Mobile signal for calls and data will soon be ubiquitous on the London Underground, even in tunnels Scott Barbour/Getty Images

One of the last not-spot bastions will finally get mobile coverage: from 2019, the London Underground will have blanket mobile service – yes, even in tunnels – after successful trials on the Waterloo & City line.

Mobile coverage is already commonplace on underground train networks around the world, including in Paris, Berlin and Tokyo. In London, commuters and tourists can already get Wi-Fi access at 97 per cent of underground stations and platforms, but it drops out as the trains travel through tunnels. The aim with these latest trials is to ensure calls aren't dropped, so commuters and tourists alike can ruin the eerie quiet calm of packed trains by nattering on their phones for the entire journey.


Each of the four major operators – EE, Three, O2, and Vodafone – took part in the Transport for London (TfL) trial, though only the first two actually tested signal inside the tunnels. The trial ran outside of passenger hours on the Waterloo & City line — which only runs between two stations — and was chosen not just because it has a more limited timetable but also because its 2.1km tunnel is considered "particularly demanding in terms of radio coverage", TfL noted in a planning document released to WIRED.

The culmination of the trial was taking a call in the ticket hall, walking through the station to the platform, hopping on a powered track-trolley for a ride through the tunnel to the second station, and exiting to the ticket hall without dropping the call.

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The technology won't interfere with existing railway signaling systems or with the existing Wi-Fi network, and TfL suggested that the Wi-Fi system would co-exist alongside the mobile coverage, as it may be useful for tourists. The two operators tested on the 800MHz, 1,800MHz and 2,100MHz bands in tunnels, and the 1,800MHz, 2,100MHz and 2,600MHz bands at the two stations, Waterloo and Bank.

Alongside checking if the system would work in the Tube's tunnel network, the trial also let TfL get some practice laying fibre cables across its network as part of plans to set up its own broadband infrastructure. With the tech side sorted, the next challenge is figuring out who is going to pay for it all. Graeme Craig, director of commercial development at TfL, said the project "will also help us generate vital commercial income to reinvest in modernising and improving transport in London”.

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The TfL planning document reveals the transport body's hopes that all three plans — mobile coverage underground, the fibre network, and 5G support — would help fund the transport system: "Our expectation is that the commercial partner will cover the capital and operating costs of the telecoms operation and would provide a revenue share for us."

It added that mobile operators said no customer data would be "directly available" from the proposed system, though TfL noted that they "offer aggregated, anonymised data services."

Commercial partners are expected to be signed up by this summer, with an incremental rollout starting by 2019. TfL said all work would be carried out within engineering hours so there would be no disruption to train services.