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.
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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.