Some of us remember that old potato chip ad.
To the point: I measured a course on a major road that had a 2-3 foot wide shoulder. Just outside the lane line (on the shoulder) the surface had been milled with a continuous series of inch deep depressions nearly a foot wide to create a "rumble strip" to alert sleepy or inattentive drivers that they are veering off the road.
There is no way anyone could run on this surface without seriously injuring themselves so I measured 20 cm off these depressions rather than the edge of the road. My feeling is they create a curb even if depressed rather than raised. Thoughts?