I mean "efficient" as it's generally defined: maximum productivity with minimal wasted effort or expense.

In the case of the Great Northern railroad, the efficiencies were passed on to the customer in terms of ever falling costs and an expanding network of service.

> The population of low-volume regions will be under-served

No, it's the opposite! Low-volume regions are underserved with centrally planned government transportation. The planner has limited resources that must be "democratically" administered.

In a free market, any underserved area provides an opportunity for an entrepreneur to serve that need in the market! It's an elegant system that serves the needs of the people faster with less waste.