The primary U.S. railroad trade association is the Association of American Railroads (AAR). The AAR
sells most of its publications through AAR.org, but apparently not the "car service" and "car hire rules," which are among the AAR's most important materials. These rules -- and the related directives -- are issued by the Association's Customer Operations Division, generally as "Circulars." Circular No. OT-10 seems to include most of the key information, and it is re-published quarterly in The Official Railway Equipment Register. You can buy the latest Register from the publisher, Primedia (800-221-5488), or get copies from NYPL Premium Services or another library that has the Register.
The AAR's interchange rules are published in the Office Manual of the AAR Interchange Rules and the Field Manual of Interchange Rules for Railroad Cars.
The Transportation Library at Northwestern University is a good resource for materials and questions.
Subway maps are posted on Amadeus Global Travel Distribution's Subway Maps page and The Subway Page by Robert Reynolds.