The London Underground will get 4G access in its tunnels and stations starting next year. The rollout will start with the eastern half of the Jubilee line between Westminster and Canning Town stations in March 2020, and the plan is to have the entire network connected by the middle of the next decade. In addition to 4G, the system will also allow passengers to connect using 2G and 3G.

London’s mayor Sadiq Khan has suggested that the network could be upgraded to 5G in the future. “Introducing 4G and, in the future, 5G will help Londoners and visitors keep in touch and get the latest travel information while on the go,” Khan said.

Installing the equipment needed to provide a cellular signal will be a challenge. Transport for London estimates that over 2,000 km (or 1,200 miles) of cabling will need to be installed as part of the project, and says that all of it will need to be installed outside of operational hours to avoid service interruption.

London will not be the first city to install cellular data connections in an underground subway network. Passengers on Moscow and Tokyo’s subway systems, for example, have been able to use their phones underground for years. However, The Guardian notes that London’s subway system is particularly challenging because of its comparatively narrow and winding tunnels, which can block phone signals. Transport for London plans to use what are known as leaky feeders to overcome this problem, using cables that are able to broadcast signals like giant aerials.

The system will allow phone signals to penetrate along the length of the transport network’s tunnels. Currently, the only connectivity available underground is Wi-Fi in the stations themselves. New York City’s subway has offered Wi-Fi and cellular connections in stations only since 2017.