You have three options: 1. Pull over, go into the forest ( at your own risk) and ket that sucker lose. 2. If your a boy and you have a cup, stand up as good as you can, place your junk in the cup, and go. I don't recommend doing that while actually driving 3. Play "How Long Can You Hold It". You see how long you can hold your pee in. You lose if you wet yourself or you die from pee acid build up (it can happen).
I always carry a coffee can or better yet one of those cheap throwaway containers ( get the sandwich one - about 4 for $2 -3 dollars _better for females) You might want one of the larger ones. Works for me :)