The ability to move about the land in a functionally unfettered manner is critical to one's ability to exercise one's vital powers; you are not truly free if you can't get around without issues. It is for this reason that it is right and proper for a government to regulate the flow of traffic within that government's jurisdiction, and thus is it necessary for a people to be involved in the ongoing negotiation and conversation that creates and revises such regulation- you need to not only understand what the rules are, but why they are and if they remain relevant to the needs of the people. (That, by the way, applies to everything
institution does.) That alone is sufficient justification for the creation and maintenance of a multiple-layered system of transportation, one that incorporates multiple modes of public transit such as buses and railroads. The increasing pressure to increasing energy efficiency only means that there is more of a reason to sustain such systems by upgrading and expanding them in a competent and efficient manner.
This is not the only reason for a people to decide, through its government, to make such a massive investment. The consequences of investing in transportation infrastructure ripple throughout a society, and always for the better in the short as well as the long run. The first benefit is the massive economic shockwave that emanates from the beginning of planning and initial construction. Road and rail infrastructure requires the employment of many people, unskilled and skilled alike, forming the logistical train from the raw materials needed to create the array of materials needed to construct the lines and roads all the way to the teams of workers shaping the earth and laying down the steel and concrete for those roads and rails. It includes the companies that produce the cars, trucks, engines and other railway cars that run along those paths. It includes the homes needed to house all of the workers, the entire medical infrastructure needed to keep those workers healthy, the schools needed to train those workers (and their children), the farms producing the food to feed them and the power stations producing the power needed to do all of this work (and the grids that distribute that power). This is the real economy, the political economy, the physical economy- the part of the economy that actually matters- that makes and breaks governments and the states they administer on behalf of the people because this is the economy that can kill a people if it fails
The creation of a public transit system is what allows a people to fully participate in the economic life of a society without needing to own private transportation. For urban dwellers, this is critically important. For rural dwellers, it is equally important because it cuts down on the necessary costs of moving themselves and what they produce out of their rural regions and to the markets in urban areas wherein they fulfill their part of the national web of economic requirements that makes a free society possible at all- and a little more on top of that. It is through such systems of transit that individuals can increase the efficiency of their activities without significant adverse impact upon their standard of living; such systems can also allow for the expansion of city parks in urban areas and wiser use of land in rural regions- for those concerned with sustainable development, insistence upon competent public transit is an obvious position to make and support.
The downside, especially in much of the United States, is that cities have to be redeveloped (or, in many cities and towns, restored) to accomodate such public transit systems. The grid of transit must operate at all times, reach all parts, be priced such that the poorest can use it without qualms and be regulated such that its use is privileged second only to emergency response vehicles. This will inconvenience a lot of people for quite some time, which will cause problems with short-sighted and foolishly selfish people that cannot (or willfully ignore) the big picture and thus obstruct such efforts; they should be exposed for what they are, ridiculed without mercy and dismissed as if they were petulant children throwing tantrums because they didn't get a toy they wanted. Once in place, however, all of that inconvenience melts away and the public transit system's worth as a vital public good quickly becomes self-evident. Only those afflicted and deluded by Empire would dare argue against its continued good health and worth. In the foreseeable future, a city will not be worth keeping if it lacks a competent system of public transit- and that as part of an overall system of transit infrastructure that connects the entire nation together. That is one of the key components to what a free republic looks like; Empire, by comparison, wants to lock all but its thralls down as if it were a slave plantation of the Antebellum South. Let's not have that return, in any form.