Ms Henderson turned 30 on Friday, defying the odds of surviving a brutal high-speed car crash.

On a warm January evening six years ago, Ms Henderson was a passenger in a car heading to a bachelor and spinsters ball when the lane conditions changed.

The car hit gravel and skidded out of control through no fault of the driver.

With no roadside barrier to absorb the impact, the car slammed head-on into a tree at about 100km/h.

Ms Henderson was thrown so far that a farmer who was first on the scene only found her some time later.

Her heart stopped, and emergency workers resuscitated her at the scene and in transit.

"From what I understand, I died at the scene and three more times in the helicopter on the way to the hospital," Ms Henderson said.

Her body was slashed by barbed wire, leaving "wicked scars across my chest." She broke her back, wrist and elbow, all of which cause ongoing pain and grief.

Ms Henderson, from the outer Melbourne suburb of Eltham, is about to graduate with a degree in agricultural science, something nobody would have expected six years ago. Her brain injuries were so severe the top of her skull was removed for 10 months to allow her swollen brain to recover.

Doctors believed she would never walk, talk, feed herself, live independently, or be able to care for her dog Blue, her "rock".

The statistics say Ms Henderson should be dead, said Samantha Cockfield senior road safety manager with the Transport Accident Commission (TAC) in Victoria.

"Hitting a tree is almost unsurvivable in any car," she said. Even the best seat belts and airbags would make little difference.

But a roadside fence, such as a wire rope barrier, would have reduced the risk of injury or death to only 15 per cent, Ms Henderson said. Rumble strips, alerting the driver to veering off course, would also have made a difference. Clearing the roadside of large obstacles such as trees, or creating a barrier near them would have also paid off.

Wire rope barriers stretch to hug a vehicle and allow it to gradually lose speed before returning the car to the road. "With a wire rope barrier, you don't stop suddenly, you gradually reduce – or wash off that energy in the travel speed – and that slows you down over time," said Ms Cockfield. Some people have been known to continue driving in these cases.

Running off the road is the most common type of accident in Australia. It accounts for about 21 per cent of insurance claims from car crashes in Victoria. In NSW, running off the road at speeds greater than 80km/h accounted for nearly 1060 accidents in 2015, twice as many as all other accidents. The next most dangerous type of crashes are head-ons.

As well as the devastation road crashes cause families and the loss of livelihood, severe injuries costs millions. The average lifetime cost of caring for someone with a severe brain injury is as much as $2.25 million, and the lifetime costs of a quardriplegia claim is $2.63 million, according to Victoria's Transport Accident Commission. These figures are similar across Australia.

Now a new international study has used Victorian data to prove that upfront investment in infrastructure is far cheaper than the cost of treatment.

The report, commissioned by the British-based road safety group FIA Foundation, provides examples of infrastructure paying off in very different conditions: Victoria, which has the lowest fatalities in Australia; Queensland's Bruce Highway, which is one the worst highways in Australia; and Cambodia, where the modelling showed providing motorbike helmets can keep many families out of poverty.

They proved in "concrete terms that investing in accident prevention can save lives and money," Rosemary Addis, executive director of road safety consultants Impact Strategist and co-author of the report Investing to Save Lives.

The modelling used Victorian data from 40,000 crashes which caused 1349 deaths, about 24,000 serious injuries and triggered 50,000 insurance claims between 2006 and 2010.

As part of the research, Rob McInerney, the CEO of the International Road Assessment Program, looked at what would happen if a range of preventative measures were installed on 400 kilometres of busy 100km/hroads in Victoria.

The costs varied: barriers cost about $1 million per kilometre to install while audible rumble strips cost about $100,000 per kilometre.

These preventions cost $33.35 million over their lifetime, but the benefits more than outweigh the costs. The model found they would prevent 24 people from dying.

They would also reduce the number of people with serious brain injuries such as Ms Henderson's by 107, stop 37 people from becoming quadriplegic 14 from becoming paraplegic, and eliminate 286 other injuries and claims.

This would reduce insurance costs by as much as $51 million, according to the report.

The modelling included increasing the number of five-star roads – where there is little chance of someone being killed and the severity of injuries is lessened.

Mr McInerney says that for every $100 spent caring for those injured on the roads, only $1 is spent on prevention, building infrastructure that could prevent or reduce injury.

"We are critically underfunding the problem," he said.

"The thing about road crashes is we do have most of the solutions to stop a death or injury from happening ... and injuries would be less severe or potentially avoided altogether."

Mr McInerney and road safety experts are lobbying for a new approach that looks on road safety as a public health issue. They talk of introducing a "vaccine" for roads to eliminate the epidemic of road deaths estimated to kill 265 million people worldwide between now and 2030, surpassing malaria, AIDS and tuberculosis.

The human cost is also enormous, and can force many families into poverty.

Ms Henderson said the impact on her friends and family has been heartbreaking and overwhelming.

Outsiders would never know what she had been through to achieve her "miraculous recovery".

She is pain every day. The acrylic plate that replaced her skull causes her searing pain she likened to a wart being burned off across a large area.

She told her neurosurgeon: "Holy crap I can't handle this cold feeling, it feels like when you eat an ice cream really fast, but 100 times worse."

Ms Henderson also had to learn how to study differently. Instead of getting angry, she decided to see how far she could go to prove doctors wrong.

"Instead of having such a negative attitude, I think this is awesome: let's see how far I can go."

Like most young people, she thought she was invincible.

"I thought that this would never happen to me because I was so sensible," she said. "My worry and concern is that this can absolutely happen to you, even if you are the best driver in the world something can go wrong, another driver, road conditions. It absolutely can happen and don't ever think this won't happen to you.

"Driving is such a privilege," she said.

Micaela thinks it is time for road safety experts to do more.

"It is up to the driver to drive responsibly and safely, but it also up to the road safety people to make our roads safer because in my case, it was the fault of the road, it was nothing to do with the driver."