Hey Adrian - there is an example in the notebook Agent-Close-Following.ipynb.
It sets up a little test env, runs a few steps / actions, and renders the chains / trains of adjacent agents using GraphViz.
At step 9 you can see that the agents in cells (1,4) and (1,5) are blocked by the others in front, and the lower-index agent in (2,6). (I couldn’t find an easy way to make GraphViz render the agent numbers in the cells, as well as the row, col node identifiers 
)
For the “close-following” (aka unordered close following or UCF) we set up a digraph for every step, and the edges are the moves the agents want to make. This is of course different to creating a (static) graph or digraph for the rails.
Apologies to anyone struggling to install GraphViz btw. If it proves to be a problem we will improve our instructions. GraphViz is not necessary for the operation of the env but it was useful for making the graphical test cases.