I-205 - Ramp to SR 14 Zipper Merge Pilot Project

Project news

In summer 2019, the Washington State Department of Transportation will implement a congestion reducing pilot project on State Route 14, in Clark County.

During peak, evening travel times, traffic from I-205 merging on to eastbound SR 14 experiences heavy congestion, causing significant backups, delays, and an increased potential for crashes. The pilot project is intended to alleviate traffic backups during peak evening travel times by encouraging travelers in the merge lane to remain in this lane until they reach the end of the merge lane; the point where traffic can take turns merging into the thru lane with the flow of traffic. This type of late merge is also known as "zipper merging."  

So, what is zipper merging, how does it work and why should I wait in the merge lane until it ends? 

Let's discuss.

A common misconception of late merging is that it's rude or cheating when a driver “cuts” in front of other drivers waiting in the thru lane. The idea behind the Zipper Merge is that drivers use the full length of all lanes during congested periods to improve efficiency. To the driver, that means less delay, and shorter backups. If everyone merged early, backups could extend to a mile or even longer.

When drivers use zipper merging, cars in the merge lane drive all the way to the end of the lane and takes turns merging, one by one, into moving traffic. By encouraging drivers to use the entire merge lane, the zipper merge can cut congestion up to 40 percent. Studies also show that the zipper merge greatly improves traffic flow. As traffic flow increases, vehicle throughput increases. When more cars get through, you get to your destination quicker. Zipper merging provides benefits to all users, but the key is everyone must take their turn at the merge point.

When do I merge?

WSDOT will install new informational signs along the shoulder of eastbound SR 14. During periods of heavy congestion, drivers will be directed to merge at the end of their lane as indicated by the signs. Signs have been located at the end of lanes intentionally to encourage drivers to use the entire lane.

During free-flow traffic conditions, (traffic volumes are low/less travelers on the road), drivers should merge normally when they find a gap in the flow of traffic and when it is safe to do so.

Needs & benefits

  • Needs: Improve mobility by reducing delays, reduce the differential in speed to improve safety, and – most importantly - reduce congestion during peak evening travel times.
  • Benefits: increased vehicle throughput, improve safety by reducing rear-end crashes, and decrease backups!


  • Summer 2019: This project is scheduled to be completed in one day.

For the safety of our crews, and to reduce the impact to travelers, work will be done during hours when traffic volumes are low.

In an effort to use our current infrastructure in a more efficient way, check out how we're implementing zipper merging on US 101 / SR 8, just outside of Olympia.


The estimated cost of this project is $5,500.00
Source: State funding for safety and mobility and low-cost enhancements


David Burkey - Transportation Engineer

Celeste Dimichina - WSDOT Communications

I-205 ramp to SR 14 - Zipper Merge Pilot Project location map