After much searching, I can't seem to find specifics. Does anyone know what the parameters are for the new roadside drugalysers the police will be using on drivers? There isn't any concrete information about how the concentration of illicit drugs found in the driver's saliva is measured. Are drivers 'clean' an hour after 1 spliff? 3 hours after 5 spliffs, 2 weeks after having been to Amsterdam and sampling local delights? I can't wrap my head around how THC levels are measured, and over what timescale. Blood alcohol is much easier to measure with accuracy. Would habitual users always fail the test due to consistently having high concentrations of THC in their system, even though driving ability is not necessarily impaired at the time of the roadside test?