Rail Buses have been manufactured by Indian Engineers also,in fact in Metre Gauge era,there used to be many rail buses running,in broad gauge also few of them are running but only in selected routes.but this 40-50 passenger carrying concept is obsolete in Indian Railway's point of view.thats why single coach rail buses have been replaced by 8 car DEMU's in India which is soon to be upgraded into 12-16 cars.
Indian Rlys believe in mass & bulk public transport