Mainline spacings

Discussion in 'HO Scale Model Trains' started by Kevinkrey, Nov 7, 2007.

  1. Kevinkrey

    Kevinkrey Member

    Joined:
    Jul 27, 2006
    Messages:
    960
    Likes Received:
    0
    Yes,......I know...........another new thread by me. Guess I have more questions than answerssign1. But that is why I LOVE this website. anyway, I was wondering if there is a common measurement for the space between two mainline tracks in HO.
  2. PWRR-2207

    PWRR-2207 Rogue Islander

    Joined:
    Oct 3, 2007
    Messages:
    156
    Likes Received:
    0
    NMRA St & RP's

    :yep: The National Model Railroad Association (NMRA) has standards and recommended practices for all scales starting at this link:

    NMRA St&RPs Index

    Personally, I usually go with the standards for modules. So, in answer to your question, 2" between centerlines of mainlines is the standard for HO in the module world. 2.5" on curves. Before you buy into it though, especially if you are reaching across stuff or deep into the layout, test the distances as you may find it better to go with 2.5" or 3" so you are not banging into things...
  3. 60103

    60103 Pooh Bah

    Joined:
    Mar 25, 2002
    Messages:
    5,135
    Likes Received:
    0
    While 2" is one standard for HO, you should check your turnouts. Take your favourites and make a crossover with them and measure that. If it's a bit bigger than 2", you may want to use that distance instead. Otherwise, when you put a crossover in, your track will have a wiggle in it. (If it's less than 2", you can add extra straight in the middle.)
  4. UP SD40-2

    UP SD40-2 Senior Member

    Joined:
    Apr 30, 2006
    Messages:
    2,812
    Likes Received:
    0
    personally, i always went 2.5 on straight and curves, occasionally 3 on curves:winki: . (HO)
    :deano: -Deano
  5. DeckRoid

    DeckRoid Member

    Joined:
    Apr 28, 2007
    Messages:
    231
    Likes Received:
    0
    Uh... standards and measures..?

    I have a spur that runs for a bit right next to my main line. I put them as close as the foam roadbed would allow and the trains miss each other. Not, you know, by alot... but they do miss.

    Don't know how I'm going to ballast that yet...

    George
  6. kutler

    kutler Member

    Joined:
    Oct 30, 2007
    Messages:
    77
    Likes Received:
    0
    Interesting, on my prototype the track centers are 14 feet between main tracks and 15 feet between main track and a siding. Yard track spacing is only 13.5.

    I don't know what that is in scale, but I bet it's less than the 1 13/16ths as per NMRA RP.

    There's probably a good reason why RPs were set up with the extra room, but personally I think it's a gross excess and unrealistic to space tangent track farther apart. I imagine as models become even more realistic this avoidable calamity will become even more obvious.
  7. PWRR-2207

    PWRR-2207 Rogue Islander

    Joined:
    Oct 3, 2007
    Messages:
    156
    Likes Received:
    0
    Distances for safety

    I had wondered about that too a while back and looked at the Pennsylvania and California Utility Commission rules. As it turns out, 13.5' (1.86" HO) is the minimum between mainline centerlines in the PA document and 18' (2.48" HO) is the maximum... I would have to hunt around to find that PAUC link because those numbers were in a Excel spreadsheet I made when trying to figure out what scale width to make roads and shoulders (with and without parking spaces alongside roads).
  8. Russ Bellinis

    Russ Bellinis Active Member

    Joined:
    Feb 14, 2003
    Messages:
    4,707
    Likes Received:
    0
    The reason the NMRA standards set the center lines as they do are as follows.
    #1- Your ho models are 1/87 scale meaning about 3.5mm=1 inch. Unfortunately you may have to rerail a car or locomotive and your fingers measure 12 inches to the foot. If you have cars on all of the tracks in a yard and need to rerail a car or locomotive, you may not be able to get your hand between the tracks without knocking over the cars on adjoining tracks.
    #2- The tightest radii used in a yard on the prototype would be the equivilant of a broad radius on our models. Long equipment will overhang on our curves, the tighter the curve, the more overhang. If models overhang another track, you will have equipment getting knocked over.

    You can build to a tighter standard, but be aware of the limitations of both your hands/fingers and the radius your equipment requires.
  9. Gary S.

    Gary S. Senior Member

    Joined:
    Oct 13, 2005
    Messages:
    1,691
    Likes Received:
    0
    Just to throw some math in to compare the model to the prototype:

    For yard track spacings of 13.5 feet between tracks:

    13.5 feet x 12 inches per foot = 162 inches

    HO is 1/87th scale : 162 inches divided by 87 = 1.862 inches

    1 13/16ths inches in decimal is 1.8125, so it would be reasonably close to the prototype spacing of 13.5 feet.

    Now, as Russ mentions, there are definite reasons to NOT make the tracks this close together. On my layout, I used 2" spacing on everything. Atlas #4 Customline Code 83 turn-outs will give right at 2" for crossovers and for yard tracks. I also could get away with 2" on the curves, because I am running only 40 foot rollingstock and short 4 axle locos, and the curves are 24 inch radius minimum.