IDIOMS

back up

(idiomatic, intransitive, of a blockage) To halt the flow or movement of something.

Example:   That beeping sound indicates that the truck is backing up.‎
  Back up the car a little, you're blocking the driveway.‎
1898, Winston Churchill, chapter 5, The Celebrity:
  We expressed our readiness, and in ten minutes were in the station wagon, rolling rapidly down the long drive, for it was then after nine. […] As we reached the lodge we heard the whistle, and we backed up against one side of the platform as the train pulled up at the other.
  I couldn't see how to finish the project, so I backed up and tried it another way.‎
  This isn't working. Let's back up and think about it.‎
  Back up your documents folder before applying the update.‎
  You should be careful. This guy is backed up by the local gang.‎
  When he said I wasn't there, I told him I was, and my buddy backed me up.‎
  When I flushed the toilet, the plumbing backed up and burst.‎