Re: more info on semaphores - PRR SG

Ed Workman Replies

Fail safe is first priority for any signal system, brake system etc. Semaphores were weighted , in the casting, to go to stop upon failure, such as disrangement of actuating rods or loss of blade

Light signals, - any signal " imperfectly displayed" meant stop, or at least "most restrictive aspect"

PRR used Type B [lower quad] as those predated upper quad.
And replaced those with upper quad etc as they became available

Lower quad were mostly two position on some RRs- the clear position was not vertical, so an intermediate position was less obvious. In those cases two specticles had the same color, red, or green, and no yellow

Upper quads could go to horizontal , 45, and 90 degrees, thus saving a signal head in some instances ERA means everything- go back a little more and you would have seen Hall Disks

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