Railway weekend October 2018 - so I had to do something!
I want to get to the point where you can run a "manually driven" train around the railway on a Traincontroller schedule. That meant being able to see where the trains are on underground sections, and see the signals. The simple answer: CCTV.
I was able to get on ebay a pair of 7" monitors, each of which could take feeds from two cameras. I also got three miniature cameras. o provide light, I got LED tape lights. The cameras are mounted to the baseboard and look along the track pretty much head-on.
My initial assumption was that I should have lights above the track I wanted to see, but not elsewhere. That resulted in very poor image quality. We added diffusers; it just kept getting worse. Eventually we found the solution was to have light everywhere, with no "blacked out" zones. The image quality was much better. We added two aspect signals, with the direction reversed so they face the cameras.
So, a simple solution, that works well!