Transport for London has tentatively started testing 4G on the Tube for emergency services. TfL's CTO said he was not "absolutely confident" it would be complete by January, 2019, however.
The £2.9bn Airwave contract, which dates from 2000, will be switched off by 2020 and replaced by the 4G Emergency Services Network (ESN) run by EE.
Earlier this year, Parliament's Public Accounts Committee (PAC) warned the UK Home Office's ESN programme "may require more testing and assurance work than the current December 2019 delivery date seems to allow for."
Shashi Verma, CTO and director of customer experience at TfL, told the Greater London Authority Oversight Committee he was confident in the technology – but said the timescales the body is aiming for could not be guaranteed.
"This is an incredibly challenging programme ... the reason we don't have 4G in the tunnels right now is because the space in the tunnels is incredibly confined."
He said it is now possible to install 4G technology, but it is not easy. As of this week, TfL has decided on the approach it will take in installing the tech, which it signed off with the Home Office on Monday. The next step will be deciding on the design, he said.
TfL had originally planned to run a pilot of the ESN across six stations, but is now conducting a test on the Waterloo and City Line instead, which has not yet started.
"The main purpose of the pilot is not to test the technology, because we don't have any concerns about the technology working. There are many other difficult aspects of this programme, including figuring out the construction rates we can achieve which is very important for scheduling and planning."
The aim is that the technology will eventually be used to allow the public to use 4G in the underground tunnels. The plan is to do the work during engineering hours.
"Our aim is to get the stations ready for January 2019," he said. If [the question is]: are we absolutely confident all of this can be delivered by January 2019, the answer is 'no'.
"But if the question is, can we give enough to the emergency services so they can start testing in the tunnels, then the answer is 'yes'."
Len Duvall, chair of the GLA Oversight Committee, said: "In particular, we will be watching TfL's progress delivering ESN on the London Underground.
"To date, TfL has struggled to deliver large-scale transport programmes on time and on budget. TfL is now responsible for delivering an IT project on London's tubes and tunnels. It must ensure that it has the right IT and commercial skills to deliver this crucial programme."
The PAC estimated that extending the Airwave contract by one year would cost an estimated £475m nationwide.
Stephen Webb, director of Law Enforcement Programmes at the Home Office, said the programme was a "considerable logistical challenge," but that there will be no turning off of Airwave until the emergency services were confident that ESN is ready. ®