Zakim, Bunker Hill Bridge, Boston, Massachusetts

The new 100 USD million Leonard P. Zakim Bunker Hill Bridge is a 429 m long, 55,8 m wide cable-stayed structure that carries 10 traffic lanes over the Charles River. The main eight-lane roadway is cradled within two inverted Y-towers. A secondary two-lane roadway is cantilevered 13,7 m to one side of the main roadway, making the bridge asymmetric in cross section. The 227,1 m main span superstructure is of steel composite design. With concrete box girder back spans, the overall layout becomes hybrid. The unusually wide deck is carried by cables spaced at 6,098 m on center in the main span and 4,573 m on center in the back spans. The bridge, which forms Boston's Central Artery/Tunnel (CA/T) Project's critical link over the Charles River just north of downtown Boston is unique among cable-stayed structures in several respects. Its cable arrangement, slender inverted Y towers and a two-lane roadway cantilevered outside the eastern cable plane are among the bridge's most notable features. In March 2003, the four northbound lanes opened to vehicular traffic and when fully open in 2004, the bridge will carry an estimated 110 000 motorists daily.