Traffic Q&A: What’s the deal with that Pacific Avenue-Interstate 5 interchange?

Q: Why did the Washington State Department of Transportation design the on-ramp to southbound Interstate 5 from Pacific Avenue in Tacoma the way it did? That interchange is a chronic bottleneck. – Dave K., Gig Harbor

A: Dave is not wrong. Merging either onto or off I-5 right there is not for the timid.

For those unfamiliar with that area, it’s where drivers can leave Pacific Avenue near the Tacoma Dome and either continue onto the lanes leading to westbound state Route 16 or cut across those lanes and try to merge onto southbound I-5.

It’s also the place where southbound I-5 traffic can exit onto westbound state Route 16.

We drive that stretch regularly, and it can be messy, especially during the morning or evening rush.

Dave calls it “insanity,” especially given that drivers coming off Pacific generally are moving much more slowly than those screaming up the hill on I-5.

“I’ve never understood the logic of trying to ‘zipper’ two lanes of high-speed traffic with one lane of slow speed,” he wrote to us here at Traffic Q&A headquarters. “It is a major reason traffic starts to back up on south I-5 near the Tacoma Dome.”

Dave asked if we could track down the engineer who designed the interchange and press him or her for answers, but we suspect that person has gone on to the Great Drafting Table in the Sky, given that I-5 opened through Tacoma in 1960.

We also suspect the design didn’t seem so insane, to follow Dave’s description, back then.

The Nalley Valley Viaduct, which connects state Route 16 to I-5, didn’t open until 1971, according to our research. State Route 16 fed onto Pacific Highway South before then.

What’s more, the population of Pierce County stood about 411,000 in 1970, less than half the 844,000 people estimated in 2015, according to the U.S. Census.

Today’s crazy merge probably was a lot less stressful four decades ago.

But that was then and this is now, when white knuckles and blaring horns rule the day.

Is there any relief in sight?

We put the question to Claudia Bingham Baker, Transportation Department spokeswoman.

Said she:

“The HOV projects now being built in Tacoma will not change the weaving configuration at this location. Other features that we are building, such as wider shoulders, new pavement, eliminating ‘ghost’ striping and improved lighting, should help.”

Continued Bingham Baker:

“Unfortunately, structures that could alleviate the weave, such as braided ramps, were beyond the scope of our current construction projects,” Bingham Baker said.

Unfortunate, indeed.

This story was originally published December 4, 2016 at 4:00 PM with the headline "Traffic Q&A: What’s the deal with that Pacific Avenue-Interstate 5 interchange?."