In using the time line to research this question, I did note a couple of exceptions. It shows some Chessie offices closing in 1975 that were actually open longer than that. How do I know? I was working some of them in 1976! There's also a post about some microwave system in the mid-70's eliminating pole lines. That's not true. We still had line-side phones to Toledo and Ludington until at least 1988. The pole line was eliminated on the Port Huron Sub around 1975, but to my knowledge the tone system that supplanted the pole line operated over leased commercial telephone lines. Direct dispatcher radio communication was not operational until 1985 and even then we still used the pole line phone system to talk to places like McGrew yardmaster and operators at Plymouth, Carleton and Alexis, etc. I know the GTW had a microwave system for communication by the mid-70's, but Chessie dispatchers in Michigan did not.