A number of "homemade devices" have been found along the O-Bahn track, north-east of Adelaide.

Key points: Police find a number of suspicious homemade devices along the O-Bahn

Police find a number of suspicious homemade devices along the O-Bahn Anyone with information is asked to call CrimeStoppers

Anyone with information is asked to call CrimeStoppers The State Government announces permanent anti-throw screens on the Southern Expressway

A section of the O-Bahn was closed as police investigated and buses were forced to take an alternate route.

SA Police said officers found a number of suspicious homemade devices at the Campbelltown section of the busway.

Emergency services were called just before 9:00am after a member of the public found one of the devices.

The bomb response unit was called to the scene and found "homemade incendiary devices".

"The devices were not explosive," a statement said.

Police have urged anyone with information to contact CrimeStoppers.

Earlier, the State Government revealed permanent anti-throw screens had been installed on all bridges along the Southern Expressway.

It followed a spate of rocks being thrown from bridges onto traffic.

Transport Minister Stephan Knoll said existing bridge CCTV had also been upgraded.

He said the Government would spend a total of $15 million on the upgrade.

The project is expected to be completed by June.