Nostalgia & History > Triangles, Diamonds, and Dots -- oh, my...

Anybody have the definitive code for these symbols?

The triangle, dot, and diamond were seen above the road numbers on Southern Pacific diesel locomotives circa 1959-72. The purpose is outlined in comments below by a noted SP diesel locomotive historian -- contained within an offline email to me, so his identity remains protected, since he wasn't on the official record while addressing this!

The purpose of the symbols normally stenciled (or reflective tape) over SP diesel unit road numbers was to signify compliance with Department of the Interior/National Forest Service directives concerning diesel engine operation within National Forests. As I understand it, SP (and other roads) were told to show that their locomotives would emit sparks only SMALLER than such-and-such a size. This meant supplemental spark arrestors (not necessarily solely the Cyclone brand). A turbo supercharged engine was supposed to break down the glowing particles by action of the turbine wheel, delivering the net effect of a spark arrestor. 

I've been able to break the code as follows: 

DOT:
Meant to signify that the prime mover has an exhaust turbocharger -- which functionally acts as a spark "reducer" (see above). Thus, it’s on PAs, DH-643s (pictured) and SD35s -- but isn’t on Roots-blown 567s like F7s and GP9s. SDP45s in Commute service still carried them in photos taken in 1972. 

TRIANGLE:
Meant to signify some type of spark arresting gear on a non-turbocharged unit. From my observations, it appeared on F7s (pictured is an FP7), GP9s, and E-units — all non-turbocharged. I can’t verify what was lurking within the carbodies above the exhaust manifolds, but there were no visible external arrestors over the stacks on such units. 

DIAMOND:
May have a later catch-all, or may have signified a mechanical spark filter or trap -- rather than a specifically-designed spark arrestor device. Evidence for this is a diamond on an NWP SD7 with those characteristic spark “hats” on both stacks. Also, SP passenger pool F7s in the early Amtrak years sported diamonds: it may be that they had some kind of internal spark catcher -- or the diamond may have been a substitute symbol for the triangle.  (Charles and David Lange, thanks for the original shot of SP 8296!)

Anybody have documentation or personal SP experience with these, and can shed more light? Thanks!

~ BZ

Oh, and by the way... in possession of the SP 9010 Krauss-Maffei restoration in Niles Canyon, California is an original and unused SP 3" Scotchlite reflective dot, in the characteristic 1960s Scotchlite-brand yellowish off-white (seen clearly in the 6457 shot below). :-)   



Edited 3 time(s). Last edit at 09/27/20 12:29 by Notch16.

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In the Southern Pacific Painting and Lettering Guide by Jeffrey Alan Cauthen and John R. Signor published by the Southern Pacific Historical & Technical Society
on page 77 the "code" is explained.
Dot = Turbocharger, Triangle = Cyclone spark arrestor equipped unit, Diamond = Spark arrestor equipped unit.



Edited 1 time(s). Last edit at 09/27/20 14:25 by PHall.

Just as Bob said