It’s a traffic tweener: The southbound I-5 collector distributor and you

By Bart Treece

So this weekend, we’re closing lanes on a section of southbound I-5 that’s not quite part of the highway, and not quite a ramp.

The formal name of this thing is the southbound Interstate 5 collector-distributor, and it’s tough to come up with a name that resonates well with folks who aren’t traffic geeks. So what is a collector distributor and how will this affect you this weekend? Good question.  Let’s define collector distributor first. It’s kind of a traffic tweener, meaning it serves many purposes.  This stretch of roadway runs parallel to I-5, and most drivers will recognize it as the southbound I-5 exit to I-90 and the International District. It also connects Spring and James Street on-ramps to southbound I-5, and gives drivers an option to head east to I-90.

Here’s how it works. This animation shows three cars heading south, with the green car peeling off to Airport Way the red car to I-90. The blue car continues south and winds up back on I-5.

Our resident traffic geeks love the collector-distributor as a way to bypass mainline congestion and maximize available roadway. Some folks might be timid to try this (and due to construction this weekend it wouldn’t be a good idea to try it until Monday), because they see the sign and think they’ll end up on Mercer Island instead of points south of downtown. Taking the collector-distributor is totally legal, except for places where it isn’t, like I-405 at NE 85th Street in Kirkland, or anywhere else that is signed exit only. Even the sign on I-405 says it’s verboten, and you could get a ticket.

Back to this weekend, here’s how traffic will move through the construction zone. If this red car is you, don’t let the orange construction stuff scare you, you will still be able to get to I-90 from I-5.

Here’s the details

All but a single lane on the southbound I-5 collector-distributor will close at 10 p.m. Friday, Feb. 21 until 5 a.m. Monday, Feb. 24. At the same time, the on-ramps from Spring and James streets to southbound I-5 will also close. Need to take a downtown ramp to I-90? Try 4th Avenue South and hop on near the Stadiums. There will be marked detours on surface streets in Seattle.

More weekend closure information can be found on our What’s Happening Now page.