The contemporary MRT system uses the 1,435mm standard track gauge with the elevated lines also having guard rails to prevent a derailed vehicle from striking fixed obstructions and viaduct parapets by keeping derailed wheels adjacent to the running rails. Three types of rail tracks are used on the MRT: ballasted track, fixed slab track and floating slab track; floating slab tracks are used at sections of the rail network located beneath densely populated and built-up areas to alleviate vibration and noise transmission to neighbouring buildings, by means of interposing rubberised supports between the tunnel wall and the tracks. When initially built, the MRT used swingnose crossings for 26 out of 131 railway points to minimise noise. From July to November 2000, these swingnose crossings were replaced with conventional ones for reliability reasons.