Chapter Three Criteria
Home Chapter One Introduction Chapter Two Threats Chapter Three Criteria Chapter Four Ranking Chapter Five Management References Cited




In the Introduction to this study we note that the Scope of Work requires us to develop a set of criteria that allows us to sort road segments and integral structures into a three-tiered “triage” system.  This ranking will provide those responsible for these resources with a tool to prioritize maintenance and repair needs for these historic resources.  Only the 45 segments and integral structures already listed or eligible for National Register Nomination provided by the Oklahoma State Historic Preservation Office are to be included in the system outlined in this chapter.  It should be noted, however, that the team developed this system so that it could be used to sort or triage other roadbed and related resources along Route 66 in Oklahoma as they are found to be eligible. 

            Table Three outlines a three tiered classification system in which historic properties under consideration in this study can be placed in one of three categories; Immediately Threatened, Moderately Threatened, or Least Threatened.  To the right of each one of these categories are a set of criteria that when applied to a resource will assist in the classification.  As the reader examines the criteria s/he will note that these take into account the threats outlined in the previous chapter. 


Table Three. Three-tiered Classification System 


Resources in this category exhibit the following characteristics:

Immediately Threatened

        1)      Experience heavy traffic volume.

2)      Resource (including roadway paving and bridge decking) is experiencing structural deterioration.

3)      Appear to have very little maintenance, which contributes to the destruction or deterioration of the resource.

4)      Unsympathetic Maintenance is contributing to the destruction or deterioration of the resource.

5)      Any bridge with deck 20 feet wide or less.



Moderately Threatened

        1)      Experience moderate to light traffic volume.

2)      Are not being used for their intended purpose.

3)      Nominal deterioration appears to be evident.

4)      Bridges with deck 22 feet to 28 feet in width.

5)      Pavement and decking threatened with substantive overlay.


Least Threatened

1)      Experience light traffic volume.

2)      No or nominal maintenance (at this time) other than some paint and cleaning.

3)      Pavement and decking in good condition

4)      Minimal amount of rusting supports or truss members (bridges).

5)      Bridges with decks 30 feet wide or wider.

6)    No or nominal overlays on original pavement


Moderately Threatened


Classification of Bridges 

          Of the 45 resources examined for this project, 25 were bridges.  As a result, the project team spent a great deal of time examining bridges and working through a rational for developing the criteria above that would give consideration to the special needs of bridges.  It is important to note that the categories into which the bridges are placed do not correspond in any way to AASHTO standards.  Rather the ranking system simply acknowledges each structure, as it exists today and considers its parameters within the general context of historical significance.   

The primary criterion for ranking a bridge rests on its pavement or deck width. Accordingly, bridges with pavement 20-foot wide or less were considered to be immediately threatened.  This means that they have 10-foot wide lanes or less.  And in most cases, they have only one-foot shoulders, if any at all.  Should a car stop on such a bridge, one lane of traffic would be halted.  Cars would have to pass it by turning into the opposing lane of traffic, an action that can be dangerous to other vehicles and the bridge alike.  Additionally, should a vehicle veer from its lane on such a bridge, it would immediately hit a guardrail, thus threatening the integrity of the historic structure.  

Structures with a width greater than 20 feet but no more than 28 are ranked in the moderately threatened category.  The width of two lanes on these bridges in most cases is either 20 or 22 feet, with the remaining width attributable to the construction of shoulders.  Clearly, passing a car that stops on such a bridge is still dangerous and will require at least partially changing lanes–especially on structures that are 25 feet wide or less.  But there is at least a nominal shoulder that would permit a vehicle to partially withdraw from traffic.  A safer situation for driver, vehicle, and historic structure alike, but it is still one that can threaten the viability of a structure.   

And finally, the least threatened structures are those with decks, the width of which exceeds 28 feet.  Given the fact that 11-foot lanes account for only 22 feet, that means more space is available for the shoulder and thus for a disabled car.  The vehicle would still be partially in traffic, but those passing it could stay, at least partially, in their lane in order to do so.  Additionally, there would be a nominal recovery zone for a car to correct its path should a driver veer out of his lane.  These are clearly subjective categorizations, but ones nevertheless that attempt to acknowledge that wider structures, while endangered, are not as threatened as narrower ones.



            The distinguishing factor in classifying roadbeds was the condition of the original pavement.  If the original roadbed was receiving unsympathetic treatment, e.g., gravel placed upon the original concrete or asphalt surface in an attempt to widen the current surface, we considered this an immediate threat.  Such treatments hasten the deterioration of the original roadbed surface.  Similarly, if patching or overlay was of unsympathetic material, e.g., asphalt patching of a concrete deck or roadbed, we considered this a moderate threat.  Though tolerable for a short time, the long-term effect of this type of patching is deterioration of the resource. 

            It should be noted that David Keene and Melvena Heisch made extensive inquiries over various “list serves” on the internet to investigate if anyone in the United States had explored the issue of patching and maintaining the pavement on historic roads and highways. They received only one response.  This response was from a civil engineer who was returning to school to finish his Ph.D. after 20 years of practice.  This student spent some time investigating the civil engineering literature and well as conferring with his contacts.  Though he himself is interested in the subject he found no examples to assist us.  We thank Fred Rutz of Colorado for his time and interest in our questions.