i went back and looked again, the Camden & Amboy and Hartford Providence & Fishkill rulebooks cited above both specify 1 long blast as the signal for a grade level crossing, this is specified as ALL GRADE LEVEL CROSSINGS, not just crossings of another rail line at grade
Kilburn's Standard Handbook (1898) specifies two long two short as the signal for crossing a wagon road and a single long blast as the signal to be given when approaching any station, draw bridge junction or RR crossing
as for rods, you and i may or may not know how long a rod is, but that's how the rulebook said it, so thats what i wrote (and why i wrote it that way)