Correct Answer - Option 5 : Climatic variations
Sleeper density means number of sleepers per rail length
It is represented by M + x
M = Length of rail in meters
x = Factor depending upon several factors such as axle loads, a section of rails, etc, generally lies between 3 to 6.
For Example, If the sleeper density is N + 5, on broad gauge track and length of rail is 13 m, then 13 + 5 = 18 sleepers will be used per rail length on that route.
The density of sleepers mainly depends upon:
1. Axle load the rail track is designed to carry
2. The nature of sleeper and materials used
3. Lateral thrust of locomotives
4. Speed of the train