Fred Salvucci ponders the role of contingency in history, and in the evolution of Boston and its transportation system. He starts from the time the glaciers pulled back from Boston, leaving a soggy near-island and a river for the first white settlers to contend with. “The reason the city is here because of an accident of history,” he says. In the 1600s, “when the English first came, they made a mistake,” Salvucci reports. Thinking that the Charles would run deep and wide for a thousand miles inland, offering vital trade routes, the English hunkered down.

Once they realized their mistake (the Charles is about a foot deep in Watertown, MA, six miles away), the settlers built on the resources at hand, which included enormous stocks of cod and good ship-building lumber. The “poverty of a place forces skills, which in turn makes the place not poor,” says Salvucci. These Protestant settlers also set about, in near record time, establishing schools like Boston Latin and Harvard.

Boston’s rapid expansion and prosperity led to innovations such as filling land, which in turn led to unexpected transportation developments. The first commercial use of rail in the New World, Salvucci tells us, was to haul in granite for the Bunker Hill monument, and to bring dirt from the suburbs for Boston builders. When people realized they could use the new technology to transport farm products, the Boston & Worcester Railroad was born. But the idea of moving people around didn’t emerge until the 1800s, when the concept of living one place and working in another led to streetcars in Boston and elsewhere. Around 1900, Boston led the nation with the first subway (“a little dinky one”) running just two blocks. In two decades, the guts of the city’s subway system emerged, making Salvucci’s own Big Dig project appear modest in comparison (adjusting for inflation).

Salvucci remarks on the numerous cases of “indirect causality” through human history, how things “built in ways that are unanticipated and probably unanticipatable.” In 1865, there were no electric street cars. By 1900, U.S. East Coast cities were covered by them. In 1900, there were 2,000 autos in the U.S., and by 1920, there were so many cars that city rail networks began dying out. Don’t be fooled into thinking you can “predict tomorrow based on yesterday plus a small delta,” warns Salvucci.