1 vote

Dow Avenue Bridge


Dow Avenue Bridge

Northern approach

Photo taken by Michael Quiet in November 2013

License: Released into public domain


BH Photo #281240

Street View 


Pin connected Lenticular pony truss bridge over Gale River on Dow Avenue
Franconia, Grafton County, New Hampshire
Open to traffic
Rehabilitated 1999
- Berlin Iron Bridge Co. of East Berlin, Connecticut
Lenticular pony truss
Length of largest span: 67.9 ft.
Total length: 72.2 ft.
Deck width: 10.2 ft.
Eligible for the National Register of Historic Places
Approximate latitude, longitude
+44.22487, -71.74208   (decimal degrees)
44°13'30" N, 71°44'31" W   (degrees°minutes'seconds")
Approximate UTM coordinates
19/280985/4900506 (zone/easting/northing)
Quadrangle map:
Average daily traffic (as of 2017)
Inventory number
BH 56221 (Bridgehunter.com ID)
Inspection report (as of October 2018)
Overall condition: Good
Superstructure condition rating: Good (7 out of 9)
Substructure condition rating: Good (7 out of 9)
Deck condition rating: Good (7 out of 9)
Sufficiency rating: 55.9 (out of 100)
View more at BridgeReports.com

Update Log 

  • October 28, 2015: Updated by Nathan Holth: Removed 1910 construction date as this bridge cannot date to after 1900.
  • May 5, 2014: Updated by Michael Quiet: Added categories "Pin-connected", "Wrought Iron"
  • April 4, 2014: New photos from Michael Quiet
  • May 12, 2013: Added by James McCray


  • James McCray - jamesinslocomb [at] yahoo [dot] com
  • Michael Quiet - mquiet [at] gmail [dot] com
  • Nathan Holth


Dow Avenue Bridge
Posted October 29, 2015, by Nathan Holth (nathan [at] historicbridges [dot] org)

I seriously doubt a lenticular truss like this would be built on a public road in 1910. Also consider details like the composition of the top chord... not using channel and instead angle and plate... thats basically unheard of for such a small top chord in 1910.

Dow Avenue Bridge
Posted October 29, 2015, by Michael Quiet (MQuiet [at] Gmail [dot] com)

I've struggled with the build date myself, but I had opted not to change it due to complications with identifying the bridges date based on my site visits and the lack of any other concrete dates about this bridge. I'm *hoping* at some point someone at the NBI had some sort of fact to base the 1910 number off of, hence my reluctant acceptance of its use.

Chester, I've also seen the suggestion that this bridge was built in 1889 put forth elsewhere, and I disagree with it due to the design elements of the bridge. Essentially, the construction method of this bridge does not fit a '89 model. The additional problem is that the methods do not fit any period from '78-1900 either, hence my hesitation to even try and estimate its fabrication date.

The first clue is the web posts, which are of a parallel configuration and connect to the upper chord on the outside. You'll find these only on models up until 1885. At this point they became tapered with the top narrowing and fitting inside the upper chord, and every example I have seen from 1886 onward to the latest extant example, the 1896 model we have in storage up here in VT, have these. The Delage farm bridge has these, as it should.

The railing also doesn't match that time frame either, and is more reminiscent of an earlier type used. Around '85 these too changed (I'm seems like they did a all around retooling at this time which coincided with the awarding of the 2nd patent on the design) with the box/cross type railing which can be seen in use on examples from the '86 Lenticular Warren truss in Grantville NY through the '99 Pennsylvania truss in Stuyvesant Falls NY. Up through '85 was the larger lattice type railing which we have here, which can be found on remaining examples like the '83 Aiken Street Bridge and, although long gone, the nearby '85 Livermore Falls Bridge had these.

So it’s an early model? Well that doesn’t fit either as there are caveats against that argument. The pins, like most components, also got a change around 1885. Prior to then, the bolt heads themselves were tiny and had a cast iron fitting behind them (I think my best detail shot for one of those can be found on the '82 Bardwells Ferry Bridge page). '85 onward had a large hexagonal nut, and these are found all the way through '99 examples. This bridge, like the Delage Farm uses the later models, and thus does not fit with this being an early example

The upper chord is built up with V lacing, which doesn't necessarily rule out an early production model, but narrows the time frame. Battens were used from the earliest known models until 1882-84 during which time V lacing took dominance (Compare the Bardwell’s Ferry Bridge with the Aiken Street Bridge for instance). An example of how this combination works is the HAER documented, and currently disassembled, Golden Hill Road Bridge, which has both the newer style pins, v lacing on its upper chord, but still has the older parallel web posts

The Endpost is completely foreign and I have no idea what to make of it. It’s not built up like standard ones, being made from I beam sections and containing X lacing (of which there are no other examples). I'm guessing it was a much later fabrication.

The location and size of the Builders plate is a curiosity. It had two, one of opposite ends of the bridge, and was a rectangular form secured by 3 bolts. This doesn’t appear on any other of the remaining examples…those having builders plate being the slightly more stylized ones seen on the Delage Farm Bridge or the older examples from Corrugated Metal Co. which, while rectangular, weren’t in this position.

So as to when this bridge was built…I can only give a few possibilities based on the fact It’s a completely unique and odd juxtaposition of styles and components. While there are no confirmed examples, I have noted that Berlin Steel Construction Co. (The successor to Berlin Iron Bridge Co.) company history states that only around 1911 did they move away from production of Lenticular truss bridges. It might just be a typo, as we have no confirmed examples of these being built by Berlin Construction Co. or even after 1896, but it still opens up the question of whether this could this have been a product of Berlin Construction. The size of the builders plates would match their standard one, as would the date (and that might explain why it doesn’t match anything from the earlier era). Or perhaps this was moved/reconstructed around the time given by NBI, at which point the plates could have been replaced and it was given a fresh set of pins. We do know that Berlin Iron Bridge Co. also resold used bridges during their time, so perhaps this was a the case here and it also received a rehab at that point.

Of course there are several caveats to all of this…the Bridge was rehabbed in 1999 and we have no idea what was changed during that process. And I’ll be the first to admit that we have nowhere near a comprehensive picture of the building practices for these bridges, as we only have a small fraction remaining today of the total output of BIBCo. Perhaps reuse of older components was more common, or certain styles persisted beyond what we can tell from extant examples. However from the evidence available, I think it’s pretty clear that this bridge is not an 1889 production, nor can it be specifically pinned to any date. So thats my rational for letting the 1910 date sit....its a guess on their part, but its just as good as mine on this one.

Dow Avenue Bridge
Posted October 28, 2015, by Nathan Holth (webmaster [at] historicbridges [dot] org)

It looks like the 1910 date came from the NBI and nobody has caught the error. Thanks for catching it. I removed the bad date.

Dow Avenue Bridge
Posted October 28, 2015, by Chester Gehman (gehmanc2000 [at] yahoo [dot] com)

I believe the build date of 1910 is incorrect. While it was almost definitely built by the Berlin Iron Bridge Co., it was more likely built around the same time as the Delage Bridge located a short distance away, in 1889. At any rate, Berlin stopped building lenticulars around 1895; and ceased being in existence in 1900, when it was bought out by the American Bridge Co. Unfortunately the builder's plaque is missing to clear up the mystery.