HOW TALL OF A BRIDGE DO I NEED?

So I have been designing my new layout ever since i saw the new Kato Metra release back in spring. I couldnt wait :music:. Well the layout is looking pretty sweet on paper. What i need to know is how much room do i need beneith a bridge. I think the normal size of the train is 15' 6" tall. So I rounded to 20 which would be 1.5" in N scale. I want to use unitrack and I am not sure how tall the uni is. From the bottom of the base to the top of the rail. just curious! I have 60" of grade to play with. I know I dont have room for a sprawling layout.

Let me know some suggestions. Thanks

 

NMRA standard for double stacks (modern cars) is 1.75 or so inches (42.1 mm) from rail head to obstruction. I just use two inches.

Here is more info.

 

I have a bridge on my layout which *barely* allows Kato Pacer intermodal cars with doublestack loads to clear it, and its clearance from the rail head below to the bottom of the bridge is about 1.75 inches. The track distance to climb from ground level to the midpoint of the bridge level from one side is about 53 inches, and from the other about 43 inches. The actual rise of the track (adding in the width of the bridge and track on it) is about 2 inches. These are pretty steep grades, but the biggest problem is not the average grade, but the necessity for quick grade transitions near the start of the grade, and near the bridge at the top on each side. This is the most troublesome area of track on my layout, and it needed to be readjusted several times after I first built it in order to avoid derailments. There are still a couple of pieces of my rolling stock which don't like this track, and increased risk of unwanted decouplings on longer trains.

I have an even steeper grade (and more rapid grade transitions) on the older part of my layout, and I had started out building that part thinking I wanted to use Unitrack on those grades. But I found that Unitrack is not well suited for these rapid grade transitions - Unitrack will not let you flex it between joints on an elevation, and you end up getting what a call a grade kink at the joint. (One possible remedy to this might be if you build a wood ramp which has the exact grade contour you want, and then firmly nail down the Unitrack to this wood ramp so that it can bend in between the joints, and thus make it follow this grade contour - but I never tried this). As a compliment to Unitrack, perhaps one might say that it prevents you from doing stupid things. I was undeterred, and switched to Atlas sectional track to build my ill-advised steep grades (this is my attempt at making fun of myself). It might be that such efforts might work even better with flex track, but back when I made these parts of my layout, I had no experience with laying flextrack in curves.

If you are saying you have 60 inches of track length starting from ground level, rising up to the bridge, and then back down to ground level, then that would be an incredibly steep grade which would cause you to have some very troublesome quick grade transitions at each end at ground level, and at where you hit the bridge in the middle.

I'm not trying to say "don't even try it" - bridges are a lot of fun. But if you still want to proceed, it might be worth building a test setup on a piece of homosote with no scenery. If you are planning to use Unitrack for your layout, you might be able to buy enough to test out ramps to your bridge, and if it does not work out there, you might still be able to use that Unitrack on the rest of your layout. Don't forget to test long trains on it!

 

Well Bridge thats going over the top is all flat. Sealevel we will call it. Then there will be a loop, On the loop far left it will start the transtion down to go underneith the layout which will be the metra yard. under the metra yard it will gradually start to go back up the grade of the loop. On the back side of the loop there will be a raised area for the pasenger train terminal above it. This will be the transtion to go back to sealevel. The more I look at it the more I wonder if I will be able to make this loop. I have a point to point layout at the moment but it would be nice to make a run around loop. I wish I had enough room for a helix. I am not that lucky.

 

Rick's point is critical. 3.3% grade is huge.

 

Lets keep it simple just allow 1/2" over the tallest car/engine on the layout you plan to have running and if there is a grade to the bridge keep the grade down that you can pull the cars up the hill you want with the engine you have the least amount of traction with. Don't try to over overthinking it its just a hobby Its your layout do what pleases YOU!