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.