_________ are the most frequent type of crashes on interstate highways.

Explanation

Rear-end collisions are the most frequent type of crashes on interstate highways. And the most frequent cause of rear-end collisions is tailgating (following the vehicle ahead too closely). The Alabama Driver Manual recommends that you maintain a following distance of at least two seconds behind the vehicle ahead of you. Under poor driving conditions, you should increase your following distance to four or even five seconds.