Who knows .......

....... what these blue and green dots are on the railing and bridge on the motorway in south France, between Bordeaux and Bayonne?

The blue dots are always on the railing before, under and after the bridge. The green dots are on the bridge itself.

We only saw them on this stretch of the road, never on any other motorway.

 

That is strange. First thing came to my mind was, some kinda traffic game, and how to keep score.

 

Na, I seriously doubt that redstar.

Perhaps I should have said that they were on and under all of the bridges along this stretch of the motorway.