Examkin

Soru

Zorluk: ZorMountain Driving and Steep Downgrades

A commercial driver is operating an 80000 lb80{}000\text{ lb} combination vehicle down a continuous 7%7\% mountain downgrade on rain-slicked asphalt. The driver has selected the correct low gear and established a designated safe speed of 20 mph20\text{ mph}. As gravity pulls the vehicle, the speedometer reaches 20 mph20\text{ mph}. Which of the following procedures must the driver execute to properly control speed and prevent catastrophic brake failure?

  1. Apply the service brakes with firm pressure to reduce speed to 15 mph15\text{ mph}, release the brakes completely, and ensure the engine retarder remains deactivated.Cevap
  2. B
    Apply continuous light, steady brake pedal pressure to hold vehicle speed constantly at 20 mph20\text{ mph} throughout the remainder of the mountain descent.
  3. C
    Engage the engine retarder at its maximum setting to maintain speed control without applying the service brakes.
  4. D
    Shift the transmission into neutral and pump the brake pedal rapidly with light strokes every few seconds to keep the drums cool.

Cevap

Apply the service brakes with firm pressure to reduce speed to 15 mph (5 mph below safe speed), release the pedal completely, and ensure the retarder remains off.
According to official CDL guidelines, proper snub braking requires the driver to apply firm service brake pressure when the vehicle reaches the designated safe speed (20 mph20\text{ mph}) until speed drops to 5 mph5\text{ mph} below safe speed (15 mph15\text{ mph}), then fully release the pedal. In addition, retarders must remain switched off whenever road surfaces are wet or slippery to prevent drive-axle lockup and jackknifing.

Adım Adım Çözüm

1
Identify the safe speed baseline and calculate the snub braking threshold
The target deceleration speed is 15 mph15\text{ mph} (20 mph−5 mph20\text{ mph} - 5\text{ mph}).
Proper snub braking requires braking hard enough to feel a definite slowdown to 5 mph5\text{ mph} below safe speed, typically taking about 33 seconds.
2
Release the service brakes completely once the vehicle slows to 15 mph
Brake linings and drums are permitted to cool as the vehicle gradually accelerates back to the safe speed.
Intermittent cooling periods prevent the extreme thermal accumulation that causes mechanical brake fade.
3
Assess environmental traction conditions for auxiliary braking systems
Keep engine retarders deactivated on wet, icy, or snow-covered roadway surfaces.
Retarder forces applied solely to drive wheels can precipitate an uncontrollable drive-wheel skid or jackknife on slick roads.

Anahtar Kavram

Proper snub braking execution and auxiliary retarder limitations on steep downgrades under adverse road conditions
Tahmini Süre:2m 0s
Bu soruyu puanla

Konular

Mountain Driving and Steep Downgrades

Bu konudan daha fazla soru