A ha-ha is a recessed landscape design that provides a stock proof boundary without the visual intrusion of a fence.

It is listed on the wiki. osm.wiki/Tag:barrier%3Dditch

See
https://en.wikipedia.org/wiki/Ha-ha

It was a stile next to a gate, now tagged accordingly.

Pretty sure it is one way for busses as well. See for example
https://www.gocornwallbus.co.uk/services/TFCN/26
where the buses take 2 routes here