If/Then poster from The Hartman Group.

“If/Then,” a new musical at the National Theatre, follows the life choices and regrets of a fictional city planner in New York. But does it also say something about the choices that cities face?

In “If/Then,” urban planning as a profession plays only a supporting role to Elizabeth (Idina Menzel), a planning Ph.D. who returns to New York after a decade in Phoenix with her ex-husband. The plot bifurcates into parallel stories of Elizabeth’s life as a single, career-driven city planner on a waterfront redevelopment project and an adjunct planning professor with a husband and two kids.

The problems Elizabeth face seem torn from the Breakfast Links: The city’s deputy mayor is in charge of a large, politically contentious redevelopment project. Community groups and the city dispute the amount of affordable housing there should be. Housing advocates blog their frustrations.

Think of a play about planning, and you can already hear a chorus of opponents chanting on key, “We weren’t consulted,” and “Too tall, too dense, not enough parking!” The musical score focuses on Elizabeth’s personal life (or lives), so if you were looking for a catchy tune on dedicated bus lanes or a ballad to nonconforming uses, you are out of luck.

But you could read the musical itself as an allegory for a city. For instance, Elizabeth’s return from Phoenix may represent America’s waning love affair with sprawl. The structure of the play also provides an interesting thought experiment. Consider what Washington would look like if history had made a few different turns.

What if Germany blitzed Washington in World War II? What if the federal government never razed and redeveloped Southwest?

What if the Metro had never been built? What if more neighborhoods were bulldozed to construct all the highways planned in 1950? What if the District had followed other American cities in loosening its height limit decades ago? What if Washington had actually become racially integrated?

It’s fun and sometimes scary to imagine our region in these alternative universes. As with Elizabeth’s parallel lives, each choice delivers its own rewards and disappointments.

Likewise, grand city plans face trade-offs, but cities, unlike people, can live for millennia. When planners make choices that in retrospect seem unwise or unjust, subsequent generations can always reconsider, repair, and reconstruct the built environment in pursuit of a better metropolis.

“If/Then” is showing at the National Theatre until December 8. The play will open in New York in March.

Eric Fidler has lived in DC and suburban Maryland his entire life. He likes long walks along the Potomac and considers the L’Enfant Plan an elegant work of art. He also blogs at Left for LeDroit, LeDroit Park’s (only) blog of record.