The rank does not give the performance of a zone for IR on absolute scale. The yearly performance of the officials heading various zones with respect to achievement of given targets is being evaluated.
It still has a loop hole, it depends on the target given by the Railway board and not the comparison of the actual parameters. It is quiet possible that RB give unrealistically high target to a zonal head and its rankings may suffer in spite of otherwise good performance on absolute scale.
Many factors are beyond the control...
more... of IR especially the bulk freight offerings which mainly on depends on the industries (power plants, steel plants, cement plants etc) and international trade scenario.