Commercial Driver’s License (CDL) Practice Exam

When determining a safe following distance for a large vehicle such as a 40-foot-long truck traveling at 50 MPH, it's important to consider both the size of the vehicle and the speed. A general guideline for following distance is that you should maintain at least one second of distance for every 10 feet of vehicle length when driving at speeds below 40 MPH. For speeds above 40 MPH, it is advisable to add an additional second.

In this case, since the vehicle is 40 feet long and the speed is 50 MPH, the calculation would indicate a need for a minimum of 4 seconds of following distance. This allows ample time to react to sudden stops or changes in traffic.

In practice, drivers are often encouraged to gauge their following distance based not only on speed and vehicle size but also on traffic conditions, weather, and road types. The 5-second following distance provides a safer buffer to allow for unexpected circumstances, such as sudden stops by vehicles ahead or changes in road conditions, ensuring the driver has enough reaction time. Hence, the choice of a 5-second following distance is not only a quantitative measure but also a qualitative approach to enhancing safety on the road.