How to measure accuracy of a route prediction
You need to define what a "quality route" is in the context of your problem and score based on that. This will likely be something along the lines of the total distance of the route, the expected time to traverse the route, the expected fuel/resource consumption required to complete the route, or some combination of these. You presumably want to predict routes that are as good or better than the routes given in your set R: you need to define what it means for a route to be "better."