Signal outage probe in Ambattur-Avadi stretch reveals safety violations

A photo taken from the driver’s cab of an EMU shows a signal showing a “double yellow” aspect, which authorizes a train to enter a track where another train is visible. | Photo credit: Special arrangement

An investigation into a signal failure that allowed an electric multiple unit (EMU) to enter a track occupied by two other trains in Southern Railway’s Chennai division has revealed serious lapses in compliance with safety protocols.

Documents accessed by The Hindu revealed that the S192 automatic signal on the Ambattur-Avadi section failed more than 50 times in February 2026 alone. It was found that the buzzer installed in the Ambattur Station Master’s office alerting the staff of signal failure was ‘disconnected’. The faulty signal was repeatedly reset by field technicians without analyzing the root cause of the failure. This allowed the problem to recur over the course of several months.

The event took place on March 5 this year in a busy suburban section. The signal displayed a “double yellow” aspect, authorizing the EMU to proceed on a line occupied by two other trains. But an alert motorist noticed the trains ahead and braked, bringing the EMU to a stop just short of the busy section and averting disaster. He photographed the situation and reported it to his superiors. A multi-agency inquiry by senior officers found that repeated signal outages had not been subjected to any root cause analysis.

During the failure of the Multi-Section Digital Axle Counter (MSDAC), a critical train detection and signaling system, field workers merely replaced faulty sensors without investigating the root cause of the failure. As a result, replacement sensors were consumed at an unusually high rate while the defect remained unresolved.

Records showed that in February 2026, dozens of signal sensor failures were reported in the section. The S192 signal alone failed 53 times, significantly more than other sections. Although alerts of the failure were sent out through WhatsApp groups, officials did not identify the root cause or initiate corrective measures, the survey found.

The investigation concluded that the incident was the result of a series of system failures. The Ambattur station master was unaware of the malfunction as the warning buzzer in his office was not working. Instead of diagnosis, the signal maintenance staff took a shortcut to reset the faulty sensor. The signaling system diagnostic panel was also found to lack safety features.

“There was a failure of SMS alerts from the data logger to notify the Section Chief Engineer of a potential reset attempt at the MSDAC cabin,” the investigation report said. According to the report, these outages together led to the S192 fault, which allowed the EMU to enter the track occupied by two other trains.

Published – 14 Jul 2026 21:03 IST