Mother and baby recovered after intensive care at Northern Rivers Koala Hospital in Lismore, NSW, and were released back into the wild in October.
But another joey, Guinevere, was not so fortunate, dying from injuries after being hit by a car along with its mother.
The pair were among an estimated 10 million native animals killed on Australian roads every year.
Though there are measures known to make roads safer for wildlife, new research has warned those optional design standards are often overlooked.
Wildlife could be protected through underpasses, canopy bridges and exclusion fencing, but their construction was usually left to the discretion of budget-conscious developers, according to a Griffith University-led analysis.
"Ten million animals ... that's an insanely massive number," road ecologist and the study's lead author Christopher Johnson told AAP.
"If we treated building a wildlife bridge with the same approach as we would a pedestrian bridge, we'd have a lot better outcomes."
Queensland and Victoria are the only states with wildlife-sensitive guidelines embedded in their road designs, although their standards are voluntary.
"Those guidelines are a nice-to-have, not a need-to-have," Dr Johnson said.
"Nice-to-haves don't always make it through to the end of the project."
The study called for biodiversity to be at the core of infrastructure planning, rather than being left open to interpretation.
Dr Johnson said wildlife-sensitive road design should be a part of the government's ongoing nature law reforms.
"This is a really good opportunity to try and get more ecology advice brought in earlier within project phases," he said.
Spring is a high-risk season for wildlife, as animals move around roadways to breed and forage.
As many as 80 koalas are killed on Northern Rivers roads each year and 80 per cent of those hit by cars do not survive their injuries, according to statistics from the local koala hospital.
Drivers were warned to slow down, particularly in known habitats, and to look out for signage that indicated recent sightings.
"These incidents occur most often along major transport corridors where habitat has been cleared or fragmented, forcing koalas to cross busy roads to reach food trees, shelter or breeding partners," the hospital's superintendent vet Kate Thomas said.
"We cannot continue relying on voluntary guidelines that leave wildlife exposed in known hotspots."
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