Switches & turnouts
A railway switch, or turnout, is the assembly of movable switch blades, fixed stock rails, and a crossing (frog) that allows a train to be guided from one track to another at a junction.
A turnout consists of three functional zones. The switch zone contains two tapered movable blades — the switch rails — that lie 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 to create a gap wide enough for wheel flanges to pass without contact.
The closure rails connect the switch blades to the crossing zone. The crossing zone 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.
Turnout geometry
In a fixed crossing frog, the tread is briefly unsupported as the wheel crosses the gap; in a movable point frog, a third movable element fills the gap for the relevant route.
Turnout geometry is characterised by the crossing angle, expressed as a ratio (1:9, 1:12, 1:18.5) or as 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 line turnouts for the TGV network and comparable lines are designed for 220–320 km/h on the through route and 60–80 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 that the set position has been reached before allowing a train movement.
Detection of the correct blade position is a safety-critical function: the point 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 that a route cannot be set unless all turnouts in the path confirm correct position.
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 to detect trends before failures occur rather than responding to them after the fact.
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 Switch Systems (headquartered in France, production in Reichshoffen), 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.