NEW speed cameras for South Australian roads will be able to catch motorists driving faster than the speed limit on average during a journey - instead of just at a single point.

The point-to-point cameras measure the time taken by a vehicle to travel between two fixed cameras to determine its average speed.

The cameras will be used on Port Wakefield Rd and the Dukes Highway.

In future, they could be installed on Victor Harbor Rd, the South Eastern Freeway, the Northern Expressway and the Sturt Highway.

Police Minister Jennifer Rankine said it was a fairer way of measuring vehicle speed.

"These cameras detect speed over a wider area, as opposed to a single point in time," she said.

Similar technology is already used to measure the speed of trucks over long distances through the Safe-T-Cam network, but now new cameras will target regular drivers.

Point-to-point technology is used in the UK, Netherlands and Scotland.

In the past five years 20 people have died on the Dukes Highway and nine on Port Wakefield Rd.

This year's road toll stands at 42.

"Speeding on highways continues to be a major cause of road crashes and road trauma," Ms Rankine said.