Unsafe driving behaviour and four wheel drive vehicles: observational study

I found the item interesting, but still leaving some basic questions:
Has there been a comparative study of ALL large/luxury car drivers as a
sub group?
Why were the commercial vehicle groups not included?
Both large car drivers and commercial vehicle drivers break these laws,
often with much larger, and therefore if we follow the authors logic much
more dangerous vehicles.
Having been on a coach recently where the driver when not talking on his
hand-held phone was texting with it, this would seem to be a very tailored
study to achieve a desired outcome?

Competing interests:
None declared