hahaha !! Actually reason of various restrictions on Speed,Coaches etc is just because of some little technological backwardness which could be delivered but not because of Population. Best Example- IR tracks are fit for 160 from the beginning but MPS is not that much because Unmanned crossings and illiterate mass of population who dont know how to treat a speeding train. Or while travelling on a highspeed rail...they dont care about doorplating or smoking. These few factors are more responsible for various restrictions.