Chief Causes for Concern

Carbon Monoxide…

• Is poisonous even to healthy people at high levels in the air.
• Can affect people with heart disease.
• Can affect the central nervous system.

Motor Vehicle Use Is Increasing

Nationwide, three-quarters of carbon monoxide emissions come from on-road motor vehicles (cars and trucks) and non-road engines (such as boats and construction equipment). Control measures have reduced pollutant emissions per vehicle over the past 20 years, but the number of cars and trucks on the road and the miles they are driven have doubled in the past 20 years. Vehicles are now driven two trillion miles each year in the United States. With more and more cars traveling more and more miles, growth in vehicle travel may eventually offset progress in vehicle emissions controls. To-date, however, efforts to decrease pollution are outpacing the growth in vehicle travel:

• Between 1993 and 2002, ambient CO concentrations decreased 42 percent. Total CO emissions decreased 21% (excluding wildfires and prescribed burning) for the same time period.
• This improvement in air quality occurred despite a 23% increase in vehicle miles traveled during the 10-year period.

Malfunctions and Tampering Reduce the Effectiveness of Emission Control Systems

Today's sophisticated emission control systems on vehicles are designed to keep pollution to a minimum, but vehicles quickly become polluters when their emission controls do not work correctly or if drivers tamper with them.