BRIDGE TYPE ALTERNATIVES

Vertical Lift Bridges are typically used to span wider navigation channels because they are capable of spanning long distances. The movable span of a vertical lift bridge is typically a truss that places the supporting superstructure above the roadway deck. By reducing the amount of superstructure below the roadway deck, the bottom of the structure is higher and the vertical clearance above the water is maximized. Maximizing the closed position vertical clearance allows more vessels to pass without having to raise the bridge, thereby reducing impacts on vehicular traffic.  For its type study, the design team considered a vertical lift bridge with a 250-foot horizontal navigation clearance and a 58.5-foot vertical navigation clearance in the closed position. This vertical clearance will help to minimize summertime openings since the clearance will allow passage of most recreational sailboats in the closed position.  

Bascule Bridges are typically used to span navigation channels of 200 feet or less. For bascule spans, each span leaf rotates about a horizontal access located at a pier.  For the type study, the design team considered a bascule bridge with a 225-foot horizontal navigation clearance and a vertical navigation clearance of 41 feet when the bridge is in the closed position. While this vertical clearance is greater than that of the 1936 bridge, it is significantly less than can be achieved with a vertical lift structure. For reference, the temporary bridge provides a vertical navigation clearance of approximately 55 feet in the closed position.  If a bascule bridge were to be built to cross the Fore River with a horizontal navigation clearance of 225 feet, it would be one of the largest bridges of this type in the United States with piers roughly 100 feet wide to accommodate the counterweights required to balance the movable spans.

For more information, please visit the Project Description page of this Web site or contact our Public Involvement Specialist.