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Air Pollution Emissions from Highway Vehicles: 

What MOVES Tells Us 

Megan Beardsley, Jim Warila, Gary Dolce, John Koupal 

U.S. Environmental Protection Agency 

2000 Traverwood Drive, Ann Arbor, Michigan 48015 

mobile@epa.gov 

ABSTRACT 

The U.S. Environmental Protection Agency is developing the Motor Vehicle 

Emission Simulator (MOVES) to estimate air pollution emissions from cars, trucks and 

other mobile sources. When complete, MOVES will replace EPA's MOBILE and 

NONROAD models. The EPA has created a draft version of MOVES that incorporates 

extensive new data and advanced algorithms to better estimate highway vehicle 

emissions of greenhouse gases, criteria pollutants and selected air toxics. This paper 

summarizes how MOVES differs from MOBILE6 in terms of capabilities, inputs, and 

preliminary results. 

INTRODUCTION 

 Since 1978, the U.S. Environmental Protection Agency has used computer models 

to estimate emissions from cars, trucks and other mobile sources. The initial MOBILE 

model was expanded many times over the years to incorporate new data on vehicle 

emissions, new vehicle emission standards and to better address new policy questions,1

but the basic structure of the model has remained constant. MOBILE uses average gram 

per mile emission rates and a series of correction factors to estimate emissions over a 

wide range of driving conditions. 

MOBILE6.22

, finalized in 2004, is EPA's current official model for highway 

vehicle emissions. It is used for EPA internal policy analyses and is required for use 

(outside California) in the evaluation of State Implementation Plans (SIPs) and 

transportation conformity determinations.3

A number of analysts have critiqued the MOBILE series of models.4

 In 2000, the 

National Research Council prepared an evaluation that recommended a number of design 

changes for MOBILE.5

 They suggested that EPA develop a modeling "toolkit" that 

would better serve the range of uses for highway vehicle modeling, including consistent 

modeling at the aggregate scale, mesoscale, and microscale analysis. The model should 

integrate the modeling of criteria pollutants, air toxics, greenhouse gases and fuel 

consumption. 

In response to these and other concerns, EPA has developed the Motor Vehicle 

Emissions Simulator (MOVES). MOVES incorporates extensive new data and advanced 
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algorithms to better estimate highway vehicle emissions of greenhouse gases, criteria 

pollutants and selected air toxics at the national, regional and project level. A draft 

version of MOVES is planned for release in spring 2009. A final version for highway 

vehicles is planned for release in December 2009. 

MOVES CAPABILITIES 

MOVES greatly extends the capabilities of MOBILE6, allowing significantly 

greater flexibility in modeling choices and offering a variety of tools designed to ease the 

use of the model in a variety of use cases. Draft MOVES2009 calculates highway 

vehicle emissions of greenhouse gases, criteria pollutants and selected air toxics. It also 

calculates energy consumption. Emissions are calculated for all the significant vehicle 

emission processes: running emissions, start emissions, evaporative emissions, extended 

idle emissions, crankcase emissions, tirewear and brakewear. 

In response to criticisms of MOBILE, MOVES was designed to allow easier 

incorporation of large amounts of in-use data from a variety of sources. MOBILE was 

written in Fortran, and many data elements were hard-coded, making them difficult to 

update. MOVES is written in Java and MYSQL, and data elements are stored in database 

tables. 

Like MOBILE6, MOVES adjusts emissions to account for changes in vehicle 

mix, fuel properties, temperatures, and speeds. Unlike MOBILE6, MOVES is designed 

to estimate emissions at multiple geographic scales. MOBILE6 emissions rates were 

based on regional-scale trip pattern, while MOVES emissions are based on operating 

modes, and thus can be customized to the unique driving patterns in a particular region or 

project area. 

MOVES has a menu-driven interface to guide users as they set up and execute 

MOVES runs. The interface includes graphical display to help users define their desired 

model run and a variety of data importers to help users create appropriate input files. 

MOVES also includes a command-line interface to facilitate batch runs. MOVES can be 

run on a single computer, or set up in a "master/worker" configuration, allowing 

distributed processing. Users can model the impacts of particular policy options using 

built-in tools. Current policy tools include vehicle inspection/maintenance (I/M) 

programs, retrofits of vehicle equipment, and the phase-in of alternative fuels and 

advanced technology vehicles. 

MOVES allows users to output emissions either in MOBILE6-like gram-per-mile 

emission factors or in total mass for a given area and time. Users can select the desired 

level of output detail through the user interface, and can apply database processing tools 

to further customize reports. 
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MOVES INPUTS 

In MOBILE6, emissions were calculated from default information in block data, 

supplemented with information provided by the user in input text files. In MOVES, 

default information is contained in a default input database. Hypothetically, users can 

run MOVES using all default data, all new data, or anything in-between. In reality, the 

inputs that users bring to the model will depend on the situation being modeled and the 

purpose of the modeling. EPA is preparing detailed technical guidance on the 

requirements for users running the model to prepare SIP inventories and conformity 

determinations. 

Generally, users are not expected to modify the default MOVES emission rates. 

The default rates were developed by assessing millions of vehicles. For Light Duty 

Vehicles, emission rates for hydrocarbons (HC), carbon monoxide (CO) and oxides of 

nitrogen (NOx) from existing vehicles were derived from ten years of second-by-second 

data from Arizona's Inspection/Maintenance (I/M), with comparisons to other I/M 

programs and remote sensing data. Particulate Matter (PM) emissions were derived 

from a major new EPA study in Kansas City6. Heavy Duty emissions were derived from 

more than 300 in-use vehicles in a number of detailed studies. 

Many of user inputs expected by MOVES are similar to those previously used in 

MOBILE6. For example, information on age distributions, local fuels and local 

temperatures are essential inputs for any accurate estimate of emissions. MOVES differs 

however, in that the categories for these inputs have changed. For example, MOBILE6 

has 28 vehicle categories, generally based on vehicle weight ratings, while MOVES has 

only 13 categories, based on observable characteristics (e.g. combination vs. single unit 

trucks) and typical use (e.g. long haul vs. short haul). The EPA is developing converters 

to allow users to automatically convert MOBILE6 inputs into MOVES formats. 

MOVES new capabilities also require new inputs. In particular, because MOVES 

can calculate inventories as well as gram per mile emission rates, MOVES relies on input 

of Vehicle Miles Travelled (VMT). The MOVES design also recognizes that vehicle 

starts and evaporative activity may not be well correlated with VMT, and thus relies on 

vehicle population estimates to calculate these emissions. 

In another example of how new capabilities require new inputs, MOBILE6 

allowed users to enter a speed distribution or an average speed for a run. MOVES also 

allows input of a speed distribution, but it can also accept specific driving cycles or 

operating mode distributions, allowing the user to model emissions resulting from 

changes in driving behavior. 

MOVES can work with inputs at the national level, with allocation to specific 

counties if desired; or MOVES can work at the county or project level, with inputs 

specific to that time and place. 
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PRELIMINARY RESULTS 

MOVES updated data and advanced capabilities enhance our understanding of 

vehicle emissions. To begin to understand how MOVES emissions differ from MOBILE6 

emissions, we ran some simple comparisons with a preliminary draft version of MOVES. 

Comparing MOVES and MOBILE6 is better done for specific local areas, as it is easier 

to align the inputs for the two models on a smaller scale, and because national default 

inputs in MOVES would not fully capture the individual variation between nonattainment 

areas. 

To best characterize the comparison most relevant for U.S. nonattainment areas, 

we ran the preliminary draft version of MOVES for three sample cities: a medium-sized 

city in the western U.S., a large city in the north central U.S., and a large city in the 

Southeast. For these preliminary runs, we used local data submitted to the U.S. EPA as 

part of the National Emission Inventory effort. This data included local information on 

the age distribution of the fleet, the fraction of light-duty and heavy-duty VMT, local fuel 

characteristics, and temperature data. This allowed us to match the activity and other 

inputs between MOVES and MOBILE and to simulate local data that would be used in a 

SIP. However, the inputs were simplified and may not be completely consistent with 

data that the state would actually use in preparing a SIP for the city. 

For 2008, 2015 and 2020, we ran this data through the MOBILE6.2 model (using 

the National Mobile Inventory Model (NMIM)) and through MOVES, adjusting inputs as 

necessary to fit MOVES data categories. Our results were generally consistent between 

the three cities, with decreases or little change in hydrocarbon (HC) emissions, moderate 

increases in nitrogen oxides (NOx) and significant increases in particulate matter (PM). 

Figures 1-3 illustrate these trends for the northern city in our sample. 

Figure 1. Hydrocarbon emissions in example northern city

City A - HC

0

10000

20000

30000

40000

50000

60000

2008 2015 2020

Annual Tons

M6

M6

M6

MOVES

MOVES

MOVES

HD

HD

LD LD
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Figure 2. Nitrogen Oxide emissions in example northern city

Figure 3. Particulate Matter emissions in example northern city 

CONCLUSIONS 

The results of our preliminary comparisons were consistent with our 

understanding of the changes in underlying emission rates. In MOVES, light duty cars 

and trucks tend to have similar or lower HC emissions than in MOBILE6. This is 

because new exhaust and evaporative emissions test data has demonstrated that 

MOBILE6 was overly pessimistic in estimating how emissions from mid-1990s and later 

City A - NOx

0

10000

20000

30000

40000

50000

60000

70000

80000

90000

2008 2015 2020

Annual Tons

MOVES

MOVES

MOVES

M6

M6

M6

HD

HD

LD LD

City A - PM2.5

0

1000

2000

3000

4000

2008 2015 2020

Annual Tons

MOVES

MOVES

MOVES

M6 M6

M6

HD

HD

LD LD
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vehicles would increase with age. Light duty trucks tend to have higher NOx emissions 

than forecast by MOBILE6, and heavy duty trucks tend to have higher NOx than 

estimated from the engine certification tests used in the MOBILE6 analysis – in part due 

to higher brake-specific emissions from in-use trucks, and in part due to the differences 

between real-world operation and the certification test. Extended idle NOx emissions 

were also given a much more careful treatment in MOVES than in MOBILE6; given 

default assumptions about extended idle activity and the projected lack of control from 

NOx aftertreatment devices during extended idle operation, they are projected to form a 

large portion of the future-year heavy duty NOx inventory. The growth in light-duty PM 

emissions from MOBILE6 to MOVES reflects the higher emissions and strong 

temperature dependence that we saw in the Kansas City study.7,8 The growth in heavyduty PM reflects new information on in-use vehicles9

 and new analysis of emission 

deterioration. MOVES also adjusts PM emissions for speed, which MOBILE6 did not 

do, which leads to a very large difference in emissions between the two models at lower 

speeds typical of congested urban operation. 

The implications of the changes in emission estimates for SIPs will depend on 

local conditions and regulatory requirements. Higher NOx and PM emissions from 

mobile sources will impact local air quality modeling and will increase the role of mobile 

source control measures in attainment demonstrations. However, it is important to note 

that for attainment analysis, a key measure is the percent reduction in emissions from the 

analysis base year. In our limited analysis, we saw a greater percent reduction for PM in 

MOVES than in MOBILE6, but a lower percent reduction for NOx. 

Table 1. Percent Reduction in On-Road Emissions, 2008 to 2015 

City A City B City C 

MOVES MOBILE6 MOVES MOBILE6 MOVES MOBILE6

HC 50% 50% 39% 32% 38% 31% 

NOx 54% 56% 40% 52% 36% 53% 

PM2.5 57% 40% 52% 40% 38% 23% 

REFERENCES 

 

1 U.S. Environmental Protection Agency, Description and History of the MOBILE 

Highway Vehicle Emission Factor Model, February 2004. 

http://www.epa.gov/otaq/models/mob_hist.txt 

2

 U.S. Environmental Protection Agency, MOBILE6.2, March 2006. 

http://www.epa.gov/otaq/models/mobile6/mobile62.zip 
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 3

 Oge, M.T. and Page, S., Memorandum to EPA Regional Air Division Directors, Policy 

Guidance on the Use of MOBILE6.2 and the December 2003 AP-42 Method for ReEntrained Road Dust for SIP Development and Conformity, February 24, 2004. 

4

 Pollack, A.K.; et al., Evaluation of the U.S. EPA MOBILE6 Highway Vehicle Emission 

Factor Model, Coordinating Research Council Project E-64, March 2004. 

5

 National Research Council. Modeling Mobile-Source Emission, Committee to Review 

EPA's Mobile Source Emissions Factor (MOBILE) Model, Board on Environmental 

Studies and Toxicology, Transportation Research Board. 2000. 

6 Nam, E.; et al., Analysis of Particulate Matter Emissions from Light-Duty Gasoline 

Vehicles in Kansas City, EPA420-R-08-010, April 2008 

http://www.epa.gov/otaq/emission-factors-research/420r08010.pdf

7

 U.S. Environmental Protection Agency, Kansas City PM Characterization Study,

EPA420-R-08-009, April 2008. http://www.epa.gov/otaq/emission-factorsresearch/420r08009.pdf 

8

 Nam, E.; et al., Analysis of Particulate Matter Emissions from Light-Duty Gasoline 

Vehicles in Kansas City, EPA420-R-08-010, April 2008 

http://www.epa.gov/otaq/emission-factors-research/420r08010.pdf

9

 Clark, N; et al, Heavy-Duty Vehicle Chassis Dynamometer Testing for Emissions 

Inventory, Air Quality Modeling, Source Apportionment and Air Toxics Emissions 

Inventory, Coordinating Research Council Report No. E-55/59, August, 2007. 

http://www.crcao.org/reports/recentstudies2007/E-55-59/E55_59_Final_Report_23AUG2007.pdf