One night without rain is all construction crews need to complete a maneuver in Tacoma’s Nalley Valley they’ve been working toward for more than a year.
When the pavement is dry enough, paint crews will lay down new roadway striping that will guide eastbound traffic off the existing alignment of state Route 16 and onto a temporary viaduct over the valley.
The state Department of Transportation hopes Thursday night will be the night.
If that’s the case, on Friday morning the 102,000 drivers who cross the valley on state Route 16 each day will find themselves on a new 1,350-foot-long viaduct as they make their trek toward Interstate 5.
If it rains Thursday night, crews will postpone the shift, possibly into next week.
“Shifting traffic onto the temporary structure is a huge milestone on this project,” Neal Uhlmeyer, the Transportation Department’s project engineer, said Wednesday.
The shift is a milestone, but it’s a long way from the end of the $115 million project.
Much of the new viaduct is only a temporary structure, and will be demolished during a future stage of construction. About 700 feet is permanent and will be used in a high-occupancy-vehicle connector project scheduled to begin in 2020.
The Transportation Department is warning drivers that all eastbound state Route 16 lanes are likely to be closed Thursday and Saturday nights. During the closures, eastbound traffic will be diverted onto the Union Avenue exit.
Traffic is being shifted to make room for demolition of what’s left of the old Nalley Valley viaduct — supported by distinctive “tetrapod” support columns — and to build a permanent eastbound viaduct in its place. That permanent structure isn’t expected to be finished until a year from now.
“Building temporary structures makes it complicated,” said Kim Mueller, the assistant project engineer, “but in a place like this, where you have to keep traffic moving, it’s about the only option.”
Demolition of the old viaduct will start immediately after the traffic shift, Mueller said, and is expected to take about two months.
The demolition work will take place immediately to the right of eastbound lanes — close enough that transportation officials have expressed concern that the spectacle might be dangerously diverting to drivers.
“It’s kind of like the situation we encountered when building the Tacoma Narrows Bridge,” said Claudia Bingham Baker, the Transportation Department’s Olympic Region communications manager. “You can’t tell people not to look, but we’ll be reminding them to pay attention to the road and drive cautiously.”
The Eastbound Nalley Valley project is part of the Transportation Department’s Tacoma/Pierce County high-occupancy-vehicle project. It eventually will add 70 carpool lane miles on state highways in Pierce County. Nearly all of the funding comes from state gas taxes.
The first phase of the Nalley Valley project, a $184 million job that streamlined the westbound half of the interchange, took 2½ years and was completed in June 2011.
That phase also was a major endeavor, including building 10 bridges, pouring 48,000 cubic yards of concrete and sinking 77 supporting piers as much as 70 feet deep.
Drivers on state Route 16 have been dealing with heavy construction since 2002, when work on the second Narrows bridge began. That project took five years.
The Transportation Department promises that this phase of Nalley Valley construction will make sense of the Sprague Avenue interchange, which, in its partially completed state, has been a sore point with many drivers.
When the project is finished, in May or June 2014, new ramps from the Sprague overpass will connect drivers to both directions of I-5. Eastbound drivers leaving state Route 16 at Sprague will be controlled by a stoplight at the top of the exit ramp.
The project also includes several technological improvements, including traffic cameras, ramp meters, traffic-data collectors and other hardware that the state says will improve its ability to manage traffic and communicate traffic conditions to the public.
The final phase of construction, scheduled for 2020-22, will incorporate carpool lanes into the complex interchange at an estimated cost of $213 million.
Rob Carson: 253-597-8693