# APPENDIX 1

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

**March 2007**Appendix X

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### Explanation of Methodology March 2007 

# TABLE OF CONTENTS
**INTRODUCTION ................................**  **................................ ................................**  **................................ .......................**  **3** O VER VIEW OF E MI SSI ONS I NVENTORI ES ................................ ................................ ................................ .................... 3 H IGHWAY V EHI CL E E MI SSI ON I NVENTORI ES ................................ ................................ ................................ .............. 3 **WHERE DOES PENNSYLVA NIA OBTAIN ITS DATA?**  **................................ ................................**  **...................... 6**  D ATA U SED I

N MOBILE
................................ ................................ ................................ ................................ ........... 6 W HAT A RE T HE N ECESSARY D ATA I NPUTS TO MOBILE?
................................ ................................ ........................ 7 E MI SSI ON AND S PEED R ELATIONSHIPS ................................ ................................ ................................ ....................... 9 R OADWAY D ATA ................................ ................................ ................................ ................................ ..................... 10 A DDITIONS AND A DJUSTMENTS TO R OADWAY D ATA ................................ ................................ .............................. 11 P RODUCI

NG F UTURE Y EAR 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 A DJUSTMENTS ................................ ................................ ................................ ............................ 19 VMT AND S PEED A GGREGATION ................................ ................................ ................................ ............................. 20 MOBILE E MI SSI ONS R UN ................................ ................................ ................................ ................................ ....... 21 T IM E OF D AY AND D IURNAL E MI SSI ONS ................................ ................................ ................................ .................. 21 P ROCESS MOBILE O UTPUT ................................ ................................ ................................ ................................ .... 21 **RESOURCES ................................**  **................................ ................................**  **................................ .............................**  **24 HIGHWAY VEHICLE INVE**  **NTORY GLOSSARY ................................**  **................................ .............................**  **25** 

# List of Exhibits E XHIBIT 1 : E MI SSI ON C ALCULATION P ROCESS FOR P ENNSYLVANIA ................................ ................................ .............. 5 E XHIBIT 2 : MOBILE I NPUTS ................................ ................................ ................................ ................................ ......... 7 E XHIBIT 3 : VOC AND NO X -- S PEED V . E MI SSI ONS ................................ ................................ ................................ ..... 10 E XHIBIT 4 : P ENN DOT C LASSIFICATION S CHEME ................................ ................................ ................................ ......... 11 E XHIBIT 5 : MOBILE6 V EHI CL E T YPES ................................ ................................ ................................ ....................... 13 E XHIBIT 6 : PPSUITE S PEED /E MI SSI ON E STIMATION P ROCEDURE ................................ ................................ ............... 16 E XHIBIT 7 : VMT/VHT A GGREGATION S CHEME ................................ ................................ ................................ .......... 20 E XHIBIT 8 : S UMMARY OF PPSUITE M ETHODOLOGY ................................ ................................ ................................ .. 22Appendix X

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# INTRODUCTION 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 constructi on 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 act ivity 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. Emiss ions 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 da y 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). For example, the annual VOC emissions from residential fuel oil heating could be estimated by: AP

- 42 emission rate X activity level = emissions 0.713 pounds/gallon X # dw elling units x % using oil x # gallons per unit # pounds of VOC per year 

### Adding up the pr oducts 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 g round
- level ozone, which is the most persistent air pollutant in Pennsylvania. Ozone is not created directly but formed in sunlight from VOCs and NOx. Both VOCs and NOx are emitted from highway vehicles. Pennsylvania’s ozone
related emission inventory e fforts have been focused on these pollutants. 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 ther e is a constant emission rate and a fairly simple measure of activity. For highway vehicles, however,Appendix X

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### 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 em itted 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 emissio n 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? started warm? running already warmed up?) and fuel. The inven tory 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) must 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 n etwork and fleet to estimate vehicle activity. For ozone
- related inventories, this is done for a typical summer weekday. For CO and PM emission inventories, this may be done for a typical winter weekday or annual conditions. Not only must this be done f or a baseline year, but it must also be projected into the future. This process 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 th e 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 h ighway 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) a s specified by the model user. MOBILE 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 fac tors that influence them. For this inventory effort, Pennsylvania utilizes MOBILE6.2 as approved by EPA. In addition to VOC, CO, and NOx, MOBILE6.2 produces emission factors for PM related emission categories as needed for other inventory efforts. **PP SUITE.**  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 conditions  Calculates highway speeds  Compiles vehicle miles of travel (VMT) and vehicle type mix data  Prepares MOBILE6 runsAppendix X

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###  Calculates emission quantities from output MOBILE6 emission rates and accumulated highway VMT. PPSUITE has become a widely used and accepted tool for estimating speed s 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 transportatio n engineering methodologies. For example, PPSUITE utilizes speed and delay estimation procedures based on planning methods provided in the 2000 Highway Capacity Manual , a report prepared by the Transportation Research Board (TRB) summarizing current knowl edge 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**  **Roadw ay 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 Processes MOBILE Output

PPSUITE Calculates Final EmissionsAppendix X

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

**TA ?** 
**Data Used in MOBILE** Two major types of informati on 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 st udies and special studies (including information from some state I/M programs). For 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 emis sions 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 while 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 connecti ons, 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 mor e. The model reflects this, using state
- specific vehicle age distributions 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 emi ssions 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 disp laced by the incoming liquid fuel and released to the atmosphere). Pennsylvania handles these emissions in the area source inventory.Appendix X

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## 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 variab les 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 Descr**  **iptions 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/Pur ge 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 ar e 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 b e determined from instrumented vehicle counts. Since 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 em issions 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.Appendix X

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### 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 calculat ed 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. Si gnificant changes have occurred in the MOBILE6.2 model as compared to previous releases. Some 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. For example, MOBILE6.2 assumes that an average speed on a freeway resu lts in a different emission factor than the same speed on an arterial roadway. Thus MOBILE6.2 is indirectly accounting for the accelerations and decelerations that typically occur on such roadways. MOBILE6.2 has four distinct facility types: Freeway, Art erial, Local, and Ramp. For any emission run, the input functional classes 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 import ant 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 u sed in Pennsylvania) and low Reid Vapor Pressure (RVP) gasoline (used in the Pittsburgh area starting in 1998). Pennsylvania chooses the MOBILE inputs appropriate to the year, season, and control strategy for the area being modeled. MOBILE also allows u sers to calculate refueling emissions, the emissions created when vehicles are refueled at service stations. Pennsylvania includes refueling emissions in its area source inventory and not in its highway vehicle inventory. However, 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 i nclude:

 program start year  stringency level  first and last model years subject to the program  waiver ratesAppendix X

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###  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. Pennsylvania uses the param eters specific for the geographic area and year for which the modeling is being performed. **Environmental Variables.** Evaporative emissions are influenced significantly by the temperatures of the surrounding air. Minimum and Maximum temperatures have bee n 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. 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.Appendix X

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### Exhibi **t 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 N ational 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 RMS database is taken and downloaded to provide an up
to - date record of the Commo nwealth’s highway system for estimating emissions. The current “snapshot”, in this case 2002, is used for the 2002 statewide inventory analysis. The RMS database contains all state highways, including the Pennsylvania Turnpike, divided into segments app roximately 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 high way segments for the 67 Pennsylvania counties contained in the RMS. Each of these segments contains an abundance of descriptive data, but only the following information is extracted for emission calculations:

 LanesAppendix X

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###  Distances  Volumes in Average Annual Dai ly Traffic (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. As discussed in the next section, adjustments are needed to conv ert the volumes to an average summer weekday, winter weekday, and monthly day. Lane 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 used 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 characte ristics 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: U**  **rban/Rural 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 Freew ay 11=Urban Freew ay 2=Rural Other Principal Arterial 12=Urban Expressw ay 6=Rural Minor Arterial 14=Urban Principal Arterial 7=Rural Major Collector 16=Urban M inor 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 adjus ted to be consistent with Highway Performance Monitoring 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) andAppendix X

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### to serv e 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 RM S database 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 summaries 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 fo r an inventory emissions analysis are both based on data from the RMS system, differences do exist between them and include the following. First, the HPMS and inventory roadway data are “snapshots” of the RMS data taken at different times. Since 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. Second, local estimates of HPMS VMT are obtained through alternative proc edures developed by PENNDOT. However, the emissions inventory makes use of those few local roads contained in the RMS system. To 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 2002) 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 t he 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 RMS database. There is, of course, a significant amount of local road mileage in the state. It is 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 mileage adjustment is appropriate. **Seasonal Adjustments to Volumes** : The RMS contains AADT volumes that ar e an average of all days in the year including weekends and holidays. An ozone emission analysis, however, is based on a typical summer weekday. PM and CO analyses require volumes representing a typical winter weekday and monthly average conditions (neede d for producing annual totals). Therefore, the RMS volumes must be seasonally adjusted. Seasonal 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 . These 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. Using these va riables 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. If specific information regarding these variables is known or obtained fo r areas, this 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.Appendix X

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### Speed/capacity lookup data provides PPSUITE with init ial (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. Speeds can al so be greatly impacted by signals and other roadway features. As 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 o f speed with varying levels of congestion. As 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 o f sources 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 (because 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 ea ch 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, according to the process in Procedures for Adjusting Traffic Count Data, 2002. **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
- Motorcycles 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 segmentAppendix X

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### volumes to the sixteen MOBILE6.2 (MOBILE5 had eight) vehicle types. Similar to the 2 4
- 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 PENND OT’s Bureau of Planning and Research, according to Procedures for Adjusting Traffic Counts, 2002  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. Using this percentage data, the total roadway volume for any segment could be divided to both auto and t ruck vehicle type categories. However, these percentages do not yet enable volumes to be divided to each of the sixteen MOBILE6.2 vehicle types. As 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. PENNDOT hourly distributions for trucks and total traffic are then used to create vehicle type percentage breakdowns for each hour of the day. **Vehicle Type Capacity 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 must be accounted for in the model. Capacity is adjusted based on the factors provided in this data. Values are developed from information in the 2000 High way 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 2002) on each highway segment in the RMS network database. For this submission, county
- specific growth rates from a PENNDOT study completed in 2005 have b een used to forecast volumes. As 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, 20 05 ”, included the development of VMT forecasts and growth rates for four functional classifications in each Pennsylvania county: urban interstate, urban non
- interstate, rural interstate, and rural non
- interstate. The forecasts used statistical relationshi ps based on historic HPMS VMT trends and future county socioeconomic projections from Woods and Poole.Appendix X

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# SPEED/EMISSION ESTIMA **TION PROCEDURE** The previous sections have summarized the input data used for computing speeds and emission rates for Pennsyl vania. 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 emissi ons 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 major 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 an d run through MOBILE with scenarios representing four separate time periods. MOBILE6.2 allows for direct input of the 24 hourly speeds as well as options to account for each link’s speed separately. These added features utilize the full extent of the inf ormation 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 dis aggregated. Such adjustments include factoring to future years (not needed for 2002 base year), seasonal adjustments, and disaggregating daily volumes to each hour of the day and to each of the sixteen MOBILE6.2 vehicle types. **Future Year Volumes** : The RM S database contains up
- to - date current year volumes. However, 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 fac tors are applied to the base year 2002 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 co de=1 w hich 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 facto r the 2002 volume to future years. For example, to factor the 2002 volume to the year 2014, a grow th factor of 1.282 w ould yield: 2014 volume = 12,077 vehicles/day x 1.282 = 15,483 vehicles/dayAppendix X

- 1 16 

### Exhibit **6 PPSUITE Speed/Em**  **ission Estimation Procedure** Data From PPSUITE Input Files PPSUITE Analysis Process Data from Roadway Source (RMS) **The Following is Performed For Each RMS Roadway Segment**  Percent Pattern Distributions Expand to 24 hourl y volumes RMS AWDT Adjusted Volumes Adjust Volumes for Peak Spreading Vehicle Type Patterns Disaggregate to Vehicle Type RMS Truck Percentages Calculate Link & Signal Capacities Roadw ay 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 Emission Factors Vehicle Age Distributions Min/Max/Ambient Temps

Humidity Calculate Emissions (VMT x Emission Factor) Prepare MOBILE6 Speed VMT File (Account for each roadw ay segment’s speed for each hour of the day)Appendix X

- 1 17 

### Seasonal Adjustments : PPSUITE takes the input daily volumes 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 da y. 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 calculations 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 freew ay link with morning peak volumes similar to evening peak hours (neutral), the fo llow ing 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 vehi cle .miles/ 0.296mi.) = 694 vph 5
- 6 p.m. 6.3% x (41,111 vehicle miles/ 0.296mi.) = 875 vphAppendix X

- 1 18 

### After dividing the daily volumes to each hour of the day, PPSUITE identifies hours that are unreasonably congested. For those hours, PPSUITE then spreads a po rtion of the volume to other hours within the same peak period, thereby approximating the “peak spreading” that normally occurs in such over
capacity conditions. **Disaggregation to Vehicle Type** : EPA requires VMT estimates to be prepared by vehicle type , reflecting specific local characteristics. As a result, for Pennsylvania’s emission inventory runs, the hourly volumes are disaggregated to the sixteen MOBILE6.2 vehicle types based on count data assembled by PENNDOT in combination with MOBILE6.2 defaul ts.

**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 LDT1 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 HDV8a 1.4% 12 vph HDV8b 5.1% 42 vph H DBS 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 speeds is a difficult and complex process. Because 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 V MT file. This represents a significant enhancement in the MOBILE model since past versions only allowed input of one average speed for each scenario. MOBILE6.2 allows the input of aAppendix X

- 1 19 

### distribution of hourly speeds. For example, if 5% of a county’s arteria l 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. For 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 c an serve before heavy congestion) and free
- flow speeds (speeds assuming no congestion) from the speed/capacity lookup data. As described in previous sections, this data contains default roadway information indexed by the urban/rural code and functional cl ass. For areas with known characteristics, values can be directly coded to the RMS database and the speed/capacity data can be overridden. However, for most areas where known information is not available, the speed/capacity lookups provide valuable defau lt 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 s ignals = 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, inc luding 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 tr avel 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 adjusted to account for differences with the HPMS VMT t otals, 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 2002 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.Appendix X

- 1 20 **Exam ple:**  Using the Luzerne County I
- 80 rural freew ay link example, the daily assigned volume is adjusted to account for reconciliation w ith the HPMS VMT. RMS VMT (in AADT) for Luzerne County rural freeways totals 962,559 vehicle miles in 2002. HPMS VMT (in AADT) as supplied by PENNDOT and reported to FHWA totals to 990,088 vehicle miles for the rural freew ays. 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 freew ay 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 1.029 = 254 vehicle miles 

## VM **T and Speed Aggregat**

**ion** As discussed in previous sections, MOBILE6.2’s ability to handle input distributions of hourly speeds has eliminated the need to aggregate speed data. For Pennsylvania runs, PPSUITE has been set up to automatically accumulate VMT and VHT by geographi c 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 Freew ay 11=Urban Freew ay 2=Rural Other Principal Arterial 12=Urban Expressw a y 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 combina tions 

### 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 urban,Appendix X

- 1 21 

### small urban and rural definitions. For an in dividual 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 MO BILE6.2 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 co ntains 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, sp eed 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 M OBILE 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 ea ch 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 emissions during each hour in the day and make the necessar y 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 allocates 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 Exh ibit 8.Appendix X

- 1 22 

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

**PPSUITE Computes Speeds PPSUITE Aggregates VMT and VHT**  RMS Roadw ay 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, FCAppendix X

- 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 shown below : Composite Emission Factors (g rams/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 emission factors from the MOBILE6.2 output file and multi plies 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 emissions as follows for this scenario: **Emission Facto rs (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 48 2.0 The emissions for this scenario are reported and stored in an output database file w hich contains a record for each scenario w ith fields containing VMT, VHT, VOC emissions, and NOX emissions. Fields exist for each vehicle type and for the total of al l 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 3,586 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 ... NOX28**  203.3 97.1 78.7 30.1 6.6 11.6 43.7 10.9Appendix X

- 1 24 

# R **ESOURCES 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 also contains documents relating to the next version o f 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 rev ised 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 MOBI LE 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, EPA420
- R
- 02
- 028, dated October 2002. Technical Guidance on the Use of MOBILE6 for Emission Inventory Preparation , US EPA Office of Transportation and Air Quality, January 2002. Policy Guidance on the Use of MOBILE6 for Emission Inventory Preparation , US EPA Office of Ai r 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.Appendix X

- 1 25 

# Highway **Ve hicle Inve**  **ntory 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 character izing 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 t ype (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 v olatile 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 e nsure 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 segmen ts 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 default will be used) or how to tailor outputs. PPSUITE: Post
- Processor for Air Quali ty, 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 field visitsAppendix X

- 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 id entify 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.