Researchers from three Australian universities issued the warning in a paper published in the Computer Law and Security Review, dubbing the problem "the driver dilemma".
They have called for legal changes in states including Queensland and South Australia to address the issue before more advanced autonomous vehicles come onto the market.
The warning comes after Tesla pledged to launch its fleet of self-driving taxis as soon as 2026, and as Australia's National Transport Commission considers rules for autonomous vehicles.
The research paper, from academics at the Queensland University of Technology, Charles Darwin University and the University of Newcastle, examined whether Australian transport laws were ready to address situations in which a 'driver' may not be human.
It found many state laws referred only to a human driver rather than self-driving features, which could create uncertainty in the case of self-driving cars.
"This means that under the existing Australian road traffic laws when an (automated driving system) is operating there is no 'driver'," the study found.
"As the (automated driving system) is not a 'person' it cannot be a driver for the purposes of Australian road traffic laws."
Laws in Queensland and South Australia, for example, only allowed for human drivers.
Charles Darwin University senior lecturer Mark Brady said the strict provisions could affect lawful directions to stop at the roadside or in determining who is held responsible in the event of an accident.
"The potential would be for protracted litigation following a collision," Dr Brady told AAP.
"If there's no one that can be held responsible, there's going to be a legal limbo."
State governments could make changes to transport laws to accommodate self-driving vehicles, the researchers found, by emulating existing passenger transport laws.
NSW taxi rules, for example, allowed authorities to stop a vehicle regardless of the driver and Dr Brady said the same provisions could be extended to private vehicles to ensure future driving systems were captured by laws.
"As levels of automation get higher and automated driving systems take greater control of the vehicles, problems will start to arise with respect to the framing of our laws," he said.
"At high levels of automation, it's going to be quite problematic."
Some modern vehicles have driver-assistance features such as assistive cruise control and lane-keeping technology that could qualify for level-two autonomy, but level-five vehicles are so self-reliant they no longer feature a steering wheel for human interventions.
Full self-driving cars have been tested in American states including California and Arizona by Google-owned Waymo and General Motors' service Cruise.
Tesla last year announced plans to launch a robotaxi service in California and Texas as early as 2026.
Australia's National Transport Commission is considering laws that would allow autonomous cars on local roads, following a public consultation last year, but has yet to announce its findings.
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