I don't think thats what they mean Naz. I think you are referring to 'node points' which are usually a pair of square or round 4" marks in the centre of the lane...sometimes they are steel road studs. They delineate areas of road for road works and maintenance. Contrary to popular belief, they are nothing to do with distance marks for use by the Police to catch speeders.
Ah, I thought the OP was referring to the painted shapes - squares, circles, triangles - that correspond with the usual signage dictating emergency routes.
you were talking about 4 inch studs above, not sure if we are discussing the same things here. sddsdean. Plod needs some sort of marker for vascar, high/low tech doesn't come into it.