Line 4 (O-Train)
Line 4 (French: Ligne 4), also known as the Airport Line (French: Antenne de l'Aéroport), is a diesel light rail line on the O-Train network in Ottawa, Ontario. The line provides a connection between Line 2 (also known as the Trillium Line) at South Keys station, and Ottawa Macdonald–Cartier International Airport.