Horseback riders are subject to, and protected by, the rules of the road. They also must ride single file near the right curb or road edge, or on a usable right shoulder, lane or path.
The law requires you to exercise due care when approaching a horse being ridden or led along a road. You must drive at a reasonable speed, and at a reasonable distance away from the horse. It is illegal to sound your horn when approaching or passing a horse.