In my experience, the relative safety of various roads isn't so much a matter of construction, traffic density, or speed, as it is one of driver expectations. If you're riding on roads often used by cyclists, drivers will (by and large) be more alert and see you sooner than a road where they don't expect to see anything other than cas moving at the same speed as you.

In this context bad pavement areas, turning traffic, children playing, parked cars and trucks, and other obstructions become your friends because they raise driver alertness and focus on their driving. As a rule, people see what they expect to see, and don't register stuff (like you on a bike) that they don't as quickly.

Other than expectations, you have to use your own judgement about other factors. Neighborhood streets are safer than main highways, multi-lane can work for you by giving cars a lane to move to, and against you if traffic is heavier, by making drivers nervous about moving to the adjacent lane, concrete roads, and those where the shoulder is detached from traffic lanes pose a unique risk because the burm itself can cause you to lose control as you cross it (do not cross back onto the main lanes over a burm except at a sharp angle, as you would if crossing RR tracks).

Probably the most important safety factor is your ability to ride in a straight line, and hold line as traffic passes. I've witnessed accidents where a cyclists swerve on being passed by one car brings them into the path of a following car, so steel nerves are definitely the order of the day when sharing roads.