Australia's peak body for truck drivers says it will launch a national campaign to stamp out an illegal courtesy used by the haulage industry for decades but fraught with danger.

In the 1950s, truckers started using indicators to signal to drivers behind that it was safe to overtake.

More than 70 years later, the habit has been widely adopted as an unofficial signal between drivers, but the road safety authority says it is "fraught with danger".

Dead cow, close call

Heather Jones, truck driver and founder of Pilbara Heavy Haulage Girls, says use of the signal has declined in recent years, but was still common on country roads.

"I saw a dead cow on the road … I indicated to go around the cow and next minute, in the bush, there was this big dust ball and this car going round and round,"

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