I'm a little confused. Where exactly does php come into play here? What I see, is a manual edit of an xml file thats necessary in order to load what you have. You can certainly open what you have now, fetch the speed element and split it up into individual speed elements by replacing the current speed. For that, I'd suspect you'll need to use the DOM instead of simplexml. I myself have used simplexml like twice, just to answer questions here.
header('HTTP/1.1 420 Enhance Your Calm');