How old is the standard crossing horn sequence?

[Thebrantfordrailfan]

I've always wondered about the standard long long short long horn sequence at crossings, does anyone know how long this rule has been around? the earliest i could find was early 1940s, i saw a railroad safety film from the time and you can clearly hear the horns blowing the sequence at a crossing. I have also seen sound videos of steam locomotives blowing that way at crossings in the 1950s. I can't help but wonder how much longer it had been around at that time? were wood burning 4-4-0s whistling long long short long at crossings in the 1870's? How long do you think this has been around?

[freebrickproductions]

From what I've heard (which might be wrong, so take it with a grain of salt), the standard crossing sequence heard today dates back to like the 1930s or something. Apparently, the sequence was originally Long-Long-Short-Short, but was changed to the current Long-Long-Short-Long because engineers found it easier to hold a long note through a crossing than a short note. Again, that's just what I've heard and I'm not sure if it's true or not.