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In HO scale what do you guys find is a workable clearance between the track below and the bridge above? I may have to make major adjustments on my layout as I have 2 3/4 inches clearance now but the grade is approaching 4% which is too steep for my 4 axle diesels.

I have been modeling for sixty years but I have never had occasion to use a crossover before. Your info would be appreciated.
 

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Yard Master & Research
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For math, scale is 8 ft per inch. 2.75 inches is 22 feet. To add two more feet in scale just go to 3 inches.
I started with O scale 1/4 inches per scale foot or 4 scale feet per inch. HO would be twice as much.
 

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Telltale is correct....when building a railroad, try to imagine possible future purchases that would be game-changers, but that you can't get unless you do some major renovations. IOW, build the widest curves, the widest clearances, and get reasonable height, at least 22' in scale. In my case, my highest object was the tip of a stack on a Canadian caboose. It was maybe 3/16" higher than anything else. Then, a couple of years later, I got a 150 ton wrecker crane. The boom was even higher. Then, I got a GG1 with a pantograph. Higher still. See what I mean? The first item to scrape the rock roof of my tunnel was the caboose.

In most cases, with simple, non-stacked rolling stock, you will find that something close to 2.7" will just suffice. Just. But you should probably be anticipating doublestacks if you're modeling the modern ear, just as an example of how to anticipate future acquisitions. Those would place you closer to the 3.5-ish", and a modern foreman of roads would insist that the engineering department make tunnel bores and bridge clearances at least 3' higher....in scale.
 

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Modeling east coast, you might one day add catenary for electric locomotives, so add another 1/2" to 5/8" for cat and pan clearance.

 

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You mention that you anticipate using a crossover and ask
for information.

First we must know which type crossover you are considering.
A. Two turnouts (or four turnouts as a double crossover)
used to go from track 1 to track 2 of a
double track main line.
B. In an OVAL layout, two turnouts used to connect,
for example, the track on the Left side of the oval
to the track on the Right side of the oval. This creates,
possibly, two reverse loops that requires isolated
sections with special DPDT toggles or, if DCC,
automatic reverse loop controllers.
C. A track device that forms an X that is usually referred to as a crossing
that creates, in essence, a figure 8.

Which of those track situations applies to your plans?

Don
 

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Surprisingly, no one has mentioned NMRA (National Model Railroad Association) standards. Their Recommended Practice 7-1 has a table of clearances. They recommend a vertical clearance anywhere from 2.34" for the "Old Time" era up to 3.17" for the Modern Era. They are based on the engineering standards used by real railroads. So depending on what equipment you intend to run, that will determine what you should use.

Here is a link to the Recommended Practices page: NMRA Standards and Recommended Practices
 
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