In July 2011, after the tunnel boring machines finished drilling through the Grand Central station box, they were left in place under 38th Street and Park Avenue, as it was more economical than disassembling them in Queens and selling them for scrap, which could have added $9 million to the project's final cost. The next step in construction was to make cast-in-place concrete sections to create the tunnel lining. Each tunnel was in diameter, with an average depth of beneath street level.