ATOS (pronounced "ah-toes") is an acronym for Autonomous Decentralized Transport Operation Control System, a computerized control system used by the East Japan Railway Company (JR) to regulate train traffic on railway lines in metropolitan Tokyo, Japan. ATOS was designed by Hitachi and deployed on the Chuo Main Line in 1997. It is currently operational on ten lines.

Train stations on ATOS-enabled lines are equipped with electronic displays, which show scheduled arrival times and train destinations in Japanese and English, warn passengers when trains are arriving or passing through, transmit updates on system delays and accidents, and display messages to advertise JR products or warn passengers not to smoke. Voice announcements in train stations are also automated by ATOS using speech synthesis.

ATOS also directs train drivers through 16 by 16 lamp matrices, which flash messages telling the train driver to speed up, slow down, or adjust their scheduled departure time in order to keep the entire network running on schedule.

Several JR lines in the Kanto region use CTC or PRC systems in lieu of ATOS.

In the Japanese language, ATOS is often referred to as the Greater Tokyo Transit Control System (Tôkyôken Yusô Kanri Shisutemu).

ATOS-enabled lines

• Chuo Main Line in metro Tokyo (Mar. 1997)
• Yamanote Line (Aug. 1998)
• Keihin-Tohoku Line (Aug. 1998)
• Sobu Line (Rapid and Local) west of Chiba (June 1999)
• Yokosuka Line north of Kurihama (July 2000)
• Tokaido Main Line (Passenger and Freight) (Sep. 2001)
• Joban Line (Rapid and Local) (Jan. 2004)
• Tohoku Main Line (Dec. 2004)
• Takasaki Line (Dec. 2004)

Future ATOS-enabled lines

• Saikyo Line
• Kawagoe Line
• Yamanote Freight Line
• Tohoku Freight Line
• Nambu Line