***UPDATE: WSDOT officials announced at 7:44 a.m. today that the Nalley Valley viaduct groundbreaking event has been cancelled due to weather and road conditions across the region. The conditions at the event site also were a factor in the decision to cancel.

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Washington State Department of Transportation Secretary Paula Hammond, Tacoma Mayor Bill Baarsma and other public officials are slated to attend a ground-breaking ceremony this morning to mark the beginning of the Interstate 5/State Route 16 Westbound Nalley Valley project.

The completed Westbound Nalley Valley project is part of a larger corridor plan aimed at improving safety for motorists, keeping freight moving, and building toward an HOV network that moves more people in fewer vehicles.

Over the course of the three-year construction project, there will be disruptions to traffic — including long-term closures of the Sprague Avenue on- and off-ramps, lane closures on I-5, SR 16 and city streets, and traffic revisions that put eastbound and westbound SR 16 traffic on temporary bridges.

The $184 million project — funded primarily by the 2003 gas-tax funding package — eliminates the weave of traffic where vehicles from I-5 change lanes in order to merge onto SR 16 or exit at Sprague Avenue. The westbound project is scheduled for completion in fall 2011, after which crews turn their attention to building the eastbound viaduct.

An average of 131,000 vehicles use the viaduct each day, compared to the 40,000 that traveled it daily in the early 1970s when it opened to traffic.

The original Nalley Valley Viaduct was built from 1969 to 1971 by Donald M. Drake Company of Portland, Oregon for $3.67 million.