Voltage that constantly changes direction. Classic analogue Märklin three-rail runs on it: the voltage sets the speed and a brief pulse above the running voltage reverses the direction.
Controlling trains by regulating the voltage on the track. All locomotives in the same electrical section respond together, so for several trains the layout is split into isolated sections.
A system in which the line is divided into blocks and only one train may be in each block at a time. A signal at the start of the block shows whether it is clear.
An amplifier that supplies extra power to part of a digital layout. Needed when the command station alone cannot provide enough current for all locomotives and lighting.
The third current-carrying conductor in the middle of the track on three-rail, from which the locomotive's pickup shoe draws current. On Märklin C and K track it consists of stud contacts between the sleepers.
The height between the top of the rail and the lowest point of whatever is above, such as a bridge or an upper track. It must exceed the tallest vehicle, overhead wire included.
The difference, in millimetres and degrees, by which two track ends that should meet do not line up. TrackDrawer shows it so you can see whether a layout really closes.
A curved piece after the diverging route of a turnout that cancels the turnout angle. The branch then runs parallel to the main track, at the track spacing.
A track piece with an insulated outer rail. As long as a train's metal wheels stand on it, the contact is closed, which is useful for occupancy detection.
A turnout where both routes curve in the same direction, with an inner and an outer curve. Useful for branching off within a curve without breaking it.
Digital Command Control: an open digital standard defined by the NMRA and used by many manufacturers. A DCC decoder works with any DCC command station.
A small electronic circuit in the locomotive that receives digital commands from the command station and controls the motor, lights and other functions.
A constant voltage with digital commands is applied to the track. Each locomotive has a decoder with its own address and can be controlled individually, including lights and sound.
A long, pinched oval: in the middle both tracks run side by side as double track, and at each end a wide loop joins them, so the whole looks like a dog bone. Electrically it remains one continuous loop, not a reversing loop.
Double slip: a crossing on which trains can also change track in both directions. Four routes in the length of one turnout, ideal for a tight station throat.
A period of railway history according to the NEM classification, from I to VI. Roughly: I until about 1920, II about 1920 to 1945/1950, III until about 1970, IV until about 1990, V until about 2006 and VI after that. Models from the same era fit together on a layout.
A long length of track that you bend to any curve and cut to length yourself. It allows smooth curves and transition curves that fixed pieces cannot give.
The part of a turnout or crossing where the rails intersect: the frog point with the wing rails beside it. The wheel must bridge a short gap here, which is why check rails sit opposite.
A large model railway scale on a 45 mm track gauge, suitable indoors and in the garden. The scale varies by prototype and maker; for LGB it is about 1:22.5.
A track that rises or falls, expressed as a percentage: millimetres of height per 100 mm of length. Gradients are usually kept modest on models, otherwise locomotives slip.
A metal frog that carries current and changes polarity with the turnout setting. Locomotives with a short wheelbase run over it better than over an insulated plastic frog.
A short straight piece that absorbs the length difference between the main track and the branch after a turnout with a compensating curve. Both tracks then line up again.
Märklin's digital protocol in which a locomotive registers itself with its name and functions at a suitable command station. No address needs to be set.
The smallest curve a particular vehicle can still run through reliably. Long coaches and large steam locomotives often need more than the system's smallest curve.
An agreement on the dimensions and interfaces at the ends of modules, such as track position, height and wiring, so that modules by different builders fit together. Groups such as FREMO use their own module standards.
The Normen Europäischer Modellbahnen: European model railway standards published by the umbrella organisation MOROP. They define, among other things, scales, wheel profiles, coupler pockets and the eras.
The National Model Railroad Association, the American model railway association that publishes model railway standards. The DCC digital standard was defined by the NMRA.
Benchwork of battens and cross members without a continuous board. The track sits on separate roadbed strips, so the terrain can drop below track level.
The contact wire above the track from which electric locomotives draw current on the prototype. On most model railways it is decorative and current comes through the rails.
A full-size print of your track plan, split into A4 tiles that you lay side by side. It lets you check the plan on the real table before buying or fixing track.
Which rail carries positive and which negative. In analogue two-rail it sets the direction of travel; where two tracks of opposite polarity meet, a short circuit occurs.
The height of the rail profile in thousandths of an inch: code 100 is 2.54 mm high, code 83 about 2.1 mm and code 75 about 1.9 mm. Lower codes look finer but need wheels with lower flanges.
A loop that returns a train to the same track in the opposite direction. On two-rail this creates a short circuit between the rails, so isolation and polarity switching are needed; on centre-conductor three-rail it is not.
The raised base under the sleepers that represents the ballast bed. On sectional track with integrated roadbed it is moulded onto the piece, which lies firmly and works on a carpet or table.
Two opposite curves directly after each other, for example a turnout followed by a curve the other way. Long vehicles can lock buffers there; a straight between them at least one vehicle long helps.
A narrow, elongated layout, often along a wall, usually with a station or industry and a fiddle yard. Fits where there is no room for a continuous run.
A direct electrical connection between the two poles, for example caused by a derailed wheel or a wrongly closed reversing loop. The power supply then cuts out.
Single slip: a crossing with a connecting curve on one side, so trains can change track in one direction. A form between a diamond crossing and a double slip.
A box with a locomotive, a few wagons or coaches, an oval of track and a controller or command station. A common starting point that you expand afterwards.
The outline around the track that must stay clear of platforms, signals, tunnel walls and other objects so vehicles pass safely. Also in curves, where vehicles swing out.
Small metal studs between the sleepers that together form the centre conductor on Märklin three-rail. They are less visible than a continuous centre rail.
A track piece that gives a switching pulse when a train passes, for example to switch a signal or turnout. On Märklin the pickup shoe presses a switch for this.
A system with a centre conductor as the third conductor: current flows out through the centre conductor and back through the rails and wheels. Reversing loops therefore cause no short circuit.
Removing dust, oxide and dirt from the top of the rails so locomotives pick up current without stuttering. With a cleaning rubber, a cloth or a cleaning car.
The distance between the centre lines of two parallel tracks. Every track system has a standard value, reached with a turnout plus compensating curve or with two concentric curves.
The angle between the straight and the diverging route of a turnout. A smaller angle gives a slimmer turnout and smoother running, but takes more length.
Three tracks in a triangle, with a turnout at each corner, that let a train or locomotive turn. Like a reversing loop it needs polarity switching on two-rail.