The horse riding sport in this video is called 'sulky racing' which sounds fun, but it's also illegal on public roads (although you wouldn't be able to tell by they way the riders are behaving). They treat the busy freeway like their own personal race track, completely ignoring all the dangerous traffic. And with all the honking, shouting and police sirens, the horses were the only ones that were staying calm in the chaos, (which is good because this could have turned really ugly, really quickly).
Like most of the drivers in this video, I was concerned for the horses' safety but that's where the similarities end. Apparently, my first instinct to pull over and let the horses pass, as to not spook them, didn't even occur to the drivers. They kept the horses 'safe' by pulling right up next to them and honk as loudly and frequently as possible.
Fortunately for everyone, at least the horses knew the rules of the road better than those drivers.