FIFO signalling is unneeded, because Factorio already does it. I just sat for a while and watched and they'll go in order of who arrived first. Even if say train 1 arrived in the middle train 2 in the last lane and train 3 in the first one, they'll still go in order.
I did some more tinkering and ...

Thanks for the replies, there was a lot of helpful info for me to review. I am going to tinker with this a bit more, might end up putting train stations into the mix.

At the start of the cache is a rail signal followed by the first chain signal, which is the blue one that I am having trouble with ...

I am having trouble with a train cache. I am trying to cache the trains as First In, First Out (FIFO). Either one of two bad options will happen. 1. In the screenshot, the train is stuck at the first chain signal, which is blue. There is 1 valid path for the train to take, but it is being stubborn ...