Whay are there potholes where white lines were?

Factual Questions
1

Over the past few weeks I’ve noticed something strange on the highways. There are potholes where there should be the dotted white lines that divide lanes. These holes are exactly where the lines should be, and are the exact same shape and size.

Before I really thought about it, my primitive lizard brain figured that some road crew was digging up the old lines so they could install new ones. The pattern is almost regular enough to suggest a systematic removal of them. Almost. Some lines are still partially there, some are still all there, and some are more than 100% gone. And why would a road crew dig up old lines when it would be easier and cheaper to repaint?

So I figured there’s some property of the paint that creates the holes. But what could it be? I have yet to see hardware stores carry Magic Acid Asphalt-Destroying Paint, but maybe I haven’t been looking hard enough.

So there must be some process in laying down the lines that weakens the asphalt or allows more frost in or something.

What would cause this?

2

Sorry for the misspelling. The title should read:

Curds and Whey are there potholes where white lines were?

3

I do not know. My first thought is that you are imaging the effect. Alternatively, perhaps you are seeing the marks a grinder makes when it removes road markers and are mistaking them for potholes.

But, let us assume you are right. I would propose the road is too highly crowned and is improperly sealed. The middle of such a road would be too high. The paving material might allow water infiltration at that point. Water would get to the road bed and freeze. The freezing water expands, further weakening the surface which allows more water to come in and so on.

4

[url=http://www.boston.com/news/local/articles/2005/06/12/a_sinking_feeling_on_white_lines/]Here’s the Boston problem:

5

Fixed link

6

Let me describe the holes better.

Along the road there are white divider lines around 4 inches wide by maybe 6 feet long. (That’s an estimate.) But in some places, in the exact places you’d expect to see these lines, there are holes 4 inches wide by 6 feet long. In the exact shape of the divider lines and in the exact place you’d expect to see them. And the lines are clean, more often than not. They are not jagged and random, but almost look like someone deliberately dug them for the express purpose of taking the lines home.

The holes that are left behind are probably and inch or so deep, and consistantly so. It’s not a mere ginder mark, as there is a definite “thump” when you drive over them (by changing lanes).

So I’m not imagining it. These holes have very definitely replaced the lines.

I’d buy the ice explanation, but why would it happen only on the painted areas?

7

Ah, thanks, Elvis.
Looks like it may just be a statewide problem.

8

I should point out that the reader in Elvis’s cite mentioned seeing this on routes 24 and 93. That’s exactly where I saw it as well.

9

Many times a road crew will grind out old markings in preperation for shifting the lanes one way or the other. This doesn’t sound like that though. It could be the melting caused by thermo-plastic on popcorn but, having done ALOT of this type application in the past I can say I’ve never see it. Usually the marking wear better than the pavemant and it will end up as a slightly raised area. Both Paul and Elvis have made good points. It may be a localized problem as differing pavements and climate issues make for differing effects.

Just an aside for you. Your guess of the size is really good. The acutal size is 4" wide by 10 feet long. The gap between the lines is 30 feet. I’ve won alot of bets with this one. The 10/30 spacing (std. 40 foot cycle) is typical thoughout he US. I’ve heard most guess it to be 18" to 3 feet long and maybe 8 or 10 between. Cops often use them to estimate skid marks and such. Count the skips and multiply by 40. :slight_smile:

10

I’m willing to go with Elvis’s explanation, as it came from a spokesperson for the highway department. As we well know, spokespeople for government organizations tend to be founts of truth. :wink:

I’m a little surprised at the 10 foot length. I’ve looked at the lines on city streets and they seem to be closer to 6 feet. But maybe they differ from city to highway.

11

I dont travel on route 24 or 93 all that much, but I’ve definately noticed it on Rt 495.

I was thinking it was moisture as well, as the idea of hot paint seeping into the asphalt didn’t occur to me - but it makes perfect sense now.

12

Yep, there as well. Pretty much all the way from Bourne to Boston. I wonder if it’s statewide or just on the South Shore routes.

13

I-95 north of Boston is being repaved with popcorn-style asphalt. Don’t know how well it’s going to hold up over next winter yet, but I can confirm that the spray off of vehicles in front of you in heavy rain is much, much reduced.

14

I’d have thought (and did, when I read the OP) that perhaps the asphault wasn’t adhering to the previously applied marker line (located on the layer below).

Amazing that a marker, made of plastic or paint could dissolve asphalt!

ElvisL1ves isn’t it amazing that even with the reduced spray, it still doesn’t help 128 traffic on rainy days? :slight_smile: (Granted, nothing short of the plague could reduce car count there)

-Butler

15

I can offer a possible solution:

First, a long and boring introduction to paving methods. When paving roads, a paving machine has a limit of how wide it can pave. Usually, on two lane roads, the paver paves from the edge of travelled way to the center, and then goes back and paves the remaining half. On roads with more than two lanes, or on busy divided highways, the paving machine will pave one lane at a time. If you have never watched a paving job (and I’ve watched far too many :rolleyes: ): the trucks back up to the paving machine, and raise their truck bodies to dump hot mix into the hopper of the paving machine. They then move ahead in tandem (like some huge, noisy, smelly, copulating insect), the truck delivering mix into the paver, and the paver spreading the mix behind to a specified thickness. Big rollers follow the paving machine, compacting the mix as it cools. When the truck is empty, the truck pulls out of the way. The paver has enough mix to keep going until the next truck can back up. Once this operation gets going, the paver can cover quite a bit of ground in a short period of time.

The trouble here is that if the paver moves too far ahead, and/or if too much time elapses before the paver goes back to do the abutting lane, the pavement will have cooled substantially at the beginning of that “pull”. This creates what is called a “cold joint”. There are two types of paving joints; longitudinal joints (between lanes, follows the direction of traffic), and transverse joints (perpendicular to travel, usually where the paver ended for the day). Cold joints are undesirable, because the mix has cooled and compacted, and there is less chance for the new pavement to interlock with the previously placed pavement. Paving contractors usually have to balance the desire to just keep paving with the necessity of backtracking to keep a hot joint.

This can be a problem even in the two lane roads mentioned above, but is especially a problem where paving takes place on highways that are still in operation. As you might expect, the paver and the highway officials only want to take one lane out of commission at a time, so miles of pavement might be placed in a day (or night). The next day the next lane is placed, but the joint between has cooled and set, and there will always be a noticeable joint between. This can be helped a bit by soaking the cold edge with asphalt emulsion, and then spreading sand to help seal the edge, but a hot joint is still preferable.

As hinted above, night paving is now more common on the busier highways, but it also allows gaps in the pavement to go unnoticed.

Over time, especially in colder climates, water works its way into the joint between the lanes. Freeze/thaw creates the potholes.
plynck

16

Nope. National Standards require 10/30. The Manual on Uniform Traffic Control Devices (MUTCD) is the bible of traffic engineering throughout the Country.

Find a street that has no cars moving at the moment and pace one off. The thermo-plastic lines (you can visibly see the thickness at the edges) is more precise than a paint gun, especially with multiple re-paints. But it is 10 feet everywhere, and 30 feet between. When you are driving and see the Raised Pavement Markers (RPM’s) they are at regular spacing, at the end of the skip line or centered between them, they are at 40 ft. cycles. When your tire hits them you can count 40, 80, 120, 160 etc.
Plynck- Spend some time behind a loot rake or were you in another area of the paving process? As a line stripper I played “Follow the Paver” on many occasions myself.

17

That’s my suspicion as well.

18

Great info, but I’m not buying it. Cold joints probably account for a good bit of potholes, but unless the cold joints just so happen to be exactly 4*120 inches, with a 30 foot gap between each, it wouldn’t account for what I’ve seen.

19

OK, well, the popcorn pavement suggestion makes the most sense, but this gave me an idea… you don’t suppose they could make the lane divider lines slightly raised or lowered to get a sort of “Hey stupid!” bump to remind the driver to get back in his lane?

20

I’m happy not to know. I have a reverse commute that doesn’t involve 128 at all. :slight_smile:

Thanks for the info, Plynck.