I would say probably almost never enforced. The railroad likely lobbied for this as a liability reason decades ago. Having train tracks on stateland could be a liability issue. Making it illegal to be on them or cross them is good for the railroad.
That bridge in sebewaing was always packed in the spring with perch fishermanI used to work for the railroad in the Bridge and Building Department and got around railroad property quite a bit. I know that there was a big problem with people fishing off railroad bridges and we were instructed to notify the police if we saw anybody on railroad bridges. Some of the bridges over the Grand River, over in Muskegon, Bay City, and Sebewaing were where we had the most issues. The train crews were also instructed to report trespassers whenever they saw them.
The bridge in Sebewaing, I showed up to inspect it and there were a bunch of fishermen there worried that I was going to kick them off the bridge because they had just been told to leave a short time earlier.