All I could find online was stuff about trails, and it makes sense you have to be ten times as careful there. The roads here are on the prairie... there's generally a field on either side so the horse would even have some place to bolt - and the roads are ten times as wide as a trail.
All the horses I've encountered have been cool, calm and controlled (but that's about 5 all told, not counting Amish buggies). It helps to hear things from teh horse peoples' mouths, though