Exactly RC, we went so far as having voice activated walkies attached to our seatbelts signalling when it was ok to pass another car on a mountain road, the first driver to pass would let the driver behind him know on the walkie that no cars are coming it's safe to overtake, and then he does the same for the guy behind him.....but that got a little to complicated as people would forget to charge the walkie or forget it at home haha.... but as you said, you have to be very comfortable with the people you drive with.....