# Old Princes Highway, South Australia

The Old Princes Highway is a 41.1-kilometre-long (25.5 mi) state-controlled highway in South Australia linking the towns of Nairne, Kanmantoo, Callington, Monarto South and Murray Bridge. It follows the previous alignment of the Princes Highway which used to run through these towns but was subsumed into the South Eastern Freeway, but it remains classified as a state road.

## History

The first section of the Princes Highway opened as early as February 1922 via Mount Barker Road and was later realigned to run further along Mount Barker Road through Mount Barker, and along Wellington Road via Wistow and Woodchester to Langhorne Creek, although by 1935 this alignment was changed to run via Nairne, Kanmantoo, Murray Bridge and Tailem Bend (along what is now known as the Old Princes Highway).
The Princes Highway functioned as Adelaide's major south-eastern approach and was heavily trafficked; government plans to upgrade this route weaving through the Adelaide Hills had begun by the early 1960s. Initial sections of the road project that eventually became the South Eastern Freeway commenced in December 1965, along a 2 km section from Measday's Hill to Stirling: the eastbound carriageway was opened to traffic in 1967, and the section was fully completed in 1969 when the remaining carriageway and the Crafers Interchange became fully operational. The next stage extended the freeway east through Bridgewater to Verdun and opened in 1972, and from Verdun to Mount Barker in 1974, completely replacing Princes Highway – renamed back to Mount Barker Road – as the main route between Mount Barker and Crafers. As this was part of Highway 1, the route was progressively re-aligned along the freeway as sections of it opened. The section from Stirling to Mount Barker was later classified as Mount Barker Road, and the Littlehampton to Murray Bridge section became known as the Old Princes Highway.

## Alignment

The western terminus of the Old Princes Highway is located at a roundabout north of the South Eastern Freeway near the Mount Barker interchange. This roundabout serves as the intersection of Mount Barker Road, Adelaide Road, and the Old Princes Highway. From this point, the highway extends eastward, passing through Littlehampton and Nairne, where it functions as the main thoroughfare for both towns.
Beyond Nairne, the road features a series of significant curves and elevation changes before leveling out as it approaches Kanmantoo. After bypassing Callington, the highway ascends a steep incline at Callington Hill. This section begins with a straight, gently sloping false flat, followed by a slight curve and an overtaking lane to assist traffic on the uphill segment.
Following the ascent, the road descends gently into the locality of Monarto. It passes the former safari park entrance and intersects Schenscher Road, where vehicles crossing or entering the highway are required to stop, while the highway maintains right of way. The route continues straight before curving to meet a railway crossing at a right angle. It then proceeds east-southeast to its eastern terminus at White Hill, concluding at a T-junction with Adelaide Road.