Brain Teaser, Courtesy of a Dying Genre

Here's a brain teaser for you, found by Steve, my always-informed and well-read friend:

"A pickup truck struck the semi a short time later and was hit by a third vehicle. Authorities say a fourth vehicle was hit by a fifth before another semi-truck struck the first, and a seventh vehicle hit the second truck."

Denver Post: Delta man cited after 7-vehicle crash in canyon