Automatic train operation (ATO) is a method of operating trains automatically where the driver is not required or required for supervision at most.^[1] Alternatively, ATO can be defined as a subsystem within the automatic train control, which performs any or all of functions like programmed stopping, speed adjusting, door operation, and similar otherwise assigned to the train operator.^[2]

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.^[3] On most systems for lower grades of automation up to GoA2, there is a driver present to mitigate risks associated with failures or emergencies. Driverless automation is primarily used on automated guideway transit systems where it is easier to ensure the safety due to isolated tracks. Fully automated trains for mainline railways are an area of research.^[4] The first driverless experiments in the history of train automation date back to 1920s.^[5]

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.^[6][7][8] These levels correspond with the automotive SAE J3016 classification:^[9][10]

Many modern systems are linked with automatic train protection (ATP) and, in many cases, automatic train control (ATC) where normal signaling operations such as route setting and train regulation are carried out by the system. The ATC and 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.^{[citation needed]}

Whereas ATP is the safety system that ensures a safe spacing between trains and provides sufficient warning as to when to stop. ATO is the "non-safety" part of train operation related to station stops and starts, and indicates the stopping position for the train once the ATP has confirmed that the line is clear.^{[citation needed]}

The train approaches the station under clear signals, so it can do a normal run-in. When it reaches the first beacon – originally a looped cable, now usually a fixed transponder – a station brake command is received by the train. The on-board computer calculates the braking curve to enable it to stop at the correct point, and as the train runs in towards the platform, the curve is updated a number of times (which varies from system to system) to ensure accuracy.^[20]

When the train has stopped, it verifies that its brakes are applied and checks that it has stopped within the door-enabling loops. These loops verify the position of the train relative to the platform and which side the doors should open. Once all this is complete, the ATO will open the doors. After a set time, predetermined or varied by the control centre as required, the ATO will close the doors and automatically restart the train if the door closed proving circuit is complete. Some systems have platform screen doors as well. ATO will also provide a signal for these to open once it has completed the on-board checking procedure. Although described here as an ATO function, door enabling at stations is often incorporated as part of the ATP equipment because it is regarded as a "vital" system and requires the same safety validation processes as ATP.^[20]

Once door operation is completed, ATO will accelerate the train to its cruising speed, allow it to coast to the next station brake command beacon and then brake into the next station, assuming no intervention by the ATP system.^[20]

In October 2021, the pilot project of the "world's first automated, driverless train" on regular tracks shared with other rail traffic was launched in the city of Hamburg, Germany. The conventional, standard-track, non-metro train technology could, according to reports, theoretically be implemented for rail transport worldwide and is also substantially more energy efficient.^[46][47]

ATO will be introduced on the London Underground's Circle, District, Hammersmith & City, and Metropolitan lines by 2022. ATO is used on parts of Crossrail. Trains on the central London section of Thameslink were the first to use ATO on the UK mainline railway network^[48] with ETCS Level 2.

In April 2022, JR West announced that they will test ATO on a 12-car W7 series Shinkansen train used on the Hokuriku Shinkansen at the Hakusan General Rolling Stock Yard during 2022.^[49]

The U-Bahn in Vienna will be equipped with ATO in 2023 on the new U5 line.

All lines being built for the new Sydney Metro will feature driverless operation without any staff in attendance.

Since 2012, the Toronto subway has been undergoing signal upgrades in order to use ATO and ATC over the next decade.^[50] Work has been completed on sections Yonge–University line.^[51] The underground portion of Line 5 Eglinton will be equipped with ATC and ATO in 2022. The underground portion will use a GoA2 system while the Eglinton Maintenance and Storage Facility will use a GoA4 system and travel driverless around the yard.^[52] The Ontario Line is proposed have a GoA4 driverless system and will open in 2030.^[53]

Since March 2021, SNCF and Hauts-de-France region have begun an experimentation with a French Regio 2N Class, equipped with sensors and software ^[fr](fr).

In 2025, regular driverless passenger services on the line from Kopidlno to Dolní Bousov will be resumed by AŽD Praha.^[54]

• Automation of the London Underground
• Communications-based train control – A moving block signalling system that can be used to automate operation of trains
• One-person operation – A method of train operation, sometimes seen as an intermediate step towards greater automation
• Signaling of the New York City Subway#Automation
• Train automatic stopping controller – An automatic braking system used on some Japanese railway lines, can also be combined with ATO as its auto-braking function
• Vehicular automation
• Guided bus
• Autonomous Rail Rapid Transit (ART)