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Difficulty: MediumSpeed on Curves and Downgrades

A commercial driver is approaching an unfamiliar, sharp highway exit curve. In what sequential order should the driver execute the necessary actions to safely navigate the curve from approach to exit?

  1. 1Assess the curve radius and posted advisory sign to determine a safe entry speed below passenger car limits.
  2. 2Apply smooth service braking while still traveling in a straight line before reaching the curve.
  3. 3Downshift into a gear that keeps the engine in its normal operating RPM range before beginning the turn.
  4. 4Steer through the turn while applying light, steady throttle to stabilize vehicle tracking.
  5. 5Accelerate gradually back to cruising speed once the vehicle exits the turn and the steering wheel straightens.

Answer

The driver must first evaluate the curve and advisory speed, decelerate in a straight line before curve entry, downshift to an appropriate gear prior to turning, maintain light steady throttle while steering through the curve, and accelerate smoothly only after the steering wheel straightens upon exit.
Proper commercial vehicle curve handling dictates that all braking and gear selection take place in a straight line prior to the curve. While negotiating the turn, the driver maintains steady light power to stabilize the vehicle, delaying acceleration until the turn is completed and the steering wheel is straightened.

Step-by-Step Solution

1
Evaluate the curve radius and posted advisory speed well before the curve.
Establishes a safe target entry speed suited for a heavy commercial vehicle.
Commercial vehicles have a high center of gravity and require lower speeds than posted advisory limits for passenger cars.
2
Brake smoothly in a straight line ahead of the point of curvature.
Brings vehicle speed down to the safe target speed before steering forces are applied.
Applying brakes inside a turn splits tire traction between braking and cornering, creating a severe risk of skidding or jackknifing.
3
Shift into the correct operating gear before turning the steering wheel.
Keeps engine pulling power ready and preserves engine braking without interrupting torque during the turn.
Downshifting mid-curve can lock drive wheels or cause a loss of vehicle control.
4
Guide the combination through the curve with light, steady throttle.
Maintains traction and directional stability across all vehicle axles.
Gentle power stabilizes the vehicle and trailer without increasing speed against centrifugal force.
5
Accelerate smoothly once the vehicle is completely on the straight roadway.
Safely resumes roadway travel speed after lateral forces diminish.
Full power should only be resumed once the steering is centered and rollover risk is eliminated.

Key Concept

Safe curve management requires all speed reduction and gear selection to be completed in a straight line prior to entry, followed by light steady throttle during the turn and acceleration only upon exit.
Estimated Time:1m 15s
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Topics

Speed on Curves and Downgrades

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