As architect Santiago Calatrava was designing the World Trade Center Transportation Hub in lower Manhattan, his priority, he says, was to make it the sort of place that his late mother could have navigated. Admittedly, the building’s extravagant design doesn’t immediately prompt such thoughts: Its centerpiece structure, the Oculus, features soaring white wings that rise, birdlike, into the air and a retractable skylight. But Mr. Calatrava says that he always had simplicity in mind.

When it opens the first week of March, the...