@scott I want to push back on the framing here: I'm saying there isn't any issue that can be identified as *the* issue.
I hold both that bigger vehicles are more dangerous and that people are getting more distracted in my head at the same time.
Another reason I'm hesitant to call vehicle size *the* issue is that truck and SUV sales have been exploding since the '90s, and the reversal in death trends is newer than that.