What technique does the Highway Code highly recommend for opening your vehicle door to avoid injuring passing cyclists or motorcyclists?

Where you are able to do so, you should open the door using your hand on the opposite side to the door you are opening; for example, use your left hand to open a door on your right-hand side. This will make you turn your head to look over your shoulder. You are then more likely to avoid causing injury to cyclists or motorcyclists passing you on the road, or to people on the pavement. - [Rule 239](rule_239)
