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I am going to add an upper level to my layout.  the majority of the upper level will consist of a bridge that I will build like the one in the picture.  My question is how wide should I make it?  Some of it I will have to make curved, how wide should I make the curves?  







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  • mceclip0
Original Post

The required width of the bridge depends on the curvature of your track and what you will be running on it.  I would use NMRA recommendations to determine what you need.

I have a few scenic express girder bridges similar to the one in your photo.  The over slung bridge needed plenty of clearance.  The underslung bridge didn’t need any, but I had to raise the level once or twice so I could run tall cars under it.  BTW, I don’t think girder bridges are curved in real life, but it’s my railroad so…



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  • IMG_5116
  • IMG_5117

Best to test unless you run NMRA standards. Post war and/or tubular? I'm not sure that is there. It's pretty scale minded, especially today.

Each ...... ( Goofle glitches if I connect these lines of type)

engine/car has overhang in a curve. It may be the pilot, steps, cab roof, or toolbox/tank in the middle that will hang up.  Some steam cabs really kick to theoutside wide up high, diesels & electrics it's usually the pilot or frame, steps & rails. Toolboxes hang to the inside of curves (along the stringline path between trucks.)  

The tighter the curve the more overhang.  The overhang also extends past the curve and onto straights an inch or three at the exit (if you only run one direction you can sometimes have a narrower entrance clear into curves a bit.)

My biggest offenders are a Berk cab roof up high,  an E-33 front rails at frame height, a General or Hudson at the pilot. And any tool/tank only hits 0-27 turnouts. On 0-27 I use a 2" portion of a rough cut 2X4 scrap (rough cut is larger than a finished 2x4) with a piece of hardboard/paneling stacked ( my go to for grade shims)....  so about 2¼" on 0-27 and 1¾" on 0-36.  Set up something kinda soft to knock over and run everything you have by it, facing both directions

And leave a little space for twisting or shifting laterally, and backing as you get shifting there too. 

@Lehigh74 posted:

... BTW, I don’t think girder bridges are curved in real life, but it’s my railroad so…


I didn't think so either until I saw two of them near Vancouver, Washington on an Amtrak trip to Seattle. I'm trying to find them on Google Maps (assuming they haven't been removed). I had posted photos on a thread a few years ago and have since gone through a couple of computers and can't find the photos i took.


I have used 5.5" between centers for concentric curves base on overhang measurements of my equipment.  Curves were O-42 to O72 and my longest overhang loco was a Railking Big Boy.  A scale Big Boy needs at least 2.5" beyond the outside rail on O89.  Lionel's Fastrack curves are 6" between centers which seems to be fine for their scale engines.  If the bridge plate height is less than the cab overhang, you can get by with tighter clearances.

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