Cars idling in traffic lead to more than 2,200 premature deaths each year, according to a new study from the Harvard School of Public Health. But lower vehicle emissions and cleaner fuels have been driving down that number for past decade, and the number of deaths will continue to decrease until about 2025, the study says.

Here's a graph from the study showing projected premature deaths connected to congested traffic from 2000-2030:

What happens in 2025? Presumably, increased emissions from congestion begin to overtake gains from greener fuel and car design. The study was funded by a coalition of transportation construction groups, which wants to reduce congestion by building more highways. But here's a different idea: Invest in public transportation and in getting cars off the roads altogether.

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