Why does asphalt crack along painted lines? My elementary school playground was made of asphalt and had a track painted on with white lines. While walking on the track, I noticed that cracks in the asphalt often followed the paint.
The conclusion I came to and that I still hold is that the white tape on the black asphalt causes a temperature difference due to the different amounts of sunlight absorbed and that this difference accounts for the cracking.
Is this correct? Is there more to the story?
 A: I don't know what is going on with your playground, but I do know what caused a similar problem elsewhere.
Over the last decade or so, the pavement of Interstate 495 northwest of Boston was wearing out quickly under the dashed white stripes used to delineate lanes.  For a while it seemed like it could be coincidence, but then it became obvious something was degrading the pavement just under the stripes.
It turns out that the contractor that did the last repaving used the wrong paint.  Apparently there are two predominant types of roadway paint, one for concrete and one for asphalt.  They used the concrete paint on asphalt, which contains a solvent that seeped a bit into the asphalt and degraded it.  The solvent was long gone by the time the problems appeared, but the degradation due to the weakened asphalt under where this paint was applied continued.
Many many asphalt roadways have had white paint applied, so we know it is possible to do this without any apparent harm.  If differential thermal expansion was a problem, then we should see it in lots more places, given the very large number of test cases for this experiment.
A: It's usually caused from the paint being laid too thick (especially oil based paints) and when the paint dries it shrinks pulling itself to the centre of the line. Because the paint has such a good hold of the asphalt it pulls the asphalt as well causing the crack. Most line markers now use a water based paint.   
A: I would say it is caused by a varying temperature difference between the heat absorbing asphalt and the cooler reflecting white.
