A relatively new commodity in the 1920's, automobiles represent wealth in a very materialistic sense as well as empowerment, for they provide a freedom from the restraints of society. Thus, the misuse of the car's power signifies a lack of responsibility as with Jordan Baker, who describes herself as a "bad driver."
When one of Gatsby's guests drives his car into a ditch in Chapter Three, there is "a violent confusion of the scene." Owl Eyes gets out and is mistaken for the driver, who then emerges confused as to what has happened. His confused state and denial of responsibility presages Daisy's automobile accident. In this same chapter, Jordan Baker leaves a borrowed car, with its top down, out in the rain.
Another accident involving an automobile is that of Tom Buchanan and a chambermaid at a hotel in Santa Barbara where he and Daisy were staying after they were married about three months. Thus, automobiles represent the carelessness of the wealthy set with other people's lives. In addition, this carelessness "parallels the theme concerning wasted potential and wasted goodness"(Enotes). After Daisy kills Myrtle Wilson and does not assume responsibility, Nick refers to her and Tom as "careless people" and Gatsby, who wishes to defend her, wastes his goodness upon her.