Alignment (AL) of Rails
Alignment (AL) refers to the deviation of rails in the horizontal plane from their intended position. This is measured for each rail individually using a specified chord length.
Anchor Length (la)
Anchor length is the track length needed to resist the pull exerted on rails by the rail tensor at temperature (tp). For practical purposes, it is approximated as 2.5 meters per degree Celsius of (to – tp). If the initial temperature (t0) is unknown, the default value can be used.
Blanket
The blanket is a granular material layer placed between the ballast and subgrade or formation across the full width of the formation.
Breathing Length
Breathing length is the segment at each end of Long Welded Rail (LWR) or Continuous Welded Rail (CWR) that adjusts for temperature-induced expansion and contraction.
Buckling of Track
Buckling of track occurs when there is a sudden or gradual lateral or vertical shift due to unbalanced thermal stress in the rail or track.
Cant Deficiency
Cant deficiency happens when a train navigates a curve at a speed higher than the equilibrium speed. It is the difference between the theoretical cant required for that speed and the actual cant provided.
Cant Excess
Cant excess occurs when a train moves around a curve at a speed lower than the equilibrium speed. It is the difference between the actual cant and the theoretical cant required for that speed.
Cant Gradient and Cant Deficiency Gradient
These gradients indicate the rate of increase or decrease of cant or cant deficiency over a given transition length. For instance, a gradient of 1 in 1000 means a change of 1 mm in cant per 1000 mm of transition length.
Catch Sidings
Catch sidings are safety features designed to absorb the velocity of an uncontrolled train on steep grades. They are equipped with devices like rising variable grades and sand drags to prevent derailments.
Centrifugal Force
Centrifugal force is the outward force experienced by a vehicle moving on a curved track. Its magnitude is influenced by the vehicle’s speed, mass, and the curve’s radius.
Cold Weather Patrol
Cold weather patrol involves inspecting tracks during winter when rail temperatures are significantly below the stress-free or de-stressing temperature.
Consolidation of Track
This process involves increasing ballast resistance to prevent sleeper movement, both initially before laying LWR/CWR and to address any subsequent loss of resistance.
Cross Level
Cross level refers to the height difference between two rails on a sleeper. It is measured with one rail as a reference.
Crossing Angle
The crossing angle is the angle between the gauge lines of the crossing, usually defined by the crossing number, which is the cotangent of the crossing angle.
Cross Over
A cross over connects two lines using two turnouts and straight or curved track segments.
Degree of Curvature
The degree of curvature is the angle subtended at the curve’s center by a 30.5-meter chord.
De-stressing
De-stressing is the process of removing stress from LWR/CWR to achieve stress-free conditions at the specified rail temperature.
Equilibrium Speed
Equilibrium speed is the velocity at which the centrifugal force on a vehicle in a curve is balanced by the provided cant.
Gauge
Gauge is the shortest distance between the gauge faces of two rails, usually measured 13 to 15 mm below the rail top.
GMT (Gross Million Tonnes of Traffic)
GMT is the total traffic carried on a line, recorded annually by the Statistical branch of each Zonal Railway as of March 31.
Hot Weather Patrol
Hot weather patrol involves inspecting tracks during summer when rail temperatures exceed the stress-free or de-stressing temperature.
Lead Curve
The lead curve extends from the toe of the curved switch to the toe of the crossing.
Machined Joint
Machined joints are fish-plated joints where zero gap is maintained between rail ends.
Maximum Permissible Speed of the Curve
This speed is the highest allowed on a curve considering factors such as radius of curvature, cant, cant deficiency, cant excess, and transition length.
Rail Failure
Rail failure refers to rail fractures or defects requiring removal from track, excluding damages from accidents or abnormal wheel burns.
Rail Temperature
Rail temperature is measured by a rail thermometer and differs from ambient temperature. Indian Railways use a rail temperature map for different zones.
Rail Tensor
A rail tensor is a hydraulic or mechanical device used to stretch the rail physically.
Rate of Change of Cant
This rate measures how quickly cant or cant deficiency changes per second, based on the maximum permissible speed over the transition curve.
Sand Hump
A sand hump is a sanded track segment placed after loop lines to prevent collisions with mainline vehicles.
Shift
Shift refers to the inward movement of the main circular arc caused by introducing a transition curve as a cubic parabola.
Slip Siding
Slip sidings are short sidings on steep grades designed to prevent uncontrolled vehicles from entering the main line.
Stock Rail Joint (SRJ)
The stock rail joint connects the stock rail with the running rail at the approach.
Super-elevation (SE)
Super-elevation is the elevation difference between two rails on a track.
Switch Expansion Joint (SEJ)
SEJs are installed at LWR/CWR ends to accommodate expansion and contraction due to temperature changes.
Symmetrical Split
Symmetrical split turnouts have a center line that coincides with the bisector of the crossing angle, with a lead curve radius twice that of ordinary turnouts.
Transition Curve
A transition curve is an easement curve with a gradual change in curvature along its length.
Turn-in Curve
The turn-in curve connects the crossing heel to the adjacent track.
Turnout
A turnout allows train movement between tracks and consists of switches, crossings, and lead tracks. It may be a left or right-hand turnout based on the direction of diversion.
Twist
Twist is calculated using cross level values at two points separated by a specific base, indicating the rate of cross level change over that base.
Unevenness (UN) of Rails
Unevenness refers to vertical deviations of rails from their intended position, measured with reference to a chord of specified length.
Versine
Versine is the perpendicular distance from the midpoint of a chord to the curved track arc.
Vertical Curve
A vertical curve is a circular curve in the vertical plane.
Welded Rails
- Continuous Welded Rail (CWR): LWR that extends through station yards, including points and crossings.
- Long Welded Rail (LWR): A welded rail section that does not undergo longitudinal movement due to temperature changes.
- Short Welded Rail (SWR): A welded rail that contracts and expands throughout its length due to temperature variations.
