Modular Layout Design.

This article first appeared in the September/October 1989 issue of AMRA's 'Journal'.
By Steve J Chapman.

The first thing to consider when talking about designing cf modular layouts is to decide exactly what we mean by modular. For the purpose of this article I am considering a modular layout to be one which is :-

  1. made up of a number of modules
  2. that the design is such that the modules can be assembled in different orders to produce effectively different layouts.

Therefore a layout is not a modular layout just because the layout is built as a number of different sections which are capable of being pulled apart. To be a modular layout, the layout must be made up of a number of modules which can be assembled in a number of different arrangements.

The advantage of the modular layout approach over conventional layouts is inherent in the above definition. The various modules which make up the layout can be rearranged in various ways. Modules can be removed, moved, or added at any time. Therefore when a new layout is desired all that is required is to build a number of new modules to replace or add to the existing ones, or alternatively just the order of the modules in making up the layout may be changed. A modular layout may be easily adapted to fit the available space simply by adding or removing modules and once a single module is built (assuming that each module has a yard or something on it capable of independent operation) the builder has a layout and need never be without a layout again since new modules can be built before all of the old ones are pulled apart. Also if a number of people build modular layouts to the same set of standards then the layouts can be combined together whenever desired to give an even bigger modular layout.


Depending on the size of each module, the modules may themselves be broken down into sections for ease of transport. Thus when we speak of a fifteen foot module we do not imply the there is one board fifteen foot long (there may be three or four sections to make up the fifteen foot length) instead we mean that the entire fifteen foot module must be considered as a unit when determining where in the layout the module is to be put.

To be a module therefore a section (or number of sections which join together) must satisfy a number of conditions. The exact conditions that a module must satisfy depend on just how modular that the modules are intended to be. By this I mean that a layout is modular if two modules of the same size can be swapped over, it is even more modular if, in addition, one module can be pulled out, rotated through 180 degrees and put back into the layout and have the layout still able to function. For this to be the case a larger number of standards must apply to each module than would in the first instance.


The major requirement for a modular layout is one of standards. Each module within a modular layout system must be designed so as to comply with the same set of standards as otherwise the various modules will be incapable of being joined together and running trains from one module to another will be impossible.

What therefore are the standards that must be applied to any modular layout design?

Standards for modular layout systems can be broken down into three groups.

  1. those which are essential for the modular system to function
  2. those which are desirable for the layout to look like a complete layout and not like a number of independent parts which have just been thrown together
  3. those which may or may not be included depending on the requirements of the builder.

Let us consider each of these types of standards separately to determine which standards belong to each.


There are a number of standards which must be applied if a modular system is to function at all. These standards are the first things that must be specified when designing a modular system. The first thing to consider with modular standards to decide what scale the modular system is to use. This consideration is particularly important when more than one person is going to be building modules. It becomes awkward to join modules together if one is N gauge and the other is HO. This may be obvious to everyone, but I mention this standard because a great number of the other standards are dependent on the choice made when setting this standard. Standards are also required with regard to baseboard construction. Standard lengths must be defined if modules are to be capable of being assembled to allow for a continuous run. Standard widths ensure extra flexibility (and are essential if boards are to be reversible - ie able to be rotated through 180 degrees). Different types of module are also possible (in fact essential if a continuous run is to be achievable). In addition to straight modules, curved modules will also normally be needed. Curved modules can be classified as inside curves or outside curves depending on whether the centre of the curve lies inside or outside the layout. Inside and outside curves are equivalent if boards are reversible.

Also important with modular standards is track standards. There are a number of things to consider with track standards, some obvious, some perhaps not so obvious. Track standards are required for :-

  1. number of through tracks passing across between modules
  2. track centres (ie distance apart) for multiple tracks across modules
  3. the angle at which the tracks cross the join between modules
  4. the code of rail to be used
  5. minimum main line curve radii
  6. loading gauge (ie clearance above the track)
  7. back to back wheel standards
  8. whether the track is to go right up to the edge of the board or, if short pieces of rail are to be inserted to join the modules together, how far back from the edge that the rails ends are to be
  9. the position of the track as it crosses between modules is also important if the greatest flexibility is to be achieved.

Each of the above must be specified before construction of modules can commence.

Wiring standards for track wiring are also essential in order that trains may be driven across module joins without it being necessary to switch controllers as the train crosses the join. The track wiring system to be used can increase or decrease the flexibility of a particular modular system irrespective of other standards selected and so should be carefully designed to ensure that the desired flexibility is catered for.

Intermodule connectors need to be standardized or (if non standard sockets are used on a module) converter cables to connect various connector types together will need to be available if the greatest flexibility is to be achieved.


If the standards specified above are clearly defined and adhered to an operable modular system will be achieved but modules built only to those standards will, when assembled to make a layout, still look very much like what they are, a series of separate modules attached together.

Further standards are required if a blended rather than a patchwork effect is to be achieved. These standards, while not essential to make a functional modular system, are what is required to make the modules appear to be part of the same layout rather than separate layouts which just happen to be connected together at the moment.

Standards of this type are concerned with baseboard construction and scenic effects. All baseboards should be to standard widths with tracks crossing the edge of the board at the same place on each module. A scenic profile for the ends of the modules needs to be defined (and if boards are to be reversible need also to allow for matching up both ways around).

Backscene height is another item which should be standardized. Also if modules are to be capable of being viewed from either side the backscenes need to be removable. Means of attaching backscenes may also be something which should be standardized. This would then permit backscenes to be interchangeable independently of the modules. Thought can also be given to having the last inch or so of scenery as part of the backscene as well, this will assist with board reversibility.

Baseboard framing should all be of similar dimensions (there is no real point in using a ply frame two inches deep on one module and a four inch by one inch timber frame on another). This will enable boards to be joined more easily and neatly and will provide a tidier appearance. There is some room for variation in this area without too great an effect on the overall appearance particularly if there is to be a curtain hung from the outside.

Perhaps hooks (or some other means) are to be provided at set intervals for hanging curtains along the outside edge of the layout to improve its appearance when at exhibitions.


The third set of standards are those which make the modular system complete, but which, if not included, do not affect the primary functioning or appearance of the layout.

These standards are mainly related to wiring for operation and do not affect the actual track wiring of the layout although some do affect the accessories wiring.

Standards of this nature include (but are not limited to) such things as :-

  1. wiring of inter module communication using buzzers or track occupancy indicators
  2. intermodule interlocking of multi-aspect signals
  3. standard control panel designs
  4. bell code charts for intermodule communication so that everyone is using the same codes
  5. coupling standards for compatibility of rolling stock
  6. type of signalling system to use.

While none of these is something which is required for the modular system to function, or even for it to look like all of the modules are part of the one layout, the inclusion of these factors in the modular standards not only makes it easier for one person to operate another persons module, but makes operation of the modular system more interesting as a whole. In fact if all of these aspects are included then the layout can he operated as a layout rather than as a group of independent modules while still having the full flexibility of modular design.


So once we have defined the standards for our modular system as a whole, what is the next step ? In fact little more remains to be done. All that remains now is to design and build each individual module. In this regard each module can be considered in the same way that you would handle the design and construction of a complete layout which was not being built in a modularized way. (Assuming of course that you design your layouts and that they don't just grow by themselves).

The first step in designing any layout is to specify the standards which are to apply. In this case some (but perhaps not all) of the required standards are specified by our chosen modular system. Further standards not specified in the modular standards may apply with respect to a particular module (and not necessarily to any others) should the builder so desire. Any track plan desired can be chosen for the module in the same way that you would choose the track plan for a complete layout. The constraints are slightly different for a module since we perhaps have a greater number of standards specified which have to be complied with.

Construction of a module also follows normal procedures with the module standards being applied where appropriate.


So, as you can see, designing a modular layout is not really that much different from properly designing a conventional layout. The flexibility of a modular layout is however much greater than with a conventional layout although standards must be applied much more strictly with a modular setup.

Consider modularizing your next layout. You may never need to start over again from scratch if you do.


Figure one : Modular layout standard specifications.

       Scale                  :
       Straight module length :
       Straight module width  :
    Right angle module length :
       Number of tracks       :
       Track centres          :
       Angle of tracks        :
       Code of rail           :
 Back to back wheel standards :
       Loading gauge          :
Platform edge to track centre :
     Main line minimum radius :
       Track set back         :
Distance (from edge of board) :
Distance back from front edge :
     to centre of front track :
       Wiring standards       :
       Type of connectors     :
       Scenic profile         :
       Backscene height       :
       Frame dimensions       :
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Copyright Stephen Chapman