Interchange 8 Reconstruction

Rank #16
Cost: $187 million

It took almost three years, but the $187 million, 3-mi. Interchange 8 Reconstruction project has been completed.

The project involved the construction of new connecting roadways linking Interstate 87 with Interstate 287 in a new configuration and two new higher-speed E-ZPass lanes. The project was aimed at easing congestion in the Tappan Zee Bridge corridor and shortening commutes for motorists in Rockland County and points north to Westchester County.

The project included:

• Widened connector roadways to and from I-87 and I-287.
  
• An additional auxiliary lane north and southbound to ease traffic flow between the Tappan Zee Bridge toll station and Interchange 8.
  
• New collector distributor roads to eliminate weaving with the interchange.
  
• New higher speed E-ZPass lanes to improve traffic flow through the Tappan Zee Bridge toll plaza.

Because of its location in one of the most congested corridors in New York State - more than 135,000 vehicles cross the Tappan Zee Bridge daily - no long-term road closures were allowed and the same number of lanes was maintained during peak travel periods throughout the project. A complex, staged construction and traffic management plan was set up to assure maximum safety and to minimize inconvenience to motorists.

Lane restrictions were limited to off-peak hours and lane closures were not permitted during commuter or holiday travel times. In addition, the authority's construction inspectors monitored operations onsite, along with traffic supervisors, engineers and construction experts.

Up to 250 workers per day worked to build 15 new lane mi. and rebuild 19.6 lane mi. using 28,000 cu. meters of concrete and 225,000 metric tons of asphalt. Four new bridges were constructed, three bridges were rebuilt and four were replaced.

Three new noise barriers and 21 retaining walls were constructed. Rock blasting on the project was more than the authority conducted for all its construction jobs in a year.

The project featured several innovations. For example, the 250-ft.-long Broadway Bridge in Tarrytown is one of the longest precast composite bridges ever built in the United States. Delivered on a "train" of tractor trailers, the huge panels were lifted into place by two giant cranes at night.

At another location on the project, high-strength steel was used on a 272-ft. bridge, the longest simple-span plate-girder bridge in New York.

Most of the project's 21 retaining walls were built with Doublewal retaining systems, saving more than $7.5 million in construction costs and efficiently securing soil and rock adjacent to the widened roadway. The highest wall measured 50 ft. and the longest, at 1,914 ft., is the longest Doublewal ever built.

The project team also had to add a lane that would cut through the mile-long Tallyrand Swamp, a marshy area where normal embankment materials likely would sink. The design team proposed using a lighter-weight expanded polystyrene fill that is being used extensively in Europe but is relatively new to road construction in the United States.

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