1. Introduction
  2. Frogs or Crossings
  3. Switches
  4. Layout
  5. Switch Stands and Targets
  6. Additional Safety Appliances
  7. Using Turnouts
  8. References


When two wagons encountered one another on a narrow road, one wagon had to turn out to let the other pass. In railway engineering, an appliance is necessary to allow a vehicle to move from one track to another. By analogy, in America this appliance came to be known technically as a turnout. In Germany, what wagons did when they met was weichen, so the railway appliance became known as a Weiche. In Britain, however, attention was focussed on the movable, pointed rails that were known from their shape as points, and this became the name of the appliance, though really there is no actual term for the complete appliance there. In France, the points were les aiguilles, the "needles," and this was the word that was adopted there. In America, the turnout is popularly called a switch, in the same vein. Most people will talk of "switches" or "points," while only an engineer will refer to a "turnout." Also, the points themselves are technically switch rails, of which the point is just one end.

Some typical uses of turnouts are sketched at the right. A train approaches a facing turnout in a direction facing the points, able to take either route; a trailing turnout is approached from the other direction. Whether a turnout is facing or trailing depends, of course, on the direction of the train, but the facing direction is always the one in which the train has a choice of routes. There is always a danger at a facing turnout of a misplaced switch, since the safe speed for a divergence is almost always much lower than for the straight route. Facing turnouts are necessary at junctions, but on double-track railways have been strongly deprecated. Early railways avoided them altogether on main lines. A trailing crossover permits a train to "shunt" by backing through the crossover onto a parallel track. With short trains, this is quite practical, but with today's long freight trains is impossibly inconvenient. Facing points were the first points of danger protected by fixed signals. The position of a turnout is often described by the terms "open" and "closed." A closed turnout is set for the normal route, usually the straight one, while an open turnout is set for the diverging route. Operating a switch to one position or the other is called "lining" it.

The "slip switches" illustrated have their points and closure rails entirely within the crossing, which must be at a small angle (less than about 10°) typical of turnout frogs. They permit a transversal track to connect selectively with the tracks crossed, double slip switches acting as crossovers. They are not used in main tracks, but are common in terminals and yards, where space is at a premium. The obtuse crossings may have movable points, especially when the angle of crossing is small. A "wye" switch is not necessarily used in a wye track, but is so named because the routes diverge as in the letter Y. It can, of course, be used in a symmetrical wye track.

Frogs or Crossings

Let us consider a turnout from a straight track to a track diverging to the left for concreteness. The straight track supports and guides the wheels with the help of the wheel flanges. Somehow, at the turnout, the flanges must both cross the left-hand rail, while the wheels are continuously supported and guided. The device that allows the left-hand flange to pass is the first encountered, and is called the switch. The right-hand flange then later crosses by means of the crossing or frog. The American term "frog" comes from the supposed appearance of early cast-iron crossings with their four splayed legs.

The frog occurs in all kinds of turnouts, consisting of rails making an angle F, the frog angle, with grooves cut in the heads of the rails to allow the flanges to pass. The wheel treads are wider than the flangeways, and so the wheel is more or less supported at all times. The toe of the frog is on the side of the switch, while the heel is the other end. The rails from the switch side form the wings on each side of the tongue of the frog. The mouth is the space between the rails approaching the frog, while the throat is the point of closest approach. The point of the frog is generally rounded off to a width of 1/2" at the actual point of the frog. The point where the flange edges of the two rails meet when extended is the theoretical point.

In America, the frog angle is specified by the frog number, which is the ratio of the length to the width, n = PH/AB. This is the ratio of the length to the sum of heel and toe spreads. The frog angle F is easily seen to be related to n by tan(F/2) = PH/2AB = n/2, or F = 2 tan-1(1/2n). Practical frog numbers range from 5 to 20, but yard frogs are seldom less than number 8, and mainline frogs seldom less than 12. Frogs have standard dimensions that are given in Reference 2. In the diagram above, k and h are the toe and heel distances measured to the theoretical point.

A necessary accessory to the frog is some device to ensure that the flange of a wheel does not strike the point of the frog, but is carefully guided to one side. This is most usually done by guard rails, which keep the backs of the opposite wheels far enough away, as shown in the figure. The check gauge c measured from the back of the wheel must be maintained at a value that will ensure flange clearance. Raised edges on the frog itself may press on the outside of the wheel tread for the same purpose; this is called a self-guarded frog. Self-guided frogs are only used at low speeds, say 30 mph or less. If the frog angle is small, it may be necessary to use moving point frogs in which the unused flangeway is completely closed by moving a "knee" to one side. This is effective, but requires additional mechanism. A "spring frog" holds one flangeway closed by spring pressure on a movable wing rail. When a wheel goes this way, the wing rail is forced out of the way so the flange can pass. These are very commonly used on main lines, and are sprung for the straight-through movement. Diverging movments are made at low speed. Spring frogs are not used at junctions, of course.

Brittle cast-iron frogs were very early replaced by built-up frogs made of rail, bolted together with spacers. These were hard to inspect, and could fail from cracking, but were much safer than cast iron. Later, cast steel frogs were introduced and proved very satisfactory. Most frogs used now are cast steel. Manganese steel gives great wear resistance because of its extraordinary work hardening.

The Hayes derail is a movable casting that can be placed on the rail to lift and divert a wheel to the outside of the rail. The opposite wheel, of course, comes off its rail and falls onto the ties. Derails are used to protect the main line from a private siding in case of loose cars on the siding. Lack of a gradient should not be sufficient; cars can be blown by the wind or moved maliciously. It can be operated by an electric switch machine, or manually by a switch stand. On main lines, point derails are used instead; these are turnouts that don't go anywhere. Derails not only forcibly prevent fouling another line, they also give incontrovertible evidence of passing a signal at danger, like a crossing gate or a smashboard. They are encouragement not to overrun a stop signal.


The kind of switch used characterizes most kinds of turnouts. A very effective switch, first developed for steam railways, was one in which the straight and diverging tracks were completely separate and side by side. A length of rail, called the switch rail, was not spiked down but slid transversely on support plates, so that it could register with one track or the other. The throw of the switch was about 5 inches, usually with stops on both sides to ensure proper registration. In America, this kind of switch was called a stub switch. It also offered the advantage of an easy way to make a three-way switch. Unlike other kinds of switches, ice and snow, odd stones or other extraneous materials cannot get in the way of a proper alignment. For this reason, it was adopted as a safety measure, for example on the London and Birmingham Railway, as well as on the Pennsylvania Railroad. It was exported to the Continent, to France in particular.

An important part of a stub switch were the headshoes, malleable iron castings that received the two stock rails on one side, and had a flat table on the other side for the switch rail, with stops on either side. A stub switch had the disadvantage that a train approaching in the trailing direction on the wrong track would certainly be derailed. A serious accident of this type happened at Rio, Wisconsin on the Chicago, Milwaukee and St. Paul on 28 October 1886, with 17 fatalities (mostly due to the subsequent fire). The Milwaukee Road then removed all stub switches from its main lines. Before 1900 they had vanished from main lines everywhere.

In the split switch the outer, or stock, rails are continuous; one remains with the undeviated track, while the other forms part of the deviated track. Switch rails, often called just points, connect one or the other closure rail to the outer rails as necessary, only one switch rail being used for each route. These points are planed down, and are supported laterally continuously by the stock rails, which are often braced outside for added strength against overturning. The switch rails are connected by tie rods, and move together to one side or the other on flat slide plates, by means of the operating rod. The operating rod must provide a means of making small adjustments in its length. At the heels, the switch rails are connected flexibly to the closure rails by joint bars. The standard throw of a split switch is 4-3/4". Despite the danger of some obstruction's getting between the point and its stock rail, presenting the danger of the flange's passing between them and derailing the train, this kind of switch proved the safest in practice, and is now universally used. Note that the main track was not continuous, but broken at the point of the switch rail. Some engineers objected to this lack of continuity.

The Wharton switch overcame this objection by leaving the main tracks continuous and complete. To take the turnout, a ramp was brought beside the main track that raised a wheel enough by its tread so that the flange could move across the rail, when the wheel pair is guided to one side. Of course, this was not suitable at full speed, but at low speeds it was not objectionable. These turnouts were intended to be used at spurs, sidings and service tracks where the speed would have been restricted at any rate.

Switch rails are usually straight, with AREA standard lengths of 11 ft to 33 ft. The point is planed down to a thickness of 1/4", and is rounded off at the top. The heel distance, the distance between the gauge sides of the switch rail and the stock rail at the heel, is 6.50 in. or 6.25 in. The stock rail is not notched to receive them, but the diverging stock rail is bent at the switch angle. The switch rails are supported by slide plates, and held apart by the head rod at the toe, and 3 or 4 back rods along the length. Rail braces support the stock rails against overturning. The switch angle is the angle between the direction of the straight track and the gauge side of the switch rail. Curved switch rails for high-speed turnouts must be carefully designed and well-supported laterally.

A single-tongue switch consists of a switch rail opposite a frog in the other rail that will permit a wheel to pass either way. The wheel is guided by one side or the other of the switch rail. This is an early kind of switch, and was even used on steam railways in some cases, but only when speeds were low. It was much more commonly used on street railways.

The curve in the closure rail cannot be superelevated, so it is necessary to restrict the speed to a comfortable level. At such a speed, the shock of the divergence at the switch rails will not be significant. Speed is generally restricted to 15 mph for a No. 8 switch, 20 mph for a No. 12, and 30 mph for a No. 15. No restriction is necessary for a straight-through movment, only for the divergence. No divergence is ever normally negotiated at a speed comparable to the overturning speed on the lead curve.

Switch rails can be used without crossings in scale tracks, where the wheels are diverted to "live" rails connected with the scale when the switch is open. When closed, wheels pass on the ordinary track. Single switch rails can also be used in "point derails" to enforce a stop signal. Frogs can be used without switch rails in gauntlet tracks, where two tracks are superimposed without connections where the roadway is of restricted width, as on a narrow bridge.


All measurements are referred to the actual point of the frog as a reference. If b is the width of the frog point, usually 1/2" or 12 mm, then the distance between the theoretical point and the actual point is nb. The analysis is done in terms of the theoretical point. The frog number n and the length of the points L are the other necessary parameters. We want to know the radius of the curve R connecting the points and the frog, as well as the distance E from the point of the frog to the toe of the points, called the lead. These measurements are sufficient for constructing the turnout.

All we need to solve this problem is trigonometry, but it gives a better understanding to approach it by some approximate solutions. In the simplest case, assume that the curve is tangent to the straight at some point Q. If the gauge is g (standard gauge is 4.7083 ft, 56.5 in, or 1435 mm), then the radius of curvature of this rail is R + g/2. This arc crosses the other rail at some point P, which will be the theoretical point of the frog. Actually, frogs are made with straight rails except in some special cases, but we'll ignore that at this point. The angle of crossing is F. It is easy to see that g = (R + g/2)(1 - cos F), so that R + g/2 = g/(1 - cos F). Therefore, with a continuous circular arc from point to frog, the frog angle F determines the radius of curvature of the closure rail. The lead is E = (R + g/2) sin F.

Let's apply this to a No. 12 frog, n = 12. then, F = 4.772°, from which R = 1355.9 ft, and E = 113.0 ft. E should be increased by the distance from the theoretical to the actual point, 12 x 1/2" = 6", or E' = 113.5 ft. Now, the frog rails are straight, and the distance from the theoretical point to the toe of the frog is k = 6.417 ft (from a table of frog dimensions). It's very easy to modify our formulas to allow for this. In fact, R + g/2 = (g - k sin F)/(1 - cos F). Recalculating, R = 1201.9 ft. We must add k cos F = 6.39 ft to E, or E = 106.4 ft, E' = 106.9 ft. The effect of the straight portion of the frog is to decrease R and E somewhat. If it is convenient to decrease the lead, we can do this by adding a straight portion near the frog.

In either case, we can easily arrange a stub switch. If we assume that the rail will assume a circular curve when deviated (which is not quite true), then the throw T = L2/2R, or L = √(2RT). For the example with a straight frog, L = 34.7 ft. This is rather long, since it is best if L is less than a rail length, so L was generally made a little shorter, and some angular misalignment was accepted. The switch rail is a cantilever beam loaded at the end, approximately. The deflection of such a beam is D = PL3/3EI, where P is the load, L the length, E the Young's modulus (for steel), and I the transverse moment of inertia of the rail section. For a modern 115 lb/yard section, I = 10.7 in4. For a 22 ft switch rail, the force P is 52.3 lb per inch of throw, or 314 lb for a throw of 6 in. When stub switches were used, rail sections were much lighter, and the force was correspondingly less.

The addition of straight switch rails adds a little complication. If t is the thickness at the toe and h the heel distance, then the switch angle S is given by sin S = (h - t)/L, where L is the switch rail length. If h = 6.25" and t = 0.25", then for L = 11 ft, S = 2.605° and for L = 22 ft, S = 1.302°. We see that switch angles vary between 1° and 3°. This corresponds to an abrupt change of direction, which limits the speed at which the divergence can be taken. The formula for R is now R + g/2 = (g - h - k sin F)/(cos S - cos F), which we see becomes the stub-switch formula for S = h = 0. The theoretical lead E = L + [(g - h - k sin F)/tan(F + S)/2] + k cos F. To find the actual lead, nb must be added.

For a No. 12 turnout with 22 ft switch rails, we find that F = 4.772°, S = 1.302°, (F + S)/2 = 3.037°, g - h - k sin F = 3.653 ft, so that R + g/2 = 1138.7 ft, or R = 1136 ft. (a 5° 3' curve). The theoretical lead is E = 97.25 ft, so E' = 97.75ft. These numbers are not far from those for a No. 12 stub switch.

The general case is illustrated at the right. The length L of the switch rails includes any straight segment at this end of the curve, while the length k at the frog includes any straight segment there. To find R, we express the distance CD in two different ways. One way is g - h - k sin F. The other way is (R + g/2)(cos S - cos F). Equating these gives R + g/2 = (g - h - k sin F)/(cos S - cos F). If we increase L, we increase the heel distance h proportionately, and this decreases R. If we increase k, then R is also decreased.

The lead E is the sum of L, the projection of AB, and k cos F. AB is (g - h - k sin F)/tan[(F + S)/2]. The angle ABD is [180° - (F - S)]/2 less 90° - F, or (F + S)/2. Therefore, E = L + [(g - h - k sin F)/tan(F + S)/2] + k cos F. If S is small, then a change in k produces an equal and opposite change in E. By increasing k, then, we can decrease E. On the other hand, increasing L will increase E by a somewhat smaller amount. By adjusting the straight segments at each end of the closure rail, we can change E by small amounts, to suit the rail lengths we have available. It is only necessary to insert an extra tangent at one end to make this adjustment. The AREA made a table of "practical leads" of this kind. For example, a No. 12 switch, with 22-ft switch rails, can use 3 24-ft rails for the curved closure rail, and 2 24-ft rails, plus a 23 ft 10-5/8 in rail for the straight closure rail. There is a tangent of 5.33 ft next to the switch rail, and no additional tangent at the frog. The actual lead is 100' 9-5/8", and the radius of the lead curve is 1098.73 ft. (Compare with the theoretical lead given above.)

Many turnout applications involve parallel tracks. North American standard-gauge railway equipment is about 10 ft (3048 mm) wide, so parallel tracks must be a minimum of 12 or 13 ft between centres. A spacing of 14 ft or 15 ft gives satisfactory clearance. On a curve of radius R, a car with a distance D between truck centres will overhang a distance of about D2/8R. For D = 60 ft and R = 500 ft, this is 0.9 ft. Therefore, increasing the spacing by 1 ft for R between 1000 ft and 500 ft, and by 2 ft for smaller radii, should be sufficient. The overhang of the car corners should also be checked. We'll assume a spacing of p = 14 ft in what follows.

Consider a crossover between two parallel tracks of spacing p. Let the frogs be the same, and suppose the connection is straight, which is the best practice, avoiding a reversed curve. If L is the distance between the point of one frog and the point opposite the toe of the other frog where the closure curve begins, then L sin F = p - q cos F + k sin F. The distance q between the frog theoretical points, measured parallel to the tracks, is then q = L cos F - g sin F - k cos F, or q = (p / tan F) - g(sin F + cos F). Subtracting 2nb then gives the distance between the actual points. When the location of the frog points is determined, the crossover can be constructed. The distance along the connecting track between points opposite the frog points is d = (p/sin F) - (g/tan F).

For a No. 12 crossover between tracks 14 ft apart, F = 4.772°, so q = 162.62 ft. and d = 111.89 ft. The total length of the crossover, from point of switch rail to point of switch rail, is q + 2E = 357.12 ft.

A second problem is to find the radius of the circular curve to connect with a parallel track. The central angle of this curve is F, so the mid-ordinate of the inner curve is (R - g/2)(1 - cos F). This is equal to p - g - s sin F, where s is the distance along a straight track from the theoretical point of the frog to the beginning of the curve (P.C.). Therefore, R - g/2 = (p - g - s sin F)/(1 - cos F). s includes the heel distance of the frog, but it is good to make s larger to avoid a reversed curve.

For a No. 12 turnout, s = 30 ft, and p = 14 ft, we find R = 1962.9 ft. This is about a 3° curve. If the maximum allowed speed on the turnout is 25 mph, a circular curve is adequate, and superelevation is not required.

Now consider a straight ladder connecting body tracks 14 ft apart. If there is no curve beyond the frog, the ladder angle is F. For a No. 8 ladder, this is 7.153°. A forward distance of 111.56 ft is required for each track, so a straight ladder occupies a great deal of space, and often ways must be found to reduce this distance by introducing curves. If E is the lead, and s the distance from the point of the preceding frog to the points of the switch rails, then p = (E + s) sin F. This can be solved for s, s = p/sin F - E. With a No. 8 ladder, and p = 14 ft, we find s = 44.96 ft. The distance between frog points is 112.43 ft.

Suppose a curve is used beyond the frog, with a distance h between the theoretical point and the P.C.. The point at which this curve, projected backward, becomes parallel to the straight track is at coordinates x = R sin F - h cos F and y = R(1 - cos F) - h sin F, with x measured towards the points and y measured towards the other rail, as shown in the diagram. This construction is often useful when designing track layouts.

Switch Stands and Targets

The mechanism for the hand operation of turnouts is usually called a switch stand in America. It usually converts a rotary motion about a horizontal or vertical axis to a linear motion, moving the switch rails by means of the operating rod, and usually includes some sort of switch target to make its position evident to an approaching train or a switchman [we'll assme this includes the switch lamp as well]. The distance moved by the switch rails is the throw of the switch, around 4-3/4 in or 120 mm. Some examples of switch stands are shown at the right. If the handle moves a distance D while the throw is d, the ratio of the forces is the ideal mechanical advantage D/d. The harp switch stand was an early type, often used with stub switches, and is a simple lever of the first class. It can easily be applied to a three-throw switch. A pin was inserted to hold the lever in the desired position. The simple ground throw, called a parallel throw, operates through a 180° angle, and is held in position by the weight of the handle (but may be latched in each position as well). The more elaborate kinds may be "safety stands" (see below) and may have a vertical target rod. The "high" switch stand has a vertical axis that rotates through 90°. A popular model was known as the "High Star" switch stand, and there was a similar "Low Star" model. The operating handle folds down into a notch in the top plate, and can be padlocked there. In other types, the handle rotates a shaft driving the main shaft through gears, for a greater mechanical advantage. If d is the crank length, then √2d is the throw. Double cranks made connections easier. The connecting rod from stand to points was generally 6 ft long. When a vertical axis rotates through 90°, targets can be attached to indicate the position of the switch. A simple circular target is shown, which displays a red disc (or other shape) when the switch is set for divergence, and shows its edge when the switch is set for the straight. For the night indication, a lamp with four 4-1/8" lenses is placed on the top of the axis. The target rod tip is rectangular (1-1/8" x 13/16") so the lamp will go on only with the correct orientation. The long side is parallel to the rail for a closed switch. Such switch stands are used on main tracks, where the target and lamp must be high enough for visibility at a distance. When two switch stands come close together, one is high, the other low.

The eccentric was used by the London & Birmingham Railway in the 1830's to control stub switches, which had been adopted as the safest choice. It gave a definite throw (twice the eccentricity) and a positive setting. The eccentric was rotated by a capstan-like device, the handle rotating through 180°. This mechanism was exported along with early railways to Europe, especially to France, where the employees operating switches at stations became known as gardes excentriques. This name long survived the eccentrics and stub switches.

The switch may be held in either position by a spring, so that it "toggles" between the two positions. A lever is provided to change the position by a sharp pull that moves the switch rails to the intermediate position where they snap over to the other setting. Such switch operating mechanisms are used in Britain in yard tracks, and are not equipped with targets. When run through in the trailing direction, they automatically take the correct position if it is not already set. Generally, these switch stands are called "automatic"; that is, if run through they change to the correct position. An example has been given above. Another was the Ramapo switch stand, operated by a vertical handle and camming the crank rod. It rotated in steps of 90°.

The sketch labelled "Racor" is only a suggestion of what these very commonly used patent low switch stands are like, of which Racor was one manufacturer. The handle rotates through 180° parallel to the track, while the vertical axis rotates through 90°, driven by bevel gears. The operating lever is held in a latch on either side, which can be released by a foot pedal. The latch can be padlocked to prevent tampering with the switch. The switch target can be a lamp with four lenses, 4 to 5 in in diameter, each surrounded by a coloured circular target, supported on this axis. At times, only the red or yellow target was used, while the other one was omitted. Some usual colours are shown in the diagram. The colours (a) were originally chosen when green was the colour of caution, and white for clear (before 1895). For main line switches, red was often used in place of green, as at (c). When yellow replaced green for caution, (b) was the result. These were the colours later used by the Pennsylvania Railroad. If green also replaced white, (d) was the result. For main line switches, (e) was popular, and was often used for all switches. (f) might be used for yard switches, if green was considered inappropriate. Actually, yellow and green is probably the best choice for yard switches, since it does not use red to mean something other than stop. The C&EI used white and yellow, the SP&S white and red, for switch lamp targets. For main lines, green and red is probably the best choice of colours. The AT&SF used green for a closed switch, red for an open main track hand-thrown switch, yellow for interlocked and yard switches. The yard switches used small rectangular yellow targets. Lunar white (bluish-white) was sometimes used for lamps on yard switches set for the straight route, as by the Southern, who used regular white (clear) for main line switches.

Some typical simple targets for high switch stands are shown at the right, usually made of painted sheet steel. The company identifications are not certain, but seem to be valid. The same company may well have used different targets in different times and places. Except where shown otherwise, there is no target for a "closed" switch, one set for the main line, in these examples. Such a target was often called blind. The target is displayed when the switch is "open," set for the divergence. The "SS" target is for a spring switch lined for the main line. The simple red disc is by far the most common target, used not only by the UP, but by the AT&SF and many other companies. Red or yellow are the only colours found; red is often used for main line switches, and yellow for yard switches, but sometimes no distinction is made and one colour is used for both. In block signal territory, switch stands did not carry lamps, to avoid confusion with signals. These switches were, of course, protected by the nearby signals, which went to Stop when the switch was open. Outside block signal territory on main lines, lamps (or reflectors) were always used. Ideally, the lamp should be at the engineman's eye level, 10 to 11 ft above the rail, but were usually somewhat lower, 7 to 8 ft. This is high enough to avoid confusion with hand signal lamps. A low lamp was at a height of 4 to 5 ft. The disc target is typically 18" in diameter, which gives an idea of the usual size of targets. The operating handle is 22" long. The crank at the bottom is 3-11/16" long, giving a throw of 5-1/4", slightly greater than the point throw to provide extra pressure. Very often yard switches had at most a lamp, often without coloured targets, to show the state of the switches by night. By day, crews were expected to observe the points. Sometimes, small targets were provided on the lamp axis if the lamps did not have them surrounding the lights. Often, yard switches are found with no lamps or targets at all. Interlocked switches never had targets.

The figure also shows the German switch indicators. They are black boxes illuminated from inside. The white areas are translucent. When approaching a switch from the facing direction, the arrow shows whether the divergence is to the right or left. When trailing into a switch, the disc is shown when the switch is set for divergence. If set for straight through, then the vertical rectangle is seen as in the facing direction. The discs with sickle-shaped black lines are used when both directions are divergences. In the facing direction, the inclined rectangles are used. Indicators of this type are very widely used in Europe. The same indicators may be found in Austria and Switzerland, while similar ones are used in Belgium and France. German-type indicators have the advantage that they cannot be confused with coloured signal lights.

At the left are shown typical main line switch targets and lamps. These examples are from the Pennsylvania Railroad, the Southern Railway and the Louisville and Nashville, all of which use the original signal colours red and white, and which give a positive indication of a closed switch. (The PRR, SOU and C&EI used white and yellow targets for yard switches). The red pierced "spectacle" is a very early and familiar shape often found on switch targets. Note the green reflective disc. This red spectacle and white inclined bar is familiar, often without the green reflector. There has been a very great variety of target shapes and colours. It is good practice to make the two targets for the straight and diverging routes of different shapes, as is clearly done here, but very often only a single target is used. Different shapes are more easily recognized than the colours under bad illumination. The use of reflective surfaces is a very good idea. With bright headlights, reflective surfaces can replace active illumination with considerable economy, since no maintenance is required.

At the right are some targets used by the Denver & Rio Grande Western, as seen in photographs. The yellow targets, on high stands, were used in Salida Yard, for example. Yellow and green circular targets also were used on switch lamps. The D&SL targets were at Utah Junction in 1947, while the small red target was seen at Craig much later. Green (or blue) is a relatively bad colour for painting any sign or signal, since it is obscure and does not stand out against the usual backgrounds. When backlighted, or in the shadows, it becomes black. White, red and yellow are excellent colours, and black makes a good contrast with yellow and white, as does white with red.

Two sets of targets showing a positive "closed" aspect are shown at the left. The Milwaukee arrow-feather target was often used alone, without the green diamond, which seems to have been an afterthought. The feather target is 2' 9" high and 1' 0" wide, the top at a height of 6' 9". The white bar and red arrow is typical of many other targets, both high and low. There may well be alternative colours, such as a white bar and a yellow arrow, and a white disc substitute for the bar. The CB&Q also used small rectangular targets on low switch stands, green above and yellow below, as well as green and yellow lamp surrounds, and the red bar for high signals. The Michigan Central made typical choices for switch target colors, as shown at the right. A yard switch set for the lead (the track from which others diverge) shows a lunar white light.

The switch stand may be located on either side of the turnout, usually on two long (15 ft) crossties, called the headblock. The origin of the term "headblock" is probably interesting, but I do not know it. It probably comes from the days of bar rail wooden track, and refers to the base on which the switch rails moved. On a ladder track, the switch stands should be on the outside, across from the body tracks, so that the switch tender will not have to cross tracks to go from one turnout to another. In other cases, the switch stand is generally placed on the right-hand side as seen when approaching the points, if space is available.

Oil lamps gave good service in switch lamps for many years, especially when mineral oils (kerosene) replaced organic oils. Their principal disadvantage was the cost of maintenance. The reservoir (fount) had to be filled, and the wicks trimmed or replaced, at regular intervals. Founts and burners could be exchanged as a unit without disturbing the whole lamp, so the maintenance could be performed in the lamp shed. The simple round- or flat-wick burners screwed or socketed into the tops of the founts. An American long-burning lamp could burn for 6 or 7 days, but was not very bright. A 4-day fount held 37.4 cu. in., while a 7-day fount held 63.9 cu. in. A quart of kerosene will burn for about six days in a long-time burner. At this burning rate, the lamps would do well to produce 1 cp. In Europe, propane lamps, using incandescent mantles, gave excellent service. Some could burn for six weeks before the gas tank had to be exchanged. Propane lights never were used in the United States. Electric lamps were excellent, of course, but involved the problem of electricity supply, which could involve a tangle of wires. Electric switch lamps are easily identified by the lack of a chimney and lamp handle. The reliability of oil lamps, and the absence of wires, were strong incentives for retaining them. The short focal length lenses were Fresnel lenses to reduce their thickness, and the glass was appropriately coloured. Optical systems were, in general, crude. Reflectorized surfaces ("Scotchlite") are also an excellent idea where headlights are bright, and should have been used more widely.

A split switch may be run through safely in the trailing direction even if the points are set incorrectly. However, if the operating connection is rigid, this will in general break it and free the switch rails. Therefore, the switch rails must be spiked in position until repairs can be made. Also, the train must not be backed once any portion has run through the switch in this way. A spring may prevent breakage of the operating rod, but in general springs are avoided except for turnouts meant to be run through, called spring switches. In this case, a dashpot retards the switch rails from moving back rapidly once they have been forced aside by a wheel. It is very important not to make a partial movement through a spring switch. In general, an accompanying signal shows when the switch rails are in the correct position for a facing movement. Spring switches are very convenient at the exit end of sidings.

Additional Safety Appliances

Track-circuited turnouts must have the the switch rails insulated from each other, so the tie rods must be provided with insulating joints. A circuit controller connected directly with the points should be adjusted so that a movement of 1/4" or 6 mm away from the stock rail will cause the track circuit to be shunted. A switch indicator in clear view of the switch stand (about 4 ft away, and 4 ft high) should show if the track circuit is shunted, that is, if a train is approaching. The indicator was usually a miniature semaphore. All arrangments to detect the position of the points, such as the switch box, must be connected directly with the points, and not to the operating rod.

A facing-point lock has the dual functions of (1) proving that the switch rails are properly set in one direction or the other, and (2) preventing motion of the switch rails while engaged. A facing-point lock is not usually provided for hand-operated turnouts, but is used with motor-operated or interlocked turnouts that are controlled remotely. Originally, a facing-point lock was provided with fouling bars in the flangeways. In order to withdraw the facing-point lock, the fouling bars had to be raised first, which could not be done if wheels were passing over them. This protection is now provided by track circuits. The facing-point lock can either be in the stretcher bar between the switch rails, or at the side of the track, connected by a rod directly to the points. The plunger then engages in one of two holes, or else the switch rails are held directly by rotating lugs in their two positions.

Using Turnouts

The failure of turnouts themselves seem to have caused very few serious accidents. The stub switch accident at Rio is one in which the turnout design contributed to the accident, but was not the cause. Spring switches have caused accidents when a partial movement is reversed, or when the points have not fit properly due to an obstruction. In general, problems with turnouts arise when they are not used properly. A misuse that has caused many accidents is that of the "open switch" when a train moving at speed encounters a facing turnout set for a low-speed divrgence. A particular case of this kind of accident is discussed in The Open Switch, in which a switch is abruptly changed to the wrong position immediately in front of an approaching train, without malicious intent. This is a psychological peculiarity that can be defended against. Open switches can also result from malicious behavior, in which points are slightly opened, or steps taken to display a clear lamp or target by mechanical means. This is disussed in Sabotage . It should be appreciated that an excessive speed may not be sufficient to cause overturning or derailment at the turnout itself; more dangerous is the possible collision with equipment on the diverted route.

Under the Standard Code of Operating Rules in the United States, the use of turnouts was governed by Rule 104 and lettered supplements to it. Rule 104 outlined the responsibilities of employees handling switches. Main track switches were to be lined for the main track, secured and locked. Switches on a siding (track used for meets) were to be lined for the siding, secured and locked. Derails were to be set to derail and locked in that position. Switches used by a train were to be left in their normal positions, and the conductor was responsible for checking that this was done. Switches were not to be left open for another train; each train was separately responsible for its own switches. Rule 104(A), drafted by the individual company, prescribed the steps to be taken to ensure that a switch was not inadvertently opened in the face of a train. These were usually that the switch should be kept lined for the main track and locked until the expected train had passed, and that the employee lining the switch should stay a certain distance away (20 ft, the clearance point, across the track) until the train had passed. Rule 104(B) might prescribe that all switches involved in a movement (e.g., both switches of a crossover) must be lined before any track is fouled, and the movement should be completed before any switch is relined. And also, that a train must not be reported in the clear before the switches are lined and secured. Rule 104(C) might govern the use of spring switches, and mention not to reverse until the train is completely clear of the spring switch, not to use sand on spring or power switches, and that their locations are specified in the time table. Of course, these supplements varied with the different companies, but generally the matters mentioned were included.

North America was unusual in the prevalence of hand-operated turnouts in main lines, a result of the light traffic density as well as of tradition. Even major passenger terminals, such as at New Orleans, Louisville and Dearborn Station in Chicago, to mention just a few, were until well after World War II operated by switchtenders that went from switch stand to switch stand setting routes, and then hand signalling to trains when they could enter or depart. This method of operation was suitable only with relatively light traffic and simple routes, but was remarkably successful and, above all, was cheap. It can be used safely only when there is a single switchtender responsible at any time, to avoid the confusion that early encouraged interlocking in Britain.

Turnouts in a limited area were not controlled from a central location in the form of a ground frame in North America. Indeed, ground frames were unknown, their functions carried out by switch stands located at the turnouts. This avoided the problem of not knowing exactly what one was doing at a ground frame that necessitated interlocking. In particular, the turnouts involved in meeting (crossing) and passing trains were handled by the crew of the train using the siding. Main-line turnouts were kept padlocked, but the padlocks were not part of the signal system, so the turnouts could be operated at any time by anyone possessing a switch key.

After about 1945, the development of CTC made the creation of small electric interlocking installations, as at important junctions, practical. These machines could be operated by the telegraph operator who also handled train orders, and controlled signals and turnouts on up to several miles of line.


C. F. Allen, Railway Curves and Earthwork, 6th ed. (New York: McGraw-Hill, 1920). pp. 79-103.

C. F. Allen, Field and Office Tables, 4th ed. (New York: McGraw-Hill, 1931). Tables XXII, XXIIA, XXIIB.

E. P. Alexander, A Pictorial History of the Pennsylvania Railroad (New York: Bonanza, 1967). Stub switches are shown in illustrations 41, 107, 122 and 188, with harp switch stands, in the 1860's. . Illustration 171 shows a split switch in 1875.

Return to Railways Index

Composed by J. B. Calvert
Created 19 June 2004
Last revised 2 August 2004