A nationwide fault in the radio system between train drivers and signalers has led to severe disruption to the UK's rail network.
The disruption has caused severe delays this morning across much of the UK, with the National Rail advising people to check their journey before traveling.
Several services have been impacted, including the Elizabeth line, Gatwick Express, Great Northern, Northern, ScotRail, Southeastern, Southern, South Western Railway, and Thameslink services.
According to the National Rail, the disruption has been caused by a fault in the onboard Global System for Mobile Communications-Railway (GSMR) radio system, which is used to communicate in case of emergencies.
The BBC reports that the fault can be traced at the national telecommunications hub in Doncaster.
A back-up manual log-in system is currently being used, although this is causing a delay of a few minutes.
In the case of such a failure, trains aren't allowed to exceed 100mph (160kmph), or 60mph (100kmph) through affected areas, which has meant slower trains or an entirely reduced service.
The GSMR radio system allows train drivers and signalers to communicate with one another, even through tunnels.
National Rail notes on its website that it has invested £1.86 billion ($2.37bn) in the GSMR. The purpose of the system is to move the comms system away from legacy technology.
To date, it claims to have covered more than 15,000km of railway lines covered, and deployed 2,500 GSM-R telecoms masts, plus 8,574 installed cab radios.
