Rails classified in weight per linear yard of a single rail (i.e., 132# rail).

The size

and type

of rail to be used in a project is the choice of the operating railroad company. Heavier weights are used on mainline tracks, while smaller sizes may be used on spur and siding track.

Panels are typically 80

foot

in length and include:

Track panels are particularly useful when replanking an existing at-grade crossing. After the existing rails are cut on both ends, an existing section of track is removed down to the subgrade. After the subgrade, subballast, and ballast are

placed

, the track panels are installed. The track panel is bolted on both ends, and a tamping machine installs ballast. The temporary joint bars are then removed, and the rails are welded together. Crossing surface panels are bolted into the ties.

Securing the rails to the ties is done by using:

Tie plates and clips also assist in distributing the load of a train over the tie.

Ties are

supporting members, either

timber or concrete, to which rail is fastened. They provide distributive support for the rail and assist in maintaining track alignment and separation between rails.

Timber ties are manufactured from hardwoods such as oak or Douglas fir and pressure treated with a creosote/tar solution to prevent decay. Timber tie size is usually 7

inch

by 9 inch by 8 foot 6 inches. Timber tie spacing is usually 18 inches or 19.5 inches on center.

Concrete ties are prestressed with rebar, resist decay, and generally have a longer useful life than timber ties. Concrete tie size is usually 11 inch by 9 inch by 8 foot 6 inches. Concrete tie spacing is usually 20 inches or 24 inches on center.

Switch ties may be timber or concrete ties of varying lengths (generally 9 feet to 20 feet) that are used to support the track structure at the location where a

single

track diverges into two or more tracks by means of the turnout and switch mechanism.

In recent years there has been increasing interest in the development and use of ties made of composite materials, primarily polymers mixed with timber or concrete. Composite ties are not in general use by any of the major railroad companies, though there are some installed at various locations around the country as test projects.

Ballast restrains the movement of crossties to prevent lateral movement of the track structure, provides distributive support to the crossties, and provides drainage for the track structure above. Desired

typical

ballast depth is within 2 inches of top of the ties and 9 to 12 inches below the bottom of the ties. The width of the ballast section is usually 6 to 12 inches from the ends of the tie with a two-to-one slope downward from that point to ground level.

Sub-ballast consists of smaller particles that provide for additional support of the track structure and a foundation course to aid further with drainage. As track structure ages and upper ballast deteriorates, those smaller particles migrate downward, effectively deepening the lower ballast layer. Maintenance and rehabilitation projects add newer upper ballast, causing the entire track structure to gradually rise vertically over time.

On new construction, core samples are usually

collected

to determine the type and depth of constructed subgrade (compacted aggregate) that should be used to support the track structure. On existing older rail lines, the subgrade is typically the native soils present when the railroad was built.

AREMA has standard track components and design plans that are often referenced for track design. The

Class I

railroad companies (BNSF, CN, CP, CSX,

CPKC

, NS, UPRR) also have their own specific engineering and design standards for some components and design that may vary from AREMA standards and supersede AREMA standards. Some of these are also common standards used by more than one railroad company, such as BNSF/UPRR common standards.

TxDOT has permission from UPRR and BNSF to use their standards and common standard sheets in PS&E packages. The designer should confirm from the railroad company the standard to use prior to developing the track design plans. Track design should only be performed by individuals with prior track design experience familiar with both AREMA and railroad company standards.

A turnout is

a track panel

that diverts trains from one track to another. The length of the turnout is determined by angle of the turnout casting (referred to as a “frog”). The shorter the turnout, the sharper the angle of divergence will be, which restricts train operating speeds through the turnout. The initial point of divergence where the two tracks effectively meet is referred to as the “switch” and the moveable rails at that location referred to as a “switch point”.

Railroad optimum design for grades is 0.5% or less, though up to 1.5% is acceptable in certain circumstances. Steeper grades result in continual reduction in train speed and can actually cause a train to stall if the grade is too steep, or require the use of additional locomotives, which is a major operating cost.

Horizontal curvature is not nearly as critical, though it can affect train speed and handling. The degree of curvature and desired train speed will impact the amount of superelevation used. Consecutive curves also require the design of a tangent length of track between curves to prevent the train from rocking, which can result in derailments.