Bridges

The Bunbury Outer Ring Road (BORR) is a new 27 km high-standard road connecting Forrest Highway to Bussell Highway, designed to ease congestion and provide a safer, more efficient traffic route for freight, tourists and locals. As part of the conditions for environmental approval, fauna crossings have been designed to maintain habitat connectivity over the road corridor. Bridges 1906 and 1916, located near Western Ringtail Possum habitats, are key components of this strategy. These bridges were designed with a strong focus on sustainability, particularly minimising tree clearing.

Bridge 1916 carries a 5 m wide fauna corridor and comprises a cast in-situ post-tensioned U-trough superstructure. The U-trough design was selected to reduce the structural depth, minimising earthworks and maintaining the vertical alignment of BORR.

Bridge 1906 is a triple-use bridge carrying Yalinda Drive, a shared path, and a 5 m wide fauna corridor. The superstructure comprises simply supported, pre-tensioned precast concrete Teeroff beams with a composite concrete deck.

Both bridges include 1 m of soil fill in the fauna corridor to support vegetation and facilitate fauna movement, with landscaping designed to promote connectivity while deterring unauthorised access. The high permanent loads required careful consideration of time-dependent effects. Drainage and waterproofing were key design considerations to ensure the bridges provide a 100-year design life. The bridges are also designed with adaptability and resilience in mind, minimising lifecycle costs and contributing to a circular economy. Asset Management Plans have been developed for both bridges, outlining inspection and maintenance activities.

This paper provides an overview of the fauna bridges and discusses the key design considerations.