What is included in the 3-tier maintenance regime?
The three-tier system divides responsibilities for track maintenance as follows: 1. On-Track Machines (OMU). Mechanized maintenance (see above) including systematic tamping, intermediate tamping, shoulder ballast cleaning, ballast profiling and redistribution, track stabilization, and periodic deep screening of ballast. 2. Mobile Maintenance Units (MMU). These are of two types. MMU-I refer to the permanent way units that are assigned to deal with spot tamping, in-situ rail welding, casual renewal and repairs, overhaul of Level Crossings, glued joint replacement, and machining of rails including cutting, drilling, grinding and chamfering. Normally there is one MMU-I unit for each Permanent Way Inspector’s office. MMU-II refers to the units specially assigned for reconditioning turnouts, switches, joints and other such intricate trackwork. 3. Sectional Gangs. These are permanent way gangs that handle patrolling (including keyman’s daily patrols, hot and cold weather patrols, and monsoon
