# Over under advice - to trestle or not to trestle



## eroc731 (Aug 4, 2010)

Hey good freinds at MLS, your advice on my 1st post about joiners verus clamps was awesome, lots of feedback and great suggestions! I will most likely be getting clamps now to decide whose to buy! 

Here is my next question:

The "Red Dog Rail Lines Company" recently aquired a beautifully weathered (read used) wood aristo truss bridge and is now contemplating wheteher to construct an over under configuration or to simply span "dog bowl lake -a water feature to be added later"...

I know that gradients should not exceed 2% or 2 " per 100" of track...can the gradient be made up on a curve or is it best to do it only on straights? This takes up a lot of length if wanting to get at least 9" clear from rail top to underside of bridge...I realize I could split thje difference and go 4.5" up and 4.5" down, but is this adviseable? Secondary to this question is any advice on what to use to achieve the grades? buy a trestle kit from aristo or elsewhere OR simply use wood shims/blocks or something else? 

Again your collective wisdom is much appreciated!
Evan


----------



## Steve Stockham (Jan 2, 2008)

Nine inches huh? (Well, let's see...) First, are you modelling narrow or standard gauge because narrow gauge (or a logging line) can see grades of 3-4%. The 2% rule is more for modern standard gauge diesel locomotives. Now, that being said... 2% at 9" of clearance? 450" which comes to...37 1/2 feet. It is certainly true that straight elevations are easier to traverse than curved ones but this in no way negates the usage of curved grades! If you have the room, a 20' dia. curve with 5' of straight on either side adding to the grade should be sufficient to allow you to do what you need to do. Of course, if at all possible, it would be best if you could extend that out to lower the grade percentage! I just finished adding 75' of loop to a grade that used to resemble a roller coaster and was only 20' long! _Much _better!! The only other thing to remember about curves is that the drag on a curve seems to add the equivalent of a 1% grade so your 2% grade, if at maximum, would need to have a longer entry to compensate. This is what I had to do on my layout!


----------



## eroc731 (Aug 4, 2010)

Ahhh..yes calrifications....thanks for the tips!
I will be running modern era stuff mostly although I do have a 4-6-2 that will see "excursion" service....the 9" was based on some other internet research I had done...if less is okay then that's cool too...

thanks again
E-


----------



## kormsen (Oct 27, 2009)

go for 10" height difference. 
there are enough locos that need the full 9", and you need 1" for the upper track and its support. 
(if you ever want to run double stack container cars, 10" is not enough) 

i generally give curves only half of the grade, i give for straights. (rule of thumb, that works)


----------



## markoles (Jan 2, 2008)

I think you have good input on the grades to use. I would plan for 10" of clearance between the bottom of the bridge and the top of the rails. Whatever that works out to be. 

I based my railroad around a bridge, and built 'earth' ramps to and from that bridge. I used large rocks to hold the stone in place. This is not a perfect grade, and tends to be steep in spots. Over time, I have worked to resolve the issues arising from steep grades. In the distant past, this bridge was built to replace twin tunnels. From the tunnel to the bridge, my rail line traversed a 3/4 circle of LGB 1600 track plus one of their switches or about 20', roughly 4%. Yes it was steep, but I ran shortish trains then. 

In the past, I had the Aristo Trestle set, and I would suggest that is really for temporary or indoor use. The grade it makes tends to be steep, too. Building your own trestle is not that hard if you have a table saw and some other woodworking tools.


----------



## East Broad Top (Dec 29, 2007)

Aesthetically, I've never been a fan of long trestles leading up to an over/under. They always scream "toy train" to me. I'd much rather see the landscaping built up to support the track, giving the bridge a physical need to be there as opposed to just supplying job security for the local sawyers. Besides, if you've got a relatively flat space to start, the space needed for the curves and grades really limits what you can accomplish in terms of a track plan because you "have" to run your track a specific way just to get the tracks in the right place for the over/under to work. In the prototype world, railroad bridges over other tracks aren't really all that common, but the bridges that do exist provide plenty of visual excitement. You can get the same amount of visual drama in the garden from having the bridge over a well landscaped dry gulch, dirt road, pond, or other non-train-related feature. I'd suggest using the bridge for something like that, and give yourself a little more flexibility as to your trackplan. 

Later, 

K


----------



## eroc731 (Aug 4, 2010)

K 
Wow....never thought about it from that perspective...trains not crossing over trains.....I agree on the "toy train" image, I had intended to burry whatever I was going to use to obtain the "lift" but not having to elevate and create the other effect is a very attractive option, given the room I have to work with or shall I say that i am willing to devote to the RR... 

The "KISS" principle at work....thanks for the insight.... 
Evan


----------



## Ironton (Jan 2, 2008)

A modification for Kevin's comment if you really want a trestle. Where the track passes under make one side a hill. That is on side, say the left, would be a cut with vertical walls and the bridge resting on an abutment. The other side would have a stream (wet or dry) and a hill slope. Then you could use a two or three bent trestle on that side leading up to the bridge which was quite common to see in the west at least. If you want a more modern look, build a drit fill for the hill side as most railroads would dump loads of dirt or rocks on the trestle until it was buried.


----------



## aceinspp (Jan 2, 2008)

Min thing is do you have the room to be able to make it to 10inch height. If so then go for it and build away based on above suggestions. Just remember make the height of the bridge on planned new equip that may be higher than what you have now. As we say plan ahead. Later RJD


----------

