I found it already answered here
A driver should evaluate the condition of the intended driving path as being open, closed, or changing.
While driving, we need to be careful. We need to know if our driving path is safe. Therefore, we need to know if it is open or safe to drive through. If it is closed, we need to find an alternative path. If a driving path is changing, that means that we can drive through it, but we need to be cautious, because at any moment something unsafe could enter the path.
Open path means that we can drive through that path with ease. Closed means that we couldn't choose that path and should find another alternative. Changing means that we could go throguh that path but we need to be careful and aware.