Railroad Switches: Engineering the Flow of Modern Rail Traffic

In the complex world of rail transport, the ability to move a train from one track to another is essential for junctions, sidings, and branching spurs. This critical mechanical installation is known as a railroad switch (in North America), a turnout, or points (in British and Commonwealth terminology). Without these precision components, the organized movement of trains through massive stations or across vast networks would be impossible.

A right-hand railroad switch with point indicator pointing to right

Foundational Components and Design

Animated diagram of a right-hand railroad switch. The green line represents direction of travel only, the black lines represent fixed portions of track, and the red lines depict the moving components. Track A divides into two: the straight track (B), named the normal, and the diverging track (C), named the reverse.

A switch is composed of several specialized parts working in unison to guide wheel flanges. The most vital moving parts are the switch rails (also called points or point blades). These are tapered rails that move to direct wheels toward either the straight path or the diverging track.

A pair of tapered moveable rails known as switch rails (points or point blades)

Where the tracks intersect, a component known as a crossing or frog is used. This allows the wheel flanges to pass through the intersection of the rails. To ensure safety, guard rails (or check rails) are often employed, particularly on sharp curves, to keep the wheels properly aligned.

Left, the crossing or frog with its adjacent wing rails; right, the guard rail or check rail

The intersection itself can be complex. A one-piece cast crossing, such as the North American "self-guarding cast manganese" type, may feature raised flanges on the crossing to guide the wheels without the need for additional guard rails.

A one-piece cast crossing. The shiny line crosses the rusty line. This North American "self-guarding cast manganese" component without guard rails has raised flanges on the crossing, which may bear on the face of the wheel as it passes through.

Switch Classification and Numbering

Railroad engineers classify switches using specific numbering or lettering systems to denote their geometry:

North American Numbering: A switch's "number" refers to the distance between rails. For example, on a No. 12 switch, the rails are one unit apart at a distance of twelve units from the center of the frog.
UK Letter/Number System: In the United Kingdom, a letter defines the length (and radius) of the switch blades, while the number defines the angle of the crossing (frog). For instance, an A7 turnout is very short for tight spaces, while an E12 is a higher-speed mainline turnout.

A low-speed No. 6 right-hand switch between a main line and a rail yard

Types of Switch Configurations

Large stations may have hundreds of switches (Frankfurt Central Station, Germany).

Depending on the operational needs of the line, engineers utilize various configurations:

Crossovers and Slips

A crossover consists of a pair of switches that connects two parallel tracks, allowing a train to move from one to the other. This is useful for detouring around obstructions or switching between local and express lines.

Slip switches allow for even more complex movements. A double slip connects multiple tracks, while an outside slip places the switch blades outside the diamond. Outside slips allow for higher speeds but require more physical space.

A double switch, or double slip—the points are set to connect the upper left and lower right tracks.

A double, outside slip in Heidelberg main station

A scissors crossover: two pairs of switches linking two tracks to each other in both directions

Specialized and Industrial Switches

Stub Switch: Lacks tapered point blades; instead, the rails have square ends and are aligned with the diverging route.
Three-way Switch: Allows a train to choose between three different directions.
Wye Switch: Often used on mainlines to lead to specific routes, such as single-track bridges.
Dual-gauge Switch: Enables tracks of different gauges to operate within the same switch mechanism.

Closeup of a stub switch in Pennsylvania

A three-way stub switch at Sheepscot station on the Wiscasset, Waterville and Farmington Railway

Unique Systems: Rack and Rotary Switches

In specialized environments like mountain railways, standard switches may not work. Rack railways often use transfer tables—movable platforms that rotate to connect a track to either a left or right passing loop. The Pilatus Railway and Mount Washington Cog Railway still utilize these systems.

A two-track transfer table used as a switch at Mount Washington Cog Railway

A Pilatus Railway turnout consisting of a bridge that rotates about its lengthwise axle

Rotary switches (Gleiswender) rotate about their long axis to present a track connection. This is used in specific systems, such as the Pilatus Railway, where the unique Locher rack system prevents the use of standard turnouts.

Operation and High-Speed Performance

Abt switch used in the 1895-built Dresden Funicular Railway (photo of 1985)

Switches can be operated manually via a switch stand or remotely using an electric switch motor. In a trailing-point movement, where a train enters the switch in the opposite direction of its intended path, the wheel flanges can sometimes force the points into the correct position, though this is typically avoided to prevent damage to the control mechanism.

The operation of a railroad switch. In this animation, the red track is the one traveled during a facing-point movement. The switch mechanism, shown in black, may be operated remotely using an electric motor or hand-operated lever or from a nearby ground frame.

The switch motor (in this case an electric motor) and associated mechanism used to operate this switch can be seen to the right in the picture.

While most switches are designed for low speeds, high-speed lines require advanced engineering. On European high-speed lines, some switches allow speeds of 200 km/h (124 mph) or more. In the United States, the Federal Railroad Administration specifies speed limits for high-speed turnouts, such as 60 mph for a No. 26.5 turnout and 80 mph for a No. 32.7 turnout.

A universal crossover at Richthof between Kirchheim and Langenschwarz stations on the Hanover–Würzburg high-speed railway

Maintaining Reliability in Cold Weather

Extreme weather poses a threat to switch functionality. To prevent snow and ice from jamming the moving parts, railways use gas heating or electric forced-air heaters to keep the mechanism clear.

Gas heating keeps a switch free from snow and ice.

Similarly, an electric forced-air heater can keep a switch free from snow and ice.

Safety and Risk Management

A railway worker operating a manual switch at a rail yard in Britain during World War I

Despite their necessity, switches present significant safety risks. Improperly operated switches or errors in interlocking (the system that prevents conflicting movements) can lead to collisions. Historical accidents, such as the 1980 Buttevant Rail Disaster or the 1998 Eschede disaster, highlight the catastrophic potential of switch-related failures.

Common causes of accidents include:

Splitting the switch: When a switch moves while a train is passing over it, causing the front and rear wheels to follow different tracks.
Maintenance failures: Poorly maintained points or missing locking pins.
Manufacturing defects: Faulty actuators that cause inverted behavior.
Tampering: Sabotage of manually operated switches.

To mitigate these risks, many unused switches are kept locked, and rigorous maintenance schedules are enforced.

Summary of Switch Characteristics

Control stand of a defunct railroad switch on the way from Pyin Oo Lwin to Goteik viaduct (Myanmar)

Comparison of Common Switch Types and Features
Type	Primary Use Case	Key Characteristic
Standard Turnout	General junctions/sidings	Tapered switch rails guide wheels
Crossover	Connecting parallel tracks	Pair of switches for track changes
Stub Switch	Industrial sidings	Square-cut rail ends; no tapered blades
Double Slip	Complex track intersections	Allows multiple path combinations
Transfer Table	Rack/Mountain railways	A physical platform that moves to align tracks

Key Facts

An example of a mechanism used at a switch. The two points are linked together with a throw bar (also known as a stretcher bar). The throw bar extends to the lever on the near side of the track, which is used to throw the switch. This is an example of a low switch stand, used at locations where there is not sufficient clearance for a tall switch stand. This particular stand is designed to be trailed through by rolling stock, which will cause the points to become lined for the route that the wheels have passed through. It has a reflectorized target.

Switch Rails (Points): The tapered, moving components that direct train wheels.
Frog (Crossing): The intersection point where rails cross.
Trailing-point movement: Entering a switch in the direction opposite to its setting.
High-Speed Turnouts: Specialized designs allowing speeds up to 200 km/h or more on certain lines.
Weather Protection: Gas or electric heaters are used to prevent ice buildup.

Frequently Asked Questions

A set of points on the Strathspey Railway in Scotland. The facing point lock in the middle will need to be withdrawn using the blue lever (behind) on the left before the points themselves can be moved using the black lever (front). Once the points have been moved the lock will be pushed in again with the blue lever to lock the points in position.

A narrow-gauge stub switch—this switch has an additional piece of movable rail instead of a frog.

A wye switch on the mainline, leading to a single-track bridge, near Ravenstein, Netherlands

Railroad switch of the Schynige Platte Railway (at Schynige Platte, Switzerland)

A switch diamond at a junction in the UK

A single-point switch on the Toronto streetcar system

Temporary or 'Californian' points installed on tramline 81 at the junction of Avenue Louise and Rue Bailli (in French), a.k.a. Louisalaan and Baljuwstraat (in Dutch), Brussels

Transport of switches by rail creates problems as they are long and wide.

What is the difference between a switch and a turnout?

In North American terminology, a "switch" is the standard term, whereas in British and Commonwealth English, the term "turnout" or "points" is more commonly used.

How do switches work in freezing weather?

Railways use specialized heating systems, such as gas heaters or electric forced-air heaters, to ensure that snow and ice do not prevent the moving parts from operating correctly.

What does "splitting the switch" mean?

This is a dangerous occurrence where a switch moves while a train is currently traversing it. This causes the front wheels to follow one track while the rear wheels follow another, often leading to derailment.

Can trains travel at high speeds over switches?

Yes, but it requires specialized, high-speed turnout designs. While standard switches are for low speeds, some European high-speed lines allow speeds exceeding 200 km/h on diverging branches.

What is a stub switch?

A stub switch is a type of switch that lacks the tapered point blades found in standard switches. Instead, it uses square-cut rail ends to align the train with a diverging route, often used in industrial sidings.