Unfortunately, there is credibility. I do not live in the area under discussion, so I don't have a horse in this race. Statistics are proving a connection between the increase in asthma in society, particularly in children, to increased exposure to auto emissions. Those children who live closest to heavily-trafficed highways are at increased risk.
Of course, I also have another idea about this. When I was a child, children spent very little time in vehicles at all. They were not being constantly transported here and there. They were not exposed to heavy traffic on a daily basis or to idling vehicles. I knew 1 classmate in 13 years of school who had asthma. Nowadays, there might be as many as 2 or 3 in 1 classroom who need inhalers.
My son's girlfriend suffers from severe asthma. We almost lost her a couple of years ago.
trafficed=trafficked
This is misleading. You left out children who live closest to heavily-trafficked arterial roadways. Since these are normally more gridlocked than interstates the problem is worse than with interstates. If the same quantity of traffic goes by at an average of 15 mph vs. 30 mph the pollution is worse in the slow condition due to engine efficiencies.
The answer, of course, is to close all roads and/or stop building new roads. and force everyone to take public transportation - which is what many liberal governments are trying to do.