DD Saga:
The high capacity coach were designed to ease trains with high AC Class demand!! The issue with augmenting AC Coach means sacrificing either SL or GEN Coach, which in-turn suffocate Non-AC Traveler..Then came DD formula to enhance Passenger Carrying capacity, without compromising on other class (& with same operating cost)!! But somewhere issue started as:
1. Coach vs Rake: DD Coach formula shifted to DD Rake Formula & instead of easing high demand train, they started competing them!!
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Fare: The coaches can easily be put-in with Shatabdi/Intercity with 110 MPS. While a new Class would have developed for Shatabdi, as AC Fare differs with Passenger Carrying Capacity/Coach. The one choose to travel in DD Coach would have to pay lesser than CC, while even then Revenue from DD Coach would have been much higher than CC & Shatabdi traveler dont feel annoyed!!
3. Overnight/3A/2A: With slight changes, these DD can be developed with Sleeping arrangement & again can easily ease trains like Punjab Mail, LKO Mail, Gujrat Mail to name few, who are too high in AC Demand and clearly impact over SL/GEN Coach count is quite visible!!
4. Slot: Never a perfect slot can be formulated, as either DD gonna compete with any Shatabdi or any ICE or any other popular train!! Its simply how the CC/AC passenger carrying capacity of trains should be increased without sacrificing Non-AC Coach!!
PS: It should be Coach utilization rather than Rake Utilization!!