Gilbert released preliminary sketches of the Hudson River bridge that March; by then, the architect had decided that the span would be a suspension bridge. The sketch accompanied a feasibility report that Ammann and other engineers presented to the Port of New York Authority, which was to operate the bridge. The central span was to be long, longer than any other suspension bridge in existence at the time, and 200 feet above mean high water. The bridge would initially carry four lanes of vehicular traffic and sidewalk lanes; the plans called for three additional phases of expansion, culminating in an eight-lane bridge deck with four rapid-transit tracks underneath. The span would be supported by two towers, each tall. There would also be space to build a second deck in the future below the main deck. Ammann's team also found that the most feasible location for the bridge was at 179th Street in Manhattan (as opposed to 181st or 175th Streets). This was both because the 179th Street location was more aesthetically appealing than the other two locations, and because a 179th Street bridge would be cheaper and shorter in length than a bridge at either of the other streets. At this point in the planning process, the Hudson River bridge's estimated cost was $40million or $50million. Because of the proposed bridge's length, engineers also had to test the strength of materials, including suspension cables, that were to be used in the span. Ammann's research department constructed scale models of various designs for the bridge and tested them in wind tunnels.