Restricted Speed came to Southern Pacific in 1977, replacing "With Caution". Probably more operating people are fired for violating the restricted speed rule (now part of the General Code rule book used by most U.S. railroads) than by most of the other rules combined, save the ones requiring a train to stop short of red signals.
After its institution in the above form, the contents of the rule changed daily according to the particulars of the previous day's big accident, or so it seemed. If SP had experienced a rash of collisions with mooses within yard limits, we are sure that Restricted Speed would have been amended to include "stop short of moose...".
As it was, if your engine cornered a box car and dumped it on its side, you were sure to be fired. If another switch engine slammed into yours while you were sitting there having coffee and minding your own business, you still probably were fired, but the company would at least have to go to the effort of trumping up a case. If you ran through a misaligned switch...yep, a restricted speed violation...unless you could find a pipe to bend back the switch before the trainmaster caught wimd of what was going on.