Transit Buses

Public transportation can be an effective way to reduce air pollution caused by automobiles. However, in order to maximize the air quality effects of mass transit, transit buses must be clean and utilize modern pollution controls. To see side-by-side videos comparing pollution levels inside a dirty vs. retrofitted bus, click here.

Although technology is available to clean up diesel bus engines, unfortunately the vast majority of buses operated by the Chicago Transit Authority (CTA) and Pace Suburban Bus Service in the Chicago metropolitan area do not use these technologies. This is a serious health threat given that soot levels inside dirty buses can be four times higher than outdoor air, and the buses present health dangers to bus passengers and workers. Recent government grant awarded to CTA and Pace to fund pollution control retrofits will help, but the job is by no means done.

Health effects

The exhaust from diesel buses contains more than 40 toxic air contaminants, carcinogens, ozone smog-forming compounds, and fine particulate matter ("soot"). Exposure to fine particles is known to cause asthma attacks, heart attacks, lung cancer, strokes and even premature death.

In Illinois alone, it is estimated that diesel exhaust triggers more than 20,000 asthma attacks, causes more than 680 heart attacks and leads to approximately 570 premature deaths each year. Although diesel pollution is unhealthy for everyone, children, seniors, occupational workers and people who live with lung disease are especially at risk. 


Today, the federal government requires all newly manufactured transit diesel buses (model 2007 and later) to be equipped with pollution controls called diesel particulate filters, which can eliminate up to 90 percent of diesel soot from a tailpipe. These same pollution controls are commercially available and should be installed in older dirty diesel school buses.

In addition to installing these controls, transit buses can reduce emissions by:

  • Installing closed-crankcase filtration devices. These can help eliminate diesel exhaust emitted directly from the engine compartment.
  • Installing anti-idling technology. Using automatic idling controls, such as auxiliary power units, engine stop/start technologies, and direct-fired heaters can reduce pollution and save fuel.
  • Implementing diesel no idling policies. These policies help schools reduce diesel pollution by curbing unnecessary idling. 


How you can help

  • Call on CTA and PACE to clean up their dirty buses.
  • Sign up for E-Advocacy to learn more about our ongoing advocacy efforts and how you can help improve the lung health of your community.
For more information, visit the Air Quality Library.