Would be cool if it could be implemented with google maps or apple maps. Like, when driving in heavy mist, snow, or poorly maintained roads and visibility of lane markers is greatly reduced, the Maps app can overlay the lane markers to keep you in your lane. Or when driving on interstate highways at night, pitch black, it could outline the upcoming curvature of turns, sidewalls, and again, lane markers to make driving easier in older cars.
I could see AR having many uses for GPS based apps, and travel apps.