CPL history lesson

NW Mailing List nw-mailing-list at nwhs.org
Thu Jan 4 02:23:25 EST 2007

These exchanges, and especially the last, prompt me to
wonder why there were and are no national standardized
signalling standards in the U.S., and why
straightforward color aspect or multiple aspect
signalling (i.e. green yellow red) not apparently
adopted. Color blindness would not have been a major
issue, I assume.

Turning to Wikipedia :-), I saw, for example, at

"Although signals vary widely between countries and
even railways within a given country, a general guide
to the lights displayed in a typical signal system
would be:

Green: Proceed at line speed. Expect to find next
signal green or yellow.
Yellow: Prepare for next signal to be at red.
Red: Stop."

That seemed quite reasonable to me, and
knowledge/experience of UK and European rail networks
suggests that by and large - though there must be many
exceptions proving the rule - not to have any doubts
about wikipedia here.

So what would have prevented (all?) U.S. rail networks
from adopting 'simple' color systems rather than
persisting with the confusing ones that this history
lesson (seems more like a workshop or seminar series

:-) ) has highlighted?

London UK

--- NW Mailing List <nw-mailing-list at nwhs.org> wrote:

> This is the reason that the PRR eventually converted

> their position

> light signals at interlockings (known as "home"

> signals) to have red

> lenses in the stop positions.


> CG Tower


> On 1/3/07, NW Mailing List

> <nw-mailing-list at nwhs.org> wrote:

> >

> >

> > "Prior to being converted to color, didn't it seem

> kind of confusing for the

> > untrained eye to distinguish a stop indication, a

> restricted indication and

> > a proceed indication? Because you figure all you

> saw was 3 lights in 3

> > different positions. How were engineer-trainees

> supposed to distinguish the

> > indications?"

> >

> > Jerry,

> > Your question isn't far fetched at all.

> Engineer C.H. Poage related to

> > me that this could indeed be a problem in the fog

> at a distance. The example

> > he recalled was rounding the curve at Port

> Republic going north and dropping

> > down onto the flat at Lynnwood. After rounding the

> curve, the track is then

> > straight for 2 1/2 miles and you can see the

> signals at both ends of

> > Lynwood. There is a siding there so these are Home

> or Stop signals.

> > Fog will tend to lay in this low lying area

> and obscuring the signals.

> > So you can well see that if you are following a

> train and running on an

> > approach signal, it could be hard to distinguish

> if the train ahead had

> > cleared the block ahead or stopped in the block.

> Since ALL of the signals

> > were yellow, you didn't know if the next one was

> Clear, Approach or Stop as

> > all you could see was a big fuzzy yellow ball of

> light.

> > Jimmy Lisle

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