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Appendix C: 

Emission Inventory Analysis and Results 
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APPENDIX C: Emission Inventory Development - Analysis and Results 

A. Emissions Inventory Data Sources 

A variety of data sources were used to establish the tractor and trailer population 

impacted by the proposed rule. These include the following: ARB Motor Vehicle 

Emissions Inventory (ARB Inventory), U.S. Bureau of Census 2002 Vehicle Inventory 

and Use Survey (VIUS)1, Americas Commercial Transportation Research Company 

(ACT Research), U.S. Bureau of Census Current Industrial Reports (CIR), and 

Commercial Carrier Journal. The following sections describe these data sources and 

the methodology used to estimate the tractor and trailer population impacted by the 

proposed regulation and the greenhouse gas emission benefits. 

1. ARB Heavy-Duty Vehicle Inventory 

On-road mobile source emissions in California are currently calculated using the 

EMFAC2007 (ARB, 2006) model that was released in December of 2006. Since the 

last EMFAC release, ARB staff members have conducted a re-evaluation of the heavy 

duty diesel truck emissions inventory to support the Proposed Regulation to Reduce 

Emissions from In-Use On-Road Diesel Vehicles. In developing this new analysis, staff 

has integrated new data and assumptions into an expanded methodology that builds 

upon current modeling in EMFAC2007. The updated inventory categorizes heavy-duty 

vehicles into separate inventory groups by body type and operational characteristics 

while keeping the existing weight class based vehicle categories (medium-heavy and 

heavy-heavy duty vehicle classes). Within the existing weight class groups, the 

updated inventory categorizes vehicles into California registered and out-of-state 

registered vehicles. California registered trucks are further split into intrastate and 

interstate trucks while the out-of-state registered trucks are split into trucks based in 

neighboring states and trucks based in non-neighboring states. The intrastate trucks 

are further sub-grouped by body type into single unit trucks and tractors. Also within the 

intrastate trucks separate inventories are developed for agricultural trucks, port trucks, 

solid waste collection vehicles, and public and utility fleets. A detailed discussion of the 

inventory development and data sources used is found in Appendix G, of the “Staff 

Report: Initial Statement Of Reasons For Proposed Rulemaking Proposed Regulation 

For In-Use On-Road Diesel Vehicles” (ARB, 2008a). 

The new baseline inventory for selected calendar years is shown in Table C-1 and C-3. 

Staff used this updated inventory as the basis for developing inventory for this proposal. 

Since only a subset of the total heavy-duty vehicle inventory is affected by the proposed 

regulation, the base inventory must be adjusted to determine the fraction of vehicles 

affected by this proposal. Furthermore, since the proposed regulation applies only to 

Class 7 and 8 tractors2

, the medium-heavy duty diesel vehicle inventory shown in Table 

 

1

 http://www.census.gov/svsd/www/vius/products.html 

2

 Class 7 tractors are tractors with gross vehicle weight rating between 26,001 and 33,000 

pounds while Class 8 tractors’ are tractors with gross vehicle weigh rating of 33,001 pounds 

and greater. 
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C-2, must be adjusted to include only Class 7 tractors. Table C-3 also shows the 

baseline population and the fraction of VMT accrued inside California by out-of-state, 

California interstate, and California intrastate heavy-duty vehicles (ARB, 2008a). 

Table C-1 – Baseline Class 8 Tractors (ARB, 2008a) 

Class 8 Tractors(Gross Vehicle Weight Rating > 33,000 pounds) 

Non-neighboring 

Out-of-state 

Tractors 

Neighboring

Out-of-state

Tractors 

CA 

Interstate 

Tractors 

CA 

Intrastate 

Tractors 

CY Population 

2010 469,323 43,049 62,239 66,037 

2015 543,681 51,132 73,924 78,519 

2020 626,853 58,008 83,866 89,294 

 

CY Vehicle Miles Traveled (106 miles per Year) 

2010 3,935 1,274 2,673 3,360 

2015 4,661 1,509 3,166 3,980 

2020 5,316 1,721 3,611 4,540 

Table C-2 – Medium-Heavy Duty Diesel Vehicles (ARB, 2008a). 

Medium-Heavy Duty Diesel Vehicles 

(Gross Vehicle Weight Rating between 14,001 and 33,000 pounds) 

 Out-of-State CA Interstate CA intrastate 

CY Population 

2010 7,631 1,752 209,116 

2015 8,282 1,901 227,426 

2020 8,898 2,042 244,223 

 

CY Vehicle Miles Traveled (106 miles per Year) 

2010 14 24 4,146 

2015 15 27 4,517 

2020 16 28 4,846 
C-4

Table C-3 – Population and CA Share of VMT (ARB, 2008a) 

CY Category Population CA Share of VMT 

 Heavy-Heavy Duty Vehicles 

2008 Out-of-State Tractors 492,340 12.1% 

2008 CA Interstate Tractors 60,263 57.0% 

2008 CA Intrastate Tractors 63,684 100% 

 Medium-Heavy Duty Vehicles 

2008 Medium-Heavy Intrastate 198,525 100% 

2008 Medium-Heavy Interstate 8,896 18.7% 

2. 2002 Vehicle Inventory and Use Survey 

The VIUS is a stratified statistical data of the nation’s trucking fleet collected every 5 

years by the Bureau of Census as part of the economic census (Census, 2002). It 

provides data, at the state and national level, on the physical and operational 

characteristics of registered private and commercial trucks. Since the state of 

registration of the truck is provided, a statistical profile of the truck fleet by state can be 

developed and analyzed to determine the characteristics of the state’s trucking fleet. 

The last survey was conducted in 2002. 

3. Bureau of Census, Current Industrial Reports (CIR): 

The U.S. Bureau of Census CIR program provides periodic reports on production and 

shipment of selected products. The CIR provides data on factory shipments of 

complete truck trailers between 1988 and 2000 (Census, 2000). Staff used these data 

to determine the fraction of box-type trailers sold each year. 

4. ACT Research, LLC. 

ACT Research collects commercial vehicle data from manufacturers, analyses it, and 

disseminates the results to its subscribers. Among other things, it collects and analyzes 

data related to North American Class 8 trucks and trailers. Among other things, it 

collects and analyses data related to North American Class 8 trucks and tractors and 

trailers. ACT provided staff with information on the fraction of 53-foot or longer box-type 

trailers sold nationwide. 

5. Commercial Carrier Magazine (CCJ) 

CCJ magazine, published monthly by Randall Reilly Publishing Company, LLC, 

provides news and business information for professionals responsible for running 

trucking companies and maintaining equipment. The CCJ publishes once a year, 

information on the nation’s top freight carriers, including the number of tractors and 
C-5

trailers owned by each company. Carrier performance data from the August 2007 and 

August 2008 issues of CCJ were used to assess the average ratio of trailers to tractors. 

Staff used these data to approximate the trailer to tractor ratio which was used to 

determine the total number of trailers affected by this rule. 

B. Fraction of Long Haul Tractors

The VIUS data (Census, 2000) were used to determine the fraction of long haul tractors 

by base state of registration for California intrastate, California interstate, and 

neighboring out-of-state tractors. Since ARB inventory does not provide a separate 

inventory for Class 7 trucks, staff also used the VIUS data to determine the fraction of 

medium-heavy duty vehicles that are long haul Class 7 tractors. 

Specifically, the VIUS data provided staff with information on (1) the primary range of 

operation (to determine the percentage of vehicles with a primary range of operation 

greater than 100 miles), and (2) jurisdiction in which the vehicle was most driven (to 

determine whether fleets operate interstate or exclusively intrastate). As shown in 

Table C-4, this information was used by staff to conclude that 23 percent of California’s 

intrastate tractors and 71 percent of California’s interstate tractors range of operation to 

be greater than 100 miles. For out-of-state registered tractors, 69 percent of tractors 

registered in neighboring states are affected, while 100 percent of non-neighboring 

states that operate in California are affected. In addition, analysis of VIUS data 

provided that approximately 5 percent of the total medium-heavy duty diesel vehicles 

are Class 7 tractors with primary range of operation greater than 100 miles (Census, 

2002). 

The VIUS database was also used to determine the VMT fraction accrued by tractors 

with primary range of operation greater than 100 miles, shown in Table C-4. This VMT 

fraction was applied to the baseline vehicle miles traveled provided by ARB inventory 

(discussed in A.1 above) to determine the total VMT accrued by the long haul tractors. 

Table C-4 - Percentage of Class 7 and 8 Tractors with Primary Range of Operation 

Greater than 100 Miles and their VMT fraction 

Fleet 

Percentage of Tractors 

with Primary Range of 

Operation > 100 Miles 

Percentage of VMT by Tractors 

with Primary Range of 

Operation > 100 Miles 

CA Intrastate 23% 34% 

CA Interstate 71% 80% 

Neighboring 

Out-of-State 69% 84% 

Non-neighboring 

Out-of-State 100% 100% 
C-6

C. Fraction of Long Haul Tractors that Pull 53-Foot or Longer Box-Type 

Trailers

Staff analyzed trailer production data from the 1997 to 2000 CIR reports (Census, 

2000), which showed that the percentage of box-type trailers sold each year from 1988 

to 2000 varied from 70 to 77 percent with an overall average of 73 percent. As shown 

in Table C-5, staff assumed that this average was appropriate for California intrastate, 

interstate, and neighboring out-of-state fleets operating in California. It was also 

assumed that since essentially all non-neighboring out-of-state tractors pull loads for 

greater distances, it would be appropriate to assume that more than 73 percent are boxtype. Staff assumed that 90 percent of these tractors pull box-type trailers. The 

fractions shown in Table C-5 include all box-type trailers of all lengths. To determine 

the fraction that are 53-foot or longer, staff consulted two trailer manufacturers and ACT 

Research. The two trailer manufacturers indicated that 90 percent or more of the boxtype trailers to be 53-foot or longer. According to ACT Research, 85 to 90 percent of 

refrigerated van and dry van trailers are 53-foot or longer (Vieth, 2008). Based on this 

information, staff assumes that 85 percent of the box-type trailers pulled by California 

intrastate, interstate, and neighboring out-of-state tractors, and 90 percent of those 

pulled by non-neighboring out-of-state tractors are 53-foot or longer. 

Table C-5 - Percentage of 53-Foot Box Type Trailers

Fleet Percent Box-Type 

Trailers 

Percent that are 

53-foot or Longer 

CA Intrastate 73 85 

CA Interstate 73 85 

Neighboring 

Out-of-State 73 85 

Non-neighboring 

Out-of-State 90 90 

Based on the above assumptions (Tables C-4 to C-5) and the baseline population and 

VMT provided by ARB inventory (ARB, 2008a), the tractor population impacted by the 

proposed regulation and the corresponding VMT are calculated and shown in Table C-6 

for calendar years 2010 and 2020. 
C-7

Table C-6: 2010 and 2020 Impacted Tractor Population and the Corresponding 

Annual VMT 

Impacted Tractor 

Population 

Annual VMT 

(106

 miles) Fleet 

2010 2020 2010 2020 

CA Intrastate 9,547 12,910 705 952

CA Interstate 27,462 37,005 1,320 1,783

Neighboring Out-of-State 18,525 24,962 663 896

Non-neighboring Out-of-State 380,152 507,751 3,187 4,306

Total 435,686 582,628 5,875 7,937

D. Impacted Box-Type Trailer Population

Available data were used to estimate the number of tractors that would be impacted by 

the proposed rule, as discussed above. For trailers, no database exists that provides a 

complete inventory on the total number of box-type trailers that would be impacted by 

the proposed rule. The ratio of trailers-to-tractors in many fleets is often not one-to-one 

(in which case the same numbers provided in Table C-6 for tractors could have been 

used to estimate trailer inventory). The ratio varies considerably from fleet to fleet. 

Many fleets typically own more trailers than tractors in order to maximize efficiency and 

reduce downtime for the tractor while waiting for the trailer to be loaded and unloaded. 

The ratio varies from zero for some owner-operators that own only tractors and pull 

trailers owned by other businesses, to “infinity” for some shippers that own only trailers 

and use the services of carriers to pull their trailers. Since data describing the tractortrailer composition of all fleets that operate in California were not available, staff 

determined an approximate trailer-to-tractor ratio using data from annual CCJ 

publications (Vise, 2007; Vise, 2008). The published data included the number of 

trailers and tractors owned by the top 250 carriers in the country in calendar years 2006 

and 2007. Analysis of the two annual datasets provided an estimated ratio of 2.5-to-1 

trailers to tractors for both years. 

The number of box-type trailers impacted by the proposed rule was then estimated by 

multiplying the trailer-to-tractor ratio of 2.5 by the number of tractors impacted by the 

proposed rule shown in Table C-6. Table C-7 shows the resulting 53-foot box-type 

trailer population impacted by staff’s proposal for calendar years 2010 and 2020. 
C-8

Table C-7: 2010 and 2020 Impacted 53-Foot Box-Type Trailers 

Fleet 2010 2020

CA Intrastate 23,868 32,275

CA Interstate 68,655 92,513

Neighboring Out-of-State 46,313 62,405

Non-neighboring Out-of-State 950,380 1,269,378

Total 1,089,215 1,456,570

E. Estimated GHG Benefits 

The GHGs associated with diesel exhaust are CO2, methane, and nitrous oxide, with 

CO2 being the major component of the three. Since CO2 is emitted in direct proportion 

to the fuel combusted, any reduction in CO2 emissions requires reduction in the fuel 

burned to propel the vehicle. The proposed regulation would reduce GHG emissions by 

reducing the fuel consumption of HDVs achieved through improvements in aerodynamic 

drag and tire rolling resistance. The GHG reductions would contribute towards attaining 

AB 32 goals for the year 2020. 

The following equation was used to calculate the GHG reductions from the proposed 

regulation. 

CO2e Reduced = Fuel Savings*EF/1000 (Equation C-1) 

Where: CO2e Reduced = average annual reduction in GHGs in metric tons CO2e 

 Fuel Savings = Annual fuel savings in gallons per year 

 EF = GHG emission factor from diesel fuel combustion (10.4 kilograms CO2e 

per gallon of diesel fuel (ARB, 2008c)) 

1000 = Conversion factor from kilograms (kg) to metric tons (1000 kg = 1 MT) 

Annual Fuel Savings: The annual fuel savings is determined from the percent fuel 

efficiency improvement, annual VMT, and the baseline fuel economy, as follows: 

Fuel Savings (gallons/year) = Annual VMT*%FS/FE 

 

Where: Annual VMT is the vehicle miles traveled per year 

%FS is the fuel consumption improvement due to improvements in 

aerodynamic drag and rolling resistance. 

FE is the fuel economy in miles per gallon. 

Percent Fuel Efficiency Improvements: The percent fuel efficiency improvements 

used to quantify the GHG benefits are shown in Table C-8. These were determined 
C-9

based on the minimum aerodynamic and tire rolling resistance performance 

requirements specified in the proposed regulation. For example, the proposed 

regulation would require a minimum fuel efficiency improvement of 3 percent from lowrolling resistance tires on the combined tractor and the trailer, a minimum of 4 percent 

from trailer side skirts, and a minimum of 1 percent from front or rear gap fairings on 

dry-van trailers. Thus, for this example, an in-use pre-2011 model year tractor pulling a 

dry-van trailer would achieve an overall fuel efficiency improvement of 8 percent, as 

shown in Table C-8. 

The fuel efficiency improvements of currently certified aerodynamic devices are 

determined from track tests conducted at speeds of 60 to 62 miles per hour and utilizing 

the “SAE J1321 Type II” test procedures. These aerodynamic devices also reduce drag 

at lower speeds, though to a lesser extent, since aerodynamic drag varies with the 

square of the vehicle speed. 

Annual VMT: The annual VMT applicable to tractors pulling 53-foot or longer box-type 

trailers was determined using the baseline VMT (ARB, 2008a) and the factors shown in 

Tables C-3 to C-5. However, the resulting total VMT cannot be directly applied to the 

fuel efficiency improvements shown in Table C-8, since the VMT is accrued at various 

speeds, while the fuel efficiency improvements are determined at speeds of 

approximately 60 miles per hour. Thus, the speed-VMT distribution of the impacted 

tractors and fuel efficiency improvements at different speeds are needed in order to 

accurately quantify the GHG emission benefits. However, such data were not available 

and therefore staff estimated the GHG benefits using only the VMT accrued at highway 

speeds, without taking into account benefits that occur at lower speeds. Accordingly, 

for non-neighboring out-of-state tractors, staff assumed 85 percent of the VMT to be at 

highway speeds, since these tractors travel long distances, spending the majority of 

their VMT at highway speeds. For neighboring out-of-state, California interstate, and 

California intrastate tractors, staff assumed 75 percent of the VMT to be at highway 

speeds, benefiting fully for 75 percent of the VMT from the aerodynamic devices and 

low rolling resistance tires. 
C-10

Table C-8: Fuel Efficiency Improvements – Based on Proposed Requirements 

 Tractor Improvements Trailer Improvements3 Fuel 

Savings 

1 

2011+ model year 

SmartWay certified sleeper 

cab tractor (3.5%) 

Dry-van trailer – 

SmartWay certified or 

retrofitted with side skirts and 

front gap fairings (6.5%) 

10.0% 

2 

2011+ model year 

SmartWay certified sleeper 

cab tractor (3.5%) 

Refrigerated-van trailer – 

SmartWay certified or 

retrofitted with side skirt 

(5.5%) 

9.0% 

3 

2011+ model year day cab 

tractors and all pre-2011 

model year in-use tractors - 

Tire Improvements (1.5%) 

Dry-van trailer – 

SmartWay certified or 

retrofitted with side skirts and 

front gap fairings (6.5%) 

8.0% 

4 

2011+ model year day cab 

tractors and all pre-2011 

model year in-use tractors - 

Tire Improvements (1.5%) 

Refrigerated-van trailer – 

SmartWay certified or 

retrofitted with a side skirt 

(5.5%) 

7.0% 

Fuel Economy of On-Road Heavy-Duty Diesel Vehicles in California 

ARB staff has recently reviewed multiple data sources to characterize the variations in 

the fuel economy values of heavy-duty tractors in California, including data from the 

United States Department of Energy (U.S. DOE, 2007), Coordinating Research Council 

E55/59 study by West Virginia University (CRC, 2007), the International Fuel Tax 

Agreement for trucks operating in California, and Consent Decree, in-use study by West 

Virginia University. The detailed methodology and results are discussed in Appendix G, 

of the “Staff Report: Initial Statement Of Reasons For Proposed Rulemaking Proposed 

Regulation For In-Use On-Road Diesel Vehicles” (ARB, 2008a). Results of the 

analysis, presented in Tables C-9, were used to estimate fuel savings and GHG 

emission benefits for this proposal. 

 

3

 The trailer aerodynamic technologies specified in the table are meant for illustration purposes. 

Fleets can meet the requirements using other aerodynamic technologies that meet or exceed 

the minimum performance requirements. 
C-11

Table C-9 - Fuel Economy Values by Model Year 

Model Year Fuel Economy 

(miles per gallon) Model Year Fuel Economy 

(miles per gallon)

Pre-1988 5.20 2003-2006 5.75

1988-1990 5.39 2007 5.61

1991-1993 5.58 2008 5.59

1994-1995 5.76 2009 5.58

1996 5.95 2010 5.78

1997-1998 5.95 2011 5.78

1999-2002 5.48 2012 5.80

 

For the purposes of quantifying the emission reductions, staff also assumed that all 

fleets would adopt the large fleet trailer compliance plan which provides a compliance 

option for in-use pre-2011 trailers based on a phase-in schedule specified in Appendix F 

of this report. Staff also assumed that in the absence of the proposed regulation, 20 

percent of the tractors sold each year from 2010 to 2020 would be SmartWay certified 

and 25 percent of the in-use pre-2011 model year tractors would use fuel efficient tires. 

The GHG emission benefits were calculated for the years 2010 to 2020 based on VMT 

accrued within California and nationwide. Table C-10 summarizes the 2010, 2015, and 

2020 statewide and nationwide GHG emission benefits of the proposed regulation. 

Staff estimates that from 2010 to 2020, as new fuel efficient tractors and trailers are 

introduced and in-use ones retrofitted with fuel efficient technologies, GHG emissions 

will be reduced by a cumulative total of approximately 8 MMT CO2e statewide and 

approximately 52 MMT CO2e nationwide. The 2020 benefits are approximately 1 MMT 

CO2e statewide and 7 MMT CO2e nationwide. Figure C-1 shows the statewide baseline 

and controlled GHG emissions for calendar years 2010 to 2020. As seen in Figure C-1, 

GHG emissions from long-haul tractors continue to increase even with implementation 

of the proposed regulation because the trucking industry will grow substantially between 

now and 2020 (ARB, 2008a). 
C-12

Table C-10: 2010, 2015, and 2020 GHG Emission Benefits - Statewide and 

Nationwide (MMT CO2e) 

 California Nationwide 

Calendar Year Baseline Reductions Baseline Reductions

2010 8.5 0.2 55.6 0.9 

2015 10.1 0.8 65.7 5.5 

2020 11.4 1.0 74.6 6.7 

7.0

7.5

8.0

8.5

9.0

9.5

10.0

10.5

11.0

11.5

12.0

2009 2011 2013 2015 2017 2019 2021

Calendar Year

GHG Tailpipe Emissions 

(MMTCO2e)

Baseline

With Regulation

Figure C-1. Statewide GHG Emissions With and Without the Regulation (Longhaul tractor pulling 53-foot box-type trailers) 

Estimated Oxides of Nitrogen (NOx) Emission Benefits 

In addition to GHG benefits, reducing aerodynamic drag and rolling resistance also 

reduces NOx emissions (Bachman, 2005; Bachman, 2006). Thus, the proposed 

regulation is expected to provide NOx emission reduction benefits that would contribute 

towards attainment of ambient air quality standards for ozone. Staff used the 
C-13

methodology specified in the U.S. EPA SmartWay State Implementation Plan (SIP) and 

Transportation Conformity guidance document (U.S. EPA, 2007) to quantify the NOx 

emission benefits from the proposed regulation. 

Because the effects of the SmartWay technologies on NOx emissions of trucks with 

particulate matter and NOx aftertreatment controls is not yet determined, the U.S. EPA 

recommends that, for SIP and conformity determinations, the NOx reductions not be 

applied to trucks of model years newer than 2006. Furthermore, the NOx emission 

reductions associated with SmartWay retrofit applications vary by speed, requiring the 

VMT to be distributed by speed. Since speed distribution data for the fleet that is 

impacted by the proposed regulation were not available, staff made the following 

assumptions on VMT-speed distribution of long-haul tractors. That is, for nonneighboring out-of-state tractors, staff assumed 85 percent of the VMT to be at highway 

speeds and a corresponding NOx reduction of 9.5 percent. For the remaining 15 

percent of the VMT staff assumed an average speed of 35 miles per hour and a NOx 

reduction of 4.6 percent. For California intrastate, California interstate, and neighboring 

out-of-state tractors, staff assumed 75 percent of the VMT to be at highway speeds and 

a corresponding NOx reduction of 9.5 percent. For the remaining 25 percent of the 

VMT, staff assumed an average speed of 35 miles per hour and a corresponding NOx 

reduction of 4.6 percent. Based on these assumptions and U.S. EPA guidelines, 

California specific NOx reductions were estimated to be 4.3 and 1.4 tons per day in 

2014 and 2020 respectively. These reductions assume a “business as usual” scenario, 

where they do not take into account the impact of other proposed regulations that would 

impact NOx emissions. 
C-14

F. References 

ARB, 2006. California Air Resources Board. EMFAC2007. Available at: 

http://www.arb.ca.gov/msei/onroad/latest_version.htm Last Accessed: October 

22,2008. 

ARB, 2008a. California Air Resources Board. Staff Report: Initial Statement Of 

Reasons For Proposed Rulemaking. Proposed Regulation For In-Use On-Road 

Diesel Vehicles. Appendix G – Emissions Inventory Methodology and Results. 

Sacramento: October 2008. 

ARB, 2008c. California Air Resources Board. Climate Change Proposed Scoping Plan. 

Appendices Volume II: Analysis and Documentation. (Appendix II, p.I-6). 

Sacramento: October 2008. 

http://www.arb.ca.gov/cc/scopingplan/document/scopingplandocument.htm

Bachman, 2005. Bachman, Leon J., Anthony Erb, Cheryl Bynum. Effect of Single Wide 

Tires and Trailer Aerodynamics on Fuel Economy and NOx Emissions of Class 8 

Line-Haul Tractor-Trailers. Society of Automotive Engineer 2005-01-3551 

http://www.epa.gov/smartway/transport/documents/tech/effects-on-fuel-economy.pdf

Bachman, 2006. Bachman , L J., A. Erb, C. Bynum, B. Shoffner, H. De La Fuente, C. 

Ensfield. Fuel Economy Improvements and NOx Reduction by Reduction of 

Parasitic Losses: Effect of Engine Design. Society of Automotive Engineer, 2006-

01-3474. http://www.epa.gov/smartway/transport/documents/tech/fuel-economyimprovements.pdf

Census, 2000. Bureau of Census. Current Industrial Reports, M336L - Truck Trailers.

http://www.census.gov/cir/www/336/m336l.html

Census, 2002. United States Bureau of Census. 2002 Vehicle Inventory and Use 

Survey Microdata. http://www.census.gov/svsd/www/vius/products.html

CRC, 2007. Coordinating Research Council, Inc. Heavy-Duty Vehicle Chassis 

Dynamometer Testing for Emissions Inventory, Air Quality Modeling, Source 

Apportionment and Air Toxics Emissions Inventory. August 2007. Available at: 

http://www.crcao.com/reports/recentstudies2007/E-55-59/E55_59_Final_Report_23AUG2007.pdf

U.S. DOE, 2008. Department of Energy, Oak Ridge National Laboratory. 

Transportation Energy Data Book: Edition 27. ORNL 6891. 

http://www-cta.ornl.gov/data/tedb27/Edition27_Cover.pdf

U.S. EPA, 2007. U.S. Environmental Protection Agency. SmartWay SIP and 

Transportation Conformity Guidance: Accounting for NOx Reductions from Trailer 
C-15

Aerodynamic Kits and Low Rolling Resistance Tires. EPA420-B-07-004. 

June 2007. www.epa.gov/otaq/stateresources/transconf/policy/420b07004.pdf

Vieth, 2008. Vieth, Ken. Telephone Communication with Mr. Ken Vieth, Senior Partner 

and General Manager of Americas Commercial Transportation Research co., LLC 

(ACT Research). July 2, 2008 

Vise, 2007. Vise, Avery. The CCJ Top 250: Mediocre at Best. Commercial Carrier 

Journal. August 2007. pp. 61-110. 

http://www.rrpub.com/etrucker/ccj/ccj0807_250.pdf

Vise, 2008. Vise, Avery. The CCJ Top 250: Slower But Solid. Commercial Carrier 

Journal. August 2008. pp. 52-103. http://www.rrpub.com/ccj/pdfs/top250_07.pdf