NEW YORK (AP) — The annual Sept. 11 commemoration ceremony has changed little over the years. But so much around it has.

The museum now sits open at the site of the tragedy.

The fences have come down around the memorial plaza, more fully integrating it into Manhattan's streets.

A new mayor is in office, Bill de Blasio, one far less linked to the attacks and their aftermath than his predecessors.

And One World Trade Center is nearly complete and set to open later this year, perhaps signaling that page in the city's history may be turning.

For some who lost loved ones in the terror attacks, the change is a sign of progress.

For others, it threatens to interfere with their grief.

The 40 passengers and crew who died when United Airlines Flight 93 crashed in southwestern Pennsylvania during the Sept. 11, 2001, terrorist attacks are to be honored in a new way during the 13th anniversary ceremony at the Flight 93 National Memorial.

A Congressional Gold Medal to them will be presented today as part of the ceremony. Bells will ring and the names of the victims will be read at 10:03 a.m., the moment the airliner crashed in Pennsylvania as passengers fought with hijackers for control of the jet.

Thursday's ceremony also comes as the National Park Service marks progress on a $17 million to $23 million project that includes a visitors' center and learning center, which officials hope will boost the number of annual visitors to the memorial from 300,000 to more than 500,000.