[Creative Commons photo by Tobias Pro User]

Pollution from motor vehicles is responsible for 72% of nitrogen oxides and 52% of reactive hydrocarbons (principal components of smog). Cars and trucks are not the only culprits - road construction causes greenhouse gas emissions both during and after the work is done. A Sightline Institute analysis (pdf) found that building 10 miles of new four-lane highway construction is the equivalent of putting 46,700 Hummers on the road, once you account for factors like materials, maintenance, congestion, and new traffic.

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