In addition, I've also noticed that road vehicles seem to get stuck behind signs, routing themselves through one-way, choose, and do not enter signs only before stopping and becoming stuck with the message "Waiting for clearance." Would you happen to know about this?
I have split and moved this from the topic about the Heathrow Connect/Heathrow Express liveries as this is a different issue, and should be in its own thread.
I am not aware of the issue to which you refer: can you upload a saved game in which this can reliably be reproduced?