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Melissa Slager |
Published: Monday, April 8, 2013, 12:01 a.m.

‘Zipper merge’ novel idea but tough for drivers to grasp

T.J. McDermott of Lake Stevens writes: Merging traffic of westbound 20th Street SE and westbound Highway 204 onto U.S. 2 is always a congestion point for the morning commute.

Why not post the 20th-204 merge point as "alternate merge," instead of having only Highway 204 drivers yield?

Posting that point as alternate merge should calm things down if everyone sees they'll get a fair chance onto U.S. 2. Alternate merge would be one car from one road passing through the merge point, then one car from the other road passing through the merge. I've most commonly seen alternate merge as part of a temporary traffic sign.

The onramps are a terrible design, with absolutely no merge lane for Highway 204, leaving the driver looking at an awkward angle over their left shoulder while in a fairly sharp right turn. The scrapes on the concrete side barriers are tribute to how bad this merge point is.

Dave Chesson, a spokesman for the state Department of Transportation, responds: We wish the answer really could be that easy. Here in Washington we have no direct experience with the "alternate merge."

It appears to be an experimental idea that a few other states have been using on a trial basis in construction zones. One of the terms used for this concept is a "zipper merge," where drivers are asked to converge together in an alternating pattern, like teeth in a zipper. The idea is so novel that informational campaigns are usually used to help explain what the terminology means and what the expectations are for the motorist. In a few key respects we think the zipper merge still lacks sufficient clarity for us to use.

There are no traffic laws established for zipper merging in Washington. To the best of our knowledge the zipper merge is only an advisory condition -- a request for the mutual cooperation of drivers in a highly congested merge setting.

Some drivers may choose to disregard it; others may honestly not understand it. Our preference is to always have clear traffic rules so the driving public will understand what a sign means and what their responsibilities are when they encounter the sign. "Stop" and "Yield" signs have this sort of clarity and legal support, while a zipper merge is an idea mostly outside the public's understanding and existing traffic code.

The zipper merge is solely for peak-hour congested conditions. The idea is for both streams of vehicles to be granted equal status and experience roughly the same wait time.

The ultimate fix is rebuilding the entire interchange, but there is no funding currently available. Drivers from Highway 204 are given fair warning to yield with two warning signs prominently placed along with flashing beacons for added emphasis.

Street Smarts adds: In four years of this column, we've had maybe more questions about this tricky interchange than any other. It's a weird situation: Drivers entering U.S. 2 from a state highway have to yield to those coming off a city street. There is, however, a good reason for it. Those coming off the city street, 20th Street NE, are headed down a very steep hill, while those coming from Highway 204 are traveling uphill on a ramp. The slow traffic must yield to the faster traffic.

The hard part is that the ramp curves to the right so it becomes almost parallel to 20th. Drivers on the ramp have to look sharply to the left, almost behind them, and past railings to see if any cars are coming down the hill -- while trying to negotiate the curve to the right at the same time.

Most of the drivers who've written Street Smarts about this intersection believe those coming down the hill should have to yield because they have better visibility. As bad as the situation is currently, consider the alternative.

At best, you'd be asking the drivers on 20th to ride their brakes down that steep hill, even more so than now. At worst, those drivers are letting it fly down the hill and hitting their brakes at the last second, maybe in time to avoid rear-ending the car merging from the ramp and maybe not. The car coming down the hill has a much greater potential to hit the car coming from the ramp than the other way around. Removing the obligation to yield from the drivers entering from the ramp could put them in greater danger by giving them a false sense of security.

As Dave Chesson said, there's no perfect solution short of tearing the whole thing down and rebuilding. Until that's done, however, the drivers entering from Highway 204 just have to take it slow and bear the burden of safety at that location.

E-mail us at Please include your city of residence.

Look for updates on our Street Smarts blog at
Story tags » Highway 204Traffic SafetyU.S. 2

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