Stationing Coordinates 000+00

[Dirt Roads]

From the "Good, Bad and Ugly" thread:

Dumb question: I've seen survey stationing numbers on structures like bridges; do these correspond to the coordinates of the marker (and thus the structure) or something else entirely?

Noelbotevera, the station refers to the location of the marker along the alignment, which is relative to the highway, but does not give you absolute coordinates, you would have to figure those out using the definition of the alignment.

To the best of my current knowledge, station numbers are not absolute numbers. They're not related to real coordinates. They're used for laying out a linear build, such as a road, and the first number represents 100 feet. To answer your question, they are just relative to whatever the plans define the initial station (0 + 00 or 1 + 00) to be.

Someone who knows more, please feel free to correct me or add on.

JoePCool14, you are correct in general, though of course the alignment is "related" in a way to coordinates since it must have a location on the coordinate grid in order to be surveyed! However, I have experience working with WSDOT, and it would seem that they define permanent alignments with stationing for each highway that carry forward beyond individual projects, which is probably why they bothered putting stationing on an actual sign (with hundredths of a foot, no less!).

My world crossed over onto roads and highways sometimes, and I've found that many civil engineers use fictitious stationing that overlay onto the existing roadway.  Take grade crossings, for instance.  Oftentimes, if we need to change the elevation and/or slope of the road when plowing new trackage, the highway designers will start at 00+00.00 at the work limits "south" of the crossing with the stationing placed down the centerline of the roadway.  Because of weird quirks with pavement width inside the crossing panel, plus additional pavement for crosswalks, the centerline of the roadway might not be where we would expect).  However, sometimes local highway departments would request that the numbers be revised to reflect their own stationing system used on that piece of highway.  If our guys were on the ball, they would convince the locals to wait until the as-builts were released.

So it's my impression that some highways actually do have "real" stationing numbers.  Somewhere, I recall county lines posted with recalculated stationing on the sign post in the direction of increasing stations.  And there are all sorts of places where you'll find permanent field signs with station forward/backward numbers to mark where the numbering changes.

On most railroads and rail transit projects, the stationing numbers are the primary means of geographic measurements and need to be carefully maintained (particular since track can move laterally and sometimes longitudinally).  Each track gets its own stationing, oftentimes on a different coordinate system.  On most of the rail transit projects I've been on, one track will start at 1000+00 and the other track at 2000+00 (some systems got 10 000+00 and 20 000+00).  Once upon a time, we didn't worry about absolute precision but now that most of the track laying and track maintenance is fully automated, we get into the hundredths as well).

Even the advent of GIS coordinates has its quirks.  Due to the curvature of the earth, none of the "GIS grids" are truly square and lengthy highway projects that criss-cross the corners of the grid get messed up as the approach those boundary lines.  Most rail transit project would assign fictitious "GIS grids" that cover the entire project, thereby avoiding the issue.  The few rail transit projects that I've seen deal with this just assigned different GIS grid coordinates (forward/backward) that were associated with official stationing.  Anybody here have any idea how most DOTs handle this?