Why does the Montreal Metro operate entirely underground?

The Montreal Metro operates entirely underground primarily due to the city's climate. The system's trains utilize rubber tires, which provide a quieter ride but are susceptible to damage from Montreal's harsh winters. Consequently, the entire network is situated underground to protect the equipment from these extreme weather conditions.1

Construction of the Montreal Metro began in 1962, with the system being inaugurated shortly before the opening of Expo 67. Beyond the subway itself, the city features an extensive underground network of pedestrian walkways, shops, and malls that are directly connected to the Metro, providing residents and visitors with shelter from the cold and snow during the winter months.1