This is not a test: I-405 peak-use shoulder lane open to traffic

At 2 p.m. on Monday, April 24, Washington State Department of Transportation (WSDOT) offered travelers in south Snohomish County a new option for their afternoon commute. The northbound peak-use shoulder lane (PUSL) officially opened to general-purpose traffic on the 1.8-mile stretch between State Route 527 in Bothell and I-5 in Lynnwood, about 20 miles northeast of Seattle.

Interstate 405 is one of the most congested corridors in Washington State. It runs northbound and southbound to the east of Seattle, intersecting with I-90 near Bellevue. It also connects to I-5 in two places: Lynnwood, approximately 20 miles north of Seattle, and Tukwila, approximately 12 miles south of Seattle.

Originally, the Washington State Legislature funded this project with an expected opening date in 2018. However, with approval to use revenues from the I-405 express toll lanes earlier, we were able to complete the project more than a year sooner than expected. What’s especially unique is that this was the first project to use toll revenue, making it the first reinvestment back into the corridor.

How do I use the lane?

As the name suggests, general-purpose traffic and buses are able to use the northbound right shoulder as an additional lane during times with the heaviest congestion—in this case, the weekday afternoon commute. That means there will effectively be three regular lanes and one express toll lane in this area.

The peak-use shoulder lane is generally open during the afternoon peak period but is dynamically controlled, so drivers need to make sure to check the overhead electronic signs before entering the lane.

A green arrow indicates that the lane is open, and a red “X” indicates that the lane is closed, similar to the signs also on I-5 near downtown Seattle. To learn more about what you might see on the signs, check out our previous blog on the subject.  

During off-peak hours and weekends, the shoulder remains closed so that crews still have space to perform maintenance and law enforcement and emergency services can use the shoulder as needed. 

As with all highway operations, our traffic management center actively monitors the shoulder lane. If there is a collision or incident, we are able to close the lane in order to allow emergency services to respond. There are also four paved emergency pullouts in the area of the peak-use shoulder lane.

Although this is the first electronically controlled shoulder lane of its kind on I-405, US 2 in Snohomish County also allows traffic on the shoulder between Everett and Snohomish during specific hours indicated on posted signs. For more information on other peak-use shoulder lanes in the growing Puget Sound region, check out the WSDOT congestion page.

Why did WSDOT add a lane in this area?

There have always been northbound bottlenecks at the SR 522 and SR 527 interchanges in Bothell because we simply don’t have enough lane capacity to handle the huge growth that south Snohomish County has been experiencing.

At the SR 527 interchange, an estimated 1,000 vehicles an hour enter northbound I-405 during the afternoon commute. For perspective, that’s roughly the equivalent of five, fully loaded, Washington State Jumbo Mark II Class ferries  (the largest in the fleet) emptying on to northbound I-405 from SR 527 every hour. The peak-use shoulder lane offers a new place for some of those vehicles to go without needing to merge right into the already crowded I-405 lanes.

After we opened the dual express toll lane in September 2015 between downtown Bellevue and SR 522, we found that traffic is flowing more smoothly just north of Bellevue through Kirkland, where we have five total lanes. But north of SR 522, where we did not add any new capacity and have only three lanes, we’re still seeing heavy traffic. (We’re looking at longer-term solutions for this area, more on that below.)

As a result, most trips between Bothell and Lynnwood on northbound I-405 are now slower during the afternoon commute than they were before express toll lanes. The peak-use shoulder lane is just one of several identified improvements that WSDOT has been able to make over the past year and a half based on driver feedback.

What’s next?

We are closely monitoring how the peak-use shoulder lane affects traffic and we know that this area of I-405 still needs more help. That’s why we’re continuing to look at how to fund and build additional improvements between SR 522 and I-5, including extending the second express toll lane farther north and improving the SR 522 and SR 527 interchanges to help traffic move more smoothly.

The Legislature gave us initial funding in the 2016 budget to study these improvements, and the Governor’s budget for next year includes $5 million more to continue our engineering.

Especially with Sound Transit planning to launch a new I-405 Bus Rapid Transit system from Lynnwood to Tukwila by 2024, we know it’s critical that we help keep traffic moving and provide travelers with a more reliable trip option.

In short, the peak-use shoulder lane isn’t the end of the road—it’s just the start of what we hope will be a series of big improvements for the north end of I-405.