CTB CTB Track Systems & Components 3

Question 1

What is 'string-lining' used for during track geometry correction?

Accepted Answer

To measure and correct horizontal alignment (surface) by establishing a reference chord along the track

Answer

String-lining uses a measured chord (string) stretched along the rail to identify mid-ordinate deviations and calculate the required horizontal shifts to restore alignment.

Question 2

In the context of track components, what is a 'frog number' (frog angle)?

Accepted Answer

A number indicating the ratio of the frog's spread; higher numbers mean a shallower, longer frog

Answer

The frog number (e.g., #10, #20) is the cotangent of the frog angle — a higher number means a shallower crossing angle and a longer, faster frog.

Question 3

What does 'ballast fouling' mean on a track?

Accepted Answer

Contamination of ballast with fines, dirt, or organic material that reduces drainage and load-bearing capability

Answer

Fouled ballast has accumulated fines that fill the void spaces needed for drainage and resilience, causing soft spots and poor track geometry retention.

Question 4

What is the purpose of a 'joint tie' (compromise joint) when connecting two different rail sizes?

Accepted Answer

To connect rails of different weights or sections using a specially designed joint bar that bridges the height difference

Answer

Compromise joint bars have an asymmetric profile to accommodate the difference in rail height between two different rail weights while maintaining smooth vertical alignment.

Question 5

What is 'track modulus' in railway engineering?

Accepted Answer

A measure of the stiffness of the track support system (ties, pads, ballast, and subgrade) expressed in force per unit deflection per unit length

Answer

Track modulus quantifies how much vertical load the support system can carry per unit of rail deflection per unit length, influencing rail bending stress and ride quality.

CTB - Certified Track Builder Practice Test

CTB - Certified Track Builder Practice Test

CTB CTB Track Systems & Components 3