12 coach DMU's also run in a few places. There is no technical issue as such, in running longer rakes. The new HPDMUs ( The rakes with the aerodynamic look that are seen commonly these days) are built as 4-car units ( 1 motor car and 3 trailer cars) and are fit to operate as 12 car consists. 16 car consists have also been tried out with the HPDMUs and while there are some issues with long EMU or DMU rakes, it is not really a serious problem and can be solved easily.