SD50 No. 5507, Engineer's Side View

As of November 1991

Rio Grande's seventeen SD50 units were an opportunistic purchase by the railroad, which was actually shopping for twenty more tunnel motors.  The SD50s became available when their order was cancelled by the Chessie, and since they were (theoretically) rated higher than the SD40T-2s, it was assumed that the same work could be done with three fewer SD50s.  It didn't really work out that way, as it turned out.  And when the tunnel motors were upgraded with PTC systems, the two types became functionally equivalent.

Rio Grande's SD50s came in a single group, although the last three units didn't show up on the property until two months after the rest.

Number Range Date Purchased Comments
5501 - 5517 Aug 1984  Several features differed from standard Rio Grande practice.

Specific information for individual units may be found on the Rio Grande Modeling & Historical Society's SD50 page.

(1) Rerail frog, one on each side of rear of unit.

(2) Bell, mounted on right side of long hood.  The bell location and the 5-chime horn are Chessie features that really set these units apart from other Rio Grande diesels.

(3) Jacking pads.

(4) Dual air filters below frame.

(5) Battery compartment doors with "mail-slot" vent.

(6) Large SP-style snowplow.

(7) Leslie P-3 horn.  The 5-chime horn has been replaced on this unit by this time.

(8) Pyle Gyralite on low nose.

(9) Anticlimber.


  • The Pyle lights were added by a third-party contractor just prior to delivery.
  • Some of these horns (such as on this unit) were replaced with a standard Leslie P-3 even before the SP modifications began.
  • The bell location, battery doors, and 5-chime horn are Chessie features that really set these units apart from other Rio Grande diesels.

The SD50s, being Rio Grande's newest six-axle units, were early candidates for modification to the new Southern Pacific Lines standards.  A number of them were repainted into the new "merger" paint scheme with SP speed lettering, lost their Pyle lights, had the horns moved to the long hood and replaced with a 3-chime version, and had ditch lights added.  After 1992, many of them worked in southern California on Tehachapi or Cajon passes, only returning "home" after the UP merger.  Now they're nearly all in UP yellow.  At last report, though (at least early 2005), this was the last remaining SD50 still in its original Rio Grande paint.


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2004, James R. Griffin.  All rights reserved.