The Circle, District, Hammersmith & City and Metropolitan lines 环线，区域线，
make up nearly 40% of the tube network,
carrying 1.3 million passengers every day
and stretch from busy central London stations to quiet countryside.
they also cover some of the oldest parts of the underground.
Some of the technology used to run these lines wouldn't look out of place in a museum.
For example, one of the signalling cabins still being used on the Circle and Hammersmith & City lines
dates from 1926.
This aging system is called fixed block signalling,
where the track is divided into segments to keep trains a safe distance from each other.
At the moment, trains run further apart than they need to, and they don't automatically send data
to the control rooms.
The system also requires a lot of regular maintenance.
That's why TfL is replacing the old equipment on all four lines.
The new technology uses Wi-Fi to constantly let controllers know where trains are
and how fast they're going.
Precise speeds will be set by computers,
so trains will be able to run much closer together,
every two minutes through central London by 2022,
dramatically cutting the journey times, and boosting the number of passengers
that these lines can carry by 33-percent.
It will take several years to finish all this complex engineering work,
but when it's finished, our customers will benefit from faster, more frequent, and more reliable tube journeys
on a brand new fleet of a hundred and ninety-two air-conditioned, walk through trains
that are already on the network.