| Designing a bridge that could accommodate the parkway drive and harmonize with the picturesque landscape of Scarsdale Lake was an architectural and engineering challenge. Hayden noted that the structure, which was about 600' long, could either preserve the natural beauty or destroy it. The engineers had originally considered a conventional arch bridge with a 45-degree skew that would provide safe approaches. When perspective sketches were drawn, the commissioners discovered that a closed-spandrel arch bridge would overwhelm the site, presenting an unacceptable expanse of concrete when viewed from either side of the lake. The heavy skew also made the structure look awkward. An open-spandrel arch with several ribs would be less intrusive, but it would require greater height and necessitate raising the grade of the drive over the lake. As a result, there would have to be a very steep south approach to carry the drive under the grade separation at nearby Ardsley Road. Delano proposed an unusual and creative solution to the problem. A curvilinear concrete ramp supported by eight concrete mushroom columns carried the drive over and above the west edge of the lake. The mushroom units were comprised of masonry piers 14' in diameter augmented by radial brackets to supported the reinforced-concrete floor slab. Edging beams were added where the units joined. The bridge was built on a curve and the deck slab had a continuous 6 percent grade. Since they would be visible from the paths around the lake, the concrete piers and abutments were faced with stone. The original bridge parapets consisted of steel posts with pipe railings. The Scarsdale Bridge was another excellent example of the fruitful collaboration between architects and engineers that characterized the entire parkway project. Delano provided the concept and architectural ideas for the bridge, with BPC engineers under Hayden’s direction determining the structural design. Directly adjacent to the Scarsdale Bridge, the BPC built a girder bridge to carry the drive over the railroad tracks. The girders were encased in concrete and the bridge had concrete parapets.(245) Delano presented his sketches for the Scarsdale Bridge a month after the commission made its final decision on the Scarsdale alignment. Observing that the proposed bridge was of an "entirely new type," the commissioners asked for a model of the structure that would clearly show its structural characteristics and architectural appearance. A few weeks later, the model was presented and considered. The BPC noted that Delano’s design would cost about $4,000 more than a conventional arched viaduct faced in stone. After examining the model and giving it "very careful consideration," the commissioners approved the design and agreed to provide Delano with the standard BPC architect’s fee based on 2 percent of the structure cost. The fees included preliminary plans and sketches; complete architectural designs with large-scale details; consultations; and inspection by the architects to insure proper execution of the architectural features as construction progressed. The New York Central Railroad Company gave its approval for the simple girder bridge that carried the parkway drive over its tracks at the north end of Scarsdale Bridge.(246) Preliminary work for the Scarsdale Bridge included securing an easement for the bridge approach from the New York City Board of Water Supply. To ensure the piers were properly designed, Holleran recommended that sub-surface borings be conducted. Boring tests were also useful for informing contractors bidding for the bridge project about the nature of subsurface conditions. Phillips & Worthington had done similar work on the Broad Street Viaduct and were chosen to conduct the borings.(247) Bids opened for the Scarsdale Bridge contract in April 1924. Twelve bids ranging from $195,230.10 to $258,720.00 were received. The low bidder, Triest Contracting Company of New York City, was awarded the contract. In October 1925, less than a month before the BRPR dedication, the contractor was granted an extension to complete the project. As the parkway project drew to a close, the commissioners discussed an appropriate memorial to recognize the contributions of former commissioner William Cannon, who had died in 1916. Because of its unique design and picturesque setting, the commissioners decided that the Scarsdale Bridge should be officially designated Cannon Memorial Bridge. Stoughton was asked to design an appropriate tablet and select a suitable location for it on the bridge.(248) |
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| (245)Hayden,
"Two Parkway Bridges," 16-17; Bronx Parkway Commission, Final
Report, 1925, 80. |
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