More recently, some curved rails have been produced to a modular design so components can be unbolted and used elsewhere, subject to design and safety considerations. In some cases, tubular section rails which are welded during manufacture, are produced by specialist rail companies so they can be used with a previously owned carriage, controls, and other components. This is, perhaps, like putting an old locomotive on new railway lines. It provides a lower cost solution than buying a totally new system.