An announcement at my station says the no. 4 and no. 5 lines will be delayed by 10 minutes between 14th Street and 96th Street. I heard the tracks are being replaced. Does this make it dangerous for trains to travel? Why are they replacing the tracks?

Tracks are replaced periodically throughout the subway system. The Transit Authority decides to replace a track after reviewing how much wear the track has sustained. Some tracks, like the ones on the Lexington Avenue line, are used more heavily than others, necessitating more frequent repairs and replacements, a spokesman for the authority, Paul Fleuranges, said. The stretch being repaired, about 800 feet of track between Grand Central and 33rd Street, sees some of the most traffic in the system. This section of the track is still embedded in a rock ballast foundation – a feature that dates back to 1904, when the Interborough Rapid Transit (IRT) was first built. The actual track being replaced dates back to 1957.

Transit workers are replacing the ballast with concrete, and replacing the track at night. When there is no work being done, they put down temporary tracks that rest on wood so trains can run. As a precaution, trains are running slower on the stretch – about 5 to 10 miles an hour, Mr. Fleuranges said. It’s not dangerous, he said. Delays are predicted by the MTA to last up to 10 minutes during rush hour until repairs are finished.

How many abandoned stations are there in the city? Are there any plans to make use of them?

There are eight completely abandoned subway stations, a subway historian, Joseph Brennan, said. (His full-time job is the e-mail system administrator at Columbia University, but he has arguably more knowledge of subway history than many who work at the MTA.) There is a station under the driveway of City Hall, the first in the city’s history. An inlaid plaque in front of the stairs that lead up to City Hill commemorates the founding of the subway system. There are also abandoned stations at Worth Street, 18th Street, 91st Street, Myrtle Avenue, and 19th Street. The abandoned station at Court Street in Brooklyn is now the site of the Transit Museum. The station at Cortlandt Street at the World Trade Center site was destroyed during the terrorist attacks on September 11, 2001.

Many of the abandoned stations were near other working stations, so by closing them down, the MTA was able to save money and shave a few minutes off the train’s trip without impacting riders’ convenience, Mr. Brennan said. The City Hall station is located on the loop the downtown no. 6 trains make after stopping at Brooklyn Bridge to go uptown. By all accounts, the station was the most opulent in the city’s history, with Guastavino arches, leaded glass skylights, and chandeliers, according to Clifton Hood’s “722 Miles: The Building of the Subways and How They Transformed New York.”

He writes that the then-mayor, George McClellan, was so enamored of the novelty of riding the subway on its inaugural day that he insisted he drive it by himself – worrying some of his aides, because the train was filled with many of the city’s top dignitaries and decision-makers.

Questions? Please send them to transit@nysun.com.