Hot answers tagged etiquette
Generally "X gives way to Y" rules can be found not just on trails but on open water (steam gives way to sail) and in rivers and channels, even on city sidewalks. They seem to be based on these (potentially contradictory) reasons: slower movers should allow faster movers to pass them and carry on away (after catching up from behind) more nimble entities ...
In the Grand Canyon, it's because it's easier for a human to get off the trail than it is for a mule. I suspect the same reasoning applies in most places.
The safe and courteous way to handle an encounter with stock (horses, donkeys, etc.) is to step off the trail to the downhill side, and also to talk to the riders. This helps the animals know you are a human and not a predator, and it moves you clear of their path should they spook. Horses are prey animals and may be sensitive to potential threats from ...
It's a similar situation here in the UK. We have routes which are designated as Bridleways which Horse-riders, Cyclists and Pedestrians can use but not motorised vehicles. I would imagine that the yielding to horses is because some horses can get spooked easily and it is safer all round to keep relatively still and let the horse and rider to pass.
Having had horses myself, here in England, part of the reason you give way if you hear a horse coming on a Bridleway is because (and I say this having been in the situation) there is no speed limit for horses on Bridleways (some might have a trot sign but not always), if you're cantering or galloping along which you have every right to do it's harder for us ...
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