Rebuilt Locos

This afternoon at 14th St., I saw a freshly repainted #155 facing north along with retired bilevel #712, Metra, RTA, and BNSF logos blotted out. About a month and a half ago, I saw #157 at 14th St. facing north. Why is it that some of the rebuilt locos from UP make a stop at 14th St. on the way to/from the Rocket House?

Not really an answer to the questions above, but what comes next for rebuilds after 150's? Back to 100, or have the F40's all ready had thier last rebuild before replacement..considering they were built only 3 years after the F40C's.