Program Announcement

EPA Releases “SmartWay SIP and 

Transportation Conformity Guidance: 

Accounting for NOx Reductions from 

TrailerAerodynamic Kits and Low-Rolling 

ResistanceTires” 

The U.S. Environmental Protection Agency (EPA) developed the SmartWay Transport Partnership to reduce greenhouse-gas 

emissions and air pollution from the ground freight-transport industry, 

including long-haul diesel trucks. EPA has developed a guidance document 

that describes how to quantify and use reductions in nitrogen oxides 

(NOx) that result when trucks are outfitted with two specific SmartWay 

fuel-efficient technologies: trailer aerodynamic kits and low-rolling 

resistance tires. 

EPA wants to encourage the adoption of SmartWay projects as a cost-effective 

way to achieve NOx emission reductions needed for state air-quality plans (i.e., 

state implementation plans known as “SIPs”) and transportation conformity 

determinations. 

How can SmartWay projects help in air-quality planning? 

Because SmartWay aerodynamic kits and low-rolling resistance tires reduce 

air pollution from trucks, these reductions can be quantified and used to help 

demonstrate achievement of air-quality goals in a SIP or in a transportation 

conformity determination. Therefore, this guidance is of interest primarily to ozone 

and particulate matter (PM2.5 and PM10) nonattainment and maintenance areas 

who are considering additional ways to reduce NOx for reasonable further progress 

SIPs, attainment demonstrations, maintenance plans, or in transportation conformity 

determinations. 

A SmartWay project under this guidance may be part of a larger effort to provide 

incentives for private and public agencies or truck owners to apply “SmartWay 

Office of Transportation and Air Quality 

EPA420-F-07-045 

June 2007 
Program Announcement

Upgrade Kits” to a truck or fleet of trucks. The document released today provides the remaining 

guidance needed for agencies to quantify and use the NOx reductions from SmartWay Upgrade 

Kits in SIPs and conformity. Additional general information about the SmartWay Transport 

Partnership, including the upgrade kits, can be found at: www.epa.gov/smartway/swresources.htm. 

How are SmartWay trailer aerodynamic kits and low-rolling resistance tires 

quantified for SIPs and transportation conformity determinations? 

For states other than California, EPA recommends the use of the National Mobile Inventory 

Model to estimate emission reductions from SmartWay aerodynamic kits and low-rolling 

resistance tires for SIPs and for transportation conformity analyses. The model estimates the 

impact of these technologies for the particular years to which they apply under local conditions. 

Due to the nature of the aerodynamic kits and low-rolling resistance tires, emission reductions 

from them will vary based on the average speed of the vehicles. See Chapter 2 of the guidance 

for more information. 

State and local agencies developing SIPs and conformity analyses for California should consult 

with EPA Region 9 for information on the current version of the emissions factor model 

approved for use in California and for information on how to apply Chapter 2 of this guidance 

with California’s model. 

What are the basic requirements for using NOx reductions from aerodynamic kits 

and low-rolling resistance tires in SIPs? 

Chapter 3 of the guidance explains the basic requirements that all control measures must 

meet to be included in a SIP. Emission reductions must be quantifiable, surplus, enforceable, 

permanent, and adequately supported. These requirements can be met with aerodynamic trailer 

kits and low-rolling resistance tires. 

Can these SmartWay technologies be included in a SIP under the Voluntary 

Measures policy guidance? 

Yes. If emission reductions from these technologies are approved into the SIP under EPA’s 

Voluntary Measures policy guidance, the state is responsible for assuring that the reductions 

credited in the SIP occur. The state would need to make an enforceable SIP commitment to 

monitor, assess, and report on the emission reductions resulting from the voluntary measure, and 

to remedy any shortfalls from forecasted emission reductions in a timely manner. See Chapter 3 

of the guidance for more information. 

How can NOx reductions from aerodynamic kits and low-rolling resistance tires be 

included in transportation conformity? 

Chapter 4 of the guidance covers this question in detail. Retrofits of highway vehicles (such as 

buses and trucks) can be included in transportation conformity determinations without a SIP 

revision by meeting the requirements in the conformity regulation at 40 CFR 93.122(a). 

EPA Releases SmartWay SIP and Transportation Conformity Guidance 
Program Announcement

For More Information: 

•	 You can access the guidance at www.epa.gov/otaq/stateresources/transconf/policy.htm 

•	 For more information about the SmartWay Transport program, visit: www.epa.gov/smartway 

or contact Cheryl Bynum of EPA’s Office of Transportation and Air Quality at 

734-214-4844 or bynum.cheryl@epa.gov. 

•	 For technical questions regarding the use of the National Mobile Inventory Model for 

calculating emission reductions from aerodynamic kits and low-rolling resistance tires, 

please e-mail mobile@epa.gov. 

•	 For general questions concerning the use of NOx reductions from aerodynamic kits 

and low-rolling resistance tires in SIPs or in transportation conformity, please contact 

Laura Berry of EPA’s Office of Transportation and Air Quality at 734-214-4858 or 

berry.laura@epa.gov or Gary Dolce (also of OTAQ) at 734-214-4414 or 

dolce.gary@epa.gov. 

EPA Releases SmartWay SIP and Transportation Conformity Guidance