A Brief History of the Queensboro Plaza Station
by John McCluskey 

Today's Queensboro Plaza is literally half of what it used to be. At the time of its construction in 1915-1916, Queensboro Plaza was the most complicated elevated structure in the United States. The eight track, Four platform station served four different lines on two levels. It served the joint BRT-IRT operations (lines to Corona and Astoria) and the Second Avenue Elevated. A fourth line was planned, but never materialized. Trains crossed from Manhattan into Queens from the Queensboro Bridge (Second Ave. El), the 61 Street Tunnel (BRT), and the Steinway Tubes (IRT). Trolleys of the Queensboro Bridge Railway, Third Avenue Railway, and the Manhattan and Queens Railway also served the station at street level. When the Second Avenue Elevated ceased operations in 1942 across the Queensboro Bridge, the additional platforms were deemed excess and in the 1950s tracks were reconfigured and half (two platforms and four tracks) the station was razed. This left the structure we are familiar with today. 
References: 
Old Queens in Early Photographs, Seyfried and Asadorian 
Under the Sidewalks of New York, Cudahy Building the New Rapid Transit System of New York City Circa 1915, Lavis