Symbolism, Imagery, Allegory
You know how some symbols take on a life of their own, and you can't even see the object without thinking of what it symbolizes? For example, the dove symbolizes peace and love, while the snake always gets a bad rap as a symbol of evil and sin. This novel takes one of those overworked symbols—the car—and does something wonderfully different with it.
Usually, when you think of a car and the open road, you think of freedom. It's just you riding along in your automobile, your baby beside you at the wheel, and you've got the ability to go wherever the road takes you.
Not in Hill House, ladies and gents. The car in this novel is often a symbol of confinement, not freedom.
When Eleanor takes to the open road, she thinks about how free she has finally become, and she imagines that she now has the ability to do anything she wants. But does she? After all, she's following Dr. Montague's instructions to Hill House; she's not really going there on her own. At one point, she thinks "[s]he might pull her car to the side of the highway—although that was not allowed, she told herself; she would be punished if she really did" (1.49). The car is only as free as the person driving it.
The car appears once more at the novel's conclusion when Eleanor uses it to off herself. The question of freedom and confinement isn't so much answered here as it is reiterated. As Eleanor drives toward the tree that'll kill her, she thinks: "I am really doing it, I am doing this all by myself, now, at last; this is me" (9.114). Whether or not you feel Eleanor has finally found freedom with her car will depend on how you feel about her relationship with Hill House. It could be that she's simply following a new set of instructions, right?
By the way, "Freedom and Confinement" just happens to be one of our themes for The Haunting of Hill House. Feel free to hop on over there if you want to read more.