Dagny is Vice-President in Charge of Operation at Taggart Transcontinental. Those in the know know she is the one who really runs the railroad.
Part 1, Chapter 1, section 2 (AtlasShrugged/112) Part 1, Chapter 1, section 3 (AtlasShrugged/113) Part 1, Chapter 1, section 4 (AtlasShrugged/114) Part 1, Chapter 3, section 2 (AtlasShrugged/132)