Elizabeth line: Direct services open to central London
Three sections of the Elizabeth line have been connected, allowing passengers to travel across London without having to change stations.
Previously anyone going from Heathrow, Reading, Abbey Wood and Shenfield had to change at Paddington or Liverpool Street to remain on the new Tube line.
Transport for London (TfL) has also said the line's seven-day services had begun through central London.
Mayor of London Sadiq Khan said the line was a "huge success".
The Elizabeth line started running in May when it was opened by the Queen.
The newest launch means passengers landing at Heathrow Airport will be able to reach destinations such as Farringdon in roughly 40 minutes or Canary Wharf in about 50 minutes.
Passengers from Reading and Heathrow can travel directly to Abbey Wood, south-east London, without needing to change at Paddington Station, while those setting off from Shenfield, Essex, can travel directly to Paddington without needing to change at Liverpool Street Station.
Those making journeys to Reading and Heathrow will also be able to do so now, by changing lines from the same platform at any central London Elizabeth line station.
Transport Secretary Mark Harper said: "Through our £9bn investment, it's great to have contributed to a line which in just five short months has shown itself to be a staple of London's transport network delivering over 60 million journeys and creating over 55,000 jobs."
London's mayor Sadiq Khan said the latest extension of the Elizabeth line would "bring a huge boost to our city" including "encouraging people to make the most of the capital" and supporting businesses.
"I'm so proud of this transformational addition to our public transport network," he said.
"The Elizabeth line is helping to build a better London - a fairer, greener and more prosperous city for all Londoners."
Mr Khan added the line would also be beneficial for people in the south of England.
"London benefits but also if you live in the west in Reading or in the Shenfield, if you live in Essex or in Windsor you benefit as well," he said.
Mr Khan urged the government to invest in more London infrastructure.
He said 60 million journeys had been made on the railway since it opened in May.
"That shows the difference good public transport can make but the really great news is that we as a global city have a new piece of infrastructure - but we can't stand still," he said.
"So my message to the government is if you invest in London the whole country benefits."
The line had previously been closed almost every Sunday to allow more testing to take place, but TfL said trains would now run every three to four minutes, seven days a week.
The line's central section between Paddington and Abbey Wood will also stay open later, with the last daily departure from Paddington at 00:22 GMT, instead of 22:58 previously.
The full peak timetable, which will see 24 trains per hour during the peak between Paddington and Whitechapel, is on track to be in place by May 2023 and TfL says it will increase capacity and ease congestion on its network.
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