I live in a suburban area, and have never felt unsafe riding my bike during the daytime, but I've already made the decision that I won't commute once the days get short enough that I would have to ride in the dark. There's one stretch where there's nothing but undeveloped forest/wetland on both sides of the road, and there's very little lighting. I feel perfectly safe riding it in the day because there's usually enough traffic, car, bike and pedestrian, but after dark I feel that 1) It would be harder to for see an obstacle or another person coming at me, 2) If I fell or was in an accident and was incapacitated it would be very difficult for me to be noticed by car traffic., 3) I've actually seen coyotes on the road at night in my car, and I'd rather not encounter them on my bike.