Get ready for big 'shift' on Nalley Valley Viaduct: route 16

Mar 10, 2010 — The News Tribune

Mike Archbold

Mar. 10, 2010 (McClatchy-Tribune Regional News delivered by Newstex) -- After nearly 40 years, the "weave" to the Sprague Avenue exit ramp on Tacoma's Nalley Valley Viaduct is going away.

This weekend's closure likely will cause its own congestion but should reduce the intense maneuvering drivers face getting onto state Route 16 from Interstate 5.

Also this weekend, westbound traffic across the viaduct will "shift" to a temporary roadway, another step in the three-year, $183 million westbound Nalley Valley redesign project.

To make the shift smoother, one lane of southbound I-5 approaching state Route 16 will be closed back to Pacific Avenue. Northbound freeway traffic will continue to be one lane leading onto the state route.

Each day, an average of 65,000 vehicles travel west on the viaduct.

"This is a huge deal for Tacoma drivers," said Kevin Dayton, region administrator of the state Department of Transportation. "We expect significant disruptions to traffic flowing in and through Tacoma for a couple of weeks until drivers get familiar with the new traffic revisions."

The shift will require westbound state Route 16 from I-5 to Union Avenue to be closed from about 10 p.m. Saturday until 10 a.m. Sunday, depending on the weather. Rain the rest of this week could delay the entire process.

During the closure, northbound and southbound freeway traffic headed for westbound state Route 16 will be detoured onto 38th Street and Union Avenue.

THE 'WEAVE'

Each day, about 12,000 vehicles use the Sprague Avenue exit, a main entrance to Tacoma's Hilltop neighborhood. Once it closes, it won't reopen until fall 2011 when the westbound Nalley Valley highway project is expected to be completed.

In the meantime, most of that traffic using the Sprague exit is expected to move to the next exit, at Union Avenue, which already draws an average of 9,300 vehicles per day.

Drivers can expect congestion delays at the Union exit, Transportation officials say.

Losing the Sprague weave, however, is considered a good thing, since it's a major cause of congestion on the viaduct.

A weave occurs when drivers taking the off-ramp of a highway and drivers using the on-ramp must make lane changes across each other to go where they want.

At the Sprague exit, one lane of northbound I-5 traffic and two lanes of southbound I-5 traffic come together. The lane-changing to get on or off state Route 16 can be intense.

And destructive.

In the last five years, there have been 132 accidents reported on the 600-foot-long stretch of viaduct leading to the Sprague exit, according to the Transportation Department.

Most were fender benders. Seven resulted in injuries, one considered serious.

Drivers in either lane of I-5 traffic can't easily see vehicles in the other lane and must depend on luck and the consideration of others to make the lane changes work. At peak commute hours it only gets trickier as congestion increases.

With closure of the Sprague exit, traffic entering state Route 16 from southbound I-5 will have no reason to move to the right lane. And drivers coming from northbound I-5 won't have to worry about drivers trying to get off at Sprague.

With the restrictions along southbound I-5, each lane of traffic entering state Route 16 now will have its own westbound lane.

To accomplish that, the two lanes farthest right on southbound I-5 will be reduced to one, starting at the Pacific Avenue/Interstate 705 entrances. That will squeeze a lot of traffic into one lane eventually going west on state Route 16.

Northbound I-5 traffic headed for state Route 16 will have its own lane, and drivers no longer will have to deal with merging into the main flow.

It's hard to forecast what will happen to traffic with the changes, said Troy Watts, the field engineer in charge of the project.

"Northbound (to state Route 16) should actually function a little better than today," he said. "Southbound, I want to reserve judgment.

"We are taking the source of all the congestion out of the picture by losing the Sprague exit. It's really difficult to forecast how everything is going to function."

THE 'SHIFT'

This weekend's closure of westbound state Route 16 initially was scheduled for next month, but good weather this winter pushed up the work.

During the closure, crews will move concrete barriers into place and restripe lanes on the viaduct to shift westbound traffic to the left onto two temporary lanes.

The temporary lanes will be used while the permanent westbound lanes are constructed over the next 18 months.

The shift will take place mid-span on the viaduct just before the closed Sprague exit. Then, just before the bridge over Cedar Street, the temporary roadway will merge back into the westbound mainline in time for drivers to use the Union Avenue exit.

Building temporary lanes and shifting traffic onto them has been one of the project's complications, said Watts. In November, eastbound traffic was shifted onto a temporary roadway and bridge.

"We first had to move the eastbound traffic out of the way so we could move the westbound traffic out of the way so we could then build the new westbound structures," he explained.

The eastbound shift went smoothly, Watts said.

"Traffic-wise this is our last major complication," he said of the weekend shift.

Once that's done the rest of the project can get under way, he said.

Watts estimated the project is close to halfway done. About 82 percent of the substructure for the bridges is done, he said, but there is still "a ton of work up in the air to do."

So far, just 28 of 200 girders are in place on the bridges.

"It should stay interesting," Watts said.

Mike Archbold: 253-597-8692

mike.archbold@thenewstribune.com

Ways around Nalley Valley

From southbound Interstate 5: Take the Tacoma Dome/Interstate 705 exit or the South 38th Street exit.

From northbound Interstate 5: Take the South 56th Street or westbound South 38th Street exits.

From eastbound state Route 16: Take the 19th Street or Union Avenue exits.

Newstex ID: KRTB-0198-42742028