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Smart-N ("Smart" stands for "Smaller Modules Are Readily Transportable") is an N-scale modular layout standard. Designed around small basic modules and a two-track mainline, Smart-N attempts to minimize the hassle involved in building, storing and (especially!) transporting modules.
Smart-N is an independent standard; it does not rely on any other modular standard to provide additional specifications. This document contains the complete Smart-N standard.
The Smart-N standard is maintained by the Meade Area Railroad Society (MARRS), a model railroad and railfan group located in Laurel, MD. The standard was originally ratified by MARRS in May 1998, and the latest version of the standard is available at the MARRS web site.
As of the date of this document, the MARRS web site is located at http://www.marrsweb.org.
This standard is entirely voluntary. Compliance with the standard does not guarantee acceptance of any given module into any given Smart-N layout. Conversely, non-compliance does not guarantee rejection. However, if a module is intended to work as part of a Smart-N layout, compliance with these standards is the best way to avoid problems.
A companion document to these standards, the Smart-N Module Design Guide, is also available at the MARRS web site listed above. The Design Guide offers suggestions for designing modules that meet the Smart-N standards.
An interface is a side of a Smart-N module at which it may be connected to another Smart-N module, to form a continuous run of mainline track.
An interface must be placed on a straight side, at least 6.00" wide. To avoid interference with neighboring modules, no part of the module may extend past the plane of the interface.
The total thickness of a module at an interface, from top of railhead to bottom of frame, must be between 3.75" and 4.50". The height of the framing at the interface must be at least 1.50"; the thickness must be between 0.50" and 1.00". (This is to ensure that modules can be clamped together.)
The nominal height of a Smart-N module at an interface, from floor to top of rail, is 40.00". To account for uneven floors, the module's design must permit this height to be continuously adjustable between 39.00" and 41.00".
At each interface, there must be two tracks designated as mainline tracks. The mainline tracks must end between 62.5mm (2.46") and 63mm (2.47") from the interface (for this measurement, the metric values are preferred). At this point, the centerlines of the two tracks must be 1.25" apart, and the direction of travel must be perpendicular to the interface. If the mainline is set on roadbed, the roadbed must continue straight from the end of track to the interface.
For each interface on a module, the owner must provide one C-clamp of 2.00" to 3.00" capacity, one straight 5" (nominal) piece of Atlas Snap-Track, and two 12.00" or longer electrical jumpers composed of stranded, insulated 18 to 22 gauge wire with tinned ends.
It is possible to design Smart-N modules that also interface to other N-scale modular standards (NTrak, Bend-Trak, etc.). Such interfaces are beyond the scope of these standards.
All S-curve situations on the mainline must incorporate at least 4.90" of tangent (straight) track between the curves.
Any crossing of the mainline at an angle less than 10 degrees must use a "movable-point" crossing or double-slip turnout. Gantlet track is not permitted on the mainline.
Parallel track centerlines on straight mainline track must be at least 1.20" apart. Recommended: Parallel mainline tracks will usually be on 1.25" centers.
Parallel track centerlines on curved mainline track must be at least 1.50" apart. Recommended: On curves of 90 degrees or less, this can be accomplished by using the same radius on the "outside" track as on the "inside" track, and offsetting the center of the curve to compensate. On curves of more than 90 degrees, the outside track could be on the same center as the inside track but with a 1.50"-greater radius, and offset curves used at both ends to transition from the tighter parallel-track spacing.
The centerline of a mainline track must never be less than 2.25" from any unprotected edge of the module. An interface is considered protected when attached to another module. Other edges may be protected by placing obstructions between the edge and the mainline. These obstructions must extend at least .50" above the railhead, and must be sufficiently "solid" so that a standard-height boxcar cannot pass through any gaps.
The centerline of a mainline track must never be more than 24.00" from the nearest accessible edge. Any tunnel or similar situation over 6.00" long must incorporate a means of ready access to the track.
All mainline wire junctions must be either soldered and insulated, or screwed together on a barrier strip.
All electrical switches used in mainline wiring must be visible and accessible to a standing or seated operator. However, it is permitted for such switches to be concealed by removable scenery when not in active use.
Each interface must have four spring or European-style block connectors, capable of accepting wire of 18 to 22 gauge, arranged in a straight line to form a "connector block." Recommended: Radio Shack has spring-loaded, stereo speaker connectors that are ideal for this purpose.
The connector block must be parallel to and within 2.50" of the interface, arranged horizontally so that the relative positions of the four connectors correspond to the positions of the four mainline rails. All connectors must be within 2.00" of their corresponding rail (or the continuation of that rail to the interface). Recommended: The connector block will usually be on the inside of the frame at the interface.
Mainline tracks must be electrically isolated from each other. This will usually be required at mainline crossovers, or where mainlines are connected end-to-end to form a loop.
Non-mainline track must be electrically isolated from mainline track.
Recommended: On any module with more than four feet of mainline distance between interfaces, the interfaces should be electrically isolated from each other.
The connector block at each interface must be electrically joined to the mainline tracks at that interface. (Note that the actual wire connection does not have to be at the interface; it must simply be connected electrically without passing through a switch or other isolation point.) Each of the four mainline rails is joined to its corresponding connector, as determined by relative position (frontmost rail to frontmost connector, etc.).
Each mainline track connecting two interfaces must be accompanied by a double-pole switch that can be used to override the isolation between the interfaces for that track (if such an isolation exists).
If there are mainline track sections that are isolated from all interfaces, a double-pole switch must be used to allow the section to be connected to an interface. (There can be no "dead spots" on the mainline that cannot receive mainline power.) Recommended: if two switches are used, one for the interface at either end, then the section can be "reassigned" between the two interfaces and becomes quite handy for dispatching purposes.
Recommended: Most modules should have a skyboard on their back side (the side opposite the normal viewing direction).
If a skyboard is used, it must not exceed 12.00" in height above the lowest mainline trackage on the module. Recommended: most skyboards will be made of 12.00"-wide material, which will then be overlapped with the back of the frame, resulting in a skyboard height of 8-9 inches.
All cut-off scenic features (mountains, streams, etc.), on any side of the module, must present a flat surface along the plane of the cut. If this surface will be visible from the normal viewing direction, it must be painted a low-gloss (matte, flat, satin, or eggshell) black. Recommended: all visible portions of the frame should also be painted low-gloss black, to avoid drawing attention to the cutoff.
All modules should have at least basic scenery completed before being displayed publicly.
Go to:
MARRS Home Page
Email:
Rob Madson, MARRS Web POC and Site Maintainer
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