Originally Posted By: Robotic
it's interesting to note that while automobile, vehicle, and car each are used in the US to designate (for most intents and purposes) the same means of conveyance, their use is not exactly interchangeable.

Car is very much the casual, standard term ("I bought a car").
Automobile is a more esoteric descriptor hearkening back to the roots of the era (The Automobile Industry, Automobile Insurance company).
Vehicle is used often in 'precision language' (official descriptions of incidents, or directions given by authority figures).

Auto is also used regularly, but typically as an adjective- a shortening of Automobile (Auto Parts, Auto Service)

/observations of a layman

Vehicles mean more than just 'cars' though. The official name of the platform I work on is an 'air vehicle'. Most of the unmanned systems being introduced are referred to as vehicles (except unmanned air vehicles (UAV) is now unmanned aerial system (UAS)), no matter what they travel in, on or under (land or sea I mean).