I noticed what looked like a side walk in the ditch in between the freeway. It repeated for a few miles. At the ends of the sidewalk were small gray slated boxes about 6” or so. The length of the sidewalks were from about .2 miles up to about a mile or so. Construction crews were building more. What are these for?
Some cable run, but this is probably country specific
But the routes are an easy way to follow if things like fibre optic have to be added.
It could always be improving or adding a traffic information system - the one that warns you of a traffic jam just after you joined it...