I have horse riders every day going past my house. They are nice to see, but they make me a little nervous when I have to drive past them. I'm always wondering if they are going to bolt into the road, so I go very slowly. So far, so good.
I live near Ramona, California, hence my screen name.
There are almost more horses in this area than people.
Most people here know that: A. You slow down going by horses-especially if you pass them from the rear.
B. If you have a noisy motorcycle, you shut it off until the horse riders get by.
Occasionally, we get some fools up here from San Diego/Los Angeles megalopolis.
My horse was a Riverside (CA) Police Horse before I got him, and those things don't bother him. But, newer horses can be startled.
Good advice.
But going too slow can also make the horse a little nervous.
Most horses that spend time trail riding get used to the cars.
I live in horse country. It's no big deal to drive past a horse. And it is polite to do it very slowly. If you are going slowly, if a horse bolts, or kicks your car, the worst that will happen is some property damage. The really dangerous collisions happen when a horse gets loose and is hit at speed. I have heard of people in a car getting kicked to death by a horse the was thrown into the passenger compartment.
Remember: the rider is MUCH more vulnerable than you are in a car.