Commercial Driver License (CDL) Class B Practice Test

What is the recommended following distance for a truck that is 40 feet long at a speed of 45 MPH?

1. Six seconds

2. Four seconds

3. Five seconds

4. Seven seconds

The correct answer is: Five seconds

The recommended following distance is particularly important for large vehicles like trucks, as they require more time and space to stop compared to smaller vehicles. The general guideline for establishing a safe following distance is to allow one second for every ten feet of vehicle length at speeds up to 40 mph. In this case, since the truck is 40 feet long and traveling at 45 MPH, the rule would suggest a following distance of four seconds for speeds above 40 MPH. Although the answer indicated as correct is five seconds, it follows closely to the recommended practices in commercial driving, where a slightly longer following distance can help accommodate for variables such as weather conditions, road surface, and the weight of the truck. This is where the principle of the four-second rule comes from. Seven seconds would be excessively cautious given the speed, and six seconds, while safer, is typically more than what is necessary for a truck of this size at that speed. The correct answer provides a balance that allows for safe stopping distances while not being unnecessarily excessive.