The Charles River Bridges
The Charles River Bridges
The new bridge replaced a deteriorating six lane double-deck bridge that was demolished in spring 2004. The CA/T Project also includes a parallel four-lane bridge, the Leverett Circle Connector Bridge, to carry traffic to and from Storrow Drive and Leverett Circle, which opened to traffic in October 1999. Together, these bridges will more than double the cross-river capacity to 14 lanes.
As part of the bridge construction, the CA/T Project is also developing 40 acres of new park land on the riverbanks below, reviving an area long abandoned under the shadow of the upper and lower deck.
The Cable-stayed Bridge
costs: $100 million
completion: see note below
With its graceful lines and 270-foot towers, the Leonard P. Zakim Bunker Hill Bridge fuses Boston's future with its historic past. Swiss bridge designer Christian Menn conceived the bridge to reflect, with its inverted Y-shaped towers, the shape of the Bunker Hill Monument in neighboring Charlestown. In addition to the Battle of Bunker Hill, the bridge is also dedicated to the life of civil rights activist Lenny Zakim. It serves as a permanent memorial to a man who bridged many gaps. The bridges cables -- which suggest a ship in full sail -- also evoke the history of East Boston as a center of shipbuilding. (Learn more about Leonard P. Zakim and The Battle of Bunker Hill.)
The bridge, at 1,432 feet long, emerges from the underground Central Artery near the Fleet Center at Causeway Street, crossing the river to make connections with both I-93 and Route 1.
The bridge is designed to carry 10 lanes of traffic; eight lanes passing through the legs of the twin towers and two cantilevered on the east side. The cantilever portion, which will accommodate northbound traffic from the Sumner Tunnel and the North End, will provide the bridge's unique, asymmetrical design.
Girders, floor beams and two planes of cables support the bridge's 745-foot-long, 183-foot-wide main span. Steel floor beams, which support the main span, are extended out to support the cantilevered lanes.
The back spans on the land side of the towers -- which measure 267 feet on the downtown side, and 420 feet on the Charlestown side -- are supported by single planes of cables. Using a one-plane cable design used on the south back span allowed traffic flow to continue on the existing I-93 connection to Leverett Circle during construction.
One of a Kind
The new Leonard P. Zakim Bunker Hill Bridge is the only one of its kind ever built. In addition to being the widest cable-stayed bridge in the world, the bridge is the first "hybrid" cable-stayed bridge in the United States, using both steel and concrete in its frame. The main span consists of a steel box girder and steel floor beams, while the back spans contain post-tensioned concrete.
The bridges were built within a busy transportation corridor that already houses the Massachusetts Bay Transit Authority's (MBTA) Commuter Rail and Orange Line. In order to avoid impact to the Orange Line and its ventilation building, the legs of the bridge's concrete towers are truncated in at a 55-degree angle and straddle the MBTA tracks as they surface from the Orange Line tunnel in Charlestown.
The Leverett Circle Connector Bridge
costs: $22.27 million
completed: october 1999
This 830-foot-long, four-lane companion to the ten-lane cable-stayed bridge connects the Leverett Circle area on the northwestern edge of downtown Boston with points north of the Charles River. Nine box girder sections - in cross section the largest in North America - were barged into place and raised into place by cranes or (in the main span) jacks. The Leverett Circle Connector bridge opened to traffic eight days ahead of schedule in October 1999.
Specifications:
Main Span Length -- 380 feet
Back Span Length -- 225 feet
Bridge Width -- 76 feet
Superstructure:
Single steel box girder 18 feet deep at the piers, 9 feet deep at center span. Concrete bridge deck.
Substructure:
2 water piers, 2 land bents, cast-in-place, supported on drilled shafts.
Photography
In our photo gallery you will find some great cable-stayed bridge construction photos of the Leonard P. Zakim Bunker Hill Bridge and steel span bridge photos of the Leverett Circle Connector Bridge.
Of special note, click on these cable-stayed bridge "virtual tours", and reporting, by others:
Boston.com -- October 2000
Bechtel Briefs -- August 2001 [193K PDF]
And see bridge videos and animations.
The Best View of the Bridges
The new bridges have been built on the west side of the existing I-93 double-deck crossing, to your right as you enter downtown Boston from the north. You can get a good view of them from the Charles River locks near Lovejoy Wharf, or from the end of the rail platforms at North Station.