Distance to the next waypoint on route?

I have loaded a route and a separate file which has waypoints (campsites) along the route. Under the route menu, I've tried both "Follow" and "Wpt. Nav." but I'm only given the distance as the crow flies. How can I get the distance to the next waypoint if traveling the route?

combined_sht.kml & campsites_sht.kml from: http://shta.org/Trail/TrailGPS.php

Thank you!