Montreal work crews were above ground on Thursday but work is actually taking place below De La Gauchetiere Street, where the city is lining a sewer pipe that is more than a century old.

"This will extend the life of the sewer for 50 years," said Urban Infrastructure Projects director Jean Carrier.

The work is part of the city's maintenance on its aging sewer system. Crews repair about 50 kilometres of the sewers using the above-ground technique every year.

"Here we are, maybe one week," said Carrier. "If we rebuild the road and all the infrastructure, it may be a project of one to two years."

It's not a new type of upkeep, but it's the city's main strategy to keep the sewer network in top shape.

Officials say it costs $1 million per kilometre of sewer, but emergency repairs would cost 10 times more.

"We have more and more worksites, and we have to explain to people we are not doing it for fun; it's necessary," said Ahuntsic-Cartierville borough mayor Emilie Thuillier.

The city said it is trying to better manage the number of cones and detours by doing projects similar to the one on De La Gauchetiere, even on the coldest days.

"We can have some works that are really concentrated on some days, and we can do it in winter so we have less impact," said Thullier.