The STM says the lifespan of some of its Metro cars will be extended to 60 years — 20 years more than their previous expected lifespan.

Montreal's public transit corporation has two generations of Metro cars: MR63 and MR73. 

It said it will replace its 336 MR63 cars with 468 AZUR cars by 2018. These cars will begin being replaced in 2015, the STM said.

STM spokeswoman Isabelle Tremblay said the new cars will be put on the orange and blue lines, and that the additional cars will be used to improve service and for possible Metro extensions.

The MR73 cars, which first started running during the 1976 Olympics, will remain on the tracks until 2036. These cars will be moved to the green line.

"It's about what should we do with the money we have," said STM Chairman Philippe Schnobb, adding the trains are reliable enough to keep on running.

"We can wait 20 years, and in 20 years we're pretty sure that we can give the same kind of service. Instead of investing in a new train, we will invest in changing our electrical system, changing our pumps, changing what needs to be changed to give better service." 

The STM said keeping old trains on the track is a good deal for taxpayers.

“If you compare that to buying new trains, it's much cheaper to do that,” said STM Chief Executive Officer Carl Desrosiers, adding that the move will save about $500 million.

The STM said it will spend $108 million on regular maintenance of the older cars.

"We will continue to do good maintenance on the trains. We realize those trains are very reliable," said Schnobb, adding that the MR73 trains are involved in only about one out of 10 service disruptions.