Pardon a slight railfan digression-
The Cleveland, Cincinnati, Chicago and St. Louis Railway was bought by the New York Central system in 1906. At that time they began flattening, straightening and double tracking the “Bee-line”, their trunk from Cleveland to Indy. The improvements were extended west to Terre Haute Indiana, for the same reason as the Cutoff got built; rolling Indiana and Illinois coal to water level at Cleveland.
The Big Four was still afforded some organizational independence, and boy did they love those open spandrel concrete arch viaducts:
https://youtu.be/XaQ_-LWVVY8&t=19m42s
https://youtu.be/0r1CYTiYVu4
If CSX runs 10,000 ft PSR land barges across theirs at track speed on a daily basis, the Lackawanna viaducts would support them structurally. The work is likely primarily cosmetic, but the nature of the viaducts involve significant job site setup, tear down, and safety costs.