The Tasmanian coroner has called for truck drivers to face more stringent licence testing after a married couple was killed by hay bales falling from an overloaded truck and trailer.

Michael Geraddus Pel and Tracie Anne Pel were travelling on a motorcycle at Lilydale in Tasmania's north in February 2015, when two half-tonne silage bales fell from the trailer of a truck they were following.

Coroner Rod Chandler found the round bales, each 1.6 metres wide, were not properly secured and killed the couple despite efforts from Mr Pel to avoid the obstacle.

Gerald Alfred Davis of Golconda lost his licence for four months and was fined $12,000 in the Launceston Magistrates Court in December 2015.

Prosecutors were unable to charge Davis with causing the deaths of Michael and Tracie Pel. ( ABC News )

Davis pleaded guilty to 12 traffic offences in the Launceston, including failing to comply with loading requirements.

The fully laden truck and trailer had been loaded by Davis and was carrying round bales of silage each wrapped in plastic.

"It is obvious that the tragic deaths of both Mr and Mrs Pel was a direct consequence of the failure on the part of Mr Davis," Mr Chandler said.

He said the bales were stacked two-high and had been secured by a single ratchet webbing strap over the top of the bales.

The coroner said national laws required loads to be secured by straps to prevent forward, rearward, side and upward movement as well as chain-bracing to prevent load shift.

He said the restraints used on the day did not comply because they did not restrict forward and rearward movement and the bales fell after the truck hit a small bump in the bitumen roadway.

"The drivers of heavy vehicles in Tasmania do not receive any formal training or instruction on load restraint," Mr Chandler said.

"This is the second incident in recent times where a road traffic fatality has resulted because of the failure to properly secure a load."

The hay bales which fell from the trailer weighed half a tonne each ( Rose Grant )

Christine Sylvia Bone, 64, of Devonport died in October 2014 after her car swerved into oncoming traffic at Latrobe while avoiding a chair that had fallen from a ute she was following.

Stephen Errol O'Connor, 63, of Latrobe, was sentenced to 28 days in prison, wholly suspended for 18 months after he was found guilty of negligent driving.

He recommended Transport Tasmania "give consideration to incorporating in its licencing test for drivers of heavy vehicles suitable questions relating to the Load Restraint Guide."

The coroner said this should include questions about appropriate loading methods.

"It is my suspicion that many licenced drivers in Tasmania are unaware of ... the safe means of restraining loads."

Mr Chandler said Transport Tasmania should also consider producing a pamphlet setting out load restraint guidelines in simple terms.

"That pamphlet could then be sent out with all licence renewal notices."

The Pel family have welcomed the coroner's findings.

Their son, Ben Pel, said the situation had not changed as he said he still saw overloaded trailers.