A new section of London Underground's Circle Line has opened, extending the traditional loop into a "lasso" shape.
The line now runs from Hammersmith station to Edgware Road, before joining the existing circle. Trains also run anti-clockwise between those stations.
It will still be called the Circle Line despite having a fixed terminus.
Chief operating officer Howard Collins said it would offer a more frequent service, especially for people going to west London shopping centre Westfield.
The Circle Line extension uses tracks it shares with the Hammersmith and City, District and Metropolitan lines.
Trains will now terminate at Edgware Road or Hammersmith station rather than moving in a continuous circle.
The extension will also enable Circle Line services to recover more quickly if there is a disruption, Mr Collins said.
"It's become the sort of an end-to-end service that still forms a circle," he said.
"What's great about it is that it's doubling the number of trains on the Hammersmith branch of the Circle and Hammersmith and City lines.
"That actually allows us to serve the new Westfield development, which is a big destination for people. Now there is a train there every five minutes instead of every 10."
The extension is part of a series of upgrades which includes air-conditioned trains and a new Tube signalling system.