Widen the bus to shorten the bus. Use it when appropriate, single up on narrow stretches, or sections with blind bends. As for calls, traditionally the only time an encroaching vehicle was an issue, was on a hill. So “car up” was for a car coming up the hill, “car down” was a car coming down the hill, as these were the times when the speed differential between rider and vehicle caused maximum risk. To stop any confusion, the clarification that “car up” was a vehicle coming up, from behind, whilst the group were facing up, and “car down” was a vehicle coming down the hill from in front of the riders. The reason “car up” and “car down” became the accepted norm, was that “car up” / “car down” gives 3 bits of info, with 2 words, and 2 syllables ( there’s a vehicle, it’s behind / in front, it’s moving towards the group, which is also why “car back” / “car front” shouldn’t be used, as ‘back’ and ‘front’ don’t carry the same inference about the vehicles relative motion) and the info is delivered as quickly as possible. It’s quicker to say “car up / down” than “car behind / in front ”. Also, because the letter r, and u, ‘flow’ ( it can make 2 words sound like 1 )where as r, and b don’t flow, so “car back” can’t be compressed to sound like one word, and that time saving could be critical. Bad calls / non existent calls, are one of my pet peeves when leading a ride ( of which I have, many times ) Particularly when someone behind me, calls “car up”, and they are referring to a vehicle approaching me, from in front ( this happens a lot ). Firstly I know, I can see it, and I’m the one closest to it, secondly, if someone behind me calls “car up” I’m assuming there’s possibly a vehicle is approaching from behind me as well, and I’d rather not have to glance backwards unnecessarily, whilst I have a vehicle approaching from in front.