The roadway, and your vehicle are all categories associated with risk that you should assess before you get behind the wheel.

you (the driver)

Explanation:

According to my research on vehicle safety rules, I can say that based on the information provided within the question the third category being mentioned would be you (the driver). You need to make sure that you or whoever is driving is in perfect condition to be driving. If the driver has had some alcoholic beverages, drugs, or is in emotional distress it may not be safe or a smart decision to let them drive.

I hope this answered your question. If you have any more questions feel free to ask away at .

answer; the intervening variable;