Are wildlife escape ramps needed along Australian highways?

Abstract

Road escape ramps are structures developed in the USA to enable large mammals that become trapped on the roadside of a wildlife fence to escape the road and avoid vehicle collision. They are now commonly installed in eastern Australia to enable the Koala (Phascolarctos cinereus) and other fauna to escape through a roadside exclusion fence and return to the forest. We investigated the use of seven of 14 escape ramps over three years on the Oxley Highway at Port Macquarie in New South Wales. The Swamp Wallaby (Wallabia bicolor) was the most frequently detected species, traversing the escape ramps on 502 occasions, followed by bandicoots (Isoodon macrourus and Perameles nasuta) on 148 occasions. Various other species were detected but no Koalas. Swamp Wallabies moved through the escape ramps in the reverse direction (i.e. towards the road) in 53% of detections of that species and bandicoots in 14% of their detections. There was no obvious pattern by these species of proportionately higher use of ramps closer to the end of the exclusion fences. The large number of reverse passages through the escape ramps reveals a poor design of these structures. Trials with taller ramps are required to determine how to minimise reverse passages. Concurrent monitoring of three underpasses detected numerous crossings by large mammals including Swamp Wallabies, and some crossings by Koalas. We believe evidence is needed to demonstrate the necessity for escape ramps along Australian highways.