If you intend to drink alcohol at a party, arrange with your partner who will drive home, or catch a lift with someone else.
If an intoxicated person is about to get behind the wheel of a car, reason firmly with him not to drive. If that doesn't work, take his car keys away and call a taxi for him, or find someone who will give him a ride home.
If you're already on the road when you realise the driver is drunk, insist that he pulls over and lets someone else drive. If he refuses, ask him to let you out at the first opportunity and call the police. Give them your location, a description of the car and driver, and the car registration number. You may lose a friend, but you may also save a life.
If you see a car being badly driven on the road in front of you, assume the driver is drunk and be prepared to take evasive action.
