Switches and turnouts
A railway switch, or turnout, is the assembly of movable switch blades, fixed stock rails and a crossing — the frog — that guides a train from one track to another.
Turnouts are among the most mechanically stressed elements of the permanent way: wheel loads traverse the blade and frog at angles that impose impact forces absent on plain line. They are also where track and signalling meet — no route can be set without them.
Three zones
The switch zone contains two tapered movable blades — the switch rails — lying between two fixed stock rails. One blade is pressed against its stock rail by a point machine; the other stands clear by 160–180 mm, creating a gap wide enough for wheel flanges to pass without contact.
The closure rails connect the switch blades to the crossing zone, which contains the frog — the point at which the two diverging rails cross.
The frog geometry defines a gap, the flangeway, that wheel flanges must traverse. In a fixed crossing frog the tread is briefly unsupported as the wheel crosses; in a movable point frog, a third movable element fills the gap for the relevant route.
Geometry and speed
Turnout geometry is characterised by the crossing angle, expressed as a ratio (1:9, 1:12, 1:18.5) or a degree value. A 1:9 turnout allows diverging-route speeds of approximately 40 km/h; a 1:18.5 turnout allows 100 km/h and higher depending on curve radius.
High-speed turnouts for the TGV network and comparable lines are designed for 220–320 km/h on the through route and 160–220 km/h on the diverging route.
Actuation and detection
Switch blades are moved by point machines — electromechanical actuators that drive and lock the blades into position and confirm the set position before a train movement is allowed.
Detection is a safety-critical function: the machine must confirm that the moving blade is fully home against the stock rail and that no obstruction — stone, ice or debris — is preventing full closure. EN 13232-4 covers the actuation, locking and detection requirements for switch and crossing work.
Detection circuits are interlocked with the route-setting logic of the signalling system, so a route cannot be set unless all turnouts in the path confirm correct position.
Failure and monitoring
Point machines are among the most failure-prone elements of railway infrastructure. Contamination of the blade-to-stock-rail contact by ballast, ice or detritus causes incomplete closure and consequent signal failure.
Infrastructure managers — Deutsche Bahn, Network Rail, Infrabel and others — have moved toward condition monitoring of point machine motor current and stroke parameters, detecting trends before failures occur rather than responding to them afterwards.
Standards and suppliers
The EN 13232 series covers switch and crossing design, geometry, actuation and acceptance for Vignole rail. Part 1 (2023 revision) provides the authoritative terminology.
The primary European manufacturers of turnout assemblies are Vossloh’s turnout division (part of the German Vossloh group, with switch production based in Reichshoffen, France), voestalpine Railway Systems (Austria), and the turnout divisions of Alstom and Siemens Mobility, which integrate physical switch equipment with signalling and asset management platforms. Vossloh claims to have supplied more than 2,500 turnouts for high-speed lines worldwide.