The legislation in relation to drug driving was updated significantly by the Road Traffic Act 2016. This legislation provided for preliminary tests for the presence of drugs, as well as specifying legal limits of certain drugs, including cannabis, while driving or in charge of a mechanically propelled vehicle.
The roadside tests of oral fluid, to which the Deputy refers, are preliminary rather than evidential, and in this sense mirror roadside breath tests for alcohol. They exist to assist members of An Garda Síochána in forming an opinion as to whether a person has consumed drugs.
Where a person is arrested on suspicion of driving while over the limit of cannabis following a preliminary test, they will be required to provide a specimen of blood for evidential testing. The limits for cannabis and other drugs were set based on expert scientific advice and international experience. These drug limits apply for blood only, unlike in the case of alcohol, where there are limits set for blood, breath and urine. This is precisely because blood is the best indicator of recent use in the case of drugs.