The elderly woman is shown clambering out of the wreckage of a car to scold her errant relative for failing to pay attention to the road.
The Scottish Government agency’s latest advertising campaign is aimed at urging male drivers aged between 20 and 29 to slow down on country roads and be better prepared for unexpected hazards such as bikes and deer.
They are the age group most likely to be involved in a crash, despite more than six in ten claiming to be good or excellent drivers.
The new campaign follows a series of ads featuring the gran character last year.
Road Safety Scotland said speeding which led to loss of control was the biggest cause of deaths on country roads, which accounted for six in ten road casualties in Scotland.
A total of 7,003 people were killed or seriously injured on such roads in 2018.
Two thirds of those killed were men.
In the 30-second advert, “gran” tells her grandson: “You need to steady on.
"Things pop out of nowhere round here, like trees you don’t see, bikes you could strike, deer just appear.
"So stop driving like a wee bam.”
It ends with the voiceover: “Prepare for the unexpected.
"Slow down on country roads.
"Drive like Gran’s in the car.”
Transport secretary Michael Matheson said: "This new campaign strikes just the right balance of humour while delivering an incredibly important message, so it is sure to stick in the minds of our target audience of young male drivers.
“Country roads are notoriously unpredictable and, with so many potential distractions both within and outside the car, it’s absolutely crucial drivers prepare for the unexpected and slow down when travelling on them – no matter how well they think they know the route.
"We’ve had great success using Gran to deliver these messages, so we’re pleased to welcome her back for this campaign too.”
The adverts will also appear at the cinema, on social media and within games such as Grid and Football Manager.
Neil Greig, the Scotland-based policy and research director of motoring group IAM RoadSmart, who advised over the campaign, said the advert’s approach had proven to resonate with young drivers.
He said: “This is a very effective approach as it is based on feedback from young drivers themselves.
"It may seem counter intuitive, but it was a clear finding from research for the campaign that young guys will listen to their gran but not their parents.
"The creative approach taken on the basis of this insight has led several campaigns, all of which have passed on that basic message in a fresh and entertaining way.”
Road Safety Scotland said independent evaluation of the previous “Drive Like Gran’s in the Car” campaign showed a “high recognition among the target audience”, with 69 per cent recognising the adverts.
It said drivers who recognising the adverts “were more likely than non-recognisers to express willingness to avoid risks, for example, never drive after taking drugs and prefer to drive carefully rather than quickly”.