Thursday, February 20, 2014

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.


Neil said...

Speaking of the CD on 405 in Kirkland... what was the reason behind making it not really a lane for people already on 405? It didn't open that way and I was sad when the big signs went up :( Thanks!

The Geezer said...

Bart writes---Taking the collector-distributor is totally legal, except for places where it isn’t, like northbound I-405 at NE 85th Street in Kirkland. Even the sign on I-405 says it’s verboten, and you could get a ticket.

But does not mention WHY it is signed that way at this loocation. Because WSDOT is so full of themselves to not deisgn this right in the first place. I ued to drive this going home several years ago, and it was faster to take the CD, wade through a merge and a lane control signal, than it was to stay in the main line.

But thank heavens, they turned bad engineering into a cash generation opportunity. Why can you get by faster, getting off, rather than staying in a multiple lane main line? Huh, spinmeisters?

Other than that, nice job, Treece.

The Geezer said...


Because the nanny state knows best. Worked fine for years, and the CD was much faster based on my many trips home from work.

But, remember, WSDOT 5 goals does NOT include congestion relief!!!!!! Affixing my tinfoil hat to my few remaining hairs, I would argue that it is part of a grand scheme to beat the sheeples down to get them to accept more tolling for additional lanes, and only use highway money to build more mosquito breeding ponds.

The Geezer as he often does, has spaketh.

WSDOT said...

The added signs at NE 85th were posted because there had been a problem with folks taking the exit (even though it is signed as an exit) and not getting off the highway. In the case of I-5, only the right lane southbound is marked exit, and it actually benefits traffic to have vehicles use the collector-distributor to balance demand during congested periods. With NE 85th, there’s just not enough room to let folks use it as a bypass with the on and off-ramps.

The Geezer said...

Not at all true, anonymous WSDOT.

You old enough to remember when it was not so signed? You note that it functioned just fine, with folks using it to not get off?

There is plenty of room to "balance" as you say.

If you are so smart, tell me why it was built so that staying in the through lanes takes MORE time, than getting off, then back on.

Answer: you can't. There is no room issue, save for WSDOT's pants, which they think are big enough to tell the sheeples what is best for them.

And use your name, rather than the anonymous handle WSDOT, so we know who to blame.

Geezer, being unusually cranky this ayem.

Anonymous said...

Shorter Geezer: Blah, blah, blah. Hey you kids! Get off my lawn!

Andrew A said...

This post was very helpful, WSDOT; thanks! I had never considered using that lane to avoid congestion.

Neil said...

Thanks for the explanation of the Kirkland situation. I kinda figured that was the reason.

The Geezer said...

WSDOT gave a non-explanation on the issue. Just more gub'mint "we know what is best for you" blather. And anon, while your post was funny, I do tell kids to get off my lawn right after I apply weed killer for their protection.

That aside, I discovered the C/D was faster by sitting in the mainline each day watching and counting cars, and determined that folks getting off were ending up ahead. Plus, I get on at 70th, and the merge to get out of the "drop" lane is difficult.

Please use your own observational abilities to understand what is at work here. And WSDOT, it was certain members of the Kirkland City Council that suggested the signage, has nothing to do with freeways or safety, just some pols swinging it around and in effect saying, "hey, kids, get off my lawn".

The Geezer, in his perfect wisdom, has opined. You are welcome.

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