Nalley Valley Viaduct...

It's that time of year for us here at WSDOT. We start making the shift from winter mode to thinking about the summer construction season. But not all construction happens in the summer. There is an interesting project happening right now in the Tacoma area on SR 16 that will eliminate one of the worst traffic bottlenecks in Pierce County.

In early January, work began on a project to replace the westbound portion of the SR 16 Nalley Valley viaduct. If you drive through this area you may not have even noticed it yet because it hasn't affected traffic, yet. All that will change in mid-February when crews begin closing the Sprague Avenue ramps and put eastbound traffic on a new alignment with narrower lanes and shoulders. For those local to the area it will mean using alternate routes or taking a different exit to get home for a couple of years. A major inconvenience, yes - but the improved safety and decreased congestion is a nice payoff at the end.

I am a big fan of "fun facts," if you will. The communications team on this project was kind enough to put some together to give you some interesting details about the project:

  • The construction contract was awarded for $120 million. The current viaduct opened in 1971 and was built for about $3.3 million.
  • Each day, about 130,000 vehicles cross the viaduct – about 90,000 more than the daily traffic in 1973.
  • Replacing the westbound portion of the viaduct requires about 200 full-time contract workers who will build 57 columns for 10 new bridges.
  • Crews will drill the columns as deep as 70 feet into the ground.
  • The new viaduct stretches more than 90 feet into the sky, about 30 feet higher than the 1971 viaduct.
  • To build the new westbound viaduct – which includes eight acres of bridge deck – crews will use 10.4 million pounds of steel and pour 48,000 cubic yards of concrete.
  • Workers also will build temporary and permanent storm water retention ponds with the capacity to hold more than 25 million gallons, and a linear storm drainage system more than three miles long.
  • And perhaps the most important number is this: Traffic engineers estimate the completed westbound Nalley Valley project to produce a 60 percent reduction in collisions; That’s 16 fewer collision per year.
For more information about this project, visit