| [[Front of an Alstom Metropolis C751A at Sengkang Depot.|250px]]|
Front of an Alstom Metropolis C751A at Sengkang Depot.
The Alstom Metropolis C751A are the first generation of communication-based train control (CBTC) rolling stock that has been in use in Singapore’s Mass Rapid Transit (MRT) lines since 2003. Alstom was contracted in 1997 and 1998 (as C751A) by the Land Transport Authority (LTA) in Singapore to supply for its North East Line in 2003.
The automated system version, previously known as “moving block systems”, CBTC systems do not require traditional "fixed-block track circuits" for determining train position. Instead, they rely on "continuous two-way digital communication" between each controlled train and a wayside control center, which may control an area of a railroad line, a complete line, or a group of lines. Recent studies consistently show that CBTC systems reduce life-cycle costs for the overall rail property and enhance operational flexibility and control.A development in Singapore's MRT history, the six-car trains on the North East Line are powered by overhead catenary, in contrast to the train cars on all the other operating lines prior to this, which are powered by a third rail. This was partially because authorities consider overhead wires to be unsightly and as such does not allow for trains to be powered using this method on elevated lines. Since this line is the first to be fully underground in Singapore, the authorities had a choice between powering the trains on this line by overhead catenary or third rail. An overhead catenary power supply was decided upon. This is also the first time in the history of Singapore's MRT history that the seats in every compartment of the train are made up of the same colours. 25 trainsets of six cars each were purchased for the North East Line. In addition, due to its driverless configuration, it is a unique type of train where there are windows at the front and back of the train, giving passengers an impressive view as the train speeds through the tunnel.
- The first digit of a car's serial number is always a seven.
- The second digit depends upon whether the car is the first, second or third car from either end of the train, where the first car equals one, the second equals two, and the third equals three.
- The third digit of a car's serial number is always a zero.
- The other two digits is the train identification number. A full length train of six cars have two different identification numbers, one for the first three cars, and the same number plus one, for the other three. The smaller number is always an odd number.
A typical SBS Transit NEL Train, for example, would consist of serial numbers 71001, 72001, 73001, 73002, 72002, 71002.