Question

Which one of the following statements is TRUE?

• A. Cant deficiency is related to train moving faster, and Cant excess is related to train moving slower.
• B. Cant deficiency is related to train moving slower, and Cant excess is related to train moving faster.
• C. Cant deficiency is related to train moving on the main line, and Cant excess is related to train moving on the branch line.
• D. Cant deficiency is related to train moving on the branch line, and Cant excess is related to train moving on the main line.

Hint:

Compare actual cant provided to the equilibrium cant needed at the train's actual speed: too little cant for a fast train is deficiency, too much cant for a slow train is excess.

Answer 1

The Correct Option is A

This question tests the basic definitions of cant deficiency and cant excess used in railway curve design. Both terms compare the cant actually laid on the track to the equilibrium cant that the train's running speed calls for.

1. Option (A): States that cant deficiency goes with a faster-moving train and cant excess with a slower-moving train. When a train runs faster than the equilibrium speed, the actual cant on the ground is less than what that speed needs, this shortfall is cant deficiency. When a train runs slower than equilibrium speed, the actual cant is more than needed, this extra amount is cant excess. This is correct and matches the standard definition.
2. Option (B): Reverses the pairing (deficiency with slower train, excess with faster train), which is the opposite of the correct relationship, so it is wrong.
3. Option (C): Ties deficiency to the main line and excess to the branch line. This description can happen at a turnout, where the common cant is set closer to the higher main line speed, but it is not the general, fundamental definition asked for here, it is a specific case, not the TRUE statement in general.
4. Option (D): Similarly ties the terms to branch line and main line running in the reverse sense of (C), which is also not the basic definition.

The equilibrium speed is the speed at which the actual cant exactly balances the centrifugal force. Any speed above it creates a deficiency of cant, any speed below it creates an excess of cant, regardless of which physical line (main or branch) the train happens to be on.

Let's summarize:

• Cant deficiency = equilibrium cant needed at running speed minus actual cant provided; happens when the train runs faster than equilibrium speed.
• Cant excess = actual cant provided minus equilibrium cant needed; happens when the train runs slower than equilibrium speed.

So the correct statement is option (A).