While 9 or 10 signal rules might sound like a lot compared to the 21 or seen in under NORAC or CSX, the D&H finds itself in good company with many other railroads not operating multi track main lines in and around busy urban terminals, especially those making use of route signaling. The D&H is a very conventional speed signaling system designed for single main track operation with passing sidings. If you remember back to my signaling dialects post you'll see that the D&H uses Y/Y for advance approach, R/Y/G for Medium Approach Medium, R/Y/R for Medium Approach and R/Y or R/R/Y for Restricting. The R/Y/G Medium Approach Medium was made possible because the D&H made a point to use high signals at siding exits and R/Y/R Medium Approach was enabled by using only three headed signals at interlockings. Here is an example of the three head policy that was still in effect up through about 2011 with brand new Unilens tri-heads installed on the former D&H Colonie Branch at CPO-5.
So that's the story of the D&H signaling system. It started out pretty conventional and then got even more-so after several new owners put their hand in the pie.