CASE STUDY OF AN ENERGY AND ENVIRONMENTAL INVENTORY FOR A MUNICIPAL HEAVY DUTY DIESEL EQUIPMENT FLEET

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1 CASE STUDY OF AN ENERGY AND ENVIRONMENTAL INVENTORY FOR A MUNICIPAL HEAVY DUTY DIESEL EQUIPMENT FLEET Phil Lewis, Ph.D., P.E. Assistant Professor School of Civil and Environmental ering Oklahoma State University Stillwater, OK 0 Telephone 0--0, Fax 0-- phil.lewis@okstate.edu Apif Hajji Ph.D. Candidate School of Civil and Environmental ering Oklahoma State University Stillwater, OK 0 Telephone 0--0, Fax 0-- apif.hajji@okstate.edu Submitted for Consideration for Presentation at the rd Annual Meeting of the Transportation Research Board and Publication in the Transportation Research Record Presented for Review by AHD0 Maintenance Equipment Text words,00 plus 0 words for Tables and 1 Figure =,0 Words TRB 01 Annual Meeting

2 ABSTRACT As the nation moves towards more sustainable practices in all industry segments, heavy duty diesel (HDD) equipment owners are encouraged to utilize strategies that make their fleets cleaner and greener. In order to determine whether or not these strategies are effective, HDD fleet managers need a methodology that not only establishes a baseline of current fuel use and emissions quantities but also quantifies the energy and environmental impacts of the various alternatives under consideration. This paper presents a practice-ready methodology for developing an energy (diesel fuel) and environmental (pollutant emissions) inventory for nonroad HDD equipment. The methodology is demonstrated via a case study for a fleet of HDD equipment items owned by a local municipal government. The approach to calculating the fuel use and emissions of each equipment unit is based on equations employed by the Environmental Protection Agency NONROAD model; however, actual equipment attribute data from the case study fleet is used in order to make the results specific to the case study fleet. The resulting energy and emissions inventory presents the total fuel use and emissions of nitrogen oxides, particulate matter, hydrocarbons, carbon monoxide, and carbon dioxide for each item of equipment, as well as totals for each equipment subgroup and the overall fleet. Recommendations for using and improving the energy and environmental inventory are provided. TRB 01 Annual Meeting

3 INTRODUCTION Nonroad heavy duty diesel (HDD) equipment plays an important role in building and rebuilding the nation s infrastructure. Much of this equipment is owned and operated by public entities, such as state and local governments, that have distressed budgets and are wondering how to acquire, maintain, and update their fleets. Not only does this equipment have substantial ownership and operating costs but it also has a significant impact on national energy consumption in the form of diesel fuel, and an impact on the environment in the form of greenhouse gases and hazardous air pollutants; hence, fleet managers are required to balance the economic, energy, and environmental demands of their equipment. In order to manage these demands, they must first be measured. This paper demonstrates a practice-ready methodology for developing an energy and environmental inventory for nonroad HDD equipment that establishes a baseline of current fuel use and emissions quantities. The same approach can easily be used to quantify the impacts of various energy and environmental mitigation strategies. As the nation endeavors to move towards more sustainable practices in all industry segments, incentive programs are becoming available that encourage fleet owners to replace their old machines with new ones, to rebuild inefficient engines, or to retrofit existing equipment with emissions reduction technology (1-). In order to take advantage of these programs, detailed information is needed to identify the worst offenders in the fleet. Although obtaining this information may seem daunting, the energy and environmental inventory methodology presented here helps fleet owners quantify fuel consumption and emissions of greenhouse gases and air pollutants for each individual item of equipment, each equipment subgroup, and the entire fleet. Furthermore, use of this methodology will help equipment owners determine strategies to make their fleets cleaner and greener, either through volunteer measures or in response to state and federal mandates. The demonstration of the energy and environmental inventory methodology is based on a case study of a nonroad HDD fleet owned by the City of Stillwater, Oklahoma. The City of Stillwater provides services to a population of approximately,000 people (), including infrastructure operations such as utility installation, road maintenance, and landscaping. To effectively provide these services, the City of Stillwater maintains a HDD fleet that includes backhoes, bulldozers, excavators, motor graders, skidsteer loaders, tractors, and wheel loaders. This equipment consumes large quantities of diesel fuel and consequently emits air pollutants including nitrogen oxides (NO x ), particulate matter (PM), hydrocarbons (HC), and carbon monoxide (CO), as well as greenhouse gases such as carbon dioxide (CO ). The following questions will be addressed by evaluating the energy and environmental inventory: What is the composition of the current fleet with regard to equipment type, equipment age, engine power, and emissions reduction technology type? How much is the equipment used, particularly on an annual basis? How much fuel is consumed and pollution emitted by the fleet on an annual basis? Which equipment subgroups, as well as which individual units, consume the most fuel and emit the most pollution on an annual basis? How can this information be used to develop new strategies for improving fleet performance? WORK RELATED TO ENERGY AND ENVIRONMENTAL INVENTORIES Much of the previous work related to energy and environmental inventories has focused on highway vehicles and specific geographic regions. For example, Bai et al. () compared TRB 01 Annual Meeting

4 emissions inventories by using traffic data of differing resolutions for the City of El Paso, Texas. This work addressed the change in direction and magnitude of regional emissions by incorporating traffic data that was generated by dynamic simulation-assignment models. Claggett and Houk () developed the Easy Mobile Inventory Tool (EMIT) for calculating mobile source emission inventories in rural and small urban areas. EMIT incorporates a graphical-user interface based on the MOBILE. model (), which allows implementation of locale-specific parameters including external conditions, vehicle fleet characteristics, vehicle activity, vehicle fuel specifications, and state programs. Although most of the previous emissions inventory work has focused on light duty vehicles, there recently has been more attention given to HDD vehicles. Barth et al. () developed a modal emissions model for HDD trucks that addressed the effects of transportation operational activities. This work contributed to a large comprehensive modal emissions modeling (CMEM) program at the University of California, Riverside. Frey et al. () estimated roadway link-based emission rates for HDD trucks that may be used for emissions inventory development. These emission rates were based on real-world data that were collected via a portable emissions measurement system (PEMS). Also using PEMS data, Lewis et al. (1) developed a fuel use and emissions inventory for a state government fleet of nonroad HDD vehicles, including backhoes, wheel loaders, and motor graders. This inventory compared the emissions impacts of various equipment replacement strategies as well as the effects of using biodiesel versus petroleum diesel in the equipment. Vallamsundar and Lin (1) incorporated local input data into the well-known Environmental Protection Agency (EPA) MOVES (1) and MOBILE () models to develop a comprehensive emission inventory for Cook County, Illinois. This study compared the differences in emissions estimates of CO and NO x that were used in the latest versions of each model. The study also provided insight for practitioners that were related to the transition from MOBILE to MOVES. In a similar fashion, the energy and environmental inventory methodology presented here utilizes equipment attribute and activity data from a local fleet to calculate fuel use and emissions based on equations found in the EPA NONROAD model (1). METHODOLOGY This section presents the methodology for developing the energy and environmental inventory for the City of Stillwater nonroad HDD equipment fleet. It addresses the key equipment attributes that were needed and how annual activity was estimated. The equations used to calculate fuel use rates and emission rates of NO x, PM, HC, CO, and CO are provided. Equipment Attributes and Annual Activity In order to develop and evaluate the energy and environmental inventory, detailed attributes of the equipment in the current fleet was collected. Based on recommendations from the EPA Construction Fleet Inventory Guide (1), these attributes included equipment type, engine model year, engine horsepower, and annual activity. In addition to these attributes, EPA engine tier classifications - a hybrid attribute based on horsepower rating and model year - were identified. tiers are emissions standards adopted by EPA for all new nonroad diesel engines (1). These standards are phased in over time and require all nonroad diesel engine manufacturers to reduce the emission rates of NO x, HC, CO, and PM; CO is not a part of these standards. Diesel engines manufactured after a specified year must meet the performance levels specified in that standard. The EPA engine tier TRB 01 Annual Meeting

5 classifications include successive Tier 1, Tier, Tier, Tier Transitional, and Tier Final, which are to be implemented in a phased sequence from 1 to 01. s manufactured prior to implementation of the engine tier standards were designated as Tier 0 and do not meet any required emissions regulations. The majority of the equipment attribute data was obtained from the City of Stillwater s equipment management database, which included the aforementioned attributes for each item of equipment in the fleet. The database also included fuel use records that indicated the date when the equipment was fueled and the hour meter reading at the time. The hour meter reading was used to determine the total activity to-date of the equipment in terms of engine-use hours; however, this data was incomplete or inaccurate for many items of equipment. When invalid or missing data were found, field measurements were used to supplement the database. For example, oftentimes the hour meter reading was not recorded when the equipment was fueled, or an invalid number was recorded, such as, which obviously did not correspond with the other hour meter readings for the equipment. In this case, the item of equipment was located in the field and a current hour meter reading was obtained. The estimated age of the equipment was determined by the difference in the date of the most recent hour meter reading and the purchase date. This age was used as the basis for estimating the average annual activity for each item of equipment. The average annual activity was calculated by dividing the total hours of activity by the estimated age at the most recent hour meter reading from the equipment. Although only a rough indicator that does not show the true year-to-year values, this annual activity estimate provided a reasonable value for hours of use each year for each item of equipment over its life-to-date. It is generally believed that equipment activity declines as the equipment gets older (1). Older items of construction equipment, for example, may be placed on standby and used only when newer equipment needs repair. There is little quantifiable data to support this claim, thus, the relationship between age and annual activity was examined for the City of Stillwater fleet. Fuel Use and Emissions Inventory In order to develop the inventory for the City of Stillwater s nonroad HDD fleet, fuel use and emission factors were needed. These factors are approximations of the amount of fuel consumed and pollutants emitted by a particular type of equipment during a unit of use. The factors used for this inventory were based on calculations and the methodology employed by the EPA NONROAD model (1). For fuel use, NONROAD uses brake specific fuel consumption (BSFC) reported in pounds per horsepower-hour (lb/hp-hr); for pollutants, emission factors are reported in grams per horsepower-hour. The factors used by NONROAD are based on engine dynamometer test data and adjusted accordingly to account for in-use operation that differs from the typical test conditions. For NO x, HC, and CO, the emission factor for a specific type of nonroad equipment with a particular model year and age is calculated as follows: (NOx, HC, CO,) = EF ss x TAF x DF (1) where: = final emission factor used in NONROAD, after adjustments for transient operation and deterioration EF ss = zero-hour, steady-state emission factor TAF = transient adjustment factor (unitless) DF = deterioration factor (unitless) TRB 01 Annual Meeting

6 The zero-hour, steady-state emission factor (EF ss ) is a function of the engine s model year and horsepower rating, which defines the engine tier category. Nonroad engines are typically monitored based on steady-state tests; however, this approach does not always accurately reflect fuel use and emissions activity for nonroad equipment applications. Some differences are due to load or engine speed whereas some are due to transient demands. Transient adjustment factors are applied to Tier 0, 1,, and engines but are not applied to Tier engines because transient emission controls will be a part of all Tier engine design considerations. Transient adjustment factors are calculated as the ratio of the transient emission factor to the corresponding steady-state emission factor and may be greater than or less than 1.0. Deterioration factors are used to account for increases in emissions over time above a new engines base emission level. Emissions may increase over time for numerous reasons including engine wear, poor maintenance, or modification of emission control systems. Emissions performance typically deteriorates at a slow rate for well-maintained engines but rapidly for poorly-maintained engines. The deterioration factors used by the NONROAD model are based on well-maintained engines and are a linear function based on engine age. The transient adjustment and deterioration factors used for the inventory computations were found in Exhaust and Crankcase Emission Factors for Nonroad Modeling Compression-Ignition (1). Since PM emissions are dependent on the sulfur content of the fuel consumed by the engine, the equation for the PM emission factor is modified from Equation 1 as follows: (PM ) = EF ss x TAF x DF - S PMadj () where: S PMadj = adjustment to PM emission factor for variations in fuel sulfur content For BSFC (or fuel use factor), deterioration factors are not applied, thus, the equation is simplified as follows: (BSFC) = EF ss x TAF () NONROAD computes CO emissions directly by using in-use adjusted BSFC, as shown in Equation. The carbon that goes into exhaust HC emissions is subtracted in order to correct the equation for unburned fuel. (CO) = (BSFC x. - HC) x 0. x (/1) () where: BSFC = in-use adjusted fuel consumption factor (lb/hp-hr). = conversion factor from pounds to grams HC = in-use adjusted hydrocarbon emissions 0. = carbon mass fraction of diesel /1 = ratio of CO mass to carbon mass The individual fuel use and emissions values for each item of equipment were computed according to the methodology presented in Median Life, Annual Activity, and Load Factor Values for Nonroad Emissions Modeling (1) and the following equation: TRB 01 Annual Meeting

7 Emissions (NOx, HC, CO, PM, CO, BSFC) = Pop Power LF A (NOx, HC, CO, PM, CO, BSFC) () where: NO x, HC, CO, CO = total annual emissions for the specified pollutant (g/yr) BSFC = total annual fuel consumption (lb/yr) Pop = equipment population Power = engine rated horsepower (hp) LF = engine load factor (fraction of available power) A = equipment average annual activity (hr/yr) (NOx, HC, CO, PM, CO, BSFC) = engine emission factor or BSFC factor (lb/hp-hr) The annual emissions and fuel use values (NO x, HC, CO, PM, CO, BSFC) were calculated for each item of equipment by setting Pop = 1. The engine rated horsepower (Power) for each item of equipment was obtained from the City of Stillwater s fleet management database, as well as field data collection, thus the individual and overall fuel use and emissions values are specific to this particular fleet. The engine rated horsepower is the maximum level of power that an engine is designed to produce at its rated engine speed. Nonroad equipment seldom operates at its rated power for extended periods and frequently operates at a variety of speeds and loads. NONROAD uses a load factor (LF) to indicate the average proportion of rated power used to account for the effects of operation at idle and partial load conditions. For example, a 0 hp engine with a load factor of 0. (or 0%) will produce an average of 0 hp over the course of normal operation. Depending on equipment usage patterns, load factors may vary widely for nonroad engines and can be difficult to quantify. Since equipment usage patterns for the City of Stillwater fleet were not observed or measured, the NONROAD model default load factors were used (1). The NONROAD model also provides default values for average annual activity for many types of equipment; however, the default values were not used here. For the City of Stillwater fleet, average annual activity was determined based on the total usage divided by the age of the equipment. This information was obtained from the fleet management database as well as field data collection; thus, the emissions and fuel use results presented here are specific to the City of Stillwater fleet. RESULTS The City of Stillwater s nonroad equipment fleet consists of a total of units, including 1 backhoes (BH), three bulldozers (BD), two excavators (EX), two motor graders (MG), seven skidsteer loaders (SS), 1 tractors (TR), and two wheel loaders (WL). The individual equipment attributes of each unit is provided in Table 1 and a summary of the fleet composition is shown in Figure 1. Table provides a summary of the fuel use and emissions inventory for each item of equipment as well as the subtotals for each equipment subgroup and the overall totals for the entire nonroad fleet. Equipment Attributes and Annual Activity Of the seven types of equipment in the fleet, backhoes and tractors comprise approximately twothirds of the total, with % and 0%, respectively. The majority of the fleet has 0 hp or smaller engines with approximately % being in the 0-0 hp range. There are only seven units that have engines over 0 hp, with EX being the largest unit in the fleet (10 hp). The fleet units have an average age of 1 years with % of the fleet being at least years old. This TRB 01 Annual Meeting

8 includes five units that are over 0 years old, with the oldest being BD 1 ( years), TR ( years), and WL ( years). With regard to EPA emissions standards, 0% of the fleet is Tier 0 and % is Tier 1; thus, approximately three-quarters of the fleet meet no standard or only the minimum standard. Furthermore, there are only three units in the entire fleet that meet the current emissions standard (Tier or Tier ) for their engine size and model year. Item Table 1 Attributes of City of Stillwater Nonroad Fleet as of 0 EPA Tier Power (hp) Load Factor Model Year Age (yr) Usage (hr) Annual Activity (hr/yr) BH , BH ,0 BH , 1 BH ,0 BH , 1 BH , BH ,1 BH ,1 BH ,0 01 BH , 1 BH , BH , BH , BH ,0 BH ,01 BH , 1 BH ,1 1 BD , BD , 1 BD EX , 0 EX , 0 MG ,0 MG ,01 00 SS SS SS SS SS , 1 SS ,01 SS TRB 01 Annual Meeting

9 EPA Tier Power (hp) Table 1 continued Load Factor Model Year Age (yr) Usage (hr) Annual Activity (hr/yr) Item TR TR TR TR , TR ,00 TR TR ,0 TR , 0 TR , 0 TR ,1 TR , TR TR TR ,1 WL , WL , During the life of the current fleet, the units have accumulated a composite total activity of over,000 hours. On an average annual basis, equipment activity ranged from hr/yr (WL ) to 0 hr/yr (EX ). An interesting finding here is that WL is years old whereas EX is 1 years old, thus supporting the general belief that annual activity declines as the equipment gets older. Furthermore, the five oldest equipment units (all over 0 years old) TR, TR, TR, BD 1, and WL ranked 1 th, 1 th, th, 0 th, and 1 st respectively in terms of total accumulated hours of activity. The five units that had the highest total accumulated hours of activity WL 1, EX, BH, TR, and BH were all 0 years old or less, with an average age of 1 years. A closer examination of the data for the entire fleet revealed a moderate negative correlation (r = -0.) between age and annual activity - as age increases, annual activity decreases. It must be noted, however, that annual activity was dependent upon age so there was an interrelationship in this case. A rigorous approach that examines the independent annual activity and age data is needed to provide more conclusive results. Fuel Use and Emissions Inventory Table presents a summary of the fuel use and emissions inventory for the City of Stillwater nonroad HDD equipment fleet. The fuel use factor (BSFC adj ) and emission factors ( ) are shown for each item of equipment, along with the total fuel use and emissions for each unit. For the purpose of reporting the results in commonly recognized units, fuel use was converted from pounds to gallons and emissions were converted from grams to pounds for NO x, PM, HC and CO and from grams to tons for CO. On an average annual basis, the City of Stillwater nonroad HDD fleet consumes nearly 1,000 gallons of diesel fuel per year and as a result emits approximately,000 pounds of NO x ; 00 pounds of PM; 00 pounds of HC;,000 pounds of CO; and over 00 tons of CO. TRB 01 Annual Meeting

10 Equipment Units 1 1 Equipment Units BH BD EX MG SS TR WL Equipment Type Power (HP) Equipment Units 1 1 Equipment Units Equipment Age (Years) 0 Tier 0 Tier 1 Tier Tier Tier EPA Tier Figure 1 Composition of City of Stillwater nonroad fleet TRB 01 Annual Meeting

11 Table Fuel Use and Emissions Inventory for City of Stillwater Nonroad Fleet Fuel NO x PM HC CO CO Item BSFC adj (lb/hp-hr) (gal/yr) (lb/yr) (lb/yr) (lb/yr) (lb/yr) (ton/yr) BH BH BH BH BH BH BH BH BH BH BH BH BH BH BH BH BH Subtotal, 1,1 10 1,0 BD BD BD Subtotal 1,1 0 1 EX EX Subtotal, 0 MG MG Subtotal 1, 1 1 TRB 01 Annual Meeting

12 Table continued 1 Fuel NOx PM HC CO CO Item BSFC adj (lb/hp-hr) (gal/yr) (lb/yr) (lb/yr) (lb/yr) (lb/yr) (ton/yr) SS SS SS SS SS SS SS Subtotal TR TR TR TR TR TR TR TR TR TR TR TR TR TR Subtotal, 1 1 WL WL Subtotal 1, 1 1 Fleet 1,0,,0 1 TRB 01 Annual Meeting

13 As the most represented equipment types in the fleet, Backhoes and Tractors rank first and second, respectively, in terms of fuel use and emissions of each pollutant. These two subgroups, which comprise about % of the total fleet, consume approximately % of the total fuel on an annual basis and emit approximately 0% of total NO x ; % of PM; % of HC; % of CO; and % of CO. Conversely, the third most represented equipment type, Skidsteer Loaders, rank last in each fuel use and pollutant category. These units make up approximately 1% of the fleet but consume only about % of the total annual fuel use and emit about % of total NO x ; % of PM; % of HC; % of CO; and % of CO. The results for Skidsteers are largely due to the fact that they have a small average engine power rating ( hp) and they are, compared to the rest of the fleet, relatively new items of equipment with an average age of years. Furthermore, this subgroup is the most up-to-date with regard to EPA emissions standards there are two Tier 1 units, three Tier, one Tier, and one Tier. On an individual basis, EX consumes more fuel than any other unit in the fleet % of the average annual total fleet fuel use. In fact, EX alone consumes more fuel on an annual basis than all three Bulldozers combined, or both Motor Graders, or both Wheel Loaders, or all seven Skidsteer Loaders; hence, EX by itself is the third largest fuel consumption subgroup in the fleet, behind Backhoes and Tractors. Similar results abound for pollutant emissions; EX and WL 1 are the highest polluting units in the fleet, ranking first or second in each pollutant category. These two units combined emit % of annual NO x for the entire fleet; 1% of PM; 1% of HC; 1% of CO; and 1% of CO. These two items of equipment (% of the fleet), therefore, are responsible for 1-% of the total fleet emissions of each pollutant. CONCLUSIONS The City of Stillwater has a substantial fleet of nonroad HDD equipment with respect to the diversity and total number of units, annual activity, fuel consumption, and emissions of greenhouse gases and air pollutants. They also have an equipment data management system in place that can be used to record and store equipment attributes and fuel use information, but much of the important data is either missing or inaccurate. The energy and environmental inventory methodology was successful at quantifying the fleet fuel use and emissions by using the data that was available from the management system and then supplementing the missing or inaccurate data with data that was collected by visual inspection from the actual equipment. The City of Stillwater has an old fleet with an average age per unit of 1 years. Although it is not uncommon for HDD equipment to last for 0 years, the fleet has five units that are over 0 years old and an additional five that are over 0 years old. As a result of retaining old equipment, the fleet is largely unregulated concerning emissions standards. Nearly three out of four equipment units either meet no emissions standard (Tier 0) or only the minimum standard (Tier 1). Furthermore, only three units are at a Tier or Tier level. The age and annual activity data for the City of Stillwater fleet tend to support the claim that equipment utilization decreases as the machine gets older. There was a moderate negative correlation between age and average annual activity but this alone was not conclusive since age was used to calculate average annual activity. Other results, however, are somewhat compelling in support of the claim. For example, the five oldest machines in the fleet, with an average age of years, ranked between 1 th and 1 st (out of total units) in terms of total accumulated hours of activity over the life of the equipment, indicating that even though they have been in the fleet the longest they are still not the most used. The five equipment units with the highest total TRB 01 Annual Meeting

14 accumulated hours of activity, however, have a much lower average age of 1 years, indicating that they have been used more frequently even though they have not been in the fleet as long. By examining the results of the energy and environmental inventory, it is possible to determine which equipment subgroups, as well as which individual equipment units, are responsible for the most fuel consumed and pollutants emitted. For example, Backhoes and Tractors rank first and second, respectively, in fuel use and emissions based on equipment type; EX by itself ranks third for the same criteria. This type of information is useful in identifying which equipment has the highest energy and environmental impacts and can be used as a new metric for fleet management decisions. RECOMMENDATIONS In order to improve the quality of the energy and environmental inventory, a top priority for the City of Stillwater should be to update their equipment data management system with current records to eliminate missing, inaccurate, or outdated information. It is also recommended that they leverage the benefits of telematics - an emerging area that uses global positioning systems (GPS) to provide real-time data in order to address fuel management, maintenance optimization, productivity improvements, job costing, and fleet sizing (1). PEMS data related to fuel use and emissions may be used along with the telematics data to produce innovative real-world emissions inventories which will allow evaluation of the relationships between the economic, energy, and environmental aspects of the fleet. The City of Stillwater must prepare itself for a large-scale equipment replacement event in the near future. Not only is the fleet continuing to get older and needs to be replaced with newer and cleaner equipment, but it is also continuing to pollute the air at an unnecessary rate due to the high percentage of Tier 0 and Tier 1 units (% of the fleet). Although it is not economically feasible to replace all of these equipment items at once, they should receive a high priority in any upcoming replacement strategy. A more rigorous approach is needed to assess the relationship between equipment activity and age in order to facilitate fleet management decisions related to the size and composition of the fleet. This assessment must occur on an ongoing basis in order to ensure that the fleet is composed of the proper types and numbers of equipment units. It is recommended that the City of Stillwater develop a methodology for determining organization-specific guidelines for measuring equipment activity on a continuous basis, which will help identify and facilitate the reassignment or removal of underutilized equipment. Furthermore, to reduce variability in the fuel use and emissions inventory estimates, specific data is needed related to the impact of engine load and engine age on fuel use and emission rates. It is recommended that future studies consider using a PEMS to collect real-world data that may be used to discern the true relationships between engine load, engine age, fuel use, and emissions. Many factors determine the performance, service life, and replacement of HDD equipment. Age alone is not the sole consideration, nor is hours of activity. In order for the fleet to be sustained properly with regard to economics, energy, and environment, fleet management strategies must be utilized that address each of these issues. If these issues are to be managed, they must first be measured. The energy and environmental inventory methodology presented here provides a means for doing that. This methodology not only establishes a baseline of existing fleet fuel use and emissions, it can also be used to perform sensitivity analyses of competing fleet management strategies to determine their respective impact on fuel consumption and pollution. It is recommended that the City of Stillwater, as well as all fleet owners, use an TRB 01 Annual Meeting

15 energy and environmental inventory as an initial step towards reducing and mitigating the energy and environmental impacts of their fleets. ACKNOWLEDGEMENT The authors express gratitude to Mr. David Higgins and Mr. John Maehs with the City of Stillwater for their cooperation in providing information from their equipment management database and providing access to the equipment in order to complete this study. REFERENCES 1. Energy Policy Act of 00, One Hundred Ninth Congress of the United States of America, Washington, D.C., Document available at hrenr/pdf/bills-hrenr.pdf. Accessed August 1, 00.. EPA. National Clean Diesel Campaign, National Funding Assistance Program, U.S. Environmental Protection Agency, available at Accessed August EPA. National Clean Diesel Campaign, Emerging Technologies Program, U.S. Environmental Protection Agency, available at Accessed August 1, 01.. EPA. National Clean Diesel Campaign, Smartway Finance Program, U.S. Environmental Protection Agency, available at Accessed August 1, 01.. EPA. National Clean Diesel Campaign, State Grant Program, U.S. Environmental Protection Agency, available at Accessed August 1, 01.. U.S. Census Bureau. American Fact Finder, available at factfinder.census.gov. Accessed August 1, 01.. Bai, S., Y. Chiu, and D. Niemeier. Using Dynamic Assignment to Improve Regional Mobile Emissions Estimation. Presented at th Annual Meeting of the Transportation Research Board, Washington D.C., 00.. Claggett, M. and J. Houk. Emissions Inventory Tool for Transportation Conformity Applications in Rural and Small Urban Areas. Presented at th Annual Meeting of the Transportation Research Board, Washington D.C., 00.. EPA. User s Guide to MOBILE.1 and MOBILE., EPA0-R-0-0, U.S. Environmental Protection Agency, Ann Arbor, MI, 00.. Barth, M., G. Scora, and T. Younglove. Modal Emissions Model for Heavy-Duty Diesel Vehicles. In Transportation Research Record: Journal of the Transportation Research Board, No. 10(1), Transportation Research Board of the National Academies, Washington, D.C., 00, pp.-0.. Frey, H., N. Rouphail, and H. Zhai. Link-Based Emission Factors for Heavy-Duty Diesel Trucks Based on Real-World Data. In Transportation Research Record: Journal of the Transportation Research Board, No. 0(1), Transportation Research Board of the National Academies, Washington, D.C., 00, pp. -. TRB 01 Annual Meeting

16 Lewis, P., H. Frey, and W. Rasdorf. Development and Use of Emissions Inventories for Construction Vehicles. In Transportation Research Record: Journal of the Transportation Research Board, No. 1(1), Transportation Research Board of the National Academies, Washington, D.C., 00, pp Vallamsundar, S., and J. Lin. MOVES Versus MOBILE. In Transportation Research Record: Journal of the Transportation Research Board, No. (1), Transportation Research Board of the National Academies, Washington, D.C., 0, pp EPA. User Guide for MOVES0b, EPA0-B-1-001b, U.S. Environmental Protection Agency, Ann Arbor, MI, EPA. User s Guide for the Final NONROAD00 Model, EPA0-R-0-01, U.S. Environmental Protection Agency, Ann Arbor, MI, EPA. Construction Fleet Inventory Guide. EPA-0-B--0, U.S. Environmental Protection Agency, Inc., Ann Arbor, MI, EPA. Exhaust and Crankcase Emission Factors for Nonroad Modeling - Compression-Ignition. EPA-0-R--01, NR-00d, U.S. Environmental Protection Agency, Ann Arbor, MI, EPA. Median Life, Annual Activity, and Load Factor Values for Nonroad Emissions Modeling. EPA-0-R--01, NR-00d, U.S. Environmental Protection Agency, Ann Arbor, MI, Ver Eecke, R. Telematics Brings Intelligence to Machine Management. Construction Equipment Magazine (reprinted with the permission of Equipment Manager magazine, the magazine of AEMP), available at TRB 01 Annual Meeting