Our area (Niagara) has a great cycling map available at all the local bike shops that shows suitable roads for bikes, bike lanes, paths, as well as hills etc. and regular map features. Ask at your bike shop or check online if cycling maps available for your area. Downtown type streets with lots of stoplights and quiet sideroads tend to be the best, busy main suburban routes (the 4 or 6 lane main traffic roads) tend to be the worst. I really find busy suburbs worse than either city or country as they were designed for high speed car traffic. I really avoid high speed, no shoulder situations if at all possible. Quality of pavement also matters - a rough road is much more dangerous if busy as more difficult to keep to a straight and certain line.

Another big fact is time of day/day of week - traffic on many routes is hugely different on a Sunday at 7 am than a Tuesday at 5 pm.