Preferably one that won't break down and leave you stranded in the middle of the Nevada desert. The car owner pays an auto transport agency to move his or her vehicle. Sometimes the owner is moving across the country, flying ahead after having stuffed your new wheels with household goods. But often, the car belongs to a large corporation that provides cars for its employees. The corporations relocate company cars from one office to another, dependent upon staff needs.
Most driveaway cars are fairly new, empty, and in good condition.
Many driveaways go from one major city to another. If your goal is to get from Boston to a small town near San Francisco, you can probably get a driveway to SF and take a bus the rest of the way. In the fall and early winter, there are usually lots of driveways from the northeast to Florida. Be flexible about cities for departure and arrival, and leave yourself lots of time, as there's no guarantee that a driveaway to your chosen destination will be available when you need it. You are assigned a set number of days and a route.