Riddoch Highway is a rural highway in south-eastern South Australia, designated as route A66 between Keith and Mount Gambier, with the remainder between Mount Gambier and Port MacDonnell designated as route B66. It is named after John Riddoch, the first white settler landholder and vigneron in Coonawarra. Route Riddoch Highway branches from Dukes Highway at Keith and travels south through Padthaway, Naracoorte, Penola, Nangwarry, Tarpeena, and Mount Gambier to Port MacDonnell and nearby Cape Northumberland. It passes through grazing and cereal-growing land, horticultural and vineyards (within the following wine regions - Padthaway, Wrattonbully, Coonawarra and Mount Gambier), and plantation timber, predominantly pinus radiata. The Royal Automobile Association of South Australia has rated the highway at 5/10. Major intersections See also Highways in Australia List of highways in South Australia References External links Riddoch Highway webpage on Ozroads website Highways in South Australia Roads in South Australia