GEOMETRICS

RAIL vs.

HIGHWAY PART II

By: Greg Toth, PE PB Americas, Inc.

Presented to the 2009 AREMA Annual Conference September 22, 2009

© AREMA 2009 ®

Biographical Sketch

W. Gregory Toth Greg Toth is a Lead Engineer in the Chicago office of PB Americas, Inc., a position he had held for over twenty years. Greg has been with PB twenty-eight years and previously worked for companies on both coasts doing railroad, transit and highway design. In 2007 he presented the paper “Geometrics – Rail vs. Highway” at the AREMA Conference in Chicago. He graduated from Purdue University and is a registered Professional Engineer. He makes his home in northwest Indiana and is a member of AREMA Committee 12.

© AREMA 2009 ®

AREMA Annual Conference and Exposition 2009 PROPOSED TECHNICAL PAPER ABSTRACT Submitted: December 15, 2008 via email Principal Contact: Greg Toth, (312) 803-6511, toth@pbworld.com Title: Railroad, LRT and Highway – A Comparison of Geometric Policies Part 2 Author: Greg Toth, P.E., PB Abstract: This paper is a continuation of comparisons between geometric design practices for railroads, light rail

transit (LRT) and highways. The paper will address the differences in design policies between rail/LRT and

highways and will cover railway interlockings with turnouts and crossings, and highway interchanges with

ramps and collector-distributor (CD’s) roadways. The comparison will be based on existing FRA, FTA,

AASHTO, and State DOT criteria along with AREMA and other current railroad standard practices and

policies.

The purpose of Part 2 of this paper is to familiarize highway engineers with more complex railroad and

LRT design. With railroads reducing their engineering staffs, and LRT system development growing, more

and more railroad and LRT design work is being passed on to the private sector where it may, in many

cases, be designed by highway engineers with little or no railroad or LRT experience. Therefore, a basic

understanding of railroad and LRT design and comparison to highway design would be beneficial to the

experienced highway engineer.

© AREMA 2009 ®

All referenced AREMA formulae, tables and figures are used with permission

from AREMA and are copyrighted by AREMA.

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Greg Toth i

Table of Contents A History Lesson ……………………………………………………………………………… Design Considerations …..…………..………………………………………………………… Comparing Rail and Highway Designs ....…………………………………………………….. Degree of Curve ….……………………………………………………………………………. Turnouts and Highway Terminals …………………………………………………………….. Highway Terminals.…………………………………………………………………………… Convergences and Divergences ……………………………………………………………….. Turnouts ……………………….…………………………………………………………….....Alignment Layout……………………………………………………………………………. ..Laying out a Turnout…………………………………………………………………………... Placing a Turnout……………………………………………………………………………..... Conclusions……………………………………………………………………………………..

List of Figures Figure 1 – Typical Layout, No. 9 Ballasted Turnout..………………………………………….Figure 2 – Standard Exit Terminal (IDOT) ……………………………………………………Figure 3 – Standard Entrance Terminal (IDOT) ………………………………………………. Figure 4 – Ramp Types (IDOT) ……………………..……………………………………….... Figure 5 – Interchange Types (IDOT) ………………………………………………………… Figure 6 – Major Convergences and Divergences…………………………………………….. Figure 7 – Single and Double Crossovers …………………………………………………….. Figure 8 – Siding Track ……………………………………………………………………….. Figure 9 – 2nd Main Crossover to Siding or Spur Track ………………………………………. Figure 10 – Universal Crossover ………………………………………………………………

List of Tables Table 1 – Turnout Data for Curved Split Switches ………………………………….…………. Table 2 – Turnout Data for Straight Split Switches.….….….….….………………………….... Table 3 – Speeds through Turnouts with Straight Switch Points (AREMA …………………… Table 4 – Speeds through Turnouts with Curved Switch Points (AREMA …………………….

List of Diagrams Diagram 1 – Rail Bound Manganese Steel Frog ……………………………………………….. Diagram 2 – Turnout w/ Curved Switch Points ………………………………………………… Diagram 3 – Split Switch ………………………………………………………………………..

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Geometrics – Rail vs. Highway – Part II

A History Lesson

About two and a half years ago I was approached by my supervisor who suggested I write and

present a paper. I told him I had been considering writing one for years and thought that a good

subject would be a comparison study between railroad and highway design. Since I had some

time on my hands, I started to write that paper and ended up presenting it at the AREMA Annual

Convention in Chicago back in September of 2007.

The paper and presentation went well and has been used within my company by emerging junior

engineers and some highway engineers who wanted to learn or were placed in a position where

they needed to know how to do rail design.

So now two years have gone by and as before, my supervisor suggested I write and present

another paper. So I figured what better subject was there to write about than another one about

comparing rail and highway design, but this time, it would have to go into a more specific and

detailed comparison - so here it goes…

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Design Considerations

Since the primary intent of this paper deals with the introduction of rail design for a highway

engineer, the discussion and explanation of highway design will not be covered in any great

detail in this paper. It is felt by the author that the likelihood of a railroad designer being placed

in a position of designing a highway layout without the assistance of a highway designer present

is – well unlikely – while it is a distinct possibility that the highway designer my be placed in the

position of being required to design some type of rail alignment that may require the placement

of turnouts. The first paper written covered the basic similarities and differences of design,

whereas what now follows will assist the highway engineer in laying out an alignment which

will include the need for one or more turnouts.

Comparing Rail and Highway Designs

The first paper covered most of the common comparisons such as ‘degree of curve’, the use of

spirals, grades, vertical curves, classification and designation of rail and highway types, basic

horizontal and vertical alignment, typical sections, clearances and finally variances to design

criteria and standards. This paper will attempt to give the engineer an idea of how more complex

designs have very similar concepts showings analogies between rail and highway design.

The most important item in design in comparing the two types of design is the concept used to

define horizontal curves. This design parameter is known as the ‘degree of curve’ and is one of

the most overlooked yet easily confused part in attempting to go from one type of design to the

other. All engineers who are required to do both rail and highway design, or ones switching roles

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to attempt the other must always be aware of the difference in these two definitions and their

application.

Railroads always use the ‘chord’ definition and highways always use ‘arc’ definition, while

transit authorities normally use the ‘arc’ definition.

A quick review is always a good idea since many a time the first comment received from a

reviewer of a rail design is, “Railroads use chord definition…” It happens more often than not so

I feel it necessary to cover it one more time…

Degree of Curve

By ‘chord’ definition, the degree of curve is the angle measured along the length of a section of

curve, subtended by a 100-foot chord. The following is the equation used to define or calculate

the radius.

R = 50 / sin (D/2)

For a curve that has a D(chord) of 1o, the radius is 5729.65 ft.

The degree of curve by ‘arc’ definition is defined as the angle measured along the length of a

section of curve, subtended by a 100-foot arc. The equation used in this case is:

R = 5729.58 / D

Where the constant 5729.58 is derived from the following ratio and usually rounded off to

hundredths.

D / 360o = 100 / 2πR

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So that pretty much covers that and now we can start in on the more interesting part of these two

types of design.

Turnouts and Highway Terminals

In any design, be it railroad, transit or highway, there will come a time when the alignment

diverges from one to two movements or converges from two movements into one. At these

locations there are specific geometric changes that occur that require a special design that meet

certain requirements and design standards.

On a railroad or transit system, this results in the introduction and placement of what is called a

turnout, which is sometimes referred to as a ‘switch’. Anyone ever playing with a train set has

probably seen these and they are very simple yet sometimes complex in their design. Below is a

typical layout for a No. 9 Ballasted Turnout.

Fig. 1 – Typical Layout, No. 9 Ballasted Turnout

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There are other types of more complex turnouts such as double-slip switches, lap switches that

have two overlapping switches in opposite directions and three frogs resulting in three separate

movements beyond the turnout, and turnouts with moveable point frogs where the frog point is

connected to a ‘switch’ machine that moves the point similar to the switch that allows for higher

speed movements through the turnout. There are also tangential turnouts that were developed to

eliminate the bend at the point of switch which is common on standard turnouts. This will be

covered in more detail later on in this paper.

Only standard types of turnouts will be covered in this paper. Further information regarding the

other types of turnouts mentioned in this paper can be found in many rail related standards,

books and documents.

Highway Terminals

For highway applications, the change in movement from one to two or two to one direction of

travel requires a terminal, which is usually defined as an ‘exit’ or ‘entrance’ terminal, or as a

‘major’ or ‘minor’ convergence or divergence. The following figures illustrate a typical entrance

and exit terminal.

Figure 2 – Standard Exit Terminal

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Figure 3 – Standard Entrance Terminal

Terminals are found along highways where one roadway crosses over another roadway. In order

to travel from one roadway to the crossing roadway, interchanges are placed to accommodate

this movement. The connections between these crossing roadways are called ramps which allow

vehicles to travel unimpeded between roadways.

There are a number of different types of interchanges, such as cloverleaf, bugle, single-point

intersection and directional, to name a few, but all have the same geometric theory in common,

the use of entrance and exit terminals to connect the ramps to the roadways. Below are some

diagrams of different types of ramps:

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Figure 4 – Ramp Types (IDOT)

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The following figure illustrates two of the more commonly used interchange designs.

Figure 5 – Interchange Types

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The design of terminals vary from state to state with standards developed for both entrance and

exit terminals. Many states have standards for both single and double lane terminals, and also

those with straight tapers and or having curved gore areas where acceleration and deceleration

lanes are added with their lengths based on the highway’s and ramp’s design speed along with

factors applied to adjust for grades.

Straight taper terminals are based on specific taper rates, such as 30:1, 50:1, etc., or may be set

by an angle which is determined by a set offset based on the ramps width (including the

pavement gore) and length along the taper.

Highway designs are all based on standards and criteria that are set forth and must meet both

State and Federal (AASHTO) requirements.

Convergences and Divergences

There are other types of layouts found along highways that are called divergences and

convergences. They are usually classified as either major (multiple lanes diverging or

converging) or minor (single lanes diverging or converging) and can be found where two

highways or single lane roadways meet that are going in the same direction.

The following figures are illustrations of a major and minor convergence.

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Figure 6 – Major Convergence and Divergence

Divergences and convergences are similar in design to that of terminals and are based on the

number of lanes and the design speed of the roadway.

Turnouts

There are a number of types of turnouts being manufactured for railroad, transit and commuter

rail service. This paper will only cover the standard turnout design used by most railroads and

transit authorities.

North American railroads have standardized turnouts that are designated by ‘number’ which are

defined by the angle of the deflection or crossing angle. Since a railroad track has two rails, there

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will be a crossing of two of these rails, at which point the crossing rails are referred to as the

‘frog’. The most common type of frog is called a ‘rail bound manganese’ frog, although there are

a variety of other types such as moveable point and solid manganese, to name a few.

As the turnouts are defined by the number ‘N’, the number is based on the turnout or frog angle

‘F’ which is defined by the following equation:

N = ½ [ COT (1/2) F ]

This equation was developed years ago and is still in use today.

In the United States, Canada and Mexico, the standard frog numbers usually start at number 5

and continue up in single integer increments. The most common values used today are 5, 6, 7, 8,

9, 10, 11, 12, 14, 15, 20, and 24. There may be other turnouts in existing track that may have a

different frog number, but they are probably of an older manufacture and have been in service

for many, many years.

It is also possible, but very uncommon, to have a non-standard frog/turnout with a fractional

number. These types of turnouts are rare and if present, usually occur on older transit systems

(Note: European design has a different designation of turnouts that will not be covered in this

paper)

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Frog lengths vary based on the number of the turnout. As the frog or turnout number increases,

the angle decreases and the length of frog will increase due to manufacturing requirements and

the actual physical components and configuration of the frog.

Shown below is a diagram of a standard rail bound manganese steel frog.

Diagram 1 – Rail Bound Manganese Steel Frog

The remaining parts of the turnout are the switch points (the moveable, machined rails at the

Point of Switch of the turnout that allow the change in direction by moving the switch points)

and the closure rails, which connect the switch to the frog.

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Other parts of the turnout are called out in the diagram below, but will not be discussed in detail

in this paper.

Diagram 2 - Turnout w/ Curved Switch Points

The switch normally comes with either straight or curved points with specific lengths for each

type of switch. Curved points normally come in 13, 19.5, 26 and 39 foot lengths, whereas

straight points normally come in 11, 16.5, 22, and 30 foot lengths, all of which are standard

AREMA switch lengths. One may also find other lengths based on individual railroad standards.

Below is a diagram of a standard split switch shown for ballasted track.

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Diagram 3 - Split Switch

In both straight and curved switch design a bend has been introduced at the point of switch,

which can be at the exact point of switch or placed slightly before the point of switch. The

distance between the bend and the point of switch is referred to as the ‘vertex distance’. Without

the introduction of the bend at the point, the milling of the switch points would have too much

flexibility that would result in stability problems and in moving the switch points from one

position to the other, whereas by introducing this bend, the result provides the necessary

structural stability of the switch points to support the loading on the rails themselves.

The following tables show some of the dimensions and angles for standard AREMA turnouts for

both curved and straight switch points.

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Table 1 – Turnout Data for Curved Split Switches

(Excerpted from AREMA publications with permission)

Table 2 – Turnout Data for Straight Split Switches

(Excerpted from AREMA publications with permission)

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One of the most important dimensions of the turnout is called the ‘Actual Lead’. This dimension

is a set distance from the ‘Point of Switch’, also known as the PS, and what is called the ½-inch

Point of Frog, or ½” PF, and will vary in length for each turnout. It will also be different (in most

cases) for the same size turnouts having straight or curved points of switch or even differ from

railroad to railroad. So it is always wise for the design engineer to determine which type of

switch will be used and which railroad standard is to be used.

Since the actual crossing location of the gage lines of the two rails – called the ‘theoretical point

of frog’ - can not be manufactured and maintained at a razor-sharp point, railroads use a point ½-

inch in width that is beyond the theoretical point as noted in the turnout diagram above. This ½”

point is a set distance (in inches) from the theoretical point, which can be calculated by taking

the frog number ‘N’ in inches and dividing it by two. As an example, the distance between the

theoretical and actual points of frog (or ½” PF) for say a No. 15 turnout will always be 7.5

inches. This simple calculation is good for all standard turnouts used by railroads and transit

authorities that use standard AREMA-type turnouts.

Another critical point in the geometry of a turnout which is necessary in designing a turnout is

known as the ‘PITO’ or Point of Intersection of the turnout. This point is the intersection of the

two centerlines of the turnout extended back along the tangents from the frog to the switch. This

is also a set distance for any given turnout number and will not change unless the frog number

changes. This distance can be calculated by the following equation:

Distance between PITO and ½”PF = gN + N/2

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Where,

g = track gage (or 4’ 8-½” for most railroads and transit agencies)

N = the Frog Number

So, to determine the distance from the PITO to the ½“ PF of a No. 15 Turnout, the distance

would be:

56.5” x 15 + 15/2 = 855” or 71.25’

This distance is the same for all standard No. 15 turnouts, regardless of the railroad or

manufacturer.

This distance can then be used to determine the location of the PITO with respect to the PS by

subtracting it from the ‘Actual Lead’. Strangely enough, this value is not always shown in

Turnout Tables and oft times left off Standard Turnout Drawings, so it is important to know how

to establish this value.

A simple example is always a good way to show how something is done, so here it is.

Let’s assume that a standard AREMA No. 15 Turnout with curved switch points will be used in

the design. From Table 1 above, the ‘Actual Lead’ is 113’-5” or 113.42’. The distance between

the PITO and the ½” PF has already been calculated to be 71’-3” or 71.25’. Subtracting this

distance from the Actual Lead gives a distance of 42’-2” or 42.17’ – which is the distance

between the PS and the PITO.

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Let’s now assume that the turnout will still be a No. 15, but it was determined that straight switch

points will be used. From Table 2 above, the ‘Actual Lead’ is 126’-4 ½” or 126.38’. By

subtracting the same value of 71’-3” or 71.25’ for the distance between the PITO and the ½” PF,

the resulting distance between the PS and PITO will be 55.13’ or 55’-1 ½”.

As one can see, the distances are different. This is very common and one can see that by

determining the PS to PITO distance for any of the turnouts in the tables above, that no two

turnouts having the same frog number, ‘N’, will have the same PS to PITO distance.

This difference in distance can be crucial under some conditions when placing a turnout in a

location where there are geometric constraints, such as increasing the tangent distance between

the PS and the end of a curve or keeping the switch off a bridge approach or some other physical

constraint. As noted earlier, there are minimums that must be met for many different conditions,

and that it is possible that by using one type of switch point over the other, it could be beneficial

changing it if the railroad or LRT authority approves the change. However, if the change is to a

switch point type that is not standard for the railroad or LRT system, it may not be approved.

Turnouts are placed at locations where there is a need to go to or from one track to two tracks or

from one track to a second track. A few examples of locations where turnouts are used are at

sidings, spurs and within yards where trains are stored. They may also be found along two-track

layouts where a crossing section of track is placed to allow movement from one track to the

other. This crossing track is called a crossover and is a combination of two turnouts of

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(normally) the same size and the crossing track. It is usually considered a single unit but can be

designated as two turnouts, depending on the distance between the two tracks.

A second configuration similar to this is a double crossover which consists of four turnouts and

two crossing tracks that allow movement between either of the two tracks. The crossing tracks of

this type of layout is referred to a diamond, which consists of what are known as two end frogs

and two center frogs.

The two sketches below illustrate these two types of crossovers.

Figure 7 – Single and Double Crossovers

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Alignment Layout

Both rail and highway layouts are a combination of straight and curved sections of track or

roadways with single or multiple track (usually no more than two) or multiple lanes of traffic.

Many rail alignments are single track allowing traffic in both directions. To allow passing

movements, a siding – or second track – is added at set distances and at predetermined lengths to

allow passing trains to continue in their respective directions with little or no delays to either

train. To connect this passing track to the main track, turnouts are installed at both ends with

their size (turnout/frog number) determined by the operating railroad’s design standard and

criteria. Normally on the mainline, these turnouts will range from 15’s or 20’s for low-speed

trains and 24’s for high-speed trains. If the tracks are designed for slower speeds, the railroad

may opt to use smaller turnouts for cost reasons, but if it is a mainline track, it is customary to

use at least 15’s.

The tables below are based on the standard railroad practices and illustrate the allowable speeds

through standard turnouts with straight and curved switch points. Note that different railroads

may use different speeds as a basis of design and the designer should always refer to the

railroad’s or transit authorities design standards before using a specific turnout for any given

speed.

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Table 3 - Speeds through Turnouts with Straight Switch Points

(Excerpted from AREMA publications with permission)

Table 4 - Speeds through Turnouts with Curved Switch Points

(Excerpted from AREMA publications with permission)

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Note: An equilateral turnout has the frog rotated such that the frog angle is split equally in both

directions from the turnout’s centerline resulting in a turnout where the diverging tracks are a

mirror image. This layout results in the turnout radius being increased approximately double that

of a standard lateral turnout.

For additional criteria, standards and policies, the design engineer may use the AREMA ‘Manual

for Railway Engineering” and for standard type drawings the ‘AREMA Portfolio of Track Work

Plans’. Both publications are undated regularly on an annual basis and the design engineer

should assure the most current version is used.

Laying out a Turnout

To actually lay out a turnout at any given location along the alignment, one must have an idea of

the geometrics of the turnout and which turnout size to use. As noted above, the turnout is based

on the frog number that sets the angle of the frog and hence the change of direction. If an angle

greater than the frog number is required, the additional difference in angle can be applied by

introducing a curve at the end of the turnout. Normally, most railroads require this curve to be

located at the end of the turnout unit, but when there are restrictions that inhibit this, it is often

allowed to place the curve at or just beyond the heel of the frog.

Also, the location of a curve prior to reaching the turnout is also critical. Most railroads have set

standard lengths of tangent required to be placed between the end of a curve and the end of the

turnout, regardless of which end of the turnout is being set and located. So it is critical that the

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engineer designing an alignment be familiar with the standards and design criteria of the

governing railroad or LRT authority, and also be aware that different railroads and authorities

may and usually do have their own standards and design criteria that may differ from each other.

The one point of design that is standard and must be adhered to with all railroads and LRT

authorities is never place a turnout within a horizontal or vertical curve. Although there may be

occasions where this has been allowed and done, it is a rarity and is only done if there are no

other options available and the railroad or LRT authority has given its expressed approval in

doing it.

LRT authorities may be more lenient in allowing turnouts in horizontal curves, but it must be

realized that in doing so, a special and ‘unique’ design would be required that would also result

in higher fabrication, maintenance and spare parts costs. This is due to a geometric layout that

would require non-standard curved components and parts in lieu of the industry ‘off the shelf’

components and parts of a standard turnout.

If for some reason there are no viable options for setting an alignment that results in a turnout

being in a vertical curve, it may still be done provided the railroad or LRT authority has

approved it. In my career this has occurred twice – and in all other cases where it was suggested

as an alternative option (on very, very rare occasions), the railroad or LRT authority prohibited

it.

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The first time was in designing my first turnout for a Weyerhaeuser facility in the state of

Washington. The geometric restrictions of placing the alignment through the area required

resulted in only one option, and that option was to use a modified standard turnout with a

horizontal curve placed between a set of standard switch points and a standard frog on both

closure rails. The deflection was very small, but it did result in the turnout being in a curve for

both sets of rails. The other obstructions were getting over an existing, large diameter wood stave

pipe and under an existing overhead conveyor belt. In order to reduce costs of relocating or

modifying either the pipe or conveyor belt, a short vertical curve was placed between the heel of

switch and toe of frog that had a small vertical deflection which was large enough to allow the

placement of a short vertical curve that provided the necessary clearance under the conveyor and

sufficient height to place the track structure over the wood stave pipe.

The second occasion was on a project in Chicago involving two railroads, one passenger and one

freight. The realignment of the tracks of the two railroads was such that there were vertical

alignment issues that could not be adjusted to allow the installation of multiple crossovers

between the tracks that were to be in service. The only solution was to place the turnouts, switch

and frog included, within the vertical curve (the restrictions of keeping switch points out of

vertical curves concerns the possibility of the binding of the switch points when the switched are

‘thrown’ or moved from one location to the other).

The design was accomplished and approved by setting the lengths of the vertical curves such that

the ‘mid-ord’ or difference in vertical distance at the mid-point along the chord for both the frog

and switch point were less than 1/8” to the same point on the vertical curve. This offset distance

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was used and agreed to since it was within the vertical construction tolerance used by both

railroads. Neither railroad liked the suggestion, but any other option would have resulted in

extremely higher construction costs. Although the design only went to 30% prior to funding

running out for the project, both railroads approved the design and it would have been in service

once constructed.

I know from inspecting existing railroads in many states over the years, that I have seen turnouts

in horizontal curves and even a few in vertical curves. They may not have been on mainline

high-speed routs, but they were in track – and in service. So it does occur, but is generally not

accepted by railroads for any reason.

Placing a Turnout

In locating and placing a turnout in an alignment, the size of the turnout must be known and the

proximity of its placement must be on horizontal and vertical tangent. Once the PS location is

determined and set, the PITO can then be located by the method described earlier and the

diverging/converging centerline set.

If the turnout is being placed for a siding or track parallel to the original track, the second track

centerline can be placed the necessary offset distance (track center) which is normally 15-ft, but

can vary depending on the railroad’s requirements. A curve can then be set between the

intersecting centerlines. The radius of this curve can vary but is normally similar to the radius of

the turnout that was placed on the original track and is commonly set at a degree of curvature

rounded to the nearest degree or half-degree.

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If the track is a siding that will tie back into the original track, the length of siding track is set and

a second turnout is placed at the other end that will tie back into the original track. If the original

track along this length has curves, the siding track will normally be placed such that the curves

on the siding are concentric to the original track – although the railroad may require the radius of

the curves to be the same for the original and siding track.

Stationing of the alignment through a turnout passes through the PITO along the tangent with a

station callout normally taken at both the PS and PITO of the turnout. If the lateral movement

through the turnout is to be set with stationing, the stationing will normally start at the PS,

continue along the tangent to the PITO and then follow the lateral movement along the diverging

alignment.

The diagram below illustrates the placement of a siding track.

Figure 8 – Siding Track

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If the turnout is being placed for a spur that diverges from the original track, the lateral centerline

of the turnout must intersect the connecting track at a point where the radius of the curve meets

the design requirements of the spur line.

If designing a second main track along an existing main is required, the second main will

normally be placed at a set track center of 15’ as mentioned above, or as specified by the

railroad’s standard practice. This may vary from railroad to railroad and sometimes from district

to district of the same railroad. Where curves are present track widening may be required based

on the railroads criteria. In this case the curves on the second track are set and determined for the

additional widening required by the railroad. This is normally determined by increasing the track

center a set amount based on the degree of curvature of the mainline curve. In many cases the

proposed track center will be sufficient to provide the necessary amount of widening without

actually making the adjustment to the track centers.

If a second main is added, there may be locations along the alignment where there are existing

sidings or spurs. If that is the case, access to the new track may need to be provided. This may be

addressed by adding crossovers between the new track and the original track ahead of the siding

that will allow access between both tracks.

See the following figure for an example.

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Figure 9 - 2nd Main Crossover to Siding or Spur Track

As one can see in the previous figure, the use of a crossover placed before a siding or spur is

very similar in function to a highway collector-distributor roadway (CD) where the crossover

acts like a ‘slip’ ramp between the mainline and CD, with the siding/spur turnout acting very

similar to a terminal leading to or from a ramp.

There may also be a need to provide what is known as a ‘universal crossover’ along the

alignment of a two-track system. This arrangement shown below allows any train on either track

to switch over to the second track in case of emergency or maintenance reasons.

Figure 10 – Universal Crossover

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Placement of a universal crossover may also be found at entrances into yards where a two-track

or multi-track main exists.

It is common practice on most 2-track LRT systems that universal crossovers are spaced at a

given distance, commonly one mile, to allow for movement between tracks in an emergency

situation or for maintenance situations when one track is out of service.

There are many other applications where turnouts and the various types of crossovers may be

located along any railroad or LRT system. In most cases the design engineer will be given those

locations by the railroad or LRT Authority, but often times will find that the locations will need

to be determined based on operations or set by the standard railroad or LRT practices or criteria.

Whenever the design engineer is required to add a second track or extend an existing siding, any

industrial side tracks or spurs must retain access to either or both tracks. This can be

accomplished by the introduction or a crossover or series of crossovers.

Conclusions

As one can see, the design of a track layout is not that complicated and by using sound

engineering judgment and common sense – and a little help from an experienced track designer -

the actual design can be performed with little difficulty. It is also recommended that the engineer

communicate with the engineering department of the railroad (or its consultant), or the LRT

Authority, to assure that the design meets the contract requirements.

© AREMA 2009 ®

Greg Toth 30

It is highly recommended and suggested that before an inexperienced engineer with little or no

track design experience attempts this type of assignment that the engineer becomes familiar with

the requirements set forth by the railroad, or LRT Authority, and its standards and criteria and to

ask an experienced railroad design engineer for direction and for their expertise before initiating

any design. An inexperienced engineer placed in this type of situation will find themselves in a

world of uncertainty that will make it very unlikely for them to meet the railroads expectations

and requirements.

© AREMA 2009 ®

I would like to dedicate this paper to my mom, known to family as ‘Mimi” and to friends

and neighbors as ‘Dolly’.

© AREMA 2009 ®