This photo is an amazing example of vantage point.  By placing the lens on the road directly where the rainbow appears to begin in the distance not only do we get a really unique perspective of the natural phenomena, but we also are left with a sense of how small we as individuals are in comparison to this beautiful display of nature.  The use of color in this photo, where everything is relatively earthy neutral tons other than the rainbow, is not only pleasing to the eye but really helps the rainbow stand out as a focal point of the picture.  I also like how the rainbow divides the picture into nice weather and stormy weather.  Almost showing that there is light and dark in everything, even things that are seemingly good like rainbows.  A rainbow can only occur if there is both rain (or rain like conditions that create moisture in the air) and sunlight.