TrainSimDev.com

As the title suggests

1. When was it made compulsory on the railway to whistle for crossings?

2. OHLE has two main cables, one for power and the other above it to basically hang the power cable off. What is the third cable for that runs either side of the line connecting to the outside of the supports? I guess it is communication, or signals or may be even to complete the electrical circuit although I don't know for sure.

Originally it was an "earth" (or return cable). On more modern systems this is actually an additional 25kv feed to auxiliary transformers.

I believe it is now called the "Along track conductor". However everyone calls it the return wire.

It is not compulsory to whistle for crossings unless there is a whistle board. Then you must blow at the whistle board between 7am and 11pm. Some locations have local instructions that allow you to ignore the whistle board (for example stopping after the whistle board and before the crossing).

I even know of one that you only whistle if there is someone at the crossing even though there is a whistle board because of a local person complaining about the noise. problem is the crossing is on a corner so if someone is on the crossing it is a bit late to whistle when you see them!

You should also only use the low tone at crossings unless you see someone. In which case two tones.

Not sure if that helps.