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What Is The Minimum HO Tunnel Height Clearance?

Kevin D asks readers for advice:

“I’m progressing with my HO layout construction and have some tracks already operational. I nearly reached the stage of building a long tunnel where the incline will be 2%. I don’t run double or tri-level auto racks or many high cars, but still need to allow enough height clearance. I’m thinking 3” to 4” clearance above the railhead if I need to rerail cars, but I don’t want to make the clearance too high and spoil the dark mystery of when the train disappears and reappears. What do you think I should go with?”

9 Responses to What Is The Minimum HO Tunnel Height Clearance?

  • Peter Murraysays:

    Remember to add height for an extended pantograph if you ever get an “electric loco“. Fully extended they sit well above the body of the loco and are easily damaged if they hit the tunnel surround.

  • Morgan Bilbosays:

    Just get a NMRA gauge for your scale and it will be all you need. Or go online to NMRA for their specifications.

  • DaveBsays:

    Height is not just the issue. You have to look at the width, the type of top (flat, arched, angled etc) and whether or not it sets on a curve. You also have to think about the rise as the train goes up the incline. Long cars will be more affected by that.

    My tunnels are arched and are 80 mm to the top of the arch and about 75mm wide. Best thing to do is get some cardboard and mock up the opening and see how things fit. I used a 3d printer to make mine so it was easy to change the dimensions and reprint until I got what I liked the looks of.

  • Herveysays:

    Kevin,
    The best place to get an answer for your question is from the NMRA Standards and Recommended Practices. You will find an answer in Recommended Practice & (RP7). The recommendations vary based on era you are modelling and if a curve is involved. Remember these are recommendations that allow you to simulate reality. You can always increase the dimensions slightly for your situation. Reducing the dimensions is not an option.

  • phil johnsonsays:

    Since you aren’t running taller modern equipment or electrics then a NMRA track gauge should suffice. One more word of advice, beware of tunnel arch on a curve. I have had problems with the Chooch portals

  • Frank Bsays:

    In addition to the above:

    Above all things, ensure good access from behind for dealing with derailments !

    To have a fully dark tunnel entrance, paint everything inside black.
    The rear access panel cover can be a black cloth to keep light out, or a hatch with close fitting edges.

    As it is totally out of site, the tunnel interior does not actually need a roof, just a few inches of walls at the entrance.
    (Unless you have used plaster scenery, which will drop dust on everything below, ruining rail contact.)

    Make sure there is clearance for car overhang on the inside of curves.

  • Tom Osterdocksays:

    The best thing to do is to purchase a NMRA clearance gauge for your scale. It is well worth it.

  • George Kernsays:

    Usually I leave about 1″ clearance over the maximum hight you think will be needed. you can camouflage the entrances to remove the extra hight not needed right now, this has worked for me. However do some research as to what all you may want to add in the future to your rolling stock just to make sure you have it right.

  • Chuck Holsclawsays:

    Invest in an NMRA gauge. It will give the height that is required, which is 3″ minimum and clearance that you need on the sides from buildings, walls etc. I use my nmra gauge in the opening and then cut out cardboard templates of tunnel portals and put them in the opening of my tunnel and run my train and rolling stock thru to see if will work or if I need to make adjustments. Good luck.

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