The last stretch of approximately 12 miles (19 km) was the most dangerous for many years, as it required precarious crossings at the Collie and Preston Rivers.
There are few services alongside the highway, although as of June 2015 a pair of roadhouses are planned near Greenlands Road.In June 2014, Forrest Highway was extended south to Bunbury by renaming much of Old Coast Road as well as Australind Bypass as part of the highway.Since the 1980s, the state government has been upgrading the main Perth to Bunbury route, by extending Kwinana Freeway south from Perth, and constructing a dual carriageway on Old Coast Road north of Bunbury, including bypasses around Australind and Dawesville.A bypass was also planned around Mandurah, which underwent detailed environmental reviews and assessments in the 1990s and early 2000s.Improvements to Old Coast Road started in the early 1950s, but with little progress made until 1954 when the Main Roads Department approved £1000 worth of works.
The name "Old Coast Road" was formally adopted on 27 January 1959, and a sealed road was completed in September 1969.
Construction of the New Perth Bunbury Highway project, which became Forrest Highway and the final Kwinana Freeway extension, began in December 2006, and the new highway was opened on 20 September 2009.
Within one year of opening, the number of road accidents in the area had decreased significantly, but tourism and businesses in the towns on bypassed routes were also affected.
It crosses the river, then curves around Eaton to head westward to the Eelup Roundabout, which it reaches after travelling for nine kilometres (5.6 mi) and crossing the adjacent Preston River. The route he – and later others – took was slow and hazardous, taking four days to cover around 80 miles (130 km), and crossing four rivers.
Following the establishment of the Swan River Colony, the earliest report of exploration of the district around what is now Bunbury is from Lieutenant H. The route began with passage from Perth to Pinjarra, before turning south-west and passing through low, open scrubland, and a medium-timbered area with low marshes.
The road curves back to the south, reaching Old Bunbury Road after ten kilometres (6.2 mi).