The Piccadilly Line, one of London's oldest and busiest deep-level Tube lines, is finally getting air conditioning after 120 years, as part of a £3.4 billion modernisation investment by Transport for London (TfL). The upgrade will see a new fleet of 94 trains, scheduled for rollout between December 2026 and June 2027, making the dark blue line the first deep-level route on the Underground to be temperature-controlled.
Passenger Comfort as a Priority
Track design engineer Jack Parry told Metro that 'passenger comfort is one of the main priorities for the railway,' and that the 'track is designed to give the passenger the smoothest and most comfortable experience possible.' Most modern trains are now equipped with air-conditioning, and Parry noted that it only seems natural to implement it on the Underground. However, he acknowledged that adding air conditioning increases energy consumption and direct emissions, but argued that the trade-off is worth it for improved passenger comfort and to encourage more people to use the Tube instead of cars.
Sustainability and Wider Benefits
Paul Herriotts, Professor of Transport Design at Coventry University, agreed that 'sustainability is not just about carbon emissions,' but includes passenger wellbeing and accessibility. He said that air conditioning can reduce heat stress, improve travel for older passengers, benefit those with medical conditions, and make travel safer during heatwaves. As the UK experiences more frequent heatwaves, he called it a 'good trade-off with clear passenger benefits.'
New Train Features and Capacity Boost
The new trains will also feature walk-through carriages, wider double doors for easier boarding, improved step-free access, on-board CCTV, and enhanced digital displays. TfL stated that once the 94 new trains replace the 86 existing ones, the number of trains through central London will increase from 24 to 27 per hour — every 135 seconds — at peak times. This will boost capacity by 10% overall and up to 23% during peak hours, helping to take more cars off the road.
Delays and Testing
The new trains arrived in the UK for testing in late 2024 but were delayed due to technical issues identified on a prototype. Mayor of London Sadiq Khan told the London Assembly in July 2025 that the 'process is taking longer than expected due to challenges with the design, build and commissioning.' Service is now expected to begin in late 2026. In August 2025, Khan posted a video on X of a prototype being tested, calling it an 'exciting change.'
Sustainability and Energy Efficiency
The upgrade is part of TfL's wider plan to boost sustainability. The new trains will be significantly lighter and consume 20% less energy compared to the old 1970s stock. TfL is also building a 'digital twin' of the line to track energy usage, capture carbon in tunnels, and identify emissions hotspots, supporting the Mayor's goal of making London Net Zero Carbon by 2030. The Piccadilly Line currently accounts for 10% of all Tube journeys, handling roughly 158 million to over 200 million passenger trips annually, making this energy-efficient upgrade a significant positive impact.
