Buenos Aires Underground 300 Series

300 Series
A 300 Series train on Line H undergoing tests before its introduction.
Manufacturer	Alstom
Family name	Alstom Metropolis
Constructed	2015-
Entered service	2016
Number built	120 60
Number in service	36+
Formation	6 cars per trainset
Operator(s)	Buenos Aires Underground
Line(s) served
Specifications
Car body construction	Stainless steel
Car length	17 m (55 ft 9 1⁄4 in)
Width	2,600 mm (102 3⁄8 in)
Doors	4 per side
Power supply	1500 V DC Overhead lines
Track gauge	1,435 mm (4 ft 8 1⁄2 in)

The 300 Series are a number of underground cars manufactured by Alstom in Brazil for use on the Buenos Aires Underground. They are used on Line H of the network, and more are to be introduced on Line D where they will serve alongside the similar 100 Series.

The 300 Series cars were initially ordered for Line H in 2012 with an initial order of 120 cars at a cost of US$ 216 million. These were to be delivered in 2015 and produced solely in Alstom's plant in São Paulo, unlike the 100 Series which also had components produced in Argentina. These were to be put into service once Córdoba, Santa Fe and Las Heras stations were opened.

On Line H, the cars replaced the Siemens-Schuckert Orenstein & Koppel cars which had served on every line of the system, with the exception of Line B at different times since 1934. When the line was originally opened, it was not deemed necessary to purchase new stock until it had been extended enough and passenger numbers were at a level where new rolling stock was warranted, thus the Siemens O&K cars were brought out of retirement temporarily. In July 2016, 36 of the Alstom cars were put into service on Line H, retiring the Siemens cars, while the remaining cars and those for Line D are set to be put into service gradually until 2017.

In late 2014, the order was expanded by 50% to include an additional 60 cars for Line D in order to replace the ageing Fiat-Materfer cars built in the early 1980s. Unlike Line H, whose entire fleet would consist of the 300 series, in Line D the cars are to serve alongside the 100 Series, which are also Alstom Metropolis cars and bear similarities.