Training outside is quite tricky, because you need a safe and suitable place to train. So following a route is IMHO not the right way to go. Depending on the type of workout, you should either look for a long, flat, uninterrupted and safe stretch (e. g. for sweet spot intervals) or a hill for short, sharp efforts that are separated by low intensity work.
Under no circumstances should you lose sight of your surroundings. That doesn’t just include cars, but you also need to pay attention to the road and so forth. I think this was also covered in one of the last podcasts.