I know this is a TAAT but it felt reasonable to start this on the back of the stopping on a motorway to pee thread.
It seems too many people are unaware of just how extremely dangerous it is to stop on a hard shoulder. What other things do you think people do dangerously in cars, because they've forgotten their training or just become blasé?
From that thread, I have had advice that if you're even planning a motorway drive, pack towels or travel johns in case someone desperately needs to pee. Or a lidded tub in case someone pukes.