This morning, Transport for London opened a new branch of the London Overground, creating a circular line connecting many of London's less-affluent neighborhoods in a giant circle:
Until recently, substantial parts of London (notably the South and East) had limited subway access, relying instead on poorly integrated, less reliable commuter rail lines run by national train companies. Some of these worked okay and some were terrible – the notoriously unreliable one near where I grew up used to be called the Cinderella Line, presumably because while you were waiting eternally for some grand carriage to arrive, all you saw on the line were mice.
The Overground has taken these old lines and knitted them together with newly constructed underground trackways and new stations (mainly in the under-served South and East). A number of these stations also have subway connections, so this once separate network is now a fully integrated extension to the subway rather than a shoddy, second-tier alternative.
The Overground’s rolling stock is also a huge improvement. While London’s subway trains are constrained by narrow tunnels, the Overground’s single carriage trains are wider and higher, with space for bikes outside rush hour and air conditioning.
(The new London Overground, as of today.)