I PROPOSE TO CREATE A TUNNEL TO CROSS UNDER MY HARBOR SCENE RATHER THAN A BRIDGE.
WHAT WOULD BE THE SHORTEST DISTANCE PLAUSIBLE TO BRING IT TO A LEVEL ABOUT THREE INCHES BELOW THE ROADBED. THREE INCHES BEING, I BELIEVE, THE NECESSARY CLEARANCE FOR EQUIPMENT TO OPERATE BELOW THE ACTUAL ROADBED.
I AM HOPING THIS COULD BE ACCOMPLISHED IN NO MORE THAT THREE TO FOUR FEET, AND PREFERABLY LESS. THAT IS THREE TO FOUR FEET DOWN AND A LIKE AMOUNT UP.
A DESCRIPTION OF HOW A TUNNEL SHOULD LOOK IN TERMS OF EGRESS AS WELL AS ENTANCE WOULD BE HELPFUL TOO.
THOUGH, I AM NOT A STICKLER FOR AUTHENTICITY, I DO WANT IT TO LOOK “GOOD”.
SUGGESTIONS AND COMMENTS PLEASE.
ALBERT OLSEN
Any grade exceeding 3 % means inviting trouble, especially when you pair a steep grade with a tight radius. To go down by 3", you therefore need a length of 8´4" - about twice of what you had figured.
First suggestion - replace your keyboard, the Caps Lock key is broken…
Second suggestion - why work so hard to avoid a bridge across water? A tunnel should really only be used when you have no alternative, as you will be cut off from your model in cases of derailment or malfunction and tunnels are a key place to hide dust bunnies and other undesirables because of this. A tunnel would make sense if your trackbed is significantly below the water level and you would exceed the maximum safe grade to bring it to a bridge (doesn’t happen terribly often in most real life scenes I’ve seen. Another facet of this is in real life, it’s usually cheaper to build a bridge over water versus a tunnel under it. For really long distances over water (ie, like an ocean) - you’d use a tunnel, but you’d also use a significant bank to get yourself below the level of the water and ocean floor - which could be tricky to model in a limited space.
To achieve a 4 inch drop (or rise), you’d need 8.5 feet of run at a 4% grade, 12.75 feet at 3%, 17 feet at 2%, or 21.25 feet at 1% grade. I could be wrong on the math here (it happens, I’ve been wrong before, the universe has NOT imploded as a result…), but I think this might give you a picture of why it might be easier to go over rather than under, especially for small bodies of water. KEEP IN MIND - if you have any turns, you will need to give yourself a break on climb, as turns will add friction like grade does to your trains movement.
You might be able to address the space issue using switchbacks, but that would be a pain if your looking for continuous run - or if you are looking to run longer trains.
DISCLAIMER: I am an N scale modeler - but the principles of grade are the same; just the represented size isn’t.
Question 1. Why the aversion to a bridge? The prototype wouldn’t dig under what they could bridge over.
Question 2. Do you have a track plan that you can post? It sounds as if you are trying to cram too much into a limited space.
Question 3. Just how big is your harbor? As a former resident of the Port of New York who has been in many other seafront and lakefront places, anything navigable by watercraft bigger than rowboats will take up a lot of HO scale real estate. If you’re thinking about commercial vessels, even barges are huge.
And a comment: I, personally, think that a properly designed bridge is a thing of beauty. The Scherzer rolling lift bridge on the ex-New Haven RR in the extreme northeast Bronx was a major influence in my interest in modeling railroads. On the other hand, a tunnel is just a hole in the ground.
Chuck (Modeling Central Japan in September, 1964 - lots of bridges and tunnels, no harbor)
Also keep in mind that those calculations above for 3% or 4% are for the incline/decline. You will also need some transition length, particularly at the bottom where you will be going from a decline to an incline. Otherwise it will be a V shape at the bottom. There is also a need for each decline and incline to have a transition at the top–much like curve easements.
The longer your equipment, such as C truck locos, the more gentler the grades and transitions should be. Short equipment(say 50’ or less) and B truck locos can be a lot more forgiving.
Richard
A harbor, like any body of water, will be significantly below the rest of the landscape. So, you need to not only get below the base level of the layout, you need to get below the seabed of the harbor. You need to add another inch or so to allow for that.
What scale are you working in? When you mentioned a 3-inch clearance, my mind say “HO,” but let us know to be sure. If you’re in N-gauge, you don’t need to go down that far.
What kind of trains do you run? The idea that a 3% grade is about the limit is a good guidline, but exceptions can be made. For example, I have subways and streetcars. My short 4-car subway trains can easily handle the “terrible” 5% grade to the surface, and the rest of my locomotives wouldn’t fit in the tunnels, anyway, so I had no reason not to use these extreme slopes.
I’ll agree with everyone else, though, that water crossings are a thing of beauty on a model railroad. High or low bridges, trestles and causeways add eyecatching scenery to any layout.
If you’re thinking that a bridge would be unrealistically low, consider lowering the harbor a few inches. Many of us have cutout benchwork to accomodate harbors, lakes and rivers. By dropping part of the scenery like this, you create the illusion of an elevation change for the trains while actually keeping the track flat.
Constructing an under harbor tunnel on a model railroad brings up a lot of problems. How do you intend to support the roadbed and, as was mentioned in an earlier post, there needs to be a transition level grade at the bottom of the tunnel that is at least 3x as long as the longest piece of equipment you intend to run. The grade leading in and out as well as the verticle curve transitions on either end present thier own issues. Cleaning and maintaining track in the tunnel as well as acess for derailments must be worked out. So, without knowing what scale you are modeling in, I would say 4 ft for an N scale approach is tight but doable, too short for both HO, O and G. So with a 4ft transition plus a mid river level grade, you are looking at at least 10 ft to get in and out of a tunnel just for N scale. That’s rough math of course, actual results may vary.
Real railroads think long and hard before building a tunnel under water. The cost of a tunnel often runs 10-20x more than a comparable bridge both in initial construction as well as long term maintenance. Real rail bridges can be of any height to accomodate the trains. In the south many bridges are less than 6ft from the surface of the water, in the mountains they can be a hundred feet or more. It all depends on the local environment and the needs of the railroad.
To cross a harbor there are only three choices, a high-rise fixed bridge, a movable bridge, or a tunnel. For the modeler with limited space who still wants a believable scene, I suggest a movable bridge. The track can be very low to the water, yet with a movable span (it doesn’t need to actualy work) the ships can still get through. A high-rise bridge can be used if you already have an elevated track that you can transition to the harbor, otherwise you are looking at a very long viaduct approach. Tunnels have the same issues as a high rise, only instead of going up they go down.
Based on the fact that the OP’s tag is “brooklyn harbor…” and that his previous posts have been about car ferry operations, I don’t see a tunnel as being that unusual. There are lots of railroad tunnels around Brooklyn.
Unless he is putting subway cars through the tunnel or short trains of MU cars, the grades would be too steep for freight trains. Since he is only dropping 3 inches I would say he is probably in N scale, which I would think would make the grade even more problematic since the pulling power would be less.
Hey Albert. Do you have the same track plan as you posted earlier? I live in Brooklyn, NY and I know that there are tunnels around the city, but only a few under the rivers. There’s also some railroad trackage that runs parallel to the subway lines.
Railroads would generally run above ground and over bridges because in order to build a tunnel, they would have to drill through bedrock. This is time consuming, tedious, and expensive.
Subway tunnels were usually built by digging up the street putting in the tunnel structure. The majority of rail lines around the city were built when there was nothing but trees and grass or on landfill after the Civil War and the early part of the Century.
If you’re using it to go to staging, just have the line go over a bridge and disappear behind a building to go into staging.