Since the main line and the New Canaan Branch are equipped with 12.5 kV 60 Hz overhead catenary, as opposed to just the 750 V DC third rail of the Hudson and Harlem Lines, different rolling stock that can operate with either power system runs on the New Haven Line. This rolling stock, originally produced by General Electric in two batches (144 in 1972–73 and 100 in 1975–77), was initially branded as the M2 Cosmopolitan, with later versions being made on license by Tokyu Car (model M4, 1988) and Morrison-Knudsen (model M6, 1994). Cosmopolitans can be easily spotted by their red stripe along the side, the presence of pantographs on the lead cars in each set, and a dynamic braking grid on the roof.
