The Centers for Disease Control and Prevention ranks car crashes as “one of the leading causes of death in the U.S.” In 2011, fatal car crashes accounted for nearly 7% of all deaths in the country.
But according to a recent study by a team from MIT, those figures don’t even begin to cover the true number of deaths caused by cars. In the long term, exposure to tailpipe pollution could cause 30% more premature deaths than car crashes, researchers report in the journal Atmospheric Environment.
MIT looked at data from 2005, the most recent year for which the EPA’s national emissions inventory measured state and city air quality at the time the researchers began the work. By attaching current estimates of heart disease and chronic respiratory diseases related to concentrations of ozone and fine particulate matter, they found that total combustion emissions caused 200,400 premature deaths that year. Road transportation caused roughly 58,000 of them, even more than power plant pollution. By comparison, car crashes accounted for nearly 43,500 deaths in the U.S. in 2005.
At the state level, the difference can sometimes be even more extreme.
Take Delaware, for example, which recorded 133 car crash deaths in 2005. The MIT researchers also identified Delaware as having one of the highest mortality rates due to road fine particulate matter exposure in the United States. The number of deaths they attribute to tailpipe particulate exposure comes to 230, more than 70% higher than the car crash figure.
Baltimore had the highest mortality rate related to exposure, with 31.4 annual premature deaths per 100,000 people. Cleveland and Washington, D.C., followed for second and third place.
Across the board, tailpipe ozone caused far fewer premature deaths than particulate matter–for 2005, researchers estimated ozone caused 5,250 premature deaths, and fine particulate matter some 52,800.
Researchers did add one caveat. Car crashes often affect people under 44 years old, and the average car crash death amounts to 35 life years lost. Heart and chronic respiratory diseases cause premature death later in life, cutting lives short by 12 years on average. If you were to measure the difference not in premature deaths, but in life years lost, car crashes are still worse, despite causing fewer deaths overall.
To be clear, this kind of comparative calculus serves mostly to prove a point and to makes sure we’re thinking about the effects of pollution in the long term, even though they aren’t as headline-grabbing as road accidents. The study is a powerful reminder of that fact.