Original service The line was announced as the
Repentigny-Mascouche line in a
press conference on March 17, 2006, and follows a major campaign by residents of eastern Montréal and the northeastern suburbs to restore commuter rail service. Originally estimated at $300 million and expected to open in 2008, the line cost $670 million and opened on December 1, 2014. The project included 10 new train stations, several civil engineering structures and 13 km of new railway track. The line used the
Mount Royal Tunnel and
Canadian National track from
Montreal's
Central Station to
Repentigny. New track was built from Repentigny to
Terrebonne along
Autoroute 640, before turning towards the Trois-Rivières Subdivision of the
Chemins de fer Québec-Gatineau at
Mascouche. Most of the route, in particular the section from Mont-Royal to Repentigny, follows a path similar to the never-built
Line 6 of the Montreal Metro, which was planned as a steel-wheeled "regional metro" line using a somewhat similar alignment. The travel time between Mascouche and downtown Montreal was 61 minutes. The line had 13 stops and offered eight departures in each direction per weekday, mainly during rush-hour. 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 rebranded itself as Exo, and rebranded each line with a number and updated colour. The Mascouche line became Exo 5, and its line colour was updated to a lighter pastel shade of purple.
Service adjustments Beginning on May 11, 2020, the
Mount Royal Tunnel closed due to the construction of the
Réseau express métropolitain (REM), ending service to and stations. The Mascouche line terminated at
Ahuntsic station, although some trains continued to Central Station via an alternate route partially using the CN Taschereau intermodal yard to access Central Station. On January 12, 2026,
Côte-de-Liesse station opened, expressly designed to ensure smooth transfer of users between the Mascouche line and the REM, and replacing Ahuntsic as the line's new terminus. In 2023, the service was renumbered to line 15 in order to be unique within the Montreal rail network. ==Locomotives==