By N. Clark Judd

Riverdale/Kingsbridge area commuters are wondering how the Metropolitan Transportation Authority allowed part of the ceiling to collapse at the 181st Street station before inspecting it for potentially serious damage — and how they neglected another station on the No. 1 line.

“A century-old system deserves a look at its infrastructure before there’s a colossal accident involving lots of passengers,” said Joyce Grossman, a Fieldston resident who works in Battery Park.

Inspections will now take place, but it will mean a second consecutive weekend of service disruptions on the No. 1 line between the 137th Street and Dyckman Street stations. Between 12:01 a.m. Saturday and 5 a.m. Monday, according to a press release from the MTA, subway service between those stations will be replaced by shuttle buses as workers make sure the ceiling at the 168th Street station won’t go the way of its uptown neighbor.

Service on the No. 1 line was severely disrupted last week after chunks of ceiling tile fell across the tracks at the 181st Street station in Manhattan. No one was injured. New York City Transit, the arm of the MTA responsible for subways and most buses, shut down subway service from the 168th Street station to the elevated tracks at Dyckman Street and set up shuttle buses to replace the trains.

Because the 168th Street station has the same type of vaulted, tiled ceiling as the one that partially fell at 181st Street, inspectors examined it last weekend. Workers shored up several areas of ceiling there, an MTA spokesman said, and though they will return this weekend, train service will continue to skip 181st Street in the meantime.

For Ms. Grossman, the whole episode exposed how dependent the Riverdale/Kingsbridge area is on the No. 1 line, which includes some of the city’s oldest stretches of track.

“For many of us, this is the only way to get to work,” she said.

Both the 168th and 181st Street stations opened for service in March 1906, said MTA spokesman James Anyansi. He could not say by press time whether or not the ceilings there had ever undergone major renovations.

That boggled the mind of Jose Rodriguez, who lives in Riverdale on Broadway and works for a union downtown.

“That, they should have stayed on top of,” he said.

Malkia Burgos, a Yonkers resident who also works for a union, agreed.

“Why wait until it’s to that point before doing any repairs?” she asked, while waiting for a ride home at the West 242nd Street No. 1 stop Monday evening.