SEPTA hasn’t released a public statement on the historic district. The designation could limit the agency as it seeks to modernize facilities. The Historical Commission has partially attributed its 10-year delay on the nomination to fears of clashing with the transit agency’s jurisdiction.

“The Historical Commission had deferred action on the subway entrance thematic district nomination because of concerns regarding its legal authority to regulate the entrances,” said commission spokesman Paul Chrystie.

At Friday’s hearing, the city’s Streets Department offered full support for the protection. In the years since graduating from Penn Design, Baker’s career moved into the realm of transportation planning. He now works at the Streets Department, although he did not mention that at the commission meeting.

The nomination took a decade to move forward, in part, because its filing traced back to a long fallow period when the Historical Commission added few new properties and no new districts to the Philadelphia Register of Historic Places.

Once a property is added to the local register, it cannot be demolished or substantially altered unless the owner can prove it would be in the public interest to do so — or that an economically viable use is impossible.

Local preservation efforts often come into conflict with property owners who fear that designation could reduce their property value.

In the 2000s, several large historic districts covering hundreds of single-family homes ran into a buzz saw of opposition in Overbrook Farms, Washington Square West, and Spruce Hill.

Councilwoman Jannie Blackwell considered legislation that would revoke the commission’s power to designate properties and give it to City Council. Although nothing ever came of the threat, the commission subsequently put an unofficial hold on the creation of new districts, such as Baker’s effort to save the subway entrances.

The protections came too late for a number of the cast-iron structures. Between Baker’s submission and the commission’s belated ruling, transit agencies removed or substantially altered 10 of the entrances.

Despite those losses, the planner celebrated the ruling.

“There were a lot of reasons given at different times [for the delay],” said Baker after the vote. “I’m just happy it was eventually taken up.”