A swingnose crossing or moveable point frog is a device used at a railway turnout to eliminate the gap at the common crossing (a.k.a.

frog A frog is any member of a diverse and largely Carnivore, carnivorous group of short-bodied, tailless amphibians composing the order (biology), order Anura (ανοὐρά, literally ''without tail'' in Ancient Greek). The oldest fossil "proto-f ...

) which can cause damage and noise.

Fixed crossing

On a fixed railway crossing, the wheels need only drift by a small angle, say 1 in 20, before the vehicle may start to go in the wrong direction at the V of a V-crossing. This problem can limit the maximum speed of vehicles using the crossing. In addition, the open gap at a fixed V-crossing forms a weak point on the railway line where the heavily loaded wheel must bump across the resulting gap of about 10 cm, supported only by the portion of the wheel tread which is on the wing rail. This pounds the rail so much that the steel can deform and/or wear away. This damage may easily spread to other components including the wheels, and the noise can be a nuisance. Scheduling repair of damage can also be a problem in high traffic locations. Swingnose crossings virtually eliminate the gap at V-crossings allowing for higher vehicle speeds. The swingnose crossing overcomes the problem of the gap by moving the point of the V-crossing from side to side, synchronised with the selected direction of the turnout. The wheels are supported the entire way on their treads, and do not produce noise and vibration that would otherwise occur. Swingnose crossings are also useful where

heavy rail Various terms are used for passenger railway lines and equipment; the usage of these terms differs substantially between areas: Rapid transit A rapid transit system is an electric railway characterized by high speed (~) and rapid accelerati ...

and light rail vehicles, which have different wheel profiles, share the same track.

Swingwing crossing

A variety of swingnose crossing, suitable for locations where a branch line turns off a higher-speed line, is the swing wing crossing. In this device, the V-crossing does not need its own motor but is moved by the flange of an approaching wheel on the branch track. It returns to its normal position when the diverging train has passed, pushed by a damped spring.

Parameters

Swingnose crossings would be used for V-crossings finer than about 1 in 20, and for

axle load An axle or axletree is a central shaft for a rotating wheel or gear. On wheeled vehicles, the axle may be fixed to the wheels, rotating with them, or fixed to the vehicle, with the wheels rotating around the axle. In the former case, bearing ...

s in excess of 25

tonne The tonne ( or ; symbol: t) is a unit of mass equal to 1000 kilograms. It is a non-SI unit accepted for use with SI. It is also referred to as a metric ton to distinguish it from the non-metric units of the short ton ( United State ...

Operation

Swingnose crossings need to operate at the same time as the main turnout switches to which they belong. This may require excessive effort for manual operation, and require a

point motor A point machine (also known as a point motor, switch machine or switch motor) is a device for operating railway turnouts especially at a distance. Overview In the earliest times, points were operated manually by levers. Gradually, these were cen ...

. The main turnout and the swingnose crossing will require separate machines.

Switched diamond

switched diamond A double junction is a railway junction where a double-track railway splits into two double track lines. Usually, one line is the main line and carries traffic through the junction at normal speed, while the other track is a branch line that c ...

is a

diamond crossing A double junction is a railway junction where a double-track railway splits into two double track lines. Usually, one line is the main line and carries traffic through the junction at normal speed, while the other track is a branch line that ca ...

in which the fixed frogs are replaced by moveable frogs.

References