Traffic pollution was identified as a significant problem
Exposure to traffic pollution could affect the development of babies in the womb, US researchers have warned.
They found the higher a mother’s level of exposure in early and late pregnancy, the more likely it was that the baby would not grow properly.
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[Baltimore Spokes: Note that being in a car you are exposed to more traffic pollution then if you are riding your bike in traffic.]
https://news.bbc.co.uk/2/hi/health/7988619.stmoldId.20090410193736732
Biking in Baltimore