When did the Luas stop running?
Services on the Luas Green Line, which runs from Broombridge in northeast Dublin through the city centre to Brides Glen in the southeast, were suspended from around 8.30am on Wednesday, December 10th, to 6pm on Thursday.
Services on the Luas Red Line were also suspended between the Smithfield and Connolly stops, but resumed later that same day.
What caused it?
Services were affected when power to the entire Luas Green Line failed, according to a Transdev spokeswoman.
Late on Wednesday night, Luas technicians and engineers had identified a fault within the 48-volt low-voltage safety circuit, which is separate from the overhead lines that power the trams.
RM Block
This circuit forms part of the safety network linking substations to the central control room and is designed to shut down the overhead lines in an emergency. The system was detecting a fault condition and, by design, would not permit power to be restored until that condition was fully understood and resolved.
The Luas network operates on a fail-safe design, meaning that if any unusual, irregular or unsafe condition is detected, the system automatically shuts down power and stops tram movements.
This is to protect passengers, staff, infrastructure and the wider public. While this design can cause service disruption, it ensures that trams cannot operate unless all safety checks are completed and the network is confirmed safe.
What is a 48-volt system?
It is a critical safety circuit that spans the length of the Green Line and includes multiple substations and safety interfaces. Substations are 20 metres underground.
How many people were impacted by the outage?
According to Transdev, around 95,000 people travel on the Luas Green Line each day.
Was the fault caused by winds from Storm Bram?
No, currently there is no indication it was related to storm or weather factors.
When did the Luas Green Line service resume?
A full service resumed at 6pm on Thursday, December 11th.
Why did the fault take so long to rectify?
According to Transdev the system, and its rectification, is complex and takes time.
From Wednesday morning, engineering, operations and executive teams inspected 12 substations to isolate potential fault locations and carry out systematic safety checks.
So how was it finally repaired?
When the issue was detected, engineers carried out detailed inspections across the line, identified issues within the safety circuit and isolated the fault.
Repairs and system resets were completed which allowed the 48-volt safety system to stabilise, enabling the safe re-energising of the overhead line and the restoration of all Green Line services.
[ Dublin’s Luas Green Line ‘operating normally’ after two days of disruptionOpens in new window ]
What happens next?
Transdev and Transport Infrastructure Ireland are undertaking a full technical review and additional diagnostics.
“Safety, reliability and system resilience remain our highest priorities,” said a Transdev spokeswoman.
How old is the Luas Green Line?
The Green Line first started operating in 2004.
A Transdev spokeswoman said the incident relates specifically to a fault detected within a safety circuit, not the age or condition of the infrastructure.
What is the current status of the Luas Green Line?
The Green Line is operating as normal as a full service resumed at 6pm on Thursday.
Minister for Transport Darragh O’Brien acknowledged the issue caused a lot of disruption to communities.
Labour’s transport spokesman Ciarán Ahern said: “The fact that one Luas line going down can cause such havoc around the city is indicative of how poorly our capital city is served by public transport.”
Jennifer Whitmore of the Social Democrats said public transport “must be dependable if we want people to choose it over cars, and that means robust contingency plans and investment in resilience”.
Has anything like this happened before?
Not really, but last August Transdev warned that its Red Line services faced weeks of disruption following a fire on a bridge in the Docklands area of the city.
