How to avoid/deal with exhaust fumes when riding in traffic
From The Guardian: (I suggest you Click through &amp; read the whole article)

"It’s a scenario familiar to any urban cyclist: you’re stuck behind a fume-belching bus or taxi, a choking diesel aroma wafting through your lungs. You think: is this really the healthy option?

The good, if simple, answer from pollution experts is: yes. Cycling does remain many, many times better for your health than not cycling, even factoring in exposure to pollution and the risk of accident. What’s more surprising is that on two wheels you might even be exposed to less of the smelly stuff * than those using other forms of transport." *(Emphasis added.)

I have read elsewhere (although I can't find the link now) that this lower exposure is due simply to the fact you are up higher than a person in a sedan, and the pollutants tend to sink.

Edit: 


  It's not so much that the rider is higher up, but that the cabin air
  intake of a car is effectively at exhaust pipe level


(Thanks @Chris H)

The science is out the anti-pollution masks, not so much because they are incapable of performing their advertised function, but because exposure levels are much lower for the typical cyclist than most people suppose.

Edit two:

To attempt to address the last crux of your question, it may be reasonable to say that you are already avoiding more exhaust just by biking &amp; not driving, other than that; take a less heavily trafficked route &amp; otherwise don't worry about it.

I suspect general air quality should be more of a concern than incidental exhaust exposure.