How do you move the car ?
If you use iTween you can fire an event on finish.
If you use unity pathfinding you can use GetRemainingDistance and then also fire an event when arrived
You can check the distance between the car and the stop, if you know their location, with a Get Distance action.
Maybe you can check the velocity of the car ?
Or you can check if its position changed over time ?
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Depends on your setup