Work on the project began in fall 1872. The first contract was awarded to Fairchild and Ward and the Watson Manufacturing Company for the section between 45th Street and 49th Street. The preexisting track level in this section was maintained as the streets crossed over the line via iron bridges. The project north of 48th Street was completed by Dillon, Clyde & Company, which submitted the winning bid of $6,395,070 (). The contract for the project had been awarded on August 1, 1872. The contract for the section between 79th Street and the Harlem River was awarded to them on November 11. On January 14, 1873, the contract for the work between 49th Street and 79th Street was awarded to Dillon, Clyde & Company, which provided the only bid lower than that expected by the New York City Board of Estimate. The contract called for the project's completion in two years. This section had been put up for bid, but since none of the bids were satisfactory, the bidding process was reopened.