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billionair31 t1_j3m69mt wrote

Fyi, If I'm remembering the area your talking about correctly, those "lines" across the highway from Seattle to Tacoma are expansion joints. The road there is made of panels of concrete, not asphalt. If the road didn't have gaps then in the summer the road would expand and buckle.


Yuppykiller t1_j3mygbg wrote

Understand expansion joints, but I assume OP was referring to those dashed groves in some lanes themselves, not between the lanes; they appear to be ground down a 1/4 - 1/2 inch from surface and are right where your tires go…I end up straddling the lane line when there is no other traffic just to stop the sound.


billionair31 t1_j3n25pc wrote

Definitely possible, I'm not super familiar with that area, as such I'm not exactly sure what it is you're describing. I just know a concrete panel section of highway is through there.


Yuppykiller t1_j3n5n9h wrote

You know, upon closer look these are ground down perpendicular to some expansion joints. Not all, and some locations have more than others. Some lanes don’t have them at all. Any ideas?

Thanks Google Street View!


billionair31 t1_j3nxnj2 wrote

Interesting, I really have no experience with concrete slab roadway design, so my ideas aren't "good" but any means, but I'm willing to guess!

My guess is it's from a repair where they ground into the slap, fixed something (rebar?) And then filled it back up.

A secondary guess would be something to do with drainage. Perhaps those spots get a little sitting water in the center so they create a little more space for it to sit as it drains, where it is less dangerous for drivers.


Grndmasterflash t1_j3pphxx wrote

My understanding is when a road has those little rectangular "divots", there are tensioning cables within the concrete, not to be confused with common rebar. I think it was supposed to be the cat's meow a decade ago, but turned out not to be a efficient as hoped.


KanyeWaste69 OP t1_j3matqw wrote

ohh that make sense, I swear wsdot never stops talking about expansion joints, yet only now im finding out what they are


I remember in June 2021 parts of the asphalt sections did buckle during that awful heatwave


Librekrieger t1_j3nkrpb wrote

But the traffic is so heavy there, and something was wrong with either the design of the joints or the way the concrete work was done. The ruts in the concrete over time created a massive transition that just hammers the suspension.

Los Angeles has used concrete for decades and generally does not have this problem. Whatever LA did, Seattle and WSDOT didn't. If it's fixed now, here's hoping the fix works long term.


billionair31 t1_j3o3did wrote

I don't do concrete roadway design, but there are a lot of factors that could cause issues that LA doesn't have. I'm fading could because I really don't know what went into the design in either location.

The concrete mix design is one thing that is pretty much impossible to comment on without seeing the original design, but could be a big factor in how the concrete holds up.

But most likely either the weather or the soil supporting the roadway is likely the largest factor in the longevity of the road. (Obviously the real answer is a combination of many factors)

LA doesn't get the same wet and freezing cycles that Seattle does (though they get way more direct sun and heat) and that can be really cause issues for roads. You'd have to ask a geotech because I don't know what the soil is like down there, but the Puget Sound region has a lot clay and silt deposits from the glaciers.

But things like that are why you can't just copy and paste a road design project anywhere in the country, or even the same county really.