Western Railroad Discussion > Signal Sunday . . .

.   .   .   one for signal Sunday taken THIS summer that MAY be a repost. Westbound UP one unit wonder baretable train about to take the great old Southern Pacific cantilever approach signal to CP Dome in Dome Valley, AZ. Sadly both signals in this photo should be gone by now as new PTC compliant replacement signals were in place about a half mile behind this train. In THIS case one new set of signals were going to retire two SETS of old SP signals with new longer distances between signals.
JB

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Fans frequently cite the PTC rule as why searchlight signals are being retired.
The PTC rule mandated a lot of changes in the signal systems and most RRs used it as an excuse to do life cycle maintenance/replacements of their signal infrastructure.
Searchlight signals were on their way out because they have moving parts and incandescent lamps; they require more periodic testing in the field.
But they sure looked great and for their time they were my favorite.
Knowing the realities, LED signals are my new favorite.

But before searchlights, we had the old US&S vertical tri-lights signals, which were replaced with single-light searchlights.  Why did they leave a "no moving parts" signal for a "moving parts" signal, and now back to a "no moving parts" signal?   The searchlights must have had some sort of advantage...

coach Wrote:
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> But before searchlights, we had the old US&S
> vertical tri-lights signals, which were replaced
> with single-light searchlights.  Why did they
> leave a "no moving parts" signal for a "moving
> parts" signal, and now back to a "no moving parts"
> signal?   The searchlights must have had some
> sort of advantage...

The searchlights can be seen much farther. They have a parabolic reflector to concentrate the light beam. The beam of light so concentrated that the early searchlight roundels came "pre-cracked" from the factory so that they wouldn't shatter in the field. Later they were conical, to remove them from the beams focal point. Tri-color signals have no reflector because, if they did, the locomotives headlight would illuminate the roundels, giving false indications.