There's no one answer. Can represent a fear of some sort, which might be symbolized in some way in the dream. Could represent a loss of control and fear of the consequences. Again, it depends on the dream. That depends on what cars mean for you.
Cars are objects of power, statements about self and more.
It could also represent the way in which you do things, e.g. your approach to life and work. It could represent something about how you feel about yourself, based on the car. An old, broken down VW is a lot different from a shiny new red Ferrari. Even if the person does die within a relatively short period of time the dream doesn't necessarily presage that. Some people have prophetic dreams but they are extremely rare and those people usually have had several dreams come true before.