Delhi Metro Rail Corporation is working to upgrade its signalling system to introduce the concept of ‘virtual signals’, reducing delays by up to 80%. Having identified glitches in the 14-year-old existing signalling system as being the main cause of the snags on the corridor running from Dwarka to Noida Electronic City and Vaishali.
At 65.5 km, the Blue Line is one of the longest corridors in the Delhi Metro network and also the busiest with 16 lakh passengers using it daily. Usually, a glitch at any point affects train movement on the entire corridor and the slightest of delays causes massive crowding, particularly during peak hours.
“The existing centralised viewing and monitoring system of Blue Line trains at the operation control centre in Metro Bhawan is more than 14 years old. At that time, the provision of ‘hot redundancy’ (system backup) did not exist since the network was small and had only a couple of interchange stations,” said Anuj Dayal, executive director (corporate communications).
He said “this sometimes led to the system losing train identification numbers, point flash and interlocking glitches, etc. From the signalling point of view, the corridor is divided between ‘interlocking sections’, the portion between stations where trains can change tracks. For example, both Laxmi Nagar and Anand Vihar are interlocking stations and the section between them, comprising three stations Preet Vihar, Nirman Vihar and Karkardooma, is an interlocking section. A signalling snag at any point in such a section disrupts the entire stretch. This affects movement because train operators have to acquire target speeds from each station in the manual mode. The speed is restricted to 20-25 kmph for the safety of passengers, but causes bunching of trains with a cascading effect on the entire corridor.
Now, virtual signalling hopes to keep the trains operating at the normal speed of 35-37 kmph, except for a distance of 500 metres from the affected zone. “A virtual signal is an intermediate entry and exit location displayed on the signalling monitor,” explained Dayal. “It may be used, wherever required, to divide the routes between two fixed signals. It is not a physical signal and only controls trains with automatic train protection.”
Dayal said that the system would be in place by end of 2021 as testing and commissioning of the system can be done only in the short period of non-revenue hours without affecting the existing signalling system. “When DMRC started Blue Line operation in 2005, there were technology constraints,” Dayal said.
“To increase line capacity during failures, DMRC plans to introduce virtual signals initially on the Blue Line and subsequently on the Red (Rithala-Shaheed Sthal New Bus Adda) and Yellow (Samaypur Badli-HUDA City Centre) lines. Lines added in Phase II and Phase III adopted virtual signalling at the time of commissioning itself.” DMRC said that apart from easing movement during a signalling glitch, the focus of virtual signals would be to ensure that trains reach the nearest interchange system faster.
For example, at Karkardooma interchange station in the Laxmi Nagar-Anand Vihar interlocking section, passengers other than those changing trains will also have the option of interchanging to another corridor not affected by a snag. They will be helped to take such decision through announcements in the trains.