For the record, these regs apply to COMMERCIAL vehicles used in interstate commerce only. Regs with-in each state can be more (or less) specific. (including commercial or NON commercial). However, It's in everyones best interest to comply with the intent of the law, commercial or NONcommercial. As with so many other gov regs, there is plenty of room for interpretation. It all boild down to what sort of mood the DOT cop is in and how nice of a judge you end up before. Best advice, IMHO, secure your load far OVER-KILL ,then find a DOT cop and quiz him on how regs are interpreted on a local/state basis. In Kentucky, the Division of Commercial Vehicle Enforcement is always more than willing to explain our states rules and regs. While they're largely responsible for interstate commerce involving big trucks, they're somewhat responsible for policing ANYTHING on interstates that could reasonably effect commerce on their highways. That often includes passenger cars, private "not-for-hire" haulers, ect.
Also, A Ky State Trooper once explained to me that even noncommercial haulers who become involved in a traffic accident may be held to "acceptable standards" by a jury in the case of a civil trial. The DOT regs can (and often ARE) those "acceptable standards". Best to comply, even if they don't apply directly to your situation.