I'm used to riding through quiet subdivisions and back roads. Also my horse is fine around cars and motorcycles. The only time I had a problem was when I had to squeeze by a bunch of people doing road construction with bobcats and jackhammers in order to get back to the barn. Looking back I probably should have dismounted and led her by... (we ended up dancing sideways across someones front lawn instead
) However, when I'm riding in a group my horse is fearless and nothing scares her. She will go over bridges, under them, etc... But if I'm riding along a main road by myself I would probably want to do more desensitizing.