Hey Everyone,
Trying to put my first bridge up, Speaking prototype on any bridge, any engine, any railroad, what is the basic height requirement between the top of the highest car and the bottom of any bridge???
Speaking about modern clearances - you want about 24' from the top of the rail to the bottom of your bridge/structure. We use 3.5"(about 25' 6") on the club layout and have had no problem with tall cars like Superliners/auto racks/double stacks....
Jim
Modeling BNSF and Milwaukee Road in SW Wisconsin
I have my tunnel portals at 2.75" and it looks 'okay'....not great, probably not realistic, but it works... or should I say worked, fine. Then I got an Athearn 200 ton wrecker crane that wouldn't enter the tunnels due to the stack height. I would urge you to get over 3" if you are using a variety of rolling stock, and if in the modern era of double-stacks, probably closer to 3.5 and up.
railroadinmedic Hey Everyone, Trying to put my first bridge up, Speaking prototype on any bridge, any engine, any railroad, what is the basic height requirement between the top of the highest car and the bottom of any bridge???
If a gnat standing in the highest point of the passing rolling stock is still there after it passes under the bridge, there's enough clearance...
More seriously, there is no single standard. The AAR has published a whole series of clearance diagrams (called Plates) to which rolling stock and loads are supposed to conform - except that, like highways, railroads are frequently called on to move oversize loads. Each railroad's engineering department maintains a big book in which the horizontal and vertical clearance at tight spots is recorded. On an older line, those restricted clearances might be a lot less than would be permitted in more recent construction.
Thanks to the low clearances in the tunnels at the Hudson Narrows, the New York Central had to have steam locomotives a foot shorter (vertical dimension) than the roads west of the Mississippi - or even south of Central Pennsylvania. Look at a model of the Niagara, and compare it to other 4-8-4s, to see what I mean.
Another joker in the deck - it isn't just the clearance under the bridge, it's the vertical profile of the track or highway. There was one bridge on Murfreesboro Road in Nashville, TN, that was a perfect example. The posted clearance between the roadway and the bottom of the (heavy, solidly-built deep deck girder with a railroad on top) bridge was a couple of inches more than the height of a hi-cube semitrailer. That clearance was measured right at the bottom of a dip. A trucker would start up the grade and hear a loud CRUNCH!!! Usually, the box hit about ten feet behind the fifth wheel. More than a few had their backs broken.
From a more practical point of view, the NMRA gauge will give you three inches of clearance, railhead to overhead obstruction, in HO. If you are running all pre-WWII rolling stock you might shave that a little. If you are stacking 18 scale feet of container height in your wells, or running a loaded Schnabel car, you might want to add to that. In my own modeling I allow a minimum of 6mm (1/4 inch) overhead clearance above the tops of my tallest rolling stock, but that has to allow for 'virtual' catenary above partially-raised pantographs.
Chuck (Modeling Central Japan in September, 1964)
Thanks Chuck, that does help. I have a railroad crossing over another and wasn't for sure about the distance. I am familiar with roads under trains, seen that many a times where trucks hit the bridges, but wasn't familiar with rail to rail. That helps, have a good day! Carl
Thanks Jim, appreciate that info. Carl
Thanks selector, appreciate that. Carl
For more information about clearances check this page on the NMRA's site http://www.nmra.org/standards/sandrp/gauge.html
Enjoy
Paul
More seriously, there is no single standard. The AAR has published a whole series of clearance diagrams (called Plates) to which rolling stock and loads are supposed to conform -
next time you see a high cube box car like an 86 foot auto parts car, look at the end of the car. if i am not mistaken the area up high that is painted white is the extent to which that car exceeds "plate c"
take a look at this. http://www.greenspun.com/bboard/q-and-a-fetch-msg.tcl?msg_id=007Fjx
grizlump