totalling a number of 355 trains running in 6-or 9-car formation are currently in use on the Mexico City Metro. Most of the stock is rapid transit type, with the exception of the Line A stock, which is light metro. Four manufacturers have provided rolling stock for the Mexico City Metro, namely the French Alstom (MP-68, NM-73, NM-79), Canadian Bombardier (FM-95A and NM-02), Spanish CAF (NM-02, FE-07, FE-10 and NM-16 and Mexican Concarril (NM-83 and FM-86) (now Bombardier Transportation Mexico, in some train types with the help of Alstom and/or Bombardier). The maximum design speed limit is (average speed ) for rubber-tired rolling stock and (average speed ) for steel-wheeled rolling stock. Forced-air ventilation is employed and the top portion of windows can be opened so that passenger comfort is enhanced by the combination of these two types of ventilation. Like the rolling stock used in the Paris Métro and the Montreal Metro, the numbering of the Mexico City Metro's rolling stock are specified by year of design (not year of first use). In chronological order, the types of rubber-tired rolling stock are: MP-68, NM-73A, NM-73B, NM-73C, NM-79, MP-82, NC-82, NM-83A, NM-83B, NE-92, NM-02 and NM-16; and the types of steel-wheeled rolling stock are: FM-86, FM-95A, FE-07, and FE-10. From May 2024, Line 1 will receive 30 new rubber-tired trains manufactured by CRRC Zhuzhou Locomotive in China, replacing earlier rolling stock. This is in line with ongoing upgrading works for Line 1, including the installation of CBTC. Gallery Major incidents On 20 October 1975, two trains crashed in Viaducto station while both were going towards Tasqueña station. The first was stopped picking up passengers when it was hit by another train that did not stop in time. According to official reports, from 31 to 39 people died, and between 71 and 119 were injured. After the crash, automatic signals were incorporated to all lines. On 18 September 2009, a man was vandalizing the walls of Balderas station with a marker before being confronted by a police officer. He took out a gun and killed the officer and a construction worker who tried to disarm him, and injured 5 others. On 4 May 2015, two trains heading towards Politécnico station on Line 5 crashed in Oceanía station. The first was leaving to Aragón station which was requested to stop and wait, while the second did not deactivate the autopilot and crashed