Ah, interesting. Thanks for the input!

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.

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.

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.

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.