put the rider in a leaning 

forward position. The footpegs are often set high and to the rear of the motorcycle to 

provide increased cornering clearance. Most are equipped with full fairings to reduce 

aerodynamic drag at high speeds, but the fairings are narrow and the windscreens are too 

short to take the wind off of a rider’s head and shoulders unless the rider is in a ―tucked‖

position that most riders would find comfortable only for short periods of time. Most 
-23- 

sport models have relatively high-output engines that provide a greater level of 

performance than is available from most high performance passenger cars. 

Representative models include the Suzuki GSX750R, the Honda CBR600RR, the 

Yamaha YZF-R1, and the Kawasaki ZX10R. 

―Dual-sport‖ models are the motorcycle equivalent of a sport-utility vehicle or a ―Jeep.‖ 

They share the upright riding position of a ―standard‖ model but they tend to be ―taller‖

motorcycles with relative long suspension travel to make them suitable for off-road 

operation, or at least operation off of paved roads. It is particularly important for the 

footpegs on a dual-sport bike to be located directly under the rider so that they are easy to 

stand on while riding in rough terrain. Representative models include the BMW 

R1200GS, the Suzuki V-Strom, and the Kawasaki KLR650. 

The design criteria for the ―cruiser‖ category are primarily focused on preservation of a 

more classic style and sound than on high performance. Most cruisers are equipped with 

relatively large displacement, V-twin engines that generate maximum horsepower at a 

relatively low engine speed. These engines produce a distinctly different sound than the 

high speed, 4-cylinder engines used in most other large motorcycles. Cruiser category 

motorcycles are also designed to provide a fundamentally different rider position, with 

higher handlebars and ―forward‖ foot controls (often with floorboards rather than 

footpegs) and relative low seat height. Cruiser models typically have a relatively long 

wheelbase and steering geometry that provides increased stability in a straight line at the 

expense of cornering performance. To preserve a classic visual appearance, cruiser 

models are equipped with either air-cooled engines or water-cooled engines that are 

designed to resemble an air-cooled engine. Minimal use of fairings or other body work 

preserves the visual prominence of the engine, an important aspect of cruiser design. 

Representative models include the Harley-Davidson Softail, the Honda VTX1800, the 

Suzuki Boulevard C90, and the Kawasaki Vulcan 900 Classic. 

While the differences between a ―scooter‖ and a ―touring‖ bike are extreme, the 

variations within an individual category are almost as extreme. For example, there are 

greater than 10:1 variations in engine power among ―scooter‖ models. 

Under current EPA regulations, highway motorcycles are divided into three classes based 

on engine displacement. Class I covers 0–169 cc; Class II covers 170–279 cc; and 

Class III covers >279 cc. Prior to model year 2006, Class I covered 50–169 cc and 

motorcycles with <50 cc engines were exempt from emission standards. Motorcycles 

categorized as ―scooters‖ fall into all three displacement classes. Motorcycles 

categorized as ―dual sport,‖ and ―standard‖ are primarily in Classes II and III. 

Motorcycles categorized as ―sport,‖ ―cruiser,‖ and ―touring‖ are primarily in Class III. 

Prior to calendar year 2000, over 90% of all highway motorcycles were in Class III. Due 

to a recent increase in the sales of small scooters, Class III motorcycles are currently 

estimated to be approximately 85% of the highway-legal fleet (as is discussed in more 

detail below). 
-24- 

3.2 Uncontrolled Emissions Characteristics

Since engine displacement and weight are correlated, Class I motorcycles are the lightest 

weight, which contributes to inherently low NOx emission levels. Class I motorcycles 

also have relatively small fuel systems, which contributes to relatively low evaporative 

emissions. However, the small displacement engines have relatively high surface-tovolume ratios, which contributes to higher HC exhaust emissions. Prior to model year 

2006, the lack of emission standards for motorcycles <50 cc allowed for the use of 2-

stroke engines, which have much higher HC exhaust emission levels than 4-stroke 

engines. Prior to 1978, high-emission 2-stroke engines were used on many models with 

≥50 cc engines and control of crankcase vent emissions was not required from 

motorcycles with 4-stroke engines. 

Crankcase Emissions – The imperfect sealing of the combustion chamber in a premixed 

charge, reciprocating engine results in ―blowby‖ of unburned fuel past the piston rings 

and into the crankcase. To prevent blowby from pressurizing the crankcase (causing oil 

leaks) and to prevent unburned gasoline from building up in the crankcase, a crankcase 

ventilation system is incorporated in 4-stroke engines. (Two-stroke engines use a 

pressurized crankcase and do not have a crankcase vent.) 

Prior to the imposition of emissions control requirements, crankcase ventilation was 

routinely provided by a road draft tube. Air flow under the vehicle created a slight 

vacuum which assisted in the removal of blowby gases from the crankcase while also 

drawing some fresh air through the crankcase breather/vent. Based on block data 

statements in MOBILE5, uncontrolled crankcase emissions were approximately 4 g/mi of 

unburned hydrocarbon, nearly half as much as uncontrolled exhaust hydrocarbon 

emissions. Subsequent versions of EPA’s vehicle emissions model assume crankcase 

emissions are proportional to exhaust emissions, with pre-controlled vehicles having 

crankcase emissions that are 33% of ―running‖ exhaust. 

For vehicles with crankcase controls, estimated crankcase emissions drop to 1.3% of 

running exhaust. Actual testing by Sierra Research determined that typical crankcase 

emissions from passenger cars without Positive Crankcase Ventilation (PCV) systems 

installed are approximately 2.5 grams per mile over the LA4 driving cycle.14

 Second-bysecond data collected by Sierra indicated that crankcase emissions increase with 

acceleration rate. As a result, actual emissions in customer service are likely to be higher 

than 2.5 g/mi for uncontrolled cars. 

Measurement of uncontrolled motorcycle crankcase emissions was conducted during a 

study conducted by Southwest Research Institute for EPA.15 Measurement of blowby 

emissions was limited to idle, 20 mph road load, and 40 mph road load operation of a 

1972 model year, 220 pound, 100 cc, 4-stroke motorcycle. Average emissions were 

calculated to be 0.421 g/mi, assuming 20% idle. Assuming average crankcase emissions 

are proportional to fuel consumption, the measured crankcase emissions rate would be 

increased by 60% to account for the difference between the 80 mpg measured for the 

100 cc motorcycle over the LA4 driving cycle and the 50 mpg of the average motorcycle. 
-25- 

It would also be appropriate to account for the expected increase in crankcase emissions 

during vehicle operation more representative of typical driving. However, analysis of the 

second-by-second data collected by Sierra Research during its testing of passenger car 

crankcase emissions indicates that crankcase emissions during a mixture of idle, 20 mph, 

and 40 mph operation are very close to average emissions over the LA4 driving cycle. 

Our best estimate of uncontrolled crankcase emissions for the average motorcycle is 

therefore 0.7 g/mi HC. Assuming crankcase emissions are proportional to fuel 

consumption, this is consistent with the 2.5 g/mi crankcase emissions rate measured on a 

full-size passenger car. 

Exhaust Emissions – Although physically much smaller than passenger cars and lightduty trucks, the uncontrolled exhaust emissions from highway motorcycles were nearly 

as high as those of cars and light trucks. This was due to the fact that a significant 

fraction of the uncontrolled motorcycle fleet was powered by 2-stroke engines with 

relatively high HC emissions. Based on information available to EPA in 1992, the 

exhaust emissions of uncontrolled 2-stroke motorcycles were estimated at 15.4 g/mi HC 

and 27.0 g/mi CO.16 The same document estimates the emissions of uncontrolled 4-

stroke motorcycles at 2.9 g/mi HC and 42.0 g/mi CO. 

Regulated Pollutants – Sierra has independently estimated uncontrolled exhaust 

emissions from motorcycles by analyzing data collected during the previously referenced 

SwRI study and CARB surveillance testing programs.17,18,19 Figures 3-1, 3-2, and 3-3 

present the FTP results for HC, CO, and NOx as a function of odometer for 35 pre-1978, 

4-stroke motorcycles ranging from 90 cc to 1340 cc displacement (average 573 cc). 

Three of the vehicles were tested only on the LA92 driving cycle rather than the LA4. 

FTP emission levels were estimated based on the correlation between LA92 and LA4 for 

29 motorcycles tested on both cycles during CARB’s third (1998) surveillance testing 

program. As shown in the figures, there is wide variation in the test results. HC 

emissions range from about 1 g/km to 7 g/km. CO emissions range from just under 

6 g/km to 60 g/km. NOx emissions range from 0.04 g/km to 1.9 g/km. Since emissionsrelated defects were identified in very few of the vehicles, the variation appears to be 

related to differences between the various models tested. Examination of the detailed 

information available for each tested vehicle also indicates no significant relationship 

between emissions and engine displacement. As evidenced by the low coefficient of 

determination (r2) values, the relationship between emissions and odometer is not 

statistically significant. 

Average emissions for pre-1978 4-stroke models were 2.92 g/km HC, 31.2 g/km CO, and 

0.27 g/km NOx. Given the variability in the available test results, these averages should 

be applied to all three displacement classes—I, II, and III. The available data do not 

support any specific deterioration rate and, as discussed below, data on later model 

vehicles indicate an insignificant increase in emissions as mileage is accumulated. 
-26- 

Figure 3-1 

Exhaust Hydrocarbons vs. Odometer 

Pre-1978 4-Stroke Models 

Figure 3-2 

Exhaust Carbon Monoxide vs. Odometer 

Pre-1978 4-Stroke Models 
-27- 

Figure 3-3 

Exhaust Oxides of Nitrogen vs. Odometer 

Pre-1978 4-Stroke Models 

Figures 3-4, 3-5, and 3-6 present the more limited data available for motorcycles with 2-

stroke engines. Data were available for only nine vehicles, ranging from 125 cc to 500 cc 

engine displacement. HC emissions range from about 6 g/km to 24 g/km. CO emissions 

range from about 5 g/km to 38 g/km. NOx emissions range from 0.0 to 0.1 g/km. As 

was the case with the 4-stroke models, the variation appears to be related to differences 

between the various models tested, rather than displacement or odometer. 

Average FTP emissions for pre-1978 2-stroke models were 11.94 g/km HC, 19.7 g/km 

CO, and 0.04 g/km NOx. As in the case of the 4-stroke models, the available data do not 

support any specific deterioration rate. 
-28- 

Figure 3-4 

Exhaust Hydrocarbons vs. Odometer 

Pre-1978 2-Stroke Models 

Figure 3-5 

Exhaust Carbon Monoxide vs. Odometer 

Pre-1978 2-Stroke Models 
-29- 

Figure 3-6 

Exhaust Oxides of Nitrogen vs. Odometer 

Pre-1978 2-Stroke Models 

Particulate Emissions – Very limited data are available for particulate emissions from 

pre-1978 model motorcycles. The above-referenced SAE paper by Hare, et al. provides 

particulate emissions estimates based on the tests of four 4-stroke and three 2-stroke 

engines tested on leaded gasoline under steady-state conditions. Translating the steadystate test results to grams per mile, the paper estimates average particulate emissions at 

0.048 g/mi for 4-stroke motorcycles and 0.36 g/mi for 2-stroke motorcycles. (However, 

it should be noted that these estimates are based on the use of fuel containing 3 grams per 

gallon of tetra-ethyl lead.) 

Particulate emissions data more representative of current fuels are available from a 2003 

SAE paper by Ricardo.20 Ten 4-stroke and two 2-stroke motorcycles were tested over 

three different driving cycles: two versions of the European test cycles and a preliminary 

version of the transient World Motorcycle Test Cycle (WMTC), which our analysis 

indicates is reasonably representative of light-duty vehicle operation in the U.S. The 2-

stroke models were both 50 cc; the 4-stroke models ranged from 150 to 1300 cc. All of 

the testing was done on unleaded gasoline. Particulate emissions were measured using 

the technique specified for Diesel particulate measurement in Europe. 

Except for one of the 2-stroke models, particulate emissions were reported to be in the 

range of 0.001 g/km to 0.013 g/km. As best we can determine from the poor quality 
-30- 

graphs in the paper, the average particulate emission rate appears to be approximately 

0.007 g/km for the 4-stroke motorcycles tested on the WMTC. 

One of the 2-stroke models was a direct injection engine that produced particulate 

emissions comparable to those of 4-strokes. The more conventional carbureted 2-stroke 

produced particulate emissions approximately ten times higher than the 4-strokes, i.e., 

approximately 0.07 g/km. 

At the time they were originally sold, the substantially higher particulate emissions 

associated with the use of leaded fuel were applicable to pre-1978 model motorcycles. 

However, when pre-1978 models are running on unleaded fuel, the measurements 

reported by Ricardo are considered to be representative of vehicles currently in operation. 

Evaporative Emissions – Uncontrolled evaporative emissions were estimated from three 

primary sources: (1) surveillance testing of uncontrolled motorcycles by CARB; 

(2) testing of uncontrolled off-highway motorcycles by ATL; and (3) permeation 

emission estimates for plastic fuel tanks from EPA’s Regulatory Support Document for 

the regulations for 2006 and subsequent model year highway motorcycles.21

Test results for uncontrolled motorcycles tested by ATL*and CARB are shown in 

Table 3-1. All tests were run on California specification fuels at the time of the testing, 

which ranged from 7 to 9 psi Reid Vapor Pressure. The resting loss portion of the diurnal 

emissions measured by ATL was calculated from the total emissions that occurred during 

the period of declining temperatures during a real-time, 24-hour diurnal emissions test. 

Since the CARB data are available only for the accelerated diurnal test, they are assumed 

to contain only a small fraction of actual resting loss emissions. Likewise, the CARB test 

results do not include running loss emissions. 

As shown in the first row of Table 1, evaporative emissions measured by ATL averaged 

6.83 grams hot soak, 9.47 grams during the heat build portion of the diurnal, 4.00 grams 

during the declining temperature portion of the diurnal (―resting loss‖), and 1.08 g/mi for 

running loss. The only two vehicles to receive a full complement of evaporative tests 

were relatively small (200-250 cc) ―off-highway‖ motorcycles (a Honda XR200R and a 

Yamaha WR250F). Although it would have been preferable to have had test results for 

highway models, these were the only tests available with ―real time‖ evaporative testing 

(i.e., a 24-hour diurnal test) and running loss measurements. 

The resting loss emissions were calculated from the continuous ATL emissions results. 

Diurnal emissions occurring during the portion of the test when temperatures were 

decreasing were considered ―resting loss.‖ The calculated resting loss emissions are 

subtracted from total diurnal emissions to determine the emissions occurring during the 

―heat build‖ portion of the diurnal. It should also be noted that the uncontrolled running 

loss emissions used in the calculations are based on very limited data. The project 

manager for the testing program reports that high levels of tank vibration occurred during 

the testing as the result of the test vehicles being equipped with knobby tires.22 This 

 

*

 See http://www.arb.ca.gov/research/apr/past/00-315.pdf. 
-31- 

Table 3-1 

Uncontrolled Highway Motorcycle Evaporative Emissions

Hot

Soak

Diurnal/

Heat Build

Resting

Loss

Running

Loss TOTAL

1. ATL, Average of 2 Vehicles 6.83 g 9.47 g 4.00 g 1.08 g/mi -

2. CARB, Average of 35 Vehicles 8.69 g 8.93 g n.a. n.a. -

3. Resting Loss Calculation

For Vehicle with Plastic Tank - - 8.6 g - -

4. Resting Loss Estimate

For Vehicle with Metal Tank - - 2.0 g - -

5. Resting Loss Calculation

For 90% Metal Tanks - - 2.66 - -

6. Best Estimate of Uncontrolled

Evaporative Emissions 8.69 g 8.93 g 2.66 g 1.08 g/mi -

7.

Grams/mile, assuming 

8.5 mi/day, 2 hot soaks/day,

Full diurnal emissions ea. day

2.04 1.05 0.31 1.08 4.48

8.

Grams/mile assuming 

8.5 mi/day, 4 hot soaks/week

Diurnals reduced by 14%

0.58 0.90 0.31 1.08 2.87

9.

Grams/mile assuming 

30 mi/day, 2 hot soaks and a full 

diurnal each day

0.58 0.30 0.09 1.08 2.05

vibration would be expected to contribute to vapor growth. Anecdotal evidence indicates 

that many motorcycles actually have a net inflow of air to the gasoline tank during 

normal operation because the effect of decreasing fuel level more than offsets the vapor 

growth caused by relatively modest fuel heating associated with tanks that are not located 

in close proximity to exhaust systems. 

As shown in the second row of Table 3-1, the average hot soak and diurnal emissions 

reported by CARB for 35 uncontrolled highway motorcycles were similar to the 

emissions reported for the two off-highway motorcycles tested by ATL. The individual 

hot soak emission results contributing to the 8.69 gram average ranged from just under 

4 grams to just over 17 grams per test. Individual diurnal emissions results contributing 

to the 8.93 gram average ranged from 1 to 20 grams per test. 

Also shown in Table 3-1 is an estimate of resting loss emissions estimated using the 

methodology described in EPA’s Regulatory Support Document (RSD) for the 2008 

model year permeation standards applicable to highway motorcycles. This calculation 

was done because of the limited amount of resting loss data and the fact that the resting 
-32- 

loss emissions measured by ATL may be higher than the highway motorcycle average 

because both of the vehicles were equipped with plastic tanks. 

The RSD estimates permeation emissions from plastic tanks at 1.32 g/gal/day, which is 

3.7 grams for the average 2.8 gallon tanks on the vehicles tested by ATL. This is just 

under the total resting loss emissions estimated from the ATL test results. For the 

average 5 gallon tank size assumed by EPA, the permeation rate for uncontrolled plastic 

tanks would be 6.6 grams per day (g/day). 

The RSD estimates emissions from ―R7‖-specification fuel line at 873 g/m2

/day at 29° C 

and assumes 1.5 feet of hose is used on the average motorcycle. Assuming 5/16‖ inner 

diameter fuel lines, this translates to 9.95 grams per day, which is more than double the 

resting loss emissions calculated from the ATL test data. If 3.7 grams of the resting loss 

measured by ATL were from plastic tank permeation, the estimate for fuel line 

permeation is high by a factor of over 30 times. It is also significant to note that CARB 

evaporative emissions test results on several 1990s vintage motorcycles with evaporative 

emissions control systems have diurnal emissions in the range of 0.1 grams measured 

during a 1-hour test. If 100% of the diurnal emissions were from fuel line permeation, 

daily emissions would be only 2.4 grams. 

The available ATL and CARB data make it clear that permeation emissions from 

motorcycle fuel lines are significantly lower than the estimates based on EPA’s assumed 

emission rate for R7 fuel line. This could be due to the fact that the fuel hose permeation 

rate assumed by EPA is the upper limit allowed under the SAE R7 standard. Actual 

emissions for typical fuel hoses, whether R7-spec or not, are obviously much lower. 

Tests of two commercial R7-spec hoses presented in a 1988 SAE paper indicated 

emissions as low as 70% below the maximum allowable.23

Based on the ATL and CARB test results, it appears that the maximum fuel hose 

permeation rate for vehicles not subject to the 2006 and later model year permeation 

standards is at or below 2 g/day. We have assumed this rate applies to pre-2006 models. 

Row 3 of Table 3-1 shows that resting losses are estimated at 8.6 g/day for uncontrolled 

vehicles with plastic tanks. This value is the sum of the 6.6 g/day estimate for a 5 gallon 

tank and a 2.0 g/day estimate for fuel hose permeation. Row 4 shows the resting loss 

estimate for uncontrolled motorcycles with metal fuel tanks, which includes only the 

estimated emissions for fuel hoses. Row 5 shows the resting loss emissions for a fleet of 

uncontrolled motorcycles with 10% plastic tanks. 

Rows 7, 8, and 9 of Table 3-1 show the estimated fleet average evaporative emissions 

translated into grams per mile. Rows 7 and 8 assume an average daily VMT of 8.5 miles, 

which is equivalent to about 3,100 miles per year (an estimate supported by activity data 

described below). 

Row 7 shows the results for the assumption that the average motorcycle, like the average 

car, experiences two hot soaks and one full diurnal per day. As described in the 
-33- 

subsequent discussion of motorcycle usage, two hot starts per day is not a reasonable 

assumption for the average motorcycle. Unlike passenger cars, most motorcycles are not 

used on a daily basis. Because they are usually stored in garages when not being used, 

the emissions associated with the full diurnal test also do not occur on a daily basis. 

Row 8 shows the results based on the assumption that there are only 4 hot soaks per week 

(which results in the same number of miles per hot soak as with passenger cars) and that 

diurnal emissions are reduced by 20% on days when the vehicle is not driven. Table 5.1-

6 of EPA’s Final Regulatory Impact Analysis done for the Marine SI and Small SI 

Engines, Vessels, and Equipment rule indicates that diurnal emissions are reduced by 

20% when a vehicle is stored in a garage.24

 Survey data obtained by MIC indicate that 

83% of motorcycles are stored in garages on days they are not driven.25 For vehicles 

driven two days per week, a 20% reduction on the non-drive days results in a 14% 

reduction in average diurnal emissions. 

Row 9 shows the results for those motorcycles that are used like cars and driven about 30 

miles per day with 2 hot soaks daily and one full diurnal. By comparing the last column 

of row 7 with the last column of row 9, it is apparent that how the vehicle is used causes 

evaporative emissions to vary by more than 100% on a g/mi basis. 

Summary of Uncontrolled Emissions – Table 3-2 summarizes the analysis described 

above with all emissions translated into grams per mile. Due to the extremely high 

exhaust HC emissions of 2-stroke models, average exhaust HC for uncontrolled 

motorcycles is about 24% higher than the estimate for uncontrolled passenger cars. In 

contrast, uncontrolled CO and NOx emissions are significantly lower. Evaporative 

emissions from motorcycles are about 30% lower than from uncontrolled passenger cars. 

Uncontrolled crankcase emissions are 90% lower. 

Table 3-2 

Uncontrolled Highway Motorcycle Emissions (g/mi) 

(FTP test conditions, 8.5 mi/day, 4 hot soaks per week, 5 reduced diurnals/week)

Exhaust Total

Vehicle HC CO NOx PM HC+NOx Evap Crankcase HC+NOx

2-Stroke

Motorcycle 19.2 31.7 0.06 0.11 19.26 2.87 0 22.13

4-Stroke

Motorcycle 4.7 50.2 0.43 0.01 5.13 2.87 0.7 8.70

Average

Motorcycle

(45% 2-stroke)

11.2 41.9 0.26 0.06 11.46 2.87 0.4 14.73

Passenger

Car 9.0 90 4.0 - 13.0 4.0 4.0 21.0

Note: Passenger car evaporative emissions based on 30 mi/day, 2 hot soaks per day. PM emissions assume 

the use of unleaded fuel. 
-34- 

3.3 Controlled Emissions

New highway motorcycles ≥50 cc have been subject to exhaust and crankcase emissions 

standards since model year 1978, ten years after the first federal standards were applied 

to passenger cars and light-duty trucks. Conventional evaporative emissions standards 

have not yet been required for highway motorcycles under federal regulations; however, 

2006 and subsequent model year motorcycles are required to use low permeation fuel 

system components. In addition, evaporative emissions controls required by the State of 

California since the 1984 model year have been voluntarily applied to some motorcycles 

sold in other states. 

Crankcase Emissions – Beginning with model year 1978, all highway motorcycles ≥50 cc 

have been required to be designed so that ―no crankcase emissions shall be discharged 

into the ambient atmosphere.‖ Although it is likely that some crankcase emissions are 

emitted as the result of deterioration of breather hoses in customer service, no data were 

identified on which a non-zero emission rate could be based. 

Exhaust Emissions – Table 3-3 summarizes the motorcycle exhaust emissions standards 

adopted by EPA and CARB. (Unlike the standards applicable to cars and trucks, the 

motorcycle standards may be met based on each manufacturer’s sales-weighted average 

emissions of the various models sold within each class.) The California standards are 

relevant to the emission factors used in MOVES for two reasons. First, as discussed in 

more detail below, many motorcycles sold in all 50 states were voluntarily certified to the 

California standards to avoid the cost associated with distributing two different types of 

motorcycles. Second, even in cases where a manufacturer produces a California and ―49-

state‖ version, the California-certified model is sometimes sold in other western states. 

As shown in the first three rows of Table 3-3, EPA and CARB standards were identical 

for all 1978 and 1979 models. Class I vehicles were required to meet a 5 g/km (8.05 

g/mi) HC standard and a 17 g/km (27.4 g/mi) CO standard. The HC standard for larger 

displacement models increased in proportion to engine displacement to a maximum of 

14 g/km (22.5 g/mi). These could be considered transitional standards intended to initiate 

a phase-out of conventional 2-stroke engines. 

For model years 1980 and 1981, a 5 g/km HC standard applied to all displacements, 

which eliminated all but a few 2-stroke models. The federal CO standard was reduced to 

12 g/km (19.3 g/mi) for all displacements. 

From 1980 through 2005, the federal standards remained unchanged; however, the 

California standards become more stringent starting with the 1982 model year when 

Class I and Class II vehicles become subject to a 1.0 g/km (1.61 g/mi) HC standard and 

Class III vehicles become subject to a 2.5 g/km (4.0 g/mi) HC standard. For 1986 and 

1987, the HC standard for Class III California motorcycles is reduced to 1.4 g/km 

(2.25 g/mi). 
-35- 

Table 3-3 

Motorcycle Exhaust Emission Standards (grams per kilometer, g/km) 

Model Engine Federal Standards California Standards

Year Size (cc) HC CO HC+NOx HC CO HC+NOx

1978–1979 50–169 5.0 17 n.a. 5.0 17 n.a.

1978–1979 170–749 5–14a17 n.a. 5–14a17 n.a.

1978–1979 ≥750 14 17 n.a. 14 17 n.a.

1980–1981 ≥50 5.0 12 n.a. 5.0 17 n.a.

1982–1985 50–279 5.0 12 n.a. 1.0 12 n.a.

1982–1985b≥280 5.0 12 n.a. 2.5 12 n.a.

1986–1987 50–279 5.0 12 n.a. 1.0 12 n.a.

1986–1987c,d ≥280 5.0 12 n.a. 1.4 12 n.a.

1988–2003 50–699 5.0 12 n.a. 1.0 12 n.a.

1988–2003 ≥700 5.0 12 n.a. 1.4 12 n.a.

2004–2005e50–279 5.0 12 n.a. 1.0 12 n.a.

2004–2005 ≥280 5.0 12 n.a. n.a. 12 1.4

2006–2007 0–279 1.0 12 n.a. 1.0 12 n.a.

2006–2007 ≥280 n.a. 12 1.4 n.a. 12 1.4

2008–2009 0–279 1.0 12 n.a. 1.0 12 n.a.

2008–2009 ≥280 n.a. 12 1.4 n.a. 12 0.8

≥2010 0–279 1.0 12 n.a. 1.0 12 n.a.

≥2010 ≥280 n.a. 12 0.8 n.a. 12 0.8

a

 5.0 + 0.0155 (D-170), where ―D‖ is engine displacement in cubic centimeters 

b

 Note: California standards apply to vehicles produced prior to March 1, 1985 

c

 Note: California standards apply to vehicles produced after February 28, 1985 

d

 Compliance is based on corporate average after February 28, 1985 for California and 2006 federally. 

e

 Note: Class I and II motorcycles subject to the 1.0 g/km HC standard, beginning in 2004 for California 

models and 2006 for federal models, may be optionally certified to a 1.4 g/km HC+NOx standard. 

For 1988 to 2003, CARB extended the 1.0 g/km HC standard to all motorcycles up to 

699 cc displacement. Motorcycles ≥700 cc remained subject to a 1.4 g/km HC standard. 

Beginning with model year 2004, CARB revised its standards for Class III motorcycles to 

incorporate an HC+NOx standard and to delete the separate HC standard. Because 

uncontrolled NOx emissions are about 0.3 g/km, the new 1.4 g/km HC+NOx standard 

requires motorcycles ≥700 cc to have HC+NOx emissions about 18% lower than under 

the previous HC-only standard. In 2008, CARB’s HC+NOx standard for Class III 

motorcycles is reduced from 1.4 g/km to 0.8 g/km (1.29 g/mi). Beginning in 2004, 

Class I and II motorcycles subject to the 1.0 g/km HC standard may optionally be 

certified to a 1.4 g/km HC+NOx standard. 

The federal 2006 and 2010 model year standards were set to be equivalent to the 2004 

and 2008 California standards. The federal and California exhaust emission standards are 

therefore identical for 2010 and subsequent model years. 
-36- 

By comparing the standards in Table 3-3 to the uncontrolled emission levels described 

above, it is apparent that nearly a 50% reduction in CO emissions was required for 

4-stroke motorcycles beginning in model year 1978. Because there were no NOx 

standards, the most cost-effective way for manufacturers to meet the CO standards 

involved enleanment of the air-fuel ratio. This also reduced hydrocarbon emissions by an 

amount that was generally sufficient to comply with the CARB HC standard through 

model year 1985. As a result, 1978 through 1985 model 4-stroke motorcycles have 

similar emissions characteristics. 

Regulated Pollutants – The available data on 1978–1985 models from SwRI and CARB 

are displayed in Figures 3-7, 3-8, and 3-9. As was the case with pre-1978 models, there 

is still a wide variation in test results from model to model. It is also apparent that there 

is little trend in emissions vs. mileage accumulation. The average of tests of 55 

Figure 3-7 

Exhaust Hydrocarbons vs. Odometer 

1978–1985 4-Stroke Models 
-37- 

Figure 3-8 

Exhaust Carbon Monoxide vs. Odometer 

1978–1985 4-Stroke Models 

Figure 3-9 

Exhaust Oxides of Nitrogen vs. Odometer 

1978–1985 4-Stroke Models 
-38- 

individual 1978–1985 model year vehicles indicated FTP emissions of 2.534 g/km HC, 

18.041 g/km CO, and 0.429 g/km NOx. 

Figures 3-10, 3-11, and 3-12 present the available test results for 1986–1999 model year 

motorcycles from CARB’s 1998 surveillance testing program. The California standards 

applicable to these model years ranged from 1.0 to 1.4 g/km HC depending on the 

displacement class. 

As with earlier models, there is a wide variation in test results from model to model. 

Models with relative high emissions continue to be allowed because compliance with the 

California standards is based on corporate average emissions beginning with vehicles 

produced after February 1985. The average of tests of 59 individual 1986–1999 model 

year vehicles indicated FTP emissions of 1.34 g/km HC, 13.31 g/km CO, and 0.36 g/km 

NOx. Since only one Class I vehicle and one Class II vehicle were tested, there are 

insufficient data to distinguish between the three classes. The use of certification data to 

distinguish between the classes is frustrated by the lack of NOx data. 

Although the federal exhaust emission standards remained at 5 g/km HC from 1986 

through 2005, the majority of models certified for sale actually met the California exhaust 

emissions standards. Thus, the emission levels depicted in Figures 3-10 through 3-12 are 

representative of 49-state motorcycles. 

Figure 3-10 

Exhaust Hydrocarbons vs. Odometer 

1986–1999 Models 
-39- 

Figure 3-11 

Exhaust Carbon Monoxide vs. Odometer 

1986–1999 Models 

Figure 3-12 

Exhaust Oxides of Nitrogen vs. Odometer 

1986–1999 Models 
-40- 

There appears to be no significant trend in emissions vs. vehicle age for motorcycles of 

this vintage based on idle emissions data collected in the Arizona I/M program. Figures 

3-13 and 3-14 illustrate the relationship between emissions and vehicle age using data 

from the late 1990s.26

Beginning with model year 2004 in California and 2006 federally, the HC-only standard 

is eliminated for Class III motorcycles and large-volume manufacturers are required to 

meet a 1.4 g/km HC+NOx standard. The CO standard remains unchanged at 12 g/km. 

Beginning with model year 2008 in California and 2010 federally, the HC+NOx standard 

for Class III motorcycles is tightened to 0.8 g/km (1.29 g/mi). Only very limited 

emissions data are available for motorcycles recruited from customer service that are 

subject to the HC+NOx standards. As a result, an alternative technique is required in 

order to estimate emissions in customer service. 

Analysis of California certification data for model year 2009 Class III motorcycles 

indicates that the average HC+NOx emission rate reflects a 30% compliance margin for 

the applicable 0.8 g/km standard. Average HC+CO emissions for Class III models were 

0.56 g/km. (This represents a 67% reduction from the average 1.70 g/km HC+NOx 

emissions of 1986–1999 models.) Average CO emissions were 4.0 g/km. Average 

emissions for the 84% of the 2009 Class III catalyst-equipped models were 0.45 g/km 

HC+NOx and 3.57 g/km CO. The non-catalyst models averaged 1.14 g/km HC+NOx 

and 6.16 g/km CO. Based on an analysis of 2008 model year certification data, HC 

exhaust emissions are about 60% of HC+NOx for both catalyst and non-catalyst models. 

Figure 3-13 

Idle HC Versus Motorcycle Age 

Arizona I/M Data – July to September 1997 

Idle HC Versus Motorcycle Age

Arizona I/M Data - July to September 1997

0 2 4 6 8 10 12 14 16 18

0

100

200

300

400

500

600

700

800

900

1,000

Age (years)

Idle HC (ppm)
-41- 

Figure 3-14 

Idle CO Versus Motorcycle Age 

Arizona I/M Data – July to September 1997 

Idle CO Versus Motorcycle Age

Arizona I/M Data - July to September 1997

0 2 4 6 8 10 12 14 16 18

0

0.5

1

1.5

2

2.5

3

Age (years)

Idle CO (%)

Because corporate averaging was allowed, compliance with the 1.4 g/km HC+NOx 

standard required for model years 2004–2007 in California was generally achieved by 

phasing in vehicles designed to meet the 0.8 g/km standard that became effective in 2008. 

As a result, model years subject to the 1.4 g/km ―Tier 1‖ standard can be represented by a 

fleet with a smaller fraction of Tier 2 compliant vehicles. Only 25% of the Tier 2 

vehicles are required to achieve the Tier 1 standard assuming the emissions of the noncatalyst vehicles are the same as 1986–1999 models. However, maintenance of a 30% 

compliance margin required about a 60/40 split of Tier 2 catalyst vehicles and vehicles 

with the average emissions of the 1986–1999 models. This yields a fleet average of 

0.95 g/km HC+NOx and 7.5 g/km CO. 

Based on analysis of 2008 model year certification test results, the average HC+NOx and 

CO exhaust emissions for Class I and Class II motorcycles are only slightly higher than 

the emissions from Class III models. NOx data were not available for all models (since 

compliance with the optional HC+NOx standard is voluntary); however, based on the 

available data, the HC+NOx emissions are 0.85 g/km for Class Ia, 0.91 g/km for Class Ib, 

and 0.95 g/km for Class II. CO emissions were 5.2 g/km for Class Ia, 6.5 g/km for 

Class Ib, and 7.1 g/km for Class II. Although catalytic converters are used on some 

Class I and Class II models, an insignificant catalyst removal rate is anticipated in 

customer service. 
-42- 

Unlike for non-catalyst motorcycles, catalyst-equipped motorcycles are not expected to 

maintain the same emissions in customer service that are demonstrated during 

certification testing. Survey data collected by the Motorcycle Industry Council indicate 

that replacement of OEM exhaust systems is a common occurrence on highway 

motorcycles. Although CARB has recently adopted regulations that provide for the 

certification of catalyst-equipped aftermarket exhaust systems, such systems will be more 

expensive than other aftermarket systems and generally quieter (because of the muffling 

effect of the catalyst). Given the current lack of any effective enforcement mechanism, it 

does not appear likely that the availability of catalyst-equipped aftermarket systems will 

have much effect on the emissions increase associated with the removal of OEM systems. 

Surveys conducted over the last 10 years indicate an OEM replacement rate of 38%. 

Analysis of the 2008 model year CARB certification data indicates that catalysts are used 

on 84% of Class III motorcycles. Replacement of 38% of the OEM exhaust system will 

therefore eliminate the emission reduction accomplished by the catalyst on 32% of the 

vehicles. 

To account for the effect of exhaust system replacement, the in-use emissions from 

vehicles certified to meet the 2008 California and 2010 federal standards can be 

estimated based on the following assumptions: 

1. 52% of the vehicles will have emissions equivalent to the certification levels 

achieved by catalyst equipped motorcycles; 

2. 32% of the vehicles will exhibit emissions similar to 1986–1999 models; and 

3. 16% of the vehicles will have emissions equivalent to the certification levels 

achieved by non-catalyst motorcycles. 

The assumption regarding emissions from motorcycles that have had their catalyst 

removed is consistent with data recently collected by CARB.*

 Based on these 

assumptions, fleet average emissions will be 0.96 g/km (1.54 g/mi) HC+NOx and 

7.1 g/km (11.4 g/mi) CO. 

After accounting for catalyst tampering, the estimated emissions for Tier 2 certified 

motorcycles are almost identical to the certification levels for Class I and Class II 

motorcycles. Since tampering is not expected to be significant for Class I and Class II 

models, the emission rates estimated for Tier 2 certified models can be applied to Class I 

and Class II models as well. 

To estimate the effect of tampering on the fleet subject to Tier 1 standards, we have 

assumed that 37% of the vehicles emit at levels of catalyst-equipped Tier 2 vehicles 

 

*

 Unpublished data provided by CARB from Project 2R0814. CARB tested four late-model motorcycles 

originally equipped with catalytic converters. With catalysts removed, the HC+NOx emissions averaged 

1.59 g/km and CO emissions averaged 8.2 g/km. 
-43- 

(reflecting a 38% tampering rate on 60% of the vehicles) and the remainder emit like the 

average of the 1986–1999 models. This yields in-use emissions from vehicles certified to 

meet the 2004 California and 2006 federal standards of 1.24 g/km HC+NOx and 

9.7 g/km CO. 

Particulate Emissions – In the absence of data on U.S. specification motorcycles, the 

Ricardo estimates for 4-stroke motorcycles running on unleaded gasoline described above 

are assumed to be applicable to all controlled motorcycles. 

Evaporative Emissions – California motorcycles have been subject to evaporative 

emissions standards since a phase-in that began in 1983 and was completed in 1984. The 

applicable test procedure is the one-hour SHED test that only partially captures resting 

loss emissions and does not require either real time or multiday diurnal tests. Federal 

standards require the use of low permeation fuel tanks and fuel hoses beginning in model 

year 2008. Table 3-4 summarizes our estimates of evaporative emissions from 

motorcycles with some form of evaporative controls. 

Hot soak and diurnal emissions test results for six California-certified motorcycles 

equipped with evaporative emissions controls are shown in the first row of Table 3-4. 

Because a simple 1-hour SHED test was used, permeation and running loss emissions are 

not accounted for. As shown in the second row of the table, running loss emissions are 

assumed to be eliminated from a motorcycle equipped with a canister and purge system.*

Rows 3, 4, and 5 of the table repeat the resting and running loss estimates presented 

earlier in the discussion of uncontrolled evaporative emissions. These estimates apply to 

California-certified motorcycles prior to the requirement for low permeation fuel tanks 

and fuel hoses. The third row of Table 3-4 shows the resting loss calculation for a 

motorcycle with a plastic tank. The fourth row of the table shows the resting loss 

estimate for just the fuel hoses that was described previously. Row 5 of the table shows 

the resting loss estimate for a fleet of motorcycles with 10% plastic tanks. 

Row 6 combines the estimates from rows 1, 2, and 5, and provides our estimates of each 

category of evaporative emissions from 1984–2007 model year California-certified 

motorcycles. Row 7 translates the evaporative emissions shown in row 6 into grams per 

mile based on a daily average VMT of 8.5 miles and 4 hot soaks per week. Diurnal 

emissions are estimated based on the assumption that 2 diurnal events per week produce 

emissions equal to the SHED test results and, on the other 5 days, diurnal emissions are 

estimated to be 32% of the uncontrolled diurnal emissions of a motorcycle parked 

outside. 

 

*

 It is theoretically possible for a canister-equipped motorcycle to have sufficient vapor generation during 

operation to cause breakthrough, but such systems would have difficulty during the hot soak test because 

the canister would already be saturated. 
-44- 

Table 3-4 

Controlled Highway Motorcycle Evaporative Emissions

Hot 

Soak

Diurnal/

Heat Build

Resting

Loss

Running 

Loss TOTAL

1. Tests of 6 CA-certified 

Vehicles 0.71 g 0.48 g n.a. n.a. -

2. Estimated Running Loss for 

CA-certified Vehicles - - - 0 g/mi -

3.

Pre-2008 Resting Loss 

Estimate For Vehicle with 

Plastic Tank

- - 8.6 g - -

4.

Pre-2008 Resting Loss 

Estimate For Vehicle with 

Metal Tank

- - 2.0 g - -

5. Pre-2008 Resting Loss For 

90% Metal Tanks - - 2.66 - -

6. Best Estimate of Controlled

Emissions, 1984–2007 CA 0.71 g 0.48 g 2.66 g 0 g/mi -

7.

Grams/mile, 1984–2007 CA, 

assuming 8.5 mi/day, 4 hot 

soaks/week, 71% of diurnals 

reduced by 68%

0.05 0.26 0.31 0 0.62

8. As Above, Plus 15% 

Tampering 0.13 0.36 0.31 0.16 0.96

9.

Grams/mile, 2008 CA, 

assuming 8.5 mi/day, 4 hot 

soaks/week, 71% of diurnals 

reduced by 68%

0.05 0.26 0.03 0 0.34

10. As Above, Plus 15% 

Tampering 0.13 0.36 0.03 0.16 0.68

11.

Grams/mile, 2008 federal, 

assuming 8.5 mi/day, 4 hot 

soaks/week, uncontrolled 

diurnals reduced by 14%

0.58 0.90 0.03 1.08 2.59
-45- 

The diurnal emissions during the 5 days per week that the average California-certified 

motorcycle is not operating were calculated based on EPA’s estimate from the earlier 

referenced Final Regulatory Impact Analysis that canisters reduce diurnal emissions by 

60% when they are not purged between repeated diurnal cycles. The RIA summarizes 

the rationale for this estimate as follows: 

...we have collected information showing that, during cooling periods, the 

canister is purged sufficiently enough so that it can be used effectively to reduce 

diurnal emissions. When the fuel in the tank cools, fresh air is drawn back 

through the canister into the fuel tank. This fresh air will partially purge the 

canister and return hydrocarbons back to the fuel tank. Therefore, the canister 

will have open sites available to collect vapor during the next heating event. Test 

data presented below show that a canister that starts empty is more than 90 

percent effective at capturing hydrocarbons until it reaches saturation. Once the 

canister reaches saturation, it is still capable of achieving more than a 60 percent 

reduction in diurnal emissions due to passive purging. Passive purging occurs as 

a result of fresh air that is pulled through the canister during fuel tank cooling 

periods.

As shown in the last column of row 7, the total evaporative emissions for a 1984–2007 

model year California-certified motorcycle are estimated to be 0.62 g/mi, which 

represents a 78% reduction from the uncontrolled evaporative emission rate of 2.87 g/mi. 

Row 8 of the table accounts for tampering with evaporative emission control systems on 

motorcycles in customer service. Sierra was unable to identify any existing survey data 

regarding evaporative system tampering, so a preliminary survey was conducted of the 

members of an Internet forum of motorcycle enthusiasts (www.ldriders.com).* A 

question was posed to members of the forum by one of the forum administrators who 

requested private responses and guaranteed that the respondents would remain 

anonymous. Owners of motorcycles that were originally equipped with evaporative 

canisters (i.e., 1984 and later models that were California or 50-state certified) were 

asked to report whether the canister was still in place. The make and model year of the 

motorcycle were also reported.†

Based on 78 responses to the above-described survey, canisters had been removed from 

28% of the motorcycles owned by the forum members. The removal rate was higher for 

 

*

 Unlike forums focused on a particular make and model of motorcycle, this forum includes members 

owning a broad range of makes and models. The focus of the forum is long distance riding and many of 

the forum topics address modifications to motorcycles to make them more suitable for long distance riding, 

such as auxiliary lighting, aftermarket saddles, GPS systems, and auxiliary fuel systems. The members are 

therefore frequently involved in modifying their motorcycles and are probably more likely to have 

tampered with evaporative emissions control system than the average owner. 

†

 Responses usually were rejected if the owner did not know whether the motorcycle was originally 

equipped with a canister or did not know where the canister was located. The exception was in cases where 

the make and model was known to be 50-state certified and the original owners reported that, although they 

didn’t know how to identify the canister, they had not removed any components. 
-46- 

the older models, many of which were near the end of their life. The removal rate for 

models up to five years old, the vehicles that have the highest annual average mileage 

accumulation, was approximately 19%. Based on this survey, 15% has been used as a 

conservative estimate of the canister removal rate for two reasons. First, motorcycle 

owners in the survey population are more likely to have tampered with their emissions 

control system than the average owner. Second, there is a likely reporting bias associated 

with the fact that owners who don’t know whether their motorcycle was originally 

equipped with a canister would be unlikely to respond (and certainly wouldn’t have 

removed the canister). 

Row 8 of Table 3-4 shows the effects of the assumed 15% canister removal rate for 

1984–2007 model year California-certified motorcycles. For hot soak, diurnal, and 

running loss, 15% of the fleet is assumed to have the uncontrolled evaporative emissions 

reported earlier in Table 1 and 85% of the fleet is assumed to have the controlled 

emissions estimates from row 8 of Table 3-4. The net effect is that total evaporative 

emissions are 0.96 g/mi, which is 67% below the uncontrolled estimate. 

Row 9 of the table shows the effect of reducing resting losses by 90% to account for the 

use of gasoline tanks and fuel hoses meeting the permeation standards required by EPA 

regulations for 2008 and subsequent models. Ignoring the effect of tampering, the total 

evaporative emissions of motorcycles certified to meet the California evaporative 

emissions standards are reduced to 0.34 g/mi, which is 88% below uncontrolled levels. 

Row 10 of the table shows the estimated evaporative emissions for 2008 and subsequent 

model year California-certified motorcycles when tampering is taken into account. The 

0.68 g/mi emission rate is 76% below uncontrolled emissions. 

The final row of Table 3-4 shows our estimate for the evaporative emissions of 2008 and 

subsequent model year federally certified motorcycles. The 2.59 g/mi composite 

emission rate is only 10% below uncontrolled emissions. 

Summary of Controlled Emissions – Table 3-5 summarizes the analysis described above 

with all emissions translated into grams per mile. Due to the combined effects of 

crankcase, exhaust, and permeation standards, 2010 and later model federally certified 

motorcycles have 72% lower HC+NOx emissions than uncontrolled, pre-1978 models. 

Due to the evaporative emissions standards, the HC+NOx emissions of Californiacertified models are 85% lower than uncontrolled. Both California and federal 

motorcycles have CO emissions that are 73% lower than uncontrolled. 

Because of the relatively high fraction of models meeting California exhaust emissions 

standards that are sold in all 50 states, relatively little error is introduced by using the 

exhaust emissions estimates for 2004 and later California models for all 50 states. 

However, California evaporative emissions systems are not routinely used on models 

produced for sale outside of California. 
-47- 

Table 3-5 

Controlled vs. Uncontrolled Emissions (g/mi)

(FTP test conditions, 8.5 mi/day, 4 hot soaks per week, 

2 regular diurnals per week, 5 multiday diurnals per week)

Vehicle

Exhaust

Evap Crankcase

Total

HC CO NOx PM HC+NOx HC+NOx

Pre-1978

Motorcycles 11.2 41.9 0.26 0.06 11.46 2.87 0.4 14.73

1978–1985

Motorcycle 4.07 29.0 0.69 0.01 4.76 2.87 0 7.63

1986–2003

Motorcycle 2.16 21.4 0.58 0.01 2.74 2.87 0 5.61

2004–2007 

California 1.51 15.6 0.47 0.01 1.98 0.96 0 2.94

2006–2009 

Federal 1.51 15.6 0.47 0.01 1.98 2.87 0 4.85

≥2008

California 1.09 11.4 0.45 0.01 1.54 0.68 0 2.22

≥2010

Federal 1.09 11.4 0.45 0.01 1.54 2.59 0 4.13

MOVES model year groups 70 (1960–1970) and 51 (1971–1977) can be used for 

pre-1978 models. Groups 6 and 7 can be used for 2011 and subsequent models. Most 

intermediate model years need to be in model year specific groups for greatest accuracy; 

however, Groups 61, 62, 63, 64, and 65 could also be used to minimize the number of 

groups. We recommend that California emission factors, except for evaporative 

emissions, be used for all 2004 and subsequent model years. 

3.4 Inspection and Maintenance Effect

Arizona is the only state in the nation that includes motorcycles in its Inspection and 

Maintenance (I/M) program. Our review of the available documentation27 indicates that 

no mass emissions data have ever been collected that can be used to provide a meaningful 

estimate of the benefits associated with subjecting motorcycles to I/M. The estimates of 

emission reductions made by the State of Arizona are based on the assumption that 

motorcycles will experience benefits proportional to those predicted by MOBILE6 for 

light-duty vehicles, with certain adjustments made to account for known differences in 

starts per day and VMT. In addition, an adjustment was made to account for the 
-48- 

observed idle emissions test results for passing and failing vehicles in the I/M lanes. (The 

difference between the idle emissions of failing vehicles and the idle emissions standard 

was apparently assumed to be proportional to excess emissions.) Based on the 

information presented in the above-referenced report, the State of Arizona’s 2004 

calendar year estimate of the benefits of subjecting motorcycles to I/M was a 13.5% 

reduction in exhaust HC and a 20.1% reduction in exhaust CO. 

Undoubtedly the Arizona I/M program required some motorcycles to have their idle airfuel ratio adjusted in order to pass the test. However, the net effect on emissions in 

customer service is unclear for several reasons. First, there are no data correlating 

changes in the concentration of HC and CO emissions at idle to mass emissions changes 

in customer service. Second, there is no evidence that the air-fuel ratio adjustments 

required to pass the idle test were permanent. Third, the previously presented data 

showing the lack of correlation between failure rate and vehicle age raise questions about 

the appropriateness of the idle emissions standards being used. 

The lack of correlation between the idle emissions failure rate and vehicle age described 

above is consistent with the lack of a significant trend between emissions and odometer 

in the surveillance testing data available from CARB. It therefore appears that the idle 

standards being used by Arizona were merely identifying that fraction of the motorcycle 

fleet at one end of a fairly broad distribution of idle emission levels. Under these 

circumstances, it does not appear reasonable to estimate I/M benefits based on a 

calculation that assumes excess emissions from failing vehicles are proportional to the 

extent to which their idle concentrations exceed the I/M standards. 

The potential benefits of I/M may be fundamentally different for later model motorcycles 

originally equipped with catalytic converters. Unlike for non-catalyst motorcycles, there 

is fairly solid evidence of significant emissions deterioration in customer service 

associated with the replacement of OEM exhaust systems. However, there is great 

uncertainty regarding how effective I/M will be as a deterrent to catalyst removal. Unlike 

with light-duty vehicles, the exhaust systems on motorcycles can be changed rather 

quickly, typically in less than one hour. Re-installation of an OEM system for one day to 

pass an I/M test may be the approach used by many owners who prefer to use an 

aftermarket exhaust system on a routine basis. 

In addition to the likelihood of repeat tampering, there are other practical problems 

associated with using a conventional I/M program as a deterrent to catalyst removal. 

There is no available analysis indicating that emission testing (dynamometer or idle) will 

be effective in identifying tampered vehicles. The existence of small-volume 

manufacturer standards and corporate averaging affects the feasibility of making an 

accurate pass/fail decision based on emissions test results. The HC+NOx standards that 

apply to recently certified motorcycle models range from 0.3 to 2.5 g/km HC + NOx. 

This is substantially greater than the difference in emissions associated with catalyst 

removal. It is also likely that visual inspections will be ineffective because OEM 

catalysts are often hidden. Checking for the presence of the EPA noise certification 
-49- 

stamp may also be ineffective because the stamp is not placed on the catalyst itself; the 

stamp can remain when the catalyst has been removed. 

For the reasons described above, the effective deterrence of catalyst tampering is likely to 

require something other than a conventional annual or biennial I/M program. There is 

greater potential for deterring tampering through more routine enforcement of noise 

standards. A substantial increase in noise level is typically associated with the use of 

aftermarket exhaust systems, especially when the system change involves removal of the 

OEM catalyst because catalysts are effective mufflers. 

Until data are available demonstrating the actual effectiveness of a particular type of 

inspection program, we do not believe there is a reasonable basis for assigning a specific 

emissions benefit to the inclusion of motorcycles in a conventional I/M program. 

3.5 Motorcycle Populations and Activity

Population – The population of highway motorcycles in customer service is difficult to 

accurately estimate and forecast for two reasons. First, registration data collected by 

individual states often fail to distinguish between highway motorcycles, off-highway 

motorcycles, and all-terrain vehicles. Second, the annual sales volume of new highway 

motorcycles is much more variable than annual sales of other highway vehicles because 

motorcycles are primarily used for recreational purposes and sales are extremely sensitive 

to the overall level of economic prosperity. During economic recessions, purchases of 

recreational vehicles decline much more than the purchase of other vehicles. 

In model year 1980, the nationwide sales volume of highway motorcycles (including 

scooters and dual sport models) was 757,000 units. By 1990, the annual sales volume 

had declined by 70% to 226,000 units.28 Sales stayed below 300,000 per year until 1998 

and then started increasing rapidly, reaching 920,463 for model year 2008.29

 Projections 

for model year 2009 are that sales may decline by 40–50%.30 How long this recent 

decline in sales will continue is impossible to accurately forecast. 

In addition to the volatility in total highway motorcycle sales, several trends are apparent. 

The scooter population has expanded substantially in recent years. Just 10 years ago (in 

model year 1999), the sales of new scooters was 7,500 units per year, which was less than 

2% of total highway motorcycle sales. Sales increased dramatically each year through 

model year 2008 when they reached 222,155 and accounted for 24% of total highway 

motorcycle sales. In addition to increasing sales, the annual average travel per scooter 

has increased by 38% in the last 10 years, to 1,331 miles per year.31 The expanding use 

of scooters is correlated with the increased use of highway motorcycles by women. As 

recently as 1990, only 6% of motorcycle riders were female. In 2008, 12% of all 

motorcycle riders were female and 27% of scooter riders were female.31

Despite the increasing fraction of scooters, the average size of all highway motorcycles is 

increasing. In 1998, only 27% of highway motorcycles were ≥1100 cc. By 2008, the 
-50- 

percentage of motorcycles ≥1100 cc had grown to 38%.31 Average engine displacement 

increased from 690 cc to 833 cc during this same period. 

In addition to becoming larger, highway motorcycles are lasting longer. The average age 

of motorcycles in customer service has gone down slightly in recent years, but this is due 

to the rapid increase in the sale of new motorcycles. When sales and registration data are 

jointly analyzed, it is apparent that the average life of each new motorcycle is increasing. 

To develop the population data required by MOVES, Sierra performed a detailed analysis 

of the highway motorcycle population and scrappage rates using a combination of 

registration data and new vehicle sales data provided by MIC. Because the registration 

data were proprietary and confidential, Sierra agreed not to retain the data at the 

completion of the analysis. 

The registration data were compiled by R.L. Polk for the 2008 calendar year. The data 

base included the total number of U.S. registrations for 9,156 unique combinations of 

make, model, and model year. Each entry was categorized as either ―On Highway,‖ ―Off 

Highway,‖ ―On/Off,‖ ―Scooter,‖ ―Moped,‖ ―ATV,‖ or ―Unknown.‖ ―Segment,‖ ―Body 

Style,‖ ―Cylinder‖ count, ―Displacement‖ (in cubic centimeters), and ―Stroke‖ (2-stroke 

or 4-stroke) were also identified. 

The level of detail in the registration data should have been sufficient to readily identify 

the total number of registered vehicles legal for highway use. Unfortunately, spot 

checking of the data uncovered numerous problems. Motorcycle models that were 

clearly legal for highway use were sometimes categorized as ―Off Highway.‖ 

Motorcycles that were clearly illegal for highway use were sometimes categorized as ―On 

Highway‖ or ―On/Off.‖ Some models labeled as ATVs were actually motorcycles. 

Sierra made hundreds of edits to correct errors in the registration data. The primary 

editing technique involved independently documenting the type of vehicle from the 

alpha-numeric model name. 

Another problem with the Polk database is that only 36 specific manufacturers were 

identified. Other manufacturers were lumped together under the category ―Other 

Motorcycle‖ and no detail was available for models produced by ―Other‖ manufacturers 

with the exception of model year. While it might appear that detailed information 

regarding 36 specific manufacturers would be sufficient to cover over 99% of sales, that 

is not the case due to the relatively large volumes of scooters produced by a variety of 

Chinese manufacturers. Our analysis of the Polk data is based on the assumption that all 

of the models produced by ―Other‖ manufacturers are Class I scooters. 

Table 3-6 summarizes our analysis of the retail sales and registration data after removing 

non-highway motorcycles from the registration data. All sales data in the table were 

provided by MIC. The last column of the table shows the ―survival fraction,‖ which is 

calculated by dividing each model year’s population estimate by the original sales for that 

model year. (The population for 2008 has been set equal to the sales estimate because the 

registration data for 2008 were incomplete.) 
-51- 

Table 3-6 

On-Highway Motorcycle Population and Survival 

Estimated from Registration and Retail Sales Data

Survival Fraction

Model Year Age Population Original Sales Raw Smoothed

2008 1 920,463 920,463 1.00 1.00

2007 2 818,017 885,000 0.92 0.98

2006 3 782,641 892,000 0.88 0.92

2005 4 685,914 831,000 0.83 0.86

2004 5 516,665 750,000 0.69 0.81

2003 6 594,481 675,300 0.88 0.76

2002 7 484,488 640,000 0.76 0.72

2001 8 405,379 577,000 0.70 0.67

2000 9 320,950 490,000 0.66 0.63

1999 10 260,149 394,000 0.66 0.59

1998 11 192,851 311,000 0.62 0.56

1997 12 163,237 260,000 0.63 0.53

1996 13 161,308 242,000 0.67 0.49

1995 14 134,027 230,000 0.58 0.46

1994 15 112,809 228,000 0.49 0.44

1993 16 100,802 217,000 0.46 0.41

1992 17 73,690 203,000 0.36 0.38

1991 18 57,066 206,000 0.28 0.36

1990 19 58,631 226,000 0.26 0.34

1989 20 64,862 245,000 0.26 0.32

1988 21 61,991 335,000 0.19 0.30

1987 22 78,866 465,000 0.17 0.28

1986 23 121,352 470,000 0.26 0.26

1985 24 107,104 565,000 0.19 0.25

1984 25 84,732 605,000 0.14 0.23

1983 26 104,797 605,000 0.17 0.22

1982 27 141,210 575,000 0.25 0.21

1981 28 109,761 695,000 0.16 0.19

Pre-1981 n.a. 516,761 n.a. n.a. n.a.

TOTAL 7,729,882

As shown in the next to last column of Table 3-6, the survival fraction does not smoothly 

and continuously decrease with age. The source of this unexpected result is not clear; 
-52- 

however, it should be noted that highway motorcycles are primarily recreational vehicles 

and it is common for owners to temporarily let the registration lapse on recreational 

vehicles after the first several years of use. The last column of the table shows the 

recommended survival fraction for use in MOVES. 

Figure 3-15 shows the curve fit to the age vs. survival fraction data from Table 3-6 that 

was used to developed the smoothed estimate. The equation represented by the curve is 

Survival Fraction = C0 * e-(C1*A), where C0 is 1.1089 and C1 is 0.0623. The coefficient of 

determination (r2) is 0.92. 

Figure 3-15 

Motorcycle Survival Fraction vs. Age 

Based on Analysis of Registration and Retail Sales Data 

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

0 5 10 15 20 25 30

Age (years) Survival Fraction

Observed

Exponential

Due to the uncertainty associated with the category of vehicles produced by ―Other‖

manufacturers in the Polk data, we are recommending the same survival curve for all 

classes of highway motorcycles, including scooters. Although the lifetimes indicated by 

the survival curve may seem excessive, this is due to the fact that many owners retain 

motorcycles that they are no longer riding.* This is supported by the discussion below 

regarding mileage accumulation rates as a function of age. 

As noted previously, sales of highway motorcycles are down significantly for model year 

2009. Our recommendation is that 2009 model sales be set at 50% of 2008 model year 

sales. For 2010 and 2011, we are recommending that sales be estimated at 67% and 83% 

 

*

 Motorcycles are more easily stored for extended periods of time than passenger cars or light-duty trucks 

because of their relatively small size. 
-53- 

of 2008, respectively. For 2012 and later model years, we are recommending that sales 

be set at 100% of 2008 values. 

Activity – Although MIC provided VMT as a function of age from its most recent survey, 

sample sizes for older vehicles were insufficient. In addition, the questions asked of 

survey respondents did not address total accumulated mileage. Based on the responses 

received, a question regarding mileage accumulated during the previous 12 months may 

have been misinterpreted by some respondents. Occasionally, responses from owners of 

vehicles more than 10 years old were representative of what would have been anticipated 

from the vehicle’s odometer reading. Because of concerns with the MIC survey data, 

Sierra used odometer readings listed in advertisements for motorcycles offered for sale at 

www.cycletrader.com. Advertisements were sorted in order of their publication date for 

each of 25 different model years ranging from 1975 through 2007. Initial results 

indicated that the average of the odometer readings tended to stabilize at a sample size of 

approximately 60. Except for the oldest model years, where insufficient data were 

available, the most recent 60 ads with odometer values were recorded for each model 

year. To avoid a manufacturer-specific bias, ads for Harley-Davidson motorcycles were 

limited to one-third of the records for each model year. A total of approximately 1,500 

ads were included in the sample. The results are presented in Figure 3-16. 

Figure 3-16 

Average Annual Lifetime Mileage vs. Age 

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

0 5 10 15 20 25 30 35

Age (years)

Lifetime Miles per Year

Actual

Modified Weibull

A modified Weibull curve fit to the data produces a coefficient of determination (r2) 

value of 0.92. The equation is of the following form: 
-54- 

Miles/Year = C0 * C1^(-((A/C2)^C3))

where: A = age 

 C0 = 872,845

C1 = 202.79 

C2 = 2.3397 

C3 = 0.0874 

The modified Weibull curve-fitted average annual lifetime mileages were then translated 

into cumulative odometer levels with age by simply multiplying the age by the curvefitted average miles per year. These curve-fit based cumulative odometer levels were 

then converted to annual mileage accumulation rates as a function of age by simply 

differentiating cumulative mileages at successive ages. The MARCalcs sheet in the 

MC_Activity_All.xls file on the accompanying delivery CD contains these translations. 

While the modified Weibull curve fits the data well up to about 25 years of vehicle age, 

the available data indicate that the average annual lifetime mileage for older vehicles 

drops below the curve. Our review of the available advertisements for motorcycles more 

than 25 years of age indicates that most of them are collector’s items that are 

infrequently, if ever, ridden. 

In addition, we observed that the actual and Weibull curve-fitted VMT at Age 1 (model 

year 2008) was significantly higher than EPA assumed for Age 1 vehicles in MOBILE6 

based on an earlier MIC survey. Actual annual VMT at Age 1 estimated from 

CycleTrader was over 6,800 miles, compared to Age 1 mileage from MOBILE6 of 4,786. 

We believe this higher recent Age 1 mileage, though real, is likely a short-term 

phenomenon that occurred in response to the run-up in retail gasoline prices during much 

of 2008, with the effect that motorcycles were driven more in households where drivers 

could choose between a motorcycle and a less fuel-efficient light-duty vehicle. 

We therefore are recommending the annual VMT distribution shown in Table 3-7, which 

is based on a ―piecewise‖ fit using the modified Weibull curve through Age 23, and a 

power curve-based fit beyond Age 23 that matches the available data for the pre-1985 

model year vehicles. To deal with the short-term effect of higher motorcycle VMT 

accumulation in 2008 likely resulting from high gasoline prices, we determined Age 1 

mileage as the average of that predicted by the Weibull fit at Age 1 (6,296) and the 

MOBILE6 Age 1 mileage (4,786), or 5,541. 

In conjunction with the scrappage curve described above, the VMT data in Table 3-7 

produce a lifetime average total mileage accumulation value of 35,378 miles. For the 

first 13 years (at which point approximately half of the vehicles have been retired from 
-55- 

Table 3-7 

Motorcycle Annual VMT vs. Age (years)

Age Annual VMT Age Annual VMT

1 5,541 26 485

2 2,958 27 452

3 2,237 28 418

4 1,852 29 392

5 1,604 30 366

6 1,426 31 339

7 1,292 32 313

8 1,185 33 287

9 1,097 34 260

10 1,024 35 234

11 962 36 208

12 909 37 182

13 862 38 155

14 820 39 129

15 783 40 103

16 750 41 76

17 720 42 50

18 692 43 24

19 667 44 0

20 644 45 0

21 623 46 0

22 603 47 0

23 585 48 0

24 551 49 0

25 518 50 0

service), the annual average VMT is approximately 1,700 miles. (The annual average 

VMT drops as age increases and some of the vehicles are periodically out of service.) 

As would be expected, the available data indicate that the mileage accumulation rate for 

scooters and Class I motorcycles is about one-third of the average for the entire highway 

motorcycle fleet. The most recent MIC owner survey indicates an average of 3,195 miles 

per year for all motorcycles vs. 1,331 miles/year for scooters and 941 miles/year for all 

motorcycles and scooters under 125 cc displacement. (It should be noted that the annual 

average VMT from the MIC survey does not include motorcycles ―not in running 

condition‖ at the time of the survey. The lower annual average VMT from our analysis is 

due in part to the fact that it accounts for vehicles being periodically not in running 

condition and accumulating 0 miles per year.) Since, as described previously, we are not 
-56- 

differentiating between the emission levels of Class I, II, and III motorcycles, there is no 

need to incorporate class-specific VMT within MOVES. 

Non-Uniformity of Activity – Most highway vehicles exhibit a relatively uniform pattern 

of activity and are used on almost a daily basis. In contrast, motorcycles are primarily 

recreational vehicles and are not practical for use in freezing temperatures. Data 

available from the MIC owner surveys and other sources indicate both seasonal and daily 

variations in use that are significant. 

Table 3-8 presents data from the most recent MIC owners survey for the distribution of 

motorcycle use by season. Not surprisingly, owners in the Midwest region of the country 

report that only 1% of their annual operation of highway motorcycles occurs in the 

winter. This is not an unexpected result of the cold and snowy conditions associated with 

Midwestern winters. Perhaps more surprising is that owners in every region of the 

country use their motorcycles less in the winter. This is in part due to the fact that wind 

chill makes the use of motorcycles below 50°F uncomfortable without the use of 

electrically heated liners or heavily insulated riding suits.*

 Significant highway 

motorcycle activity occurs only when temperatures are above 50°F. The daily average 

VMT in the summer is approximately twice what would be expected from the annual 

average VMT. In the Spring and Summer months, daily average VMT is approximately 

the annual average divided by 365. 

Table 3-8 

Portion of Annual Operation by Season

Season East Midwest South West U.S.

Spring 25% 22% 27% 26% 25%

Summer 53% 58% 41% 44% 48%

Fall 19% 19% 22% 22% 21%

Winter 3% 1% 10% 8% 6%

Available data make it clear that highway motorcycle operation is more frequent on 

weekends than on weekdays. According to a study by the U.S. Department of 

Transportation,32 ―[t]here were 1.5 times as many two-vehicle motorcycle crashes 

involving passenger vehicles in 2005 during weekends than during weekdays.‖ 

Assuming accidents are proportional to VMT, 60% of MC activity is on the two weekend 

days. Since weekend days are only 28.6% of all days, this indicates that VMT on the 

average weekend day is over twice as high as on the average week day. 

 

*

 Electrically heated riding gear is available to extend the range of comfortable riding temperature to 

approximately freezing; however, very few motorcyclists own heated gear and many motorcycles lack the 

electrical system capacity necessary to operate such gear. 
-57- 

Data from the most recent MIC owner survey are consistent with the DOT accident data, 

indicating 56% weekend use. 

The disproportionate use of motorcycles on weekends is consistent with owner responses 

to questions in the MIC owner survey regarding the ―type of riding‖ done. ―Casual 

Pleasure Riding‖ was reported to be the primary type of riding in all regions of the 

country. 

Driving Patterns – In the absence of motorcycle-specific data, it is not unreasonable to 

assume that highway motorcycle driving patterns in customer service are similar to those 

for light-duty vehicles. Although motorcycles typically have higher performance than 

passenger cars and light trucks, previous surveys conducted by Sierra demonstrate that 

high-performance passenger cars have a similar driving pattern to other vehicles because 

they are constrained by traffic. Although lane sharing/splitting is allowed in California, 

motorcycles are similarly constrained by the flow of traffic in most areas. 

Unlike the wealth of data that exists for light-duty vehicles, Sierra was not able to obtain 

detailed, second-by-second data for highway motorcycle operation in customer service. 

Efforts to obtain the data used to develop the World Motorcycle Test Cycle (WMTC) 

were unsuccessful. A representative of Harley-Davidson, the company that originally 

collected the U.S. data, reported that the data are no longer available at Harley. 

Discussions with representatives of Harley-Davidson led us to the conclusion that the 

database from which the WMTC was developed was not demonstrated to be truly 

representative of highway motorcycle operation in the U.S. The selection of the road 

routes was somewhat arbitrary and only professional riders were used. It is not clear how 

these riders’ patterns of operation compare to other riders. 

Notwithstanding the concerns about the data used to develop the WMTC, Figures 3-17 

and 3-18 compare the Speed-Acceleration Frequency Distributions (SAFDs) and relevant 

driving statistics for the WMTC to Sierra’s best estimate of passenger car operation in 

customer service based on chase-car data collected in California subsequent to the 

elimination of the national 55 mph speed limit. 

In Figure 3-17, the joint frequency distributions of vehicle speed (horizontal axis) and 

acceleration (vertical axis) for the WMTC are in the SAFD table for the WMTC. Below 

the SAFD table, a series of key statistics for the WMTC are shown, including MOVES 

VSP bin distributions. 

Figure 3-18 presents similar distributions and key driving statistics for a driving cycle 

referred to as the ―CalWtd‖ cycle. It was developed from light-duty vehicle driving data 

collected in California under a series of chase car-based driving studies33,34 conducted in 

2000 that were jointly sponsored by the California Department of Transportation 

(Caltrans) and the California Air Resources Board (CARB) encompassing four study 

areas: 
-58- 

Figure 3-17 

World Motorcycle Test Driving Cycle SAFD (%) World Motorcycle Test Driving Cycle SAFD (%)

ACCEL SPEED BIN

BIN (mph)

(mph/s) 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 TOTALS

-20

-19

-18

-17

-16

-15

-14

-13

-12

-11

-10

-9

-8

-7

-6

-5

-4 0.056 0.333 0.278 0.333 0.222 0.222 0.056 1.500

-3 0.444 0.389 0.333 0.222 0.222 0.389 0.444 0.222 0.278 0.056 0.056 3.056

-2 0.722 0.333 0.444 0.667 0.556 0.333 0.778 0.444 0.444 0.389 0.278 0.222 0.222 0.333 0.167 6.333

-1 0.778 0.167 1.222 1.556 0.889 0.778 1.444 1.000 0.556 0.667 0.222 0.278 0.333 0.389 0.556 10.833

0 8.889 0.056 0.556 3.667 4.500 2.278 3.000 3.833 2.500 2.944 3.222 2.444 2.556 0.667 7.278 6.778 0.667 55.833

1 0.444 0.500 0.611 1.500 1.222 1.056 0.833 2.167 1.556 1.056 1.000 0.722 0.556 0.722 0.444 0.278 14.667

2 0.111 0.333 0.333 0.333 0.444 0.500 0.889 0.500 0.278 0.222 0.278 0.111 4.333

3 0.611 0.167 0.278 0.333 0.444 0.056 0.056 1.944

4 0.167 0.056 0.222 0.056 0.056 0.556

5 0.222 0.167 0.222 0.056 0.667

6 0.111 0.056 0.056 0.056 0.278

7

8

9

10

11

12

13

14

15

16

17

18

19

20

Totals 9.444 3.889 3.222 8.333 9.556 6.278 6.556 9.278 6.056 5.500 5.611 3.833 3.611 1.944 8.444 7.778 0.667 100.000

Summary Statistics

Avg Speed (mph) Time at Idle (%) Avg Specific PKE (hp-sec/lb) Min Speed (mph) Time at Cruise (%) Avg Total Specific Power (hp/lb) Max Speed (mph) Time in Accel (%) Avg Non-Zero Specific Power (hp/lb)

Avg Non-Idle Speed (mph) Time in Decel (%) Max Specific Power (hp/lb)

Avg Cruise Speed (mph) Avg Trip Length (miles) Spec Pwr Freq (%): 0 hp/lb

Avg Acceleration (mph/sec) Avg Trip Time (min) Spec Pwr Freq (%): >0-0.1 hp/lb Max Acceleration (mph/sec) # Stops per Mile Spec Pwr Freq (%): >0.1-0.2 hp/lb

Avg Deceleration (mph/sec) # of 1-Sec Observations Spec Pwr Freq (%): >0.2-0.3 hp/lb Max Deceleration (mph/sec) # of Trips Spec Pwr Freq (%): >0.3 hp/lb

EPA VSP (Vehicle Specific Power) Statistics

EPA Avg Veh Spec Pwr, VSP (kW/tonne) 4633.103

---------------------------------------------------------------------------------

Bin 0 % (braking) 6122.715

Bin 1 % (idle) 8657.902

------------------------------------------------------------------------ --------------------------------------------------------------------------------- ------------------------------------------------------------------------------------------------

Bin 11 % (0-25 mph, <0 kw/tonne) 5883.523 Bin 21 % (25-50 mph, <0 kw/tonne) 5166.000

Bin 12 % (0-25 mph, 0-3 kw/tonne) 8562.099 Bin 22 % (25-50 mph, 0-3 kw/tonne) 3970.147

Bin 13 % (0-25 mph, 3-6 kw/tonne) 3778.853 Bin 23 % (25-50 mph, 3-6 kw/tonne) 5835.704

Bin 14 % (0-25 mph, 6-9 kw/tonne) 861.000 Bin 24 % (25-50 mph, 6-9 kw/tonne) 3204.803

Bin 15 % (0-25 mph, 9-12 kw/tonne) 861.000 Bin 25 % (25-50 mph, 9-12 kw/tonne) 3396.136

Bin 16 % (0-25 mph, >=12 kw/tonne) 956.657 ----------------------------------- 0.000 ----------------------------------- 0.000

Bin 27 % (25-50 mph, 12-18 kw/tonne) 3300.482 Bin 37 % (>50 mph, 12-18 kw/tonne) 8131.599

Bin 28 % (25-50 mph, 18-24 kw/tonne) 861.000 Bin 38 % (>50 mph, 18-24 kw/tonne) 7079.294

Bin 29 % (25-50 mph, 24-30 kw/tonne) 191.335 Bin 39 % (>50 mph, 24-30 kw/tonne) 1195.846

Bin 30 % (25-50 mph, >=30 kw/tonne) 143.500 Bin 40 % (>50 mph, >=30 kw/tonne) 143.500

35.93

0.00

77.90

39.68

41.95

0.86

6.03

-1.10

-4.47

9.444

68.444

9.667

12.444

17.967

30.000

0.612

1,800

1

4.68

0.0467

0.0977

0.6480

52.22

31.44

8.72

5.28

2.33

Bin 33 % (>50 mph, <6 kw/tonne) 3109.148

Bin 35 % (>50 mph, 6-12 kw/tonne) 4687.619
-59- 

Figure 3-18 

California Urban & Rural Weighted (CalWtd) 

Driving Cycle SAFD (%) 

California Urban & Rural Weighted (CalWtd) Driving Cycle SAFD (%)

ACCEL SPEED BIN

BIN (mph)

(mph/s) 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 TOTALS

-20

-19

-18

-17

-16

-15

-14

-13

-12

-11

-10

-9 0.100 0.100

-8

-7 0.100 0.100 0.015 0.214

-6 0.100 0.214 0.115 0.015 0.031 0.115 0.031 0.621

-5 0.015 0.214 0.146 0.146 0.146 0.031 0.031 0.100 0.031 0.015 0.874

-4 0.100 0.329 0.513 0.429 0.329 0.345 0.115 0.115 0.314 0.015 2.604

-3 0.398 0.429 0.314 0.597 0.314 0.214 0.245 0.046 0.130 0.115 0.015 2.819

-2 0.873 0.444 0.429 0.597 0.498 0.513 0.498 0.827 0.161 0.261 0.130 0.130 0.100 0.015 0.100 5.575

-1 1.324 0.115 0.398 0.398 0.697 0.796 1.141 0.842 0.698 0.790 0.622 0.936 0.331 0.744 0.254 0.108 0.015 10.210

0 9.180 1.616 0.329 0.612 1.455 2.167 2.711 2.971 2.995 2.636 2.731 3.187 4.169 4.633 4.381 2.288 0.493 0.154 48.709

1 0.245 1.172 0.299 0.697 1.011 1.324 1.470 1.731 1.379 1.005 0.814 0.837 0.936 0.598 0.897 0.223 0.062 14.699

2 0.100 0.758 0.758 0.812 0.842 1.103 0.804 0.720 0.422 0.276 0.376 0.146 0.130 0.130 0.015 7.393

3 0.559 0.758 0.751 0.590 0.376 0.230 0.261 0.214 0.115 3.854

4 0.413 0.314 0.214 0.230 0.115 0.214 1.501

5 0.100 0.299 0.214 0.115 0.727

6 0.100 0.100

7

8

9

10

11

12

13

14

15

16

17

18

19

20

Totals 9.625 7.627 4.404 5.215 6.509 7.083 7.360 7.843 6.971 5.366 5.118 4.937 6.302 5.792 6.037 2.979 0.663 0.170 100.000

Summary Statistics

Avg Speed (mph) Time at Idle (%) Avg Specific PKE (hp-sec/lb) Min Speed (mph) Time at Cruise (%) Avg Total Specific Power (hp/lb) Max Speed (mph) Time in Accel (%) Avg Non-Zero Specific Power (hp/lb)

Avg Non-Idle Speed (mph) Time in Decel (%) Max Specific Power (hp/lb)

Avg Cruise Speed (mph) Avg Trip Length (miles) Spec Pwr Freq (%): 0 hp/lb

Avg Acceleration (mph/sec) Avg Trip Time (min) Spec Pwr Freq (%): >0-0.1 hp/lb Max Acceleration (mph/sec) # Stops per Mile Spec Pwr Freq (%): >0.1-0.2 hp/lb

Avg Deceleration (mph/sec) # of 1-Sec Observations Spec Pwr Freq (%): >0.2-0.3 hp/lb Max Deceleration (mph/sec) # of Trips Spec Pwr Freq (%): >0.3 hp/lb

EPA VSP (Vehicle Specific Power) Statistics

EPA Avg Veh Spec Pwr, VSP (kW/tonne) 4209.310

---------------------------------------------------------------------------------

Bin 0 % (braking) 8072.835

Bin 1 % (idle) 8762.598

------------------------------------------------------------------------ --------------------------------------------------------------------------------- ------------------------------------------------------------------------------------------------

Bin 11 % (0-25 mph, <0 kw/tonne) 4475.686 Bin 21 % (25-50 mph, <0 kw/tonne) 5249.241

Bin 12 % (0-25 mph, 0-3 kw/tonne) 4279.244 Bin 22 % (25-50 mph, 0-3 kw/tonne) 4570.025

Bin 13 % (0-25 mph, 3-6 kw/tonne) 3969.049 Bin 23 % (25-50 mph, 3-6 kw/tonne) 3521.147

Bin 14 % (0-25 mph, 6-9 kw/tonne) 2406.305 Bin 24 % (25-50 mph, 6-9 kw/tonne) 4886.247

Bin 15 % (0-25 mph, 9-12 kw/tonne) 1556.606 Bin 25 % (25-50 mph, 9-12 kw/tonne) 3852.850

Bin 16 % (0-25 mph, >=12 kw/tonne) 1273.095 ----------------------------------- 0.000 ----------------------------------- 0.000

Bin 27 % (25-50 mph, 12-18 kw/tonne) 3115.659 Bin 37 % (>50 mph, 12-18 kw/tonne) 6726.784

Bin 28 % (25-50 mph, 18-24 kw/tonne) 964.072 Bin 38 % (>50 mph, 18-24 kw/tonne) 4665.725

Bin 29 % (25-50 mph, 24-30 kw/tonne) 494.750 Bin 39 % (>50 mph, 24-30 kw/tonne) 1704.819

Bin 30 % (25-50 mph, >=30 kw/tonne) 112.219 Bin 40 % (>50 mph, >=30 kw/tonne) 581.568

34.73

0.00

83.20

38.14

42.06

1.22

5.81

-1.50

-9.05

9.625

59.088

16.092

15.195

8.888

14.789

0.721

2,003

2

6.29

0.0586

0.1319

0.6104

55.54

20.44

15.02

5.87

3.14

Bin 33 % (>50 mph, <6 kw/tonne) 5471.770

Bin 35 % (>50 mph, 6-12 kw/tonne) 5388.292
-60- 

1. Sacramento metropolitan area; 

2. San Francisco Bay Area; 

3. Stanislaus County (including the Modesto metropolitan area); and 

4. South Coast (i.e., Los Angeles) combined metropolitan area. 

These datasets contained driving in both urban and rural areas. In the post-processing 

that was performed under each of these studies, the type of roadway the vehicle was 

traveling on during each second was also recorded in the output dataset and categorized 

using the HPMS (Highway Performance Monitoring System) Functional Class scheme. 

These driving data were binned into urban and rural Functional Class groups and reweighted using California VMT weightings by functional class obtained from HPMS.*

 

Driving cycles for urban and rural light-duty operation in California were then developed 

from the data in these re-weighted groups. The second-by-second speed traces for these 

individual urban and rural cycles, called Cal-Urban and Cal-Rural, were then weighted 

together using a VMT-based split of 81.8% urban vs. 18.8% rural operation for California 

from HPMS. Figure 3-18 presents the SAFD and key statistics for this combined 

urban/rural driving cycle called ―CalWtd.‖

The tabulations for WMTC and CalWtd cycles contained in Figures 3-17 and 3-18 show 

that they are fairly similar. Average speeds are 35.9 mph and 34.7 mph, respectively. 

Top speeds are 77.9 mph for the WMTC and 83.2 for the CalWtd. Acceleration and 

specific power statistics are also generally comparable between the two cycles. Average 

VSP (based on EPA’s VSP definition) is 5.38 kW/tonne for the WMTC and 4.89 

kW/tonne for the CalWtd cycle. And the VSP distributions for both cycles are in 

relatively close agreement. 

Despite the aforementioned concerns regarding the origins and methods used to develop 

the WMTC, the statistical comparisons reflected in Figures 3-17 and 3-18 indicate that 

the WMTC appears to closely resemble overall driving patterns of light-duty vehicles. 

Thus, until additional motorcycle-specific driving data are collected, we believe 

motorcycle driving patterns can be reasonably represented with those of light-duty 

vehicles. 

3.6 Incorporation into MOVES Tables

The final element in the development of motorcycle emission and activity rates for 

MOVES consisted of translating the FTP-based exhaust and evaporative emission rates 

and activity data presented in the preceding sub-sections into the specific data tables used 

within the MySQL database underlying the MOVES model. These steps are described 

below, first for the emission rates, then the activity data. 

 

*

http://www.fhwa.dot.gov/policy/ohim/hs02/vm2.htm
-61- 

Motorcycle Emission Rate Tables – For the emission rate table, two key elements were 

performed to incorporate the basic exhaust and evaporative emission rates presented 

earlier in Table 3-5 into the specific tables and their data structures required by MOVES: 

1. Translation of FTP-based exhaust rates into emission rates by operating mode bin; 

and

2. Conversion of ―mode‖-based evaporative emission rates into new process-based 

evaporative emission categories. 

Translation of Running Exhaust Rates to Operating Mode Bins – A spreadsheet called 

MOVES_MC_EmissionRates_FT01.xls was developed to perform these detailed 

translations. (This spreadsheet was also provided to EPA as a deliverable on CD.) 

First, FTP-based running exhaust emission rates by model year range for HC, CO and 

NOx were translated into emission rates by individual VSP/speed bin based on an 

analysis of modal, second-by-second emission tests collected under an in-use motorcycle 

emissions surveillance study35 sponsored by CARB. Under that study, over 100 

motorcycles were randomly procured and FTP and Unified Cycle (UC) bag and 

composite emissions were measured. Second-by-second FTP and UC cycle emission 

measurements were collected for a 15 vehicle subset, although modal data for one UC 

test were missing. 

This modal emissions sample of 15 motorcycles ranged from model years 1966 through 

1996. Only one of these motorcycles was catalyst-equipped. Thus, given the size of the 

sample and available resources, no effort was made to divide the test data by age or 

model year range to reflect their effects on emission distributions by VSP bin. In the 

supporting analysis spreadsheets, separate relationships for non-catalyst vs. catalyst 

groups were developed and examined, but the resulting catalyst group bin allocations 

contained anomalies caused by the fact that the data were based on a single motorcycle 

(run over both FTP and UC cycles). Thus, given the sample of available modal data for 

motorcycles, a single set of emission rates by operating mode bin was developed simply 

from averaging of the entire 15-vehicle sample. 

Sierra performed fairly extensive data validation and cleaning on these modal emission 

test results prior to their use under this analysis. Second-by-second dilute concentration 

measurements were converted to a mass basis and properly time-aligned with the 

measured driving traces. This time alignment was carefully performed and applied on a 

test-by-test basis using comparisons of the second-by-second speed traces and dilute 

measurements. 

The time-aligned second-by-second mass exhaust emissions were then binned into 

MOVES-based operating mode/VSP bins by calculating second-by-second VSP using the 

speed traces, dynamometer coast-down data and vehicle weights recorded for each test 

from the following equation: 
-62- 

m

Av Bv Cv amv

VSP ttttt

t

32

where 

VSPt is vehicle specific power (kW/tonne) at time t; 

vt is vehicle speed (m/sec) at time t; 

at is vehicle acceleration (m/sec2) at time t; 

m is vehicle mass (tonne); and 

A, B and C are track road load coefficients, representing rolling resistance, 

rotational resistance and aerodynamic drag, in units of kW-sec/m, kW-sec2/m2

and kW-sec3/m3, respectively. 

(In the original modal motorcycle emissions testing study, track road load horsepower at 

50 mph and mass was measured and recorded for each vehicle . The A, B, and C values 

were then calculated from these measurements using 0.35, 0.10 and 0.55 weightings, 

respectively.) 

Note that the second-by-second VSP and mass emissions were binned only for the 

warmed-up portions (Bags 2 and 3) of the FTP and UC cycles. Modal measurements 

during Bag 1 were not used for this element of the analysis, which focused on 

development of stabilized/running exhaust emission allocations by VSP bin. 

Binned VSP and exhaust emission measurements over the stabilized portions of the FTP 

and UC tests were assembled in a separate spreadsheet called MC_OpModeBinned.xls. 

In the OpBinEmis sheet within this spreadsheet, a series of curve fits of HC, CO and NOx 

emissions vs. VSP were developed to address ―hole-filling‖ issues in bins where there 

were little or no data. From this 15-vehicle sample of modal FTP and UC cycle 

measurements, most of the operating mode bins contained at least 50 single-second 

observations. However, Bins 30, 39, and 40—which reflect high VSP ranges at the edge 

of, or beyond that, in the FTP or UC cycles—contained fewer observations. Upon 

examination, the 23 and 11 data points in Bins 30 and 39, respectively, were not found to 

substantially affect the resulting curve fits, so data in these bins were used. However, the 

few data points in Bin 40 were not included in the curve fitting process. 

These curve fits were developed using the following exponential equation: 

([ )] E

, ji EXP 10 VSPCC j

where 

Ei represents predicted emissions (g/hr) of pollutant i (either HC, CO or NOx) for 

operating mode bin j; 

VSPj is the measured mean VSP (kW/tonne) within each bin j; and 

C0 and C1 are least-squares derived coefficients determined separate for each 

pollutant and operating mode bin range (i.e., Bins 11-16, 21-30 and 31-40 using 

EPA’s numbering scheme as applied in MOVES). 
-63- 

Within the MC_OpModeBinned.xls analysis spreadsheet, the C0 and C1 coefficients were 

determined using Excel’s built-in ―Solver‖ utility. As noted above, separate curve fits 

were generated for each pollutant and set of operating mode bins within a speed range. 

Emissions for Bins 0 (deceleration/braking) and 1 (idle) were not based on curve fits but 

simple means of measured values within each of those bins. As shown in detail in 

highlighted cells inRows 91-207 and Columns N, U, and AC of the OpBinEmis sheet in 

MC_OpModeBinned.xls, these exponential curve fits generally produced correlations 

(expressed as R2) to the actual binned measurements in excess of 0.9 for each of the bin 

groups and pollutants. However, correlations for the high speed (> 50 mph) group 

covering Bins 31-40 were generally lower than those for the other speed groups—for this 

speed range, the correlation for NOx was only R2

=0.30. 

The resulting curve-fitted emission rates by operating mode bin (in grams/hr) reflect the 

emission levels of the 15-vehicle test sample upon which they were based, not the 

broader fleet of all on-highway motorcycles. Adjustments were made to translate the 

emission rates by bin from the test sample to hot-FTP ―allocation factors‖ that could be 

applied to the FTP-based fleet exhaust emission factors presented earlier in Table 3-5. 

The first step involved calculating composite emissions (in grams) from hot FTP 

weighting of the curve-fitted emission rates (in g/hr) each bin. In the OpBinEmis sheet, 

these composite emission calculations are performed in Column AD and Rows 218-236 

where the bin weightings are simply the number of seconds of observation in each bin 

over an FTP test. 

The second and final step consisted of normalizing the curve-fitted bin emission rates 

from the measured study sample by their composite hot FTP emissions calculated above 

to yield operating mode bin emission rates in g/hr per gram of hot FTP emissions. This 

step is reflected in the table within the OpBinEmis sheet in Rows 259-271 and Columns E 

through AC. 

These normalized bin rates could then be applied directly to the FTP-based fleet emission 

factors to generate running (hot) exhaust emission rates by operating mode bin for 

incorporation into MOVES. 

The modal motorcycle emission measurement study only measured HC, CO, NOx and 

CO2 exhaust emissions. PM exhaust measurements were not collected. Thus, the 

distribution of PM running exhaust by operating mode bin for motorcycles was assumed 

to be identical to that of gasoline-fueled passenger cars. Passenger car PM running 

exhaust emission rates were ―harvested‖ from the EmissionRatebyAge table in the Draft 

MOVES2009 database and loaded into the PMRatesOC and PMRatesEC sheets in the 

MC_OpModeBinned.xls file, for the organic carbon (OC) and elemental carbon (EC) 

components of exhaust PM, respectively. (Rates for both the OC and EC components 

were loaded from MOVES to confirm that the emission distributions by bin were the 

same for each, and they were.) A series of Excel pivot tables were generated in the 

PMPvts sheet to tabulate and aggregate these MOVES-based PM OC and EC rates across 

age and model year. These rates were then loaded into the OpBinEmis sheet and 
-64- 

normalized to a gram/hour per gram of hot-FTP basis across the operating mode bins as 

was done for the HC, CO, and NOx data from the modal study. 

The complete set of normalized running exhaust rates by operating mode bin for HC, CO, 

NOx, and PM (the latter separately as PM-OC and PM-EC) are presented below in 

Table 3-9. 

Table 3-9 

Normalized Motorcycle Running Exhaust Emission Rates (g/hr per gram Hot FTP) by 

Operating Mode Bin

Poll

Poll

ID

Running Exhaust Operating Mode Bin

0 1 11 12 13 14 15 16 21 22 23 34 25 27 28 29 30 33 35 37 38 39 40

HC 1 1.7 1.5 2.4 2.8 3.1 3.4 3.8 4.5 2.7 3.1 3.4 3.7 4.1 4.6 5.5 6.6 7.9 3.8 4.3 4.7 5.1 5.6 6.5

CO 2 1.7 1.2 1.9 2.2 2.4 2.6 2.9 3.3 2.9 3.4 3.7 4.0 4.4 5.0 6.0 7.1 8.7 7.6 8.5 9.1 9.8 10.6 12.0

NOx 3 1.3 0.6 0.8 1.1 1.5 1.9 2.5 4.0 3.3 3.8 4.2 4.6 5.0 5.7 6.9 8.3 10.1 13.7 14.4 14.8 15.3 15.8 16.7

PM-OC 111 1.5 1.8 2.0 2.4 2.5 3.6 5.4 17.7 2.2 1.8 2.1 2.9 5.8 8.5 44.4 128 365 4.6 4.1 5.7 9.7 24.7 27.1

PM-EC 112 1.5 1.8 2.0 2.4 2.5 3.6 5.4 17.7 2.2 1.8 2.1 2.9 5.8 8.5 44.4 128 365 4.6 4.1 5.7 9.7 24.7 27.1

The normalized rates were then loaded from the MC_OpModeBinned.xls file into the 

―main‖ spreadsheet used for translation to specific MOVES data tables and record 

structures, MOVES_MC_EmissionRates_FT01.xls, into a sheet called BinEmis.

Within the main MOVES_MC_EmissionRates_FT01.xls spreadsheet, motorcycle 

running exhaust emission rates by pollutant, model year, age, and operating mode were 

then calculated and stored within the MOVES_MC_EmissionRateByAge sheet, which is 

similar in field structure to the EmissionRateByAge data table in the MOVES database. 

(This sheet also housed the calculations of motorcycle emission rates for the other 

evaporative and crankcase emission processes required by MOVES explained later in this 

section.) The FTP-based fleet emission rates by model year range presented earlier in 

Table 3-5 were loaded into a sheet called FTPExh. Within this sheet, FTP emission 

factors were translated into ―Hot FTP/LA4‖ and Cold Start Increment‖ components using 

FTP bag measurements from the 15-vehicle modal motorcycle study sample discussed 

above and contained in the neighboring ColdHotFactors sheet in the 

MOVES_MC_EmissionRates_FT01.xls workbook. 

Beginning in Row 22 of the FtpExh sheet, the FTP-based emission factors, now separated 

into Running Exhaust and start Increment component, were asssigned to the specific set 

of model years or model year ranges mandated by EPA in MOVES for light-duty 

vehicles (and motorcycles). For the MOVES ModelYearIDGroup=19601980 (1980 and 

older models), this involved the development of separate allocation factors for the pre1978 and 1978-1985 model year groups for which motorcycle FTP rates were developed 

and shown earlier in Table 3-5. These allocation factors are contained in a sheet called 

MYGAlloc within the workbook. The splits for the 1980 and older range were based on 

default motorcycle data in MOBILE6. 
-65- 

In Column V (labeled RevRun) of the MOVES_MC_EmissionRateByAge sheet, the FTPbased running exhaust emission factors by pollutant and MOVES model year group (in 

g/mi) from the FTPExh sheet were then combined with the normalized running exhaust 

operating mode emission rates discussed earlier using a series of table lookups. The 

calculation was performed as follows: 

RunExhm,p,y (g/hr) = HotFTPp,y (g/mi) × 7.5 mi × OpModeERm,p (g/hr per g FTP) 

where HotFTP is the Hot FTP (Bag 3 + Bag 2) emission rate; OPModeER is the 

normalized distribution of FTP-based running exhaust emissions by operating mode; and 

indices m = operating mode, p = pollutant, and y = model year group. 

As explained earlier in Section 3.3, highway motorcycle in-use emissions deterioration is 

believed to largely result from tampering that occurs in the first few years of ownership. 

All of the assumed deterioration was modeled to occur in the first MOVES Age Group 

(0-3 years). Thus, Age Group was not incorporated in the above equation since 

motorcycle emissions were not assumed to vary by age after accounting for deterioration 

within this first 0-3 year old Age Group. 

Translation of Starting Exhaust Rates to Operating Mode Bins – Translation of FTPbased starting exhaust rates into the MOVES-required structures was much simpler than 

running exhaust. MOVES uses eight discrete operating mode bins to represent the 

starting emissions reflecting different soak time intervals ranging from <6 minutes 

(OpModeID=101) to ≥ 12 hours (OpModeID=108). Unlike with running exhaust, there 

were no motorcycle-specific emission test data available from which to develop start 

increment vs. soak time relationships by MOVES operating mode bin. 

In the absence of data, the distribution of starting exhaust emissions by MOVES 

operating mode bin for motorcycles was developed using starting exhaust rates extracted 

from MOVES for gasoline-fueled passenger cars. These extracted MOVES starting 

exhaust rates are contained in the PCStartRates sheet. A series of Excel Pivot tables 

were constructed from these passenger car starting exhaust rates in the StartPvts sheet, 

tabulating by model year group and operating mode bin for each pollutant. Separate 

tabulations were performed for two age groups (0-3 years) and (20+ years) at each end of 

the Age Group categories employed within MOVES to determine whether EPA has 

modeled age dependence into the distributions of starting exhaust rates, not their absolute 

levels, which are age dependent. It was confirmed that the normalized distributions 

(normalized to the >12 hour soak bin) are neither age nor model year dependent. 

These normalized starting exhaust emission distributions for each pollutant were then 

loaded into Rows 38-42 of the ColdHotFactors sheet. 

MOVES starting exhaust emission rates (in g/start) were then calculated in Column W 

(labeled RevStart) of the MOVES_MC_EmissionRateByAge sheet using lookup formulas 
-66- 

for these normalized distributions and the FTP Cold Start Increment rates by model year 

group (reflecting a >12 hour soak) contained in the FTPExh sheet as follows: 

StartExhm,p,y (g/start) = ColdFTPIncrp,y (g/start) × OpModeESm,p

Where ColdFTPIncr is the FTP cold start increment (Bag 1 – Bag 3); OPModeES is the 

normalized starting emission rate for a specific soak bin; and indices m = starting 

operating mode bin (soak bin), p = pollutant, and y = model year group. 

Translation of Crankcase Rates – In the MOVES database, crankcase emissions are 

represented in a separate data table called CrankcaseEmissionRatio. Motorcycle 

crankcase emissions were thus entered into a separate sheet in the main workbook called 

MOVES_MC_Crankcase that resembled the field structure of the corresponding MOVES 

table. MOVES requires that the emission rates in this table be stored as ratios of 

crankcase-to-running exhaust emissions. 

As discussed earlier in Sections 3.2 and 3.3, crankcase emissions on highway 

motorcycles were controlled starting in model year 1978 and no data were available to 

support an assumption of non-zero crankcase emissions from in-use deterioration for 

1978 and later motorcycles. Thus, crankcase ratios for all 1978 and later models were set 

to zero in the MOVES_MC_Crankcase sheet. 

As shown earlier in Table 3-5, crankcase emission rates for pre-1978 motorcycles were 

estimated to be 0.4 g/mi, reflecting an assumed 45%/55% split between two- and fourstroke engines for those models. (Two-stroke engines use a pressurized crankcase and do 

not have a crankcase vent; thus they have no crankcase emissions.) For pre-1978 models, 

the crankcase ratio for motorcycles was then simply calculated as: 

CC Ratio = 0.4 g/mi ÷ 10.6 g/mi (running exhaust FTP) = 0.0363 

and stored in the MOVES_MC_Crankcase sheet for HC and for these model years. 

Evaporative Emission Rate Conversions – As described earlier, the evaporative emission 

data compiled under this study consisted of one-hour SHED (hot soak and diurnal) 

measurements from roughly 20 highway motorcycles, plus ―resting loss‖ (i.e., non-heat 

build portion) and running loss estimates developed from real-time 24-hour evaporative 

tests of two off-highway motorcycles. These older tests had to be translated to represent 

the three evaporative processes defined in MOVES: 

1. Permeation – defined as the migration of hydrocarbons through elastomers in a 

vehicle’s fuel system; 

2. Tank Vapor Venting (TVV) – expulsion of fuel vapor generated from fuel 

evaporative within the fuel system; and 
-67- 

3. Liquid Leaks (LLs) – fuel in liquid form leaking from the fuel tank or fuel system 

which ultimately evaporates into the atmosphere. 

In addition, the ambient conditions and diurnal temperature changes reflected in the 

California evaporative test data had to be adjusted to reflect the reference conditions EPA 

established for these processes in MOVES: base permeation at 72°F and vapor venting 

based on a 72-96°F diurnal temperature change. 

Two different database tables are used in MOVES to store evaporative emission rate 

data: 

1. EmissionRateByAge – contains permeation, liquid leaker and ―hot soak‖ TVV 

rates; and 

2. CumTVVCoeff – contains ―cold soak‖ TVV coefficients used during MOVES 

execution to dynamically generated cold soak TVV emissions from hourly 

ambient temperature and tank fuel temperature changes. 

In the EmissionRateByAge table, MOVES uses a combination of the OpModeID and 

PolProcID fields to ―map‖ and store process-specific evaporative rates as shown below in 

Table 3-10. 

Table 3-10 

MOVES Evaporative Processes by Pollutant/Process and OpMode 

PolProcID

OpModeID

150 – Hot Soak 151 – Cold Soak 300 – All Running

111 – Permeation - - Base Permeation

112 – TVV Hot Soak TVV - Running Loss

113 - LL - Cold Soak LLs -

The first step in translating the one-hour SHED test data and running loss estimates for 

motorcycles into this structure consisted of assembling basic rates for the old evaporative 

process definitions (hot soak, diurnal, resting and running losses) by model year range. 

For federally certified motorcycles, three model year ranges were employed: (1) pre2004; (2) 2004-2007; and (3) 2008 and later. These rates, based on motorcycle 

evaporative estimates described in detail earlier in Sections 3.2 and 3.3, were loaded into 

the MOVES_MC_EmissionRates_FT01.xls workbook at the top of the FTPEvap sheet. 

MOVES base permeation rates (in g/hr) were calculated from the resting loss (non-heat 

build) rates (in g/day) by dividing by 24 and adjusting these rates to reflect the difference 

between the ambient temperature during which these resting loss emissions were 

measured, best estimated to be 70.5°F, and the 72°F reference temperature used by EPA 

from the following equation: 
-68- 

(0385.0 Tadj Tbase)

adj

base

e

P

P

Base permeation rates were calculated to be 0.117 g/hr for pre-2008 models and 

0.012 g/hr for 2008 and later models. As shown in Table 3-10, these base permeation 

emission rates were coded into the records in the EmissionRateByAge sheet for 

combinations of OpModeID=300 and PolProcID=111. 

Running loss rates were converted from grams per mile to grams per hour. A value of 

17.81 g/hr was applied to represent running loss emissions for federally certified 

motorcycles across all model year. Federal evaporative emissions standards for 2008 and 

later model years apply only to permeation; thus, running loss rates for all model years 

were estimated to be the same. In the EmissionRateByAge sheet, these running loss rates 

were applied for OpModeID=300 and PolProcID=112 records as noted in Table 3-10. 

As described in EPA’s MOVES Evaporative Emission Calculation Methodology,36 the 

―remaining‖ evaporative emissions from the hot-soak and diurnal portions of SHED test 

measurements are accounted for under the Tank Vapor Venting process in MOVES. 

First, hot soak TVV emission rates were calculated by subtracting out base effects from 

the hot soak SHED measurements using a five-step procedure detailed in Section 3.3.2 of 

the MOVES Evaporative Emission Calculation Methodology that accounts for tank 

temperature rise from the LA-4 cycle run prior to hot soak SHED measurement as well as 

temperature adjustments to the base permeation rates (at the 72°F reference temperature) 

to reflect the average temperature during the hot soak test. These calculations were 

performed in the TankTempCalc sheet and Rows 153 through 186 of the FTPEvap sheet 

in the MOVES_MC_EmissionRates_FT01.xls workbook. The resulting hot soak TVV 

rates by model year range were then loaded into the EmissionRateByAge sheet for records 

with OpModeID=150 and PolProcID=112 as indicated in Table 3-10. 

Second, diurnal SHED measurements were translated into cold soak TVV emission rates 

following these steps contained in Section 3.3.1 of the MOVES Evaporative Emission 

Methodology. For cold soak TVV emissions, MOVES first finds the amount of tank 

vapor generated (TVG) as a function of fuel tank temperature and RVP during the 

temperature rise portion of a 24-hour diurnal temperature profile based on the Reddy 

Equation.37

 

To perform these calculations in a manner consistent with the MOVES approach, the 

1-hour diurnal SHED measurements had to be translated to a real-time, 24-hour basis. 

These translations were based on regression equations developed from 1-hour and 

24-hour testing performed by Automotive Testing Laboratories (ATL) for CARB in 1994 

and cited in Section 5.3 of CARB’s EMFAC emission factor model technical support 
-69- 

documentation.* A linear regression of 1-hour to 24-hour diurnal emissions developed 

from 19 vehicles over a diurnal range of 60-84°F were used to convert the 1-hour diurnal 

measurements to an equivalent 24-hour basis as follows: 

24-Hour Diurnal = 1-Hour Diurnal × 1.303 + 4.902 (R2 = 0.46) 

(The ATL testing also included measurements over a 65-105°F range. However, only 

the 60-84°F data were used since they more closely resembled the 68-86°F temperature 

cycle used in the actual 1-hour diurnal measurements from the CARB Motorcycle 

Surveillance Testing study.19) 

Once these 1-hour to 24-hour diurnal adjustments were made, hourly permeation rates 

were calculated over the 68-86°F temperature cycle upon which the diurnal 

measurements were based. These permeation rates were then summed over the entire 

24-hour period and subtracted from the adjusted 24-hour diurnal emissions to calculate 

Total 24-Hour TVV emission rates by model year range. 

Within Rows 33-149 of the FTPEvap sheet, hourly Tank Vapor Generation rates (in 

g/gal) were then calculated over this temperature cycle as a function of the hourly 

temperature and the fuel RVP based on the Reddy Equation. Once the hourly TVG rates 

were known and summed over the entire 24-hour period, cold-soak TVV rates were then 

calculated by apportioning Total TVV based on the hourly TVG rates. 

In EPA’s MOVES Evapororative Emissions Methodology documentation,36 TVV rates 

for light-duty vehicles were determined based on polynomial curve fits of hourly 

measurements over a 24-hour diurnal test as a function of TVG using the following form: 

Total TVV = A0 + A1 TVG + A2 TVG 2

For motorcycles, these curve fits were not necessary since real-time diurnal 

measurements were not available. Thus, the second-order A2 coefficients described in 

this documentation were not applicable and were set to zero for the motorcycle cold-soak 

TVV rates. 

In the FTPEvap sheet, the non-zero A1 coefficient was then calculated simply as: 

A1 = Total TVV ÷Total TVG

In addition, since MOVES is designed to perform the TVV emission rate calculation 

dynamically during execution based on a user-selected geographic modeling area and 

associated diurnal temperature profiles, these cold-soak TVV rates themselves were not 

stored in the MOVES database. Instead, the calculated coefficients†

are stored within a 

 

*

http://www.arb.ca.gov/msei/onroad/doctable_test.htm

†

 In the MOVES Evaporative Emission Calculation documentation these coefficients are labeled A1 and A2. 

Within the MOVES database, these TVV coefficients are referred to as ―B‖ and ―C.‖ (The intercept 

coefficient A0 or A is set to zero, based on EPA’s constraint that the TVV curves pass through the origin.) 
-70- 

separate table in the database called CumTVVCoeff. A separate sheet named 

MOVES_MC_CumTVVCoeff within the MOVES_MC_EmissionRates_FT01.xls

workbook was created based on the field structure of the corresponding MOVES 

database table and used to store the calculated cold-soak TVV coefficients. 

Finally, Liquid Leak (LL) emission rates for motorcycles were assumed to be zero. This 

assumption was made because of the absence of liquid leak measurements specifically for 

motorcycles coupled with the inherent uncertainty in extrapolating LL rates from lightduty vehicles. This assumption also reflects the belief that, unlike cars and trucks, liquid 

fuel leaks from motorcycles are much more visible (i.e., puddles or drips are not hidden 

by the body/chassis) and that when detected, motorcycle owners would have their 

vehicles repaired in short order. 

All of the MOVES evaporative process emission rates as a function of OpModeID, 

PolProcID, and ModelYearGroupID were then assembled into a table in Rows 193-270 

of the FTPEvap sheet and used to populate the evaporative process-specific records 

within the EmissionRateByAge sheet in the MOVES_MC_EmissionRates_FT01.xls

workbook. 

Motorcycle Activity Data Tables – The updated motorcycle activity data described earlier 

in Section 3.5 were also converted into a series of Excel spreadsheets that conformed to 

the data structures of corresponding activity data tables in the MOVES database. The 

workbook MC_Activity_All.xls (provided on the delivery CD) was used to perform these 

conversions. Updated motorcycle activity data were provided for the six separate 

MOVES database tables listed below. 

1. SourceTypeAge – normalized survival rates and mileage rates with age 

2. SourceTypeAgeDistribution – normalized populations (registrations) with age 

3. SourceTypeYear 

4. HPMSVTypeYear 

5. SampleVehicleDay 

6. SampleVehicleTrip 

First, the survival fractions and mileage accumulation rates presented earlier in Tables 3-

6 and 3-7, respectively, are contained in the sheets SurvivalCurve and MARCalcs within 

the MC_Activity_All.xls workbook. The SourceTypeAge table of the MOVES database 

requires survival rates and annual mileage rates (normalized to a value of 1 at Age 0) for 

ages 0 through 30 years. The properly normalized survival rates and mileage rates with 

age were computed in the SurvivalCurve and MARCalcs sheets and loaded into a sheet 

within the MC_Activity_All.xls workbook called MOVES_MC_SourceTypeAge with the 

same field structure as the corresponding table in the MOVES database. 

Second, normalized registration distributions with age were computed from the 

population data by model year presented in Table 3-6 within the PopnAge sheet. These 
-71- 

normalized registration distributions were then loaded into the sheet named 

MOVES_MC_SourceTypeAgeDistribut in the MC_Activity_All.xls workbook. 

Next, updated motorcycle sales growth and migration rates for calendar years 2000 

through 2008 were calculated in the GrowthCalcs sheet and loaded into the 

MOVES_MC_SourceTypeYear sheet in the MC_Activity_All.xls workbook. It was 

necessary to calculate updated sales growth and migrates rates over this calendar year 

range (2000-2008) to account for differences between the default 2008 population 

projections contained in the MOVES database (projected from 1999 base year 

populations) and those obtained directly from MIC under this effort. 

VMT growth rates between 2000 and 2008 were similarly updated based on calculations 

performed in the PopnAge sheet and loaded into the MOVES_MC_HPMSVTypeYear

sheet. The updated VMT growth factors (expressed in MOVES as the change in VMT 

relative to the previous calendar year) between 2000 and 2008 were based on annual U.S. 

motorcycle VMT estimates by calendar year obtained from FHWA.*

Finally,the motorcycle-specific records in the SampleVehicleDay and SampleVehicleTrip 

database tables were updated using a FORTRAN program called SynTables09 to 

incorporate constraints on weekday (WD) vs. weekend (WE) trip ratios and activity. As 

noted earlier in Section 3.5, U.S. DOT crash data32 suggests the weekday/weekend 

activity split for motorcycles is about 40% weekdays and 60% weekends. (If motorcycle 

trip/activity rates were constant across all seven days, the weekend fraction would only 

be about 29%.) 

SynTables09 is a modified version of an earlier program called SynTables developed by 

Sierra under a 2007 MOVES-related EPA study.38 The earlier program was modified to 

ensure engine on-off trips by day of week matched this 40%/60% WD/WE split in the 

SampleVehicleDay and SampleVehicleTrip tables for motorcycles. 

MySQL Table Loading –The sheets in the MOVES_MC_EmissionRates_FT01.xls and 

MC_Activity_All.xls Excel workbooks containing the emission rate and activity data in 

structure identical to their corresponding MOVES database tables were exported to a 

series of comma-delimited (CSV) files. 

Two short MySQL batch scripts called Make_MOVESTable_MC_092809.txt and 

Load_MOVESTables_4-03_092809.txt were then written and executed to load the new 

emission rate data and updated activity data for motorcycles into the appropriate MOVES 

database tables in MySQL format. 

###

 

*

 FHWA Highway Statistics VM-1 Table VMT by Year 
-72- 

4. AIR TOXIC SPECIATION RATIOS 

Draft MOVES2009 currently relies on algorithms carried over from MOBILE6.2 that are 

used to calculate air toxic emissions from on-road vehicles. These algorithms cover the 

following seven species: benzene, 1,3-butadiene, formaldehyde, acetaldehyde, acrolein, 

naphthalene, and ethanol. The final analytical task under this effort envisioned 

development of new speciation ratios for a broader list of Hazardous Air Pollutants 

(HAPs) included in EPA’s National Mobile Inventory Model (NMIM) that were not 

included in Draft MOVES2009. 

This section of the report describes the work performed under this air toxics task. It 

begins with an explanation of the form of air toxic emission rates defined and used in 

MOVES and identification of the list of additional HAPs contained in NMIM that EPA is 

seeking to integrate into MOVES. It then presents separate discussions on the data 

assembled and emission rates for individual air toxic species estimated for light-duty 

gasoline- and heavy-duty Diesel-fueled vehicles, respectively.*

4.1 MOVES Speciation Ratios

Table 4-1 lists the additional HAP species that EPA is integrating into MOVES. Along 

with the MOVES PollutantID and NEI pollutant codes that uniquely identify each 

compound, it also lists the PollutantDisplayGroupID for each species. This value is used 

internally within MOVES to group pollutants/compounds into logical groups for which 

specific calculations or processing options are performed within the model. For the 

HAPs listed in Table 4-1, values of ―7,‖ ―8,‖ and ―9‖ refer to ―Additional Air Toxics,‖ 

Dioxins/Furans,‖ and ―Metallic Air Toxics,‖ respectively. 

The rightmost column in Table 4-1 (and the row shading) identifies whether each 

compound was included in the speciation ratios developed from the data sources 

employed under this effort. Values of ―G‖ and ―D‖ refer to those species represented in 

the light-duty gasoline and heavy-duty Diesel study datasets, respectively. Species for 

which no data were available from the datasets examined under this effort are noted with 

 

*

 EPA originally envisioned development of MOVES air toxic emission rates for other vehicle/fuel types 

including heavy-duty gasoline vehicles, heavy-duty Diesel using bioDiesel, light and heavy-duty CNG and 

LPG vehicles, as well as non-road engines. During the study, resources were re-prioritized into other tasks 

such that air toxic emissions for these other vehicle/fuel types were not considered. EPA plans to pursue 

development of MOVES air toxics rates for these vehicles under a separate study. 
-73- 

Table 4-1 

List of New MOVES HAPs and Numerical Codes

PollutantName

MOVES

PollutantlD

NEIPollutant

Code

Pollutant

DisplayGrouplD

Included 

in Study

2,2,4-Trimethylpentane 40 540841 7 G,D

Acenaphthene 41 83329 7

a D

Acenaphthylene 42 208968 7

a

D

Anthracene 44 120127 7

a

D

Benz(a)anthracene 45 56553 7

a D

Benzo(a)pyrene 46 50328 7

a D

Benzo(b)fluoranthene 47 205992 7

a

D

Benzo(g,h,i)perylene 48 191242 7

a

D

Benzo(k)fluoranthene 49 207089 7

a

D

Chrysene 50 218019 7

a D

Dibenzo(a,h)anthracene 51 53703 7

a

D

Ethyl Benzene 52 100414 7 G

Fluoranthene 53 206440 7

a D

Fluorene 54 86737 7

a

D

Hexane 55 110543 7 G,D

lndeno(1,2,3,c,d)pyrene 56 193395 7

a

D

Phenanthrene 57 85018 7

a

D

Propionaldehyde 58 123386 7 G,D

Pyrene 59 129000 7

a

D

Styrene 60 100425 7 G

Toluene 61 108883 7 G,D

Xylene 62 1330207 7 G

2,3,7,8-Tetrachlorodibenzo-p-Dioxin 301 1746016 8 -

1,2,3,7,8-Pentachlorodibenzo-p-Dioxin 302 40321764 8 -

1,2,3,4,7,8-Hexachlorodibenzo-p-Dioxin 303 39227286 8 -

1,2,3,6,7,8-Hexachlorodibenzo-p-Dioxin 304 57653857 8 -

1,2,3,7,8,9-Hexachlorodibenzo-p-Dioxin 305 19408743 8 -

1,2,3,4,6,7,8-Heptachlorodibenzo-p-Dioxin 306 35822469 8 D

Octachlorodibenzo-p-Dioxin 307 3268879 8 D

2,3,7,8-Tetrachlorodibenzofuran 308 51207319 8 D

1,2,3,4,6,7,8-Heptachlorodibenzofuran 309 67562394 8 -

1,2,3,4,7,8,9-Heptachlorodibenzofuran 310 55673897 8 D

1,2,3,4,7,8-Hexachlorodibenzofuran 311 70648269 8 -

1,2,3,6,7,8-Hexachlorodibenzofuran 312 57117449 8 -

1,2,3,7,8,9-Hexachlorodibenzofuran 313 72918219 8 -

1,2,3,7,8-Pentachlorodibenzofuran 314 57117416 8 D

2,3,4,6,7,8-Hexachlorodibenzofuran 315 60851345 8 D

2,3,4,7,8-Pentachtorodibenzofuran 316 57117314 8 -

Octachlorodibenzofuran 317 39001020 8 D
-74- 

Table 4-1 

List of New MOVES HAPs and Numerical Codes

PollutantName

MOVES

PollutantlD

NEIPollutant

Code

Pollutant

DisplayGrouplD

Included 

in Study

Mercury (elemental gaseous) 201 200 9 -

Mercury (divalent gaseous) 202 201 9 -

Mercury (particulate) 203 202 9 D

Arsenic & compounds 204 93 9 D

Chromium (Cr3+) 205 16065831 9 -

Chromium (Cr6+) 206 18540299 9 -

Manganese 207 7439965 9 D

Nickel 208 7440020 9 D

a Pollutants within the 16-compund Polycyclic Aromatic Hydrocarbon (PAH) group (that also includes 

naphthalene) defined by EPA that occur in both gaseous and particle phases. 

a dash (―-‖) symbol. As indicated in this column, measured test data were found for 

most, but not all, of the additional HAPs identified for inclusion in MOVES. 

Within MOVES, air toxic emission rates are calculated based on toxic ―speciation ratios‖ 

that represent the mass emission fraction of an individual species relative to VOC 

(volatile organic compounds) or PM (particulate matter) of the following form: 

 Speciation Ratio = Species Mass Emission Rate / VOC Mass Emission Rate 

 or 

 = Species Mass Emission Rate / PM Mass Emission Rate 

Speciation ratios for those compounds listed Table 4-1 with on-road measurement data 

were calculated by dividing the species emission rate by the VOC emission rate for the 

gaseous compounds (those with PollutantDisplayGroupID=7 or 8) or by the PM emission 

rate for metal-based compounds (PollutantDisplayGroupID=9). Within MOVES, these 

speciation ratios are multiplied by either VOC or PM emission rates as appropriate to 

produce air toxic emission rates (in grams per hour) by vehicle type, model year, etc. and 

generate composite rates for the vehicle fleet. 

There was one exception to this basic approach. Polycyclic aromatic hydrocarbons 

(PAHs) identified as footnoted in the PollutantDisplayGroupID column in Table 4-1 are 

found in multiple phases: (1) gas phase, (2) particle phase, and (3) as semi-volatile 

organic compounds. As explained later in Section 5.3, multi-phase apportionment of 

PAH species measurements were performed based on factors from EPA’s SPECIATE 

database. 
-75- 

Thus, the basic approach to this task consisted of reviewing literature and previous testing 

study datasets in which either individual air toxic emission rates were measured in 

conjunction with measurements of denominator pollutant emission rates or speciation 

ratios were developed from these measurements. EPA requested development of separate 

speciation ratios by vehicle type (i.e., SourceType), model year range or certification 

standards group (e.g., Tier 0, 1, 2), and fuel type where sufficient data were available. 

Given this overall approach, the remaining two sub-sections provide further detail on the 

assembly of data and development of speciation ratios for light-duty gasoline and heavyduty Diesel-fueled vehicles, respectively. 

4.2 Light-Duty Gasoline-Fueled Ratios

Development of light-duty gasoline-fueled toxic speciation ratios was relatively 

straightforward. Of the nearly 50 additional toxic species listed earlier in Table 4-1, 

measurement data and ratios were available for seven species for light-duty gasoline 

vehicles. 

Ratios for Tier 1 and earlier (model year 2003 and earlier) vehicles were assembled from 

SPECIATE model profiles39 developed for EPA by ENVIRON. Separate speciation 

ratios were developed for exhaust and evaporative emission processes and the following 

fuels/blends: gasoline (i.e., E0), E10 (10% ethanol, by volume), and E85 (85% ethanol). 

Table 4-2 presents these Tier 1 and earlier speciation ratios assembled from the 

ENVIRON study.

Table 4-2 

Tier 1 and Earlier Light-Duty Gasoline Vehicle Speciation Ratios

Pollutant

Name

Exhaust Emission Ratio Evaporative Emission Ratio

Gasoline E10 E85 Gasoline E10 E85

2,2,4-Trimethylpentane 0.01823 0.01849 0.00898 0.01984 0.03354 0.01949

Ethyl Benzene 0.02147 0.01932 0.00222 0.02521 0.01721 0.00651

Hexane 0.01570 0.01593 0.00213 0.02217 0.02536 0.00606

Propionaldehyde 0.00086 0.00087 0.00019 n/a n/a n/a

Styrene 0.00108 0.00097 0.00022 0.00000 0.00000 0.00043

Toluene 0.09619 0.08657 0.00813 0.09643 0.14336 0.05193

Xylene a0.07814 0.07032 0.00699 0.07999 0.06423 0.02205

n/a – not available 

a

 Xylene is reported as the sum of O-xylene and M- and p-xylene. 
-76- 

Toxic speciation ratios for Tier 2 and later vehicles (model year 2004 and newer) were 

based on SPECIATE model profiles developed by EPA.40 There were only exhaust 

emission data available for Gasoline and E10. No evaporative emission profiles or E85 

profiles were available. Table 4-3 lists these available Tier 2 speciation ratios. 

Table 4-3 

Tier 2 Light-Duty Gasoline Vehicle Speciation Ratios

Pollutant

Name

Exhaust Emission Ratio

Gasoline E10

2,2,4-Trimethylpentane 0.0319 0.0123

Ethyl Benzene 0.0168 0.0166

Hexane 0.0028 0.0291

Propionaldehyde 0.0012 0.0005

Styrene 0.0009 0.0008

Toluene 0.0754 0.0744

Xylenea0.0613 0.0605

a

 Xylene is reported as the sum of O-xylene and M- and p-xylene. 

4.3 Heavy-Duty Diesel-Fueled Ratios

Diesel-fueled speciation ratios were calculated from emission measurements that were 

assembled into a comprehensive spreadsheet database that was assembled under the 

Coordinating Research Council (CRC) E-75 study.41 This database organized speciated 

exhaust emission measurements from on-road medium- and heavy-duty Diesel vehicles 

from several earlier studies that are listed in Table 4-4. 

The E-75 database is a large spreadsheet with information from the prior testing studies 

organized into individual sheets as summarized below. 

Engine_Data – Contains descriptive data of the vehicle/engine that was tested, 

such as make/manufacturer, vehicle type, engine application, model, model year, 

engine size, horsepower, etc. 

Fuel_Data – Lists basic name or type of fuel used for each test (e.g., conventional 

Diesel, bioDiesel, low-sulfur Diesel, etc.) and properties (cetane number, sulfur, 

oxygen, aromatic content, etc.) of that fuel. 
-77- 

Table 4-4 

Study Data Represented in CRC-75 Speciation Database

Study Name Vehicles Tested

Model Years 

Covered

Southwest Research Institute (SwRI) School Bus Study 2 school buses 2001 

SwRI study for the Ad Hoc Diesel Fuel Test Program 1 LDDV N/A 

New York City Clean Diesel Demonstration Program 2 Diesel transit buses 1999 

California Institute of Technology 2 MHDDT, 2 HHDDT 1995 1987 

BP Southern California ultra-low sulfur Diesel 3 HDDT 1996-1999 

(ULSD)/DPF/CNG Heavy-duty study 1 transit bus 1 school bus 1998 1998 

SwRI Fischer-Tropsch study 2 HDD engines 1999, 2000 

CRC Mass vehicle tests 16 LDDVs 1977-1994 

CRC AVFL-10a & 10b 4 LDDV/T, 

~110 L/HDDV 2004 1978-2000 

CE-CERT 14 HDDT, 28 LDDV/T 1996-2000 1983-

1999 

Gasoline-Diesel particulate matter (PM) Split Study 30 HDDT 2 buses 1982-2001 1982, 

1992 

CRC E55/59 1 MHDDT 8 HHDDT 1997 1985-2003 

Desert Research Institute 4 LDDV 4 Diesel trucks 1991, 1998, 1999, 

2000 N/A 

Environment Canada 1 LDDT 2 urban buses 1998 1989, 1998 

Pollutant_List – Provides a cross-referenced list of nearly 1,000 individual 

pollutant species represented in the assembled test data that included primary and 

alternate pollutant names, Chemical Abstracts Service (CAS) numbers, and 

pollutant ID codes. 

Test_Cycle – Provides a description for each of the test cycle codes used in the 

database that identified the driving cycle over which emission measurements for 

each test were collected. 

Emissions – The emissions data were stored in several individual sheets broken 

into the following compound groups: regulated pollutants (e.g., THC, CO, NOx, 

PM, etc.), carbonyls, dioxins/furans, PAHs, speciated hydrocarbons, SVOCs and 

elements/inorganic compounds (i.e., metals). 

The data records in each of the individual sheets in the E-75 database could be related or 

linked to one another using Project ID, Study ID, and Test ID fields contained in each 

sheet that uniquely identified data for a specific emission test. 
-78- 

Data Processing and Validation – Despite the organization of the E-75 spreadsheet, 

development of toxic speciation ratios for heavy-duty Diesel vehicles was much more 

involved than for the gasoline-fueled vehicles because a number of quality assurance 

checks, data linkage processes, and record culling steps had to be performed. A modified 

version of the original E-75 database called MOVES_AT_Speciations_Diesel_E-75.xls

was created in which these steps were performed. (Both the original and modified E-75 

spreadsheet databases are included on the delivery CD.) These processing steps are 

summarized below. 

Removal of Invalid Data – Data that had ―bld,‖ ―N/A,‖ ―nd,‖ or ―-99‖ entries in 

either the Emission or Emission Unit columns were excluded. 

Assembly of Paired Measurements – Paired measurements for the same vehicle 

and test that have both toxic emission measurements (numerator) and regulated 

emission measurements (denominator) were located in different sheets within the 

database. They were combined into a single sheet in the spreadsheet called 

AllPollutants by lookup formulas based on ProjectID, StudyID, and TestID fields 

in each individual sheet in order to calculate speciation ratios. In a number of 

cases, paired measurements of both the numerator and denominator measurements 

were not found using this lookup approach. Further investigation of these cases 

indicated that some of the mismatches occurred from incorrect entries (e.g., typos) 

in one of these three lookup fields (usually the TestID field) as originally stored in 

the database. Where it was obvious that this type of error had been made, 

corrective edits were made to values in the lookup fields to properly retrieve both 

the toxic species emission measurement and the paired ―denominator‖ or base 

pollutant measurement for the same vehicle and test. 

Unit Conversions – In a number of instances, the emission units for the paired 

measurements were different. In these instances, the denominator emission unit 

was converted to a numerator emission unit to properly calculate the toxic 

speciation ratio. In some cases, incompatible emission units were observed—for 

example, if the numerator emission unit was ―mg/mile‖ and the denominator unit 

was ―g/mode.‖ (The testing studies included both transient cycles and steadystate modes.) In these cases where incompatible units were observed, the paired 

measurements were excluded. 

Removal of Non-Conventional Fuel Tests – The E-75 database included test 

measurements from a number of research studies for which a variety of Diesel 

blends and other alternative fuels were used. For this analysis, EPA directed 

Sierra to exclude all tests for fuels other than those that reflect conventional or 

low-sulfur Diesel blends currently or recently in-use within the U.S. As a result, 

tests for all other types of fuels contained in the E-75 database were excluded or 

removed from further analysis. These non-conventional blends included FischerTropsch, bioDiesel, ethanol-Diesel blends, emulsified fuel, European blends, and 

other obvious research fuels. 
-79- 

MOVES Source Type Categorizations – Based on vehicle description, engine 

application, make, and model entries in the Engine_Data sheet, classifications of 

vehicles into the MOVES SourceType scheme were performed when possible. In 

many cases, such for vehicles marked as ―Refuse Hauler‖ or ―School Bus,‖ it was 

simple to assign the appropriate SourceType category. For others, internet 

searches performed based on manufacturer, model, and engine size clearly 

revealed the type of heavy-duty vehicle application (e.g., single- vs. combinationunit or delivery vehicle). In instances were there was ambiguity, a missing code 

was simply entered for the SourceTypeID field. The purpose behind these 

categorizations was to enable development of separate speciation ratios by 

SourceType for use in MOVES. However, once the categorizations were made 

and sample sizes were tabulated by SourceType, it became apparent that 

insufficient data were available for most of the SourceType categories containing 

Diesel-fueled vehicles. Given these small sample sizes, subsequent tabulations of 

Diesel speciation ratios under this effort were not SourceType-specific, but based 

on averages across all valid SourceTypes. (However, these SourceType 

categorizations were preserved for later use when these data are combined with 

other datasets for which MOVES SourceType categorizations are needed.) 

Removal of Non Heavy-Duty Vehicle Tests – When performing the SourceType 

categorizations, a small number of tests were found to have been included in the 

E-75 database for light-duty Diesel vehicles (e.g., Volkswagen Jetta and Toyota 

Corolla, Ford F-250). Because of the decision described above to simply 

calculate average speciation ratios across all valid vehicle types due to insufficient 

sample sizes), it was jointly agreed with EPA to remove these few light-duty 

vehicle tests from the validated E-75 sample. Thus, the resulting speciation ratios 

were solely representative of heavy-duty Diesel vehicles. 

Outlier Treatment – A simple screening threshold of 0.5 was used to filter and 

remove data with implausible speciation ratios. Ratios greater than or equal to 0.5 

are considered as outliers and the data for these test records were removed from 

the final, validated sample contained in the AllPollutants sheet of the 

MOVES_AT_Speciations_Diesel_E-75.xls file. 

Treatment of Multi-Phase PAH Species – In addition to the data processing and 

validation steps described above, additional processing was performed for the PAH 

compounds identified earlier in Table 4-1. This additional process was performed to 

account for the fact that PAHs occur in multiple phases: gas phase, particle phase, and as 

SVOCs. 

Multi-phase allocation factors were developed for the 15 individual PAH species 

contained in Table 4-1 using estimates from EPA’s SPECIATE4.2 database42 where 

available. For species where allocations were not found in the SPECIATE database, 

emissions were estimated to occur either in the gas or particle phase based on each PAH 
-80- 

compound’s physical properties. Those with lower molecular weights tend to be volatile, 

and were allocated to the gas phase; ―heavy‖ higher weight compounds with higher 

molecular weights were allocated to the particle phase. 

Table 4-5 summarizes the multi-phase allocation factors used to apportion emission rates 

for individual PAH compounds to the gas and particle phases. In the E-75 database, the 

speciation data were organized in a manner that identified whether the test measurement 

reflected the gas phase, particle phase, or both phases. If a test record was marked as 

―Gas Phase,‖ the speciation ratio calculated from the specie (numerator) and base 

(denominator) pollutant emission rates was adjusted by the Gas Phase fraction listed in 

Table 4-5. This adjustment was applied similarly for those records identified as ―Particle 

Phase‖ tests. When the E-75 Phase field indicated the measurements were collected in 

both phases, no PAH allocation adjustments from Table 4-5 were used. PAH records for 

which no information was recorded in the Phase field were assumed to be collected in 

particle (PM) phase. 

Table 4-5 

Mult-Phase PAH Allocation Factors Used

PAH Species

Molecular

Weight

Allocation Fraction

PM Phase Gaseous Phase Reference

Acenapthene 154 0 1 EPA/SPECIATE

Acenaphthylene 152 0 1 EPA/SPECIATE

Anthracene 178 0.466 0.534 EPA/SPECIATE

Benz(a)anthracene 228 0.723 0.277 EPA/SPECIATE

Benzo(a)pyrene 252 1 0 Sierra Research

Benzo(b)fluoranthene 252 1 0 Sierra Research

Benzo(g,h,i)perylene 276 0.773 0.227 EPA/SPECIATE

Benzo(k)fluoranthene 252 1 0 Sierra Research

Chrysene 228 0.823 0.177 EPA/SPECIATE

Dibenzo(a,h)anthracene 278 1 0 Sierra Research

Fluoranthene 202 0.516 0.484 EPA/SPECIATE

Fluorene 166 0.215 0.785 EPA/SPECIATE

Indeno(1,2,3-cd)pyrene 276 1 0 Sierra Research

Phenanthrene 178 0.335 0.665 EPA/SPECIATE

Pyrene 202 0.552 0.448 EPA/SPECIATE

Heavy-Duty Diesel Speciation Ratios – Once the processing, validation, and PAH 

allocations were completed, average speciation ratios for each available toxic pollutant 

were then calculated across all vehicle types and model years represented in the validated 
-81- 

sample. Table 4-6 below shows these mean speciation ratios, along with the sample sizes 

(number of vehicle tests) and standard deviations (to provide a sense of the variation of 

the individual observations). 

Table 4-6 

Heavy-Duty Diesel Speciation Ratios and Basic Statistics

Pollutant Name Pollutant Group Count Average Std Dev

1,2,3,4,6,7,8-HpCDD DioxinFuran 1 1.95E-10 n/a

1,2,3,4,7,8,9-HpCDF DioxinFuran 1 2.49E-11 n/a

1,2,3,7,8-PeCDD DioxinFuran 1 5.14E-12 n/a

2,2,4-trimethylpentane TOG-VOC-NMOG 43 1.90E-03 5.19E-03

2,3,4,6,7,8-HxCDF DioxinFuran 1 1.98E-11 n/a

2,3,7,8-TCDF DioxinFuran 1 4.11E-11 n/a

Acenaphthene PAH 105 2.46E-04 5.75E-04

Acenaphthylene PAH 104 7.49E-04 1.63E-03

Anthracene PAH 102 1.44E-03 6.70E-03

benz[a]anthracene PAH 115 2.49E-04 9.87E-04

benzo[a]pyrene PAH 101 9.44E-04 7.48E-03

benzo[b]fluoranthene PAH 15 1.17E-05 1.07E-05

benzo[ghi]perylene PAH 89 1.08E-05 3.97E-05

benzo[k]fluoranthene PAH 13 6.52E-06 1.09E-05

Chrysene PAH 115 7.87E-05 1.39E-04

dibenz[ah]anthracene PAH 2 2.12E-06 1.80E-06

Fluoranthene PAH 123 1.72E-03 7.85E-03

Fluorine PAH 108 2.20E-03 7.21E-03

Hexane TOG-VOC-NMOG 38 2.07E-03 7.21E-03

indeno[123-cd]pyrene PAH 88 8.40E-06 2.47E-05

OCDD DioxinFuran 1 7.71E-11 n/a

OCDF DioxinFuran 1 6.94E-11 n/a

Phenanthrene PAH 106 2.80E-03 9.31E-03

Propionaldehyde carbonyl 60 4.91E-03 7.34E-03

Pyrene PAH 123 1.95E-03 8.75E-03

Toluene TOG-VOC-NMOG 49 4.54E-03 5.17E-03

As Pm 95 1.67E-05 4.63E-05

Hg Pm 98 4.87E-05 1.33E-04

Mn Pm 98 3.57E-05 8.00E-05

Ni Pm 97 2.65E-05 4.69E-05

###
-82- 

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