The borough council voted to lower the speed limit at a meeting on Monday night. They're following the lead of other boroughs, including Rosemont—La Petite-Patrie and the South West, which have done the same thing.
The new speed limits will take effect in the next couple of weeks.
"The Plateau-Mont-Royal streets are active environments where children rub shoulders with parents, the elderly and young professionals," said the borough's mayor, Luc Ferrandez.
"Whether they are pedestrians or cyclists, they must be able to travel safely."
The mayor said that reducing speed limits reduces risk of accident and increases chance of survival by 60 per cent.