Sunday, February 11, 2018
The term Functionally Obsolete has been retired, and Structurally Deficient is being redefined more narrowly so that it exactly matches the Poor condition on the new scale.
This seems like a good thing, as Good/Fair/Poor is much easier to explain. I'm looking forward to no longer fielding questions about the intricacies of the terms Structurally Deficient and Functionally Obsolete.
The Good/Fair/Poor scale is based on the ratings for Superstructure, Substructure, and Deck, as determined during each bridge inspection. If any of these three ratings are scored as 4 (Poor) or below, then the bridge is considered Poor. If all of the ratings are at least 7 (Good), then the bridge is considered Good. Otherwise the bridge is Fair. (Culverts have a separate rating field which works the same.)
States will be expected to decrease the number of Poor bridges and increase the number of Good bridges, and will be penalized by FHWA if they don't make adequate progress in that direction.
Interestingly, the new system does not take into account NBI ratings for "Structural Appraisal" and "Waterway Adequacy Appraisal." This means that it's possible for bridges previously considered Structurally Deficient to end up as Fair (instead of Poor) on the new scale. Indeed, doing some back-of-the-envelope calculations shows that this applies to 6,815 bridges. Of these, 756 are truss bridges.
Likewise, the elimination of the term Functionally Obsolete also makes a difference. Of those bridges previously declared as Functionally Obsolete, 53,937 now fit into the Fair category, and 21,750 qualify for the Good category. Among both of these groups, 1,972 are truss bridges.
The upshot -- and we can always dream -- is that a significant number of historic bridges, particularly truss bridges, won't be quite as juicy a target for replacement. It's been frustrating to watch perfectly sound bridges being demolished simply because they were too narrow and therefore "obsolete."
Of course, we have no idea how this will actually play out, but perhaps this will help some historic bridges avoid the wrecking ball. State DOTs will now be "on the clock" to prevent bridges from slipping from Good to Fair to Poor, and this will hopefully spur an emphasis on preventative maintenance and rehabilitation.
The latest NBI dataset from 2017 does not incorporate the new Good/Fair/Poor scale. However, it's easy enough to apply the new scale, so I've updated the data shown on Uglybridges.com and here on Bridgehunter.com to reflect the new system. I've retroactively applied the new scale to the archived data to make it easier to look at trends.