Sleepers
A Railway Sleeper is a rectangular object used as a base for railroad tracks. Sleepers are members generally laid transverse to the rails, on which the rails are supported and fixed, to transfer the loads from rails to the ballast and subgrade, and to hold the rails to the correct gauge. Traditionally, sleepers have been made of hardwood, but concrete is now widely used.
They are often heavily creosoted to reduce insect infestation and rot. However, creosote is also carcinogenic and environmentally damaging. Less often, sleepers are treated with other preservatives, although some timbers are durable enough that they can be used untreated.
Problems with wood sleepers include rot conducive to timber pest activity, splitting, insect infestation, plate-cutting (abrasive damage to the tie caused by lateral motion of the sleeper plate) and spike-pull (where the spike is gradually worked out and loosened from the sleeper).
WIKIPEDIA ENTRY FOR RAILROAD TIE.
