If you need to pass behind a tractor-trailer that is backing up, you should:

Question

Large vehicles have large blind spots to the rear. If you are behind a large vehicle, it is very likely that the driver does not know you are there. Because of this, if you need to pass behind a large vehicle that is backing up, it is always the safest option to wait for the truck's backup maneuver to finish before you pass.

Accepted Answer

Wait for the truck to stop backing up before you begin passing.

Answer

Pass quickly.

Answer

Honk to let the driver know you are passing.

Answer

Assume that the driver can see you.