3 pieces

I see three pieces, the vertical piers, a thick arch and then the deck (with balustrades and smaller arches).

You could create patterns and trace the patterns on plastic sheet, then cut out the pieces and cover them with .010 plastic to make 3D sections and assemble those.

Or you could make one master, make molds and cast plaster pieces.  Or cast resin pieces.  Or cast expanding foam pieces.

Styrene

I'd build that in layers out of styrene. First I'd make templates for the arches, then I'd make a master for the inner piece with 6 small arches, a master for the broad arch, and a master for the supports with the three tall arches. These will be used to lay out side frames, as many as you need. You'll need a pivoting knife like a mat cutter to cut smooth curves. Those bosses at the sides of the piers will be interesting, maybe you can cast those from a hand carved master.

The side frames will attach to the top, a piece thick enough to hold the sides square. The arches will be filled with sheet styrene thin enough to be flexible. The upper arches only need to extend far enough to suit the sight lines, then the bottom arch will cover the entire width for strength.

Of course a laser guru like Michael Rose could finish the whole thing by suppertime.

pqe

" I am hoping someone might

    That repetitious work might be best done with a laser cutter? I'd contact Bill Brillinger and see what he thinks. If I had to do it by hand I'd probably scratch build one complete section then cast copies for the others. If I had to do all the sections by hand I'd pick a different prototype to model :> ) .........DaveB 

forsnter bits

If you know how to make molds, take a block of wood and line up three forstner bit cuts for those smaller arches.  Then cut down to where the large span will be.  Make a mold and  multiple copies, flipping half of them so they are reverse (mirrored).  Attach to the bottom of the roadway, then that part just needs the large arches made (and then mark and cut out of your copies).  I'd maybe just use a template for that large arch shape for that cut.  For the physical arch, I see thin bass- or balsa wood- thin and strong enough for such a large curve can be found.  A custom tapered arch front can easily be made with a sharp blade.

Mock it up on computer

It's mostly flat pieces of different depths, so layered pieces of styrene seems like the natural choice to me.

I'd start out by mocking up the design on a computer program like inkscape or illustrator, and then you can easily use that to either print out patterns for hand cutting or sending off to get laser cut.  I would personally go with laser cutting, but doing it by hand doesn't seem like it would be too bad.

The cornice can be made with layers of styrene strip.  The curved parts at the ends of the piers are a bit tricky and whatever you do for that I'd suggest only doing it once and casting the rest.

Looks like the suggestions

Looks like the suggestions run the gamut from traditional to modern. I might as well take it to the future by suggesting this would be a perfect 3d build project. Design one section, print as many as you need.

Foam Board

A lot of the large scale modeler are using foam board for bridge projects such as this. It is cheap and readily available from HD, Lowe's and other DIY stores. Made by either Dow or Owens-Corning, the pink version is found at HD and the blue version at Lowe's.

Foam Board

A lot of the large scale modelers are using foam board for bridge projects such as this. It is cheap and readily available from HD, Lowe's and other DIY stores. Made by either Dow or Owens-Corning, the pink version is found at HD and the blue version at Lowe's. Easy to carve and light weight.

Carve and Pour...

Carve your basic shapes out of florist foam, and then pour Water Putty, or Plaster of Paris in it... let the pieces dry, and then carve your details into it using a walnut pick (or hobby knife, or needle, or... whatever you like to carve plaster with)

You'll get the shapes you want, and the look you want for that steel reinforced concrete feel.

Wow. OK, so now I am

Wow. OK, so now I am beginning to know what I don't know. So many approaches. Almost none of these ideas had occurred to me. Thanks to everyone for the suggestions. I'd like to ask a few follow up questions if I may:

(First, I should mention that I model in HO scale - maybe that's relevant for one or more of the approaches.)

Question to Pelsea - I was originally thinking about somehow cutting sides, or pieces of sides, out of sheet styrene or wood (or foam board, but I didn't think of that) but it seemed to me that would be hard to get nice, smooth cuts with my X-acto knife and a #11 blade. You mentioned a pivoting knife/mat cutter. I snooped around on the Internet a found a few products that sounded similar but didn't immediately see how they would be used to do reliable detail cuts. (I also found a lot of videos of women cutting cucumbers using something that looked like a Northwest Short Line chopper that used a meat cleaver on a hinge, but I was pretty sure that wasn't it ). Do you have a specific reference to something I could look at (like on Micromark or Amazon)?

Question to several responders - A few people suggested making a drawing and sending it out to have it fabricated in styrene or wood or perhaps have a 3D print made (trying to resist buying a 3D printer just yet). Are there some favorite "go to" places for this sort of work? Finding an MRH advertiser would be nice -- I looked thru the page of sponsors but didn't see anything that looked related.

Question to Warflight - My inexperience at work here, but I wasn't sure if the florist foam was being used as a mold or if it was used as the actual pieces and the water putty/plaster was being used to impregnate it for strength.

Question to several responders - The molding idea sounds interesting. I have never made my own molds. From the photos I have and the amount of Kankakee river width I have, I think I will need three sections of bridge (the photo shows four). Is there some notion of crossover point when doing molding? That is, if I needed 20 sections of bridge, it seems I would clearly want to mold to save time. If I only needed one, it seems like I would never want to mold (unless I wanted the casting material characteristics for some reason). Is that the right way to think about it? If so, where does the payoff happen? Two? Three or more?

Everybody also picked up on the curved pieces at the base of the piers. I, too, expect that to be "fun." My first thought was to use a quarter of a ping pong ball. Probably too big, but maybe a plastic or foam or wooden bead of some sort sitting on top of a section of semicircular dowel. No idea how to cut them, of course....

Thanks again,

Vince

If it were me...

First off, scale, to a degree, matters. It is a lot easier to use some materials in one scale compared to another but generally the larger the scale the more materials you have to work with while maintaining scale.

That said, if I were going to tackle that project I would do a couple of things. I would first lay it out on the computer so I could produce scale prints of the bridge pieces. If you can't do that then a single pen drawing so you can photocopy it will work as well. Next I would use mixed media to get this thing built unless you go plaster and molding the thing up. My choice would be foamboard for the sides, thin styrene for the inside curved portions, and clay for those round protrusions. I would set about making a metal cutting template for the curved holes. That allows you to guide a straight xacto around the metal guid to get your curves. The diameter of curve is the same on every one of them. The only difference is the height of the sides. That is where your drawing and perhaps etching some markers in the side of your metal template can come into play. Once I had the foam sides cut I would glue in the styrene to fill the arches in. Your concern about the clean cuts is good but you have ways to fix it. Almost certainly you will tear the surface of the paper on the foam board and not get a perfect edge on the syrene foam joint. That is where some plastic putty comes in handy. Get your gluing done and then fill the gaps with the putty before sanding smooth. Under the paint you will never see it. For the protrusions I would use a polymer clay. Get your basic shape done as well as you can but you won't get it perfect and that is okay. Bake the piece for half as long as the directions say. It will be brittle but highly sandable/cuttable. Now finish your piece with all the detail you want. Make a mold of it and pour the rest in plaster. Glue them to the foam board and repeat the putty process for a perfect fit. I would do the central columns with the thinnest styerene I could get and cut the relief holes. Glue it to the foamboard. You shouldn't need the putty here but if there is an inproper gap, or a slice went a little errant fix it with the putty. Primer the whole thing and paint it up for concrete. The best thing is the dollar store sells the foam board for a $1 a sheet, the putty is inexpensive and the clay is cheap as well. The most expensive part will be making the mold for the protrusions but you may find that you can get the pieces created close enough and just make them all from clay...

That is certainly not the only way to do it but it is how I would do it.

swivel knife

The knife I use is an Xacto craft swivel knife:

The tiny blade turns as you cut, so gentle curves come out smooth. The blade is long enough to cut 1/16" stock. I would make a cutting template out of thin brass.

Depending on your scale, the smaller arches could be cut with a Forstner bit.

The trick is to only cut halfway, from the back. You can just hold the bit in your hand. Then you would intercept the round grove with straight cuts for the side and finish the part of the arch you want to keep. That will give a semicircular arch, which is probably close enough. There will be extra grooves (To learn how to lay out more complicated arches, look at this article.)

pqe

Florist Foam as a mold

I was thinking using it as a mold, but, using it covered in plaster for strength could work as well.

If you did water putty, you could make a simple mold (foam, wax, whatever) bend some paper clips, and pour the putty, and then when it dries, do a bit of sanding in a "damaged" area to expose a bit of the paperclips, and now you have some weathered and damaged concrete with a bit of rebar sticking out!

This TMTV segment might be helpful.

^{Roadshow - Build an overpass}

https://trainmasters.tv/videos/2015-02-4-tmtv-february-2015-edition-act-iv

One man's method

Looking at the photo provided, my first question is 'How accurate do you want this model to be?' I think that question needs to be answered first.

I see this model in several components First component is the piers that show from the waterline (and obviously below) all the way to the top of the structure. These could be made as a single master component, using a keying system to attach the bridge spans to. I notice that these piers are also the widest part of the structure. The master pattern could be made from wood, styrene, foam, or what ever material you are most comfortable working in.

Next would be the bottom arch. This is where I asked bout fidelity. The photo shows a distinct differenc in the arch between the top and bottom chord. A little artistic lisence here could simplify the build. This arch could be made from multiple layers of styrene, or cut from a single block ow wood (depending on tooling available), or whittled from foam. This time this part is part one of a multi part master. Part of that lisence would be to modify the arches so that the tangency of the top cord would be at the intersection of the small arch and the vertical member.

The next part would be the deck and the tops of the small arches. As was mentioned earlier, a Forstner bit of appropriate diamter (this will most likely be a close enough is good enough because I believe the only come in .0625 increments). If cutting this out of wood, drill the six small arches first. Then dado out the deck for the track, and lastly rip the height to the intersection point of the small arch and the vertical member.

The two vertical members on each side of center will be a trial and error fitment until they all go toghter. Assemble the arch, deck piece and vertical members. Seal all  the components with a good quality sealer and them polyurethane the entire piece. Make molds, cast copies and your bridge can be what ever length you wish it to be.

I have skipped over the thickness portion of this as you didn't mention how many tracks you plan to run. It apperas from the photo that thiw would be something in the magnatude of a four track main. IF that is the case I would make my casting half the thickness and glue of the castings for the width.

My preference, as likely indicated is for a wood master and casting.

Those small arches...

sure look elliptical to me.  If you make them circular, they will be noticeably different from the big arches, and the graceful lines of the bridge would be lost.  I like the template approach per Wabash Banks.

Or, maybe you could find someone with a Cricut or a laser cutter...

Incidentally, Mark Dance (who appears on this forum from time to time) wrote a nice article in either MRP or MR about selective compression of bridges recently.  He found that simply removing a panel wasn't always the best approach.

Good luck with your project!
Rene'

The small arches?

in google street view ( seen from the next bridge over) look pretty circular. One could draw up a side view of the bridge on construction paper and cut it out to see if using half circles for the arches would look okay....DaveB

Get an inexpensive cutter

Get an inexpensive cutter used in scrap booking.  Cut the outer face from multiple layers of thin plastic.  If you watch you can find them for less the $100.

-Doug M

Kankakee bridge

There was a guy on another forum who built a model of this same scene in N scale, unfortunately it appears all the photos got nerfed by photobucket.

https://www.therailwire.net/forum/index.php?topic=12358.msg98737#msg98737

Elliptical arches

Elliptical arches are easy to lay out. See this article on the same site I referenced before.

A Cricut or similar would be a fine tool for this project, as would a CNC milling machine. It just depends on your inclination, space and budget.

pqe

BALSA FOAM

Lots of good suggestions. Here's another...

Look for Balsa Foam... it is a wood product that will match your concrete texture. You will need to make a template as suggesed and then cut the balsa foam out. May be a bit simpler than making masters and casting. 

Kris Blackmarr recently gave clinics on this at the NNGC last week. Check his website for detailed instructions. http://railroad-line.com. 

One other thing - foam board - I believe the gentleman meant the extruded polystyrene insulation board in the materials department of any big box lumber store. 

Yes he did! Here is a

Yes he did! Here is a picture of the "pink" that is sold by HD. It also comes in other thicknesses and sizes ...

I use Sketchup (free) for

I use Sketchup (free) for design. There's some learning curve, but it's more fun than work.  One hint, draw at full size, then scale when you print. I have a printer, but I know lots of folks use and get good results with Shapeways.

Sketchup

Sketchup looks like a great tool. You can use the free version (Sketchup Make) to export the models? That wasn't clear to me from the Make vs. Pro matrix.