What does it mean to dream of a tractor trailer?

This dream would have very different interpretations depending on where the tractor trailer is seen, and whether it is moving toward or away from you , or not moving at all. The underlying factor is traveling, and could represent moving forward into the future, or making progress toward your goals. A tractor trailer general hauls a huge amount of freight, and in the dream that freight probably represents the "load" you carry through life.