1. REVIEW OF CRITERIA FOR REALIGNMENT OF A CURVEBy
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V. B. Tiwari
T. S. Khawas

2. Running of train on curves is governed by gauge, versine and superelevation. Most important parameter to be considered for riding comfort is Rate of Change of Lateral Acceleration which in turn depends on
Station to station variation in versine
Degree of curve
Speed on curve

3. The current provision for realignment of curve given in para 421 of IRPWM is as below
Speed Range in Kmph.
Limit of station to station versine variation (mm)
120 and above
10 mm or 25% of the average versine on circular curve which ever is more
Below 120 and up to 80
15 mm or 25% of the average versine on circular curve which ever is more
Below 80 and up to 50
40 mm or 25% of the average versine on circular curve which ever is more

4. Following observations were discussed in TSC about criteria laid down in para 421 of IRPWM
For 10 curve on MG, permissible station to station versine variation is 40 mm which is more than the design versine of 28.5 mm.
2. For high speeds i.e, 140 Kmph, the rate of change of lateral acceleration comes to 1.18 m/Sec3 which is much higher than service tolerance of 0.85 m/Sec3 (As mentioned in sub committee report)

5. 10 mm (Δv) 15 mm (Δv) 40 mm (Δv) D vd 120 0.740 1.123 2.980 0.510
Rate of change of Lateral Acceleration for Station to Station variation in versine (Δv) as per existing criteria
Speed kmph
10 mm (Δv)
15 mm (Δv)
40 mm (Δv) D 1o 2o 3o 4o vd 28 57
85.5
114
25% vd 7 14 21
28.5 40
0.027
0.045
0.110
0.019
0.038
0.057
0.076 60
0.030
0.135
0.360
0.060
0.129
0.190
0.250 80
0.220
0.330
0.880
0.150
0.310
0.470
0.620
100
0.420
0.630
1.680
0.300
0.590
0.890
1.200
120
0.740
1.123
2.980
0.510
1.050
1.560
2.100
140
1.180
1.770
4.720
1.660
2.500
3.130

6. Adverse effects of permitting high rate of change of lateral acceleration
Such high rate of change of lateral acceleration may adversely affect life of suspension springs and cause increased rail wear.
2. In case of LWR on curves bursting forces may get compounded due to sharp curvature in short length due to permissible variation in versines.

7. Permitted values of rate of change of lateral acceleration in advance countries (As per Esveld book)
Class
Normal
Maximum
Exceptional
Speed range Kmph
Class 1
0.16
0.46
0.59
80 – 120
Class 2 -
Class 3
0.24
>250
Class 4
0.20
0.49
The table permits higher values for high speeds

8. SUGGESTIONS
(1) As per TSC minutes and standard adopted in advance countries, we suggest following values of Rate of Change of Lateral Acceleration considering riding comfort for adoption on Indian Railways
Speed Kmph
Value m/Sec3
< 80
0.70
Below 120 and upto 80
0.75
Below 160 and upto 120
0.85

9. (2) Suggested criteria (Δv) for realignment of curve as derived from calculations
Speed Range in Kmph. *
Limit of station to station versine variation (mm) (Δv)
Below 160 and upto 140
6 mm or 25% of the average versine on circular curve which ever is less
Below 140 and upto 120
9 mm or 25% of the average versine on circular curve which ever is less
Below 120 and upto 100
12 mm or 25% of the average versine on circular curve which ever is less
Below 100 and upto 80
15 mm or 25% of the average versine on circular curve which ever is less
Below 80
15 mm for curves of 10 and 20
20 mm for curves 30 or sharper
* Maximum Permitted Speed on curve

10. Rate of change of Lateral Acceleration for Station to Station variation in versine (Δv) as per suggested criteria
Speed kmph
6 mm (Δv)
9 mm (Δv)
12 mm (Δv)
15 mm (Δv)
20 mm (Δv) D 1o 2o 3o 4o vd 28 57
85.5
114
25% vd 7 14 21
28.5 40
0.02
0.03
0.04
0.06
0.08 60
0.05
0.11
0.14
0.18
0.13
0.20
0.26 80
0.33
0.44
0.15
0.31
0.47
0.63
100
0.25
0.40
0.51
0.64
0.85
0.30
0.61
0.92
1.22
120
0.66
0.89
1.11
1.48
0.52
1.05
1.58
2.11
140
0.71
1.10
1.41
1.76
2.35
0.84
1.68
2.51
3.35

11. (3) Modification of para No. 420 of IRPWM
Following part of para is to be deleted as the limiting values of versine variation have been categorically specified in para 421 and there is no need to draw CFD.
“ Curve registers of groups ‘A’ and ‘B’ routes should also be provided with cumulative frequency
diagrams for each curve to get a graphic idea about the condition of geometry of curve.”

12. Note:
1. If more then 20% of stations are having versine variation above the limits prescribed, complete realignment of curve should be planned within a month.
2. In cases where the variation of versines between adjacent stations is only at few isolated locations, local adjustments may be resorted to.
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