When there are no more cards to take and you can play the only ones your hand has, you can not play any kind of special card even if you were saving them to use in future cases. I suppose that is a bug and it is good that we can discard them with the letter j, otherwhise the game would get stuck.
Hmm, interesting. I was able to play them. Maybe in your case it happened that you couldn't play the right of way card, because that card wont work when you have speed limit but aren't stopped.