Sentence:  The rail <WSD>orbital</WSD> routes outside of the M25 and South Coast are challenging. The corridors aren't particularly reliable, and in some places they don't exist. [...] But the reliability and journey times, particularly on the <WSD>orbital</WSD> routes: one train an hour from Gatwick Airport to Reading? Surely we can do better than that? 
Meaning of the word marked with <WSD> tags:  (roads, railways) passing around the outside of a certain area.