On HistoricBridges.org, the general rule I follow is that I select the construction date that applies to the majority of main spans in the superstructure. This policy differs from other websites (including BridgeHunter) which sometimes list the construction date for substructure, approach spans, etc. Good example: Benwood Bridge: I list it with a 1905 construction date, which reflects the date of the main spans, BridgeHunter lists 1870, which applies to the approach spans.
The National Bridge Inventory often does the same sort of thing, listing dates for approach spans, substructure, etc.
In regards to NBI dates, if the NBI date appears to be completely false (Ohio has a serious NBI problem), I do not include it on HistoricBridges.org and I list the construction date unknown. Sometimes, the construction date appears to refer to a relocation or a rehabilitation, so I place the NBI construction date in my slot for rehab date, and mark the construction date unknown.
That's how we do it over at HistoricBridges.org for what its worth.
Michael, your answer was perfect since it goes to my deeper question regarding the "actual" age of a bridge. Much of the data on bridgehunter comes from the NBI and if there is no data plate on the bridge and the engineering of the bridge is clearly of a different era from the NBI published date, what are bridgehunters doing with the discrepency? Leaving the NBI year in place, leaving the year field blank on bridgehunter?
Reconditioning, moving, recyling and re-using bridges happens regularly (but not regularly enough) and it seems to me, that the age of the bridge is the year of first construction of the truss, not the reconditioned year.
Curious how others are handling this topic.
I would guess it was relocated as well.
However, the abutments were most likely rebuilt in the past few years. The concrete looked new, and there were form impressions on the weather exposed concrete.
The bridge shows no sign of major alteration, so I would vote for it having been relocated.
In response to your question have two guesses for this bridge.
The first is the easy guess.
The bridge was moved to this location in 1975.
A couple of factors would lead one to this conclusion. First, judging by the design of the bridge, mainly the riveted connections and the riveted built-up sections I would estimate this truss to have been fabricated much earlier than 75. The second factor would be Siskiyou Countyís history of using recycled bridges. These two main factors would lead me to guess that the bridge was in fact moved here in 1975.
The second guess is a little more of a stretch.
I know that this data is from the National Bridge Inventory (NBI). I also know if you change too many of the core bridge elements (change the deck material, rehabilitate the truss, rebuild the bridge or a majority of it) the date of construction may be reset to the rehabilitation date in the NBI.
So it could be that the bridge was overhauled in 1975 and the date now reads as built in that year.
I would lean towards the bridge was moved here in 1975, as oppose to the other. This was probably more of an answer that you wanted but thatís my take on this particular structure.
Michael, I am not fully familiar with steel truss history, but I would like to know, in your opinion, was this bridge first constructed in 1975 for this location, or, was it moved to this location in 1975?