Protecting Public Health and the Environment.

Vehicle Emissions

Vehicle emissions are created from the incomplete combustion of gasoline or diesel. Other factors such as emission controls, engine design, and vehicle maintenance may affect vehicle emissions.

Vehicles emit many pollutants into the air, including carbon monoxide, carbon dioxide, hydrocarbons, nitrogen oxides, sulfur oxides, and volatile organic compounds. These pollutants then combine to form secondary pollutants such as fine particulate matter and ozone. While emissions from an individual vehicle may be minimal compared to an industrial source, emissions from many vehicles on the road at one time can have a serious impact on air quality.

Health and Other Impacts

Pollutants emitted from vehicles can lead to poor visibility and health problems such as asthma and respiratory illness. Pollutants also can damage buildings and affect the quality of water resources.

Under the Clean Air Act, the US Environmental Protection Agency (EPA) has set protective health-based standards for ozone and other pollutants in the air we breathe. Failure to meet the ozone and other standards over a period of time can result in an area being designated nonattainment by EPA. States strive to achieve attainment with the standards to ensure that public health is protected, promote economic growth, avoid the potential loss of federal highway funding, and preclude the time and cost required to develop and implement plans to reattain attainment status. Learn more.

How to Help Reduce Vehicle Emissions

Drive Less

The most effective way to reduce emissions from your vehicle is to use it less.

  • Ride the bus, carpool, and share trips to reduce the number of cars emitting pollutants. If possible, choose nonpolluting travel such as walking or biking.
  • Reduce commuting. Choose to live close to your work.
  • Organize a carpool at your work. Call 345-POOL for help.
  • Combine trips to the same areas. Once you arrive, park your car and walk between destinations.
  • Avoid driving during peak traffic hours or in stop-and-go traffic.

Maintain Your Car

All cars emit some pollutants; poorly maintained cars emit the most. A properly tuned car runs better, gets better gas mileage, and pollutes less.

  • Get regular tune-ups. Vehicles with worn spark plugs or clogged fuel or air filters do not run efficiently and emit more pollution.
  • Keep tires properly inflated and wheels aligned to reduce tire drag on the road. Gas mileage drops 1% for every pound below the recommended level of pressure.
  • Do not top off the gas tank. This allows harmful chemicals to escape into the air.

Drive Wisely

The harder your engine works, the more gas it burns, and the more tailpipe emissions you create.

  • Avoid carrying unneeded items. Each extra 100 pounds increases the amount of gas used by 4%.
  • Place items inside the vehicle instead of on roof racks. Remove roof racks when not in use. The wind drag from a rack increases gas consumption by almost 1 mile per gallon.
  • Drive at a medium speed. Most cars get the best gas mileage between 35 and 45 miles per hour.
  • Drive at a steady speed. Avoid stop-and-go traffic and take it easy on the brake and gas pedals.
  • Use the air conditioner only when necessary. Air conditioners can reduce your gas mileage by 20%.
  • Avoid long idles at drive-up windows or when waiting. Restarting a warm engine takes less fuel than letting it run for just 30 seconds.
  • During hot summer months, fuel vehicles in the evening to facilitate dissipation of volatile organic compounds that contribute to ozone formation.

Low-Emissions Vehicles

Hybrid vehicles use both a conventional gas-powered engine and an electric motor to power the vehicle. Intelligent power electronics decide when to use the motor or engine and when to store electricity in advanced batteries for future use. The electric motor is used primarily for low-speed cruising or to provide extra power for acceleration or hill climbing. When braking or coasting to a stop, the hybrid uses its electric motor as a generator to produce electricity, which is then stored in its battery pack.

Unlike all-electric vehicles, hybrid vehicles do not need to be plugged into an external source of electricity. The gasoline engine generates all the energy the hybrid vehicle needs. With the assistance of the electric motor, the gasoline engine can be smaller (and therefore less polluting). Hybrid vehicles can reduce air emissions of smog-forming pollutants by up to 90% and cut carbon dioxide emissions in half. 

Staff Contacts

Vehicle Inspection and Maintenance Coordinator
Michael Hahn
DEQ Boise Regional Office
1445 N. Orchard St.
Boise, ID 83706
(208) 373-0550

DEQ Resource

Vehicle Emissions, Air Quality, and Your Health: Five Things We Can All Do to Minimize Air Pollution from Our Vehicles

More Information

Green Vehicle Guide

Related Pages

Clean Air Zone Program for Citizens

Treasure Valley Vehicle Emissions Testing