In the same quote below, why is the first occurrence of road is followed by a comma while the second is not? Who or what is curving in the first occurrence, the road or the writer? Can I get evidence as to who or what is curving from the text or grammar rules?
I was on a high, open road, curving over the swell of hillside that I saw as the flanks of some prehistoric animal, deep in slumber. The moonlight was so strong as to throw my shadow beside me on the road as a mute companion; and so I found myself not quite alone after all, taking a childish pleasure in my shadow-self as it matched me stride for stride. I could see quite clearly my road curving ahead, and the clump of trees, inky black, that marked my turning point.