Sending two uninitiated people without experience and qualifications - especially without CDLs (commercial driver licenses) - such as Damon and Ziva - is an invitation to disaster and the intervention of the fuzz. Driving an 18-wheel rig is a challenging and demanding task; even shifting gears on an unsynchronized manual transmission requires much training and practice. The behavior of an unqualified driver would quickly attract the attention of law-enforcement technicians (who would also overhear the acid comments made by the real truckers on the CB radio, to which state troopers listen routinely).
When Gibbs orders Fornell to turn around after passing the rendezvous point and Fornell does a screeching U-turn, you can see there is only one person in the car.
McGee says that one suspect got a traffic ticket in "Am-uh-ree-yo", Texas. Although that was the original pronunciation of the city, it changed to the current "Am-uh-rill-oh" nearly 100 years ago.