 Eyre Highway is the only sealed road linking the states of Western Australia and South Australia , running east from Norseman in Western Australia for 1 @,@ 200 kilometres ( 750 mi ) across the Nullarbor Plain to Ceduna , South Australia . It then crosses the top of the Eyre Peninsula as it continues eastwards for 470 kilometres ( 290 mi ) , before reaching the city of Port Augusta . Eyre Highway is part of the National Highway route between Perth and Adelaide , and also forms part of Australia 's Highway 1 . It is signed as National Highway 1 in Western Australia , and National Highway A1 in South Australia . The vast majority of the highway is a two @-@ lane single carriageway with a speed limit of 110 kilometres per hour ( 70 mph ) , except in and around built up areas . Road trains ( A @-@ double or B @-@ triple ) up to 36 @.@ 5 metres ( 120 ft ) are permitted on Eyre Highway , but are limited to the slightly lower maximum speed of 100 kilometres per hour ( 62 mph ) . 
