Boxed Pony Howe Truss Overpass (from RR-Line)

[jbvb]

This 2017 thread documents researching and modeling a distinctive bridge type that survived longer on the B&M than anyplace else, as far as I know:

12-Feb-2017:

The Boston & Maine used wood for many bridges into the 1920s. Our Library of Congress' Historic American Engineering Record documented a couple (links valid 5/2025). This one still stands AFAIK:

http://www.loc.gov/pictures/item/nh0283/

This one in Arundel, ME was replaced in 1995, but it's a better example to follow for the Chipman St. overpass west of Bexley Depot on my B&M Eastern Route layout:

http://www.loc.gov/pictures/item/me0275/

The Sinnott Rd. (Meetinghouse) bridge from railroad west (Boston side):



The signal bridge stands but is unused - 8 years later I still need to photograph it.... The end of one of the enclosed trusses:



One of the angle braces keeping the skewed trusses from folding up or falling over and collapsing:



I wish I'd known where this was in 1990; when I cross its replacement I'm about 5 minutes from Seashore Trolley Museum.

[jbvb]

I started this project not long after I began layout construction in earnest: I made a sketch with dimensions and bought the wood I'd need to build it. The model will be right at the edge of the layout, so it has to be durable. I decided not to do the hidden trusses as my bridge will be fairly well-maintained. Instead, I made formers for the truss enclosures out of hardboard.

I planed an angle on the top edge; the tin roof covering the truss had to shed rain. I painted them black and then my attention shifted to something else.



When the (old RR-Line) challenge was launched, I thought I'd join with a signal scratchbuild. But the materials were slow to arrive and I want a couple more photos before I start. So I restarted this today: Here one of the formers is ready to be sheathed with Northeastern 1/32" thick 1/16" scribed basswood:




Pete (Orionvp17) commented:

Looks like a fun project, James!
I do hope you'll make it in good repair to showcase the proud part of Minuteman life, and not the run-down stuff in some of the photos....
Looking forward to more.

Michael_Hohn commented:

Very interesting prototype. Particularly being skewed with the additional braces

14-Feb-2017: Thanks, Pete and Mike. Here's glue drying on the first side subassembly's second lamination:



A little scary when it first curled, but it came back overnight. The second (longer) side is waiting to be straight enough for its 2nd lamination. This morning I went to Michaels for flooring material - I was looking for 1/16" plywood, but they had 1/8 and 1/32, so I'll laminate two 1/32 strips together, with their from-the-factory curls opposing.

Louis (desertdrover) said:

Great idea, different from the usual bridge overpass builds. Nice use of materials, looking forward to the end result.

Robert (railman28) said:

What a neat bridge James. I'm glad you have the prototype picture a modeler could end up skewed for building it as it was. Not on this board though. Those
 who hang out here know better.

15-Feb-2017: Thanks, Louis and Robert. Besides the HAER, the last few B&M boxed pony truss bridges were written up in Mainline Modeler (4/92), Trains (2/94) and Railpace (4/98). When I was a teenager, two spanned Newburyport's City RR branch, and two more  were nearby (Salisbury and Newbury, MA). Space didn't allow me to model any of the prototypes, but putting this one in Bexley will help with the feel. Even though I don't have any photo evidence of multi-span boxed pony truss bridges, I expect they existed, but perhaps didn't last past the '30s.

At any rate, I got the floor lamination done last night:



And that really wasn't enough clamps. I probably should have weighted it on a flat metal or glass surface.



Here's the test fit. Over breakfast I'll consider: Glue it together as-is, with the main floor beams the only floor components modeled. Or I model the whole floor system, which makes a Merit Award a possibility but might make it more fragile.

I chose the full floor system. 8 years and quite a few operating sessions later, no damage (knock on wood).



Prototypes with heavy traffic used two layers of deck boards instead of the one sketched. Chipman St. will model two layers with asphalt applied on top.

Guff (Dave) commented:

James, what a unique bridge! This will make a great addition and conversation piece on your layout.

[jbvb]

15-Feb-2017: Thanks, Dave.  I was browsing RR-Line while glue dried on the first stage of the flooring system:



I drew the floor plank joints in pencil, rather than add a layer of scribed sheetwood to the lamination. The 0.7mm lead I used didn't make much of a depression in the plywood, so putting the base color and weathering on this will be tricky. And I wish I'd used six stringers rather than five.

deemery (Dave) commented:

A lot of the bridge plans I've studied have two stringers under the rail (with a small space between for drainage). You could add more stringers, this looks a
bit "light" to me.

16-Feb-2017: Dave, this bridge is road-only. If I ever put trolley tracks in Bexley, the line down to the harbor will pass over the B&M at the tunnel farther east.

Last night I finished installing the floor beams, including the outriggers that will carry the truss braces. This morning I'm fitting the trusses to the floor:





The floor beams that are square to the sides are hung from the bottom of the trusses. Those at an angle (and the cutoff ends of others above the piers) will bear on cribbing atop the masonry bridge piers and abutments.



I didn't get the same projection on all the floor beams, so filing is required to make the floor/truss joint stand up to handling. But I won't glue them together till everything is stained/painted. First, I'll get the wood bearing pieces and cribbing atop the piers worked out.

miekec commented:

Nice! Glad to see that the cutting mat is coming in handy too.

Ray Dunakin commented:

Looking good!

wvrr (Chuck) commented:

Interesting bridge, James. I really like these types of unique structures. Looking forward to seeing the completed model!

Dutchman (Bruce) commented:

The logging railroads of Pennsylvania had a number of those boxed 'through' truss bridges. Here is a favorite "oops" photo. I look forward to your build, James.

[jbvb]

17-Feb-2017: Bruce, that does indeed look like the same kind of bridge. A couple of boxed pony truss RR bridges over streams survive on the B&M's Berlin NH line - it was abandoned before 2000 but the bridges were retained through the rail-trail conversion.

One of the Berlin NH branch bridges was dismantled and repaired by historic bridge fans. It's now in service on the 2-foot gauge Wiscasset, Waterville & Farmington line in Alna, ME.

I'm not quite ready for final assembly - needs NBWs, roofs for the truss enclosures and the outrigger braces. But I'll leave it on the RR for tomorrow's op session.



Unless I use something like a GoPro, this is all anyone will ever see of the floor framing (the NBWs will only be of interest to AP evaluators). But it clears AAR Plate C, sits properly on the abutments and piers, and exposes a good-looking amount of floor beam. And it looks like I (a one-time Civil E student) would dare to walk under it. So the basics are satisfied.

20-Feb-2017: In the era I'm modeling, the B&M's capital assets were maintained in fairly good condition. So I'm not trying to model the makeshift repairs and broken boards in the HAER photos. But it's a working bridge, it has to show history to fit in its setting.

The history I'm imagining has it built around 1890, probably using Chestnut timbers. The boxes only protect the trusses, so replacement of floor planks and timbers probably started within 10 years. After the Chestnut Blight passed through during WWI (here), creosoting plants were built and their products were used for repairs and rebuilds. By the 1950s, the floor would have been all creosoted, with parts between 1 and maybe 20 years old. The trusses are probably all creosoted by now, but with the boxes intact you can't tell.



Visitors won't see the floor system unless I turn the bridge over, but since I'm thinking about AP evaluation, I can't just spray it monotone 'creosote' color. I was worried about warping with A&I, and I've successfully used Minwax Dark Walnut for creosoted wood elsewhere.

Note: when looking for how to thin Minwax, I found unhappy postings about Minwax having changed formulas. I've got 3/4 of a quart, which should do the remainder of the RR, but YMMV.

I had drawn plank joints on the plywood floor in pencil. I tried full-strength stain in the upper RH corner, which will be on/behind the abutment. It hid the pencil lines completely. So I set a dish of mineral spirits beside the can of stain. Some timbers are getting full-strength stain. The deck and the rest of the timbers are getting a brush dipped in stain first, then mineral spirits. I may come back later with some Ebony stain to detail a few timbers replaced in the past year or two.

The diluted stain has exaggerated the grain of the plywood, which I'll remember when I next cut something from it. But the timbers look good enough to proceed, fixing up the 'floor grain' later.

21-Feb-2017: It's almost time for NBWs: 1.25" bolts holding up the floor beams and 1.75" tension rod ends in each truss bay, both with square washers. Nothing of the correct size on hand, so time to order. But Tichy's site gives the same dimensions for three different part numbers: 8035, 8082 and 8143 are all described as 3" bolt, 6" washer. From the site's picture, the first two are much smaller. Could anyone having any of these and a caliper handy post the real or scale dimensions?

Later that day, Don Tichy got back to me about my question above - he referred me to the HO catalog link, which is correct where the web store descriptions aren't. I ordered #8016 (1" bolt) and #8034 (1.75" bolt).

This afternoon I built one of the 'roof' pieces for the truss enclosures. I used .040 x .375 styrene for the top and .010 x .040 for the trim boards. Gluing the trim in the right place was pretty fiddly; it would have been easier if I'd had .015 x .040 or even .020 x .040 stock.



Once you've got the roof held against the truss assembly, you can use bits of wood to hold the trim strips in position while gluing. I applied MEK with a brush. I need a deeper MEK container to fill my old capillary applicator from - none were handy.

This photo also shows some roughness left from filing, along with some paint-covered wood fuzzies. I used a brass brush to remove these from all of the outside surface and the upper part of the inner. We'll see how well they pass for 'old vehicle scrapes' once it's assembled; I can always brush the lower part if I don't like them.



This shows the stained floor system and the unpainted truss roof from the visitor's side.

Orionvp17 (Pete) approved:

This all looks good to me, James.
 Congratulations!

desertdrover (Louis) agreed:

Looking good James. As you know a picture always shows you what needs to be fixed, or re-tuned over. But in your case it's all easy fixes. This project
appears to be a fine looking overpass IMO.

deemery (Dave) commented:

You'll want black tire rubs underneath those vehicle scrapes

22-Feb-2017: Thanks, Pete & Louis. Dave, I agree. I think I'll try a model tire with paint on it (on scraps first). If that doesn't work out, then maybe pencil.

This afternoon and evening the sub-assemblies lost their independence:



Initially, I applied glue to the tops and upper ends of the floor beams, and the edge of the roadway. I'd had those little 'tool dealer' ratchet bar clamps for more than a year; they were very handy even though this was their first use.



Then I added the 6x8 outrigger braces. The roadway guard timbers are glued to both the roadway and the sides. So far the joint seems pretty durable. Finally, I airbrushed more EL Gray on the truss enclosure roofs.

The bridge won't really be finished till I get the NBWs installed, but I'll probably do a little weathering and detailing in the mean time.

[jbvb]

21-Mar-2017: Having spent a week away from home and another week on Town Meeting season, I got back to the bridge the previous weekend:



I checked widths before paving: I won't be putting the bus and truck next to each other when showing the layout. The deck is 25 feet wide, 20:20 hindsight says 28' or 30'. I painted the deck with yellow glue, put the sidewalk curb in place and then sprinkled on 'Raven' grout sand. Also, somewhere earlier in the build a warp left one end with about 3/16" of twist relative to the other. The bridge needs to be easily removable, so I put on my thinking cap:



3/32" brass bar with 1/16" rod soldered in one hole, the other hole drilled #53 and tapped 1-72 (much simpler to have had a 1-72 nut handy, but it would have taken a couple of days to get one).



A locating stud fixed to the backdrop will hold that corner down on the abutment. The other end also needed to be held down.

I was going to show it in the next post, but must take the necessary picture before continuing.

[deemery]

I suspect that's the same truss pattern as the bridge I used as my prototype for an unboxed pony truss:


dave

[GPdemayo]

Wild looking bridge, looking forward to seeing how this one finishes up.....

[jbvb]

Not sure, Dave. The last surviving B&M boxed pony truss in Rollinsford NH has sloping ends, as did one in Lebanon NH I found a photo of, so Howe Truss is a possibility. But many others had squared ends like my model. A website calls that a Flat Truss, but their diagram puts all the diagonals in tension. That's reasonable if diagonals are steel rods, but not for wood.



Aisle end fastened down with a flathead wood screw into the core of the abutment.  Originally I covered the screw head with grout sand, but then I had to take the bridge out and haven't re-covered it.

21-Mar-2017: The boxed pony truss is installed and lightly weathered with A&I. I'll do some testing out-of-place before I try to paint a centerline, or add anything like tire marks or cracked boards.



I tried to put myself in the shoes of a Division Superintendent who's getting an earful about the narrow lanes and danger to pedestrians, but knows this bridge won't be replaced till Beacon Hill gets involved: "Ed, you know the black and yellow paint you have for crossing gates? Send Billy's gang to paint that curb the next warm day."

The sanded grout paving looks a little rough when magnified. This might be helped by adding another coat and smoothing it with a putty knife while it's still wet. In the process of trying to make oil stains down the center of each lane, I found that applying plain 70% isopropyl alcohol darkens the grout consderably.

Michael Hohn asked:

Nice looking model. WV has a few one-lane bridges and I would not be surprised if a few survived in New England.
The prototype photo posted earlier has some squarish panels on the inner sides. Do you think they were removable for inspection?

21-Mar-2017: Thanks, Mike. The HAER text says the square panels are plywood repairs; I haven't heard from any B&M employees who actually worked on boxed pony truss bridges or wound up with as-built plans or photos when Billerica Shops were cleaned out. The rest of the HAER photos demonstrate that the lower inside parts of the housing took a beating, and that the inside boarding was divided horizontally. Inspection/repair would certainly have been done from the road deck when possible.

[edit later] A larger image of the (RR) East side on the HAER site shows a few boards that are continuous from top to bottom. So apparently all the boards on the West side and almost all on the East got damaged and replaced. Guess I'll need to model that.

Orionvp17 (Pete) commented:

Looks good to me, James!
I remember a lot of very narrow streets in the Boston area, so tell people to drive carefully. At least these aren't clogged with snow

13-Apr-2017: The Chipman St. boxed pony truss overpass is pretty much finished. Last month, I'd gone over the sides and roadway with A&I. I used a candle to make stack blast stains over the active tracks. I was careful not to char any of the thinner bits of wood. Then I toned it down a bit with a plastic brush.



Then several weeks overseas intervened. Today I made a try at modeling repairs and damage on the inside sheathing. I used a hobby knife to cut the joint where boards along the bottom had been replaced. I highlighted the cuts with a sharp pencil. Then I dented some boards with the end of a 4" knife file, and cut one partly loose - it's about an inch in front of the Checker Cab, but it's barely visible. Then I used the pencil to make tire marks on the boards in a number of places.



Most of the wear & tear went on the side that's next to the traffic. I did do a little on the sidewalk side; I'm thinking about dinging up the curbs like they'd been jumped a few times.

Looking back at this picture, the figure looks Andre The Giant big compared to the bus and cab. Maybe I wasn't as far off as I first thought.

12-Sep-2017 Bror Hultgren commented: Link works 5-2025:

Evidently a boxed pony truss bridge (one of eight) is being donated to the 2 foot gauge WW&F.

https://fundrazr.com/NarrowBridgeAhead?ref=ab_9Gfqbj5TPBO9Gfqbj5TPBO

12-Sep-2017: Yes; work is ongoing to push the railhead another mile or so towards Waterville and Farmington.


13-May-2018: Bror Hultgren followed up:

Bump.. From the pics it looks like the original Howe truss was rebuilt into some other type of truss....Brown Truss? Current status on the WW&F:

but his link is for North Shore Model RR Club members only.

13-May-2018: Interesting. I don't have a North Shore MRC login, but in 2018 the Covered Bridge Society had what looked like the original document. Alas, I can't find it in 2025, but you might get somewhere by asking:

http://www.coveredbridgesociety.org/

One of the opposing diagonals was visible in the post-arson pictures, making me think they were added by the B&M. The Berlin line was upgraded circa WWII to take 2-10-2s whose weight distribution had been adjusted.

http://forum.wwfry.org/index.php/topic,2553.new.html

The WW&F's forum (still valid in 2025, 56 pages) has much better images, showing that the space between the main diagonals varies; the counter-diagonals get bigger from the ends to the middle, so it's possible those at the ends were completely burned. If I'd had those when I started, I'd have at least thought about building one span with its sheathing in the process of being renewed.

[jbvb]

I made a quick pass over the Wiscassett, Waterville & Farmington boxed pony truss thread :

Plans of their bridge, as installed, are on page 19: https://forum.wwfry.org/index.php/topic,2553.270.html

Useful photos of the trusses being assembled begin on page 10. Photos of the assembled trusses, upright and unsheathed, are posted between pages 15 and 22.  There are also links to issues of The Newsletter of the National Society for the Preservation of Covered Bridges, Inc. with content about the Moose Brook Pony Truss Bridge of Gorham, NH (original location when it was a B&M standard gauge bridge).

[ACL1504]

James,

Very interesting. I've never heard of a boxed pony truss and enjoyed your narrative and the construction. Well done.

Tom

[jbvb]

Thanks, Tom.  Should you ever visit Maine, the WW&F and its rehabilitated bridge are about an hour beyond Portland and far enough inland to avoid the tourists and shoppers along US-1. And for teakettle fans, they are well along scratchbuilding a 1:1 Forney (yes, I'm a member, no, the trolley museum keeps me too busy to go up there and volunteer).