"As Zheng approached around a curve she steered too close to the left onto the gravel shoulder, braked and steered back onto the road but over-corrected to the right, causing the vehicle to cross the road completely," the coroner said.
"The riders had no time to react."
Mr Pederson and Mr Roberts were both thrown from their bikes and died from impact injuries. Mr Roberts' partner, a pillion passenger, was thrown about 23m but survived.
Even if police had made it to Zheng before the crash, the Coroner's enquiries found there was nothing they could do to get some problem drivers off the road.
Police said unless a driver was arrested for a serious driving offence, and a police officer was able to impose a bail condition banning someone from driving, there was "nothing to stop the driver from driving a motor vehicle and continuing to present a danger to other road users".
Zheng had little solo driving experience, had never previously driven on the left side of the road, and probably never previously drove faster than 40km/h.
"This case has highlighted an urgent need for legislative change" to help police deal with unsafe drivers and allow police who witnessed a "demonstrable lack of ability" to ban such drivers, Coroner McElrae said today.
He recommended the Government consider ways to stop drivers with foreign licences but inadequate driving experience from driving in New Zealand.
He also suggested giving thought to ways of assessing driver competency before overseas visitors could hire cars.
Craig Foss, associate minister of transport, said the Visiting Drivers Signature Road Safety Project, involving the rental car and tourism industries, was already working on ways to make roads safer.
"Measures such as directional arrows and educational information are already provided," he said. "We urge tourists and recent arrivals to take advantage of the free information available about the different driving conditions on New Zealand roads."
Mr Foss said he took the new recommendations seriously.
Last month, the Tourism Industry Association set up new guidelines for rental vehicles. These included providing links to road safety videos and travel distance calculators, and encouraging drivers arriving after long-haul flights to rest overnight before driving.
This followed earlier suggestions from Coroner McElrae after he investigated another fatal crash involving a foreign driver.
Seventeen days after the crash, Mr Roberts' family forgave Ms Zheng and embraced her after telling a judge in Alexandra they did not want her imprisoned.
She was ordered to pay $10,000 in emotional harm reparation and disqualified from driving for two years.
