Air Brake Practice Test

What is the average stop distance at 55 mph under normal circumstances?

1. 50 feet

2. 100 feet

3. 150 feet

4. 200 feet

The correct answer is: 100 feet

The average stop distance at 55 mph under normal circumstances typically ranges around 100 feet. This measurement accounts for both the perception-reaction time, which is the time it takes for a driver to recognize the need to stop and to engage the braking process, as well as the actual braking distance required to bring the vehicle to a complete stop. When a vehicle is traveling at 55 mph, the perception-reaction time can be approximately 1.5 seconds, which results in covering about 121.5 feet during that time. Following this initial response period, the braking distance is contingent upon several factors, including the vehicle's weight, road conditions, and brake efficiency. When these elements are considered, the sum of the distance traveled during the perception-reaction time and the braking distance generally results in an average stop distance of around 100 feet. This figure is a standard reference point used in driver education and safety courses to provide drivers with an understanding of safe stopping distances at higher speeds. In comparison, shorter distances like 50 feet would not adequately account for the necessary braking time and distance at that speed, while estimates like 150 feet or 200 feet can be seen as excessive for a properly functioning vehicle on a dry road under typical conditions