LOUD freeways in Seattle!!!

May 8, 2012 7:06 PM

Seattle freeway pavement is rough and loud. Why?

Having jus driven across the country (well, half of it anyway) I now have verification of what I have long suspected: Seattle freeways are abnormally rough and loud. You can see the difference: it's easy to see the large pieces of aggregate rock in the concrete and the ruts cut into the lanes. Why is this so? Why do we have to put up with it?

My first thoughts were the roughness was caused by studded tires, and/or tolerated/created because the roughness increased traction. If that was the case I can't imagine only Seattle would do it and not Cle Elum, Coeur d'Alene, Bozeman, Livingston, Dickinson, Fargo, St Cloud or
Minneapolis. Also I race and quite often quiet pavement is sticky pavement. I'm tired of my ears ringing and having to drive up out of the ruts just to cut the noise!

Let's get to the bottom of this! Quiet pavement for the people!

posted by skybolt to travel & transportation around Seattle, WA (10 answers total)

More of it is cement vs asphalt? Cement lasts longer as I understand it, as long as salt is not a major factor. But cement is noisier.
posted by Tandem Affinity at 7:10 PM on May 8, 2012 [1 favorite]

Northbound I-5 between Tukwila and West Seattle is pretty loud, because it's old concrete that has been worn down in the tire tracks. As I change lanes it gets quieter. Is that the kind of thing you had in mind? Besides that area it seems quiet to me, but I hardly drive on anything besides I-5.
posted by Kwine at 7:20 PM on May 8, 2012

i seem to recall that rain-draining asphalt is somewhat louder... but i have no clue whether this is the reason in seattle.
posted by 3mendo at 7:23 PM on May 8, 2012 [1 favorite]

Could it be that the semis stick to the right hand lane. Virtually all of the road deterioration is due to their high wheel loadings, and poor suspension which exacerbates the problem. (Air suspension here is mandatory for higer vehicle mass limits for this reason.) You probably will see that the right hand lanes are generally the worst wherever you go, but some places may be worse than others.

How old is the road? Here some of the older concrete pavements have performed pretty badly, partly simply due to age, and partly to mistakes made and lessons that had to be learnt the hard way.
posted by GeeEmm at 7:33 PM on May 8, 2012

Maybe they use a higher proportion of coarse aggregate in the asphalt so that rainfall can drain away between the aggregate, reducing the risk of cars aquaplaning on flat 'sheets' of water?
posted by Flashman at 8:31 PM on May 8, 2012

Are you thinking of Seattle city limits or of the greater King County area? The freeway infrastructure inside the city of Seattle is in terrible shape due to budget cuts and staring matches with the state government. Two of the four major freeways are well overdue for critical overhauls (the 99 viaduct and the SR-520 bridge). These projects have been the source of years of legislative gridlock and have far reaching impacts on other stretches of these roads. Smaller upgrades, like the regular repaving seen elsewhere in Washington, fall by the wayside until road quality declines to critical levels.
posted by SakuraK at 8:46 PM on May 8, 2012

You can see the difference: it's easy to see the large pieces of aggregate rock in the concrete and the ruts cut into the lanes. Why is this so?

Concrete is a mixture of gravel, sand, cement and sometimes a few other things, and you can use different mixtures for different purposes. It's a lot like pastry dough, where different mixtures of flour and water and other ingredients gives you bread, cake and hard biscuits.

In Seattle's case, concrete is generally mixed with a lot of granite-based because a) it's locally abundant, and b) that formulation resists water better than other mixtures. I don't know if you've heard, but it rains a lot up here. ;-)

Also, when concrete wears over time under assault from water, the top layer of small, finer particles wash away, leaving the bigger, rockier pieces.
posted by Cool Papa Bell at 9:14 PM on May 8, 2012 [3 favorites]

Oh, and by the way, the Washington DOT has been mucking around with different "low noise" tests for a while now.
posted by Cool Papa Bell at 9:18 PM on May 8, 2012

US36 between Denver and Boulder gets the same kind of ruts from commuter and heavy traffic in the winter, but the pavement is a different composition and is a little bit quieter, although it's still noticeably louder than the newer roads where the surface hasn't been so badly eroded. I think studded tires do play a significant role in this because the left lane is often as deeply rutted as the right.

The utterly baffling thing to me is why Seattle drivers think they need studded tires at all, much less between November and April.
posted by hackwolf at 12:45 AM on May 9, 2012

when concrete wears over time under assault from water, the top layer of small, finer particles wash away, leaving the bigger, rockier pieces.

This is the answer: this, plus the fact that the ground hardly ever freezes here, so the road doesn't develop the potholes and cracks that would mandate its replacement before the top layer erodes. Also, a fair number of people go up into the mountains in the winter and leave studded tires on their vehicles all season, which doesn't help.
posted by kindall at 7:16 AM on May 9, 2012