More likely with general fear/dislike of air pollution combined with dislike of noise and high traffic itself. Living close to freeway is unpleasant, rich can afford something else, poor can not. Where it is not about about direct money, it is usually rich not poor who make decisions.

While today it is largely a question of where one chooses, and can afford, to buy or rent, the freeways haven't been here forever. They were built within the last several generations, and always located so that they would destroy the livability of lower-class neighborhoods. The freeway concept is inherently unjust; it doesn't merely reflect the injustice of society.

There were and are lots of reasons for not wanting freeways in ones neighborhoods, the exhaust is only one of them.