Right Hand Rule - How De-Regulation Ruined US Signaling

Why the US railroads seem to go from having a pathological need to mount their signals to the right hand side of the tracks they governed, like this...

Or this...

Or even this...

To, seemingly overnight, just doing this...

Well in 1939 most locomotives provided the engineer with visibility like this...

So in 1939 the ICC decided to legislate the obvious and required that all railroad signals be situated to the right hand side of the track they governed.  Of course the usual system of waivers and grandfathering applied so that left hand running lines such as the CNW didn't have to rip out its fireman-side signals, but all of that created barriers to cost cutting, even after the 1960's rolled around and all of the main line steam locomotives had been retired. 

By the 1980's, chopped short hoods on the F end had been the norm for the better part of two decades with only a few out-layers like the Southern, still holding on to the practice.  In 1985 the ICC successor, FRA decided that the Right Hand Rule was obsolete and railroads could put signals on whichever side of the track they wanted. 

  

The effect was immediate with back-to-back masts replacing split masts automatics and end-of-siding signal bump-outs becoming some sort of vestigial organ. Bracket masts, the go-to low cost option for bi-directional automatics on two track main lines were hit particularly hard along with the two track automatic signal bridge.  Multi-track cantilever signals have hung on, but only in areas of restricted visibility like curves.

Now in Europe many of the right (or left) hand replacement requirements are either still in force or at least still practiced by the state owned railways and as such there is much more diversity in the signal mounting systems, typically in the form of signal bridges.  It just goes to show how important the regulatory environment can be for something as esoteric as signal diversity.