Construction crews on the expressway near where I live have been working on the road surface for the past week or so. What they’re doing is sawing “slots” in the road surface, perhaps two inches wide and twelve inches long, parallel to the direction of traffic flow. These slots come in groups of three, about eight inches apart. There are three or four groups of three in each lane, in a line like so:
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(only farther apart) all the way across the highway. These groupings are repeated every thirty feet or so down the length of the highway.
Now, once these slots are cut in the road, they’re then filled back in with concrete. I’ve also noticed them on other highways, and my question is: What the heck are they there for? Nothing I can think of (weather-related? utilities? traffic sensors?) makes any sense.
Zut, I believe they’re grading the area in question for repair.
Say an area gets damaged. Instead of just piling on more concrete, they grade it down a bit to repair it. It yields a nice, level(mostly), repair area.
Also by grading, I’d imagine they’d be able to remove some inherent flaws in that section of road and then repair it.
No, no, I think you misunderstood me (damn, I knew this was gonna be hard to explain). They’re not grading the entire surface (which I’ve seen before), but they’re actually cutting, with a saw, small individual slots, about two inches wide by twelve inches long. These slots are spaced in a regular pattern, and it’s important to note that the remaining 99.9% of the road surface is untouched.
It’s pretty pathetic to be the author of 3/4 of the posts in one thread, but I thought I should add that this is in the Detroit area. Perhaps this phenomenon is something that’s specific to this area? Has anyone else seen these slots in other areas?
MassHighway did the same thing on Rte 44 in the Taunton/Lakeville/Middleboro area a year or two ago. They also cut a 1/2" grove perpendicularly across the entire road every 50 feet, only to seal the groves back up. Makes your car go “thumpthumpthump” as you drive. Very irritating, might I say.
I won’t go into my usual rant about MassHighway…that “Big Dig” crap has me all in a tizzy.
It’s the same effect as roughing up a surface to be painted. The concrete or asphalt adheres better to a rough, uneven surface (think about it for a minute). Why the grooves are parallel rather than perpendicular to the traffic, I don’t know. Maybe it’s less irritating to drive on while the spot is being repaired.
No, I don’t think so kunilou. The slots are small and precise and only 12" long, not covering the entire road surface. In fact, 99.9% of the road surface is untouched. Plus, after the workers cut the slots, they immediately fill them back in, without paving the whole road at all.
You cut the slots so that the concrete slab that makes up the roadway can expand and contract from changes in temperature without cracking the entire slab.
You fill up the slots with newly poured concrete that that moisture won’t have easy access to the innards of the concrete slab, thus causing more erosion.
The fill in the slots is essentially sacrificial - it will be beaten up by the slab expanding and contracting around it. In a few years, you replace the fill.
Is there anything special about the places where they are installed? If they are at inclines and curves, maybe they are speed bumps for slowing down cars. You say the slots are 8 inches apart - it’s just close enough that you can’t pass without driving over one of them. In Japan, downhill slopes on major highways have bumpy surfaces - not exactly the kind you described, but the purpose may be the same.
I don’t think they are for absorbing thermal expansion - for that you need a slot going all the way across the road. It also doesn’t make sense to have to cut slots after the road is completed - concrete roads are built with expansion joints, and asphalt is flexible enough not to need them.
Perhaps it’s a variation of “rumble strips,” those slots – similar to what you’ve described – in the roadbed that run along the shoulder to alert a driver he/she is drifting off the straight and narrow (they make your wheels “hum” as you drive over them). Very, very ingenious and effective.
I notice they’ve also begun using “rumble (…shall we say…) patches” right in the middle of the roads to warn drivers to slow down 'cause a toll booth is coming.
Now here’s my theory: maybe your average “rumble patch” has a very short lifespan because it is engraved in a soft, plastic medium (asphalt, tar, macadam, blacktop… whatever it is) and it gets rolled over constantly, hence it flattens out to a “no-rumble patch.” So they embed the concrete (ummm…) ingots which won’t flatten out; the asphalt squishes low into the “valleys” between these concrete ingots and the rumble patch will live forever.
C’mon, you say, what “mountains”? The concrete is level with the roadbed! Maybe it only appears so. I’ve driven over some very effective “rumble patches” that are nothing more than thick traffic PAINT stripes across the roadbed… so it doesn’t take much height to work.
One theory no one has tried yet is that perhaps they are testing a new road surface or paving method. There are all kinds of crazy ways different highways are paved, and in the U.S. they all seem to suck. Now, say you have a new method you want to try. What follows is a TOTAL wag, but the spirit of the idea is what I am getting at:
Say you want a highway with the durability of concrete and the give of asphault (concrete roads last longer, but provide a less smooth ride). Or perhaps you have divised a way of impregnating an asphault road with concrete so as to allow it to expand and contract better and thus minimize frost-heave/pot-hole cycles. Or any of another of a multitude of inovations. Eventually, you have to test this road surfacing system in a real world condition. So you pick a few different environments. Suburban Southeastern Massachusetts gives you one set of traffic conditions, Urban Detroit goves you another. Mayber there’s a patch of highway on I-15 in the Nevada Desert with the same thing on it. So you test it for a year or two of driving conditions, and check back again to see what it looks like.
So my two cents is that they may be testing a new paving system or something like it, and seeing what will happen to it.
Well, some good guesses, but I don’t think any of 'em quite jibe.
I don’t think the slots are expansion joints for the same reason scr4 gives.
I don’t think the slots are speed bumps, because a) they’re everywhere, not just at curves, and b) they’re filled back in completely level with the original road surface, so they’re not a bump.
I don’t think the slots are rumble strips because a) they’re filled in level with concrete (in a concrete roadway, not asphalt), so your car doesn’t “rumble”, b) they’re in the lanes, as well as being on the shoulder, and c) the slots are parallel with the traffic flow, not perpendicular, as rumble strips are.
I don’t think the slots are test coupons of concrete, because they’re so small. It seems like you’d need larger pieces to adequately test a new surface. Unless, jayron, you’re saying that cutting and filling slots is the new paving method? That’s plausible, maybe, but I can’t for the life of me think of any reason why that would be a good idea, particularly since, by cutting into the roadway, you’re introducing a weak spot.
Are they, perhaps, just checking the existing concrete. Say they laid down some new type orconcrete a year or two ago, perhaps these grooves allow them to take a look at the interior of the slab without ripping a whole section out. Erverything’s ok? Fill it right back up!
Did you notice whether or not the strips could be connected by a narrow groove running across the freeway? If so, they could be sensors to monitor the speed and number of cars on the freeway. Even witout a connecting groove, they could have a wireless setup, possibly powered by the car pressing on the slots themselves. Do you know whether they are puting something in the slots before filling them with concrete?
I agree that expansion joints, rumble strips, speed bumps, or test coupons don’t make sense.
Oho, a local, I see by your profile. What got me started wondering is the current work being done on the Lodge (M-10) in Detroit just north of I94. However, I’ve noticed filled-in slots on M-14 east of Ann Arbor (I go home that way, so I can look tonight and tell you exactly where), and I think I remember, on I75 south of Detroit and on I96 in Detroit.
As for the rest of your questions, there’s no connecting groove that I can see, and I don’t know if anything is going into the slots. Your guess of traffic sensors was the best that I could come up with, but, man, there are a lot of slots in the highway.
And, Gazoo, I don’t think the slots are inspection holes, because there are so many of them.
I notice that in UK and now here in Iowa someone has painted white rectangles maybe a foot by two feet on the road. These appear about 2 to a lane and no specific distance apart. Could it be some sort of aerial mapping method? Regarding the slots I suppose the sound of tyres hitting something with a piezo crystal underneath could generate enough electricity to run a self powered sensor array of some kind. Since the entire world seems to be suffering from information gathering addiction lately I would think some sort of census might explain both?
It’s not just Michigan. I see them out here a lot, too. (The legal definition of “here” left intentionally blank - but it’s far away) In fact, I see them often enough that the only explanation that will make sense to me is some sort of regular maintenence. They’re always cutting up the roads for some reason.
Maybe one of the workers lost his car keys somewhere around there when they were first building the road?
Here’s an idea. Get up early one day and drive out to the site and park somewhere and amble over to the workmen, maybe even bring a box of donuts if they look gruff, and get the, ahem, Straight Dope.