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Difficulty: MediumStopping Distance Components

A heavy commercial vehicle equipped with air brakes is traveling at 55 mph55\text{ mph} on dry, level pavement. The driver requires 142 feet142\text{ feet} during perception time and 61 feet61\text{ feet} during reaction time before the brake pedal is depressed. The air brake system introduces a brake lag distance of 32 feet32\text{ feet} before the linings contact the drums, followed by an actual vehicle braking distance of 216 feet216\text{ feet}. What is the total stopping distance required to bring this vehicle to a complete stop?

  1. 451 feet451\text{ feet}, because total stopping distance for an air brake vehicle is the sum of perception distance, reaction distance, brake lag distance, and effective braking distance.Answer
  2. B
    419 feet419\text{ feet}, because total stopping distance includes only perception distance, reaction distance, and braking distance, ignoring brake lag.
  3. C
    309 feet309\text{ feet}, because stopping distance is calculated by adding reaction distance, brake lag distance, and braking distance while excluding perception distance.
  4. D
    248 feet248\text{ feet}, because stopping distance consists strictly of the mechanical brake lag distance added to the physical braking distance.

Answer

451 feet451\text{ feet}, which represents the sum of all four stopping distance components for an air-braked vehicle (perception distance, reaction distance, brake lag distance, and braking distance).
Total stopping distance for a commercial motor vehicle equipped with air brakes is composed of four distinct sequential parts: perception distance (142 ft142\text{ ft}), reaction distance (61 ft61\text{ ft}), air brake lag distance (32 ft32\text{ ft}), and effective braking distance (216 ft216\text{ ft}). Adding these together yields 142+61+32+216=451 feet142 + 61 + 32 + 216 = 451\text{ feet}.

Step-by-Step Solution

1
Identify the four sequential components of total stopping distance for an air-braked commercial vehicle.
The components are Perception Distance (142 ft142\text{ ft}), Reaction Distance (61 ft61\text{ ft}), Brake Lag Distance (32 ft32\text{ ft}), and Braking Distance (216 ft216\text{ ft}).
Air brake systems require an extra mechanical phase (approximately 0.5 seconds0.5\text{ seconds} or 32 feet32\text{ feet} at 55 mph55\text{ mph}) for air to flow through the lines and actuate the brakes.
2
Calculate the sum of all four distance components.
142 ft+61 ft+32 ft+216 ft=451 ft142\text{ ft} + 61\text{ ft} + 32\text{ ft} + 216\text{ ft} = 451\text{ ft}
Total stopping distance is the cumulative distance traversed from the moment the hazard appears until the commercial vehicle comes to a complete rest.

Key Concept

Air Brake Total Stopping Distance Formula: Total Stopping Distance = Perception Distance + Reaction Distance + Brake Lag Distance + Braking Distance
Estimated Time:1m 15s
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Topics

Stopping Distance Components

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