"Disguised Conjunction" -- What's going on here?

I've been reading Brian A. Garner's The Chicago Guide to Grammar, Usage, and Punctuation and have been running through the section on conjunctions. I am confused by one of Garner's passages, which I've quoted below.

275 Disguised conjunctions. So-called disguised conjunctions are participles that have been long been used as conjunctions--e.g., barring, considering, provided, regarding, speaking, and supposing. A disguised conjunction does not have a subject, while a verb does {considering the poor road conditions, we traveled swiftly [considering as a preposition]} {we traveled swiftly, considering the poor road conditions [considering as a disguised conjunction]} {the committee is considering a budget increase [considering as a verb]}. The key distinction is that a conjunction does not take an object but a preposition does.

1. Specifically, can someone help me understand how "considering" functions as a conjunction in his second example (i.e., "we traveled swiftly, considering the road conditions")?
2. Also, with his example, Garner explains that one distinguishing characteristic of a conjunction (as least as compared to a preposition) is that is doesn't take an object. But then, grammatically, what is the function of "the poor road conditions" in his second example?

Solution 1:

My first reaction is to call that a typo. This would seem a disguised conjunction:
"We traveled swiftly, considering road conditions were poor."
I can also imagine something like:
"We traveled swiftly, if we are considering the poor road conditions." And it takes the place of 'if'. And the 'we' doing the considering are the speaker and the listener, not the 'we' who traveled.

That's the case for all of these: "barring, considering, provided, regarding, speaking, and supposing" The person speaking now is doing all of the barring, considering, supposing, etc., NOT the subject of the other clause.
"It took you long enough to find the place, considering you live here."
"I will go, provided he goes."
Those are the only 2 ways I can think of any of these being used to link clauses, so my honest belief is that all of them are used to mean "if we are..." or "if it is" in the case of provided:

(If we are) barring an earthquake, nothing bad can happen.
(If we are) considering his age, he should not join us.
(If it is) provided that A = B and A =/= C, B =/= C.
(If we are) regarding our previous discussion, I think you are right.
(If we are) speaking of lunch, I'm hungry.
(If we are) supposing he is rich, you should date him.

"Not including," "keeping in mind" and "ignoring" could also fit this description.