# APPENDIX C

TRANSIT FLEET VEHICLE EMISSIONS INVENTORY

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The EMFAC model used by the Air Resources Board (ARB) does not specifically address the emissions inventory of vehicles owned or operated by transit agencies, These vehicles are included as buses and trucks as part of the heavy-duty diesel truck fleet. This is largely because of the lack of emission and activity data specific to transit agency vehicles. Transit fleet vehicles (TFVs) operate differently from trucks driving on highways or freeways. While some vehicles operate on highways and freeways, most operate within cities or urban areas, in fixed or on-demand routes. In addition, ARB has not previously needed a specific inventory for TFVs. As ARB developed this regulation, however, staff required a more detailed inventory of TFV emissions than was previously available. The following sections discuss the population and present an emissions inventory for TFVs in California.

A. Transit Fleet Vehicle Population and Activity Data Transit fleet vehicles are those vehicles that are operated or owned by transit agencies but which are not urban buses. This distinction is important because new urban bus engines are certified to more stringent exhaust emission standards than are trucks, at least until 2010, and because ARB has an adopted rule that forces transit agencies to reduce emissions, on a fleet-wide basis, of oxides of nitrogen ( NOx ) and diesel particulate matter (PM). The following discussion provides detailed information on how ARB determined the number and characteristics of transit fleet vehicles.

1. Engine Exhaust Emission Standards The following tables (Tables 1-5) illustrate the differing certification standards for engine exhaust emissions from urban buses and trucks. Table 1. California and Federal NOx Emission Standards for Urban Bus Engines
Emission Standards (g/bhp-hr) Model Year California Federal 1988 6.0 10.7 1990 6.0 6.0 1991 5.0 5.0 1996 4.0 5.0 1998 4.0 4.0 October 2002 2.2 (1) 

### 2.2 (1) 

### 2004 0.5 (2), 

### 2.2 (3) 

### 2.2 (1) 

### 2007 0.2 (4) 

### 1.2 (4) 

### 2010 0.2 (4) 

### 0.2 (4)

1. Nominal expected NOxlevel based on emission standards of 2.4 g/bhp-hr NOxplus non-methane hydrocarbons (NMHC) or 2.5 g/bhp-hr NOxplus NMHC with 0.5 g/bhp-hr NMHC cap to take effect in October 2002 for those engines subject to the Settlement Agreements between the heavy-duty engine manufacturers, the United States Environmental Protection Agency

### C-2 (U.S. EPA), and ARB. As part of the Settlement Agreements, the federal heavy-duty engine emission standards adopted for 2004 took effect in October 2002.

2. Standard applies to urban bus equipped with diesel-fuel, dual fuel, or bi-fuel, engines.

3. Standard applies to urban bus equipped with alternative-fueled engines. Nominal expected NOx level of 2.2 g/bhp-hr is based on ARB emission standards of 2.4 g/bhp-hr NOx plus NMHC or 2.5 g/bhp-hr NOx plus NMHC with 0.5 g/bhp-hr NMHC.

4. Between 2007 and 2009, U.S. EPA requires 50 percent of heavy-duty diesel engine family certifications to meet the 0.2 g/bhp-hr NOx standard. Averaging is allowed, and it is expected that most engines will conform to the fleet NOx average of approximately 1.2 g/bhp-hr. 

### Table 2. California and Federal PM Emission Standards for Urban Bus Engines Emission Standards (g/bhp-hr) Model Year California Federal 1988 0.6 0.6 1991 0.1 0.25 1993 0.1 0.1 1994 0.07 0.07 1996 0.05 (1) 

### 0.05 (1) 

### October 2002 0.01 (2) 

### 0.05 (1) 

### 2007 0.01 0.01 1. In-use standard of 0.07 g/bhp-hr.

2. Standard applies to urban bus equipped with diesel-fuel, dual fuel, or bi-fuel, engines. Urban bus equipped with alternative fueled engines may certify to optional standard of 0.03, 0.02, or 0.01 g/bhp-hr. 

### Table 3. California Optional, Reduced-NOx Emission Standards for Urban Buses Emission Standard (g/bhp-hr) Model Year Optional Standards Increment 2000 2.5 - 0.5 0.5 October 2002 1.8-0.3 (3) 

### 0.3 2004 – 2006(1,2) 

### 1.8-0. 3 (3) 

### 0.3 1. Emission standards apply only to alternative fueled engines.

2. Engine manufacturers may sell diesel hybrid-electric buses certified at 1.8 g/bhp standard to transit agencies with approved NOx offset plans.

3. Optional emission standards of 1.8 – 0.3 g/bhp-hr are for NOx plus non-methane hydrocarbons (NMHC). Engines certified to the optional NOx standard are excluded from participating in the Averaging, Banking and Trading (ABT) program.

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Table 4. California and Federal NOx Emission Standards for Heavy Duty Truck Engines
Emission Standards (g/bhp-hr) Model Year California Federal 1988 6.0 10.7 1990 6.0 6.0 1991 5.0 5.0 1996 5.0 5.0 1998 4.0 4.0 October 2002 2.2 (1) 

### 2.2 (1) 

### 2004 2.2 (1) 

### 2.2 (1) 

### 2007 1.2 (2) 

### 1.2 (2) 

### 2010 0.2 (2) 

### 0.2 (2) 

### 1

. Nominal NOxvalue of 2.2 g/bhp-hr is based on emission standards of 2.4 g/bhp-hr for NOxplus non-methane hydrocarbons (NMHC) or 2.5 g/bhp-hr NOxplus NMHC with 0.5 g/bhp-hr NMHC cap, which took effect in October 2002 for those engines subject to the EPA Consent Decrees and the California Settlement Agreements. The Consent Decree-complying engines had to comply with 2004 standard by October 1, 2002.

2. Between 2007 and 2009, U.S. EPA requires 50 percent of heavy-duty diesel engine family certifications to meet the 0.2 g/bhp-hr NOx standard. Averaging is allowed, and it is expected that most engines will conform to the fleet NOx average of approximately 1.2 g/bhp-hr. 

### Table 5. California and Federal PM Emission Standards for Heavy Duty Truck Engines Emission Standards (g/bhp-hr) Model Year California Federal 1988 0.6 0.6 1991 0.25 0.25 1993 0.25 0.25 1994 0.10 0.10 2007 0.01 0.01



### 2. Department of Motor Vehicles Database In January 2004, staff conducted a data extraction of the 2002 Department of Motor Vehicles (DMV) database. The search criteria included "YY" - cutaway and "BU"- bus Body_Type_Models that resulted in 50550 "BU" records and 3076 "YY" records. The data were extracted from DMV2002B, which was extracted by the DMV in late September 2002. Staff's best guess is that it represents about the first 9 months of 2002. Staff evaluated each record and placed the record into one of four different bins : a) reporting urban bus (UB) fleet; b) new TFV fleet, including reporting UB fleet, TFVs, and new non-reporting TFVs; c) Public Fleets, such as airports, police department, prisons,

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universities and colleges; d) other, including tribal fleets. Private vehicles used solely for private applications and school districts were deleted from the database. Using a web search and a membership list from the California Association for Coordinated Transit (Cal/ACT), staff followed up on unknown ownership names and deleted vehicles falling into one of the following categories: vehicle owner that does not conduct transit operations, vehicle is not owned by a public transit agency, or the vehicle is not under contract to a public agency. Other vehicles in the DMV database were cross checked with survey data. Additional deletions included sold or “graveyard” vehicles not operating but still on the DMV database and school buses identified by a DMV analysis conducted for the NOx reflash requirements (discussed below). Staff identified that 6.8 percent of the vehicles in the DMV data extraction were listed under a financial institution or leasing corporation name. In addition, the DMV data extraction did not include trucks. The truck population represented 1.2 percent of the survey data population. After determining the total vehicle numbers above, the final total number was increased by 8 percent to account for the ownership by the financial institutions and to include trucks. The final 2003 TFV population was estimated to be 5,411 vehicles.

3. Transit Fleet Vehicle (non-urban bus) SurveyFrom April through December 2003, staff conducted a survey of reporting and nonreporting transit agencies. Reporting transit agencies are those that have been reporting to the ARB since adoption of the Fleet Rule for Transit Agencies in 2000. The survey was included in the annual reporting forms for the agencies subject to the current Fleet Rule for Transit Agencies. In addition, the survey was distributed by e-mail to the 250 Cal/Act membership which consists of smaller, rural and paratransit agencies, a majority of which were not subject to the current Fleet Rule for Transit Agencies and was distributed at the California Transit Association November 2003 conference. Other surveys were distributed as contacts were developed. Ninety-one transit agencies responded to the survey, reporting a total of 2,187 buses and trucks that would be included in the definition of transit fleet vehicle. Table 6 lists the total vehicles by transit agency. Gasoline vehicles and transit agencies operating only gasoline vehicles are not included. Eighty-one percent of the reporting transit agencies and 15 percent of the non-reporting agencies responded to the surveys. The percentage of non-reporting agencies was determined by using dividing the number of non-reporting surveys received by the number of individual agencies identified from the DMV data that currently are not subject to the Fleet Rule for Transit Agencies, not including contracting companies. Seventy four percent of the surveyed vehicles were reported from transit agencies currently subject to the regulation. Staff categorized the reported vehicles by model year (MY), fuel type, and <14,000 pounds (lbs) ,14,000-33,000 lbs, and >33,000 lbs gross vehicle weight rating (GVWR) (Table 7).

### C-5 Table 6. Transit Agencies and Vehicle Population from Survey 1
,2 

### Transit Agency Total Transit Agency Total A/C Transit 49 Paratransit, Inc. (Sacramento) 1 42 Amador Regional Transit1,2 10 Placer County 16 Antelope Valley Transit Authority 9 Plumas County Transit1,2 4 Arcata & Mad River Transit System 2 2 Porterville 1,2 10 Auburn1,2 3 Redding Area Bus Authority 19 Barstow Area Transit 1,2 13 Riverbank-Oakdale Transit Authority 1,2 9 Butte County 13 Riverside 1 19 Calaveras Transit 1,2 5 Riverside Transit Agency 19 Chico Area Transit System 3 Roseville 12 Chula Vista Transit 2 Sacramento Regional Transit District 23 Corcoran1,2 8 San Benito Co. Local Trans. Authority 1,2 7 Eastern Contra Costa Transit Authority 25 San Francisco Municipal Railway 1 El Centro (Dial-a-Ride) 1,2 3 San Joaquin Regional Transit District 42 El Monte1 10 San Luis Obispo Transportation Auth. 2 11 Fairfield/ Suisun Transit 14 San Luis Obispo2 1 Folsom 12 San Mateo County Transit District 48 Fresno County EOC1 43 Santa Barbara County Association of Gov. 4 Gardena Municipal Bus Lines 1 Santa Barbara Metropolitan Transit Dist. 15 Golden Empire Transit District 18 Santa Clara Valley Transportation Auth. 13 Golden Gate Transit 4 Santa Clarita Transit 18 Humboldt Transit Authority 2 3 Santa Cruz Met. Transit District 11 Imperial County Transit 10 Santa Maria Area Transit 9 Imperial1,2 2 Santa Monica Big Blue Bus 19 Inyo Mono Transit1,2 2 Santa Rosa City Bus 12 Kern Regional Transit1 61 SD Metropolitan Transit Dev. Board 150 Kings County Area Public Transit 1 Simi Valley Transit 11 Lake Transit Authority 1,2 13 Siskiyou County STAGE2 11 Lincoln 2 1 Sonoma County Transit 16 Livermore/

Amador Valley Transit Auth. 28 South Coast Area Transit 16 Long Beach Transit 33 South Lake Tahoe 2 2 Los Angeles DOT 53 Stanislaus Regional Transit 11 Mendocino Transit Authority 2 1 SunLine Transit Agency 29 Modesto 12 Tehama 1,2 10 Modoc Transportation (Sage Stage) 1,2 2 Thousand Oaks 3 Montebello 3 Torrance Transit System 14 Monterey Park1 7 Unitrans 10 Monterey-Salinas Transit 15 Vacaville 5 North County Transit District 31 Victor Valley Transit Authority 10 Norwalk 5 West Hollywood 1,2 1 Orange County Transportation Authority 329 Yolobus 6 Palo Verde Valley Transit 1,2 8 Yuba-Sutter Transit 1 37

1 Transit Agency is currently not subject to the Fleet Rule for Transit Agencies.

2 Population of Transit Agency's service area is less than 50,000.

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Table 7. Survey Population Distribution by Gross Vehicle Weight (GVWR) and Fuel Type
Gross Vehicle Wt. Diesel Gasoline Alternative Fuel Electric Total % By GVWR <14,000 342 164 63 0 569 26.0% >14,000 1028 381 155 5 1569 71.7% >33,000 49 0 0 0 49 2.2% Total 1419 545 218 5 2187 100.0% Percent By Fuel 64.9% 24.9% 10.0% 0.2% 100.0%

4. Analysis of Transit Fleet Vehicle Population Data Staff compared the fuel and GVWR distribution of the survey and DMV data. Staff used the fuel, MY, and GVWR classification percentages derived from the survey, rather than from the DMV database because the DMV data appeared to under represent diesel vehicles, skew the model year distribution to older vehicles, over represented <14,000 GVWR and >33,000 lb GVWR class. The DMV data appeared to under-represent diesel vehicles as much as by 13 percent. Staff accounted for the difference for the reporting of one common engine type that could be diesel or gasoline. Staff had initially identified those vehicles as all gasoline, but determined that some were diesel-fueled. The DMV database appeared to skew the model year distribution toward older vehicles. This is most likely the result of the DMV database data representing vehicles two years older at the time of extraction and older "retired" vehicles owned by transit agencies, but not being operated (waiting for auction or stored in the back lot), remaining on the DMV database. The GVWR weight distribution over represented <14,000 GVWR and >33,000 GVWR classes compared to the survey data. Staff believed this is the result of using GVWR DMV classifications of 2 and 3 for the <14,000 GVWR class. The range for the DMV Classifications 2 and 3 are 6,501 lbs to 10,000 lbs, and 10,001 lbs to 14,000 lbs, respectively. To adjust for the lighter vehicles, staff reviewed the DMV data and deleted vehicle classifications and engine sizes that were not used for the heavy-duty engine certification such as passenger cars, medium duty vehicles and light duty trucks. The >33,000 lb GVWR category, as discussed previously, contained school bus information and older "retired" vehicles. To correct for the >33,000 GVWR classification, staff deleted the school bus data obtained for the analysis of the NOx retrofit regulation. In addition, staff compared fleet number and make up with the surveys received and deleted older vehicles not in operation. As previously stated, the baseline population was based on the ending population after staff's manipulation of the DMV data extraction and survey analysis. The final data

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represented buses most likely operated by a transit agency. This value did not include vehicles owned by a financial institution or trucks. Staff only extracted vehicle data that met database body type definition of "bus" or "cutaway" from the DMV database therefore trucks were not included in the final number. To adjust for these two factors, staff increased the total number of vehicles after DMV data extraction by 8 percent to reflect the portion of vehicles currently owned by a financial institution but operated by a transit agency (6.8 percent of the DMV data) and to include the truck population (1.2 percent of the survey data). Including all fuels, staff determined that the total of TFVs equals 5,411. For the purpose of emissions inventory calculation, the TFVs were grouped into the following three different classes according to their GVWR:

• 

### Light heavy-duty TFVs (LHTFV): 14,000 lbs or less;

• 

### Medium heavy-duty TFVs (MHTFV): 14,001 to 33,000 lbs;

• 

### Heavy heavy-duty TFVs (HHTFV): 33,001 lbs or more. To estimate population data for emissions inventory calculation, staff applied the fuel, MY, and GVWR distributions obtained from the transit fleet survey to the total TFV population determined above to obtain the 2003 population distribution by GVWR and fuel type. Finally, as the proposed regulation does not regulate gasoline vehicles, vehicles fueled by gasoline were deleted from the total TFV population, resulting in a final TFV population of 4,054. Five electric vehicles (classified as alternative fuel vehicles) reported in the survey data were not included in this analysis.

5. Transit Fleet Vehicle Activity Data The following transit fleet activity data were then estimated for each group of vehicles:

• 

### Annual mileage accrual rate;

• 

### Population (POP) and age distribution;

• 

### Total vehicle miles traveled (VMT). The annual mileage accrual rate for TFVs was estimated from the annual mileage data provided by transit fleet agencies. Because of the considerable scatter in the annual mileage data, a population-weighted annual average was calculated from the annual miles of individual model years and used for all model years of TFVs. Statewide fleet populations of 3,504 and 550 vehicles were estimated for diesel and alternative fuel TFVs, respectively, for 2003. The age distributions (number of vehicles by age) for diesel and alternative fuel TFVs were also calculated using transit fleet survey data. The population for future years was projected based on the following assumptions:

• 

### A growth rate of 1.5% was used for the fleet between Years 2004 and 2020; This value is based on the growth rate observed from transit agencies currently reporting under the Fleet Rule for Transit Agencies;

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### Since the population data from transit fleet agencies could not provide information on fleet turnover, the survival rate of heavy heavy-duty trucks from EMFAC was used for diesel TFVsof 33,001 and greater GVW and the rate of urban diesel buses was used for TFVsof 33,000 lbor less GVW (survival rate quantifies the fraction of new vehicles that remain in the fleet after certain years). The populations of diesel and alternative fuel TFVs for 2004 and later model years were estimated using their 2003 populations as the base year. The projected populations for future years were adjusted using the fleet growth rate and vehicle survival rates. The TFV mileage accrual rate, survival rate, and population distribution for years 2003 and 2020 are given in Tables 12 through 14. The TFV daily VMT for any given year was estimated from the population (POP) and accrual rate using the following equation:
VMT = Σ POP age

### x (Accrual Rate) (1) where, age

= 0-22 years for LHTFVs and MHTFVs and 0-45 for HHTFVs. Table 8 shows the estimated annual VMT of transit fleet vehicles for selected calendar years. Table 8. Annual VMTs of Diesel and Alternative Fuel TFVs (in 1,000,000 mile/year) Vehicle Group 2000 2004 2005 2010 2015 2020 LHTFV(DSL) 20.2 21.9 22.2 23.9 25.8 27.8 LHTFV(Alt) 3.7 4.0 4.1 4.4 4.7 5.1 MHTFV(DSL) 73.5 79.5 80.7 86.9 93.6 101 MHTFV(Alt) 11.0 12.2 12.2 13.0 14.0 15.1 HHTFV(DSL) 3.3 3.6 3.7 4.1 4.4 4.7



### B. E mission Rates for Transit Fleet Vehicles The emission rates of diesel TFVs used in inventory calculations are those for light, medium, and heavy heavy-duty diesel trucks in EMFAC2002 (version 2.2; for details of heavy-duty truck emission rates as well as the complete emission rate tables, refer to EMFAC2002 documentation at www.arb.ca.gov/msei/msei.htm). The emission rates used for alternative fuel TFVs are the same as the rates of alternative fuel transit buses. These rates were estimated from emission data collected by West Virginia University (WVU), which includes emission data of 71 1991-1998 model year CNG powered transit buses. The data were first divided into model year groups corresponding to the model year groups of diesel transit buses and the data in each group was then averaged. Emission rates for model years after 1998 were estimated using the

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ratio of the standards. The HC, NOx, and PM emission rates for alternative fuel transit buses are given in Table 9.

Table 9. Emission Rates of Alternative Fuel Transit Buses (g/mi) Model Year Group HC NOx PM
1991-93 14.6 25.4 0.02 1994-95 15.5 11.2 0.02 1996-98 20.7 20.0 0.02 1999-02 20.7 20.0 0.02 2003 7.96 10.0 0.04 2004-06 0.80 2.5 0.04 2007 0.80 1.0 0.04 2008+ 0.80 1.0 0.04



### C. Emis sions Inventory of Transit Fleet Vehicles
Tables 10 and 11 summaries the NOx and PM baseline inventories of diesel and alternative fuel TFVs for selected calendar years. Table 10. NOx Baseline Inventories of Transit Fleet Vehicles (in lbs/day) Vehicle Group 2000 2004 2005 2010 2015 2020 LHTFV(DSL) 960 1,000 1,000 840 440 188 LHTFV(Alt) 420 400 400 340 174 66 MHTFV(DSL) 5,800 5,280 5,240 4,460 2,340 980 MHTFV(Alt) 1,280 1,120 1,100 940 500 200 HHTFV(DSL) 500 400 400 360 280 186



### Table 11. PM Baseline Inventories of Transit Fleet Vehicles (in lbs/day) Vehicle Group 2000 2004 2005 2010 2015 2020 LHV(DSL) 8 8 8 8 4 2 LHTFV(Alt) 0.4 0.4 0.4 0.4 0.2 0.2 MHTFV(DSL) 142 134 134 120 72 72 MHTFV(Alt) 1.4 1.0 1.0 0.8 0.6 0.4 HHTFV(DSL) 6 6 6 4 4 2

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Table 12. Accrual Rate, Survival Rate, and Population Distribution of TFVs (14,000 lb or less GWV) Age Accrual Rate

(mi/year) 1 Survival Rate 2003 Diesel Population 2 2020 Diesel

Population 3 2003 Alt Fuel

Population 2 2020 Alt Fuel

Population 3
0 25,537 1.0000 0 84 35 15 1 25,537 1.0000 22 80 32 15 2 25,537 0.9930 124 77 25 15 3 25,537 0.9930 121 77 22 16 4 25,537 0.9894 17 79 5 17 5 25,537 0.9877 213 84 22 18 6 25,537 0.9840 166 89 2 19 7 25,537 0.9791 116 94 0 18 8 25,537 0.9329 10 90 12 14 9 25,537 0.9329 15 82 12 10 25,537 0.8453 10 73 9 11 25,537 0.7196 7 58 6 12 25,537 0.6022 10 31 4 13 25,537 0.4952 0 21 2 14 25,537 0.3997 2 13 2 15 25,537 0.3166 5 9 1 16 25,537 0.2459 2 5 1 17 25,537 0.1872 2 4 7 18 25,537 0.1395 0 17 4 19 25,537 0.1016 0 12 3 20 25,537 0.0718 2 1 2 21 25,537 0.0296 6 0 22 25,537 0.0007 0 0 1. Population-weighted annual mileage average. 2. Estimated from DMV registration and transit fleet survey data. 3. Projected from year 2003 population and growth rate.

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Table 13. Accrual Rate, Survival Rate, and Population Distribution of TFVs (14,001- 33,000 lb GWV) Age Accrual Rate

(mi/year) 1 Survival Rate 2003 Diesel Population 2 2020 Diesel

Population 3 2003 Alt Fuel

Population 2 2020 Alt Fuel

Population 3
0 30,885 1.0000 7 241 17 36 1 30,885 1.0000 453 242 136 37 2 30,885 0.9930 369 245 106 38 3 30,885 0.9930 460 253 10 40 4 30,885 0.9894 302 265 20 43 5 30,885 0.9877 339 280 22 45 6 30,885 0.9840 163 292 35 48 7 30,885 0.9791 200 287 15 42 8 30,885 0.9329 37 238 12 27 9 30,885 0.9329 30 219 2 25 10 30,885 0.8453 35 162 20 21 11 30,885 0.7196 25 118 14 12 30,885 0.6022 15 75 10 13 30,885 0.4952 30 54 7 14 30,885 0.3997 10 34 6 15 30,885 0.3166 5 28 0 16 30,885 0.2459 35 19 4 17 30,885 0.1872 2 86 25 18 30,885 0.1395 7 51 15 19 30,885 0.1016 10 47 1 20 30,885 0.0718 0 22 1 21 30,885 0.0296 2 10 1 22 30,885 0.0007 0 0 1. Population-weighted annual mileage average. 2. Estimated from DMV registration and transit fleet survey data. 3. Projected from year 2003 population and growth rate.

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Table 14. Accrual Rate, Survival Rate, and Population Distribution of TFVs (>33,001 lb GWV) Age Accrual Rate

(mi/year) 1 Survival Rate 2003 Diesel Population 2 2020 Diesel

Population 3
0 30,244 1.0000 0 11 1 30,244 0.9760 5 10 2 30,244 0.9760 25 10 3 30,244 0.9760 47 10 4 30,244 0.9760 15 10 5 30,244 0.9760 0 10 6 30,244 0.9760 7 9 7 30,244 0.9698 2 8 8 30,244 0.9599 7 7 9 30,244 0.9525 7 6 10 30,244 0.9143 0 5 11 30,244 0.8747 0 4 12 30,244 0.8243 0 3 13 30,244 0.7636 0 3 14 30,244 0.6933 0 2 15 30,244 0.6425 0 2 16 30,244 0.5875 0 3 17 30,244 0.5290 0 3 18 30,244 0.4664 0 12 19 30,244 0.4049 0 19 20 30,244 0.3439 0 5 21 30,244 0.2962 0 0 22 30,244 0.2541 2 2 23 30,244 0.2071 2 0 24 30,244 0.1674 2 1 25 30,244 0.1404 2 1 1. Population-weighted annual mileage average. 2. Estimated from DMV registration and transit fleet survey data. 3. Projected from year 2003 population and growth rate.