CHAPTER 7 - ON-ROAD EMISSIONS

1996 Emission Inventory for the Alamo Area Council of Governments Region

 

Introduction

The inventory of on-road mobile source emissions includes all vehicles registered for use on public roadways. The primary source of emissions within this category is automobiles. Trucks and passenger buses also contribute significant amounts of emissions.

The Texas Natural Resource Conservation Commission (TNRCC) contracted with the Texas Transportation Institute (TTI) to provide on-road emission inventories for all 254 counties within the state (Contract #9880066900). The Rider 17 Ozone Near Nonattainment contract allows local agencies to use TTI's data to estimate on-road emissions instead of locally-generated mobile source inventories.

TTI utilized 1996 vehicle miles traveled (VMT) data compiled by the Texas Department of Transportation (TxDOT). VMT data collected was based upon federally-required Highway Performance Monitoring System (HPMS) reports. Because the inventory is geared toward estimating emissions for the ozone season, VMTs had to be adjusted from September-May school year to July weekday VMTs. TxDOT used automatic traffic recorders (ATR) to make the necessary adjustments to the data. ATRs are machines that record axles when a vehicle drives over the sensor in the pavement. A total of 91 ATR machines represent all 25 TxDOT regional averages.

Methodology

The TxDOT collected data over 24 hour time periods within the San Antonio area for FY1996. TTI then applied four models to the data to better compute the mobile source emissions for the San Antonio area. These models are: PREPIN, POLFC5HB, IMPSUMA, and VMTSUM. These models will be explained in detail in the enclosed and accompanying report by TTI (Development of Mobile Source Emissions Estimates for the San Antonio Area, 1996).

Data that has been run through the applicable models is represented in pounds of pollutant per year. These numbers are gathered for eight vehicle types and twelve roadway classifications within the surrounding 11-county region. These categories are as follows:

Vehicles	Roadways
Light duty gasoline vehicle (LDGV)	Rural interstates
Light duty gasoline trucks 1 (LDGT1)	Rural principal arterials
Light duty gasoline trucks 2 (LDGT2)	Rural minor arterials
Heavy duty gasoline vehicles (HDGV)	Rural major collectors
Light duty diesel vehicles (LDDV)	Rural minor collectors
Light duty diesel trucks (LDDT)	Rural locals
Heavy duty diesel trucks (HDDT)	Urban interstates
Motorcycles (MC)	Urban other freeways
	Urban principal arterials
	Urban minor arterials
	Urban collectors
	Urban locals

Once final numbers were gathered for each category, they were converted to tons per year and then tons per day. Final numbers for the San Antonio area can be seen in On-road Pollutant tables below.

AACOG 12 County Region On-Road Emissions

On-Road Emissions	VOC ton/day	NOx ton/day	CO ton/day
Atascosa County	3.95	6.41	46.51
Bandera County	0.84	1.04	6.76
Bexar County	94.59	95.66	715.71
Comal County	5.96	8.55	52.13
Frio County	2.85	5.48	35.90
Gillespie County	1.77	2.51	15.74
Guadalupe County	6.72	11.53	68.72
Karnes County	1.08	1.60	8.85
Kendall County	1.70	2.99	19.62
Kerr County	3.13	4.45	31.36
Medina County	2.68	4.06	26.03
Wilson County	1.74	2.51	14.20
TOTAL	127.01	146.80	1041.53

 

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