I was looking at a 1914 copy of the SVRy Rules and Regs. book last weekend. One thing that caught my eye was the prescribed whistle signal for crossing public roadways. It is shown as 2 longs and 2 shorts instead of the usual 2 longs 1 short and 1 long blown all the way through the crossing. I have seen this whistle signal listed in a turn of the century rr book I have as well. Was this signal universal at that time, and later changed to the present by the ICC, and when?
The SVRy rules book also lists 1 long blown continuously as a signal for grade crossings, so it seems like the 2 earlier whistle signals could have evolved to what we use today. Any thoughts?