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Question

Difficulty: MediumSpeed on Curves and Downgrades

A driver operating a loaded commercial combination vehicle approaches an off-ramp marked with a 35 mph curve advisory speed sign. Which speed management practice should the driver execute to negotiate the curve safely?

  1. A
    Maintain highway cruising speed until reaching the sharpest part of the curve, then apply firm brake pressure to match the advisory speed.
  2. B
    Enter the curve at the posted 35 mph advisory limit and apply continuous light service braking throughout the entire turn.
  3. Reduce road speed to below the posted advisory speed before entering the curve, then maintain a steady speed without braking while turning.Answer
  4. D
    Engage maximum auxiliary retarder braking upon entering the curve to control vehicle momentum without generating heat in the service brakes.

Answer

Reduce road speed to below the posted advisory speed before entering the curve, then maintain a steady speed without braking while turning.
Commercial motor vehicles have a significantly higher center of gravity than passenger cars, meaning posted curve advisory speeds are often too fast for loaded trucks. Safe operating procedure requires drivers to reduce speed to below the posted advisory speed before entering the curve. Completing all braking prior to the turn preserves full tire traction for lateral cornering forces, preventing loss of vehicle control.

Step-by-Step Solution

1
Assess the curve advisory sign and vehicle load dynamics prior to curve entry.
Recognize that posted advisory speeds are calculated for passenger cars and that high-center-of-gravity commercial vehicles require a lower entry speed.
Commercial vehicles are much more susceptible to rollover and off-tracking than passenger cars at identical curve speeds.
2
Decelerate to a safe speed (typically 5 to 10 mph below the posted advisory speed) on the straight section before the curve.
The vehicle enters the curve at a controlled, stable velocity.
Braking requires tire traction; braking in a straight line avoids combining lateral turning forces with longitudinal braking friction.
3
Maintain a smooth, steady throttle or light pull through the curve without applying the brakes.
Maximum tire traction is dedicated to lateral stability and steering control.
Applying service brakes or harsh retarders mid-turn can overwhelm available tire-to-road friction, leading to jackknife or skid.

Key Concept

Pre-entry speed reduction and lateral traction management on curves
Estimated Time:1m 0s
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Topics

Speed on Curves and Downgrades

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