Diesel exhaust has a number of important health effects, primarily cardiovascular and respiratory. It increases the burden of emphysema. It makes you more likely to have heart disease. It makes you more likely to have a heart attack if you do have heart disease. It also can cause lung cancer. Radon only causes lung cancer. Effectively, it doesn't do anything else.
In terms of the impact, I don't know what the concentrations of diesel are by people's houses, but you don't live next to a locomotive or with a locomotive. I grew up in a basement in Winnipeg that had high levels of radon. And I don't blame my mother for that.