== Amended whole article == 

 I found the initial article very confusing to read, especially given that to understand anything of the differences between the three main notation systems (AAR, UIC, Whyte) one had to click on each link in turn. So I set to work rephrasing several words and passages, and reordering the run of sentences etc. There were also some inconsistencies in the article - three bullet points at the end of the article contradicted statements in previous paras, causing reader confusion about whether or not Whyte notation is used in the US. So I checked all thoroughly while reworking the whole, so as to give a proper "overview" of the subject. Lastly I tried to find any decent sources - there are loads on the web describing the various steam wheel arrangements, but almost nil about the overall nature of wheel arrangements as a subject, ie. why and how they matter. Finally found one source that defined it reputably as "the distribution of wheels under (etc)", and referenced it accordingly. The article's still not great, but at least it's now a whole lot better to read / easier to understand. Hopefully others will agree.