Not only track savings, but mostly the cause of getting rid of steam was the cost of so many extra employees to run and service steam. N&W did studies with steam and diesels and in general the steam proved itself. However they lashed up 4-5 diesels with 2 crew members versus a 1200 (2-6-6-4) as I recall. With the diesels you could add more but with steam it was another crew. 1200 Class A routinely handled 200 car trains from Williamson to Portsmouth and Columbus, Ohio. President Stuart Saunders was the death nail for N&W Steam. Sadly some engines that were built only lasted 8 years. 611 was built in May 1950, and made its last revenue run in 1958, and last excursion in 1959.
By the way there have been no 611 trips announced for 2018!!! If you ever get the chance to see this engine in action go for it. Quite impressive.
Greg