EPA-420-P-98-028
Geographic Allocation of State Level Nonroad Engine
Population Data to the County Level
Report No. NR-014
September 16, 1998
Greg Janssen
Mike Sklar
Nonroad Engine Emission Modeling Team
Assessment and Modeling Division
EPA, Office of Mobile Sources
I. Purpose
The purpose of this report is to discuss the methodology and data that the Nonroad
Engine Emission Modeling Team (NEEMT) decided to use in the NONROAD model to allocate
equipment populations from the national to the county level.
II. Background
The NEEMT is developing a national nonroad air emissions inventory model called
NONROAD. This model will provide a tool for EPA, States, regional air pollution
organizations, and local air pollution control agencies to use in estimating pollution from
nonroad vehicles and equipment for State Implementation Plans (SIPs), as required by the 1990
Clean Air Act Amendments, and other regulatory needs.
The model uses national engine population data from Power Systems Research (PSR), a
company that tracks the sales and populations of all types of engines sold in the U.S. Since PSR
also matches the engines to the equipment in which they are used, the term "equipment
populations" will be used for the purpose of this report. The NEEMT believes that PSR provides
the most comprehensive national nonroad equipment population data currently available. PSR
updates these data on a yearly basis.
The PSR database also geographically allocates equipment populations from the national
to the county level and then aggregates the county-level populations to generate state totals.
However, the methods and data that PSR uses to perform these allocations have only been
explained in general terms, since PSR considers their methods to be proprietary information.
Since the NEEMT wants the methods that it uses to allocate equipment populations in
NONROAD to be fully understood by EPA and the public, we have decided to use publicly
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available data as much as possible to serve as factors to allocate the national PSR equipment
populations to the county level. State and local users may elect to substitute well-documented
specific local (i.e., county, nonattainment area) equipment population data gathered by
conducting surveys or from some other local source that they believe is more accurate.
III. Allocating Activity Versus Engine Population
One central feature of the NONROAD model is that it uses the same methods to allocate
engine populations, engine activity, and engine emissions to specific geographic areas. To the
extent that engines are operated at the same power level and for the same number of hours in all
areas, the distribution of engine populations will match the distribution of engine activity and
engine emissions. In general, population, activity, and emissions will tend to track one another,
since emissions are a direct function of engine activity and the conditions that stimulate increased
engine activity are likely to stimulate increased engine populations.
In reality, however, the geographic distribution of nonroad engines may differ from the
geographic distribution of emissions from those engines. The amount of activity that each piece
of nonroad equipment of a given type experiences can vary from area to area as a result of
variations in local economies, weather patterns, or other local conditions. For example,
agricultural equipment and residential lawnmowers may experience more use per year in areas
with longer growing seasons; construction equipment is likely to be used more intensively in
areas experiencing an economic boom and less intensively where the economy is not as robust.
Currently, NONROAD is capable of handling only one activity level for each equipment
type across all parts of the U.S. As a result, the model uses the same factors to allocate engine
populations and their associated activity. Wherever possible, the NEEMT has sought indicators
of engine activity, since it is engine activity that results in emissions (except for diurnal and hot
soak emissions, which are more closely related to engine populations). In some cases, however,
the NEEMT was unable to find a suitable activity indicator and had to rely on population
indicators as a surrogate for engine activity. In this report, the NEEMT has attempted to be
explicit as to whether each equipment type's geographic allocation factor is an activity-oriented
indicator, a population-oriented indicator, or an indicator that is reasonable for both population
and activity.
For several equipment categories, the NEEMT has had particular difficulty finding either
activity or population indicators for several equipment categories. These categories include
recreational, railway maintenance, and AC/refrigeration equipment. The NEEMT welcomes
suggestions from the nonroad industry, state and local air quality agencies, and other interested
parties concerning improved methods to allocate these equipment categories to the county level.
The NEEMT also invites state and local air quality agencies to substitute adequately documented
local data for the national default allocation estimates, in accordance with EPA guidance, for
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these categories and for other categories such as recreational marine engines where the national
default estimates may not adequately reflect local conditions.
The NEEMT plans to initiate an effort to develop methods to perform surveys of nonroad
equipment activity at the county level that state, regional and local air agencies will be able to use
to collect local data for input into NONROAD. This effort may include a pilot program that
focuses on recreational equipment and recreational marine vessels. The NEEMT has not found
fully satisfactory default geographic allocation factors for these categories, which comprise a
large part of the total nonroad emission inventory. The initial pilot project is envisioned to
include three parts:
1) performing a review and analysis of known survey methods that have been used by state and
local air agencies to collect local nonroad equipment activity data,
2) choosing one of the survey methods reviewed and analyzed in part 1 or developing a new
method to be included in EPA guidance to state and local air agencies, and
3) applying the chosen method to selected areas to ensure that it works properly and produces
reasonable and useful results.
If this effort proves to be successful, the NEEMT will consider developing guidance on creating
improved local population and activity estimates for other categories, such as construction and
lawn and garden equipment. The NEEMT welcomes suggestions and comments about this effort,
as well as information about surveys of nonroad equipment that have been conducted in the past
or are presently being conducted, from stakeholders and other interested parties.
IV. Methodology
Since the NONROAD model only has the ability to allocate equipment populations from
the state to the county level, the national PSR population data for each equipment type must be
processed outside of the model to allocate these data to the state level. The same equation and
allocation factors that the NONROAD model uses to allocate equipment populations from the
state to the county level are applied to the PSR national equipment populations to allocate them
to the county level, since these allocation factors are county-based. The county equipment
populations are then aggregated by equipment type for each state to produce the total state
equipment population input files used in the model. Due to the large amount of data that needs
to be manipulated, modifying the model so that it could do all of this processing would increase
the time it takes NONROAD to run a scenario beyond reasonable limits.
The NONROAD model uses information related to equipment population or activity to
distribute the state equipment populations and their associated activity to the county level. This
information constitutes a geographic allocation factor. The model can use a single allocation
factor for entire categories of nonroad equipment, or it can use separate factors for one or more
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equipment types within a category. The model multiplies the state population of the equipment
type by the ratio of the county level allocation factor to its state total. In essence, the allocation
factor serves as a surrogate for population or activity. Mechanically, the model assumes that
each type of equipment experiences the same annual activity, which reduces the allocation
problem to one of allocating engine populations. The basic calculation is as follows:
(Equip. Population)county = (Equip. Population)state x Surrogate,.^,
Surrogatestate
V. Sources and Types of Data
There are three basic types of data that are potentially useful as allocation factors:
population, business activity, and geographic data. Most of these data are available from the U.S.
Census Bureau or other federal agencies except for data concerning construction activity, which
is discussed separately below. Information from the U.S. Census Bureau is especially attractive
for use in the NONROAD model because census data undergo rigorous statistical analyses and
quality assurance reviews.
Population Data
The U.S. Census Bureau conducts a nationwide census on a decennial basis. The census
includes data on population, housing (e.g., number of homes by type, number of occupants per
home), and income. The most recent census occurred in 1990. The Census Bureau produces
updated human population estimates on an annual basis, but does not produce an annual update
for housing or income data.
Business Activity Data
The U.S. Census Bureau publishes an annual report called County Business Patterns
(CBP), which tracks the number of establishments and employees for various types of businesses
and industries at the national and county level using Standard Industrial Codes (SICs). The most
recent CBP data covers 1995. EPA used County Business Pattern indicators to allocate state-
level populations to the county level for the 1991 Nonroad Engine and Vehicle Emissions Study1
(NEVES).
Geographic Data
Geographic data include factors related to an area's location or physical characteristics.
Such factors include water or land surface area, weather data, and land use data. Such data are
available from government agencies such as the U.S. Census Bureau, the National
Oceanographic and Atmospheric Administration, and the U.S. Geological Survey.
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VI. Allocation of Specific Populations Equipment Categories/Types
The allocation indicators that the NEEMT examined and selected for use in the draft
version of the NONROAD model are discussed below. The indicators chosen for use in the draft
version of the model and the revisions being planned for the final version are summarized in
Table 1 at the end of this report.
Residential Lawn and Garden Equipment (except snowblowers)
To allocate lawn and garden equipment used by private households, the NEEMT plans to
use U.S. Census data on one and two unit housing (i.e., single family homes and duplexes) by
county from the USA Counties database. Structures containing more than two units tend to be
condominiums or apartments that use commercial lawn care services. One and two unit housing
information is used as an allocation factor in the NEVES, and an analysis of this set of data
during the writing of the NEVES showed that it provided a good predictor of lawn and garden
equipment populations. In addition, the NEEMT has not been able to find alternative types of
data to use as an allocation factor for residential lawn and garden equipment that offer the high
quality, the necessary county-level detail, and the predictive strength of one and two unit housing
data from the U.S. Census Bureau.
The one and two unit housing data found in the USA Counties database and used in the
draft version of the model come from the 1990 census. As stated in section V, housing
information is only updated during each decennial census. However, using the 1990 one and two
unit housing data will cause the model to underestimate lawn and garden emissions in more
urbanized parts of the country because of the continuing creation and growth of suburbs in
counties that were still partially or largely rural in 1990. To try to address this underestimation
for the final version of the model, the NEEMT plans to try to account for this growth by
adjusting the housing data by a ratio of 1997 human population estimates to human population
data by county from the 1990 Census. It should be noted that if the 1997 human population
estimate for a county is less than the 1990 census value, then the 1990 single and double housing
unit value for that county will remain unadjusted. In such cases, the relative longevity of most
housing structures suggests that the number of one and two-unit housing sites would not decline
as quickly as human population. For counties which experienced an increase in population
between 1990 and 1997, the equation to adjust the housing unit data is as follows:
1997 Adjusted Housing = 1990 Housing x 1997 human population estimate
1990 census human population
This adjustment could result in an overestimation of lawn and garden emissions to the extent that
a disproportionate share of the population growth in the county is housed in multi-unit housing.
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Any such overestimate would be offset by a concomitant underestimate in the growth in
commercial lawn and garden activity levels.
One and two unit housing is most properly thought of as a population allocation factor for
residential lawn and garden equipment. The population of such equipment in an area should be
roughly proportional to the number of single and double housing units in the area, since the
average household occupying such units would have the average probability of owning any given
type of lawn and garden equipment. But the amount of use such equipment experiences may
vary considerably from area to area based on such variables as the average size of yards, length of
growing season, and amount of rainfall. Allocation factors based on residential lawn and garden
equipment gasoline consumption, tons of yard waste removed, or the land area occupied by
single and double housing units could, in principle, provide a more direct measure of activity.
However, the information regarding such potential activity allocation factors are either not
available, of questionable quality, or subject to confounding influences that make the potential
allocation factor even less reliable than the one used in NONROAD.
Commercial Lawn and Garden Equipment (except snowblowers)
To allocate commercial lawn and garden equipment, the NEEMT plans to use the number
of employees in landscape and horticultural services (SIC 78) from the CBP database. The 1991
NEVES study uses this factor to allocate commercial lawn and garden equipment. An analysis
performed during the writing of the NEVES shows that the number of employees in landscape
and horticultural services is a good predictor of commercial lawn and garden equipment
populations. In addition, the NEEMT does not know of any other sources to adequately serve as
a geographic allocation factor for commercial lawn and garden equipment.
The number of employees in landscape and horticultural services is better suited for
allocating the population of commercial lawn and garden equipment than the activity associated
with this type of equipment. The level of mechanization in the landscape services industry is
likely to be relatively constant from county to county. By contrast, the number of hours per year
that the average piece of commercial lawn and garden equipment operates is likely to vary
considerably from county to county as a result of different growing seasons and rainfall patterns.
Reliable information on allocation factors more directly related to activity levels, such as gallons
of fuel consumed per county and year by commercial lawn and garden equipment, are not
available.
One caveat for using the number of employees in landscape and horticultural services to
geographically allocate commercial lawn and garden equipment populations is that this factor
does not include municipal employees that perform landscape maintenance duties for schools,
parks, and other properties owned and maintained by local governments. The implicit
assumption used in NONROAD is that the population and activity level of such equipment is
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proportional to commercial lawn and garden equipment population and activity levels. The
NEEMT welcomes comments from interested parties concerning methods or sources of data that
can better account for lawn and garden equipment used by municipal landscape employees.
Snowblowers
Allocating snowblower populations and activity levels requires the use of allocation
factors that account for the impact of climatic differences among regions, in addition to the
factors used to allocate residential and commercial lawn and garden equipment. Put simply,
snowblower populations and activity levels depend on snowfall. Snowblower populations in
warm-weather states like Florida, Louisiana, and Hawaii should be zero. Snowblowers may be
present in parts of states such as Texas and California because part of their territories receive
snow (e.g., Texas Panhandle, Sierra Nevada Mountains in California), while snowblower
populations in other parts of the state should be zero.
The approach chosen by the NEEMT involves examining the National Oceanographic
and Atmospheric Agency (NOAA) long-term average snowfall data for major U.S. metropolitan
areas and reallocating snowblower populations only to those areas that receive at least a certain
minimum amount of annual snowfall. Since NONROAD cannot perform this reallocation
internally, the NEEMT will reallocate snowblower populations manually and will revise the
input files accordingly for the final release of NONROAD. Due to time and resource constraints,
snowblower populations at the state and county levels have been set to zero for the draft version
of the model to avoid misallocation problems. However, the model will still calculate national
annual snowblower emissions.
Construction Equipment
Initially, the NEEMT planned to use the number of employees engaged in construction by
county (CBP SIC 15) to geographically allocate construction equipment. However, early
comments from some stakeholders correctly pointed out that using this indicator could lead to
errors in estimating construction equipment population and activity in a county because
construction employees and equipment move from project to project, often crossing county lines.
In some parts of the county, such as the Northeast, construction employees and equipment may
cross state lines quite frequently. The CBP data only reflect where construction employees and
establishments are headquartered, not where they work.
The NEEMT believes that the dollar value of construction offers the best means available
to allocate construction equipment activity to counties. The dollar value of construction provides
a good reflection of activity, since there is a proportional relationship between the dollar value of
construction and the amount of construction activity in a given area. Also, using the dollar value
of construction by county as an allocation factor will distribute construction equipment to where
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it is actually being used, as opposed to where it is headquartered. Furthermore, this indicator
provides a reasonable allocation factor for construction equipment populations: competitive
forces encourage construction companies to obtain the maximum return on their investments in
costly pieces of construction equipment by maximizing their use as much as possible, thereby
strengthening the correlation between construction activity and construction equipment
population.
Data on the dollar value of construction is collected and maintained by the Census Bureau
only for metropolitan statistical areas (MSAs) instead of counties. Construction valuation data
by county for 1997 is available from the F.W. Dodge Company. The NEEMT plans to use the
F.W. Dodge data in NONROAD to allocate construction equipment to the county level.
Agricultural Equipment
For this category, the NEEMT considered using the number of employees involved in
agricultural work by county as an allocation factor (CBP SIC 78), as was used in the NEVES.
However, this allocation indicator may not correlate well with either agricultural activity or
agricultural equipment populations. A small number of agricultural employees in a county could
cause the model to underestimate the population and activity of agricultural equipment if the
predominant type of farming in that county is highly automated or relies on migrant labor that is
recorded as being based in a different county. Conversely, a large number of agricultural
employees in a county could cause the model to overestimate the population and emissions of
agricultural equipment if the predominant type of farming is labor intensive or if migrant labor is
recorded as being based in the county. Instead, NONROAD uses the acreage of cropland
harvested by county to allocate agricultural equipment populations and activity. This information
is available from the U.S. Census Bureau's USA Counties database. It should be noted that in
some cases where a county only contains a few small farms the Census Bureau does not publish
crop acreage data out of a concern for confidentiality. However, agricultural equipment
emissions in a county that only has a few small farms are likely to be small relative to other
nonroad sources within this county and to agricultural equipment emissions in other counties
within the state where farms and agricultural equipment are more numerous.
Using the amount of harvested cropland as an allocation factor provides a good predictor
of agricultural equipment activity, since a proportional relationship generally exists between the
amount of cropland harvested and how much equipment activity is needed to prepare the land
and plant, maintain, and harvest the crops. However, the amount of cropland harvested does not
necessarily provide as accurate a predictor of agricultural equipment population as it does for
activity for several reasons. First, the same amount of cropland in a county can be plowed,
planted and harvested by a few pieces of large equipment or several smaller ones. Second, the
amount of equipment present in a county may be more dependent on the number of farms than on
the amount of acreage harvested (although this source of inaccuracy in estimating populations
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may be mitigated by the presence of equipment-sharing arrangements in areas with smaller
farms).
Recreational Marine Equipment
Because the county in which the equipment is purchased, registered, and/or stored may
not be the same county where the equipment is used, the geographic allocation of recreational
marine equipment presents a significant challenge. An urban or suburban county where a boat is
sold, registered, and/or stored may not contain a body of water that can support recreational
marine traffic, or water bodies near where a boat owner lives may be overcrowded. Small and
medium recreational marine craft, which constitute most of the recreational marine fleet, can be
transported by trailer over a wide area, further complicating matters. Thus, sales and registration
data are not sufficient to accurately allocate recreational marine equipment to the county level.
Fuel consumption would provide a direct measure of recreational marine activity, but such data
are not collected specifically for recreational boating.
The NEVES report estimated the population of boats actually being used in each of the 24
urban nonattainment areas covered by the NEVES through the use of data from a 1991 National
Marine Manufacturers Association survey of boat owners.2 These data included where the boat
owners said they primarily operated their boats, where the boats were registered, the boat owners'
estimates of the amount of hours they used their boats per boating season, and their estimates of
the amount of fuel their boats consumed per boating season. In general terms, the data from these
surveys were used to adjust registration-based boat populations so that only the boats actually
operating within the nonattainment area (as opposed to boats registered in the nonattainment area
but used elsewhere) were included when calculating the recreational marine emissions for each
area addressed in the NEVES. In order to check the reasonableness of the NMMA-based results,
the total square miles of water surface area in a nonattainment area, the estimated square miles of
water surface area needed for a typical boat to operate, and the maximum number of possible
hours per boating season in each nonattainment area were used to ensure that the use of NMMA
survey data did not result in a boat population estimate that exceeded the maximum number of
boats that could theoretically operate during the boating season of a particular area. If the
NMMA-based boat population estimate exceeded the theoretical maximum, then this population
was adjusted downward.
This method cannot be incorporated into the current design of the NONROAD model, but
at least some of its elements might be adapted to allocate recreational marine equipment
populations and the activity associated with them to specific counties within a state for direct
input into the NONROAD model. A limitation of the NEVES method was that it focused solely
on urban areas. Since most boating tends to occur outside of urban areas, it is likely that NEVES
significantly underestimated recreational marine emissions in the U.S. In order to be usable for
the NONROAD model, the NEVES method would have to be modified to estimate the
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population and accompanying activity of recreational marine equipment being used in both urban
and non-urban counties. Also, new survey data would need to be collected, since much of the
1991 NMMA survey data are most likely outdated. This would be especially true in regard to the
rapid population growth and usage of personal watercraft (jet skis), which also would have
different activity profiles from other types of boats.
Presently, the NONROAD model allocates recreational marine populations using water
surface area data by county from the U.S. Census Bureau. However, using this type of data has
some limitations. Water surface area does not make a distinction between navigable bodies of
water and those that are too shallow for boating or have obstructions through which boats are
unable to pass. Also, water surface area does not account for convenience of location (proximity
to areas of significant population) or the recreational quality of the water body (which includes
such factors as its attractiveness for fishing, its visual appeal, and its water quality), both of
which could be expected to affect a body of water's recreational marine activity per unit area.
Lastly, water surface area alone does not account for access restrictions that may prevent boating
or limit the number of boats permitted to operate on a given body of water. However, even with
these limitations, the NEEMT has decided to use water surface area as an allocation factor for the
allocation of equipment populations because either the other potential approaches described
above have even greater limitations or, as in the case of the NEVES approach, additional work is
needed to determine the best way to adapt the approach to be compatible with NONROAD (or
vice versa) and collect the data necessary to implement the approach.
The NEEMT hopes to conduct a study to investigate ways to improve upon the water
surface area allocation method currently used in the model and also explore whether there might
be other methods and data available to use in NONROAD to better allocate the population of
recreational marine equipment for all of the counties in the U.S. Local surveys of recreational
boating activity focusing on things such as marina and boat ramp usage offer the most accurate
means to assess boat populations and activity at the county level. One early stakeholder comment
suggested using data on boating violations and accidents to allocate recreational marine
equipment. Surveys better capture the actual activity on local lakes, rivers, and other waterways,
as well as account for boats registered in one county but used in another. If States, regional air
organizations, and local air pollution control districts have such types of data, then the NEEMT
is interested in learning about them. Furthermore, EPA encourages state, regional, and local air
organizations to use these local data in the NONROAD model for county-level boat populations,
subject to appropriate guidance.
Recreational Equipment (except for snowmobiles and golf carts)
The allocation of recreational equipment, such as all terrain vehicles (ATVs) shares the
same challenge as the allocation of recreational boats, namely where the equipment is registered,
purchased, serviced, and stored is usually not the location where the equipment is actually used.
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Because of convenience, people tend to purchase recreational equipment, like other products,
near where they live. Hence, most recreational equipment is purchased in urban and suburban
areas, where the majority of the U.S. population lives, and this equipment also is registered,
stored and serviced in these areas. However, there are relatively few places in urban and
suburban areas where it is possible and legal to operate recreational equipment. Generally
speaking, recreational equipment usage tends to be concentrated in rural and semi-rural areas
near a metropolitan area; such areas are conveniently accessible to the owners of most of the
recreational equipment, have more area that is attractive for recreational equipment use, and tend
to impose fewer restrictions on recreational equipment use than more densely populated areas.
Thus far, however, the NEEMT has not found an adequate allocation factor that can be used with
the current allocation method contained in the model (discussed in Section HI, Methodology) to
reflect this population/activity distribution pattern.
The NEVES report used CBP data set SIC 557 (number of motorcycle establishments) to
allocate recreational equipment to the county level. However, this data is not available for one or
more counties in some States. The NEVES report also used SIC 55 (number of employees in
auto dealerships and service stations), of which SIC 557 is a subset. Neither of these data sets
provide a reasonable allocation factor for recreational equipment because most motorcycle
establishments, auto dealerships and service stations are located in urban and suburban areas
instead of rural and semi-rural areas where most recreational equipment activity occurs.
Registration data also exist for ATVs in most States, but there may be some cases where
these data are not available or up to date. Sales data also are available from PSR or
manufacturers. However, using registration or sales data as allocation factors presents the same
drawback as using the CBP data: the location of population does not correlate well with the
location of recreational equipment activity outside of heavily urbanized or suburbanized areas.
The NEEMT has considered using the simple alternative approach of allocating
recreational equipment population and activity based on the inverse of population or population
density (i.e., the higher the population or population density of a county, the less recreational
equipment activity is allocated to that county). The NEEMT has also considered allocating
activity based on the amount of non-urbanized land area per county within a State. While these
approaches would reduce the risk of overestimating urban activity, they would tend to
overestimate activity in remote rural areas, such as the North Slope of Alaska, Michigan's Upper
Peninsula, the Mojave Desert, or the Texas Panhandle. Yet another approach would use
employment or Gross Domestic Product (GDP) economic activity directly associated with
recreational equipment usage to allocate recreational equipment. However, the NEEMT has been
unable to locate these data at the county level. The CBP database does not include recreational
equipment GDP data, and the Bureau of Economic Analysis (BEA) only tracks GDP data down
to the state level.
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Given these problems, the NEEMT has chosen to use the number of camps and
recreational vehicle park establishments (CBP SIC 7030) in the draft version of NONROAD.
CBP SIC 7030 includes sporting and recreational camps, trailer parks, and campsites. The data
subset from CBP SIC 7030 containing the number of establishments offers better coverage of the
U.S. than the subset containing the number of camp and recreational vehicle park employees.
The data subset containing the number of employees appears to be missing information for areas
known to contain national and state parks, near which camps and recreational vehicle parks are
likely to be located. The NEEMT acknowledges that this approach may not adequately account
for recreational equipment being used on private and public lands that are not associated with
and/or adjacent to camps and recreational vehicle parks. In addition, using the number of camps
and recreational vehicle parks as an allocation factor is only loosely correlated to the level of
recreational equipment activity occurring in a county. At the present time, however, the NEEMT
is not aware of other allocation methods that are both practical and reasonably accurate. The
NEEMT welcomes suggestions of alternative methods and requests reviewers and stakeholders
with such suggestions to share them with the team.
Golf Carts
Golf carts have a different pattern of usage from other types of equipment in the
recreational category. Unlike ATVs or snowmobiles, golf carts are predominantly used in a
central location (golf courses), which is usually within or close to an urban/suburban area. The
NEEMT initially planned to use public golf course employees (CBP SIC 7992) as an allocation
factor for this equipment type. However, the NEEMT has discovered that these data are
incomplete for many counties in the U.S. For example, no employees of golf courses are
reported for the state of Colorado. Since another allocation factor has not yet been selected to
replace the number of public golf course employees, the draft version of NONROAD uses this
factor as a temporary place holder. For the final version of the model, the NEEMT believes that
using number of golf courses by county may provide the best means available for allocating golf
carts. The NEEMT has examined data on the number of golf courses from the CBP SIC 7992
data and hopes to examine similar data from another source, such as the Professional Golf
Association (PGA), to ensure that NONROAD uses the most robust set of data available.
Using the number of golf courses to allocate golf carts and their emissions to the county
level does not provide a precise reflection of golf cart population or activity. Like the allocation
factor presently being used to allocate the other types of recreational equipment (the number of
camps and recreational vehicle parks), the relationship between the number of golf courses on the
one hand and the population and activity level of golf carts and on the other is a loose one. The
population and activity of golf carts at a given golf course depends on the size, popularity, and
type of course. A large, popular, 36-hole championship golf course will have more golf carts that
are used more intensively than a small, less intensively used 9 hole course. The location of a golf
course also affects golf cart activity. A golf course adjacent to an urban area or in a suburban
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area will tend to have more players than one located in a rural area, resulting in higher golf cart
activity at the urban or suburban course. An additional complication is that many golf courses
use electrically powered carts instead of carts using gasoline-powered engines. However, the
NEEMT does not know of any nationally applicable allocation factors that account for these
influences. In the case of golf carts, the use of local activity and/or population data may be the
best alternative. The NEEMT welcomes comments from stakeholders and other interested
reviewers concerning the existence of better factors or methods to allocate golf carts from the
state level to the county level, as well as sources of local data on golf cart activity and/or
population.
Snowmobiles
The allocation of snowmobile activity presents the same challenges as for other
recreational equipment and uses the same allocation factor, the number of camps recreational
vehicle park establishments, used by other recreational equipment types, except golf carts. In
addition, climatic factors must be considered, since snowmobile activity is restricted to areas that
receive significant snowfall. These climatic factors are similar to those related to snowblowers,
except that snowmobiles need more snow on which to operate than do snowblowers and require
significant, persistent snow cover. Due to time and resource constraints, snowmobile
populations at the state and county levels have been set to zero in the draft version of the model
to avoid misallocation problems (the draft version will calculate national annual total emissions
for snowmobiles, however). The NEEMT plans to modify the recreational equipment allocation
factor (camps and recreational vehicle parks) in the final version of NONROAD to incorporate
NOAA long-term average snowfall data for significant metropolitan areas in the U.S. By linking
metropolitan areas to counties in the same vicinity, the NOAA data can be used to ensure that
snowmobiles are only allocated to areas that receive the significant amounts of annual average
snowfall required to support the use of snowmobiles.
Airport Ground Support Equipment
For the draft version of NONROAD, the NEEMT uses the number of people employed in
air transportation by county (CBP SIC 4500) to allocate ground support equipment. However,
this indicator may include employees that are not directly connected to aircraft operations, such
as airline reservation staff and ticket agents. Using this factor may lead to an overestimation of
aircraft ground support equipment population and activity in a county, especially in counties that
either have airports with one or more airline "hubs" or that do not have a commercial airport but
have branch ticket offices for various airlines.
For the final version of NONROAD, the NEEMT plans to use the number of landings and
take-offs (LTOs) by airport to allocate ground support equipment populations. This data may
only be available for airports with commercial air carrier operations, but commercial airports
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operations contribute the bulk of ground support equipment emissions in most areas. The
NEEMT believes that using LTO data is the best method currently available for allocating
ground support equipment activity because landings and take-offs are the primary determinant of
the level of aircraft ground support equipment activity at a given airport; to the extent that
airlines strive to avoid having excess ground service equipment, LTO data would provide a good
allocation factor for ground support equipment populations as well. An allocation factor based
on LTO data would not be subject to the problems associated with using the number of
employees in air transportation as an allocation factor. In addition, LTO data can be broken
down by wide and narrow-bodied aircraft, allowing an adjustment to be made to account for the
larger amount of activity (expressed in NONROAD by increasing the equipment population
allocation) needed to service large wide-bodied aircraft.
Light Commercial and Industrial Equipment
For light commercial and industrial equipment, the NEEMT chose to use the same
indicators as those used in the 1991 NEVES report. For light commercial equipment,
NONROAD will use the number of wholesale establishments by county (CBP SIC 50). For
industrial equipment, the NEEMT chose to use the number of employees in manufacturing (CBP
SIC 20). Analyses done for the NEVES report showed that these indicators provided reasonable
predictors of light commercial and industrial equipment populations. Because these types of
equipment are expected to remain close to a fixed central base of operations, as opposed to types
of equipment that tend to move around a wide area (e.g., construction equipment), one would
expect that the number of establishments and employees would be good factors with which to
allocate light commercial and industrial equipment populations, respectively. The NEEMT
acknowledges that the number of establishments may not be a good indicator of activity, which is
a function of the size of the average establishment and the mix of establishment types in addition
to the absolute number of establishments. The NEEMT requests comment on possible sources of
alternative activity-related allocation factors such as the dollar value of commercial, wholesale,
or industrial output, including their advantages and disadvantages relative to the number of
employees and establishments and their availability on a county-by-county basis for the entire
U.S.
Logging Equipment
For logging equipment, the NEEMT used the number of employees in logging (CBP SIC
2410) combined with the number of employees in saw and planing mills (CBP SIC 2420) in the
draft version of the model. However, the number of employees in saw and planing mills
allocated logging equipment populations to unlikely places such as Southern California and
various urban areas in Texas. For the final version of NONROAD, the NEEMT plans to use only
the number of employees in logging operations to allocate logging equipment. The number of
logging employees should provide a good reflection of logging equipment activity: generally
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speaking, each employee most likely uses one piece of equipment at a time. Economic pressures
would discourage logging companies from having expensive logging equipment sit idle for long
periods of time, which suggests that the number of employees in logging operations can also
serve as an allocation factor for logging equipment populations. The NEEMT requests comment
on potentially more reliable activity and population allocation factors, such as the number of
acres of forest harvested per county, and on possible sources of data for those alternatives.
Oil Field. Underground Mining. Railroad Maintenance, and AC/Refriaeration Equipment
To allocate oil field equipment population and activity, the NEEMT plans to use the
number of employees in oil and gas extraction operations (CBP SIC 1300) in both the draft and
final versions of the model. To allocate underground mining equipment population and activity,
the draft version of NONROAD uses the number of employees engaged in metal mining (CBP
SIC 1000). However, the NEEMT no longer believes that this indicator represents underground
mining operations because most metal mining is now performed above ground through the
excavation of large open pits. As a result, the NEEMT plans to use CBP employment data on
coal mines (CBP SIC 1200) to allocate underground mining equipment in the final version of the
model. Employment data provide reasonable allocation factors for oil field and underground
mining equipment activity because a proportional relationship between the number of employees
and the amount of equipment they use is likely to exist for both of these categories. Furthermore,
economic incentives to avoid leaving expensive equipment idle suggests that activity and
equipment populations will be closely correlated. Finally, these types of equipment tend to not
move around (unlike construction equipment, for example), so the location of activity for oil
field and underground mining equipment usually coincides with the location where the
employees are based. A production-based allocation factor, such as gallons of oil pumped or
tons of coal mined, might be an even better allocation factor, but the NEEMT has been unable to
find these types of activity-related data at the county level.
To allocate railroad maintenance equipment populations, no applicable CBP SIC exists
and no other reasonable alternatives have been found. The NEEMT is investigating the
possibility of using railroad track mileage for the final version of NONROAD, if such data are
available by county. The NEEMT has also been unable to find a targeted allocation factor for air
conditioning/refrigeration units used on trucking trailers to keep food cold and fresh while it is
transported to restaurants and markets. In the absence of an allocation factor that is more directly
related to such activity, the NEEMT has decided to use human population as the allocation factor
for railroad maintenance and AC/refrigeration equipment in the draft NONROAD model. The
NEEMT acknowledges that human population is unlikely to correspond well to the location and
usage of railroad maintenance equipment. The NEEMT is considering using miles of railroad
tracks as the allocation factor for such equipment in the final NONROAD model and requests
comment on this approach. Human population may be a sufficiently reliable indicator of
AC/refrigeration unit populations and activity levels, since the number of units being used to
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transport food into or within a given county is likely to be directly related to the size of the
population in the county. The NEEMT has not yet determined whether to retain this allocation
factor in the final model for AC/refrigeration equipment and welcomes comments concerning
better allocation factors for this equipment category.
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Table 1
NONROAD Surrogate Allocation Factors
Nonroad Equipment
Category
Lawn and Garden
Residential
Lawn and Garden
Commercial
Residential
Snowblowers
Commercial
Snowblowers
Construction
Agricultural
Recreational Marine
Allocation Factor
Draft Version
Number of single and double
(duplex) family housing units
from 1990 Census by county.
Number of employees in
landscape and horticultural
services, County Bus. Patterns
(CBP), Standard Industrial Code
(SIC)78.
Snowblowers set to zero pending
implementation of proper
allocation based on snowfall.
Snowblowers set to zero pending
implementation of proper
allocation based on snowfall.
Total dollar value of construction
by county.
Harvested cropland (U.S. Census
Bureau, USA Counties database).
Ratio of county water surface
area to total national water
surface area.
Activity vs.
Population
Allocation*
Population
Population
Not
Applicable
Not
Applicable
Activity and
Population
Activity
Activity
Allocation Factor
Proposed For Final Version
Adjusted by 1997 county human
population estimates from U.S.
Census Bureau.
Same as draft version.
Same as residential lawn and
garden, adjusted by annual average
snowfall.
Same as commercial lawn and
garden, adjusted by annual average
snowfall.
Same as draft version.
Same as draft version.
Same as draft version.
Activity vs.
Population
Allocation*
Population
Population
Population
Population
Activity and
Population
Activity
Activity
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Nonroad Equipment
Category
Recreational (except
snowmobiles and golf
carts)
Snowmobiles
Golf Carts
Aircraft Ground
Support Equipment
Light Commercial
Industrial
Logging
Oil Field Equipment
Railroad Maintenance
Equipment
Allocation Factor
Draft Version
Number of camps and
recreational vehicle park
establishments (CBP SIC 7030).
Snowmobiles set to zero pending
implementation of proper
allocation based on snowfall.
Number of public golf course
employees (CBP SIC 7992).
Number of employees in air
transportation (CBP SIC 4500).
Number of wholesale
establishments (CBP SIC 50).
Number of employees in
manufacturing (CBP SIC 20)
Number of employees in logging
plus saw and planing mills (CBP
SIC 24 10 and 2420).
Number of employees engaged in
oil and gas extraction (CBP SIC
1300).
1990 Human Population
Activity vs.
Population
Allocation*
Activity
Not
Applicable
Population
Activity and
Population
Population
Activity w^
Population
Activity and
Population
Activity and
Population
Activity and
Population
Allocation Factor
Proposed For Final Version
Might be revised for final version,
pending review.
Same as recreational equipment
and annual average snowfall.
Number of public golf courses.
(CBP SIC 7992)
Revised to be based on number of
landings and takeoffs (LTOs) of
commercial aircraft.
Same as draft version.
Same as draft version.
Number of employees in logging
only (CBP SIC 24 10).
Same as draft version.
Might be revised for final version,
pending review.
Activity vs.
Population
Allocation*
Activity
Population
Population
Activity and
Population
Population
Activity and
Population
Activity and
Population
Activity and
Population
Activity and
Population
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Nonroad Equipment
Category
Underground Mining
Equipment
AC/Refrigeration
Equipment
Allocation Factor
Draft Version
Number of employees engaged in
metals mining(CBP SIC 1000).
1990 Human Population
Activity vs.
Population
Allocation*
Activity and
Population
Activity and
Population
Allocation Factor
Proposed For Final Version
Number of Employees in Coal
Mining (CBP SIC 1200).
Might be revised for final version,
pending review.
Activity vs.
Population
Allocation*
Activity and
Population
Activity and
Population
These columns indicate whether the allocation factor is more directly related to nonroad equipment activity levels or equipment population.
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Endnotes
1. Environmental Protection Agency, Office of Air and Radiation. Nonroad Engine and Vehicle
Emission Study. 21A-2001, November 1991.
2. Irwin Broh & Associates, Inc., NMMA Boat Usage Survey, prepared for the National Marine
Manufacturers Association, Des Plaines, IL, August 1991.
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