In London there are about 4 types of Trains used on their metro rail system, Deep Level trains, they're small and shaped like Swiss rolls, foreigners often think they look like toy trains, they can pass through deep tunnels that were built in the late 1800s. Then you have Sub Surface trains, they're shaped like loaves of bread and can run on the same tracks as Deep level trains but can't go through deep level train tunnels. They have their own square tunnels that run under the old broad way roads of London. Then you have overground trains, they're more like the commuter trains, they even use ac power from overhead power lines. Recently the mayor decided to give the different parts of the overground network different line names because life wasn't complicated enough. Finally you have the DLR, Docklands light railway, they're small self driving trains, they're also often compared to toy trains. I think you have to press the open door button to get off.
Some people that I know think Deep level and Subsurface trains can't run on the same rails. Those people should visit 'Ealing common' station, they share the same northbound and southbound platforms. The same is true of 'Rayner's Lane'.
To me the key stations are the ones that give you a smooth way to change lines by simply stepping off and waiting on the same platform. Stations that take you places beyond. Ealing common lets you get off a Piccadilly train and Catch a district line train going in the same direction. The district line will go to Barking, trains at Barking station go to the Thames Estuary and as far as Southend on sea, the Nearest coastal town to London. The District line also goes to Victoria station, the national coach station, national express, mega bus and flixbus coaches from there go across Britain and Europe. Three subsurface lines share two platforms at kings cross station, Hammersmith line trains also go to Barking and the circle line trains also go to Victoria. St Pancras Station is next door to kings cross and there is a pedestrian tunnel connecting the two stations, Trains from St Pancras go to France and Kings Cross is also a Terminal station for trains from the north on the surface. Kings Cross and St Pancras are sometimes considered the same station because of the way they sit side by side. Some people say, there is a route to everywhere from those two stations. They wouldn't be wrong.
