Steel ties are formed from pressed steel and are trough-shaped in section. The ends of the tie are shaped to form a "spade" which increases the lateral resistance of the tie. Housings to accommodate the fastening system are welded to the upper surface of the tie. Steel ties are now in widespread use on secondary or lower-speed lines in the UK where they have been found to be economical to install due their ability to be installed on the existing ballast bed. Steel ties are lighter in weight than concrete and able to stack in compact bundles unlike timber. Steel ties can be installed onto the existing ballast, unlike concrete ties which require a full depth of new ballast. Steel ties are 100% recyclable and require up to 60% less ballast than concrete ties and up to 45% less than wood ties.