An upgrade of the third rail of the north-south or Blue line of Metro Rail, meant to save energy and equip itself to run trains at shorter intervals, saw its first phase completed on Saturday.

The Mahanayak Uttam Kumar (Tollygunge) station saw the steel third rail replaced with aluminium on Saturday.

The existing third rail, made of steel, is being replaced with one made of aluminium, in phases.

The third rail provides power to the trains.

“Aluminium is a much better electricity conductor than steel. Aluminium third rail will reduce the system voltage drops and subsequent energy losses. Less voltage drops will help in achieving faster acceleration of trains,” said an engineer.

Now, the interval between two trains during rush hours is around five minutes. When the entire 34km stretch of the Blue Line gets the aluminium third rail, the carrier will be one step closer to achieving a rush-hour frequency of two-and-a-half minutes.

“The first phase covered the down line (New Garia-bound line) from Shyambazar to Tollygunge and the up line (Dakshineswar-bound line) between Shyambazar and Park Street. The second phase will cover the up line between Park Street and Tollygunge and both the lines between Shyambazar and Dum Dum. It is expected to be completed before December 2025. In the third phase, the line between Tollygunge and Kavi Subhas (New Garia) will be covered,” a Metro spokesperson said.

The upgrade happened after the commercial hours.

Metros in London, Munich, Moscow, Istanbul and multiple other cities have an aluminium third rail, said a Metro official. The preparatory work started at Girish Park and Maidan yards in September last year.

The main component, shipped from Hamburg in Germany, arrived in Calcutta in the last week of July 2024.