More than a month after a woman was shoved to her death in front of a moving subway train, the Metropolitan Transportation Authority will install barriers that block access to the tracks at three stations, the agency’s chief executive said on Wednesday.The move is a reversal for the transit authority, which has long resisted calls for such barriers, calling them impractical, expensive and incompatible with such an old subway system.As recently as last month, Janno Lieber, the M.T.A.’s chief executive, said that the barriers — known as platform edge doors or platform screen doors — were unfeasible given the “special complexities” in New York’s subway, a sprawling, 104-year-old system with 472 stations and 665 miles of track.But the agency said it needed to address the problem of more people ending up on the tracks, so officials have decided to test platform doors as a possible solution.In an interview on NY1 on Wednesday, Mr. Lieber said that transit officials would move to install the doors in a pilot program at the Times Square station, the Sutphin Boulevard—Archer Avenue–JFK Airport station in Queens and the Third Avenue station in Manhattan.At Times Square, one of the system’s busiest stations, doors will be placed on the No. 7 line platform, but not the R train platform where a 40-year-old woman, Michelle Alyssa Go, was shoved to her death last month. A homeless man who confessed to having pushed Ms. Go was charged in her killing, which shocked a city already worried about safety on the subway.It also prompted renewed demands for action from riders and elected officials, many of whom wanted the transit agency to explore platform doors, which are used on many subway systems in Europe and Asia and on airport shuttle train systems, including the AirTrain at Kennedy International Airport.The doors create a barrier that closes off the track area from platforms, a stark change from the subway system’s open design. Though the transit agency has studied implementing them many times in recent years, previous leaders have concluded that they were too expensive or unsuitable.Last month, as calls for the doors mounted, the transit authority released a detailed 3,000-page report from 2019 that found the doors would be able to be installed at only 128 stations — about a quarter of all stops on the system — because of station layout, subway car design and the need for wheelchair access.Mr. Lieber acknowledged on NY1 that engineering concerns meant the doors would not “work at a lot of places.” But he and other officials opted to proceed with the pilot program as the number of people on subway tracks has risen in recent years and concerns over shoving have grown.The agency did not offer a timetable for installing the doors at the three stations. More details will be presented at the transit authority’s monthly board meeting on Thursday, a spokesman said.New York’s subway system has seen an increase in attacks, including people being shoved onto the tracks. Thirty people were pushed to the tracks in 2021, up from 20 in 2019 — before the pandemic, when ridership was significantly higher.