Assuming it can be considered a portrait, I do not really appreciate the crop that makes quite unclear which the subject is.
If the main subject is the horse all the other details are quite distracting. On the other side if the subjects are intended to be the person or the entire coach than the crop is too tight on the left making them appear as secondary elements.
Not a bad shot, but I think the framing/crop is the main downfall. The buggy is cut off, which distracts the viewer. I know there's not much you could do about it, but the background (and some of the foreground elements) are very busy (coats draped randomly, a water bottle, etc.)
Back to comment: Sorry to say but this is more of a candid photo than a portrait in my opinion. This image would be easier to accept as a portrait of the coachmen if it were more closely cropped and you could see both of their faces. The color and focus are nicely done but the cropped of back end of the buggy looks a little odd.