If we built trains we would start at the most densest areas. Most of these would move people (subways). This builds more railway tracks that could aslo send goods to rural arras as well.

The trains would do 2 things. One would most likely start clustering people together do to the ease of use of having more railways. Second, it creates more economic opprunties for the rural folks (like having a means to work in the city more or just having a way to sell goods) could cause enough economic success for buses.