My current HO scale layout under constuction is an 8' X 10' duck under. The 8' sections are 30" wide and the 10' sections are 36" and 24" wide. My hole in the middle is 3' X 5'. My plan calls for two bridges, one over a highway/road and one over a single track. The track road bed will be about 3/16" thick and I plan on using .060" styrene for the highway. I'm trying to stay below 3% on my grade approaching these bridges. What is the minimum bridge height I can get by with to keep my grade low? I'm basically trying to get up to the bridge and down the other side in the least amount of space. And one bridge is a truss and the other a girder. Thank You in advance.
You'll want at least 3-inch clearance above the track rails and two inches above the road surface. So, you'll need to add the rail/roadbed, road, and below-rail bridge thicknesses to determine the minimum height separation. So you're probably talking a total of 4 and 3 inches, respectfully, assuming your bridges are the "through" type where most of the structure is above the rails.
Mark
We need to know what your minimum clearance can be without compromising visual appeal and actual clearances for all items that must pass under the structure now and in the foreseeable future. Once you know that value, and then add the thickness of all layers to the running surface of the rail heads above the void below, you will have an idea how high you must climb. That, plus the distance you have at your disposal to get up to that height determines the grade....those two key bits of information.
Generally you can get away with something like 2.8" of clearance and still have it look okay with room to spare. Add a layer of seacans on a flat car and you are in a heap of trouble. Add a 150 ton wrecker crane with its stack and you are in a heap of trouble. And so on....
Note that if the resultant grade is too steep (and 3% is right on the margins of too steep), you may be able to make the tracks below it be at the bottom of a slight dip. If you want to keep your top grades manageable, then maybe make the nether tracks take some of the load by imparting a grade to them as well...split the difference type of deal.
-Crandell
With the bridge like below (deck girder), greater rail height is required above the road surface. Sure wish the clearance height showed in the picture.
selector We need to know what your minimum clearance can be without compromising visual appeal and actual clearances for all items that must pass under the structure now and in the foreseeable future. Once you know that value, and then add the thickness of all layers to the running surface of the rail heads above the void below, you will have an idea how high you must climb. That, plus the distance you have at your disposal to get up to that height determines the grade....those two key bits of information. Generally you can get away with something like 2.8" of clearance and still have it look okay with room to spare. Add a layer of seacans on a flat car and you are in a heap of trouble. Add a 150 ton wrecker crane with its stack and you are in a heap of trouble. And so on....
Crandell is right. You need to know your current and future rolling stock sizes for finding your minimum. My 3-inch figure was taken off the NMRA HO standards gage. If you plan on something like a wrecker crane, better measure one first before building the layout. (Although irrelevant to me since I'm modeling the mid-twentieth century, I wonder how NMRA's old standards work with the large railroad cars operating nowadays?)
> Some of my freight cars have the marking of a rectangle with "Plate C" printed on the sides. I also have one that says "Plate E". Can someone tell me what this means? How many different ones are there?
It refers to the height of the car above the railhead: Plate B - 15'1", Plate C - 15'6", Plate E - 15'9", Plate F - 16'0", Plate H - 20'2" (Double Stacks) - (source - April 2001 Official Railway Equipment Register) - Don Z.
So - the 20'2" for double-stacks would translate to 2.78" for HO, meaning the 2.8" quoted earlier is just a little tight... But I know of people who run strictly 1950's equipment who get away with 2.5", which does exceed the Plate F 16'0" or 2.2" in HO.
Btw, Mark - Where did you get that spectacular picture of the 2 bridges crossing in the sky?
- Gerhard
gerhard_k Btw, Mark - Where did you get that spectacular picture of the 2 bridges crossing in the sky?
Traveling westbound on the highway along the Feather River in California. Original Western Pacific right-of-way is on the upper bridge, now UP-owned but BNSF has trackage rights.
Sometimes you can both raise the upper track and lower the lower track, making the upper grade a little less severe. So let's say it takes a 4% grade to raise the track 3" to clear the lower line. If you can lower the lower track an inch, then the upper only has to go up 2" so maybe it's a 3% grade now. If you use Woodland Scenics risers, it's easy to do it that way.
If possible, I'd advise trying to stick to 2% maximum grades.