Re: khi ↔ isb (via bus)
Tezgam is the only train which operates between Karachi to Peshawar. But journey on Tezgaam will surely make you the most unhappiest man on the earth. Don’t do that!
Take Karakaram or Night coach. Karakaram has 4 stops and Night Coach has 6. But both are for Karachi-Lahore-Karachi. You will be better to travel through Daewoo bus service to get Islamabad from Lahore. And to make it a bit interesting, travel in Lower AC in train, that will solve your heat, dust and noise problem but you will still have experience of interacting with other passengers. Best of luck 
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