# APPENDIX E **- 1** 

**Mobile Source Highway Emissions Inventory An Explanation of Methodology** 

**July 2009** Appendi x E

- 1 2 

### Explanation of Methodology

July 200 9 

# TABLE OF CONTENTS
**INTRODUCTION ................................**  **................................ ................................**  **................................ .......................**  **3** O VERVIEW OF E MI SSIONS INVENTORIES ................................ ................................ ................................ .................... 3 H IGHWAY VEHICLE E MI SSION INVENTORIES ................................ ................................ ................................ .............. 3 **WHERE DOES PENNSYLVA NIA OBTAIN ITS DATA?**  **................................ ................................**  **...................... 6**  D ATA U SED I

N MOBILE
................................ ................................ ................................ ................................ ........... 6 WHAT ARE T HE NECESSARY D ATA INPUTS TO MOBILE?
................................ ................................ ........................ 7 E MI SSION AND S PEED RELATIONSHIPS ................................ ................................ ................................ ....................... 9 ROADWAY D ATA ................................ ................................ ................................ ................................ ..................... 10 ADDITIONS AND ADJUSTMENTS TO ROADWAY D ATA ................................ ................................ .............................. 11 P RODUCI

NG F UTURE YEAR V OLUMES ................................ ................................ ................................ ..................... 14 **SPEED/EMISSION ESTIM ATION PROCEDURE**  **................................ ................................**  **............................... 15**  V OLUME/VMT D EVELOPMENT ................................ ................................ ................................ ............................... 15 S PEED/D ELAY D ETERMI NATION ................................ ................................ ................................ .............................. 18 HPMS AND VMT ADJUS TMENTS ................................ ................................ ................................ ............................ 19 VMT AND S PEED AGGREGATION ................................ ................................ ................................ ............................. 20 MOBILE E MI SSIONS R UN ................................ ................................ ................................ ................................ ....... 21 T IM E OF D AY AND D IURNAL E MI SSIONS ................................ ................................ ................................ .................. 21 P ROCESS MOBILE O UTPUT ................................ ................................ ................................ ................................ .... 21 **RESOURCES ................................**  **................................ ................................**  **................................ .............................**  **24 HIGHWAY VEHICLE INVE**  **NTORY GLOSSARY ................................**  **................................ .............................**  **25** 

## List of Exhibits EXHIBIT 1 : E MI SSION C ALCULATION P ROCESS FOR P ENNSYLVANIA ................................ ................................ .............. 5 EXHIB IT 2 : MOBILE INPUTS ................................ ................................ ................................ ................................ ......... 7 EXHIBIT 3 : VOC AND NO X -- S PEED V . E MI SSIONS ................................ ................................ ................................ ..... 10 EXHIBIT 4 : P ENNDOT C LASSIFICATION S CHEME ................................ ................................ ................................ ......... 11 EXHIBIT 5 : MOBILE6 VEHICLE T YPES ................................ ................................ ................................ ....................... 13 EXHIBIT 6 : PPSUITE S PEED/E MI SSION E STIMATION P ROCEDURE ................................ ................................ ............... 16 EXHIBIT 7 : VMT/VHT AGGREGATION S CHEME ................................ ................................ ................................ .......... 20 EXHIBIT 8 : S UMMARY OF PPSUITE M ETHODOLOGY ................................ ................................ ................................ .. 22Appendi x E

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## INT **RODUCTION** The purpose of this document is to explain how Pennsylvania estimates emissions from highway vehicles for inclusion in its emission inventories and State Implementation Plans. 

## Overview of Em **issions Inventories** Pennsylvania’s inventories generally categorize emissions into four categories:

 highway vehicles  stationary sources (major industrial, commercial and utility sources)  area sources (smaller industrial/commercial sources, consumer products)  nonroad mobile sources (including construction and agricultural equipment, lawn and garden equipment) An evaluation of emissions from point, area, and mobile sources is needed to develop a complete inventory needed for a maintenance demonstration plan. This inventory provides the mobile source activity and emissions for base and future years that can be used to support such a demonstration. Of all of the sources of air pollution, only the emissions of some stationary sources are measured directly and continuously through instrumentation. Emissions from all other sources must be estimated in some fashion, including those from highway vehicles. In their very simplest form, estimates of emissions follow the following pattern: Emission rate x activity level = emissions per time period (usually day or year) Most emission rates have been developed by EPA, in cooperation with industry and states, over many years and are compiled and documented in a reference volume, Compilation of Air Pollution Emission Factors (AP
-42). F or example, the annual VOC emis sions from residential fuel oil heating could be estimated by: AP

- 42 emission rate X activity level = emissions 0.713 pounds/gallon X # dwelling units x % using oil x # gallons per unit # pounds of VOC per year Adding up the product s of the emission rates and activity levels for all sources of a given pollutant constitutes the emission inventory for that pollutant. 

## Highway V

**ehicle Em ission Inventories**  Highway vehicles contribute significantly to air pollution, particularly to ground
- level ozone, which is the most persistent air pollutant in Pennsylvania. O zone is not created directly but formed in sunlight from VOCs and NOx. B oth VOCs and NOx are emitted from highway vehicles. 

### Inaddition, f ine particulates are also emitted directly by motor vehicles as a result of the combustion process (tailpipe emissions), re - entrained and transportation construction dust; and formed through reactions in the atmosphere among the precursors VOC, NOx, NH3 and SOx.Appendi x E

- 1 4 Obviously, direct measurement of emission levels from all vehicles in use is impossible. In comparison to highway vehicles, estimating residential heating emissions is a fairly simple calculation because there is a constant emission rate and a fairly simple measure of activity. F or highway vehicles, however, estimating the emission rate and activity levels of all vehicles on the road during a typical summer day is a complicated endeavor. If every vehicle emitted the same amount of pollution all the time, one could simply multiply those emission standards (emission rate in grams of pollution per mile) times the number of miles driven (activity level) to estimate total emissions. But, the fact is that emission rates from all vehicles vary over the entire range of conditions under which they operate. These variables include air temperature, speed, traffic conditions, operating mode (started cold? s tarted warm? r unning already warmed up?) and fuel. The inventory must also account for non - exhaust or evaporative emissions. In addition , the fleet is composed of several generations, types of vehicles and their emission control technologies, each of which performs differently. This requires that the composition of the fleet (vehicle ages and types) m ust also be included in the estimation algorithm. In order to estimate both the rate at which emissions are being generated and to calculate vehicle miles traveled (activity level), Pennsylvania examines its road network and fleet to estimate vehicle activity. For ozone -related inventories , this is done for a typical summer weekday. F or CO and PM emission inventories, this may be done for a typical winter weekday or annual conditions. Not only must this be done for a baseline year, but it must also be projected into the future. This proce ss involves a large quantity of data and is extremely complex. Computer models have been developed to perform these calculations by simulating the travel of vehicles on the Commonwealth’s roadway system. These models then generate emission rates ( also called emission factors) for different vehicle types for area - specific conditions and then combine them in summary form. The “area
- specific conditions” include vehicle and highway data, plus control measure characteristics and future year projections of all variables. **MOBILE.** The heart of the highway vehicle emission calculation procedure is EPA’s highway vehicle emission factor model, MOBILE. This is a FORTRAN program that calculates **average** in
-use fleet emission factors for ozone precursors for each of twenty- eight categories of vehicles under various conditions affecting in
-use emission levels (e.g., ambient temperatures, average traffic speeds, gasoline volatility) as specified by the model user. M OBILE produces the “emission rates” referred to in the previous section. The model was first developed as MOBILE1 in the late 1970s, and has been periodically updated to reflect the collection and analysis of additional emission factor data over the years, as well as changes in vehicle, engine and emission control system technologies, changes in applicable regulations, emission standards and test procedures, and improved understanding of in
-use emission levels and the factors that influence them. F or this inventory effort, Pennsylvania utilizes M OBILE6.2 as approved by EPA. In addition to VOC, CO, and NOx, MOBILE6.2 produces emission factors for PM related emission categories as needed for the PM 2.5 inventory analyses
. **PPSUITE.** Pennsylvania also uses a post processor named PPSUITE (formerly named PPAQ
- Post Processor for Air Quality), which consists of a set of programs that perform the following functions:

 Analyzes highway operating conditionsAppendi x E

- 1 5  Calculates highway speeds  Compiles vehicle miles of travel (VMT) and vehicle type mix data  Prepares MOBILE6 runs  Calculates emission quantities from output MOBILE6 emission rates and accumulated highway VMT. PPSUITE has become a widely used and accepted tool for estimating speeds and processing MOBILE emission rates. It is currently being used for the New York City region, for the north and south New Jersey regions, and in other states including Louisiana, Virginia, and Indiana. The software is based upon accepted transportation engineering methodologies. F or example, PPSUITE utilizes speed and de lay estimation procedures based on planning methods provided in the 2000 Highway Capacity Manual , a report prepared by the Transportation Research Board (TRB) summarizing current knowledge and analysis techniques for capacity and level
- of
- service analyses of the transportation system. These two computer programs interact as shown in Exhibit 1. 

### Exhibit **1 Emission Calculation Process for Pennsylvania**  **Roadway Data Source Growth Method**  **Method to Calculate Method to Calculate**  **Used for Analysis to Future Years**  **VMT and Speeds Emissions**  PENNDOT Use 2005 DOT data for each county study of potential PPSUITE MOBILE grow th PPSUITE Input Data PPSUITE Processe s MOBILE Output

PPSUITE Calculates Final EmissionsAppendi x E

- 1 6 

## WHERE DOES PENNSYL **VA NIA**  **OBT AIN ITS DA** 

**TA ?** 
**Data Used in MOBILE** Two maj or types of information are written into the MOBILE model by EPA: basic emission rates and travel weighting rates. EPA’s Office of Mobile Sources obtains this information from a number of sources, including its new vehicle certification program, in
-use vehicle random sample studies and special studies (including information from some state I/M pro grams). F or more information on MOBILE, a users guide and various documents (as well as the model itself) are available through EPA’s website (http://www.epa.gov/OMSWWW/models.htm). **Basic emission**  **rates** are those which are produced under very standardized conditions. The model then modifies (corrects and/or weights) these rates based on other model or input parameters. Rates are incorporated for model year and vehicle type. MOBILE also calculates an assumed amount of increase in emissions as vehicles accumulate mileage. In addition to exhaust emissions, evaporative VOC emission sources from gasoline
-powered vehicles are also included 1 :

 diurnal emissions (evaporated gasoline emissions generated by the rise in temperature over the course of a day when the vehicle is not being driven),  hot soak emissions (evaporated gasoline emissions occurring after the end of a vehicle trip, due to the heating of the fuel, fuel lines, fuel vapors),  running loss emissions (evaporated gasoline emissions occurring whil e a vehicle is driven, due to the heating of the fuel and fuel lines),  resting loss emissions (small but continuous seepage and minor leakage of gasoline vapor through faulty connections, permeable hoses and other materials in the fuel system). Evaporative emissions are very dependent on temperature and fuel volatility as well as vehicle model year. **Travel Weighting**  **Fractions.** Research has found that newer cars tend to be driven more. The model reflects this, using state
- specific vehicle age distributi ons from registration data. The model also contains assumptions about trips per day and miles per day by age of the vehicle. This is important for exhaust emissions because these emissions are greater when the vehicle is not warmed up (cold start). Also , this information helps characterize evaporative emissions.

1 Some states use MOBILE to estimate refueling emissions (gasoline vapor emissions generated by the refueling of vehicles, where in the absence of controls the vapor in the vehicle fuel tank is displaced by the incoming liquid fuel and released to the atmosphere). Pennsylvania handles these emissions in the area source inventory.Appendi x E

- 1 7 

## What Are The Necessary Data Inputs to MOBILE? A large number of inputs to MOBILE are needed to fully account for the numerous vehicle and environmental parameters that affect emissions including traffic flow characteristics (as determined from the PPSUITE software), vehicle descriptions, fuel parameters, inspection/maintenance program parameters, and environmental variables as shown in Exhibit 2. With some input parameters, MOBILE allows the user to choose default values, while others require area
- specific inputs. 

### Exhibit **2 MOBILE Inputs** 

**Vehicle Fuel**  **Inspection/ Environm** **ental Descriptions**  **Param eters**  **Maintenance Variables**  Age Mix RVP Start Year Min, Max Model Years Tem peratures Vehicle Type Reformulated Ty pe, Mix Fuels Vehicle Types, Humidity Frequency Stringency, Speeds Oxygenated Waiver Rate, Cloud Cover (PPSUITE) Fuels Compliance
Basic Refueling Anti
- Tam pering Sunrise/Sunset Emission Rates Controls Pressure/Purge Tests

Calculate Emission Factors (Grams per Mile) for VOC and NOx

For an emissions inventory, area specific inputs are used for all of the items shown in Exhibit 2 except for the basic emission rates , which are MOBILE defaults. In addition, Pennsylvania uses the MOBILE6.2 default starts -per- day data and soak distributions that are used to calculate the number of starts in cold and hot start modes. EPA requires that the number of starts occurring per vehicle be determined from instrumented vehicle counts. S ince such local data is not available, the MOBILE6.2 national defaults are used for the Pennsylvania analyses. A vehicle will generate more emissions when it is first operated (cold start). It generates emissions at a different rate when it is stopped and then started again within a short period of time (hot start). Soak distributions are used to determine the time between when an engine is turned off to the next time it is restarted.Appendi x E

- 1 8 **Vehicle Descriptions.**  Vehicle age distributions are input to MOBILE for each county based on registered vehicles reflecting July 1 summer conditions. These distributions are obtained from PENNDOT’s Bureau of Motor Vehicle Registration Database. Vehicle Type Mix is calculated from algorithms using a combination of MOBILE6.2 default percentages and PENNDOT truck percentages from roadway data. (See also the discussion of Vehicle Type Pattern Data in the next section.) Speeds are discussed extensively in the next section. Significant changes have occurred in the MOBILE6.2 model as compared to previous releases. S ome of the information previously applied by the post processor after running MOBILE can now be input directly to the MOBILE6.2 model run. This includes information on the hourly distribution of VMT and the hourly speeds that occur during the day. Another important change in MOBILE6.2 is the influence of facility type on output emission factors. F or example, MOBILE6.2 assumes that an average speed on a freeway results in a different emission factor than the same speed on an arterial ro adway. Thus MOBILE6.2 is indirectly accounting for the accelerations and decelerations that typically occur on such roadways. M OBILE6.2 has four distinct facility types: Freeway, Arterial, Local, and Ramp. F or any emission run, the input functional clas ses analyzed must be mapped to the above facility types. The following mapping scheme is used for the Pennsylvania runs:

**PENNDOT Functional Classes MOBILE6.2 Facility Type**  1,11,12 Freeway 2,6,7,8,14,16,17 Arterial 9,19 Local Since ramps are not directly represented within the RMS database information, it is assumed that 8% of the Freeway VMT is Ramp VMT. This is consistent with the recommendations provided in EPA’s Technical Guidance on the Use of MOBILE6.2 for Emissions Inventory Preparation
. **Fuel Parameters.**  The same vehicle will produce different emissions using a different type of gasoline. Fuel control strategies can be powerful emission reduction mechanisms. An important variable in fuels for VOC emissions is its evaporability, measured by Reid Vapor Pressure. MOBILE allows the user to choose among conventional (used in most of Pennsylvania), federal reformulated (now used in the Philadelphia area), oxygenated (not used in Pennsylvania) and low Reid Vapor Pressure (RVP) gasoline (used in the Pittsburgh area starting in 1998). P ennsylvania chooses the MOBILE inputs appropriate to the year, season, and control strategy for the area being modeled. MOBILE also allows users to calculate refueling emissions, the emissions created when vehicl es are refueled at service stations. P ennsylvania includes refueling emissions in its area source inventory and not in its highway vehicle inventory. H owever, that calculation uses a grams per gallon emission rate generated by MOBILE. **Vehicle Emission**  **Inspection/Maintenance (I/M)**  **Parameters.** MOBILE allows users to vary inputs depending on the I/M program in place for the area or, of course, choose “no I/M program.” The inputs include:

 program start year  stringency level  first and last model years subject to the program  waiver ratesAppendi x E

- 1 9  compliance rates  program type (test
- only, test
- and
-repair, etc.) and effectiveness  frequency of inspection (annual, biennial)  vehicle type coverage  test type (idle, loaded, etc.)  pass/fail standards or “cutpoints”  technician training program Some cutpoints (the emissions at which vehicles are failed) are contained in MOBILE, while others must be put in by the model user. P ennsylvania uses the parameters specific for the geographic area and year for which the modeling i s being performed. **Environmental Variables.**  Evaporative emissions are influenced significantly by the temperatures of the surrounding air. Minimum and Maximum temperatures have been compiled for each county based on information from EPA’s CHIEF bulletin board reflecting airport temperatures on emission violation days. For annual and winter weekday analysis, average monthly temperatures are compiled for each county. A summary of the MOBILE related inputs used for the inventory and future year estimates are attached with the submission. 

## Em **ission and Speed Relationships** Of all the user
- supplied input parameters, perhaps the most important is vehicle speed. Emissions of both VOC and NOx vary significantly with speed, but the relationships are not linear, as shown in Exhibit 3. While VOCs generally decrease as speed increases, NOx decreases only at the low speed range and increases steeply at higher speeds. Unlike ozone precursors, the MOBILE6.2 calculation of PM 2.5 emission factors is not sensitive to many key input parameters including vehicle speed. To obtain the best estimate of vehicle speeds, Pennsylvania uses the PPSUITE set of programs, whose primary function is to calculate speeds and to organize and simplify the handling of large amounts of data needed for calculating speeds and for preparing MOBILE input files.Appendi x E

- 1 10 

### Exhibit **3**



### 0

1 2 3 4 5 6 7

2.5 5 10 15 20 25 30 35 40 45 50 55 60 65 **Speed (mph) C** **o m** **p o** **s i** **t e** **E m** **i s** **s i** **o n** **F a** **c t** **o r** **( g** **/ m** **i )** 



### NO **X** 

## MOBILE6 VOC and NOx **Speed v s. Emissions** 

**VOC**



## Roadway Data The roadway data input to emissions calculations for Pennsylvania uses information from the Roadway Management System (RMS) maintained by PENNDOT’s Bureau of Planning and Research. PENNDOT obtains this information from periodic visual and electronic traffic counts. RMS data is dynamic since it is continually reviewed and updated from new traffic counts and field visits conducted by PENNDOT. Information on roadways included in the National Highway System is reviewed at least annually, while information on other roadways is reviewed at least biennially. On a triennial basis, a current “snapshot” of the RM S database is taken and downloaded to provide an up
to - date record of the Commonwealth’s highway system for estimating emissions. A 2002 “snapshot” is used as the basis for 2002 base year inventory calculations. The current “snapshot”, in this case 200 5 , is used as the basis for future year inventory estimates
. Growth rates are used to factor the 2005 volumes to each future analysis year. The RMS database contains all state highways, including the Pennsylvania Turnpike, divided into segments approximately 0.5 miles in length. These segments are usually divided at important intersections or locations where there is a change in the physical characteristics of the roadway (e.g. the number of lane changes). There are approximately 99,000 state highway segments for the 67 Pennsylvania counties contained in the RMS. E ach of these segments contains an abundance of descriptive data, but only the following information is extracted for emission calculations:Appendi x E

- 1 11  Lanes  Distances  Volumes in Average Annual Daily Traf fic (AADT)  Truck percentages  PENNDOT urban/rural classifications  PENNDOT functional class codes RMS volumes and distances are used in calculating highway VMT totals for each county. A s discussed in the next section, adjustments are needed to convert the volumes to an average summer weekday, winter weekday, and monthly day. L ane values are an important input for determining the congestion and speeds for individual highway segments. Truck percentages are used in the speed determination process and are us ed to split volumes to individual vehicle types used by the MOBILE software. Pennsylvania classifies its road segments by function, as well as whether it is located in an urban, small urban or rural area, as indicated below in Exhibit 4. The PENNDOT urban/rural (UR) and functional classes (FC) are important indicators of the type and function of each roadway segment. The variables provide insights into other characteristics not contained in the RMS data that are used for speed and emission calculations. In addition, VMT and emission quantities are aggregated and reported using both UR and FC codes. 

### Exhibit **4 PENNDOT Classification Scheme: Urban/Ru**  **ral Codes and Functional Class Codes** Urban/Rural Code 1=Rural 2=Small Urban 3=Urban Functional Class Rural Functional Classes Used Urban Functional Classes Used For Rural Areas For Small Urban and Urban Areas

---------------------- --------------- ------------------------------------------ 1=Rural Freeway 11=Urban Freeway 2=Rural Other Principal Arterial 12=Urban Expressway 6=Rural Minor Arterial 14=Urban Principal Arterial 7=Rural Major Collector 16=Urban Minor Arterial 8=Rural Minor Collector 17=Urban Collector 9=Rural Local 19=Urban Local Note: Functional Classes 3,4,5,10,13,15,18 are not currently used in PENNDOT’s RMS database 

## Additions and Adjustm **ents to Roadway Data** Before the RMS data can be used by PPSUITE for speed and emission calculations, several adjustments and additions must be made to the roadway data. **HPMS Adjustments**  : According to EPA guidance, baseline inventory VMT computed from the RMS highway segment volumes must be adjusted to be consistent with Highway Performance MonitoringAppendi x E

- 1 12 System (HPMS) VMT totals. The HPMS VMT reported for Pennsylvania is a subsystem of the RMS established to meet the data reporting requirements of the Federal Highway Administration (FHWA) and to serve as PENNDOT’s official source of highway information. Although it has some limitations, the HPMS system is currently in use in all 50 states and is being improved under FHWA direction. The HPMS VMT totals are developed from the data contained in the RMS datab ase at the time of reporting and serves as a “snapshot” of the RMS data for a particular year. Since the RMS database does not contain many local roads, a separate procedure is used by PENNDOT to estimate total local VMT for the HPMS system. HPMS VMT sum maries are prepared each year and reported by PENNDOT urban/rural and functional class codes. The VMT contained in the HPMS reports are considered to represent average annual daily traffic (AADT). Although the HPMS VMT and the roadway data used for an inventory emissions analysis are both based on data from the RMS system, differences do exist between them and include the following. F irst, the HPMS and inventory roadway data are “snapshots” of the RMS data taken at different times. S ince the RMS is dynamic, changing constantly due to new data, differences will result between the data used for calculating HPMS VMT totals and the inventory data used for an emissions analysis. S econd, local estimates of HPMS VMT are obtained through alternative procedures developed by PENNDOT. However, the emissions inventory makes use of those few local roads contained in the RMS system. T o account for such differences, adjustment factors are calculated and used to adjust the inventory roadway data to the reported HPMS VMT totals submitted to FHWA. Adjustment factors are calculated which adjust the base year RMS download (in this case 200 5 ) VMT to the reported HPMS totals for that year. These factors are developed for each county, urban/rural code, and functional class combination and are also applied to all future year runs. Adjustments for the “higher” functional classes (e.g. Freeway, Arterials
- maj or routes) were very close to 1.000 since HPMS VMT is derived from RMS information, and the only difference in the data is that the “snapshot” for the emission calculations is taken at a different time than for the HPMS. “ Lower” classes (e.g. local roads) require greater adjustment since a large part of the local system is not under state jurisdiction and is not in the RM S database. There is, of course, a significant amount of local road mileage in the state. Iti s assumed that those local streets that are in RMS are representative of all local streets in their area with respect to volume and speed, so that roadway mileag e adjustment is appropriate. **Seasonal Adjustments**  **to Volumes**  : The RMS contains AADT volumes that are an average of all days in the year including weekends and holidays. An ozone emission analysis, however, is based on a typical summer weekday. P M and CO analyses require volumes representing a typical winter weekday and monthly average conditions (needed for producing annual totals). Therefore, the RMS volumes must be seasonally adjusted. S easonal factors were developed for each functional class and urban/rural code based on yearly count information prepared by PENNDOT’s Bureau of Planning and Research. Thes e factors are applied to the existing RMS AADT volumes to produce the July volumes. **Additional Network**  **Information:** The PPSUITE software system allows for many additional variables other than those available in the RMS database. U sing these variables improves the ability of Pennsylvania to incorporate real roadway conditions into its estimates. The variables include information regarding signal characteristics and other physical roadway features that can affect a roadway’s calculated congested speed. PPSUITE’s ability to estimate congested speeds by road segment improves Pennsylvania’s emissions inventories because of the overwhelming role speed plays in emission rates. I f specific information regarding these variables is known or obtained for areas , thisAppendi x E

- 1 13 information can be appended to the RMS database. Otherwise, default values are assumed based on information provided by the PPSUITE input speed/capacity lookup data as described below. Speed/capacity lookup data provides PPSUITE with initial (free - flow with no congestion) speeds and capacities for different urban/rural code and functional class groupings. The initial speeds and capacities are used by PPSUITE in determining the final congested speed for each roadway segment. S peeds can also be greatly impacted by signals and other roadway features. A s a result, this data provides default signal densities (average number of signals per mile for different functional classes) as well as default values for variables that determine the decay of speed with varying levels of congestion. A s discussed above, values from the speed/capacity data can be overridden for specific links by directly coding values to the roadway database segments. The speed capacity data was developed from a combination of sourc es including the following:

 Information contained in the 2000 Highway Capacity Manual  PENNDOT information on speeds and signal densities  Engineering judgment **24 -**  **hour Pattern**  **Data** : Speeds and emissions vary considerably depending on the time of day (becau se of temperature) and congestion. Therefore, it is important to estimate the pattern by which roadway volume varies by hour of the day. The 24
-hour pattern data provides PPSUITE with information used to split the daily roadway segment volumes to each of the 24 hours in a day. Pattern data is in the form of a percentage of the daily volumes for each hour. Distributions are provided for each county and functional class grouping. This data was developed from 24
-hour count data compiled by PENNDOT’s Bureau of Planning and Research
. **Vehicle Type**  **Pattern Data**  : Basic emission rates may differ by vehicle type. These types are listed below in Exhibit 5. 

### Exhibit **5 MOBILE6.2 Input Composite Vehicle Classes**  1. LDV
- Light
-Duty Vehicles (Passenger Cars) 2. LDT1
- Light
-Duty Trucks 1 (<6,000 lbs) 3. LDT2
- Light
-Duty Trucks 2 (<6,000 lbs, LVW=3,751
- 5,750) 4. LDT3
- Light
-Duty Trucks 3 (6,001
- 8,500 lbs) 5. LDT4
- Light
-Duty Trucks 4 (6,001
- 8,500 lbs, LVW>5,751) 6. HDV2B
- Class 2b Heavy Duty Vehicles 7. HDV3
- Class 3 Heavy Duty Vehicles 8. HDV4
- Class 4 Heavy Duty Vehicles 9. HDV5
- Class 5 Heavy Duty Vehicles 10. HDV6
- Class 6 Heavy Duty Vehicles 11. HDV7
- Class 7 Heavy Duty Vehicles 12. HDV8A
- Class 8a Heavy Duty Vehicles 13. HDV8B
- Class 8b Heavy Duty Vehicles 14. HDBS
- School Buses 15. HDBT
- Transit and Urban Buses 16. MC
- MotorcyclesAppendi x E

- 1 14 MOBILE summary reports by vehicle type are also useful in knowing what kinds of vehicles generate emissions. The vehicle type pattern data is used by PPSUITE to divide the hourly roadway segment volumes to the sixteen MOBILE6.2 (MOBILE5 had eight) vehicle types. S imilar to the 24
-hour pattern data, this data contains percentage splits to each vehicle type for every hour of the day. The vehicle type pattern data was developed from several sources of information:

 Hourly distributions for trucks and total traffic compiled by PENNDOT’s Bureau of Planning and Research, according to 2005 Pennsylvania Traffic Data  PENNDOT truck percentages from the RMS database  MOBILE6.2 default vehicle type breakdowns for the analysis year The vehicle type pattern data is developed for each county and functional class combination. First, RMS truck percentages are averaged for all roadways within a county, functional class grouping. U sing this percentage data, the total roadway volume for any segment could be divided to both auto and truck vehicle type categories. H owever, these percentages do not yet enable volumes to be divided to each of the sixteen MOBILE6.2 vehicle types. A s a result, MOBILE6.2 default vehicle type breakdowns are then used to divide the auto and truck percentages, calculated above, to each specific MOBILE6.2 vehicle type. Note that the defaults used vary by analysis year; as a result, each forecast year will utilize a unique vehicle mix distribution. P ENNDOT hourly distributions for trucks and total traffic are then used to create vehicle type percentage breakdowns for each hour of the day. **Vehicle Type**  **Capaci ty**  **Analysis Factors**  : Vehicle type percentages are provided to the capacity analysis section of PPSUITE to adjust the speeds in response to trucks. That is, a given number of larger trucks take up more roadway space than a given number of cars, and this mu st be accounted for in the model. C apacity is adjusted based on the factors provided in this data. V alues are developed from information in the 2000 Highway Capacity Manual and are specific to the various facility types. 

## Producing Future Year V **olum es**  Growth factors are used to project future highway volumes from the volumes provided in the RMS database. In the past, separate factors were derived for each county and highway functional class from an analysis of historic global update factors provided by PENNDOT’s Bureau of Planning and Research, coupled with estimates of population and employment growth from the U.S. Department of Commerce’s Bureau of Economic Analysis (BEA). The factors were then applied to base year traffic volumes (in this case 20 0 5 ) on each highway segment in the RMS network database. For this submission, county- specific growth rates from a PENNDOT study completed in 2005 have been used to forecast volumes. A s part of that study, a statewide traffic growth forecasting system was developed that incorporates traffic data from PENNDOT’s Traffic Information System and socioeconomic forecasts. The forecasting system was developed to support Department research endeavors related to transportation conformity and air quality planning. The study, as documented in the report “Statistical Evaluation of Projected Traffic Growth, Traffic Growth Forecasting System: Final Report, March 14, 2005 ”, included the development of VMT forecasts and growth rates for four functional classifications in each Pennsylvania county . The forecasts used statistical relationships based on historic HPMS VMT trends and future county socioeconomic projections from Woods and Poole.Appendi x E

- 1 15 

## SPEED/EMISSION ESTIMA **TION PROCEDURE** The previous sections have summarized the input data used for computing speeds and emission rates for Pennsylvania. This section explains how PPSUITE and MOBILE use that input data to produce emission estimates. Exhibit 6 on the following page summarizes PPSUITE’s analysis procedure used for each of the 99,000 highway segments in the state. Producing an emissions inventory with PPSUITE requires a process of disaggregation and aggregation. Data is available and used on a very small scale
-- individual 1⁄2 mile roadway segments 24 hours of the day. This data needs to first be aggregated into categories so that a reasonable number of MOBILE scenarios can be run, and then further aggregated and/or re - sorted into summary information that is useful for emission inventory reporting. One of the maj or enhancements of MOBILE6.2 is the increased detail of traffic that can be input to the emissions model. The PPSUITE post processor calculates hourly speeds for each roadway segment. Since previous versions of MOBILE only allowed one average speed as input for each scenario, the post
processed speeds had to be aggregated and run through MOBILE with scenarios representing four separate time periods. M OBILE6.2 allows for direct input of the 24 hourly speeds as well as options to account for each link’s spee d separately. These added features utilize the full extent of the information output from the speed processing programs and provide for more accurate emission estimates of the available traffic data. 

## Vo **lum e/V** 

**MT Developm ent**  Before speeds can be calculated and MOBILE run, volumes acquired from RMS must be adjusted and disaggregated. S uch adjustments include factoring to future years (not needed for 200 5 ), seasonal adjustments, and disaggregating daily volumes to each hour of the day and to each of the s ixteen MOBILE6.2 vehicle types. **Future Year**  **Volumes** : The RMS database contains up -to - date current year volumes. H owever, to conduct a future year analysis, these volumes must be factored to the year being analyzed. Growth factors have been prepared for each county and functional class grouping. These growth factors are applied to the 200 5 RMS volumes to obtain future year estimates that can be utilized by PPSUITE.

**Exam ple:**  A typical freeway link in the RMS database is I
- 80 segment 2500 in Luzerne County, Pennsylvania. This link has an urban/rural code=1 which indicates the link is in a rural area, and a functional class=1 indicating a rural freeway. The average annual daily traffic (AADT) from the RMS database for this link in 2002 is 12,077 vehicles/day. Grow th factors have been developed to factor the 2002 volume to future years. For example, to factor the 2002 volume to the year 20 14 , a grow th factor of 1.282 would yield: 20 14 volume = 12,077 vehicles/day x 1.282 = 15,483 vehicles/dayAppendi x E

- 1 16 

### Ex **hibit 6**  **PPSUITE Speed/Emission Estimation Procedure** Data From PPSUITE Input Files PPSUITE Analysis Process Data from Roadway Source (RMS) **The Following is Performed For Each RMS Roadway Segment**  Perc ent Pattern Distributions Expand to 24 hourly volumes RMS AWDT Adjusted Volumes Adjust Volumes for Peak Spreading Vehicle Type Patterns Disaggregate to Vehicle Type RMS Truck Percentages
Calculate Link & Signal Capacities Roadway Attributes (Lanes, FC code, UR code) Speed/Capacity Lookup Table Calculate Link Calculate Midblock Speed Approach Delay Calc VMT, Aggregate Link Speed Accumulate VMT, VHT (Aggregate by UR code, FC code, and time periods) **The Following is Performed For Each Area, Functional Class**  HPMS VMT Adjustments Apply HPMS VMT adjustments
MOBILE Parameters Run MOBILE6.2 for Emi ssion Factors Vehicle Age Distributions Min/Max/Ambient Temps

Humidity Calculate Emissions (VMT x Emission Factor) Prepare MOBILE6 Speed VMT File (Account for each roadway segment’s speed for each hour of the day)Appendi x E

- 1 17 **Seasonal Adjustments**  : PPSUITE takes the input daily vo lumes from RMS which represent AADT and seasonally adjusts the volumes to an average weekday in July. This adjustment utilizes factors developed for each functional class and urban/rural code. VMT can then be calculated for each link using the adjusted weekday volumes.

**Exam ple:**  Again, assume the rural freeway link: I
- 80 segment 2500 in Luzerne County, Pennsylvania. The average annual daily traffic (AADT) for this link in 2002 is 12,077 vehicles/day. Seasonal factors have been developed for urban/rural code and functional class combinations. For an urban/rural code=1 and a functional class=1, the factor to convert from AADT to an average we ekday in July is = 1.15 Average Weekday July Volume = 12,077 x 1.15 = 13,889 vehicles/day Total VMT (daily) for this link is calculated as volume x distance. The distance of this link as obtained from RMS is 0.286 miles. 2002 VMT = 13,889 vehicles/day x 0.296 miles = 41,111 vehicle
-miles / day **Disaggregation to 24 Hours** : After seasonally adjusting the link volume, the volume is split to each hour of the day. This allows for more accurate speed calculations (effects of congested hours) and allows PPSUITE to prepare the hourly VMT and speeds for input to the MOBILE6.2 model.

**Exam ple:**  To support speed calcul ations and emission estimates by time of day, the July weekday volume is disaggregated to 24 hourly volumes. Temporal patterns were previously developed from PENNDOT count data and input to PPSUITE. For the I
- 80 rural freeway link with morning peak volumes similar to evening peak hours (neutral), the following temporal pattern is applied:

0 1 2 3 4 5 6 7 8 9 101357911131517192123 **Ho ur**  **o f**  **Da y** **P e** **r c** **e n** **t o** **f D** **a i** **l y** 

Using the I
- 80 segment for 1990, typical hourly volumes which result include: 8
- 9 a.m. 6.0% x (41,111 vehicle miles/ 0.296mi.) = 833 vehicles/hour (vph) 12
- 1 p.m. 5.0% x (41,111 vehicle .miles/ 0.296mi.) = 694 vph 5
- 6 p.m. 6.3% x (41,111 vehicle miles/ 0.296mi.) = 875 vphAppendi x E

- 1 18 After dividing the daily volumes to each hour of the day, PPSUITE identifies hours that are unreasonably cong ested. F or those hours, PPSUITE then spreads a portion of the volume to other hours within the same peak period, thereby approximating the “peak spreading” that normally occurs in such overcapacity conditions. **Disaggregation to**  **Vehicle Type**  : EPA requires VMT estimates to be prepared by vehicle type, reflecting specific local characteristics. A s a result, for Pennsylvania’s emission inventory runs, the hourly volumes are disaggregated to the sixteen MOBILE6.2 vehicle types based on count data assembl ed by PENNDOT in combination with MOBILE6.2 defaults.

**Exam ple:**  Disaggregation of the total I
- 80 volume (by hour) to the various vehicle types would include the following: Total Volume 8
- 9 am = 833 vph Vehicle Type Volume 8
- 9 am: LDV 40.7% 338 vph LD T1 7.4% 62 vph LDT2 24.8% 207 vph LDT3 7.6% 63 vph LDT4 3.5% 29 vph HDV2b 5.0% 42 vph HDV3 0.5% 4 vph HDV4 0.4% 3 vph HDV5 0.3% 3 vph HDV6 1.1% 9 vph HDV7 1.3% 11 vph HDV 8a 1.4% 12 vph HDV8b 5.1% 42 vph HDBS 0.3% 3 vph HDBT 0.1% 1 vph MC 0.5% 4 vph 

## Speed/Delay Determ **ination** EPA recognizes that the estimation of vehicle sp eeds is a difficult and complex process. B ecause emissions are so sensitive to speeds, it recommends special attention be given to developing reasonable and consistent speed estimates; it also recommends that VMT be disaggregated into subsets that have roughly equal speed, with separate emission factors for each subset. At a minimum, speeds should be estimated separately by roadway functional class. The computational framework used for this analysis meets and exceeds that recommendation. Speeds are individually calculated for each roadway segment and hour and include the delays encountered at signals. Rather than accumulating the roadway segments into area/functional groupings and calculating an average speed (as done in past), each individual link hourly speed is represented in the MOBILE6.2 speed VMT file. This represents a significant enhancement in the MOBILE model since past versions only allowed input of one average speed for each scenario. M OBILE6.2 allows the input of aAppendi x E

- 1 19 distribution of hourly speeds. For example, if 5% of a county’s arterial VMT operate at 5 mph during the AM peak hour and the remaining 95% operate at 65mph, this can be represented in the MOBILE6.2 speed input file. F or the Pennsylvania runs, distributions of speeds are input to MOBILE6.2 for separate scenarios representing county and functional class groupings; VMT is accumulated by the same groupings for the application of the emission factors to produce resulting emission totals. To calculate speeds, PPSUITE first obtains initial capacities (how much volume the roadway can serve before heavy congestion) and free
- flow speeds (speeds assuming no congestion) from the speed/capacity lookup data. A s described in previous sections, this data contains default roadway information indexed by the urban/rural code and functional class. For areas with known characteristics, values can be directly coded to the RMS database and the speed/capacity data can be overridden. H owever, for most areas where known information is not available, the speed/capacity lookups provide valuable default information regarding speeds, capacities, signal densities and characteristics, and other capacity adjustment information used for calculating congested delays and speeds.

**Exam ple:**  The speed/capacity lookup table is used to obtain important data used for link speed calculations. For the I
- 80 link with an urban/rural code = 1 (rural) and a functional class = 1 (freeway), the lookup table provides information including the following: freeflow speed = 65 mph capacity = 1800 vph per lane number of signals = 0 This information is used along with the physical characteristics of the roadway to calculate the delay (including congestion) to travel this link during each hour of the day: For example: The I
- 80 link is calculated to have a travel time, including delay of 17.76 seconds for the 8
- 9am hour Total travel time, in vehicle hours, for the 8
- 9am hour is calculated as: VHT (8
- 9am) = 17.76 seconds x 833vph / 3600 sec/hr = 4.12 vehicle hours
The result of this process is an estimated average travel time for each hour of the day for each highway segment. The average time can be multiplied by the volume to produce vehicle hours of travel (VHT). 

## HPMS and V

**MT Adjustm ents**  Volumes must also be adjus ted to account for differences with the HPMS VMT totals, as described previously. VMT adjustment factors are provided as input to PPSUITE, and are applied to each of the roadway segment volumes. These factors were developed from 200 5 data; however, they are also applied to any future year runs. The VMT added or subtracted to the RMS database assumes the speeds calculated using the original volumes for each roadway segment for each hour of the day.Appendi x E

- 1 20 **Exam ple:**  Using the Luzerne County I
- 80 rural freeway l ink example, the daily assigned volume is adjusted to account for reconciliation with the HPMS VMT. RMS VMT (in AADT) for Luzerne County rural freeways totals 962,559 vehicle miles in 200 5 . HPMS VMT (in AADT) as supplied by PENNDOT and reported to FHWA totals to 990,088 vehicle miles for the rural freeways. A factor is developed by dividing the HPMS VMT by the RMS VMT: HPMS adjustment factor for Luzerne County rural freeways = 990,088 / 962,559 = 1.029 This factor is held constant in all future years. As an example, this adjustment is made to the I
- 80 freeway link VMT for the 8
- 9am hour after speed calculations are made, and produces the final July weekday VMT for this hour used for Ozone runs. I
- 80 Link VMT (8
- 9am) = 833vph x 0.296 miles x 1.0 29 = 254 vehicle miles 

## VM **T and Speed Aggregation** As discussed in previous sections, MOBILE6.2’s ability to handle input distributions of hourly speeds has eliminated the need to aggregate speed data. F or Pennsylvania runs, PPSUITE has been set up to automatically accumulate VMT and VHT by geographic areas and highway functional class. The speed files input to MOBILE6.2 for each scenario contain the actual distribution of roadway speeds for that aggregation group. Exhibit 7 illustrates the scenario aggregation scheme used with MOBILE6.2. 

### Exhibit **7 VMT/VHT Aggregation Scheme**  County 67 entries Urban/Rural Code 1=Rural 2=Small Urban 3=Urban Functional Class 1=Rural Freeway 11=Urban Freeway 2 =Rural Other Principal Arterial 12=Urban Expressway 18 entries 6=Rural Minor Arterial 14=Urban Principal Arterial 7=Rural Major Collector 16=Urban Minor Arterial 8=Rural Minor Collector 17=Urban Collector 9=Rural Local 19=Urban Local
1,206 potential combinations Geographic aggregation is performed by urban, small urban, and rural areas of each county. Functional class aggregation is according to PENNDOT’s eighteen standard functional classes, respecting ur ban,Appendi x E

- 1 21 small urban and rural definitions. F or an individual county, this creates a potential for 18 possible combinations, each of which becomes an input MOBILE6.2 scenario. This allows each MOBILE6.2 scenario to represent the actual VMT mix and speed for that geographic / highway combination. Altogether then, there are potentially 1,206 combinations for which speeds and VMT are computed and emissions are calculated with MOBILE. 

## MOBILE Em **issions Run** After computing speeds and aggregating VMT and VHT, PPSUITE prepares input files to be run in EPA’s MOBILE6.2 program which is used to produce VOC and NOx emission factors in grams of pollutant per vehicle mile. The process uses an unmodified version of the MOBILE program that was obtained directly from EPA. The MOBILE input file prepared by PPSUITE contains the following:

 MOBILE template containing appropriate parameters and program flags  Tem perature data specific to the county and season being run  Vehicle age and diesel sales fraction data for the county being run  Scenario data
- contains VMT mix, speed distributions specific to scenario as produced by PPSUITE

**Exam ple:**  A MOBILE input file is created by PPSUITE for Luzerne County. This file contains separate scenarios for each urban/rural code, functional class. A scenario represents a separate MOBILE run with different emission factors calculated and output for each run. For this example, Luzerne County rural freeways will be run as a scenario with a specific VMT mix file and a speed distribution file accounting for all the roadway speeds within the grouping.


## Tim **e of Day and Diurnal Em issions**  Unlike in the past using MOBILE5, VMT and speeds are no longer aggregated as separate scenarios representing time periods. This was done in the past to account for the unique speeds encountered during each time period in the day. S ince MOBILE6.2 allows for hourly roadway speeds to be represented in the speed VMT file, such a process is no longer needed. M OBILE6.2 will internally account for the emission s during each hour in the day and make the necessary diurnal calculations. 

## Process MOBILE Output After MOBILE has been run, PPSUITE processes the MOBILE output files and compiles the emission factors for each scenario. U sing the above methodology, it al locates daily diurnal emissions to each of the time periods. U sing the MOBILE emission factors, PPSUITE calculates emission quantities by multiplying the emission factors by the aggregated VMT totals. P PSUITE then produces an emissions database summarizing VMT, VHT, VOC, and NOx emissions as shown in Exhibit 8.Appendi x E

- 1 22 

### Exhibit **8 Summary of PPSUITE’s Methodology in Producing Emissions Summary** 

**PPSUITE Computes Speeds PPSUITE Aggregates VMT and VHT**  RMS Roadway Data (120,000 records) VMT & VHT Aggregated By: * County (67) PPSUITE Computes VMT & Speed * Functional Class and by Hour and Vehicle Type urban/rural codes (18)
**PPSUITE Runs the MOBILE Program** MOBILE Run for each County with UR, FC Scenarios **PPSUITE Processes MOBILE Output** Multiply VMT x Emission Rates
**PPSUITE Produces Emission Database** Fields Exist For: VOC CO By Vehicle Type & Total NOx By County, UR, FCAppendi x E

- 1 23 **Exam ple:**  Luzerne County rural freeways were run as a scenario in MOBILE. Based on the input information, MOBILE6.2 outputs emission factors by vehicle type for this scenario as show n below : Composite Emission Factors (grams/mile) from MOBIL6 output Vehicle Type: LDGV LDGT1 LDGT2 LDGT3 LDGT4 HDDV7 ..... For all 28 M6 types VOC: 1.22 1.86 2.42 3.68 0.36 1.13 NOX: 2.41 3.16 3.66 7.14 1.84 5.84 PPSUITE reads these emissi on factors from the MOBILE6.2 output file and multiplies them by the Luzerne County rural freeway VMT to obtain emission totals for this scenario. (Note: emissions shown in kg/day which is converted to tons/day in SIP narratives) PPSUITE computes emissio ns as follows for this scenario: **Emission Factors (g/m i)**  **Emissions (kg/day) Veh Type**  **VMT VOC**  **NOX VOC**  **NOX** LDGV 84,344 x 1.22 2.41 = 102.9 203.3 LDGT1 30,713 x 1.86 3.16 = 57.1 97.1 LDGT2 21,515 x 2.42 3.66 = 52.1 78.7 LDGT3 4,209 x 3.68 7.14 = 15.5 30.1 LDGT4 3,586 x 0.36 1.84 = 1.3 6.6 HDDV7 7,483 x 1.13 5.84 = 8.5 43.7 ..... Repeated for all 28 MOBILE6.2 vehicle types

--------------------------------------------------------------------------------------- ---------------- Total 155,903 244.6 482.0 The emissions for this scenario are reported and stored in an output database file w hich contains a record for each scenario with fields containing VMT, VHT, VOC emissions, and NOX emissions. Fields exist for each vehicle type and for the total of all vehicle types as shown below.

Reported by Vehicle Type 1

- 28 and Total

--- Repeated for VHT,HC,NOX **Cnty UR**  **FC VMT1**  **VMT2 VMT3**  **VMT4 VMT5**  **VMT6 VMT7 VMT8**  **... VMT28** Luze 1 1 84,344 30,713 21,515 4,209 3,5 86 2,806 7,483 1,248

**VHT1 VHT2**  **VHT3 VHT4**  **VHT5 VHT6**  **VHT7 VHT8 ... VHT28**  1,298 473 331 65 55 43 115 19 **VOC1 VOC2**  **VOC3 VOC4**  **VOC5 VOC6**  **VOC7 VOC8 ... VOC28**  102.9 57.1 52.1 15.5 1.3 1.5 8.5 5.7 **NOX1 NOX2**  **NOX3 NOX4**  **NOX5 NOX6**  **NOX7 NOX8 ... NOX2**  **8** 203.3 97.1 78.7 30.1 6.6 11.6 43.7 10.9Appendi x E

- 1 24 

## RESOURCES **MOBILE model** Modeling Page within EPA’s Office of Mobile Sources Website (http://www.epa.gov/omswww/models.htm) contains a downloadable model, MOBILE users guide and other information. It als o contains documents relating to the next version of MOBILE (MOBILE6.2) expected in 1999. "AP
-42" document, "Compilation of Air Pollutant Emission Factors, Volume II: Mobile Sources," as updated by Supplement A (January 1991), available in hard
- copy only. This material is also in the process of being revised and updated. Contact AP
-42 Project, Test and Evaluation Branch, EPA, 2565 Plymouth Road, Ann Arbor, MI 48105. Highway Vehicle Emission Estimates (June 1992) and Highway Vehicle Emission Estimates II (May 1995) discusses how EPA obtains data for MOBILE and some of the shortcomings in earlier models. Similar discussions of the present version’s shortcomings are discussed in papers available at the website. User’s Guide to MOBILE6.1 and MOBILE6.2 , Mobile Source Emission Factor Model, EPA Office of Air and Radiation, EPA420
-R
- 0 3
- 0 10 , dated August 200 3
. Technical Guidance on the Use of MOBILE6.2 for Emission Inventory Preparation , US EPA Office of Transportation and Air Quality, August 200 4
. Policy Gu idance on the Use of MOBILE6 for Emission Inventory Preparation , US EPA Office of Air and Radiation, January 18, 2002. **Traffic Engineering** 2000 Highway Capacity Manual, Transportation Research Board, presents current knowledge and techniques for analyzing the transportation system. Traffic Data Collection and Factor Development Report, 2001 Data, Pennsylvania Department of Transportation, Bureau of Planning and Research. Traffic Data Collection and Factor Development Report, 2002 Data, Pennsylvania Department of Transportation, Bureau of Planning and Research.Appendi x E

- 1 25 

## Highway **Ve hicle Inventory Glossary**  AADT: Average Annual Daily Traffic, average of ALL days. AWDT: Average Weekday Daily Traffic Basic emission rates: MOBILE emission rates based on the applicable Federal emission standards and the emission control technologies characterizing the fleet in various model years. Cold start: parameter in MOBILE that accounts for additional emissions resulting from a cold
- started engine. Diurnals: the pressure - driven evaporative HC emissions resulting from the daily increase in temperature Emission rate or factor: expresses the amount of pollution emitted per unit of activity. For highway vehicles, usually in grams of pollutant emitted per mile driven. FC: Functional code, applied in data management to road segments to identify their type (freeway, local, etc.) Fuel volatility: The ability of fuel components to evaporate, thus entering the atmosphere as pollution. Fuel volatility is usually measured as Reid Vapor Pressure (RVP) in pounds per square inch. The lower the RVP, the less volatile the fuel. Growth factor: Factor used to convert volumes to future years HPMS: Highway Performance Monitoring System, PENNDOT’s official source of highway information and a subset of RMS. I/M: Vehicle emissions inspection/maintenance programs ensure that vehicle emission controls are in good working order throughout the life of the vehicle. The programs require vehicles to be tested for emissions. Most vehicles that do not pass must be repaired. MOBILE: The model EPA has developed and which Pennsylvania uses to estimate emissions from highway vehicles. Pattern data: Extrapolations of traffic patterns (such as how traffic volume on road segment types varies by time of day, or what kinds of vehicles tend to use a road segment type) from segments with observed data to similar segments. Program flag: In MOBILE, a numeric code which tells the program such things as how data will be provided by user (or whether def ault will be used) or how to tailor outputs. PPSUITE: Post
-Processor for Air Quality, a set of programs that estimate speeds and processes MOBILE emission rates. RMS: Roadway Management System, a database maintained by PENNDOT from traffic counts and f ield visitsAppendi x E

- 1 26 Scenario: a MOBILE run with a specific set of geographical, time period, highway facility and control strategy assumptions. Segment: (referred to as link) division of roadway in the PENNDOT Roadway Management System. Usually represents 0.5 mile segments of roadway. UR: Urban/rural code, applied in data management to identify whether a road segment is urban, small urban or rural. VHT: vehicle hours traveled

. VMT: vehicle miles traveled. In modeling terms, it is the simulated traffic volumes times link length. Vehicle Type : One of eight types, distinguished primarily by fuel type and/or weight, used in MOBILE modeling.