I will begin with pointing out the peculiarity that the previous method to establish guilt was to use a medical professional to assess the suspects of THC-impaired driving. After the new blood level method has been rolled out, Norwegian newspapers has noted cases where the suspects have been assessed to be sober by a doctor in connection with blood sampling (1). An argument from defense attorneys has been that the suspect has been assessed as sober by a medical professional, so it is unreasonable to find him guilty in accordance to the limits of impairment set by lawmakers. Nulla poena sine culpa.
Proceeding to another peculiarity in the totality of the regulation. In the outdated list of impairment levels (2) we can see that a plethora of drugs have been marked as not having any scientifically proven impairment limit equivalent to 0,05 % BAC. In the updated list of impairment (3) we can see that they still maintain that there is no equivalent to 0,05 BAC in a few drugs. Absent having a blood value to gauge from, they retain the old system of a health professional to access impairment.
What we see is that the courts are using a peculiar form of scientism where they refuse to presume innocence after a standard of professional assessment if it can exonerate the individual for THC-impaired driving, while (reasonably) relying on the same standard to pursue impairment by other drugs.
What is also overlooked is that the police and courts have an opportunity to uphold the lawmakers intent of not punishing residual THC levels by relying on the assessment of a medical professional in cases where THC is present in blood and there is an absence of observed impairment.
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Sources:
(1) From Norwegian public broadcaster:
(2) Outdated list of impairment, Norwegian government site:
https://www.regjeringen.no/globalassets/upload/sd/vedlegg/brosjyrer/sd_ruspavirket_kjoring_net.pdf
(3) Updated list of impairment, official database of Norwegian law:
https://lovdata.no/dokument/SF/forskrift/2012-01-20-85