Train Driver Braking Systems and Train Dynamics 2 — Questions and Answers
Question 1: Which factor has the greatest effect on increasing a train's stopping distance?
- Rail temperature
- Train speed (Correct answer)
- Number of cars in the consist
- Grade of the track
Correct answer: Train speed
Speed has the greatest effect because kinetic energy increases with the square of velocity, meaning doubling speed quadruples the energy that brakes must dissipate.
Question 2: What does 'percentage of braking' measure for a train?
- The percentage of cars in the train with operative brakes
- The efficiency rating of brake shoe material
- The ratio of total braking force to total train weight (Correct answer)
- The reduction in speed achieved per minute of braking
Correct answer: The ratio of total braking force to total train weight
Percentage of braking is calculated as total braking force divided by total train weight, expressed as a percentage, and is used to determine expected stopping distances.
Question 3: Why does a fully loaded freight train require a longer stopping distance than an empty train traveling at the same speed?
- Loaded trains generate excessive heat in brakes, reducing effectiveness
- Wheel-to-rail friction decreases significantly under heavier loads
- Greater mass produces greater momentum that brakes must overcome (Correct answer)
- Air brake systems lose efficiency when supporting heavier cars
Correct answer: Greater mass produces greater momentum that brakes must overcome
A loaded train has greater mass, resulting in greater momentum (mass × velocity), which requires more braking force and distance to stop at the same speed.
Question 4: What is 'brake lag' in a pneumatic train braking system?
- The delay between the brake valve input and when brakes set throughout the train (Correct answer)
- The difference in braking force between front and rear cars
- Reduced effectiveness caused by worn or overheated brake shoes
- The recharge time required after an emergency application
Correct answer: The delay between the brake valve input and when brakes set throughout the train
Brake lag is the propagation delay for a pressure change to travel through the full length of the brake pipe, causing brakes to set sequentially from front to rear.
Question 5: What is the recommended braking strategy when approaching a long downgrade?
- Apply emergency brakes at the steepest section of the grade
- Rely primarily on dynamic braking for the entire descent
- Control and reduce speed before entering the grade (Correct answer)
- Use maximum service braking continuously throughout the descent
Correct answer: Control and reduce speed before entering the grade
Reducing speed before the grade prevents overheating brake shoes and gives the operator better speed control throughout the descent rather than reacting to runaway speed.
Question 6: Under FRA regulations, what is the minimum percentage of operative brakes required before a train may depart a terminal?
- 75%
- 85% (Correct answer)
- 90%
- 100%
Correct answer: 85%
49 CFR Part 232 requires that at least 85% of a train's cars have operative brakes before the train departs a terminal for initial terminal brake tests.
Question 7: What is the function of 'bail-off' in a locomotive braking system?
- Emergency venting of all air from the brake pipe
- Manually bypassing the penalty brake detection circuit
- Releasing the independent locomotive brakes while train brakes remain applied (Correct answer)
- Overriding dynamic braking during an emergency stop
Correct answer: Releasing the independent locomotive brakes while train brakes remain applied
Bail-off allows the operator to release only the independent locomotive brakes while the automatic (train-wide) brake application remains active, which is useful when repositioning power.
Train Driver Braking Systems and Train Dynamics 2
Which factor has the greatest effect on increasing a train's stopping distance?