Minimum vertical clearances for model trains have many implications when planning a layout. Of course you'll need to make sure that all of your tunnel portals, signal bridges, structures and other overhead obstructions are high enough. If your plans call for an over-under track arrangement, like a figure "8," helix, or multi-level layout, then the minimum vertical clearance will also impact your grades as trains climb between levels.
Obviously, different scale trains will have different minimum requirements for all clearances. In addition to the scale, the prototype of the model also has a big difference. Trains have been growing since their inception. Early railroad builders could not have imagined that trains would one day stand as tall as a modern double-stack car. Nor did they build their railroads to accomodate them. Since the 1980s, railroads have invested millions of dollars in clearance improvements to accomodate these or other large cars.
If you model an earlier era, or smaller trains like narrow gauge or industrial railroads, not only do your trains not need as much clearance as contemporary prototype models, they may look better with tighter spacing.
The National Model Railroad Association has standards and recommended practices for just about every aspect of the hobby, including clearances. The table below is based upon their recommendations. For more detailed information, see their Standard S-7. Remember, these are only recommendations and only the minimums...you may desire greater vertical clearances in some areas for scenic effect or for access to the trains.
(Our fingers don't scale down.)Also, these figures do not take into account any additional height required for the roadbed and benchwork used to support your tracks.
Minimum Vertical Clearances
- Z Scale: 1 3/16 - 1 1/4" 30 - 32mm
- N Scale: 1 9/32 - 1 23/32" 32 - 44mm
- TT Scale: 1 11/16 - 2 5/16" 43 - 58mm
- HO Scale: 2 11/32 - 3 5/32" 59 - 80 mm
- S Scale: 3 3/16 - 4 5/16" 81 - 110mm
- O Scale: 4 1/4 - 5 3/4" 108 - 146mm
- Large Scales: 6 3/8 - 9 17/32" 162 - 242mm*
- 1/1 Scale (Prototype): 17 - 23' 5.181 - 7.01m
*Large scale trains include a variety of scales that all operate on the same gauge of track, commonly called G gauge. The scale of the models vary by manufacturer, hence the greater variation in these minimum requirements.