From Miniature to BIG

In tri-mode configuration the 'Power Pack' car contains a diesel generator set and the batteries.  The diesel generator produces electricity rather than driving any wheels directly. The cars are linked by unpowered articulating bogies, while the conventional bogie at each end of the train beneath the driver's cab carries the electric traction motors. Even when a FLIRT train is solely diesel-powered the principle is the same, it's a diesel-electric unit with electric motors.