The University of Arizona

Reducing Greenhouse Gases from Cars and Commercial Vehicles

By Joe Abraham | The University of Arizona | May 18, 2009

Transportation is responsible for a large portion of all greenhouse gases emitted in the Southwest region. It is also a significant source of other air pollutants that impact human health, including particulate matter and others that contribute to ground-level ozone. Approximately 23 percent of all greenhouse gases emitted in the U.S. in 2007 were from cars, trucks, and buses, according to the U.S. Environmental Protection Agency.1 In the Southwest U.S. estimates of emissions in 2000 from road vehicles and, to a much lesser extent, aircraft vary from 39 percent of total emissions in Arizona,2 to less than 17 percent in New Mexico.3

photo of polluting cars

Cars and light trucks are a significant source of emissions in the Southwest.
Credit: ©Dave Parsons,

Options for reducing transportation-based emissions identified by southwestern state climate action planning processes generally fall into three categories:

These categories are based on state plans created between 2005 and 2007 in Arizona, New Mexico, Utah, and Colorado to help achieve statewide greenhouse gas emission reductions. Gubernatorial executive orders instigated the planning processes in Arizona, New Mexico, and Utah, while a coalition of stakeholders (including the state of Colorado) led by a regional non-profit organization initiated the Colorado plan. Each planning process produced a set of recommended options for reducing emissions.

Reducing emissions from private passenger and light-duty vehicles

Graph of transportation emission reduction recommendations

Figure 1. Recommendations for transportation emission reductions from state climate action plans.
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Credit: Joe Abraham and Rebecca Macaulay, CLIMAS, The University of Arizona

To reduce greenhouse gas emissions from cars and light trucks, California adopted laws in 2004 that are being phased in from 2009 through 2016. The laws require the gradual adoption of technologies and alternative fuels—that are already used and available4—for all new cars and light trucks sold in the state. In May 2009 the U.S. federal government announced plans to develop a set of national automobile emission and mileage standards that will take effect in 2012 and will be similar to the California rules but national in scale.

Adopting the California clean car regulations is the single largest and most cost-effective transportation emission reduction option in the Arizona, Colorado, and New Mexico climate action plans. State-wide estimates of cost savings from this policy option for 2007 through 2020 range from $1.2 billion (New Mexico) to almost $3 billion (Arizona). Emission reduction estimates range from 10 to more than 30 million metric tons of CO2-equivalent (MMtCO2-e) for New Mexico and Arizona, respectively, for the period 2007 through 2020 (Figure 1). As an example, a person who drives 12,000 miles per year and switches from a car that gets 20 miles per gallon (mpg) to 30 mpg will reduce CO2 emissions by approximately 1.75 metric tons over the year.5

State action plans also recommend financial incentives that will help reduce emissions. Requiring “pay as you drive” auto insurance would create clearer incentives for driving fewer miles and result in significant emission reductions (Figure 1). State “feebate” programs would apply fees to the cost of relatively high emission/low fuel economy vehicles and apply rebates or tax credits for low emission/high fuel economy vehicles.6

All four southwestern state plans recommended financial incentives for citizens and businesses (e.g., tax rebates) as well as government vehicle purchasing requirements that would increase the use of clean vehicles (Figure 1). The Arizona plan also proposed government participation in the U.S. Environmental Protection Agency “SmartWay” program, which helps public and private organizations save fuel costs, reduce emissions, and protect the environment. New Mexico’s plan recommended increasing the production and availability of biofuels around the state.

Arizona and New Mexico plans advocated for standards that reduce tire friction and improve consumer education at tire dealerships about the fuel-efficiency benefits of low-friction tires and adequate tire pressure. Estimates for these two options alone would save approximately $506 million in fuel savings in New Mexico from 2007 through 2020 while reducing emissions by more than 5 MMtCO2-e (Figure 1).

Reducing emissions from commercial heavy-duty commercial vehicles

photo of trucks at a rest stop

Commercial trucks traditionally leave engines idling for to heat, cool, and use electricity for hours while drivers rest. Idle-reduction technologies can reduce these emissions.
Credit: ©Jane and Aaron Photography,

State climate action plans in the Southwest identify separate options for reducing emissions from heavy-duty commercial trucks and vehicles.

The Arizona and New Mexico plans recommended reducing emissions from commercial vehicles that idle at rest stops to power air conditioned trailers and provide power for drivers (Figure 1). Several technologies already available could be used to meet these power needs instead of idling the truck’s large diesel engine: electrified parking spaces at interstate rest stops, auxiliary power units, fuel operated heaters, battery air conditioning systems, and thermal storage systems for cooling.7 Estimated fuel cost savings from these options for 2007 through 2020 ranged from $23 million in New Mexico to $260 million in Arizona. Emission reduction estimates for that time period vary from less than one to more than 11 MMtCO2-e, (Figure 1) with the additional benefit of reducing diesel particulate matter air pollution.

Reducing the speed limit for commercial trucks to 60 mph was also recommended to improve fuel economy and reduce emissions. This option would produce moderate emission reductions (Figure 1) but at a cost of as much as $182 million ($35/ton) in Arizona alone. None of the southwestern states have reduced speed limits for trucks in response to this recommendation.

list of smart growth and land use planning options

Figure 2. Smart growth and land use planning options for reducing transportation-based greenhouse gas emissions.
| Enlarge This Figure |
Credit: Joe Abraham, CLIMAS, The University of Arizona

Additional options for reducing emissions from heavy duty trucks included incentives to retrofit or replace inefficient trucks and increasing the shipping of goods by rail (New Mexico). All four state plans also suggested creating and strengthening state “buy local” programs that could help reduce emissions associated with the transportation of goods bought in each state while helping grow local economies.

Smart growth and other land use planning options

Urban and regional “smart growth” and other land use planning options can have a significant impact on reducing greenhouse gas emissions from vehicles by improving low-carbon transportation options for citizens in developed areas. In general, such options are realized by investing in low-carbon transportation infrastructure and designing compact, mixed-used development near transit stops.8 Figure 2 lists smart growth and other land use planning options recommended by the Arizona, New Mexico, Utah, and Colorado climate action plans. Emission reduction estimates could not be provided for specific options because the four state plans bundled specific options differently. Also, some options are currently difficult to estimate due to a lack of data and model limitations.

Related Links

Clean cars campaign – information about state and federal clean car policy
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California Air Resources Board Climate Change Emission Control Regulations
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U.S. Environmental Protection Agency SmartWay program
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U.S. Department of Transportation’s Transportation and Climate Change Clearinghouse
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Arizona Department of Commerce Office of Smart Growth
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Growing Cooler: The Evidence on Urban Development and Climate Change
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American Planning Association Policy Guide on Planning and Climate Change
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  1. U.S. Environmental Protection Agency. 2009. Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990 – 2007. U.S. EPA report EPA 430-R-09-004.
  2. Arizona Climate Change Advisory Group. 2006. Arizona Climate Change Action Plan
  3. Bailie, A. and M. Lazarus. 2006. New Mexico Greenhouse Gas Inventory and Reference Case Projections, 1990-2020. Appendix D.
  4. California Clean Cars Campaign. 2004. Off-the-Shelf Technologies to Reduce Global Warming Pollution.
  5. U.S. Environmental Protection Agency. 2009. Emission facts: greenhouse gas emissions from a typical passenger vehicle.Site Visited May 26, 2009.
  6. Mims, N. and H. Hauenstein. 2008. Feebates: A legislative option to encourage continuous improvements to automobile efficiency. Rocky Mountain Institute report T08-1.
  7. U.S. Environmental Protection AgencySmartWay Transport Verified Technologies.
  8. Emerine, D., C. Shenot, M.K. Bailey, L. Sobel, and M. Susman. 2006. This is Smart Growth. International City/County Management Association publication.