As a horse person who has gone on many 'road rides', I feel that not enough drivers are aware of just how dangerous it is for the rider, horse, and others around them when they are on the road. Here are some guidelines for drivers to be aware of.
If your vehicle has a loud engine it can spook the horse. To help prevent this, you can idle in place until the horse is past you (by past you, I mean about thirty feet away from your rear bumper), or turn your car off until the horse is a safe distance away.
Horse and rider riding the same direction as you are driving
If a horse and rider are riding int he same direction you are going, slow to a crawl and drive on the opposite side of the road until you are about thirty feet ahead of them, then slowly start speeding up. If you step on the gas too soon your engine noise increases and can harm the rider and/or the horse as well as you.
If you are blaring your music and having a great time, that's fine. Do it all you want; when you are not near a horse. Horses' ears are way more sensitive than your own. Loud noises can irritate them, or even frighten them. So when going by a horse and rider, turn down the music to a lower level. Preferably a level that you can hear the rider talk to you as you go by.
Hooting and hollering
This one is simple. Don't. Making loud noises encourages the horse to act up, leading to possible injury of the horse or rider. Especially show horses, because we hoot and holler in the stands when we know it is safe to do so. And never, ever on concrete.
Chasing the horse with your vehicle
I know it sounds stupid to do so, but people have done it. Please, please don't chase a horse with a vehicle. Making a horse run on concrete can lead to fractures in the bones of the legs, which often leads to the horse having to be put down. Also, the rider could fall off and sustain a serious injury.
If a horse starts acting frightened
Yes, you will know if a horse is frightened even if you are not a horse person. If a horse starts speeding up, bucking, turning its bum at you, or spinning around, stop your vehicle. Wait for the rider to regain control, let them move off the road or tell you it's okay to start moving again. And remember, horses can misbehave and get scared at random times, so be careful!