### APPENDIX E

URBAN DIESEL TRANSIT BUS EMISSIONS INVENTORY

### E-2

The EMFAC model used by the Air Resource Board (ARB) to obtain on-road motor vehicle emissions also calculates an emissions inventory for urban buses. However, for two reasons staff believes that the urban diesel bus inventory in EMFAC may not be suitable, without modification, for developing regulations that address only urban diesel transit buses. First, the population of the urban diesel bus vehicle class in EMFAC is derived from the Department of Motor Vehicles (DMV) registration database and contains urban transit buses as well as other categories of non-public transit buses, such as Greyhound and tour buses. The population reported by transit bus agencies is smaller than that used in the EMFAC model. Second, the urban bus fleet in EMFAC consists of 45 model years of vehicles, and buses of all ages are assumed to accrue 37,700 miles per year on average. Data reported for the years 2000-2002 by transit agencies show that the transit bus fleet consists of only 22 model years and buses of different ages accrue different mileage as a function of the age of the buses. In support of the ARB transit bus fleet rule regulation amendments, staff has constructed an inventory model specifically for diesel-powered transit buses that uses the population and activity data reported by transit agencies and emission rates from the EMFAC model. The following sections discuss the transit bus activity and emission rate estimate and present a revised urban diesel transit bus inventory. Urban Diesel Transit Bus Activity Data The following urban diesel transit bus activity data were obtained and analyzed:

• Annual mileage accrual rate;
• Population (POP) and age distribution;
• Total vehicle miles traveled (VMT). The annual mileage accrual rate for diesel transit buses was estimated from the annual mileage data provided by transit agencies. The average annual mileage data by model year was statistically fit to obtain a relationship between annual mileage accrual rate and vehicle age. A statewide diesel transit bus population (POP) of 6,303 vehicles was reported for 2002 by transit bus agencies. The age distribution (the number of vehicles by age) for diesel transit buses was calculated from the 2002 population data. Population for future years was projected based the following assumptions:

• No growth in 2003;
• Forty new diesel buses each year for 2004, 2005, and 2006;
• One percent growth for 2007, 2008, 2009, and 2010.

### E-3

The population of diesel transit buses for 2002+ was estimated using 2002 population as the base year. The projected population for each future year was adjusted with the survival rate (the fraction of the new vehicles that remains in the fleet after certain years) used for urban diesel buses in the EMFAC model. The diesel transit bus accrual rate, survival rate, and population distribution for years 2002 and 2010 are given in Table 1. Table 1. Diesel Transit Bus Accrual Rate, Survival Rate, and

Population Distribution

Age Accrual Rate

(mi/year) Survival Rate Year 2002 Population* Year 2010

Population** 0 30,868 1.0000 467 107 1 31,679 1.0000 945 160 2 32,332 1.0000 539 144 3 32,824 0.9930 269 96 4 33,158 0.9930 400 40 5 33,332 0.9930 506 40 6 33,346 0.9930 230 40 7 33,201 0.9894 188 52 8 32,897 0.9894 144 462 9 32,434 0.9878 326 933 10 31,811 0.9877 496 532 11 31,028 0.9840 462 267 12 30,087 0.9840 412 396 13 28,986 0.9791 362 499 14 27,725 0.9791 340 227 15 26,305 0.9746 18 185 16 24,726 0.9329 69 136 17 22,987 0.9329 45 308 18 21,089 0.9329 2 468 19 19,032 0.9251 10 434 20 16,815 0.9151 23 383 21 14,439 0.9099 9 336 22 11,904 0.9032 41 314 * Reported by transit bus agencies. ** Projected from year 2002 population and growth rate. 

### The diesel transit bus annual VMT for any given year was estimated from the population (POP) and accrual rate using the following equation:

### E-4 VMT = Σ(POP age

### x Accrual Rate i

### ), age = 1 to 22. (1)
Figure 1 shows the estimated diesel transit bus fleet annual VMT for 2001 to2010.

Figure 1. Urban Diesel Transient Bus Annual Mileage VMT

The diesel transit bus fleet shows a decline in VMT from 2001 to 2010. According to transit agency reporting, the population of diesel transit buses decreases from 6,738 vehicles in 2001 to 6,303 in 2002. From 2003 to 2006, the population is projected to remain essentially constant at 2002 level and then grow slightly each year from 2007 to 2010. However, from 2002 to 2010, the average transit bus fleet is projected to transform from mostly newer buses to mostly older buses (see Table 1). Since the annual mileage data shows that newer buses accrue more mileage than older buses, the annual VMT is projected to decline from 2001 to 2010. It is believed that this decline in diesel transit bus fleet VMT should be compensated by buses powered by alternative fuels and therefore the total VMT of the transit bus fleet should remain essentially constant or show an overall increase. Transit Bus Emission Rates The transit bus emission rates used for this analysis are the same as those used in EMFAC2001 version 2.08. Table 2 shows the speed-corrected NOx and PM emission rates obtained from EMFAC2001. 150,000 160,000 170,000 180,000 190,000 200,000 210,000

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 Calendar YearVMT (x 1000 mi/yr)

### E-5 Table 2. EMFAC2001 Diesel Urban Bus Emission Rates (g/mi)
Model Year Group NOx PM Pre 1987 23.2 0.310 1987-1990 20.3 0.294 1991-93 12.9 0.278 1994-95 15.1 0.339 1996-98 19.8 0.407 1999-02 10.3 0.139 2003 5.15 0.028 2004-06 1.2 0.024 2007 0.478 0.037 2008+ 0.426 0.032


### Transit Bus Emission Inventory Table 3 shows the diesel transit bus baseline inventories for selected calendar years. Table 3. Statewide Transit Bus Baseline Emissions Inventory

2001 2002 2004 2006 2008 2010 NOx (ton/day) 10.3 8.82 8.49 7.98 7.31 6.49 PM (lb/day) 372 321 309 290 267 239 

### The inventory given in the table does not include the ARB’s 2002 low sulfur diesel fuel and adopted retrofit regulations for transit buses and the U.S. EPA 2006 low sulfur diesel fuel regulation.