 As the early 1960s progressed , the East Side experienced an increase in development , and the Lexington Avenue Line became overcrowded . In 1962 , construction began on a connection between the Manhattan and Williamsburg Bridges and the Sixth Avenue Line . This segment , the Chrystie Street Connection , was first proposed in the 1947 plan as the southern end of the Second Avenue line , which would feed into the two bridges . When opened in 1967 , the connection included a new station on the Sixth Avenue Line — Grand Street ( another station , 57th Street , opened in July 1968 ) — and introduced the most significant service changes ever carried out in the subway 's history . Grand Street , located under Chrystie Street ( the southern end of Second Avenue ) was designed to include cross @-@ platform transfers between the Sixth Avenue and Second Avenue Lines . Although the connection only served Sixth Avenue Line trains , it was essentially the first part of the Second Avenue line constructed . 
