The May Amtrak derailment outside of Philadelphia put the sorry state of passenger rail in the United States briefly back on the public agenda, leaving many people wondering not just about the specifics of the crash but about the more general issue — how is it that a rich and powerful country that was a pioneer in railroad adoption in the 19th century has such terrible trains? The United States is a big country, with lots of trains in it. So you can really think of this big generic question as composed of three separate questions with separate answers. One...