Originally published January 10, 2017, we can now update this article with news that WSDOT will be installing signs for a zipper merge in late June, 2019. Click here to read the entire article, including ‘Update #2’.
Most weekday mornings traffic begins to stack up where southbound US-101 merges from two lanes, to one, under WA-8. Drivers line up in the left hand lane and sometimes traffic slows almost all the way back to the onramp at Steamboat Island Road. As traffic slows, drivers entering US-101 at Steamboat Island Road scramble to join the line forming in the left lane. It sometimes creates a dangerous situation. And those drivers who cannot move left, or choose to remain in the right lane, feel like they are cheating, cutting into the line closer to the actual point the two lanes merge into one.
Transportation engineers call it a “zipper merge.” It is not taught in driver’s education. And the Washington Department of Transportation doesn’t normally provide the correct signage instructing drivers how it’s supposed to work. And it turns out we’ve been doing it wrong, all along.
At normal highway speeds, when traffic is moving smoothly through the WA-8 underpass, it’s correct for drivers to move to the left lane early, when the sign indicates there is a merge ahead.
But, when traffic begins to stack up and slow down, the correct way to use a zipper merge is for drivers to fill in both lanes. If the roadway was signed correctly, long before the right lane merges into the left, there would be a sign reading, “Use both lanes to merge point.”
Then, actually at the point the right lane merges into the right, drivers should file through the underpass one at a time. First a car from the left lane, then a car from the right, then the left, and so forth.
Cars from each lane file together, at the merge point, just like the teeth of a zipper.
If the roadway was signed correctly, there would be a sign at the merge reading, “Take turns merge here.”
Or perhaps a single sign, like the one pictured at the bottom of this article, would suffice to notify drivers that, when there is congestion, they should use both lanes and then take turns at the merge.
When both lanes are used correctly, a zipper merge could reduce by 50% the length of the backup along US-101. At the height of out little morning rush hour, drivers using the Steamboat Island Road onramp would easily be able to get into either the right or left lane. And everyone would get under WA-8 and on their way, just as quickly as before.Read More