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Difficulty: MediumSharing the Road with Large Vehicles

At 55 mph under dry road conditions, a fully loaded commercial tractor-trailer typically requires nearly double the total stopping distance of a standard passenger car.

Answer: Answer

Answer

True. Fully loaded commercial tractor-trailers require nearly double the total stopping distance of standard passenger cars at highway speeds due to their immense mass, kinetic energy, and air brake lag time.
The statement is true because a fully loaded commercial truck weighing up to 80,000 pounds generates immense kinetic energy. In addition to physical braking distance, commercial vehicles use air brake systems that experience brake lag—the delay while air flows through the lines to apply the brakes—adding critical feet to total stopping distance at 55 mph.

Step-by-Step Solution

1
Evaluate the effect of vehicle weight on stopping distance.
Recognize that a fully loaded commercial truck weighing up to 80,000 pounds possesses vastly more kinetic energy than a 3,000-to-4,000-pound passenger car.
Greater mass requires significantly more work and distance for the braking system to dissipate energy into heat.
2
Account for mechanical air brake lag time.
Identify that truck air brakes experience a slight delay (approximately 0.5 seconds) while compressed air moves through the lines to engage the brake shoes.
During brake lag, the truck travels additional feet at full speed before deceleration even begins.
3
Compare total stopping distances at 55 mph under ideal conditions.
A standard passenger vehicle stops in about 130–140 feet, while a fully loaded tractor-trailer requires roughly 300–400 feet.
This empirical comparison confirms that a large commercial truck requires nearly double the stopping distance.

Key Concept

Large Vehicle Stopping Distance and Brake Lag
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Topics

Sharing the Road with Large Vehicles

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