When Roebling was called to the Niagara Suspension Bridge project in 1851, he had six suspension structures to his name. He found Ellet's final plan to be impractical; the bridge would have been too heavy and expensive. Roebling had another design in mind: the double-deck bridge he had proposed earlier during the bidding. The lower deck, level with the edge of the chasm, would convey passengers and carriages, and the upper deck, above, would allow fully laden trains to continue their journeys non-stop, albeit at a speed of . Roebling reasoned that the decks and sufficient trusses would form a rigid tube, making the bridge stiffer than a normal suspension bridge. The theory was similar to that of the tubular bridge but implemented at a lower cost. The engineering community was critical of Roebling's project. Robert Stephenson, builder of the tubular Britannia Bridge, was among those shortlisted to complete the Niagara Suspension Bridge before Roebling's selection. Stephenson had submitted a design for a tubular bridge, and in 1859 he built a large and expensive tubular bridge for the Grand Trunk Railway at Montreal, Quebec. The bridge builder then said in derision of Roebling's suspension railway, "If your bridge succeeds, mine is a magnificent blunder."