Signal Color/Style Standardization

NW Mailing List nw-mailing-list at
Fri Jan 5 08:41:17 EST 2007

I believe signal lenses were standaradized by the American Association
of Railroads. Kopp and Corning Glass were two well know glass
manufacturers that led the research in this field. Remember the
original green lenses were more blue-green then pure green, reason,
you had a yellow flame behind! ;-) The other colors were standardized
as well.

The yellow that the PRR (and N&W) used on "pure" PL signals (i.e. no
color added), was designed to be fog penetrating, so the color
spectrum is a bit different in terms of the yellow. I have the
technical specifcations at home.

The "yellow" factor was just that. At a mile/two miles away, all you
see start seeing is a yellow blob with a PL signal. Add more extreme
conditions and you have even more difficulty. The B&O was able to get
around this by adding color and tightening down that diameter of the
signal head so that the center light was not needed...I can see the
basic indication (i.e. red/yellow/green) of a CPL signal on some clear
evenings from over 4 miles away...(tangent track, no obstructions). IT
wasn't just the 1958 wreck at Sardinia that was the contributing
factor, I'd say that it was the last straw as there were many, many
collisions in which the crew reported Signal was hard to see because
of sun, rain, etc...

Replacement of signals is now based on more of economics then
standardization. NORAC tried, but not all railroads are NORAC
complient. A PL signal (and their cousin's the B&O inspired CPL's) are
old. Parts are no longer made for some and they are becoming dangerous
to work on and climb. NS has, in several locations, placed "Do not
climb" placards on the signals, they are that unsafe!

To find accident reports, there are two great sites:


CG Tower

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