What term describes a person who illegally takes control of a vehicle during transit?

The correct term for a person who illegally takes control of a vehicle during transit is "carjacker." This term specifically refers to the act of forcibly taking a car from a driver or passenger while the vehicle is in motion or parked. Carjacking involves a direct confrontation with the victim and generally includes the use or threat of violence.

The term "hijacker," while similar, primarily refers to the unlawful seizure of a vehicle or transportation mode, particularly an aircraft, during its operation rather than personal vehicles like cars. The other terms, such as "abductor" and "smuggler," relate to different crimes; an abductor typically refers to someone who unlawfully takes a person, while a smuggler refers to someone who illegally transports goods or people across borders. Thus, "carjacker" directly and accurately describes the act described in the question.