Frog 1 : A track structure used at the intersection of two running rails to provide support for wheels and passageways for their flanges, thus permitting wheels on either rail to cross the other
Ilan Kelman (ed.), Vulnerability and Resilience Definitions and References, Version 2, 2007. http://www.islandvulnerability.org/docs/vulnres.pd f, (Vulnr and Resilience - Brit) {524}