Found this thread all about using nuvi GPS https://advrider.com/f/threads/garmi...-setup.863174/
Apparently they do not support tracks, so you do not get turn by turn instructions. But it sounds like you should be able to display the track on your map then follow the line.
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Actually I do get turn by turn directions. If I create a route on a navigation program like Tyre, Furkot, MyRoute, etc, the file I upload to my Nuvi will give me turn by turn directions. Those routes are created pretty much the same way a route is created on Google maps; you add waypoints to locations on the map, and the program chooses the route between those points. If the route isn't where you want it to be, you can drag it to where you want it, or you can add waypoints to a route not chosen by the program and force the route to follow the roads you want. Those types of routes may only generate 20 waypoints for a trip a hundred miles long. If I upload a route created like that to my Nuvi, it follows it turn by turn.
Now, if I try to upload a track that was created by someone who was actually riding the route, and the GPS is recording a waypoint at specific intervals, those routes won't even load to my navigation program; there are too many points. I think the MABDR file had thousands of waypoints (I keep calling them that, but maybe that's the wrong term). It looks like a point gets created about every tenth of a mile. maybe even more. Neither my navigation program nor my Nuvi can open a route like that. My guess is that you're right, and a Nuvi can't support route tracks. I'd like to be able to use a track, because (if I'm correct) a GPS following a track will try and return you specifically back to that track if you wander off it. With the kinds of routes I usually create, if I'm riding along and I miss a waypoint, the GPS will try and route me back to that waypoint. If I tell the GPS to skip that waypoint and go to the next one, it may not have me follow the original route, and will route me along the shortest distant to the waypoint I want to skip to. On the routes I create to use on a trip, that's usually not a problem, since I use enough waypoints that are close enough together that the GPS can't waver too much from the path in order to route me to the next waypoint. However, I'd still like to use the already created MABDR tracks (either the ones from the website or the ones that were created by others). That's a lot easier than me having to recreate the file from scratch in a form that my Nuvi can read, plus I lose all that POI information that's included on the original files. And if the MADBR route gets updated, as it already has, I can't simply download the newly updated route; I have to open the MABDR update in Basecamp, then search it for the updated section to see what it looks like, then make those corrections to my own files. It ends up just creating a lot of work.
The answer to all this may be as simple as "a Nuvi can't do what I'm asking". I'm hoping someone joins in the thread here who's actually downloaded this file from the MABDR website and used it on their GPS, and how they went about it and what sort of GPS/equipment they used.
For what it's worth, this is a screenshot of what a recreated version of Section 1 of the MABDR looks like, for use on a Garmin Nuvi. I'm sure it'll work, but when I do it this way I lose a lot of info from the original file, including alternate routes, expert sections, workarounds, water crossings, etc.