EMD introduced the SD-50 in the early 1980s with
a 16 cylinder, 3500 h.p. engine to attain the power that they had
early gotten from a 20 cylinder locomotive. The new, longer frame
allowed the dynamic brake resistors to be relocated to a cooler
area found between the central air intake and the cab.
The SD-60 varied little from its predecessor
visually, the main changes taking place internally with the aging
645F engine being replaced by the 710G. The two locomotives can be
distinguished by the door panels; the SD-50 features four latched
doors in six door panels whereas the SD-60 has six latched doors in
eight door panels.
The "wide nose" or "safety cab" was first
offered as an option to US railroads in 1988. Union Pacific
received the first units in early 1989. In 1991, the contour of the
nose was changed slightly, going from a 3-piece to 2-piece
windshield and tapering the sides of the nose to improve visibility
for the crew. Burlington Northern was the first recipient of the
revised model.
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