German President Frank-Walter Steinmeier signed into law a bill Friday regulating driving under the influence of cannabis. In June, the Bundestag set a maximum allowed limit of THC – the psychoactive substance in the cannabis plant – for drivers at 3.5 nanograms of THC per milliliter of blood. That’s equivalent to 20 milligrams of alcohol per 100 milliliters of blood. Even stricter rules are set for new drivers as mixing cannabis with alcohol is not allowed under the new law,writes Taz, according to translation. Under the new law, which takes effect this week, anyone driving with 3.5 nanograms…