Station 5 is a point in the project. Stations are/were set up as a straight line. Now this could be the center line, or one of the outside lines. Or it could be that they started some where and were going to another project down the way and this was just a intermediate point.
It looks like they are measuring the surface distance along the route. STA stands for Station and each station is 100 feet (one full tape in length). Your marker is 500 ft from the starting point STA 0+00.
Why they are measuring the distance is only going to be determined by asking.
Finally, a question I think I can answer with some authority. But I am not a surveyor so my answer will be incomplete. (But I will add you really are wasting time by having loaded such large photos. I have dial up and it was slow.) But hear my answer please.
Survey1.jpg is telling the road crew that this is Station 5. Probably of the BL or baseline of the road. Sometime BL's are confused with CL's or centerlines that can be found in or near the center of the road.
Survey2.jpg shows the center of the road and the station mark.
It is hard to tell what the surveyors were doing by looking at one point. If the road department was considering changing the road, you might see such markings every fifty feet or if metric every 100 meters. Are there any other markings and what about colors?
Maybe a surveyor was surveying a residential lot that was recently sold? They would need to find a spot that was well known and proceed along until they found the first course point of the lot. I can see them starting in the road for reference. Today's surveyors use GPS technology, but they still need to mark the points either with a nail or just paint. The nail has more permanence. That's my non-surveyor answer for now.
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