Multiple incidents of people running into the back of stopped or slowed traffic on interstate in the last few years. You might be correct, the drivers must be gazing into the skies searching for an aircraft.I can't speak to the marker you mention and showed, but in some other states, they put markings on highways to "calibrate or certify" equipment that is surveying their road and pavement conditions.
Years ago, there were some states that simply had a white line (roughly 8 inches wide) across the paved shoulder. (Texas comes to mind.) It could have been for aircraft to use to get a driver's speed. If I remember right, there would be something like 6 marks in a mile, which would allow an observer in a plane to "verify" a previously observed speed. However, those markings weren't on each and every mile, so I don't see how effective they would be. A pilot would have to keep circling to see those lines and that would be a give-away to wary drivers.