Well if you had that only bus photo, I would most likely create another folder with the trip's date on it, so in the future it will be easier to search for it, even though it's just one picture in the folder, it's a lot easier than to hassle around and trying to find something specific like this. If you have made a lot of trips for a lot of folders, you'll start to see it really works. Now for example if you mix both of the divisions together (ex: IRT and BMT/IND) you should still create separate folders for those pics in your PC, but make only one thread in the General Subway section and put them all in there. Just a word of advice!