I’ve noticed this before, but I saw some really obvious examples of this driving today. The asphalt on the road was obviously cracked underneath the old dashed lane stripes. The pattern of cracks followed a dashed pattern just like the original paint.
Any ideas what would cause this?
Perhaps the pigment resulted in different rates of temperature change through differing levels of absorption of sunlight or simply by acting as a physical barrier that retarded temperature changes.
It might be nothing more than that the striping is applied over the seams in the asphalt - most multi-lane roads are laid down in lane-wide swaths.
There’s also the fact that nobody drives on the stripes. All the stress is on either side of them, so the seam in between is where it’s going to buckle.
I’d say this observation points to the paint somehow. Is it paint, or that rubberized stuff?
I’m with this dude/dudette.
I don’t think this is what I saw.
The cracks clearly followed a dashed pattern, not one continuous or irregular series. When I was driving by, it was pretty clear where the old paint had been. I’ll take a photo if I remember tomorrow.
It could be that the cracks are just more visible in the painted portions. If you’re driving. it’s not like you’re getting a clear look at the unpainted sections.
There’s also a possibility that only the paint was cracked (i.e not the actual asphalt).
Asphalt is not rock hard like concrete. It is essentially sand and gravel, held together with tar. It can normally move around some without cracking. What probably is happening is that the asphalt is settling a little bit, maybe expanding and contracting with the heat. The painted lines are holding a big chuck of asphalt together, not allowing it to move with the rest.
dark asphalt heats and cools at a very different rate than white paint on the asphalt.
heat causes expansion, so you have parts of the asphalt under the paint expanding and contracting less than the unpainted asphalt. Hence, eventual cracking.
Civil Engineer here.
The lines are likely not paint, but thermoplastic. It is pretty much molten plastic that is placed on the road surface. The temperatures are over 400 degrees F and the thermoplastic actually melts the top of the asphalt to create a good bond. This heat can stress the asphalt. It is not uncommon for the top layer of asphalt to eventually delaminate from the underlying layer near the lines especially if the top is an Open Graded Friction Course (often called popcorn mix). The thermoplastic lines can last much longer than paint in most instances and that is why it is sometimes used.
Now I need to know if I am crazy. I ride a bicycle regularly and, in my experience, riding on the painted (or plastic) line is the smoothest and least cracked portion of the road. Not the safest, because it puts you too close to the cars, but, if there is no traffic, the line has always been the least cracked portion of the road. Anyone else have this experience?
Here is an example of a street without lane markers but a big tarred crack down the middle. The asphalt on this street was laid down around 1980ish and never had lane markers at any time (it was a nice and smooth street when I was growing up on it) 
This perhaps would suggest cracks have little to do with whether the “paint” is laid down or not…
But that’s not the pattern of cracking described by the OP. He’s talking about cracks that closely follow the faded paint. The linked picture shows a continuous crack down the middle of the street.
OK, I stuck my camera out the window as I was driving, and took this photo.
It’s not the greatest, but you can see what I’m talking about, especially towards the top of the photo.
Notice how the cracks follow the old dashed lane stripes?
Were the old stripes removed? I mean, as opposed to just fading away. Perhaps the removal method caused the cracking.
I don’t think so - I don’t see evidence of grinding, which is usually how old stripes are removed.
Here sometimes they use heat. Some kind of torch, I think. That made me wonder if, as jeffgorc mentioned about the application of thermal plastics, the heat removal tool caused some stress.
Wait a minute - in your OP, you said that the street was cracked “underneath the old stripes.” And the responses were directed to that description. But your picture shows them adjacent to the stripes - an entirely different situation. Can you clarify exactly what your question is with reference to the picture you posted?
Those ARE the old stripes.
You can see the old paint as it’s whizzing past my truck at the bottom of the photo.