The problem is that pedestrians treat those trails like sidewalks and cyclists treat it like a road.

Mutual yielding (where two pedestrians approach each other on a sidewalk) works perfectly fine at walking speed. It doesn't work at vehicular speeds, which is why the rules of the road exist that determine positioning and right of way. In order to travel at faster speeds, one must follow a set of rules. Relying on mutual yielding results in the collisions you mention.