My take on route planning, when you have never seen the roads in question and have no idea about their traffic density, surface condition, and shoulder is this. I choose U.S. highways that are not going through the larger cities in the area. They usually have some traffic but almost always have a shoulder which gets you out of the traffic pattern. My reasoning goes like this. When I choose small state and county roads, I usually end up with lighter traffic but they usually do not have a shoulder to ride on. When you have committed to a small road with no shoulder and then the traffic turns out to be heavy with, logging trucks for example, you are the target and there is no place to go to get out of their way.

I much prefer to ride on the lonely country road with no traffic but the consequences of ending up on a heavily traveled road with no shoulder is not a choice I like to make.

Just my thoughts.