Currently, the routes cannot be changed or modified within the app, mostly because the route we show doesn't necessarily mean it's the route your navigation app will suggest.
For example, if you use Apple Maps to get turn-by-turn directions on the iPhone, it won't give directions avoiding highways, even if your trip's route avoids highways. Apple Maps simply doesn't support this. However, Google Maps does.
The best way to modify your route is to go to Roadtrippers.com and create or edit your trip there. After modifying the route, go to the trip's itinerary then click the Directions button. The directions shown there will be the directions needed to follow the route on the map. The directions can be printed or saved as a PDF if your computer supports it.
We have some solutions in the works to solve this problem within the app, so stay tuned!