Scott Nazelrod
Like New York, ODOT posts green reference markers throughout the highway system, conveying information important to the DOT workers tasked with maintaining the roads, useless to anyone else, and generally puzzling roadgeeks. In New York, these reference markers often provide insight into highway history, allowing for the discovery of previously unknown routes by virture of the markers typically being left in place when a route is decommissioned. Or else kicked into the weeds.
The New York reference markers are useful to roadgeeks mostly because the top line of the markers contains the route number of the highway they reside upon. Not so for Oklahoma ref markers. Sorry. But I have at least managed to decipher what the Sooner State's markers mean, just in case you were wondering. And you were, right?
The most common type of reference marker is found attached to the back of stop signs lining the highway. (That is, the stop sign faces down the cross street that must give way to the highway, while the reference marker is mounted on the back, facing the highway. These signs are green with white text, and are about as tall as the stop sign they are attached to. Not all stop signs have these, for unknown reasons, though it may be for cost reasons or simply because they sometimes fall off and are never replaced.
Another type of reference marker is a small size version, about the size of New York's. These are typically placed just before bridges or culverts, either on a small post behind the guardrail, or underneath the sign stating the name of the feature crossed. These also occasionally appear on large, two-pole stop signs and on other various places.
Oklahoma's reference markers revolve around the concept of the "control section". It seems logical that since two of the three lines of the marker refer to the control section explicitly, and the top line is necessary to further identify the section, the reference markers are placed primarily for workers in the field to determine what control section they happen to be visiting at the time.
Therefore, an understanding of what a control section is, exactly, is necessary for understanding the markers. ODOT isn't exactly helpful in explaining what they are for, however, but they do at least have PDF maps of all 77 counties on their website, complete with the control sections illustrated in color. A book containing all these maps is also available from the ODOT print shop for $13.15. So until an ODOT guy actually confirms what these are about, we can use these resources to at least hypothesize about what their use may be. With the lack of a comprehensive mileposting system (at least not one posted in the field), control sections are likely used as an internal inventory scheme by ODOT; they are probably used to express positions on the highway system for work orders and contracts. Thus the reference markers would be vital to identifying locations where work is to be performed.
Control sections break highways into smaller, presumably more manageable chunks. There is always a boundary between control sections at county lines. Most of the time, an intersection between highways will result in a new control section for one or the other or both. (It would appear that this depends on traffic control—at a four-way stop, both highways would get a new control section going forward, but if one highway stops for the other, the highway with the right-of-way remains on the same control section. One would presume that if access control were changed at an intersection, the control sections would remain the same for accounting purposes.) Concurrencies may or may not result in new control sections, generally the "through" route seems to remain on one control section, with the other route ending its control section at the start of the concurrency, and after the highways depart in their own separate directions, the "non-through" route gets a new control section.
It makes a lot more sense looking at the maps, trust me.
The ODOT website at least shows us how control sections are numbered. It gives the example of 77-42-02, and explains this as the first number being the route number, the second number being the county code, and the third number being the control number. (The county code is the number assigned to all counties alphabetically, ranging from 1 for Adair County to 77 for Woodward County. They're listed on the counties and towns page of my website. If you live in Oklahoma, this number also appears on the back of your driver's license.) The route number in this case is only present for reference; it is not 100% true to the actual route numbering decause of the way concurrencies are handled. The county code is necessary to positively identify the control number, as they are only unique within each county and are duplicated in other counties.
Routes that have yet to be built, but have been surveyed, are also assigned control sections. These "projected and surveyed" sections are assigned a route number of "P&S" but are otherwise labeled identically to normal control sections.
Lengths of each control section are supplied in the control section map, in miles and kilometers. Each is listed to two decimal places. Unfortunately, these mileages are generally unusable for roadgeeks, as the roadgeek's need to calculate the length of a highway or the milepost of some point on it is incompatible with these numbers, since they do not follow the highway numbering. (For highways with no concurrencies, especially shorter ones, one can indeed calculate the length of a highway by totaling all of the control section mileages, however this is not often possible, as the vast majority of routes in Oklahoma concur with something else along their route.)
The control section maps do fulfull one incredibly useful role to the roadgeek—they are the final "word of God" on what is and what isn't part of the state highway system. All routes, even unsigned and unnumbered routes, are assigned control section numbers. So through this book we can conclude that SH-35 is still in existence, unsigned, along with SH-135. More interesting is the presence of unnumbered routes, which are of course by necessity unsigned, including the Duncan Bypass, a spur into Langston, and Lincoln Blvd. in Oklahoma City. (Lincoln was quite amusing to see on the map, as it was for a time labeled as State Highway 00—I'm sure every roadgeek wishes that would have been accidentally signed in the field!)
The control section book is also useful for reconciling occasions where the signs in the field say one thing and the official state map says another. Using the book, we can determine that SH-87 does indeed end where the signs say they do, and not in Idabel like the state map says, and also that SH-14 continues into Alva along US-64 for no apparent reason like the map says, and not ending at US-64 like the signage indicates.
Now that you know what control sections are, deciphering the markers is the easy part. The top line is the county code number. The middle line is the control number, and the bottom line is the mileage since the beginning of the control section. So, if you have a marker like the example one at the top of the page, you would be in County 44 (McClain County), on control section 42, at 11.30 miles since the beginning of the control section.