Later, when we stopped at a small town library for a mid-day rest stop. I spent a bit of time on the Internet and discovered some interesting facts on trains. Freight trains can be quite fuel efficient on a ton-per-mile basis. But because passenger trains carry a much lighter human cargo within a large, heavy car, they don't realize the same efficiencies. The primary advantage of human train travel, it seems, is to relieve road traffic, and they make the most sense when moving passengers in and out of centralized cities such as Manhattan, or between major metro areas. But given the way the rest of our nation has developed around the roadway and the automobile, it's likely that many of us will be driving some sort of personal vehicle for many years to come. The day of the three-ton gas-guzzler may be numbered, but its replacement will likely be a new generation of ultra-efficient personal transportation.