The Hounslow Loop Line is a railway line in southwest London which was opened by the London and South Western Railway in 1850. It leaves the Waterloo to Reading Line at Barnes Junction and after some seven and a half miles rejoins it at a triangular junction between Whitton and Feltham. Passenger services, all operated by South West Trains, either loop back to Waterloo by the junctions or continue southwest via Feltham. More information on the Wikipedia page [1].