[buellerbueller]

that's called a hypothesis. now go author a study to test it, like the study being reported on. hypotheses without evidence don't stand up to hypotheses that have been tested.

[kortilla]

And how did this study rule out smartphones?

[amanaplanacanal]

You could compare rates to other countries that do have smartphones like the US, but don't drive the large vehicles like Americans. That might be illuminating.