There are instances where we know if the routes between the two points are impossible (for e.g. There can be no route between Australia and New Zealand). In instances like these, where OSRM shows nothing, we can have an error message displayed stating that it's an impossible route

Currently, after receiving the route failures, the script filters out the impossible routes with the help of the polygons. So for every failure we check the location of the waypoints, if any of them lie in a different polygon a route cannot exist.

/cc @TheMarex @geohacker @planemad