Tube commuters in London have been given a glimpse of new air conditioned train carriages set for introduction to the network from 2025.
The images show how they will look inside once they are used on the Piccadilly line.
"The first trains are being put through rigorous testing on a test track and in a climate chamber with extreme weather conditions," TfL said on X, formerly Twitter.
The Piccadilly line has been upgraded as part of a £2.9bn investment programme.
It stops at central London stations such as Leicester Square and Kings Cross St Pancras and runs all the way to Heathrow Airport in west London, accounts for more than 10% of all journeys on the London Underground, according to TfL.
This equates to around 200 million annual trips.
Alongside air-conditioning - the first time it has been used on a deep Tube train - the improvements include walk-through carriages, electronic digital display screens for customer information, CCTV cameras and wider double-doors.
The new carriages will replace the 86 existing ones which have been in service for 48 years. The move should also increase the number of services through central London from 24 to 27 trains an hour.
Many of the new carriages are being built by Siemens Mobility Ltd at the company's rail facility at Goole, in the East Riding of Yorkshire.