1920s

On June 27, 1922, the New York State Transit Commission commissioned its engineers to examine platform-lengthening plans for 23 stations on the lines of the Brooklyn–Manhattan Transit Corporation (BMT), the successor to the BRT, to accommodate eight-car trains. As part of the project, Prospect Avenue's platforms would have been lengthened from 435 feet (133 m) to 530 feet (160 m).^[13][14] Though the Transit Commission ordered the BMT to lengthen these platforms in September 1923, no further progress was made until February 16, 1925, when the New York City Board of Transportation (NYCBOT) commissioned its engineers to examine platform-lengthening plans for this and eleven other stations along the Fourth Avenue Line. It estimated the project would cost $633,000 (equivalent to $10,998,000 in 2023).^[15] The NYCBOT received bids for the project on February 25, 1926.^[16] The contract was awarded to the Corson Construction Company for $345,021 (equivalent to $5,938,000 in 2023).^[17] The extensions opened on August 1, 1927.^[6]

1950s and 1960s

The city government took over the BMT's operations on June 1, 1940.^[18][19] In July 1959, the New York City Transit Authority (NYCTA) announced that it would install fluorescent lighting at the Prospect Avenue station and five other stations along the Fourth Avenue Line for between $175,000 and $200,000. Bids on the project were to be advertised on August 7, 1959 and completed by fall 1960.^[20]

In the 1960s, the NYCTA started a project to lengthen station platforms on its lines in Southern Brooklyn to 615 feet (187 m) to accommodate 10-car trains.^[7] On July 14, 1967, the NYCTA awarded a contract to conduct test borings at eleven stations on the Fourth Avenue Line, including Prospect Avenue, to the W. M. Walsh Corporation for $6,585 (equivalent to $60,172 in 2023) in preparation of the construction of platform extensions.^[21] The NYCTA issued an invitation for bids on the project to extend the platforms at stations along the Fourth Avenue Line between Pacific Street and 36th Street, including those at Prospect Avenue, on March 28, 1969.^[22] Funding for the renovation projects came out of the NYCTA's 1969–1970 Capital Budget, costing $8,177,890 (equivalent to $67,946,000 in 2023) in total.^[23]

As part of the renovation project, the station's platforms were extended,^[7] and the station's elaborate mosaic tile walls were covered over with 8-by-16-inch (20 by 41 cm) white cinderblock tiles. The latter change, which was also made to 15 other stations on the BMT Broadway and Fourth Avenue Lines, was criticized for being dehumanizing. The NYCTA spokesman stated that the old tiles were in poor condition and that the change was made to improve the appearance of stations and provide uniformity. Furthermore, it did not consider the old mosaics to have "any great artistic merit".^[24]

2017

Under the Metropolitan Transportation Authority's 2015–2019 Capital Program, the station, along with thirty other New York City Subway stations, were scheduled to undergo a complete overhaul as part of the Enhanced Station Initiative. Upgrades were to include cellular service, Wi-Fi, USB charging stations, interactive service advisories and maps.^[25][26] From January to May 2016, Grimshaw Architects worked on a design for the station's renovation, with Arup Group acting as a consultant.^[27] The contract for Package 1 of the renovations, which covers renovations at the Prospect Avenue, 53rd Street, and Bay Ridge Avenue stations on the BMT Fourth Avenue Line, was awarded on November 30, 2016^[27] to Citnalta-Forte Joint Venture for $72 million, the first design–build contract in the subway system's history.^[28] The station closed on June 5, 2017 for these renovations,^[29][30][31] and reopened on November 2, 2017, a month ahead of schedule.^[32]