This would be 'pretty easy' to demonstrate by comparing cancer rates by people who live adjacent to busy highways against those who live in rural areas. 'Pretty easy' is always nonsense in observational studies because the confounders have confounders that are confounded by other confounders; even more so for things that are relatively poorly understood, like cancer. But it's at least something that would certainly get (and probably already has been?) funded.
We got at least a link between heavy road traffic and stunted lung growth in children, as well as at least 10% increased lung cancer rates [1]. Additionally, noise from road traffic has been linked to increased rates of cardiovascular disease and mental health issues [2].
Both of this is compounded by the fact that people living next to major roads tend to be poorer, so there is a socio-economic issue present as well.
