Metro services were disrupted for several hours on Thursday afternoon after the newly installed automatic signalling system developed a glitch.
Thousands of commuters were inconvenienced as Dum Dum-bound trains were delayed by nearly 15 minutes on an average. Metro officials claimed the disruption delayed services between 2.11pm and 3.20pm but it actually continued till the evening peak hours, said sources.
A Metro official said the problem occurred on the Dum Dum-bound tracks between Belgachhia and Dum Dum stations. The signal outside Dum Dum station started malfunctioning because of a glitch. So trains had to be delayed at all stations, said Protyush Ghosh, the deputy general manager (general) of Metro Railways.
He said the trains had to be operated through a manual system, which caused the delays. The glitch was repaired at 3.20pm, Ghosh said.
In the new technology, which has been in use since April 22, the signalling system is integrated with the railway tracks. The technology is supposed to increase train frequency and enhance passenger safety.
As soon as a train enters a particular stretch, the circuit integrated with the tracks sends a signal and the stretch shows up as occupied on the monitor, an official explained. Once the train leaves the stretch, the system sends a signal that the track is unoccupied.
On Thursday, however, because of the glitch, the system was showing the track between Belgachhia and Dum Dum as occupied although there was no train on it, he said.
As a result, manual clearance had to be given to the driver at Belgachhia station, who could run the train on that stretch at just 15kmph. Usually, the trains run at 55kmph, the official said.
Because of the cascading effect, many trains were forced to stop for longer periods at various stations.
Call centre employee Sudeshna Basu, who had taken a Dum Dum-bound train from Shahid Khudiram (Birji) station at 2.45pm, said: The train stopped at Kalighat for 10 minutes and then at Maidan for more than 12 minutes. There were announcements at both stations that the train could not start because there were trains at the next stations.
Even after the signalling system started functioning properly at 3.20pm, trains continued to be delayed for about an hour, said sources.
Installation of the automatic signalling system began in September 2010. The original deadline for the Rs 11crore project was October 2010 but it could not be met because of technical problems in the tendering process, said sources.