One example used on a section of the East Gippsland Rail Trail in Victoria. Sign reads 'Rail Trail Maintenance Vehicles Only'.
One of the barriers on the main Hobart (Tas) shared pathway. I could ride through this comfortably at 13 kmph. Barriers can be 'opened' for vehicular access by undoing the padlock on the fixed leg of each barrier.
[Click image for enlargement]
Another example from a more heavily used
part of the East Gippsland Rail Trail in Victoria (also
used by horse riders).
Wire looped over wooden pole can be removed, thus
allowing wire & posts to be put to one side for
vehicular access.
Giraween Ck cycle path, Giraween, NSW - Beside Oklahoma Ave.
Quite awkward - and an amazingly elaborate structure, which can be easily circumvented through a gap in the pine log barrier several metres away.