LEC Train Handling and Performance 3 — Questions and Answers
Question 1: How does increased train length affect the propagation speed of a brake pipe pressure change?
- Longer trains have faster brake propagation due to higher air volume
- Brake pipe pressure changes travel at the same speed regardless of train length
- Longer trains experience slower brake response at the rear due to greater pipe length (Correct answer)
- Pressure changes travel faster at the rear because of lower resistance
Correct answer: Longer trains experience slower brake response at the rear due to greater pipe length
In longer trains, the brake signal must travel farther through the brake pipe, causing rear cars to respond later than head-end cars.
Question 2: What is the purpose of a 'precautionary brake application' when approaching a meeting point?
- To ensure the train can stop before the siding switch if the opposing train has not cleared (Correct answer)
- To reduce speed per timetable requirements at all named meeting points
- To signal to dispatchers that the meet is acknowledged
- To test the automatic brakes before coupling with the opposing train
Correct answer: To ensure the train can stop before the siding switch if the opposing train has not cleared
A precautionary brake application ensures the engineer can stop short of a switch if an opposing train has not fully cleared the main track.
Question 3: Which factor has the greatest influence on the amount of locomotive tractive effort available at a given speed?
- Ambient temperature and humidity levels
- The number of powered axles and adhesion coefficient (Correct answer)
- Fuel quality and injector timing calibration
- Coupler type and draft gear spring rating
Correct answer: The number of powered axles and adhesion coefficient
Tractive effort is limited by the product of axle load, number of powered axles, and the wheel-to-rail adhesion coefficient.
Question 4: When should an engineer 'notch up' (increase throttle) after a speed restriction?
- As soon as the locomotive clears the end of the restriction zone
- Only after the entire train has cleared the end of the restriction zone (Correct answer)
- When the speedometer shows the train is 5 mph below maximum authorized speed
- At the engineer's discretion regardless of train position
Correct answer: Only after the entire train has cleared the end of the restriction zone
Speed restrictions apply to the entire train, so throttle increase is permissible only after the last car clears the end of the restricted zone.
Question 5: What is the result of making a brake pipe reduction that is too large when initially applying brakes on a heavy freight train?
- Brakes may apply unevenly from front to rear causing coupler stress
- The train will stop too quickly, damaging wheel treads
- Air flow from the brake pipe may cause emergency applications at the rear (Correct answer)
- Dynamic brakes are automatically disabled by the control system
Correct answer: Air flow from the brake pipe may cause emergency applications at the rear
An excessively large initial reduction can cause the rear cars' triple valves to sense an emergency rate of pressure drop and initiate emergency applications.
Question 6: In train handling, what is 'bunching' and what hazard does it create?
- Running with excessive throttle that overheats traction motors
- Compressive slack accumulation that can cause derailments or coupler failures (Correct answer)
- A crew scheduling method that pairs engineers on difficult territory
- Grouping multiple locomotives together on pusher assignments
Correct answer: Compressive slack accumulation that can cause derailments or coupler failures
Bunching occurs when slack runs in and couplers are in compression, creating buff forces that can kink or derail cars, especially on curves.
Question 7: How does grade resistance affect the horsepower required to maintain a constant speed?
- Grade resistance reduces required horsepower on descending grades and increases it on ascending grades (Correct answer)
- Grade resistance has no effect on horsepower requirements at constant speed
- Grade resistance increases horsepower requirements on both ascending and descending grades
- Grade resistance only matters when train weight exceeds locomotive rated capacity
Correct answer: Grade resistance reduces required horsepower on descending grades and increases it on ascending grades
On an ascending grade, gravity adds to rolling resistance requiring more power; on a descending grade, gravity assists movement, requiring less power or braking.
LEC Train Handling and Performance 3
How does increased train length affect the propagation speed of a brake pipe pressure change?