Final answer:
To determine the number of seconds of following distance needed when traveling at 55mph in a 30-foot vehicle, you should leave approximately 5.2 seconds of following distance.
Step-by-step explanation:
To determine the number of seconds of following distance needed when traveling at 55mph in a 30-foot vehicle, we can use the concept of stopping distance. Stopping distance is the sum of the distance traveled during the reaction time and the distance traveled during the braking time.
First, let's calculate the reaction time distance. The general rule of thumb is to allow for one second of following distance for every 10 feet of vehicle length. In this case, the vehicle is 30 feet long, so we need 3 seconds of following distance.
Next, let's calculate the braking distance. The stopping distance is affected by the speed of the vehicle and the coefficient of friction between the tires and the road. Given the speed of 55mph, we can use the stopping distance for dry pavement from Figure 2.34, which is approximately 180 feet. To convert this distance to seconds, we need to divide it by the speed in feet per second. 55mph is equivalent to approximately 80.7 feet per second. Dividing 180 feet by 80.7 feet per second gives us approximately 2.2 seconds.
Therefore, the total following distance should be around 3 seconds (for reaction time) + 2.2 seconds (for braking distance), which is approximately 5.2 seconds.