With today's America dominated by the automobile, it is difficult to believe that until the 1920s nearly 100 percent of the US population traveled via rail. Conventional passenger-train service spread rapidly by the 1850s, but another form of rail transportation did not emerge until the turn of the 20th century: the interurban. Almost always electric, interurbans linked cities with burghs. Rockford, one of Illinois's three largest urban centers during...