The main factors responsible for low speeds over turnouts on Indian Railways are as follows.
(a) A sudden change in the direction of the running edge upon entry onto the switch from a straight track
(b) Absence of a transition between the curved lead and the straight crossing
(c) Non-transitioned entry from the curved lead to the straight crossing
(d) Absence of superelevation over the turnout curve
(e) Gaps in the gauge face and the running table at the crossing
(f) Variation in cross level caused by raised switch rails
In order to achieve higher speeds on turnouts, it is necessary that all the limitations of the design of a turnout be overcome as far as possible. In European countries, the design of turnouts has been greatly improved and speeds of more than 100 km/ h are permitted on turnout curves. The main features of the design of these turnouts are the following.
(a) Long curved switches are provided to avoid the abrupt change in the direction of the vehicle at the entry to the switch.
(b) Switches and crossings are curved to the same radius as the lead curve or, alternatively, a transition curve is provided between the toe of the switch and the nose of the crossing. This provides a smooth passage to the trains on the turnout curve.
(c) Higher cant deficiency is permitted so that the disadvantage of not providing superelevation on the turnout curve is duly compensated.
In keeping with the trend in the railways of the world to permit higher speeds on turnouts, Indian Railways is considering standardization of high-speed turnouts for the following conditions of the track.
(a) For goods yards for a maximum permissible speed of 25 km/h and for passenger yards for maximum permissible speed of 50 km/h.
(b) In peripheries of big yards for bypass lines for a maximum permissible speed of 75 km/h.
(c) At junction joints of single-line and double-line sections for a maximum permissible speed of 100 km/h.
A design of 1 in 12 turnouts for passenger yards with thick web tongue rails and CMS crossings (RDSO Drg. no. T-2733) has already been finalized for enabling a maximum permissible speed of 50 km/h. Similarly, a new design of 1 in 24 turn outs for BG routes with curved switches and thick web tongue rails with a speed potential of 160 km/h is being finalized by Indian Railways.