Prototype Information
A turnout is an arrangement of track which diverts rolling stock from one track to another.
The principal parts of a turnout are a switch, a connecting piece of track called the lead, and a frog.A turnout is an arrangement of track which diverts rolling stock from one track to another.
- The switch is the device for shifting the route at the entrance of a turnout.
- The rails connecting the switch with the frog, in both main track and turnout, are lead rails, (alternatively named the main lead and the turnout lead).
- The frog is the union of two rails which cross each other, in such a manner that a wheel rolling along either rail will have an unobstructed flangeway while passing the other rail.
There are three types of switches: stub, wharton, and split switch.
- A stub switch is a railroad track switch that lacks the tapered point rails of a conventional switch. The movable rails and the ends of the rails of the diverging routes have their ends cut off square. The switch mechanism aligns the movable main line rails with the rails of one of the diverging routes.
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| Stub Switch |
- The Wharton switch is not used today. The main track rails are unbroken and continuous. The switch rails consist of one point or grooved rail, which works against the main-track rail on the side opposite the frog, and another rail to which it is cross connected, working against the outside of the main-track rail on the frog side.
- The split switch is made up of a rail from each track, both rails being tapered a long way back and connected together, so as to throw alongside the through rail of either track. The split switch is the most common switch type used by the prototype today.
Frogs
There are two types of frogs: rigid and sprung.
- The rigid frog is the most common frog found on railroads. In a rigid frog all the parts composing it are supposed to be rigidly connected. The parts of both rigid and spring-rail frogs are joined together in three different ways: ( 1) by placing filler blocks between the pieces of rails and holding them together with bolts passing through the webs; (2) by riveting the flanges of the pieces of rails to a plate; and (3) by clamps or by clamps and wedges.
- The sprung frog is found on main line tracks, and especially for those sections where the heavy traffic moves principally in one direction. It gives to the main line the smoothness of an unbroken track. In an ordinary spring-rail frog the wing which takes the bearing of wheels on main track is movable, and, except when it is spread by the flange of a wheel passing through the turnout, it rests against the point pieces. With such a frog there ia normally but one channel. As successive wheels pass the movable wing, or "spring rail," as it ia called, is pushed aside by the flanges and returned to normal postion by the spring.
Turnout comes in various sizes, the geometry based on the degree of curvature of the diverging route. The degree of curvature is identified by the frog number. A turnout has its unique engineering to determine the degree of curvature but for simplification purposes, the frog number is a 'rise-run' calculation - a No.6 frog diverges one unit for every six units of length. The smaller the number, the sharper the curve. The Union Pacific has a Common Standard for No 6, No 7, No 8, No.9, No 10, No 12 and No 14 turnouts.
Here is an example of the UP Common Standard No 6 turnout.
The frog number also determines the maximum speed through the turnout. Here is a chart of frog number and authorized maximum speed from the AREMA.
switch points, referred to as "switch stands", may be used in main tracks, branch lines and secondary
tracks, yard and sidetracks, without restriction.
There are two types of switch stands: locking switch stands and
Manually operated mechanisms, combined in one unit, which throw the switch points and
also provide for locking them in normal and/or reverse position, referred to as "locking switch
stands", may be used as follows:
(e) Manually operated mechanisms, the position of which is automatically reversed by
wheels trailed through a switch set for the opposite route, and referred to as "semi-automatic switch
stands", may be used in yards and sidings where authorized by Timetable Special Instructions.
Switch point position indicators. Switch point position indicators are located on switchstands to give train crews a clear and distinct indication of the position of the turnout's switch points. Those position indicators can be lamps, colored targets, or both. Lamps and targets are set at right angles to the track and perpendicular to the head ties. Where targets are used, the upward point of the inclined blade shall be away from the track, when the switch is set normal for the main track.
Manually operated mechanisms, combined in one unit, which throw the switch points and
also provide for locking them in normal and/or reverse position, referred to as "locking switch
stands", may be used as follows:
(e) Manually operated mechanisms, the position of which is automatically reversed by
wheels trailed through a switch set for the opposite route, and referred to as "semi-automatic switch
stands", may be used in yards and sidings where authorized by Timetable Special Instructions.
Switch point position indicators. Switch point position indicators are located on switchstands to give train crews a clear and distinct indication of the position of the turnout's switch points. Those position indicators can be lamps, colored targets, or both. Lamps and targets are set at right angles to the track and perpendicular to the head ties. Where targets are used, the upward point of the inclined blade shall be away from the track, when the switch is set normal for the main track.
The target consists of two pieces of sheet
iron fastened to the target rod at right angles to each other.
The design of the target is railroad dependent. DepeOne-half of the target is usually painted white, indicating
safety, and the other half red, indicating danger.
They are so adjusted that an open switch always indicates
danger.
Lamps and targets are colored based on the type of switch and its position.
red yellow green orange
Manually operated switch stands shall be placed so that the operating rod is in tension
when the switch is set in normal position in main track, and at the siding end of crossovers between
main track and siding.
(e) Switch stands for all other tracks shall be located to serve the safety and efficiency of
employees in the best manner.
spring switches
A spring switch has a cylinder, in the middle of the throwbar, that contains heavy springs. In normal position, the points are lined for the normal route. The switch can be aligned to the siding for entry moves in the traditional way. But a train coming in from the trailing end will reach the points and push them agianst the spring, opening the turnout for those wheels. Once the wheels clear the points, the points snap back to normal. Ergo, listening you will hear the points snap back between the trucks under a freight car. Once the last car passes, the switch will return to the normal setting.
The pressure from the wheels forces the points into the desired
position. That's why spring switches only work for trailing-point
movements. To go the other way, a switch has to be hand-lined.
The switch stand for a spring switch is, commonly, marked with an
indicator that has a huge black letter "S" on a white background.
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