Reference sheet
Bridge and pole types
Nine ways to get a tree-dwelling animal across a road, with heights on one scale. Pick a column to open its drawing, or pick an animal to see which types it has been recorded on.
Show where this animal was recorded
Column heights are to one scale. Orange hatching shows a recorded height range. A dashed green mark means the source gave no height, so the mark is only a placeholder.
Type 1 of 9
Flat rope net
A long strip of rope net hung between poles across the whole road. It is the usual design on freeways.
- Span
- 60 to 85 m1
- Width
- 50 cm1
- Height
- At least 6 m above the road1
- Build
- About 15 mm marine-grade rope on two steel cables1
- Where
- Hume Freeway1
Recorded using it
Squirrel gliders, both common possums and brush-tailed phascogales on the Hume1. Sugar and feathertail gliders on rope mesh bridges on the Pacific Highway3.
What the record shows
Cameras logged 455 squirrel glider, 386 ringtail and 229 brushtail crossings on Hume bridges3. Two of the five bridges were not used by any species1.
Type 2 of 9
Narrow flat bridge
A much narrower strip for a smaller road, with steel wires as the edges and rope netting as the deck.
- Span
- About 26.5 m2
- Width
- 300 mm2
- Height
- Poles about 8.5 m tall2
- Build
- Two steel wires with marine-grade rope netting2
- Where
- Caves Road near Busselton, WA2
Recorded using it
Western ringtail possums. Other species recorded on it were birds resting2.
What the record shows
1,300 complete crossings in 270 nights, with the first only 36 days after the bridge was finished2.
Type 3 of 9
Rope ladder
Two long ropes joined by rungs. Simple, light and well tested on rainforest roads.
- Span
- 14 m in one trial3
- Width
- 25 to 50 cm3
- Height
- Not stated in the sources we read
- Build
- Rope rungs between side ropes3
- Where
- Wet Tropics, Queensland3
Recorded using it
Nine mammal species across Wet Tropics rope designs6. Possums, Lumholtz's tree-kangaroos and fawn-footed melomys were recorded at three trial bridges3.
What the record shows
More than 50 crossings on one elevated ladder over a 15 m tourist road6.
Type 4 of 9
Rope tunnel
A square tube of rope, built on the idea that animals want cover. Later designers dropped it.
- Span
- 14 m long3
- Section
- 50 by 50 cm3
- Height
- 7 m3
- Build
- 10 mm silver rope on wooden poles3
- Where
- Wet Tropics, Queensland3
Recorded using it
Part of the same Wet Tropics trials, with five to seven species at each crossing3.
What the record shows
It was used, but the Caves Road team chose a flat bridge because the box design had been found unnecessary2.
Type 5 of 9
Single rope on poles
One thick rope run along a row of poles on a wildlife overpass.
- Span
- Overpass 36 m by 15 m3
- Rope
- 40 mm diameter3
- Height
- Poles 6.5 m high3
- Build
- Eight poles joined by one rope3
- Where
- Road overpass, Queensland3
Recorded using it
Squirrel gliders, plus one brushtail and one ringtail possum3.
What the record shows
Squirrel gliders were detected on 33 occasions during 27 of 166 survey nights3.
Type 6 of 9
Median glider pole
A tall hardwood pole in the median with a cross-beam to launch from. It splits one long gap into two glides.
- Height
- 13 to 18 m1
- Thickness
- 40 to 50 cm1
- Cross-beam
- 10 by 10 cm, 2.4 m long, 50 cm below the top1
- Planning
- Glide ratio of 2.5:11
Recorded using it
Squirrel and sugar gliders on the Hume1. Feathertail and sugar gliders on the Pacific Highway8.
What the record shows
842 crossings by squirrel gliders and 258 by sugar gliders across 15 arrays4. Four arrays were not used by any species1.
Type 7 of 9
Roadside poles
Poles on the verges that give gliders a launch point closer to the road on each side.
Recorded using it
Squirrel gliders in Queensland4. Sugar, squirrel and feathertail gliders at Port Macquarie, with yellow-bellied gliders twice7.
What the record shows
Gliders were on the poles on 60 of 310 nights, and road crossings were confirmed on 16 of 125 nights4.
Type 8 of 9
Line of poles
A row of shorter poles leading gliders across open ground or over a wildlife overpass.
- Poles
- Five to eight in a line4
- Height
- 5 to 12 m4
- Spacing
- 5 to 22 m apart4
- Gap
- 50 to 70 m4
- Where
- Queensland pasture and highway sites4
Recorded using it
Squirrel gliders4.
What the record shows
Gliders were recorded on 130 of 240 and 32 of 114 pole checks at two highway sites4. None were detected in the middle of overpasses with no poles4.
Type 9 of 9
Trees in the median
Not a structure at all. Tall trees left standing in the median act as natural stepping stones.
Recorded using it
Squirrel gliders5.
What the record shows
Movement across the freeway was similar at sites with structures and at sites with tall median trees9.
Sources
- Monitoring the use of road-crossing structures by arboreal marsupials, Soanes, Vesk and van der Ree, Wildlife Research, 2015
- A remarkably quick habituation and high use of a rope bridge by an endangered marsupial, the western ringtail possum, Yokochi and Bencini, Nature Conservation, 2015
- Install rope bridges between canopies, Conservation Evidence
- Install pole crossings for gliders/flying squirrels, Conservation Evidence
- Evaluating the success of wildlife crossing structures using genetic approaches and an experimental design, Soanes and others, Journal of Applied Ecology, 2018
- Using canopy bridges to link habitat for arboreal mammals: successful trials in the Wet Tropics of Queensland, Weston and others, Australian Mammalogy, 2011
- Installation of wooden poles could save Aussie gliders, Australian Geographic, 2018
- Frederickton to Eungai Pacific Highway Upgrade: Aerial Crossing Monitoring 2020, Niche Environment and Heritage for Transport for NSW
- Research to inform management and restoration works for squirrel gliders, Kylie Soanes, Glideways Symposium, 2016
Drawings are schematic. Dimensions describe the structures named in each study, not a design standard.