Meade Area Railroad Society (MARRS)
Standards for HO Scale Modular Layout

revised through 1/9/98

1. General Arrangement and Trackwork

1.1. Standard modules are 24" deep (front-to-back) by 48" wide. Modules may be built to other widths (2', 4', etc.); module width must be a multiple of two feet.

1.1.1. Modules that are deeper than standard will have tracks placed in the appropriate position to mate with tracks on adjacent standard modules.

1.1.2. The module superintendent retains the right to decide which modules will or will not be used if conflicts arise.

1.2. Standards. The following standards are derived from NMRA Standard MS-1.0:

Scale Height from Floor to Top of Rail Rail Code Clearances
(H=Horizontal, V=Vertical) Distance, Track Center Lines from Module Front Track Setback from Ends of Module Curved Track Centerline Spacing Straight Track Centerline Spacing
HO 40" 100* H=1-¹/₃₂", V=3" 5", 7" 4-¹/₂" 2-¹/₂" 2"
*Other rail codes may be used, but track at ends of module must be code 100.

Scale	Height from Floor to Top of Rail	Rail Code	Clearances (H=Horizontal, V=Vertical)	Distance, Track Center Lines from Module Front	Track Setback from Ends of Module	Curved Track Centerline Spacing	Straight Track Centerline Spacing
HO	40"	100*	H=1-¹/₃₂", V=3"	5", 7"	4-¹/₂"	2-¹/₂"	2"

1.3. Recommended Practices. The chart below is extracted from NMRA Recommended Practices MRP=1.0:

Scale Maximum Main Line Grade Minimum Main Line Turnout Minimum Main Line Radius Minimum Industrial Radius
HO 3%* #6 32" 24"
*MARRS Recommended Practice: 0%

Scale	Maximum Main Line Grade	Minimum Main Line Turnout	Minimum Main Line Radius	Minimum Industrial Radius
HO	3%*	#6	32"	24"

1.4. NMRA Standard S-7 applies to all trackwork.

1.5. Tracks shall be designated "Main Tracks" and "Secondary Tracks."

1.6. Modules must contain at least two Main tracks. Other Main tracks terminating at the ends of the module must have the same center-to-center spacing as Main tracks.

1.7. Main Tracks.

1.7.1. Main tracks must terminate 4-¹/₂ inches from the end of the module (allowing use of 9-inch section of snap-track to connect modules).

1.7.2. Main tracks may be constructed with any appropriately-sized rail, but shall use Code 100 rail for at least the last 3 inches of track at each end of the module.

1.7.3. Main tracks shall have center-to-center spacing of 2 inches on straightaways, 2-¹/₂ inches on curves.

1.7.4. Main tracks may contain curves, but are required to be 5 inches and 7 inches, respectively, from the front of the module at the point where the modules join and for a distance of 7-¹/₂ inches from the end of the module (i.e., the 4-¹/₂ inches mentioned in 1.7.1 above and an additional 3 inches).

1.8. Secondary Tracks.

1.8.1. Secondary tracks must be isolated from all Main tracks.

1.8.2. Secondary tracks, if powered, must have a power supply separate from Main track power supply.

1.8.3. Secondary tracks must be located so that equipment placed on them will not interfere with trains on Main tracks.

2. Electrical

2.1. Track power is to be carried by 16 gauge (or larger) 2-conductor stranded cable.

2.2. MARRS modules use a ¹/₄" mono phone plug/jack assembly in place of the Cinch-Jones 2-blade polarized plug and socket assembly specified in the NMRA standards. The rail nearest the viewing side is connected to the barrel of the plug and the inside rail is connected to the tip. This is in keeping with the CJ plugs, which use the wide blade for the outer and narrow blade for the inner rails.

2.3. The female jack is attached at the left end (as seen from the public viewing side) of the module; the male plug is attached at the right end.

2.4. Track power connectors should be color-coded as follows: first Main track (counting from public viewing side of the module), RED; second Main track, YELLOW; third (optional) Main track, BLUE; fourth (optional) Main track, GREEN.

2.5. Each module must have feeder wires and connectors as described above. No module shall depend on track power being fed through connector tracks.

2.6 All electrical connections shall be soldered and taped or otherwise insulated.

3. Scenery

3.1. The following are recommendations only:

3.1.1. Paint the sides of the rail before ballasting. Prototype rails are rusty rather than shiny. Floquil Grimy Black and/or Rail Brown are appropriate.

3.1.2. Although the plastic crossties of prefab track will eventually collect a coat of dust and become less shiny, it is recommended that they be painted before ballasting. Floquil Grimy Black mixed with varying amounts of Roof Brown will resemble creosoted ties of varying ages.

3.1.3. Use Woodland Scenics Gray ballast on Main tracks, Woodland Scenics Cinders on sidings.

3.1.4. Other considerations being equal, use Woodland Scenics Green Blend ground foam for the basic grassy cover.

4. Benchwork

4.1. Benchwork must be constructed so that the height of the module is adjustable; the railhead of the main tracks must be 40" from the floor.

4.2. Other than the above, there are no standard specifications for benchwork. The following are intended as recommendations:

4.2.1. 1x3 or 1x4 clear pine is recommended for framing, 2x2 pine for legs.

4.2.2. The module must be sufficiently sturdy to withstand transport, set-up and tear-down. Size 8 or larger wood screws and/or ¹/₄" carriage bolts are recommended as fasteners.

4.3. See the "Modular Specifications" chapter of The Model Railroading Handbook, Vol. III for other recommendations on module construction.

Summary of Track Placement Details

48" module
Operating (Rear) Side ("North")
Track Diagram
Viewing (Front) Side ("South")

Legend:

4¹/₄" open space to allow for 9" connecting tracks between modules.
Minimum 3" straightaway. These three inches must not contain curves, turnouts, crossings, etc.
Track center lines 5" and 7" from front edge of module.
Main tracks (minimum of 2) may be straight or curved (32" minimum curve radius).
Secondary tracks must be electrically isolated from Main tracks.
Dummy tracks (not connected to other tracks) are permitted.