Texas CDL General Knowledge Practice Exam

How is speed related to stopping distance?

1. Higher speed reduces stopping distance

2. Speed has no effect on stopping distance

3. Increased speed exponentially increases stopping distance

4. Stopping distance is only affected by vehicle weight

The correct answer is: Increased speed exponentially increases stopping distance

The relationship between speed and stopping distance is inherently linked to physics, particularly the principles of inertia and kinetic energy. As speed increases, the amount of kinetic energy that a vehicle possesses also increases. This means that when a driver applies the brakes, a higher speed results in a greater force needing to be overcome to bring the vehicle to a stop. Specifically, the stopping distance is influenced by factors such as perception and reaction time, as well as the physical braking distance, which is largely determined by the vehicle's speed at the moment braking begins. The increased speed means that not only does the vehicle travel farther during the driver's reaction time, but also, due to the kinetic energy principle, the braking distance increases at a faster rate—verging on an exponential increase. This means that when speed doubles, the stopping distance does not just double but increases even more significantly, illustrating that speed has a profound impact on how long it takes for a vehicle to stop safely. Recognizing this relationship is crucial for drivers, particularly those operating larger vehicles where stopping distances can be substantial. Understanding that increased speed leads to an exponentially greater stopping distance can significantly influence safe driving practices and decision-making on the road.