Large Scale Central

Height between track that cross over each other

Track and Trestles
#1

I need some input as the what is the recommended height between two tracks that cross over each other. I plan on using deck bridge where they actually cross over each other. The second question is how much running sistance is required to acheive this elevation difference and keep it a a reasonable grade.

My existing plan has a 33 foot run of track from the lower track to the upper where is crosses over the lower and most of it will be ladder track type if support as the area it is located in is the narural drainage for the back yard and I can not fill it is. I have been contimplating building an 8 foot diameter concrete or stone arch bridge alow 3/4 of the 8 foot curve to allow for drainage, but also give a good foundation for the track.

Oh the largest Locomotive I am using is the bachmann 2-8-0 consolidation 1:20.3 scale if this makes any difference.

Dan S.

#2

A specific height I can’t give you, but a safe formula I can. Measure from the top of the rail to the top of the highest point on the loco (should be the stack or possibly the hatch on top of the cab). Add to that 2" for clearance and hand access. Next add the thickness of whatever is going to hold up the track, plus the thickness of the track.

As for the run necessary, that is dependent on the grade you want to keep. If you use that math and say the total top of rail to top of rail is 13 inches and you want a grade of 2%, that would be 2" rise per 100 inches of run, or 650 inches of run for 13 inches of rise.

Hope this helps

Bob C.

#3

I’d go with at least 9" from the top of the rail head but 10" would be better. There is probably a formula for your track footage to achieve the needed elevation but I don’t know it.

If you run out of room to keep the grade reasonable to achieve the 9-10" clearance then you could cheat a bit and drop the low track down a bit.

#4

Thanks guys for the input. Todd as for dupooring the lower track down . it would cause issues with the track already in place and furthur increase the grade percentage. Bob: I have 396 inches of running distance so if I go with 10 inches then I am looking at roughly a 4% grade. I might be able to redesign that section to add more running distance and drop the grade down to 3%.

Dan S.

#5

Don’t forget to add the thickness of your bridge deck and track on the bridge to the final height when calculating the grade. The clearance needed is from the top of the rail head of the lower track to the lowest part of your bridge. My 1:20.3 clearance gauge is 10" from the rail head. I give more when possible.

I had a cross-over planned for my RR. Even had the bridge abutments poured. When I got around to figuring the grade it was well over 10%. No way to drop the lower track, so it was cancelled. I may still do the cross-over with a siding where I can keep the grade down by extending the track run, but it can’t connect back and be a loop without the crazy grade as there is no space to add run after crossing over.

#6

Hi Dan,

You may want to consider using a truss bridge or covered bridge instead of a deck bridge. While through-type bridges work well at 9 in, a deck bridge will push your track up over a foot above the lower to provide clearance. To maintain a 1% grade, your track would need to climb for over 100ft.

A nice way to add a lot of climb in a smaller space is to use a helix. A full box of 20ft dia curves would provide about 60ft of climbing circumference which is a little less than a 2% grade. While 2% is a bit steeper, the wide radius provides some relief. My primary concern about grade is locomotive surging when going downhill.

#7

Dan, 3 and 4 percent gets into mountain railroading territory. Most mainlines prefer to be a close to dead flat as possible. 3% being an extreme grade in most cases. My railroad, since its a short-line, narrow gauge affair, settled on 2.58% grade. With that grade, my trains are limited in length. You may not think that will matter to you, but trust me, someday it will matter.

The last thing you want to do is build your railroad for what you have now, and then buy that sweet locomotive that calls out to you, bring it home, and find out that you cannot run it. So more clearance is best. I also second the suggestion that you use a truss bridge, with a slim lower beam, to get more clearance.

#8

Thsnks guys for your input. I guess I used the wrong term when I mentioned the deck bridge. What I will actually be be doing is a wooden trestle leading up the a Pratt Truss bridge and the a curved Tresstle of the other side of the Truss bridge and then this will continue on for 36 feet where it will connect to the elevated town deck that are 22 inches above the ground. I am trying to keep the grade to 2% if at all possible. As I am modeling Narrow Gauge, all of my passenger trains will be limited to 4 or 5 cars max, and Freight to no more than 10 cars. All cars are fitted with metal wheels for easier rolling.

I like the Idea of 20ft diamter curve, but I don’t have the space for the where the loop needs to go. I was trying to use an 8 ft diamter one as thats about space I will be able to use. I might be able re-configure the track plan to eliminate the cross over bridge and increase the run leading into and out of the loop to gain more run as it leads into the run up to the elevated deck. Again trying to keep max grade at 2% up to that town deck, everything after that is .25% grade leading into the 42 foot yard.

I will try and do a couple drawings and post them to see what you think about design options.

Dan S.

#9

I am having the same issue as you. I want a cross over on mine and have done almost exactly what everyone here has suggested in my design. Mine is a mountain RR but I am still sticking to 2% or less. I have also decided on a through bridge (thank fully for my purist heart I discovered my RR used them). I am trying to achieve a min of 12" top of rail to top of rail. My loco that I have now is a little over nine. But like was suggested here you never know a what you will buy and two who you will eventually invite over that might want to run what they brung. At 396 inches at 2% is 7.92" of clearance. at 2.5% your at 9.9 inches and at 3 % your 11.8inches. This is top of rail to top of rail. The formula unless am wrong is simply to take the distance and multiply by the percentage gives you the height.

If I did the math right to get 12 inches at 2% requires 600 inches. That’s fifty feet. 12 inches at 3% is 400 inches and at 2.5 its 480 inches. That’s working backward. Take the height you want and divide by the percentage.

Someone please check my math as I m no math major.

#10

Rockwall Canyon Jeff said:

My primary concern about grade is locomotive surging when going downhill.

I can confirm that this is definitely a problem, especially with a string of heavy 1:20 cars.

#11

Sometimes it is impossible to get here from there so we try and do the best we can. The answer is to add track and extend the run. You can’t help physics, a 10 car train up a 2% grade will be strained even more in tight curves.

If the over and under proves ot be too much to conquer you could turn it into a switch back arrangement but that would end the continous run but it would add a new dimension to your RR. You could run a bypass around this “mountain” to allow uninterupted running. The special trains would go up the switch back. Just a thought…

#12

Dan,

Prototypes were/are creative when it came to making grade. If you think on it hard enough I believe in the space you have you can create what you need and want. Here is one example of a section of track NP designed. It is an out and back sort of affair. The part that crosses the creek is wonderful engineering feat; it is a s trestle bridge. My thoughts on this is can you traverse the 33 feet you have twice with an 8 foot loop at the end and then cross. Basically turn that 33 feet into a valley with a loop at the head a cross over at its entrance. Don’t know since I am guessing as to your layout and space.

Just be creative. I am looking at a new way to gain height. I have enough for my cross over I want now but I would like to throw in another.

Here is another interesting way to gain elevation. Doesn’t work in your case as it has two cross overs but it is creative.

https://www.google.com/maps/@51.4281105,-116.4075642,14z

#13

Devon Sinsley said:

I am having the same issue as you. I want a cross over on mine and have done almost exactly what everyone here has suggested in my design. Mine is a mountain RR but I am still sticking to 2% or less. I have also decided on a through bridge (thank fully for my purist heart I discovered my RR used them). I am trying to achieve a min of 12" top of rail to top of rail. My loco that I have now is a little over nine. But like was suggested here you never know a what you will buy and two who you will eventually invite over that might want to run what they brung. At 396 inches at 2% is 7.92" of clearance. at 2.5% your at 9.9 inches and at 3 % your 11.8inches. This is top of rail to top of rail. The formula unless am wrong is simply to take the distance and multiply by the percentage gives you the height.

If I did the math right to get 12 inches at 2% requires 600 inches. That’s fifty feet. 12 inches at 3% is 400 inches and at 2.5 its 480 inches. That’s working backward. Take the height you want and divide by the percentage.

Someone please check my math as I m no math major.

TANSTAAFL. There ain’t no such thing as a free lunch. Said differently, if you want to dance, you have to pay the piper.

That means more track, or shorter trains, or doubling the hill, or helpers, or a combination. This is the fun of operations. Some people call it work. (http://largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-tongue-out.gif)

#14

Steve Featherkile said:

TANSTAAFL. There ain’t no such thing as a free lunch. Said differently, if you want to dance, you have to pay the piper.

That means more track, or shorter trains, or doubling the hill, or helpers, or a combination. This is the fun of operations. Some people call it work. (http://largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-tongue-out.gif)

Just like real life. I actually find the challenge fun as I am planning my RR setting real parameters and making it work. I might never have a layout if keep creating challenges to overcome. I have a workable plan I jus tneed to work it instead of trying to make it more complicated.

Dan, keep us posted I for one would love to see what oyu come up with.

#15

Dan, another thought on the bridges. You can use any type of bridge or trestle right up until where the upper track crosses the lower. Then switch to any type of through truss or girder bridge for that bit and then back to the normal style on the other end. This may save you a few inches of climbing and keep the grad as low as possible. The trestle shot doesn’t use a through type span but it could be easily substituted.

#16

When climbing on a curve, many lower the grade to ease the drag on their locos.

I’m sure you’ll work something out…

John