By Caitlin Morris
The problem—congestion on I-405 at SR 520
If you drive northbound on I-405 often, chances are you’ve run into traffic at the northbound I-405/SR 520 interchange, where drivers from both highways converge and traffic can back up. We’ve heard about it from drivers, and we’ve seen it ourselves. You’re frustrated and we want to fix it.
We’ve been looking for opportunities to improve traffic flow at this critical interchange. With the express toll lanes now open, we’ve had the chance to monitor traffic patterns and create plans that respond to drivers’ choices.
What we’ve seen
Many drivers entering the express toll lanes at SR 520 are coming from downtown Bellevue. While Northeast 6th Street provides a direct access into the express toll lanes from downtown, we are seeing that people are not always choosing this new option and instead they’re using the SR 520 access from Northeast 4th Street and Northeast 8th Street ramps. But as the name indicates, the SR 520 access point occurs right near the on-ramp from SR 520, meaning that a lot of cars are converging at the same point on the highway, creating the bottleneck.
Our goal is to open up this chokepoint, allowing more space for cars to flow. To do that, we need to get cars into the express toll lanes earlier and give vehicles from SR 520 more time and room to safely and easily merge onto the highway.
How we’ll improve access into the express toll lanes
Our plan to improve traffic flow has two components. First, crews will extend the SR 520 to northbound I-405 on-ramp by a half mile to give drivers more room and time to merge into the I-405 general purpose lanes. Second, crews will triple the length of the express toll lane access point at SR 520, extending it southward, allowing drivers from downtown Bellevue earlier access into the express toll lanes.
That means the access point will change from a weave lane to a skip stripe type of access. As you can see in the before and after diagrams, a weave lane has striping that acts like a cushion, allowing drivers space to merge in and out of the express toll lanes without holding up the drivers behind them.
A skip stripe is made of simple dashed lines that indicate it’s OK to enter and exit the express toll lanes. A longer skip stripe provides more access and more opportunity to find a gap in traffic when moving from slower to faster speeds.
These changes will allow drivers to access the express toll lanes sooner from Northeast 4th Street and Northeast 8th Street in downtown Bellevue. By the time express toll lane users reach SR 520, they’ll be out of the general purpose lanes, providing more space for the drivers entering I-405 from SR 520.
What to expect
Crews will make these changes Friday, March 18 through the morning of Sunday, March 20 with the following closures:
From 8:30 p.m. Friday, March 18 to 9 a.m. Saturday, March 19
- Up to four right lanes of northbound I-405 between Northeast 8th Street to Northeast 70th Place
- The SR 520 on-ramp to northbound I-405
- The Southeast and Northeast 8th Street to northbound I-405 on-ramps
- Up to three left lanes of northbound I-405 between Northeast 8th Street to Northeast 70th Place
Keep in mind that it may take drivers awhile to get used to the new striping. So be alert when you’re driving through the area as the road will look a little different. And remember, the bottleneck won’t disappear overnight; drivers will need time to adjust to the new configuration.
In case you love to access the express toll lanes via the Northeast 6th Street Direct Access ramp, don’t worry, the ramp won’t be affected by this work.
We’ve made changes along I-405 based on driver feedback and we’re looking forward to continuing the trend. So drop us a line. What other changes might help traffic flow? We’d love to continue the conversation.