Automatic train operation (ATO) is a technology used to automate the operation of trains. The degree of automation is indicated by the Grade of Automation (GoA), up to GoA4 in which the train is automatically controlled without any staff on board. ATO is primarily used on automated guideway transit and rapid transit systems where it is easier to ensure the safety of people. On most systems, there is a driver present to mitigate risks associated with failures or emergencies. Many modern systems are linked with automatic train control (ATC) and, in many cases, automatic train protection (ATP) where normal signaling operations such as route setting and train regulation are carried out by the system. The ATO and ATC/ATP systems will work together to maintain a train within a defined tolerance of its timetable. The combined system will marginally adjust operating parameters such as the ratio of power to coasting when moving and station dwell time in order to adhere to a defined timetable. Grades of automation According to the International Association of Public Transport (UITP) and the international standard IEC 62290‐1, there are five Grades of Automation (GoA) of trains. These levels correspond with the automotive SAE J3016 classification: Additional types History of train automation MP 51, the first prototype of Paris' rubber-tyred metro was fitted with GoA2 ATO from the start. It operated a quiet 770 m shuttle service with sharp turns and steep grades on la voie navette of the Paris Métro with passengers from 13 April 1952 until 31 May 1956. It featured a GoA2 system with an ATO "mat" fitted onto the underfloor of the train continuously in contact with a guide-line between the tracks nicknamed "Grecque", and often prompted passengers to "operate the train" by pushing the ATO start button. Lack of funds prevented installation on the rest of the Paris Metro until 1966, starting with line 11. Line 14, opened in 1998, was the first newly built Paris Métro to operate in GoA4, and Line 1 later also had its GoA2 ATO system replaced to a newer GoA4 CBTC system from 1972. The Barcelona Metro's (old) line II (now L5) was the first metro line in the world to install a GoA2 photoelectric cell-based ATO system on an existing metro line and on its FMB 600 series () rolling stock. This system was implemented in 1960–1961 and decommissioned in 1970. Currently, L9 (Europe's longest