Like Troy, Pennsylvania Station is best known for its destruction. “New York City has never got over tearing down Penn Station,” observed the late Senator Daniel Patrick Moynihan, whose name will someday go on its planned successor, in the James Farley Post Office building next door.

Famously, photographs showed statues dumped in New Jersey swamps. Ada Louise Huxtable may have gotten a little carried away but reflected the popular mood when she declared that “tossed into the Secaucus graveyard are about 25 centuries of classical culture and the standards of style, elegance and grandeur that it gave to the dreams and constructions of Western man.” But surely the loss of the station in 1963 remains a primal cultural wound in New York City and a symbol for a wider loss of public space and public planning. It marked the end of innocence and beginning of knowledge, similar to if not as profound as the death of President Kennedy later that year. The story is familiar to everyone literate about architecture: Penn Station died so that other old buildings could live, so that landmarks commissions and preservation movements could flourish.

But there is more to the story as we are reminded by a new exhibit called “The Once and Future Pennsylvania Station” at the Transit Museum’s Annex and Store in Grand Central Terminal. (Check the maps and guides to find the spot.) The small show is made up of a couple of rooms of photographs, artifacts such as a great milky spherical light fixture left from the station, and a few video clips, including a brief sound clip of Philip Johnson and others protesting the station’s destruction.

New York’s great Beaux Arts Monuments are all around a century old—Grand Central’s big birthday comes up in 2013, the Public Library’s  this spring; and last year would have been the 100th for Penn Station, which barely made it to age 50.

Inspired by the Baths of Caracalla, the station was conceived to join the transcontinental lines of the Pennsylvania Railroad with those of the Long Island Railroad. It was known not just for its soaring concourse and waiting room with arched glass roof but also for heroic sculpture and murals by Jules Guerin. However, the station was the result of planning, engineering, and building of infrastructure. It is hard now to grasp that to cross the Hudson River—a full mile wide—trains were once ferried on huge barges. To make the station possible trains had to be electrified and new tunneling techniques developed.

The show suggests something else. A wall caption quotes historian Hilary Ballon: “Pennsylvania station embodied the imperial grandeur and self-confidence of America at the turn of the century, a symbol of imperial confidence.” Today, by contrast, one sees long lines of passengers waiting outside the Farley postal building for buses, huddling against the cold like a Depression soup line. They are a symbol, too.

The station was a great piece of architecture, but was it a great piece of city planning? In addition to a close reading of some of the histories of the station, the show also invites comparisons between Penn Station and Grand Central as urbanism.  At Grand Central, the show points out, the New York Central and its planners profited from rights to the space above the station, and the junction of commuter rail lines and subway helped turn the station into the anchor of a commercial neighborhood. Not so over on Eighth Avenue, where Penn Station had to wait eight years before the Westside IRT arrived. Yes, rail traffic dropped steeply after World War II and the arrival of intercity airplane service. But stranded far west, almost like the current Javits Center, Penn Station was never knitted into a vital commercial area. Ultimately, the value of the land above the tracks rose: what replaced the station building was the huge drum of Madison Square Garden so that Mick Jagger and Walt “Clyde” Frazier could cavort in the concourse space once transfixed by sunbeams.

The parable of Penn Station has long been read simply as a cautionary tale about the need to save the grandly-built past. To this lesson might be added: plan well when you build.

The show also includes a look at current plans for the much-revised Moynihan Station in the Farley post office. The plan for the new station, by David Childs of Skidmore Owings Merrill, calls for a large interior space under glass. But the future station, suggested by the show’s title, needs to be part of a wider plan. Without improvements in the tunnels that bring trains to the city and to the wider train system, it risks becoming little more than a memorial to the old station and a memento of what might have been.