I did a search on this that returned hundreds of posts. Keyword was "snap tool" too many to sort through and found none that were revelant after a couple of pages.
Although new to BC I was a long term user of Mapsource with my Zumo 550. I know how to do this having created more than a few cross country routes. I've been to California several times using nothing but state and county roads, routes created on Mapsource and DL to the zumo 550. The zumo 550 died, thus the upgrade to the 390 and basecamp.
I have a tour to SD coming up next month. I created the routes in BC, on my Window 7 PC. Soon after I bought a new PC with 8.1. Transefered the routes over using the 390, and now those routes ain't worth the pixels they use. They are over the place, the purple line nothing but straight lines connecting points.
Same is true for any new route I try to create. Put waypoint A here, B here, and the purple line takes me as the "Crow Flies" I mean it will fly me right over St. Louis without one turn LOL. If I recall there is something on the tool bar to make the route follow the road? If so I can't find it, but maybe I'm missing it. Any help would be good.