Page 61 - IRSEM_Main Book

 If the versine difference is not within the limits of + 4 mm between std value and
any recorded value and/or within + 3 mm between any two reading then the track
curvature is defective.

Note: A crossover point is a track in curvature, but without any super elevation. Hence all
the parameters need to be maintained correctly.

4.3 Track Twist: It is an important parameter having crucial impact on safety. The rate of
change of cross-levels is called ‘twist’. Cross-level means difference of level of rails. Cross-
levels are measured on left rail as seen in the direction of train involved in derailment.

LEFT

RIGHT
A B

Fig No: 4F3

Track Twist = Algebraic difference of Cross Level at A & B in
Distance between A & B

Example: Cross level at ‘A’ = +5 mm (Left rail is higher than right rail by 5 mm)
Cross level at ‘B’ = -7 mm (Left rail is lower than right rail by 7 mm)

If the distance between A & B is 3 meters,
Then Track Twist = (+5) – (-7) = 12/3 = 4 mm / Mts.
3
4.4 Permitted Cross Level Difference (Twist):

For a new track, cross level difference permitted is 1 in 720. A vehicle with defective spring
gear travelling on a track with twist can cause derailment. In cases of improper loading, the
chances are further increased.

4.5 Draw a Sketch of the Accident Site and note

(a) Make the exact position where engine & vehicles came to rest.
(b) Prepare a diagram of the Engine and all the vehicles with reference to track indicating
the position of derailed vehicles etc.
(c) Exact position where loose components of vehicles and track are found.
(d) Whether Engg. staff were on work
(e) POM/POD, damage to sleepers, rails and other track fastenings.
(f) Position of wheels in relation to displaced rails in normal alignment.
(g) Condition of track at least ½ a mile in rear.
(h) The condition of signals, points, L/Bars, Levers/Knobs and their relevant indications,
SM slides, position of Block Instrument etc.
(i) Whether any S & T Staff working
(j) Check the records, register, PN books etc. Seize the order books, if required.
(k) In case of shunting operation whether proper locking & clamping of points done or not.

Chapter 3: Duties Of Signal Supervisors And Technical Staff Page 39 of 535