This does not weaken the argument. The amount of cargo that different types of vehicles can haul has no bearing on how we assess the safety of those vehicles. This claim is just irrelevant to the argument.

This weakens the argument by undermining the author’s comparison of triple-trailer fatality rates from the West against other vehicles’ national rates. This claim undermines the conclusion that triple-trailers are overall safer—instead, they’re just being driven in safer areas.

This does not weaken the argument. Whatever else the opponents have ever opposed is totally irrelevant to how safe triple-trailers are. Even if we knew how safe twin-trailers are, which we don’t, this wouldn’t do anything to the argument.

This does not weaken the argument. If anything, this could strengthen by providing a mechanism for triple-trailers’ safety. We don’t know whether other commercial vehicle drivers also need special licenses, though, so it’s hard to compare. Either way, no weakening here!

This does not weaken the argument. How triple-trailer fatality rates have changed over the last few years tells us nothing without more information. How big was the change? Do we know what caused it? We don’t know. As it is, this is just irrelevant to the argument.