Other thoughts... markings go along the left side of the road. (I've ridden courses where, for example, the turn arrows for a left turn made a sweeping arc from the right shoulder over to the road. The net effect was nobody saw the turn arrows, and the only people that didn't miss the turn were the ones that knew the route. Often there are markings indicating "go straight" at intersections and side roads.
And to reiterate one of demoncyclists final points... it's not unusual to be riding solo, with no other riders in sight late in a ride. Under those circumstances I get nervous if I go more than several miles without some indication I'm on the right course.