MONTREAL – Montreal’s newest fleet of metro cars isn’t fitting quite right.

The new cars are larger than their predecessors and in some spots just a bit too big for the city’s underground tunnels.

“We had to measure the tunnels,” said the Societe de Transport de Montreal’s CEO Carl Desrosiers.

“We used a laser scan, and we found out of 71 kilometers, there were 200 metres where we had to shave off a really little bit of concrete to be really safe.”

He said this discovery was no surprise, and something the STM had been aware of before the contract for the new cars had been signed.

“So, we did it – it’s been finished since last year,” he said.

The cars being replaced are, according to the STM, the oldest working fleet of metro cars in operation -- the currently used models being almost half a century old.

They’re called MR-63’s, and look quite different than the incoming Bombardier-manufactured “Azur” ones.

The new model of car is heavier, can hold more commuters, and will offer a continuous passageway between each car, instead of the closed-off separated cars that currently exists.

With increased volume and weight, these new cars stand to move more, and risk hitting the sides of the tunnels surrounding them, as they wind quickly  through the city's underground.

As a result of the additional required adjustments, the STM admitted to being roughly eight months behind schedule in making the transition to the new set of cars.

It hopes that the orange line will be up and running with the new cars by year’s end, and that the entire fleet will have been replaced by 2017.