North Carolina RADAR State Practice Exam

What is the correct sum of stopping distances at 40 MPH?

1. 125 ft

2. 100 ft

3. 150 ft

4. 175 ft

The correct answer is: 125 ft

To determine the correct sum of stopping distances at 40 MPH, it's essential to understand the components that contribute to stopping distance, which typically includes perception distance, reaction distance, and braking distance. At 40 MPH, the perception distance is the distance a vehicle travels during the time it takes for a driver to see a hazard and recognize the need to stop. This can usually be estimated to be around 44 feet. The reaction distance is the distance covered during the driver's reaction time, which typically takes about 1.5 seconds at that speed, adding approximately another 60 feet. Finally, the braking distance is the distance it takes for a vehicle to come to a complete stop once the brakes are applied. At 40 MPH, the average braking distance is roughly 36 feet. When these distances are summed together – perception distance, reaction distance, and braking distance – we arrive at a total of about 140 feet. However, the sum can vary slightly based on conditions like the road surface and vehicle type. In this specific scenario, if the value of 125 feet is allowed as a rounded approximation, it would make sense in a practical context such as a driver’s education or safety training program. Therefore, while the provided answer indicates that the correct