# how many inches would it take to get elevation for a bridge over a road?



## DT&I (Dec 6, 2013)

playing with ideas for my yet revised again plan. bottom track would be at road level


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## wvgca (Jan 21, 2013)

depends on a few variables...
assuming ho, era matters, for size and height of rolling stock
nmra specs for old time are 2 11/32 height, classic is 3 1/32, and modern is 3 5/32
next variable is how much grade you are willing to tolerate... 1% easy climb, 2% recommended modern era max, 3% or more for old time logging or mountain lines..
my layout is old time, and 2.2 max grade.. it works for me..
for modern maybe 3" clearance, and say a 2% grade means you need 100 inches of track for 2 inches of clearance for 2% grade, so 3 inches means 150 inches [ on each side] of the bridge for incline length, twelve and a half feet..so if your bridge is a foot long, the total length from start to finish would be 26 feet..
my 'old time' clearance of 2 11/32 and 2.2% grade lets me have a 'shorter' total ramp length...
by the way, you also have to add more length if you have a 'thick' track support and sub roadbed, clearance is measured from top of lower track rail height to bottom of upper support plywood or what ever you decide to use there.


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## boxoftj (Mar 15, 2013)

I've read standard practice clearance for railroads is 20' scale, or 2-3/4". Buuuut, since its a standard road, clearance is usually 14.5' to 16.5' scale feet, about 2" to 2-1/4".


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## DT&I (Dec 6, 2013)

so in other words, that's not quite enough length at an easy grade


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## wvgca (Jan 21, 2013)

depends on your construction methods as well... if there is a foam or other easily workable "base" on this part of your layout, you can also lower the bottom track, and by lowering the bottom 'half' of the needed clearance, you cut your ramp length in half as well, and wind up with two grades, one for the upper, and again for the lower track ..
lots more work if it's just plywood base...


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## DT&I (Dec 6, 2013)

yeh, that would be cool, but like I posted elsewhere, it doesn't look like I'll be able to afford the insulation board for the project


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## wvgca (Jan 21, 2013)

here is the left hand end of my layout, the lower track with the loco, and the upper trestle track are the same track, behind this is a loop just under four foot diameter, 20" radius, with a 2.2% grade inside the mountain.. and a nmra standards gauge in front... just a little more than 'modern" clearance, gave me room to add some supports under the trestle for a better appearance, the right hand side of the trestle keeps rising up to a four inch level over base..


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## DT&I (Dec 6, 2013)

since it would be just a road, could always do the low clearance trick


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## wvgca (Jan 21, 2013)

thats only half of the 3 inch clearance for tracks underneath, so thats cuts ramp length
in half... yep, its doable...
enjoy..


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## Elwood P Dowd (Dec 8, 2013)

Just a thought but instead of a bridge could you put a sort of modified 2 rail version of your Ironton tunnel on that back wall. It wouldnt be exactly the tunnel because I believe it was a single rail but with a little artistic license it could fill the need.


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## DT&I (Dec 6, 2013)

Elwood P Dowd said:


> Just a thought but instead of a bridge could you put a sort of modified 2 rail version of your Ironton tunnel on that back wall. It wouldnt be exactly the tunnel because I believe it was a single rail but with a little artistic license it could fill the need.


having to shove the right side up a foot sorta screwed the left corner up like you said. the new version was something I whipped up this afternoon after the wife asked to see where it would fit in the room. I pretty much have it cleared out now (the spare bedroom) and she could get a full feeling of the size of the layout. I can kinda see her point of not having it right on you in the doorway as you enter. I'll prob sit and watch the mini blizzard tomm and play with the design some more.
stay warm elwood, it's gonna be a cold one


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