We've got a cow underpass like that too, since 50 years ago when they built the new highway, they moved the road and split our pasture....Ours is built like a little bridge about 10-12 foot wide-- just high enough that the saddle horn clears when you take a tall horse thru....I used to just lean over and ride thru--but about 10 years ago I started in when a flock of swallows came flying out, spooked old Buttercup- she jumped 20 feet sideways and lost me at about the 10 foot mark...Took the air out of me so bad the kids thought I was dead for awhile- until I got enough back to start cussing...Now I dismount- lead the horse thru- and remount...
The Highway Boys said that if they ever replace it they will do so with a big culvert like that one....