> Unless a policeman is staring at you intently through you car window in the exact moment that you open your door, how can they know what hand are you using to

> Unless a policeman is staring at you intently through you car window in the exact moment that you open your door, how can they know what hand are you using to do it? That's silly hyperbole. More likely, the main "enforcement" would be losing points when taking a driving test. That encourages driving instructors to teach it; and that causes drivers to learn it. In the case of a collision (e.g. knocking down a passing cyclist), if the driver was seen (by CCTV/dashcam/witnesses) to not use this procedure, then that could be taken into account regarding liability, insurance claims, etc.