London's Circle Line is going to be a spiral as of next year. Trains will start off at Hammersmith and follow the Hammersmith and City line route. From Edgware Road onwards they will run on their existing line, go clockwise once around the track and terminate at Edgware Road on the next cycle, then head back in the opposite direction.
Allegedly this will make everything more robust and less likely to suffer delays if something goes wrong.The snag, of course, is that if you're taking the Circle Line clockwise from e.g. High Street Kensington towards King's Cross you're going to have change trains at Edgware Road; that's already a busy station, since the District Line also terminates there. From the look of things it'll benefit me, since there ought to be more trains on the line between Hammersmith and Edgware Road and that's the route I use if I travel to work by train.
One thing bugging me though - what are they going to call it? The Spiral Line?