Railings on top on locomotives questions.

I've noticed that a lot of PRR diesel locomotives have what appear to be railings on on the roof. Can anyone explain what they were used for and why no other railroads seem to have used them?

What you likely saw was the "Train-Phone" antenna on the roofs. That was a very early form of communication
that PRR used, prior to more advanced forms (i.e. radio-systems).

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Charlie