communications-based train control (CBTC) system to replace the fixed-block ATC system and also to retrofit the existing 102 VAL 256 256 cars with the CITYFLO 650 CBTC system. Integration of Bombardier's trains with the existing proved to be difficult in the beginning, with multiple system malfunctions and failures during the first three months of operation. Retrofitting older trains also took longer than expected, as the older trains must undergo several hours of reliability tests during non-service hours. The VAL 256 trains resumed operations in December 2010. The Hitachi Rail Italy Driverless Metro is used on the , which entered service in January 2020 with the opening of the first section. Each train consists of a 4-car EMU set and with open-gangway connection between cars. The train runs on without onboard operators. Heavy-capacity trains The heavy-capacity trains have steel wheels and are operated by an on-board train operator. The trains are computer-controlled. The operator, who is both driver and conductor, is responsible for opening and closing the doors and making (not all) announcements. Most announcements are pre-recorded in Mandarin, English, Hokkien and Hakka, with Japanese at busy stations. The ATC provides the functions of ATP, ATO and ATS and controls all train movements, including braking, acceleration and speed control, but can be manually overridden by the operator in case of an emergency. Newer trains also use a Train Supervision Information System (TSIS) supplied by Mitsubishi Electric that allows the operator to monitor the conditions of the train and identify any faults. Each train consists of two 3-car Electric Multiple Unit (EMU) sets, with a total of 6 cars. Each 3-car EMU set is permanently coupled as DM–T–M, where DM is the motor car with full-width cab, T is a trailer car and M is the motor car without cab. Each motor car has four 3-phase AC traction motors. The configuration of a 6-car train is DM–T–M+M–T–DM, not interchanged with other car types. Like many contemporary metro rolling stock designs such as the MOVIA by Bombardier, each train features open gangways, allowing passengers to move freely between cars. All carriages of the heavy-capacity trains are wide by high, and have a total capacity of 368 passengers, 60 of which seated. Their design maximum speed is , which is limited to in service. The first digit of a DM car is 1, while that of a T car is 2 and that of