Not surprisingly, no elevated risk was found in the three studies listed at bottom, which looked at urine metabolite levels rather than blood THC. This confirms that urine testing has no bearing on driving impairment. Despite this fact, US Department of Transportation regulations force millions of commercial drivers to submit to random urine testing. The government has never produced convincing scientific evidence that this policy is necessary or effective to protect public safety. But they're the government, so they don't have to provide any evidence!
There are now two companies, called Acorn and Mosaic, that have gone further. They use census data, retailers’ own information, and other sources (all those times you forget to tick the “don’t pass on my information” box) to split Britain’s million postcodes into about 60 different social groupings. All of these categories are given names, some of which are innocuous, such as “summer playgrounds” or “sprawling subtopia”. Others are a fairly stark assessment of the householders’ prospects: “white van culture” and “multi-ethnic crowded flats”. These data are then sold back to retailers to help them chase some customers – and avoid others.