The L-Gauge standard defines the fundamental characteristics, specifications, and geometry of key items such as the track, wheels, couplers, loading gauge, etc. of LEGO® System trains. The standard is not official nor binding to any organization or individual. It is mainly a descriptive rather than a prescriptive standard. Some of the specifications in the standard have evolved by convention either for convenience or for interoperability among individuals and clubs. Adherence to the standards described here is purely optional and in many cases, only a sub-set of the standards may be of relevance and interest.
The L-Gauge standard describes several key aspects of the LEGO® train system. These are:
A description of the track gauge, clearances, track elements, and geometric relationship of the track elements.
A reference guide to useful track configurations which can be made from commercially available track elements and which also conform to conventional geometric standards of alignment and spacing. The track configurations are helpfully grouped into categories such as junctions, S-bends, return curves, etc.
A description of train wheel elements and their associated profiles.
Wheelbase standards specify geometric limits of wheel-set placement on train vehicles for smooth running characteristics. These limits can apply to single and multiple axle bogies, fixed and swivel bogie assemblies, and flanged wheel spacing.
The standard coupling mechanism that has evolved from the beginning of the LEGO® train theme, is the use of magnets to couple adjacent train vehicles. The specification of nominal coupler height and placement is described as well as the loading limits on pull-strength for long train configurations.
The loading gauge refers to suggested clearances and easements to the "right-of-way" that track may occupy on a layout. These clearances are mainly useful for the construction of features such as tunnels, bridges, platforms, landforms, etc. built adjacent to the right-of-way.