LUL - Faults in the 4LM Signalling System

Our ref: HSR/2/6

Head Office Circular: NP/106/23

16th June 2023

To: The Secretary




Dear Colleague,




I have received alarming reports from my Tier 2 safety reps in the Trains and Service Control functions of LUL; a number of software issues have come to light as the Thales 4LM automatic train system is rolled out. LUL was unable to contradict my representatives’ assertion that the railway no longer fails safe. The company accepts that a risk of derailment and/or collision has been imported with the roll out of the 4LM project.


London Underground had, on 12/5/23, 76 operational restrictions in place on the 4LM signalling system. This means that Service Control staff and Train operators are required to remember 76 sets of circumstances in which they should act in accordance with temporary instructions rather than the rule book.


On 12th May this year my representatives met with the company, and put the position that the next phase of the 4LM project, Signal Migration Area (SMA) 8, should not go ahead at this time. RMT also argued that LUL has sought to rollout the 4LM project without proper testing in place. 


The company stated to my representatives that it intends to put a number of software “alarms” in place to warn service controllers when problems may arise. However, they remain unable to develop a fail-safe fix. LUL’s solution largely relies on so-called floor walkers at the Hammersmith Service Control Centre.


At its meeting on 7th June 2023, your National Executive Committee resolved as follows:


We note the report from the Lead Officer.


We instruct the General Secretary to write to LUL, in line with the report, demanding that the Signal Migration Area (SMA) 8 planned extension is stopped until a safe method of working is agreed. 


Affected members and branches to be informed by email and text. 


I have acted in line with the decision. Please bring the contents of this circular to the attention of relevant members. 


Yours sincerely



Michael Lynch

General Secretary