Causes of Creep
The main factors responsible for the development of creep are as follows.
Ironing effect of the wheel The ironing effect of moving wheels on the waves formed in the rail tends to cause the rail to move in the direction of traffic, resulting in creep.
Starting and stopping operations When a train starts or accelerates, the backward thrust of its wheels tends to push the rail backwards. Similarly, when the train slows down or comes to a halt, the effect of the applied brakes tends to push the rail forward. This in turn causes creep in one direction or the other.
Changes in temperature Creep can also develop due to variations in temperature resulting in the expansion and contraction of the rail. Creep occurs frequently during hot weather conditions.
Unbalanced traffic In a double-line section, trains move only in one direction, i.e., each track is unidirectional. Creep, therefore, develops in the direction of traffic. In a single-line section, even though traffic moves in both directions, the volume of the traffic in each direction is normally variable. Creep, therefore, develops in the direction of predominant traffic.
Poor maintenance of track Some minor factors, mostly relating to the poor maintenance of the track, also contribute to the development of creep. These are as follows.
(a) Improper securing of rails to sleepers
(b) Limited quantities of ballast resulting in inadequate ballast resistance to the movement of sleepers
(c) Improper expansion gaps
(d) Badly maintained rail joints
(e) Rail seat wear in metal sleeper track
(f) Rails too light for the traffic carried on them
(g) Yielding formations that result in uneven cross levels
(h) Other miscellaneous factors such as lack of drainage, and loose packing, uneven spacing of sleepers.