Even though the American road and rail system is probably the best ever built by humans, the basic technologies are from near the beginning of the industrial age around 200 years ago. Any person from that time would marvel at the speed and convenience of it today. However, humans and their technology have advanced significantly since then and what was once acceptable has developed into a system that is unsafe, inefficient, expensive, and unsustainable as it exists now. The fact that over 40,000 people die and hundreds of thousands more are injured along with lost billions of dollars in other costs is a matter of record (see U.S.D.o.T. website). This makes transportation one of the most dangerous activities Americans undertake on a frequent basis. If any other imaginable activity had such a high rate of mortality it seems like a sure bet that activity would be outlawed. The only reason it is now tolerated, is that the current transportation paradigm evolved from one for use by horses or beast-drawn carts or carriages, a time when there were few or no deaths from transport accidents. When the automobile began coming into fashion, so few people owned and used them that deadly accidents were still infrequent enough to draw little notice from citizens used to many dangerous things in their lives. As use and ownership increased, so did mortality, eventually becoming one of the major causes of death and injury and causing enough public outcry to spawn things like speed limits, seatbelt laws and crash standards. While those things have surely saved some lives over the years, the biggest difficulty in truly making transportation safe has been the need to have error-prone humans in control. There are certainly many good drivers out there but even the best ones are occassionally distracted and the worst ones are in a near perpetual state of not paying enough attention. Until the past decade or so there has been little means of solving this particular problem, but we now have the means to completely eliminate human error from driving if we automate the system.
Our current system of mining fuel, refining it to a usable state, then distributing it to various points for use is highly inefficient. A system powered by solar and wind with hydrogen or compressed air backup would do away with the whole process at the current scale of doing it. While it is true that solar panels are now less than 20% efficient and both solar and wind are intermittent sources (but essentially free) they could both generate excess power enough to store to make up for slack production periods (can you imagine a national strategic hydrogen reserve instead of a strategic petroleum reserve?). There are other inefficiencies like not maintaining vehicles, how many hours each vehicle is used, and losses from death and injury, but the main one that automation will solve is traffic jams. Anyone who lives or travels near a major city can relate stories about sitting in traffic. With a fully automated system traffic should never stop completely and only slow significantly under unusual circumstances. In addition to saving the time and frustration of rush-hour like traffic, anyone riding would be free to relax or do something productive during their commute.
The price we pay for the opportunity to risk our lives on the roads is very high. In addition to inefficiency costs the U.S. D.o.T. says that we collectively spend more than 1.5 trillion dollars every year on transportation of all kinds, about $5,000 for every citizen, and not including gas or insurance costs. Anyone who owns and drives a car can relate to how expensive it is even though they only directly see part of the cost. For that kind of money one could buy many unlimited use eurorail passes and should be able to do the same on a national personal transit system.
For those who believe in human caused global climate change, I need not outline the unsustainability of widespread use of fossil fuels but even a skeptic would find it difficult to make the case that continued extraction and use is not becoming geopolitically more untenable as the rest of the world tries to play catch-up in modernizing their societies. The stark fact of the matter is that even if the planet could tolerate every human using resources at the rate of your average American, there just are not enough here to go around. By reducing our nationwide energy consumption from current sources by more than 1/4 we should see savings from not having to compete for increasingly scarce fossil fuels.