i once pulled up at a junction to see a beautiful shiny sturdy black stallion, at least 18 hands high, walk past with it's rider. They were going towards a small roundabout approx 150 yards away. Suddenly a black sports car raced past them with such speed I closed my eyes sure there was going to be an awful accident. Why the driver was going that fast approaching a horse, let alone a roundabout, is beyond me. to be honest, i don't even think he registered there was a horse there, he passed it so close. Lucky for him, and the rider, the horse was bomb proof. i can only presume it was an ex police horse because i couldn't believe it didn't even flinch. i certainly did!
drivers are as bad around horses as they are around cyclists. i'm not sure if horses see hi-vis but i took a very wide berth around one today when i was wearing mine, just in case i spooked it.