The problems with curves and how to solve them.

When building a model railroad, curves are a necessary part of the design. They are defined by their radius and for any track plan should be as large as possible to fit the available space. Model trains look much better rounding a sweeping bend than they do on straight track and for this reason modelers are usually happy to include them. Although broad radii are desirable, it is often necessary to settle for less in order to fit the design in the available space. Radius measurements are stated in inches and are specified to centerline of track.

A major problem when planning for the location of track and turnouts is the S-curve monster. No matter how carefully you plan the track arrangement, this headache seems to inadvertently creep into the design, especially where crossovers are concerned. The flaw is usually not even noticed until derailments or unwanted uncouplings occur. The solution is often painful and could require a complete re-building of the affected area. As a general rule, s-curves should have a straight track section between the reverse section that is at least as long as the longest equipment that will negotiate them. For an 85’ passenger car this straight track length would be 12 “in HO gauge. The standard is easily attainable for a single track section but can be a problem when a crossover is needed between tangent tracks. The saving grace of turnouts, however, is that the radius of the closure rail actually forms a transition or easement curve which reduces the S-curve effect. When laying out a track plan it is easy to miss this problem in our eagerness to cram as much track as possible into a given space.

The transition from straight track to a sharp curve generates a sideways jolt to couplers and trucks and in some cases can cause uncoupling or derailment. This is most noticeable where sharp radii are concerned and the effect may be reduced by employing an easement section.

As shown above, a short section of broad curvature (36”) between the straight section and the sharp curvature (18”) “eases” the sudden change and leads gently into the transition.As always, if at all possible, test track sections as they are installed on the layout. This is especially true for sharp radii and any special track work.

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