Research shows that about 4% of drivers in Europe participate in traffic after having taken drugs and/or medicines. With 3.4% this share was lower in the Netherlands; traces of drugs were found in approximately 2.8% of the car drivers and traces of drugs were found in 0.6%. Substance use is highest among young male drivers. Alcohol and cannabis (hashish and weed) are used by far the most in Dutch traffic, followed by cocaine and benzodiazepines (sleeping pills and tranquilizers). The exact number of road traffic casualties due to drug use in traffic is unknown. A hospital study indicates that approximately 10% of the seriously injured drivers tested positive for drugs. Police enforcement of drug use in traffic will benefit when legal limit are set for drug use in traffic. Such limits will be introduced in the Netherlands on 1 July 2016. The new limits for each individual drug are based on the relationship with behaviour, i.e. impairment of the ability to drive. The new legislation uses the zero limit for ‘combined use of substances’. As the use of alcohol leads to a greater number of traffic casualties, it is important that the enforcement on drugs use in traffic is not at the expense of the enforcement on alcohol.