All but a small handful of “Pedestrian Only” trails are open to equestrian use. That said, Ridge to Rivers trails are heavily used by hikers and mountain bikers and in addition, many trails are narrow and located along steep hillsides - offering short sight distances. While it is the responsibility of other users to yield to equestrians and most do so readily, there is always the chance of a surprise encounter along a narrow trail.
The following trails are wider, and/or generally offer better sight distances:
While most Ridge to Rivers trailheads offer somewhat limited parking, there are a few where it is relatively easy to park a trailer to enjoy the trails on horseback. Here are some to choose from: