Crews will start work in two weeks on a replacement for the westbound portion of the Nalley Valley viaduct in Tacoma, a $120 million project that’s expected to take three years.

The long-awaited replacement will ultimately help open one of the worse bottlenecks in Pierce County – but in the meantime, get ready for some disruptions.

Construction of a new connection between Interstate 5 and Highway 16 will permanently affect 32,000 drivers a day who now use South Sprague Avenue to get onto I-5 and off Highway 16. The project also will periodically disrupt traffic on South Tacoma Way and Center Street, both of which are below the viaduct.

The existing viaduct, which was built in 1971, will remain in use until its westbound and eastbound replacements are finished. An average of 131,000 vehicles use the viaduct each day.

However, parts of the viaduct will be altered to get traffic out of the way so the new interchange structures can be built. And two of the ramps that now connect Sprague Avenue to Highway 16 and I-5 will be closed, probably in late February or early March, and will remain closed for nearly three years.

“They’re in the way of the new viaduct,” said Karri Workman, a spokeswoman for the state Department of Transportation.

Overall, the new interchange will cost $525 million and most likely won’t be completed until some time after 2021. But the bulk of the work will be done in the next five years. The first phase, construction of the new viaduct to carry traffic from I-5 west onto Highway 16, will open to traffic in fall 2011. The next phase, to carry traffic from eastbound Highway 16 to I-5, will be done by late 2013.

Prospects for the final phase were dealt a setback last week when Gov. Chris Gregoire unveiled her budget proposal to the Legislature. The governor is recommending the $213 million for the third phase of the project be put off until sometime after 2020. That project would pay for direct connection of car-pool lanes on Highway 16 to car-pool lanes on I-5.

Crews for Atkinson Construction Co. of Renton will begin preliminary work on Jan. 5, Workman said.

Signs will announce impending closures and suggest detours.

Sprague Avenue will be reduced from the current four-lane roadway between South 19th Street and the viaduct to only two lanes – one in each direction. That’s because drivers no longer will be able to use the on-ramp from Sprague to get to I-5. It will be closed this spring and remain closed until fall 2011. However, drivers still will be able to drive south on Sprague and get onto westbound Highway 16 for one more year. Then, that ramp also will be closed and remain so for 2010 and 2011.

The other closure scheduled for late February is the off-ramp from eastbound Highway 16 to Sprague. That, too, will remain closed for three years.

The combination of those first two closures is expected to drive more traffic to the Union Avenue on- and off-ramps.

“That added volume will slow traffic approaching Nalley Valley” from the west, said Jamie Swift, another DOT spokesman.

Crews also will be working in the median of Highway 16 between Cedar Street and Sprague Avenue, paving part of the median so traffic can be shifted there and give crews more room to work on the outside (far right) eastbound lanes, he said.

“That space allows crews to build new temporary bridges for eastbound and westbound traffic,” Swift said. “Putting traffic on temporary bridges moves vehicles away from construction of the new westbound Nalley Valley bridges.”

Both directions of I-5 and Highway 16 will be closed for a few nights during the construction project to allow crews to set bridge girders.

Also, construction periodically will affect local traffic on South Tacoma Way and South Center Street because of work above those local streets. Workman said those heavily traveled arterials will have traffic restrictions on some days and nights, but at least one lane in each direction will remain open during daytime business hours.

The replacement for the viaduct over the Nalley Valley, which got its name from longtime Tacoma cannery Nalley’s Fine Food, has been a long time coming. An environmental review was done in 1993, but the Legislature was unable to agree on the gas tax increase that was needed to pay for the project. Later, Tim Eyman’s Initiative 695 helped delay the project because it prompted the Legislature in 2000 to repeal the state motor vehicle excise tax. That cut transportation and other funding by $800 million a year

Most of the money for the viaduct is coming from the 5-cent gas tax increase that was approved by the Legislature in 2003.

Today, drivers getting on and off Interstate 5 have only 600 feet to change lanes in order to get onto Highway 16 or get off at the Sprague Avenue exit, creating daily traffic snarls. The new interchange will eliminate the weave of traffic. The DOT estimates the change will reduce collisions by 60 percent, or about 16 accidents per year.

Eventually, the existing viaduct will be torn down.

Joseph Turner: 253-597-8436

blogs.thenewstribune.com/politics

THE NALLEY VALLEY PROJECT

Some numbers from the westbound section of the project:

10
Number of bridges

57
Number of piers (columns)

10.4 MILLION
Pounds of steel expected to be used

48,000
Cubic yards of concrete expected to be poured

100 HOURLY
Workers on new viaduct project

25
Number of subcontractors (with an additional 100 hourly workers)

50 TO 70
Depth of piers

40 TO 84 FEET
Height of piers

64 FEET
Height of current viaduct

94 FEET
Height of new viaduct

3.14 MILES
Linear storm drainage

3 MILLION
Capacity, in gallons, of temporary stormwater retention ponds

22.4 MILLION
Capacity, in gallons, of permanent stormwater retention ponds

Source: Washington Department of Transportation