I believe Lao Tzu used his words like a poet, to reveal an experience of life, the realm from which all words emerged. If someone points his finger at the moon, we must look at the moon and not at the finger. It can mean a physical road, it can mean a spiritual road, or it can mean a way of life. The Tao is also the way of nature. Nature grows spontaneously, according to the inner promptings of its being.
Nature is incapable of habitual, compulsive, or contrived behavior.
Thus nature becomes the model of the Tao. Nature is always in a constant state of flux and transformation. You can't step twice into the same river. Lao Tzu could have said that. Thus the term Tao implies vitality and movement.