Money is nothing; RailFanning is Everything

Justification of the cost of electrification is based on the savings in the running cost (fuel cost and regeneration savings) achieved by electric operation, which should be high enough to recover the cost of electrification project.
When electrification was less say 20% or IR routes, satisfying the above condition for electrification warranted a very high level of traffic on the route. Once electrification reach a very high level say 60-70%, the dieselised routes will be very small due to which, the diesel loco utilisation shall become much lower thereby further increasing the cost of train operation with diesel traction. In that case, the electrification shall be justified with much lesser traffic as the operational savings with electric traction shall be much...
more...

higher.
Even with 100% electrifition, I feel it would always be a wise thinking to maintain a certain level of diesel locomotives which shall come very handy in emergency situations like accidents etc. when the OHE traction wires get snapped and diesel locos could handle the situation.