The Collaborative International Dictionary of English v.0.48:

carjacking \car"jack*ing\ n. [car + hijacking.]
   the forcible taking of a car while the driver is in it; the
   robber may force the driver out, force the driver to drive
   while under threat of harm, or be forced to relinquish the
   controls while also being forced to remain in the car. In the
   latter two cases, the act also constitutes a kidnapping.
   [PJC]

WordNet (r) 3.0 (2006):

carjacking
    n 1: the violent theft of an occupied car