The Horsley Drive (Main Road 609) provides east-west access through the Fairfield Local Government Area between Wallgrove Road and the Hume Highway. Currently a two-lane single carriageway exists in this section of the Horsley Drive and the arrangement has sufficient capacity for current and projected traffic flows. The Horsley Drive is frequently used by heavy haulage trucks and is the principal access into the Smithfield/Wetherill Park industrial area. The Roads and Traffic Authority (RTA) proposes to upgrade The Horsley Drive at Wetherill Park from the current two-lane arrangement to an ultimate six-lane dual carriageway between Mimosa Road and Elizabeth Street. This review of environmental factors (REF) assesses the environmental effects associated with an interim upgrade to four-lane dual carriageway as the first stage of the ultimate six-lane upgrade.