It's based on your surroundings and probably the car's recent movements. To get it to switch you have to do a series of actions which should pretty much confirm that it's what you want to do. For example, if you're backing out of a parking space it'll only trigger a switch to drive if you come to a stop and then turn the wheel some amount to switch to drive. It tells you what to do on screen if you want to trigger it and don't know how.
It's based on your surroundings and probably the car's recent movements. To get it to switch you have to do a series of actions which should pretty much confirm that it's what you want to do. For example, if you're backing out of a parking space it'll only trigger a switch to drive if you come to a stop and then turn the wheel some amount to switch to drive. It tells you what to do on screen if you want to trigger it and don't know how.