A new report by the AAA Foundation for Traffic Safety concludes there is no scientific basis for setting legal limits for marijuana and driving. These limits are arbitrary and unsupported by science, the group says.

States that allow recreational use of marijuana have legal tests for driving while impaired by the drug, the Associated Press reports. The AAA Foundation for Traffic Safety is calling for repeal of those laws.

These laws could result in unsafe drivers going free, while others are wrongfully convicted for impaired driving, the group said.

In five of the six states that have legalized recreational marijuana, it is presumed a driver is guilty of drugged driving if the person tests higher than the blood-test threshold for THC, the psychoactive ingredient in marijuana.

The foundation is recommending that states replace these laws with measures that would allow specially trained police officers to determine if a driver is impaired. Police could test for the presence of THC, instead of looking for a specific threshold.

“There is understandably a strong desire by both lawmakers and the public to create legal limits for marijuana impairment in the same manner we do alcohol,” Marshall Doney, AAA’s President and CEO said in a statement. “In the case of marijuana, this approach is flawed and not supported by scientific research.”

According to the report, people with relatively high levels of THC in their systems may not be impaired, especially if they use marijuana regularly. In contrast, some drivers with relatively low THC levels may drive unsafely. This finding is very different from alcohol, where it is known that crash risk increases significantly when a person has higher blood-alcohol concentrations, the foundation notes.

The report found the percentage of drivers involved in deadly crashes who recently used marijuana more than doubled from 8 to 17 percent between 2013 and 2014 in Washington, which legalized recreational marijuana in December 2012.