This original bridge has a tube like hollow box form because Rupert assumed smaller animals would go through the inside to gain protection from hawks and owls (many Oz animals are nocturnal). The concept has been proven through research, although it has been found most animals used the top so recent bridges have been simplified to a single deck. Scattered all up and down the country bridges like this are helping possums and other creatures cross freeways and other man made obstacles.
Arthur Russell my Grandfather Central Provinces (later Madhya Pradesh) Police
Beryl Essai Russell in her Garden, Madhya Pradesh 1960s