Deux-Montagnes line

Electric Boxcab locomotive used on the Deux-Montagnes from 1918 to 1995.

The Deux-Montagnes line was built by the Canadian Northern Railway. While other railways including Canadian Pacific and Grand Trunk Railway already had prime downtown locations for their terminal stations, Canadian Northern did not, having only a station out of the way on Moreau Street in Hochelaga.

In 1910, it was decided that the best way for Canadian Northern to get downtown was to drill their way downtown — through Mont Royal. The construction started at both ends and met halfway through with only an inch difference. In 1918 the electrified (2400 V DC catenary), double-track 3.2 mi (5.15 km) tunnel was dubbed Montreal's first subway. Because the tunnel is on a steep grade and inadequately ventilated[10][11] it was decided from the very beginning that the locomotives would be electric. The ventilation shaft is located SW of the intersection of Édouard-Montpetit Boulevard and Vincent-d'Indy Avenue very close to the Édouard-Montpetit Metro Station.[12][13]

The structure gauge of the Mount Royal Tunnel limits the height of bilevel cars to 14 ft 6 in or 4.42 m.[14]

Map of 1927 of the Île de Montréal with the position of the tunnel under Mount Royal shown by dashes on the yellow line. The red line shows a proposed, but never completed, access to Central Station. This is the Doney spur[15]

In order to finance the project, Canadian Northern built a ‘model city’ north of the tunnel, modeled after Washington, D.C. The Town of Mount-Royal has grown to be an upper-income neighbourhood today. Construction began in 1912 and finished in 1918.[16] The first train was pulled by electric locomotive #601 (retired as #6711), which left Tunnel Terminal at 8:30 a.m. on October 21, 1918. The Canadian Northern Railway went bankrupt and was absorbed into what is now Canadian National. Tunnel Terminal was replaced by Central Station in 1943. CN added electric multiple units from Canadian Car and Foundry in 1952.[17]

An Electric Boxcab locomotive hauling CN electric multiple unit coaches in September 1979.

In the 1960s, the first plans were announced to renovate the line, whose equipment was 40 years old at the time. First, it was to become metro line 3 (red), but plans were shelved because of the importance to build line 4 for service to Expo 67. With the equipment ageing, and ridership declining, CN wanted to close the line in the 1970s, but their proposals were rejected. The Quebec Ministry of Transport considered using the line for a high-speed connection to Mirabel Airport (Transport rapide régional aéroportuaire Montréal Mirabel, 1974) or as the first line of a BART-style regional metro system (Réseau express de Montréal, 1977; Métro régional, 1979). None of these projects progressed beyond the planning stage.

In 1982, management of commuter trains was transferred to the publicly owned Montreal Urban Community Transit Commission (STCUM). The STCUM set fares and schedules, while the Canadian National retained ownership of the equipment (passenger cars and locomotives). CN continued to provide the tracks, stations, storage, maintenance, and train crews needed to keep the line running. For Montreal commuters, the transfer of ownership was positive because the trains were integrated into the bus and metro system.

In 1992, the government of Quebec announced a modernisation plan for the line which would include electrifying the entire line at 25 kV AC (and converting the existing catenary in the Mont-Royal Tunnel to this voltage), 58 state-of-the-art MR-90 electric multiple unit trains built by Bombardier Transportation, new tracks, and centralised traffic control. Service was shut down completely in the summers of 1993, 1994 and 1995 to allow for major work to be done. The last of the old rolling stock left Central Station at 6:30 p.m. on June 2, 1995 – 76 years, 8 months, 11 days, and ten hours after it first went into service. The same locomotive, #6711 (with #6710 (pictured)), hauled the last train through the tunnel.

The line was transferred to the former Agence métropolitaine de transport (AMT) on January 1, 1996.

CN built a railway overpass to route its Saint-Laurent subdivision over the commuter train line just south of Montpellier station. The overpass was a prerequisite for increasing commuter train frequencies on the Deux-Montagnes line as well as the commissioning of the Mascouche line. The $60 million project was begun in 2010 and was completed by the end of 2013, when the new line also was commissioned.[18]

On February 28, 2014, the AMT announced that it had purchased the Deux-Montagnes line from CN for a sum of $92 million. While CN owned the line, freight trains could use it within two time windows: during the day from 08:30 to 15:30 and during the night from 20:30 to 05:30. Purchasing the line allowed AMT to give commuter trains priority all day, between 05:30 and 20:30.[19] This gave the AMT flexibility for scheduling trains and allows it to save rent money in the long term.

On June 1, 2017, the AMT was dissolved and replaced by two new governing bodies, the Autorité régionale de transport métropolitain (ARTM) and the Réseau de transport métropolitain (RTM). The RTM took over all former AMT services, including this line.

In May 2018, the RTM formally re-branded itself as Exo; and renamed each line with a number and updated colour. The Deux-Montagnes line became Exo 6, and the blue line colour was updated to a light peach colour.