I think more likely is that no-one has a clue!
The hints provided so far suggest north of the line from Maryborough to Monto, (or at least the southern reach of that line) but south of Rockhampton, as well as being within a half hour drive of the Bruce Highway. We know it's not at Kingaroy (but could be on the Kingaroy line), not between Taragoola and Calliope (but maybe on that line to Monto) and a tantalising hint it could be around Mount Morgan. But the bridge itself looks to be in good repair and may even still be in regular use, which suggests it's not the Mount Morgan line itself - which in any event is probably more than half an hour from the Bruce Highway. It also has to be close enough to a major road to allow a Google street view to be possible.
So where is it? I have no real idea, and don't have the time or inclination to Google every line looking for this bridge, but my guess is somewhere on the line to Kingaroy or either of the lines to Monto.
Further hints may well be needed!