Of highways and lung capacities
Rich people live further away from highways. Children of rich people have better health care. Children with better health care have higher lung capacity.
This does not imply "this study
shows there are health effects from childhood exposure to traffic exhaust ...," and it certainly doesn't beg a policy prescription
like "..regional air quality regulations may need to be adjusted based on local factors, including traffic volume."
I once lived 50 yards from a major freeway
for two years. Exhaust from the freeway was never a concern. If anything, the noise was my biggest complaint.
(Note: I haven't accessed the study itself yet. Perhaps the researchers controlled for income, but nothing in any of the stories I read online suggested it. They did appear to control for 'general health' but what does that mean when you testing for a health outcome?)