I ride on the road a lot, especially on distance training days.
I don't wear any special vests unless its gross out or I'm going to be gone all day. Then I wear a high-vis reflective mesh vest.
If I feel like a car is being reckless/rude I step off into the grass where possible or just scoot really close to the edge of the road. Otherwise I just stay to the far side of my lane.
If going up hill stay on the right, downhill stay on the left.
Oh, and making sure your horse isn't afraid of vehicles is a good idea!
I live in the country, so I have the chance to pass a lot of different things. Eg; Trailers full of various animals, those huuugeee tractors they use to plant fields
Most likely you will want to be sure your horse can handle being followed/barked at by dogs. I've found that if you trot toward them threateningly they will leave you alone. Most just want to sound terrifying.
Really just simple things, the road can be dangerous but most things are just common sense to keep yourself and your horse safe.
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