Bought a house with a 4 lane road behind our yard. a few small trucks go past. its only start and stop traffic when in peak hour. apart from that it flows. worried about pollution. will we develop heart attacks and cancer from living here?

Closer than 500 or 1000 feet to a freeway is considered problematic. Your house doesn't appear to be exposed to heavy,dense freeway traffic. Nevertheless avoid outdoor activities during peak traffic hours. I would tend to keep windows closed much of the time also. It is estimated that up to 45% of urban dwellers in North America are living near heavy traffic. Children are more vulnerable to asthma