English: Double cross platform interchange looking from one train through another train (which has its doors open on both sides) to see a third train! This image comes from Barking station in London where the eastbound underground trains open their doors on both sides so as to provide cross-platform interchange with two different mainline railway services, these being the C2C service between Fenchurch Street and Shoeburyness stations (as seen on the other side of the District Line train) and the London Overground Barking - Gospel Oak service, with this photograph having been taken inside one of the trains on this route.