UP RS-27 #675, Valley, NE, Sept. 2, 1962, photo by Lou Schmitz

UP RS-27 #675 and #676, Valley, NE, September 2, 1962, photo by Lou Schmitz, Chuck Zeiler collection

Alco built five RS-27 (DL-640) demonstrators, numbered 640-1 through 640-5, which toured 22 railroads between January - April 1960. After the tour, three of the demonstrators were sent to the NYC for road tests, where they were assigned primarily to the Flexi-van trains. There they replaced normal motive power consists of 4-6 1800 hp units, and met tight schedules repeatedly. Track speeds of 70 mph were consistently maintained over 580 miles permitted over the 950 miles between New York City and Chicago, with an additional 130 miles at above 60 mph. Numbers 640-2 through 640-5 were sold to the UP, becoming 675-678, the only RS-27's on the UP. All were retired by late 1970, early 1971, and sold to MLW, becoming the basis of a lease fleet.

http://www.utahrails.net/all-time/all-time-08.php#rs27-675
http://www.thedieselshop.us/Alco_RS27.HTML